help button home button Endocrine Society Molecular Endocrinology
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
Molecular Endocrinology, doi:10.1210/me.2005-0107
This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow All Versions of this Article:
20/1/114    most recent
Author Manuscript (PDF)
Right arrow Purchase Article
Right arrow View Shopping Cart
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow Request Copyright Permission
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by He, J.
Right arrow Articles by Kobayashi, M.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by He, J.
Right arrow Articles by Kobayashi, M.
Molecular Endocrinology 20 (1): 114-124
Copyright © 2006 by The Endocrine Society

Interleukin-1{alpha} Inhibits Insulin Signaling with Phosphorylating Insulin Receptor Substrate-1 on Serine Residues in 3T3-L1 Adipocytes

Jianying He, Isao Usui, Ken Ishizuka, Yukiko Kanatani, Kazuyuki Hiratani, Minoru Iwata, Agussalim Bukhari, Tetsuro Haruta, Toshiyasu Sasaoka and Masashi Kobayashi

The First Department of Internal Medicine, Toyama Medical and Pharmaceutical University, Toyama 930-0194, Japan

Address all correspondence and requests for reprints to: Isao Usui, M.D., Ph.D., The First Department of Internal Medicine, Toyama Medical and Pharmaceutical University, 2630 Sugitani, Toyama 930-0194, Japan. E-mail: isaousui-tym{at}umin.ac.jp.


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 RESULTS
 DISCUSSION
 MATERIALS AND METHODS
 REFERENCES
 
Proinflammatory cytokines are recently reported to inhibit insulin signaling causing insulin resistance. IL-1{alpha} is also one of the proinflammatory cytokines; however, it has not been clarified whether IL-1{alpha} may also cause insulin resistance. Here, we investigated the effects of IL-1{alpha} treatment on insulin signaling in 3T3-L1 adipocytes. IL-1{alpha} treatment up to 4 h did not alter insulin-stimulated insulin receptor tyrosine phosphorylation, whereas tyrosine phosphorylation of insulin receptor substrate (IRS)-1 and the association with phosphatidylinositol 3-kinase were partially inhibited with the maximal inhibition in around 15 min. IRS-1 was transiently phosphorylated on some serine residues around 15 min after IL-1{alpha} stimulation, when several serine kinases, I{kappa}B kinase, c-Jun-N-terminal kinase, ERK, and p70S6K were activated. Chemical inhibitors for these kinases inhibited IL-1{alpha}-induced serine phosphorylation of IRS-1. Tyrosine phosphorylation of IRS-1 was recovered only by the IKK inhibitor or JNK inhibitor, suggesting specific involvement of these two kinases. Insulin-stimulated Akt phosphorylation and 2-deoxyglucose uptake were not inhibited only by IL-1{alpha}. Interestingly, Akt phosphorylation was synergistically inhibited by IL-1{alpha} in the presence of IL-6. Taken together, short-term IL-1{alpha} treatment transiently causes insulin resistance at IRS-1 level with its serine phosphorylation. IL-1{alpha} may suppress insulin signaling downstream of IRS-1 in the presence of other cytokines, such as IL-6.


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
RESULTS
 DISCUSSION
 MATERIALS AND METHODS
 REFERENCES
 
INSULIN RESISTANCE contributes importantly to fundamental pathophysiology of various diseases including type 2 diabetes mellitus. Many factors are implicated in the development of insulin resistance, e.g. counterregulatory hormones such as GH (1) or glucocorticoid (2), nutrition-related materials such as a high-glucose condition (3), free fatty acid (4, 5, 6) or amino acid (7, 8, 9), and proinflammatory cytokines such as TNF{alpha} (10, 11, 12, 13) or IL-6 (14, 15). Especially, proinflammatory cytokines have recently been attracting considerable attention for their role as mediators or coordinators of the insulin resistance observed in insulin resistance with the inflammatory diseases or obesity (10, 11, 12, 13, 14, 15, 16, 17, 18).

IL-1 is one of the major proinflammatory cytokines. It induces fever, synthesis of hepatic acute phase proteins, and the release of neutrophils as a mediator of acute inflammatory responses together with some other cytokines. The close relationships between IL-1 and TNF{alpha} are well documented, i.e. both cytokines are being produced at sites of local inflammation and the stimuli that produce either IL-1 or TNF{alpha} are common. Although the receptors for TNF{alpha} and IL-1 are clearly different, most of their signal transduction pathways and postreceptor events are very similar (19, 20). Furthermore, IL-1 and TNF{alpha} each enhances its production with each other and acts synergistically (20). Compared with the huge numbers of reports on the roles of TNF{alpha} as an endogenous mediator of insulin resistance (10, 11, 12, 13, 14, 15, 16, 17, 18), studies on the relationship between IL-1 and insulin signaling are scarce. Dinarello et al. (21) have reported that the production of IL-1 is increased in diabetic patients as well as in patients with rheumatoid arthritis or with cancers, suggesting that IL-1 may play a role in the pathogenesis of diabetes mellitus. However, it remains unclear whether, or how, IL-1 affects insulin signaling at the cellular level.

We recently have reported altered insulin signaling as the cellular mechanism for insulin resistance observed after the treatment with insulin. Briefly, serine/threonine kinases, including mammalian target of rapamycin (mTOR), are activated by insulin, and phosphorylate insulin receptor substrates (IRSs). IRSs phosphorylated on serine residues are then ubiquitinated and finally degraded in proteasomes. Through the process of serine phosphorylation and the sequential decrease of IRS proteins, the insulin signal is negatively regulated (9, 22). IL-1{alpha} also activates some serine/threonine kinases, such as c-Jun-N-terminal kinase (JNK) or I{kappa}B kinase (IKK), which are reported to phosphorylate IRS proteins after other ligands’ stimulations (23, 24, 25, 26, 27, 28). Thus, we have hypothesized that IL-1{alpha} may also induce cellular insulin resistance by phosphorylating IRSs on serine residues. In the current study, we examined the mechanisms of IL-1{alpha}-induced insulin resistance focusing on the activation of serine kinases and the subsequent changes of insulin signaling in 3T3-L1 adipocytes.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 RESULTS
DISCUSSION
 MATERIALS AND METHODS
 REFERENCES
 
IL-1{alpha} Inhibits Insulin Signaling at the Level of IRS-1
To study whether IL-1{alpha} causes insulin resistance in 3T3-L1 adipocytes, we first examined the effect of IL-1{alpha} treatment on insulin signaling at different signaling levels. IL-1{alpha} treatment from 5 min to 4 h failed to alter the expression level and tyrosine phosphorylation of insulin receptor (Fig. 1AGo). The expression levels of IRS-1 and p85, a regulatory subunit of phosphatidylinositol 3-kinase (PI3-kinase), were not altered, but insulin-stimulated tyrosine phosphorylation of IRS-1 and the association of IRS-1 with p85 were transiently but significantly decreased to 72% and 74% of the control levels by 15 min IL-1{alpha} treatment (Fig. 1Go, B–D). These results indicate that IL-1{alpha} treatment inhibits insulin signaling at the level of IRS-1.



View larger version (32K):
[in this window]
[in a new window]
  		Fig. 1. Effects of IL-1{alpha} on Insulin Signaling

3T3-L1 adipocytes were serum-starved for 16 h, treated with 10 ng/ml IL-1{alpha} from 5 min to 4 h, and then stimulated with 20 nM insulin for 5 min. Total cell lysates or immunoprecipitates with anti-IRS-1 antibody were separated by SDS-PAGE, and analyzed with antiinsulin receptor (IR), antiphosphotyrosine (PY20), anti-IRS-1 or anti-p85 antibody as described in Materials and Methods. Representative images are shown from three independent experiments (A and B). Tyrosine phosphorylation of IRS-1 and the association of IRS-1 with p85 were quantitated by the National Institutes of Health (NIH, Bethesda, MD) Image program (C and D). Results are shown as mean ± SE from three independent experiments (*, P < 0.05). IB, Immunoblotted.

 
IL-1{alpha} Induces Serine Phosphorylation of IRS-1
Some recent studies have reported that serine phosphorylation of IRS-1 is one of the mechanisms for diminished activation of IRS-1 (9, 22, 23, 24, 25, 26, 27, 28, 29). Thus, we hypothesized that the transient inhibition of IRS-1 tyrosine phosphorylation after IL-1{alpha} treatment might be due to its serine phosphorylation. We examined serine phosphorylation of IRS-1 by using phospho-specific IRS-1 antibodies that recognize different serine residues on IRS-1, i.e. Ser307, Ser612, and Ser636. Remarkable responses of serine phosphorylation on the three residues were observed 5–30 min after IL-1{alpha} stimulation (Fig. 2Go). Because the time courses of serine phosphorylation and the diminished tyrosine phosphorylation were almost similar, IL-1{alpha} inhibited tyrosine phosphorylation of IRS-1 and the association with p85 possibly through the serine phosphorylation. The maximal response on Ser307 was around 30 min, whereas Ser612 or Ser636 were phosphorylated in around 15 min, suggesting that different serine kinases would be involved in the phosphorylation of Ser307 and Ser612/636.



View larger version (54K):
[in this window]
[in a new window]
  		Fig. 2. Serine Phosphorylation of IRS-1 by IL-1{alpha}

3T3-L1 adipocytes were serum-starved for 16 h and treated with 10 ng/ml IL-1{alpha} from 5 min to 4 h. Total cell lysates were separated by SDS-PAGE and analyzed using anti-nonphospho- or phospho-IRS-1 (p-IRS-1) antibodies against Ser307, Ser612, and Ser636 as described in Materials and Methods. Representative images are shown from three or four independent experiments. IB, Immunoblotted.

 
Several Serine Kinases Are Activated by IL-1{alpha}
Next, we tried to identify which serine kinases were involved in IRS-1 serine phosphorylation after IL-1{alpha} stimulation. We first compared the time course of IL-1{alpha}-induced activation of several serine kinases including IKK, JNK, ERK1/2, p70S6K, and p38. As shown in Fig. 3Go, A–D, IL-1{alpha} transiently stimulated phosphorylation of IKK, JNK, ERK1/2, p70S6K in around 10–30 min when the maximal response of IRS-1 serine phosphorylation was also observed. On the other hand, p38 was activated after 30 min IL-1{alpha} stimulation with the maximum response around 4 h, when the maximal response of IRS-1 serine phosphorylation was restored to the basal level (Fig. 3EGo). We could not detect any Akt phosphorylation after IL-1{alpha} stimulation using phosphor-specific Akt antibodies (data not shown). These results suggest that serine kinases such as JNK, IKK, ERK1/2, and p70S6K may phosphorylate IRS-1 and it is less likely that p38 or Akt is involved in serine phosphorylation of IRS-1 after IL-1{alpha} stimulation.



View larger version (51K):
[in this window]
[in a new window]
  		Fig. 3. Activation of Serine Kinases by IL-1{alpha}

Activations of IKK pathway (A), JNK pathway (B), ERK1/2 (C), p70S6 kinase (D) and p38 MAPK (E) by IL-1{alpha} are shown. 3T3-L1 adipocytes were serum-starved for 16 h and treated with 10 ng/ml IL-1{alpha} from 5 min to 4 h. Total cell lysates were separated by SDS-PAGE and analyzed using anti-nonphospho- or phosphoantibodies against IKK{alpha}/ß or I{kappa}B (A), JNK or c-jun (B), ERK1/2 (C), p70S6 kinase (D) or p38 MAPK (E) as described in Materials and Methods. Representative images are shown from three independent experiments. IB, Immunoblotted; p-, phosphorylated.

 
IRS-1 Serine Phosphorylation Is Inhibited by Multiple Kinase Inhibitors
To more directly demonstrate which serine kinases phosphorylate IRS-1 after IL-1{alpha} treatment, we next examined the effects of kinase inhibitors on IL-1{alpha}-induced IRS-1 serine phosphorylation (Fig. 4Go, A–E). Specific chemical inhibitors used in this study are 15d-prostaglandin J2 (15d-PGJ2) for IKK, SP600125 for JNK, LY29004 for PI3-kinase, rapamycin for mTOR-p70S6 kinase pathway, and PD98059 for MAPK kinase 1-ERK1/2 pathway. Before examining their effects on IRS-1 serine phosphorylation, we checked the specificity of these inhibitors for each serine kinase because such chemical inhibitors sometimes inhibit several enzymes nonspecifically, especially at a high concentration. Most of the inhibitors used in this study specifically inhibited only one kinase expected among the six kinases studied here even at the highest concentration (only the result of the specific kinase is shown), with only the exception of SP600125, a JNK inhibitor, which inhibited p70S6 kinase as well (Fig. 4BGo). Phosphorylations of IRS-1 on the three serine residues were inhibited by the kinase inhibitors basically in a dose-dependent manner. All the inhibitors at the highest concentration inhibited IRS-1 phosphorylation on all three residues partially or completely. 15d-PGJ2, an IKK inhibitor, SP600125, a JNK inhibitor, and LY20004, a PI3-kinase inhibitor, showed the strongest inhibition. Because Akt phosphorylation was not induced directly by IL-1{alpha} stimulation (data not shown), inhibition of IRS-1 serine phosphorylation by PI3-kinase inhibitor may not be through the inhibition of Akt, but probably due to the inhibition of PI3-kinase itself. These studies do not directly determine the relative importance of each kinase, but suggest that multiple serine kinases are involved in IRS-1 serine phosphorylation after IL-1{alpha} treatment.



View larger version (54K):
[in this window]
[in a new window]
  		Fig. 4. Effects of Kinase Inhibitors on IL-1{alpha}-Stimulated Serine Phosphorylation of IRS-1

Effects of IKK inhibitor (A), JNK inhibitor (B), PI3-kinase inhibitor (C), mTOR inhibitor (D), and MAPK kinase inhibitor (E) on IL-1{alpha}-stimulated serine phosphorylation of IRS-1 are shown. 3T3-L1 adipocytes were serum starved for 16 h, treated with the indicated concentrations of 15d-PGJ2 (A), SP600125 (B), LY294002 (C), rapamycin (D), or PD98059 (E) for 30 min, and then stimulated with 10 ng/ml IL-1{alpha} for 15 min. Total cell lysates were separated by SDS-PAGE, and analyzed with anti-nonphospho-IRS-1, phosphospecific IRS-1 antibodies against Ser307, Ser612 or Ser636, nonphospho-I{kappa}B (A), or phosphospecific c-jun (B), p70S6 kinase (B, C, and D) or ERK1/2 (E) antibody as described in Materials and Methods. Representative images are shown from three independent experiments. IB, Immunoblotted; p-, phosphorylated.

 
Tyrosine Phosphorylation of IRS-1 Is Recovered Only by IKK Inhibitor or JNK Inhibitor
We next investigated which serine kinases should be activated to suppress insulin signaling after IL-1{alpha} treatment. The effects of the same inhibitors used in Fig. 4Go on insulin-stimulated IRS-1 tyrosine phosphorylation and the association with p85 were examined (Fig. 5AGo). In contrast to their effects on serine phosphorylation, only 15d-PGJ2, an IKK inhibitor, or SP600125, a JNK inhibitor, recovered insulin-stimulated tyrosine phosphorylation of IRS-1 and the association with p85, whereas the other inhibitors had no effects, suggesting a specific involvement of IKK and JNK in the mechanisms for the diminished insulin signaling after short-term IL-1{alpha} treatment. However, these two inhibitors recovered insulin signaling to the levels higher than the control without IL-1{alpha} treatment. To exclude a possibility that they may cancel the inhibitory effects by another pathway besides IL-1{alpha}, we examined the effects of the inhibitors on insulin signaling in the absence of IL-1{alpha}. SP600125 and 15d-PGJ2 slightly enhanced tyrosine phosphorylation of IRS-1 and the association with p85 (~10%), but the effects of these inhibitors were clearly less than their effects observed in the presence of IL-1{alpha} (Fig 5BGo). These results indicate that SP600125 and 15d-PGJ2 mainly cancel the effect of IL-1{alpha}.



View larger version (29K):
[in this window]
[in a new window]
  		Fig. 5. Effects of Kinase Inhibitors on Insulin Signaling after Short-Term IL-1{alpha} Treatment

3T3-L1 adipocytes were serum-starved for 16 h, treated with the 50 µM SP600125, 50 µM 15d-PGJ2, 10 µM LY294002, 20 nM rapamycin or 50 µM PD98059 for 30 min, in the presence (A) or absence (B) of 10 ng/ml IL-1{alpha} for 15 min and stimulated with 20 nM insulin for 5min. Total cell lysates or immunoprecipitates with IRS-1 antibody were separated by SDS-PAGE, and analyzed with antiphosphotyrosine (PY20) or anti-p85 antibody as described in Materials and Methods. Representative images are shown from four or five independent experiments. Tyrosine phosphorylation of IRS-1 and the association of IRS-1 with p85 were quantitated by the NIH Image program (C and D). Results are shown as mean ± SE from three independent experiments (*, P < 0.05). IB, Immunoblotted; SP, SP600125; PD, PD98059.

 
IL-1{alpha} and IL-6 Synergistically Inhibit Insulin Signaling
Next, we examined whether IL-1{alpha}-induced partial and transient inhibition of insulin signaling at the level of IRS-1 led to the inhibition of its downstream signaling. Insulin-stimulated 2-deoxyglucose (2-DOG) uptake showed a tendency to decrease by approximately 10% at 15 min, but the inhibition was not statistically significant (Fig. 6AGo). Akt phosphorylation was not suppressed by IL-1{alpha} treatment around 5–30 min (Fig. 6BGo). These results indicate that short-term IL-1{alpha} treatment inhibits insulin signaling only at IRS-1 level, but the partial inhibition is not great enough to suppress its downstream signaling. Because synergistic effects of several cytokines on insulin signaling are previously reported in the different tissues (30, 31, 32, 33), we hypothesized that the inhibitory effects of short-term IL-1{alpha} treatment might also be enhanced in the presence of other cytokines. We could not observe enhanced IL-1{alpha}’s effects on insulin signaling even with the coexistence of IL-1ß or TNF{alpha} (data not shown). When the cells were treated with IL-1{alpha} for 15 min, after 45 min treatment with IL-6, the activations of insulin signaling, at the level of tyrosine phosphorylation of IRS-1, the association of IRS-1 and p85 and Akt phosphorylation, were synergistically inhibited (Fig. 6Go, C and D), although IL-6 treatment alone had no significant effects on insulin signaling (Fig. 6EGo).



View larger version (41K):
[in this window]
[in a new window]
  		Fig. 6. Effects of IL-1{alpha} on Downstream Insulin Signaling

A, Effects of IL-1{alpha} on insulin-stimulated 2-DOG uptake. 3T3-L1 adipocytes were treated with 10 ng/ml IL-1{alpha} from 5 min to 4 h, and then stimulated with 20 nM insulin for 15 min. 2-DOG uptake was measured as described in Materials and Methods. Results are shown as mean ± SE from three independent experiments. B, Effects of IL-1{alpha} on insulin-stimulated Akt phosphorylation. 3T3-L1 adipocytes were serum starved for 16 h, treated with 10 ng/ml IL-1{alpha} from 5 min to 4 h, and stimulated with 20 nM insulin for 10 min. C and D, Effects of IL-1{alpha} and/or IL-6 on insulin-stimulated IRS-1 activation or Akt phosphorylation. 3T3-L1 adipocytes were serum-starved for 16 h, treated with 10 ng/ml IL-1{alpha} for 15 min after a 45-min treatment with IL-6, then stimulated with 20 nM insulin for 10 min. E, Effects of IL-6 on insulin signaling are shown. 3T3-L1 adipocytes were serum starved for 16 h, treated with IL-6 from 15 min to 2 h, then stimulated with insulin for 5 min. Total cell lysates or immunoprecipitates with IRS-1 antibody were separated by SDS-PAGE, and analyzed with anti-IRS-1, phosphotyrosine (PY20), p85 or Akt, and phosphospecific Akt antibody as described in Materials and Methods. Representative images are shown from three independent experiments (B, C, and E). Tyrosine phosphorylation of IRS-1 (closed column), the association of IRS-1 with p85 (open column) and phosphorylation of Akt (Ser473) (shaded column) were quantitated by the NIH Image program (D). Results are shown as mean ± SE from three independent experiments (*, P < 0.05). IB, Immunoblotted; p-, phosphorylated.

 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 RESULTS
 DISCUSSION
MATERIALS AND METHODS
 REFERENCES
 
Recent studies have demonstrated the involvement of IL-1 in the pathogenesis of diabetes mellitus (21, 34, 35). However, the most studies have shown the role of IL-1 in pancreatic ß-cell destruction as a mechanism for the pathogenesis of type 1 diabetes (21, 35). The studies focusing on the role of IL-1 to cause insulin resistance are rarely found (34) compared with the other proinflammatory cytokines such as TNF{alpha} and IL-6. In this study, we first examined the effect of IL-1{alpha} on the initial step of insulin signaling at the cellular level using 3T3-L1 adipocytes. Insulin-stimulated tyrosine phosphorylation of IRS-1 and its association with p85 was inhibited partially and transiently around 10–30 min with IL-1{alpha} stimulation, whereas expression and tyrosine phosphorylation of insulin receptor were not altered. These results indicate that IL-1{alpha} may cause cellular insulin resistance, and the direct target of insulin signaling is not insulin receptor but IRS-1.

We and other groups have recently reported that serine phosphorylation of IRS-1 is enhanced by various ligands stimulations, such as TNF{alpha} or insulin, causing diminished activation of IRS-1 (9, 10, 22, 25, 26, 27, 28, 29). Thus, we hypothesized that partial and transient inhibition of IRS-1 tyrosine phosphorylation observed after IL-1{alpha} treatment was also due to its serine phosphorylation. We compared the time course of IRS-1 serine phosphorylation and the activation of several serine kinases. IRS-1 was transiently phosphorylated on Ser307, Ser612, and Ser636 around 10–30 min after IL-1{alpha} stimulation, when several serine kinases, IKK, JNK, ERK, and p70S6K were activated. And chemical inhibitors for the kinases inhibited serine phosphorylation of IRS-1 partially or completely. These results suggest that IRS-1 is phosphorylated by multiple serine kinases after IL-1{alpha} stimulation. Interestingly, these three serine residues were phosphorylated with a little different time course, i.e. only the maximal response on Ser307 was observed around 30 min, whereas that on Ser612 or Ser636 was around 15 min. Furthermore, the inhibitory effect of each chemical inhibitor was different among the residues, suggesting a possibility that different kinases phosphorylate the different serine residues. To examine which kinases are actually involved in the mechanisms for the inhibition of insulin signaling, we next compared the effects of the inhibitors on the activation of IRS-1. As shown in Fig. 5Go, insulin-stimulated tyrosine phosphorylation of IRS-1 and the association with p85 were recovered only by IKK inhibitor or JNK inhibitor, suggesting the specific involvement of these two kinases in the mechanisms for insulin resistance induced by short-term IL-1{alpha} treatment. Because these two inhibitors recovered insulin signaling to the levels higher than the control, we wondered whether the inhibitors might cancel the inhibitory effects by another pathway besides IL-1{alpha}. But the effects of these inhibitors without IL-1{alpha} treatment were clearly less than the effects in the presence of IL-1{alpha} as shown in Fig 5BGo. Thus, we believe that SP600125 and 15d-PGJ2 mainly inhibits IL-1{alpha} signaling, and that JNK and IKK play important roles especially in the presence of IL-1{alpha} treatment. Yet we can’t completely deny the possibility that these inhibitors enhanced insulin signaling through the inhibition of IKK and JNK, which were slightly activated by unknown stimuli or through the nonspecific inhibition of unknown kinases, we could not examine in the current study. Further experiments are necessary to address these possibilities. Furthermore, SP600125 inhibited not only JNK but also p70S6 kinase as shown in Fig. 4BGo. This result may be explained by the nonspecificity of SP6000125 on these kinases, or a possibility that p70S6 kinase may be regulated downstream of JNK. In any case, p70S6 kinase might also be involved in the mechanisms for insulin resistance after IL-1{alpha} treatment. However, because rapamycin, a specific inhibitor for mTOR-p70S6 kinase, failed to enhance tyrosine phosphorylation of IRS-1 (Fig. 5Go), the involvement of p70S6 kinase is less likely. Because the other kinase inhibitors could not enhance IRS-1 tyrosine phosphorylation, although they actually suppressed the serine phosphorylation, serine phosphorylation of IRS-1 is not the only mechanism for the diminished insulin signaling by IL-1{alpha} treatment. Some other possible mechanisms should be addressed in the future.

The cytokine family is generally known to elicit their functions not only by themselves but also by producing some other cytokines. Thus, we tried to exclude the possibility that IL-1{alpha} stimulated the production of some other cytokines that caused serine phosphorylation of IRS-1 and/or inhibition of insulin signaling. We measured the concentrations of IL-6 and TNF{alpha} in the cell culture media after IL-1{alpha} stimulation because their productions are widely known to be induced by IL-1{alpha} in other cells or tissues (36, 37, 38), and they may cause insulin resistance. IL-1{alpha} treatment from 5–30 min did not increase the concentration of either IL-6 or TNF{alpha} remarkably, suggesting that serine phosphorylation of IRS-1 observed after IL-1{alpha} treatment was not through the production of IL-6 or TNF{alpha}, but probably through the activation of IL-1{alpha} signaling itself. Interestingly, in contrast to TNF{alpha}, the production of IL-6 was enhanced after IL-1{alpha} treatment longer than 4 h (data not shown). Thus, the influence of IL-6 production should be considered when the effects of longer term IL-1{alpha} treatment on insulin signaling would be studied. Next, we examined the involvement of SOCS (suppressor of cytokine signaling) as a mediator of insulin resistance in our system. SOCSs were originally reported as a negative regulator for Janus kinase-signal transducer and activator of transcription pathway in cytokine signaling (39), and some recent studies have revealed that SOCS-1 or SOCS-3 inhibit insulin signaling by degrading IRS-1 or inhibiting tyrosine kinase activity of insulin receptor to IRS-1 (40, 41, 42, 43, 44). The expression of SOCSs is induced by various cytokines or hormones. Thus, we examined whether IL-1{alpha} induces SOCSs in 3T3-L1 adipocytes using real-time RT-PCR. SOCS-1 and SOCS-3 mRNA expressions were enhanced by IL-1{alpha} stimulation longer than 4 h, but the expressions of these genes could not be detected around 5–30 min (data not shown). These results indicate that short-term IL-1{alpha} treatment induces IRS-1 serine phosphorylation with decreased tyrosine phosphorylation not through the production of some other cytokines, such as IL-6 and TNF{alpha} nor induction of the expressions of SOCS, but through the activation of some serine kinases stimulated directly by IL-1{alpha}.

Acute IL-1{alpha} treatment partially but significantly decreased tyrosine phosphorylation of IRS-1 and the association between IRS-1 and PI3-kinase, whereas Akt phosphorylation and glucose uptake were unaltered (Fig. 6Go, A and B). Two explanations are possible as the reasons for the failure to observe inhibited downstream insulin signaling. The first explanation is that insulin signaling other than IRS-1 was increased and compensated for the inhibition of IRS-1 pathway. However, as far as we examined, tyrosine phosphorylation of IRS-2 was also inhibited partially (~20%) and transiently as IRS-1 was (data not shown). Another possible explanation is as follows. In the current study, IL-1{alpha} treatment caused inhibition of insulin signaling at IRS-1-PI3 kinase level by approximately 25%, and the residual 75% of the maximum activation may be strong enough for the full activation of the downstream insulin signaling, including Akt phosphorylation or glucose uptake. We confirmed the latter possibility by using different concentrations of wortmannin, a chemical PI3-kinase inhibitor. For example, when a lower concentration of wortmannin inhibited insulin-stimulated PI3 kinase activity by 50%, it did not alter Akt phosphorylation or glucose uptake. Insulin-stimulated Akt phosphorylation and glucose uptake were inhibited by higher concentration of wortmannin, which inhibited PI3-kinase by more than 80%. These results suggest that approximately 75% of IRS-1-PI3 kinase activity observed after short-term IL-1{alpha} treatment may fully activate the downstream signaling. Thus, the greater inhibition at IRS-1 level would be necessary to suppress glucose uptake or Akt phosphorylation. Recent studies have demonstrated that there are synergistic effects of several cytokines on insulin signaling in the different tissues (30, 31, 32, 33). For example, Ling et al. (32) have reported that IL-1{alpha} and TNF{alpha} synergistically inhibit insulin-stimulated muscular glucose uptake and suppression of hepatic glucose production in rat infusion study. We hypothesized that the effects of short-term IL-1{alpha} treatment might also be enhanced in the presence of other cytokines. The effects of IL-1{alpha} treatment for 15 min on insulin-stimulated tyrosine phosphorylation of IRS-1 or Akt phosphorylation were examined either in the presence or absence of TNF{alpha}, IL-1ß, or IL-6. In contrast to the report of Ling et al., synergistic effects of IL-1{alpha} with IL-1ß or TNF{alpha} were not observed (data not shown), probably because we used different cells. As shown in Fig. 6CGo, only the combination of IL-1{alpha} and IL-6 caused the remarkable inhibition of insulin signaling at the levels of IRS-1 and Akt. Importantly, the time course study revealed that IL-6 treatment alone up to 2 h had no significant effects on insulin signaling (Fig. 6EGo). The great inhibition of insulin signaling was not the additive effects of IL-1{alpha} and IL-6, but the enhancement of the effect of IL-1{alpha} by IL-6. Thus far, the mechanisms for the enhancement have not been clarified. Our recent preliminary results have shown that IL-6 treatment transiently enhances the expression of SOCS1 and SOCS3 in around 30–60 min. Coexistence of SOCS and serine phosphorylation of IRS-1 might be a mechanism for the remarkable inhibition of insulin signaling. Further experiments will be necessary to address this issue.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 RESULTS
 DISCUSSION
 MATERIALS AND METHODS
REFERENCES
 
Materials
DMEM and fetal bovine serum were purchased from Invitrogen Life Technologies (Rockville, MD). [1,2-3H]-2-DOG was from DuPont New England Nuclear (Boston, MA). Monoclonal antiphosphotyrosine antibodies (PY) were purchased from Transduction Laboratories (Lexington, KY). Anti-IRS-1, antiphospho-IRS-1(Ser307), and anti-p85 antibodies were purchased from Upstate Biotechnology (Lake Placid, NY). Horseradish peroxidase-conjugated antimouse and antirabbit IgG antibodies were purchased from Santa Cruz Biotechnology (Santa Cruz, CA). Protein G Sepharose was purchased from Pharmacia Biotech (Uppsala, Sweden). Electrophoresis reagents were from Bio-Rad (Hercules, CA). Antiphospho-IRS-1 (Ser612, Ser636), anti-JNK, antiphospho-JNK (Thr183/Tyr185), anti-c-jun, antiphospho-c-jun (Ser63), anti-IKK{alpha}, anti-IKKß, antiphospho-IKK (Ser180/Ser181), anti-I{kappa}B, anti-ERK1/2, antiphospho-ERK1/2 (Thr202/Tyr204), anti-p70S6K, antiphospho-p70S6K (Thr421/Ser424), anti-p38, antiphospho-p38 (Thr180/Tyr182), anti-Akt, and antiphospho-Akt (Thr308/Ser473) were purchased from Cell Signaling Technology (Beverly, MA). IL-1{alpha} was kindly provided by Dainippon Pharmaceutical Co., Ltd. (Osaka, Japan). All other reagents were from standard suppliers.

Cell Culture and IL-1{alpha} Treatment
Murine 3T3-L1 cells were obtained from American Type Culture Collection (ATCC, Manassas, VA). Cells were cultured, maintained, and differentiated as described previously (9). Briefly, cells were plated and grown for 2 d after confluence in DMEM/high glucose supplemented with 100 U/ml streptomycin, and 10% fetal bovine serum in a 10% CO2 environment. Differentiation was induced by changing the culture medium to the same one containing 0.5 mmol/liter 3-isobutyl-1 methyxanthine, 1 µmol/liter dexamethasone, and 1 µmol/liter insulin for 3 d, followed by the culture in the medium containing 0.8 µmol/liter insulin for another 3 d. The medium was then changed every 3 d until the cells were used for experiment, i.e. 14–16 d after the induction of differentiation, when more than 95% of the cells had the morphological and biological properties of adipocytes. IL-1{alpha} dissolved in PBS with 0.1% BSA was added to the cell culture medium from 5 min to 4 h.

Western Blotting and Immunoprecipitation
3T3-L1 adipocytes were lysed in a cell-solublizing buffer containing 30 mmol/liter Tris (pH 7.4), 150 mmol/liter NaCl, 10 mmol/liter EDTA, 1% Nonidet P-40, 1 mmol/liter phenylmethylsulfonyl fluoride, 10 µg/ml aprotinin, 1 µmol/liter leupeptin, 1 mmol/liter Na3VO4, and 50 mmol/liter NaF. For immunoprecipitation, the whole cell lysates were centrifuged at 4 C for 20 min to remove the insoluble materials and the supernatants were incubated with the indicated antibody for 4 h, followed by incubation with protein G-Sepharose for 1 h at 4 C and washing the beads with cell lysis buffer three times. The cell lysates or immunoprecipitates were boiled with Laemmli sample buffer for 5 min, resolved by 7.5% or 12% SDS-PAGE, and transferred onto polyvinylidene difluoride membranes (Millipore, Bedford, MA) in the Trans-Blot cell apparatus (Bio-Rad). The membranes were blocked and incubated with the indicated antibodies, followed by incubation with horseradish peroxidase-conjugated secondary antibodies. The proteins were visualized with chemiluminescence reagents according to the manufacturer’s protocol (Amersham, Arlington Heights, IL). In some experiment, the intensities of blots were quantitated using a scanning densitometer.

2-DOG Uptake Assay
Fully differentiated 3T3-L1 adipocytes in 12-well plates were deprived of serum for 3 h and then were stimulated with 20 nmol/liter insulin for 15 min in Krebs-Ringer phosphate buffer [10 mmol/liter HEPES (pH 7.4), 131.2 mmol/liter NaCl, 4.7 mmol/liter KCl, 1.2 mmol/liter MgSO4, 2.5 mmol/liter CaCl2, 2.5 mmol/liter NaH2PO4] with 1% BSA at 37 C. Unlabeled 2-DOG and [3H]-2-DOG (0.1 mmol/liter, 0.74 kBq/well) were added and the cells were incubated for 4 min. Reaction was stopped by adding 10 µmol/liter cytochalasin B and washing cells with ice-cold PBS three times. The cells were solubilized in 1 ml of 0.2% SDS and 0.2 N NaOH. The radioactivity was quantitated in a liquid scintillation counter. The results were corrected for nonspecific absorption determined by [3H]-2-DOG uptake in the presence of 10 µmol/liter cytochalasin B. Nonspecific absorption was always less than 10% of total uptake.

Statistical Analysis
All data are presented as mean ± SE. The statistical comparison between groups was carried out using Student’s t test. P < 0.05 was considered significant.


   ACKNOWLEDGMENTS
 
We thank Ms. Barbara Baehr for editorial assistance.


   FOOTNOTES
 
This work was supported in part by a grant-in-aid for scientific research from the Ministry of Education, Science, Sports and Culture, Tokyo, Japan (15590932 to M.K.).

First Published Online September 8, 2005

Abbreviations: 2-DOG, 2-Deoxyglucose; 15d-PGJ2, 15d-prostaglandin J2; IKK, I{kappa}B kinase; IRS, insulin receptor substrate; JNK, c-Jun-N-terminal kinase; mTOR, mammalian target of rapamycin; PI3-kinase, phosphatidylinositol 3-kinase; PY, monoclonal antiphosphotyrosine antibodies; SOCS, suppressor of cytokine signaling.

Received for publication March 2, 2005. Accepted for publication August 31, 2005.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 RESULTS
 DISCUSSION
 MATERIALS AND METHODS
 REFERENCES
 

  1. Takano A, Haruta T, Iwata M, Usui I, Uno T, Kawahara J, Ueno E, Sasaoka T, Kobayashi M 2001 Growth hormone induces cellular insulin resistance by uncoupling phosphatidylinositol 3-kinase and its downstream signals in 3T3-L1 adipocytes. Diabetes 50:1891–1900[Abstract/Free Full Text]
  2. Sakoda H, Ogihara T, Anai M, Funaki M, Inukai K, Katagiri H, Fukushima Y, Onishi Y, Ono H, Fujishiro M, Kikuchi M, Oka Y, Asano T 2000 Dexamethasone-induced insulin resistance in 3T3-L1 adipocytes is due to inhibition of glucose transport rather than insulin signal transduction. Diabetes 49:1700–1708[Abstract]
  3. Maegawa H, Ide R, Hasegawa M, Ugi S, Egawa K, Iwanishi M, Kikkawa R, Shigeta Y, Kashiwagi A 1995 Thiazolidine derivatives ameliorate high glucose-induced insulin resistance via the normalization of protein-tyrosine phosphatase activities. J Biol Chem 270:7724–7730[Abstract/Free Full Text]
  4. Roden M, Price TB, Perseghin G, Petersen KF, Rothman DL, Cline GW, Shulman GI 1996 Mechanism of free fatty acid-induced insulin resistance in humans. J Clin Invest 97:2859–2865[Medline]
  5. Shulman GI 2000 Cellular mechanisms of insulin resistance. J Clin Invest 106:171–176[Medline]
  6. Usui I, Takata Y, Imamura T, Morioka H, Sasaoka T, Sawa T, Ishihara H, Ishiki M, Kobayashi M 1997 Fatty acid induced insulin resistance in rat-1 fibroblasts overexpressing human insulin receptors: impaired insulin-stimulated mitogen-activated protein kinase activity. Diabetologia 40:894–901[CrossRef][Medline]
  7. Kahn BB, Flier JS 2000 Obesity and insulin resistance. J Clin Invest 106:473–481[Medline]
  8. Murakami S, Sasaoka T, Wada T, Fukui K, Nagira K, Ishihara H, Usui I, Kobayashi M 2004 Impact of Src homology 2-containing inositol 5'-phosphatase 2 on the regulation of insulin signaling leading to protein synthesis in 3T3-L1 adipocytes cultured with excess amino acids. Endocrinology 145:3215–3223[Abstract/Free Full Text]
  9. Takano A, Usui I, Haruta T, Kawahara J, Uno T, Iwata M, Kobayashi M 2001 Mammalian target of rapamycin pathway regulates insulin signaling via subcellular redistribution of insulin receptor substrate 1 and integrates nutritional signals and metabolic signals of insulin. Mol Cell Biol 21:5050–5062[Abstract/Free Full Text]
  10. Hotamisligil GS, Murray DL, Choy LN, Spiegelman BM 1994 Tumor necrosis factor {alpha} inhibits signaling from the insulin receptor. Proc Natl Acad Sci USA 91:4854–4858[Abstract/Free Full Text]
  11. Hotamisligil GS, Peraldi P, Budavari A, Ellis R, White MF, Spiegelman BM 1996 IRS-1-mediated inhibition of insulin receptor tyrosine kinase activity in TNF-{alpha}- and obesity-induced insulin resistance. Science 271:665–668[Abstract]
  12. Peraldi P, Hotamisligil GS, Buurman WA, White MF, Spiegelman BM 1996 Tumor necrosis factor (TNF)-{alpha} inhibits insulin signaling through stimulation of the p55 TNF receptor and activation of sphingomyelinase. J Biol Chem 271:13018–13022[Abstract/Free Full Text]
  13. Uysal KT, Wiesbrock SM, Marino MW, Hotamisligil GS 1997 Protection from obesity-induced insulin resistance in mice lacking TNF-{alpha} function. Nature 389:610–614[CrossRef][Medline]
  14. Fernandez-Real JM, Vayreda M, Richart C, Gutierrez C, Broch M, Vendrell J, Ricart W 2001 Circulating interleukin 6 levels, blood pressure, and insulin sensitivity in apparently healthy men and women. J Clin Endocrinol Metab 86:1154–1159[Abstract/Free Full Text]
  15. Pickup JC, Mattock MB, Chusney GD, Burt D 1997 NIDDM as a disease of the innate immune system: association of acute-phase reactants and interleukin-6 with metabolic syndrome X. Diabetologia 40:1286–1292[CrossRef][Medline]
  16. Grimble RF 2002 Inflammatory status and insulin resistance. Curr Opin Clin Nutr Metab Care 5:551–559[CrossRef][Medline]
  17. Hemi R, Paz K, Wertheim N, Karasik A, Zick Y, Kanety H 2002 Transactivation of ErbB2 and ErbB3 by tumor necrosis factor-{alpha} and anisomycin leads to impaired insulin signaling through serine/threonine phosphorylation of IRS proteins. J Biol Chem 277:8961–8969[Abstract/Free Full Text]
  18. Pirola L, Johnston AM, Van Obberghen E 2004 Modulation of insulin action. Diabetologia 47:170–184[CrossRef][Medline]
  19. Dinarello CA 1996 Biologic basis for interleukin-1 in disease. Blood 87:2095–2147[Abstract/Free Full Text]
  20. Dinarello CA 2000 Proinflammatory cytokines. Chest 118:503–508[Abstract/Free Full Text]
  21. Dinarello CA, Wolff SM 1993 The role of interleukin-1 in disease. N Engl J Med 328:106–113[Free Full Text]
  22. Haruta T, Uno T, Kawahara J, Takano A, Egawa K, Sharma PM, Olefsky JM, Kobayashi M 2000 A rapamycin-sensitive pathway down-regulates insulin signaling via phosphorylation and proteasomal degradation of insulin receptor substrate-1. Mol Endocrinol 14:783–794[Abstract/Free Full Text]
  23. Aguirre V, Uchida T, Yenush L, Davis R, White MF 2000 The c-Jun NH(2)-terminal kinase promotes insulin resistance during association with insulin receptor substrate-1 and phosphorylation of Ser(307). J Biol Chem 275:9047–9054[Abstract/Free Full Text]
  24. Aguirre V, Werner ED, Giraud J, Lee YH, Shoelson SE, White MF 2002 Phosphorylation of Ser307 in insulin receptor substrate-1 blocks interactions with the insulin receptor and inhibits insulin action. J Biol Chem 277:1531–1537[Abstract/Free Full Text]
  25. Gao Z, Hwang D, Bataille F, Lefevre M, York D, Quon MJ, Ye J 2002 Serine phosphorylation of insulin receptor substrate 1 by inhibitor {kappa}B kinase complex. J Biol Chem 277:48115–48121[Abstract/Free Full Text]
  26. Gao Z, Zuberi A, Quon MJ, Dong Z, Ye J 2003 Aspirin inhibits serine phosphorylation of insulin receptor substrate 1 in tumor necrosis factor-treated cells through targeting multiple serine kinases. J Biol Chem 278:24944–24950[Abstract/Free Full Text]
  27. Hirosumi J, Tuncman G, Chang L, Gorgun CZ, Uysal KT, Maeda K, Karin M, Hotamisligil GS 2002 A central role for JNK in obesity and insulin resistance. Nature 420:333–336[CrossRef][Medline]
  28. Rui L, Aguirre V, Kim JK, Shulman GI, Lee A, Corbould A, Dunaif A, White MF 2001 Insulin/IGF-1 and TNF-{alpha} stimulate phosphorylation of IRS-1 at inhibitory Ser307 via distinct pathways. J Clin Invest 107:181–189[CrossRef][Medline]
  29. Paz K, Hemi R, LeRoith D, Karasik A, Elhanany E, Kanety H, Zick Y 1997 A molecular basis for insulin resistance. Elevated serine/threonine phosphorylation of IRS-1 and IRS-2 inhibits their binding to the juxtamembrane region of the insulin receptor and impairs their ability to undergo insulin-induced tyrosine phosphorylation. J Biol Chem 272:29911–29918[Abstract/Free Full Text]
  30. Cai D, Yuan M, Frantz DF, Melendez PA, Hansen L, Lee J, Shoelson SE 2005 Local and systemic insulin resistance resulting from hepatic activation of IKK-ß and NF-{kappa}B. Nat Med 11:183–190[CrossRef][Medline]
  31. Dunger A, Cunningham JM, Delaney CA, Lowe JE, Green MH, Bone AJ, Green IC 1996 Tumor necrosis factor-{alpha} and interferon-{gamma} inhibit insulin secretion and cause DNA damage in unweaned-rat islets. Extent of nitric oxide involvement. Diabetes 45:183–189[Abstract]
  32. Ling PR, Bistrian BR, Mendez B, Istfan NW 1994 Effects of systemic infusions of endotoxin, tumor necrosis factor, and interleukin-1 on glucose metabolism in the rat: relationship to endogenous glucose production and peripheral tissue glucose uptake. Metabolism 43:279–284[CrossRef][Medline]
  33. Yew KH, Prasadan KL, Preuett BL, Hembree MJ, McFall CR, Benjes CL, Crowley AR, Sharp SL, Li Z, Tulachan SS, Mehta SS, Gittes GK 2004 Interplay of glucagon-like peptide-1 and transforming growth factor-ß signaling in insulin-positive differentiation of AR42J cells. Diabetes 53:2824–2835[Abstract/Free Full Text]
  34. Arkan MC, Hevener AL, Greten FR, Maeda S, Li ZW, Long JM, Wynshaw-Boris A, Poli G, Olefsky J, Karin M 2005 IKK-ß links inflammation to obesity-induced insulin resistance. Nat Med 11:191–198[CrossRef][Medline]
  35. Thomas HE, Irawaty W, Darwiche R, Brodnicki TC, Santamaria P, Allison J, Kay TW 2004 IL-1 receptor deficiency slows progression to diabetes in the NOD mouse. Diabetes 53:113–121[Abstract/Free Full Text]
  36. Ikejima T, Okusawa S, Ghezzi P, van der Meer JW, Dinarello CA 1990 Interleukin-1 induces tumor necrosis factor (TNF) in human peripheral blood mononuclear cells in vitro and a circulating TNF-like activity in rabbits. J Infect Dis 162:215–223[Medline]
  37. Lonnemann G, Engler-Blum G, Muller GA, Koch KM, Dinarello CA 1995 Cytokines in human renal interstitial fibrosis. II. Intrinsic interleukin (IL)-1 synthesis and IL-1-dependent production of IL-6 and IL-8 by cultured kidney fibroblasts. Kidney Int 47:845–854[Medline]
  38. Silvera MR, Sempowski GD, Phipps RP 1994 Expression of TGF-ß isoforms by Thy-1+ and Thy-1– pulmonary fibroblast subsets: evidence for TGF-ß as a regulator of IL-1-dependent stimulation of IL-6. Lymphokine Cytokine Res 13:277–285[Medline]
  39. Naka T, Narazaki M, Hirata M, Matsumoto T, Minamoto S, Aono A, Nishimoto N, Kajita T, Taga T, Yoshizaki K, Akira S, Kishimoto T 1997 Structure and function of a new STAT-induced STAT inhibitor. Nature 387:924–929[CrossRef][Medline]
  40. Emanuelli B, Peraldi P, Filloux C, Chavey C, Freidinger K, Hilton DJ, Hotamisligil GS, Van Obberghen E 2001 SOCS-3 inhibits insulin signaling and is up-regulated in response to tumor necrosis factor-{alpha} in the adipose tissue of obese mice. J Biol Chem 276:47944–47949[Abstract/Free Full Text]
  41. Emanuelli B, Peraldi P, Filloux C, Sawka-Verhelle D, Hilton D, Van Obberghen E 2000 SOCS-3 is an insulin-induced negative regulator of insulin signaling. J Biol Chem 275:15985–15991[Abstract/Free Full Text]
  42. Mooney RA, Senn J, Cameron S, Inamdar N, Boivin LM, Shang Y, Furlanetto RW 2001 Suppressors of cytokine signaling-1 and -6 associate with and inhibit the insulin receptor. A potential mechanism for cytokine-mediated insulin resistance. J Biol Chem 276:25889–25893[Abstract/Free Full Text]
  43. Rui L, Yuan M, Frantz D, Shoelson S, White MF 2002 SOCS-1 and SOCS-3 block insulin signaling by ubiquitin-mediated degradation of IRS1 and IRS2. J Biol Chem 277:42394–42398[Abstract/Free Full Text]
  44. Ueki K, Kondo T, Kahn CR 2004 Suppressor of cytokine signaling 1 (SOCS-1) and SOCS-3 cause insulin resistance through inhibition of tyrosine phosphorylation of insulin receptor substrate proteins by discrete mechanisms. Mol Cell Biol 24:5434–5446[Abstract/Free Full Text]



This article has been cited by other articles:


Home page
 J EndocrinolHome page
S. Weise, S. Kralisch, G. Sommer, U. Lossner, M. Bluher, M. Stumvoll, and M. Fasshauer
Tissue inhibitor of metalloproteinase-1 mRNA production and protein secretion are induced by interleukin-1{beta} in 3T3-L1 adipocytes
J. Endocrinol., July 1, 2008; 198(1): 169 - 174.
[Abstract] [Full Text] [PDF]

Home page
 J EndocrinolHome page
E. Park, V. Wong, X. Guan, A. I Oprescu, and A. Giacca
Salicylate prevents hepatic insulin resistance caused by short-term elevation of free fatty acids in vivo
J. Endocrinol., November 1, 2007; 195(2): 323 - 331.
[Abstract] [Full Text] [PDF]

Home page
 EndocrinologyHome page
K. Ishizuka, I. Usui, Y. Kanatani, A. Bukhari, J. He, S. Fujisaka, Y. Yamazaki, H. Suzuki, K. Hiratani, M. Ishiki, et al.
Chronic Tumor Necrosis Factor-{alpha} Treatment Causes Insulin Resistance via Insulin Receptor Substrate-1 Serine Phosphorylation and Suppressor of Cytokine Signaling-3 Induction in 3T3-L1 Adipocytes
Endocrinology, June 1, 2007; 148(6): 2994 - 3003.
[Abstract] [Full Text] [PDF]

Home page
 J ANIM SCIHome page
M. M. Vick, A. A. Adams, B. A. Murphy, D. R. Sessions, D. W. Horohov, R. F. Cook, B. J. Shelton, and B. P. Fitzgerald
Relationships among inflammatory cytokines, obesity, and insulin sensitivity in the horse
J Anim Sci, May 1, 2007; 85(5): 1144 - 1155.
[Abstract] [Full Text] [PDF]

Home page
 EndocrinologyHome page
J. Jager, T. Gremeaux, M. Cormont, Y. Le Marchand-Brustel, and J.-F. Tanti
Interleukin-1{beta}-Induced Insulin Resistance in Adipocytes through Down-Regulation of Insulin Receptor Substrate-1 Expression
Endocrinology, January 1, 2007; 148(1): 241 - 251.
[Abstract] [Full Text] [PDF]

This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow All Versions of this Article:
20/1/114    most recent
Author Manuscript (PDF)
Right arrow Purchase Article
Right arrow View Shopping Cart
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow Request Copyright Permission
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by He, J.
Right arrow Articles by Kobayashi, M.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by He, J.
Right arrow Articles by Kobayashi, M.

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
Endocrinology Endocrine Reviews J. Clin. End. & Metab.
Molecular Endocrinology Recent Prog. Horm. Res. All Endocrine Journals