Although growth is a gradual process, many events leading to growth are likely to be triggered by rapid changes which take place very early when growth is stimulated by regulators such as growth hormone (GH). The PI's laboratory recently found that GH stimulates two growth- related genes, c-fos and c-jun, in less than 30 minutes of exposure of cells to GH. These very rapid changes in gene expression are likely to be among the initial events triggered by GH in target cells. Since these genes are known to act coordinately to activate other genes in growing and differentiating cells, induction of c-fos and c-jun by GH would be expected to lead to activation of other genes important in the effects of GH on differentiation and/or metabolism. Thus, the overall objective of this grant is to define the mechanisms for the stimulation by GH of the expression of c-fos and c-jun, and to determine the consequences of such stimulation by GH in differentiation of 3T3-F442A cells. Whether the effect of GH involves the production of messenger RNA (transcription) for c-fos and c-jun, and/or whether GH affects the stability of existing messenger RNA for each of the genes will be determined. Whether known regulatory regions on the c-fos gene are sensitive to GH will be examined. To determine the importance of GH- induced expression of c-fos and c-jun in 3T3-F442A differentiation, the PI will prepare cells which produce too much of the products of these genes, or cells in which expression of c-fos and c-jun is blocked, and will examine the consequences of such changes on differentiation. 3T3- F442A cells are well-suited for these studies, since: (a) GH is a key factor in promoting their differentiation in fat cells, (b) the gene products Fos and Jun/AP-1 are known to activate other genes in these cells, and (c) these cells also exhibit a variety of other responses to GH. The results of these studies will provide important new insights into early molecular events in GH action and into the role of the growth-related genes c-fos and c-jun in GH action.
