Regulation of preadipocyte factor-1 gene expression during 3T3-L1 cell differentiation.

Preadipocyte factor-1 (Pref-1), a novel gene product isolated from murine preadipocyte 3T3-L1 cells, is thought to function as a negative regulator of adipocyte differentiation. We investigated the regulation of Pref-1 expression in 3T3-L1 preadipocytes during proliferation, growth arrest, and early differentiation in the presence and absence of three well described differentiation antagonists: interleukin-11 (IL-11), transforming growth factor-beta, and tumor necrosis factor-alpha. Northern blot analysis was used to determine messenger RNA (mRNA) steady state expression of Pref-1 and two differentiation-specific genes, adipsin and glycerol-3-phosphate dehydrogenase. We confirmed that Pref-1 mRNA is abundant in proliferating preadipocytes and that its expression is dramatically reduced early in differentiation. However, proliferating and growth-arrested cells treated with the differentiation inhibitor IL-11 demonstrated a modest decrease in Pref-1 mRNA abundance. Transforming growth factor-beta and tumor necrosis factor-alpha had little effect. The reduction of Pref-1 mRNA was most dramatic in differentiating preadipocytes treated with IL-11, occurring despite inhibition of adipogenesis, as judged by cell morphology and adipocyte-specific gene expression (adipsin and glycerol-3-phosphate dehydrogenase). This effect of IL-11 on Pref-1 suggests that different mechanisms are responsible for the IL-11-induced and the differentiation- associated down-regulation of Pref-1, thus dissociating Pref-1 regulation from differentiation. We conclude that Pref-1 expression is not a reliable marker of preadipocytes, and that decreased Pref-1 abundance does not function as a trigger for adipocyte differentiation.