Growth Hormone Induces c-fos and c-jun Expression in Cells with Varying Requirements for Differentiation*

GH is one of the major factors required for the differentiation of 3T3-F442A preadipocyte fibroblasts into adipocytes. An early event following the addition of GH to 3T3-F442A preadipocytes is induction of the expression of c-fos and c-jun. Although c-fos and c-jun expression has been observed in conjunction with growth factor-stimulated differentiation in several cell types, it is not clear whether protooncogene expression and differentiation are necessarily related. In this study the relationship between the induction of these protooncogenes and differentiation was evaluated by taking advantage of several cell lines that are related to 3T3-F442A cells but have varying GH requirements for differentiation. Adipose differentiation in the adipogenic cell lines 3T3-L1 and 3T3-GI-16 is known to be GH independent, requiring insulin or insulin-like growth factor-I. In both 3T3-L1 and 3T3-GI-16 preadipocytes, GH, nevertheless, induced the expression of mRNA for both protooncogenes. GH (2.2 nM) was more effective...