Regulation of transcription factor mRNA accumulation during 3T3-L1 preadipocyte differentiation by antagonists of adipogenesis

Abstract

3T3-L1 predipocytes differentiate into cells having the biochemical properties of adipocytes; tumor necrosis factor-α (TNF), retinoic acid (RA), and transforming growth factor-β (TGF-β), attenuate this process. Inhibition of differentiation by these agents, thought to be at the level of transcription, has been investigated by examining the accumulation of mRNA for six transcription factors and the autocrine growth factor interleukin 6 (IL-6). Upon induction of differentiation, a rapid and major accumulation of c-fos and jun-B mRNA was observed that returned to near basal levels within 4–6 h. In contrast, c-jun mRNA, although rapidly expressed following induction of differentiation, remained at relatively constant levels throughout the time course. Exposure of the cells to 5 nM TNF potentiated the accumulation of all 3 mRNAs but most significantly c-jun (12-fold), which remained elevated for at least 24 h after treatment. In control differentiating cells, krox-20 and fox-B were expressed transiently, 30 min to 2 h, while fra-1 mRNA accumulated over an extended period, 1 to 8 h. Again, TNF enhanced the accumulation of these mRNAs. Accumulation of mRNA for C/EBP, a transcription factor proposed to control expression of genes involved in the terminally differentiated state was attenuated after exposure of the cells to TNF. C/EBP expression was also inhibited in cells exposed to RA or TGF-β. IL-6 mRNA was expressed briefly (30 min to 2 h) and again transiently (at 8 h after induction of differentiation). TNF treatment markedly enhanced accumulation of IL-6 message. We propose that increased cellular content of one or more transcription factors or the suppression of C/EBP may be responsible for the attenuation of differentiation induced by exposure of the cells to TNF, RA, and TGF-β.