Transcriptional regulation of the resistin gene.

Resistin, which is a protein that is secreted exclusively by adipocytes, plays an important role in insulin resistance and adipocyte differentiation. Adipocytes express significant amounts of resistin mRNA, while preadipocytes express low levels of resistin mRNA. The mechanism that causes this difference is unclear. Therefore, we studied the mechanism regulating resistin expression and the roles of different transcriptional factors in this process. The results from fluorescent photography and semi-quantitative RT-PCR showed that sterol regulatory element-binding protein 1c (SREBP1c) and cyclic AMP response-element-binding protein (CREB) had no effect on resistin expression. By contrast, CCAAT/enhancer-binding protein-alpha (C/EBPalpha) increased resistin mRNA levels both in 3T3-L1 preadipocytes and in 293T cells. The relative increase in the amount of resistin mRNA in the 293T cells was much larger than that in the 3T3-L1 preadipocytes. Moreover, while C/EBPalpha was necessary for resistin expression, we found that up-regulating C/EBPalpha levels alone was not sufficient to induce a similar level of resistin in preadipocytes to that in adipocytes.