Molecular Endocrinology, Vol 6, 450-458, Copyright © 1992 by Endocrine Society
The effect of glucocorticoid on the subcellular localization, oligomerization, and processing of mouse mammary tumor virus envelope protein precursor Pr74
JL Corey and MR Stallcup
Department of Pathology, University of Southern California Health Sciences Center, Los Angeles 90033.
Mouse lymphoma cell line W7MG1 is stably infected with mouse mammary tumor
virus and produces the viral envelope glycoprotein precursor Pr74, but the
mature envelope proteins gp52 and gp33, which are derived from Pr74 by
posttranslational processing, are produced only when the cells are cultured
with a glucocorticoid agonist. The current study demonstrated that even
when W7MG1 cells are grown with hormone, the conversion of Pr74 to gp52 and
gp33 is an inefficient process in this cell line. At least 2 h of exposure
to glucocorticoid were required to induce the appearance of gp52 and gp33;
furthermore, Pr74 labeled in the absence of hormone was not converted to
gp52 and gp33 upon subsequent addition of hormone. RNA synthesis inhibitors
blocked the hormonal induction of gp52 and gp33, indicating that the
hormone acts by promoting the expression of a new gene(s) required for the
production of gp52 and gp33, rather than by inhibiting the expression of a
gene(s) that prevents processing of Pr74. Subcellular fractionation studies
demonstrated that Pr74 produced in either the presence or absence of
hormone was associated primarily with the ER, whereas gp52 and gp33 were
found in the Golgi and plasma membrane fractions. The Pr74 molecules from
W7MG1 cells grown either with or without glucocorticoid
coimmunoprecipitated with BiP/GRP78 and sedimented as aggregates of
heterogeneous size. In contrast, Pr74 from virus-producing GR3A mouse
mammary tumor cells, which process Pr74 more efficiently, sedimented as
apparent monomers, dimers, and trimers.(ABSTRACT TRUNCATED AT 250 WORDS)
