Expression of growth hormone-independent adipogenesis by a 3T3 cell variant.
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 serum-induced 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 GH-independent 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 insulin-induced 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.
Guller
S
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Department of Medicine, Memorial Sloan-Kettering Cancer Center, New York, New York 10021.
Sonenberg
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M
Corin
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D000273:Adipose Tissue / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D001391:Azo Compounds; D002454:Cell Differentiation / Q000187:drug effects; D002460:Cell Line; D004396:Coloring Agents; D004591:Electrophoresis, Polyacrylamide Gel; D005347:Fibroblasts / Q000378:metabolism; D014644:Genetic Variation; D005993:Glycerolphosphate Dehydrogenase / Q000378:metabolism; D013006:Growth Hormone / Q000494:pharmacology*; D007328:Insulin / Q000494:pharmacology; D050356:Lipid Metabolism; D051379:Mice; D008970:Molecular Weight; D014176:Protein Biosynthesis; D013194:Staining and Labeling
D001391:Azo Compounds; D004396:Coloring Agents; D007328:Insulin; D013006:Growth Hormone; D005993:Glycerolphosphate Dehydrogenase; C011049:oil red O