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Submitted on November 14, 2005
Accepted on June 20, 2006
INSERM, U568, F-06107 Nice, France; Université de Nice Sophia-Antipolis, Faculté de Médecine, F-06107, Nice, France; CHU de Nice, Service de Chirurgie Digestive et Centre de Transplantation Hépatique, Nice, France; CHU de Nice Fédération d'Hépatologie, Nice, France
* To whom correspondence should be addressed. E-mail: tanti{at}unice.fr.
APS (Adaptor protein with PH and SH2 domains) initiates a PI 3-kinase independent pathway involved in insulin-stimulated glucose transport. We recently identified Enigma, a PDZ and LIM domain-containing protein, as a partner of APS and showed that APS/Enigma complex plays a critical role in actin cytoskeleton organization in fibroblastic cells. Since actin rearrangement is important for insulin-induced Glut 4 translocation, we studied the potential involvement of Enigma in insulin-induced glucose transport in 3T3-L1 adipocytes. Enigma mRNA was expressed in differentiated adipocytes and APS and Enigma were co-localized with cortical actin. Expression of an APS mutant unable to bind Enigma increased the insulin-induced Glut 4 translocation to the plasma membrane. By contrast, overexpression of Enigma inhibited insulin-stimulated glucose transport and Glut 4 translocation without alterations in proximal insulin signaling. This inhibitory effect was prevented with the deletion of the LIM domains of Enigma. Using time-lapse fluorescent microscopy of GFP-actin, we demonstrated that the overexpression of Enigma altered insulin-induced actin rearrangements, whereas the expression of Enigma without its LIM domains was without effect. A physiological link between increased expression of Enigma and an alteration in insulin-induced glucose uptake was suggested by the increase in Enigma mRNA expression in adipose tissue of diabetic obese patients. Taken together, these data strongly suggest that the interaction between APS and Enigma is involved in insulin-induced Glut 4 translocation by regulating cortical actin remodelling and raise the possibility that modification of APS/Enigma ratio could participate in the alteration of insulin-induced glucose uptake in adipose tissue.
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