Growth hormone regulation of the expression of differentiation-dependent genes in preadipocyte Ob1771 cells

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Abstract
The adipose conversion of Ob1771 preadipocytes, during exposure to medium containing bovine serum and supplemented with growth hormone, is accompanied by the acquisition of phenotypic markers and the increased accumulation of specific mRNAs. The expression of lipoprotein lipase, and that of unidentified pOb24 and pGH3 mRNAs, are early events which are independent of growth hormone supplementation. By contrast, the late expression of mRNAs encoding for glycerol-3-phosphate dehydrogenase and p422 protein (a myelin-P2 homologue) and that of glycerol-3-phosphate dehydrogenase activity require the presence of growth hormone. The abundance of beta-actin mRNA does not change during differentiation. Runoff transcription by nuclei isolated from untreated or growth hormone-treated cells reveal little or no change in the rates of transcription of pOb24, pGH3 and beta-actin mRNAs. By contrast, the transcription rate of the p422 gene increases markedly (greater than 6-fold) in nuclei of growth hormone-treated cells. However, the p422 mRNA is more abundant than would be predicted by its nuclear transcription alone, suggesting, in Ob1771 cells exposed to growth hormone, that there is a post-transcriptional level of control. These results indicate that the permissive role of growth hormone during adipose cell differentiation is related to terminal events only and that its effects can be seen both at the protein and mRNA level. These results strongly suggest that an increased rate of specific transcription is primarily responsible for the accumulation of mRNAs during exposure to growth hormone.