Regulation of cellular growth and differentiation by novel kinase like proteins, TRB family

我们最近发现一种新的假激酶TRB3可被内质网（ER）应激诱导并调节内质网应激诱导的细胞凋亡。最近有报道称，TRB3在某些癌症中高表达。然后从细胞周期的角度探讨了TRB3在细胞增殖中的作用。TRB3可下调HeLa细胞周期相关磷酸酶之一异位CDC25A的表达水平。另一方面，使用RNAi方法敲除TRB3时，内源性CDC25A水平升高。我们观察到TRB3以细胞周期依赖的方式表达，这种表达模式与CDC25A在G2/M期呈负相关。当我们检测TRB3敲除对细胞周期的影响时，其进展在G2/M期被延迟，CDC25A在M/G1期的下调被显著抑制。这些结果表明，TRB3是G2/M期细胞周期进程的调节剂，抑制CDC25A的表达可能是TRB3的靶点之一。其次，观察其对细胞分化的影响。我们利用小鼠脂肪前细胞系3T3-L1细胞检测内源性TRB3在脂肪细胞分化过程中的表达水平，发现其表达在早期呈暂时下降趋势，随后随着细胞分化在mRNA和蛋白水平上逐渐升高。这种表达谱与胁迫诱导转录因子CHOP10/gadd153的出现密切相关。TRB3在3T3-L1细胞中过表达时，细胞内甘油三酯总量和脂肪细胞分化主要调控因子之一PPARγ下游靶点mRNA表达水平发生变化。另一方面，当shRNA法破坏TRB3 mRNA水平时，脂肪细胞分化受到严重阻碍。此外，TRB3和PPARγ在细胞中相互关联，PPARγ过表达诱导的脂肪细胞分化被TRB3的异位表达强烈抑制。结果表明，TRB3通过负向控制PPARγ的转录活性来调节脂肪细胞分化。少

We recently found that a novel pseudokinase TRB3 was induced by endoplasmic reticulum (ER) stress and regulated the ER stress-inducible apoptosis. It was recently reported that TRB3 was highly expressed in some kind of cancers. Then we examined the function of TRB3 in the cell proliferation from the viewpoint of the cell cycle. The expression level of ectopic CDC25A, one of the cell cycle associated phosphatases, was down-regulated by TRB3 in HeLa cells. On the other hand, endogenous CDC25A level was increased when TRB3 was knockdowned by using the RNAi method. We have observed that TRB3 expressed in a cell cycle dependent manner and this expression pattern was reversely correlated with that of CDC25A at the G2/M phase. When we examined the effect of TRB3 knockdown on the cell cycle, its progression was delayed at the G2/M phase and the down-regulation of CDC25A at the M/G1 phase was significantly suppressed. These results suggest that TRB3 is a modulator of cell cycle progression at t … More he G2/M phase and that the inhibition of CDC25A expression will be one of the targets of TRB3.Next, the influence on the cell differentiation was examined. When we had examined the expression level of the endogenous TRB3 in the adipocyte differentiation process using a mouse preadipocyte cell line, 3T3-L1 cell, its expression have temporarily decreased at the early stage, and then have gradually increased according to the cell differentiation at mRNA and protein level. This expression profile was closely related to the appearance of the stress-inducible transcription factor CHOP10/gadd153. When TRB3 was over-expressed in 3T3-L1 cells, the gross amount of intracellular triglyceride and the mRNA expression level of the downstream targets of PPARγ, which is one of the mastering regulator of adipocyte differentiation. On the other hand, when TRB3 mRNA level was impaired by shRNA method, the adipocyte differentiation was potently obstructed. Moreover, TRB3 and PPARγ were associated each other in the cells, and the adipocyte differentiation induced by PPARγ overexpression was strongly suppressed by the ectopic expression of TRB3. It was shown that TRB3 regulates the adipocyte differentiation by negatively controlling the transcriptional activity of PPARγ. Less