UP-REGULATION OF VINCULIN EXPRESSION IN 3T3 PREADIPOSE CELLS BY GROWTH-HORMONE

In an effort to define biochemical events relevant to the adipogenic action of GH, the effect of GH on expression of the cytoskeletal element vinculin was studied in 3T3-F442A preadipose cells. Results from Western blotting indicated that in serum-free medium 2 nM met-hGH induced an approximately 100% increase in vinculin expression relative to that in cells maintained in serum-free medium alone. GH-elicited alterations in vinculin expression were dose dependent. GH treatment elevated levels of tubulin to a lesser extent, whereas actin expression was unaffected by GH. Immunoprecipitation experiments revealed that GH treatment promoted a 200% increase in vinculin synthesis on day 4 relative to that in control cells. GH had no effect on phosphorylation of vinculin in 3T3-F442A cells. Based on Northern blotting, we noted that GH induced approximately a 200% increase in levels of vinculin mRNA on day 4. GH responsiveness as well as levels of vinculin were similar in 3T3-GI-16 (a highly adipogenic subclone of the 3T3-F442A cell) and 3T3-F442A cells. The GH-dependent increase in vinculin protein expression was not observed in nonadipogenic 3T3-C2 cells, suggesting that this effect of GH was related to the program of differentiation. Interestingly, levels of vinculin in nontreated 3T3-C2 cells were approximately 10-fold lower than levels in 3T3-F442A cells. GH-mediated alterations in vinculin expression in 3T3-F442A cells were abolished by treatment with fetal bovine serum, a potent mitogen. Our data indicate that increased expression of vinculin is a component of the GH-induced portion of the adipose differentiation program.