THE EXPRESSION AND REGULATION OF STATS DURING 3T3-L1 ADIPOCYTE DIFFERENTIATION

STATs (Signal Transducers and Activators of Transcription) comprise a family of transcription factors that reside in the cytoplasm of restin g cells, In response to a variety of stimuli, STATs become tyrosine-ph osphorylated and translocate to the nucleus where they mediate transcr iptional regulation, We have used the 3T3-L1 murine cell line to exami ne the expression of STAT proteins as a function of their differentiat ion into adipocytes, The expression of STATs 1, 3, and 5, but not of S TAT 6, is markedly elevated in adipocytes as compared with their fibro blast precursors, Exposure of 3T3-L1 preadipocytes to tumor necrosis f actor alpha (TNF alpha) blocks their differentiation into adipocytes, Therefore, we examined STAT expression as a function of differentiatio n in the presence of this cytokine, The expression of STATs 1 and 5 is markedly attenuated in the presence of TNF alpha, whereas STAT 3 expr ession is unaffected by this treatment, Only STAT 1 is down-regulated by TNF alpha in fully differentiated cells, Thus, although the express ion of STATs 1, 3, and 5 is markedly enhanced upon differentiation, on ly STAT 5 expression is tightly correlated with the adipocyte phenotyp e, These data suggest that STAT 5, and possibly STAT 1, could be poten tial inducers of tissue-specific genes, which contribute to the develo pment and maintenance of the adipocyte phenotype.