Takahashi Yu, Ohoka Nobumichi, Hayashi Hidetoshi, Sato Ryuichiro
Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, University of Tokyo, Tokyo 113-8657, Japan.
J Lipid Res. 2008 Apr;49(4):880-92. doi: 10.1194/jlr.M700545-JLR200. Epub 2008 Jan 10.
In the course of an effort to identify the regulators for peroxisome proliferator-activated receptor gamma (PPARgamma)-dependent perilipin gene expression, we found that tribbles homolog 3 (TRB3), containing a single kinase domain without enzymatic activity, downregulates PPARgamma transcriptional activities by protein-protein interaction. We examined the role that TRB3 plays in adipocyte differentiation in 3T3-L1 cells. TRB3 gene and protein expression was increased during adipocyte differentiation concomitantly with an increase in the mRNA levels of CCAAT/enhancer binding protein homologous protein. The physical interaction between TRB3 and PPARgamma was also verified in 3T3-L1 adipocytes. Forced TRB3 expression in 3T3-L1 cells decreased the mRNA levels of PPARgamma-target genes and intracellular triglyceride levels, whereas knockdown of TRB3 expression by RNA interference increased them. TRB3 also inhibits PPARgamma-dependent adipocyte differentiation in lentivirus-mediated PPARgamma-expressing 3T3-L1 cells. These results provide evidence that TRB3 acts as a potent negative regulator of PPARgamma, a master regulator of adipocyte differentiation, and tightly controls adipogenesis.
在一项旨在鉴定过氧化物酶体增殖物激活受体γ（PPARγ）依赖性脂滴包被蛋白基因表达调控因子的研究过程中，我们发现含单个无酶活性激酶结构域的TRIB3同源物3（TRB3）通过蛋白质-蛋白质相互作用下调PPARγ转录活性。我们研究了TRB3在3T3-L1细胞脂肪生成中所起的作用。在脂肪生成过程中，TRB3基因和蛋白表达增加，同时CCAAT/增强子结合蛋白同源蛋白的mRNA水平也增加。在3T3-L1脂肪细胞中也证实了TRB3与PPARγ之间存在物理相互作用。在3T3-L1细胞中强制表达TRB3会降低PPARγ靶基因的mRNA水平和细胞内甘油三酯水平，而通过RNA干扰敲低TRB3表达则会使其升高。TRB3在慢病毒介导的表达PPARγ的3T3-L1细胞中也抑制PPARγ依赖性脂肪生成。这些结果证明TRB3作为脂肪生成主要调节因子PPARγ的有效负调节因子，严格控制脂肪生成。
