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Expression of Growth Hormone-Independent Adipogenesis by a 3T3 Cell Variant^*

SETH GULLER, MARTIN SONENBERG and ROBERT E. CORIN

Memorial Sloan-Kettering Cancer Center and the Department of Medicine, Cornell University Medical College New York, New York 10021

Address requests for reprints to: Dr. Martin Sonenberg, Department of Medicine, Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, New York 10021.

Abstract

We have examined the regulation of adipogenesis of a 3T3-F442A cell variant. The variant, designated 3T3- GH-independent clone 16 (GI-16), was isolated after seruminduced adipogenic commitment. 3T3-GI-16 fibroblasts displayed a lower serum requirement for adipogenesis than the 3T3-F442A parent cell. Insulin-stimulated adipogenesis of 3T3- GI-16 cells in serum-free medium (SFM) was extensive in the absence of GH, as judged by oil red O staining or glycerol-3- phosphate-dehydrogenase activity, a property not associated with the 3T3-F442A cell. In SFM devoid of GH the concentration of insulin required to promote half-maximal adipogenesis of 3T3-GI-16 fibroblasts was 5 nM. The expression of GHindependent adipogenesis by 3T3-GI-16 cells was not due to exposure to adipogenic stimuli during routine passage, as insulin- stimulated differentiation was not a function of the inoculation density in nonadipogenic cat serum. We noted that nine proteins resolved by polyacrylamide gel electrophoresis behaved in a differentiation-dependent manner during adipogenesis of 3T3-GI-16 and 3T3-F442A fibroblasts in SFM. The concentrations of all nine proteins were regulated in a GH-independent manner during insulin-stimulated adipogenesis of 3T3-GI-16 fibroblasts. In contrast, the presence of insulin alone markedly altered the expression of only two of the proteins during differentiation of 3T3-F442A cells. The observed changes in the expression of five presently uncharacterized differentiation-dependent proteins were most likely due to employment of SFM. Our results suggest that expression of GH-independent insulininduced adipogenesis of 3T3-GI-16 fibroblasts reflects a prior commitment by GH during our selection protocol. These results are discussed in the context of a model in which adipogenesis in vivo is postulated to proceed through the sequential action of GH and insulin on target cells. (Endocrinology 124: 325–332, 1989)

Footnotes

^* This work was supported in part by NIH Grant CA-38627 (to M.S.) and an ADA Feasibility Grant (to R.E.C.).

Recipient of NIH Fellowship 1-F32-AM-07839.

Received July 2, 1988.

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