REGULATION OF PREADIPOCYTE FACTOR-I GENE-EXPRESSION DURING 3T3-L1 CELL-DIFFERENTIATION

Preadipocyte factor-1 (Pref-1), a novel gene product isolated from mur ine preadipocyte 3T3-L1 cells, is thought to function as a negative re gulator of adipocyte differentiation. We investigated the regulation o f Pref-1 expression in 3T3-L1 preadipocytes during proliferation, grow th arrest, and early differentiation in the presence and absence of th ree well. described differentiation antagonists: interleukin-11 (IL-11 ), transforming growth factor-beta, and tumor necrosis factor-alpha. N orthern blot analysis was used to determine messenger RNA (mRNA) stead y state expression of Pref-1 and two differentiation-specific genes, a dipsin and glycerol-3-phosphate dehydrogenase. We confirmed that Pref- 1 mRNA is abundant in proliferating preadipocytes and that its express ion is dramatically reduced early in differentiation. However, prolife rating and growth-arrested cells treated with the differentiation inhi bitor IL-11 demonstrated a modest decrease in Pref-1 mRNA abundance. T ransforming growth factor-p and tumor necrosis factor-alpha had little effect. The reduction of Pref-1 mRNA was most dramatic in differentia ting preadipocytes treated with IL-11, occurring despite inhibition of adipogenesis, as judged by cell morphology and adipocyte-specific gen e expression (adipsin and glycerol-3-phosphate dehydrogenase). This ef fect of IL-11 on Pref-1 suggests that different mechanisms are respons ible for the IL-11-induced and the differentiation-associated down-reg ulation of Pref-1, thus dissociating Pref-1 regulation from differenti ation. We conclude that Pref-1 expression is not a reliable marker of preadipocytes, and that decreased Pref-1 abundance does not function a s a trigger for adipocyte differentiation.