Molecular mechanism of CHOP dependent cell death induced by extracellular stresses

内质网应激是由基因突变或蛋白质异常修饰引起的错误折叠或错误折叠蛋白在内质网中的积累而引起的。近年来研究表明，内质网应激诱导的细胞凋亡是神经退行性疾病和糖尿病的重要原因。申请人正在推进对在ER应激下诱导的并且与细胞凋亡相关的转录因子CHOP的分析的研究。在这里，我们已经表明，TRB 3，果蝇激酶样分子Tribbles的人类同源物之一，是由ER应激诱导的，其启动子通过ER应激诱导的转录因子，CHOP和ATF 4激活。TRB 3蛋白抑制CHOP和ATF 4的转录活性，表明CHOP（可能也是ATF 4）信号通过负反馈机制受到TRB 3的严格调控;此外，TRB 3的过表达增强了ER应激诱导的细胞死亡，而通过siRNA方法敲低TRB 3则降低了细胞死亡。我们有 关于我们 用免疫沉淀-Western blot方法观察TRB 3与CHOP的结合。TRB 3对CHOP转录活性的抑制作用不依赖于蛋白质降解。TRB 3的表达不影响CHOP的二聚体形成和DNA结合活性。然而，TRB 3通过其转录结构域与CHOP相关，并且该结构域与p300结合结构域重叠。TRB 3过表达可显著抑制p300-CHOP复合物的形成。这些结果表明TRB 3可能作为拮抗剂替代CHOP中的p300，并控制其转录效应。TRB 3可能通过降低ATF 4的稳定性和p300与ATF 4的解离而抑制ATF 4的反式激活活性。已知ATF 4的下游靶点是细胞生存所必需的一些产物，提示TRB 3下调ATF 4可能通过内质网应激而促进细胞凋亡。少

The endoplasmic reticulum(ER) stress is induced by the accumulation of misfolding or malfolding proteins in ER caused by genetic mutation or abnormal modification of proteins. Recently, it is clarified that the ER stress-induced apoptosis cause the neurodegenerative diseases and the diabetes. Applicants are advancing the study of analysis on transcription factor CHOP to which are induced at the ER stress, and are related of apoptosis. Here we have shown that the TRB3, one of the human homologs of a Drosophila kinase like molecule Tribbles, is induced by ER stress and its promoter is activated via ER stress-induced transcription factors, CHOP and ATF4. TRB3 proteins suppress the transcriptional activities of CHOP and ATF4, suggesting CHOP(probably also ATF4)signaling is strictly regulated by TRB3 via a negative feedback mechanism.In addition, overexpression of TRB3 enhances the ER stress-induced cell death, while the knockdown of TRB3 by a siRNA method decreased the cell death. We have … More also observed the association between TRB3 and CHOP by the immunoprecipitaion-Western blot methods. Inhibitory effect of TRB3 on the transcriptional activity of CHOP is Independent of protein degradation. Moreover, the expression of TRB3 did not influence the dimer formation and DNA binding activities of CHOP. However, TRB3 associated with CHOP through its transcriptional domain and this domain is overlapped with a p300 binding domain. Overexpression of TRB3 remarkably inhibited the formation of p300-CHOP complex. These results suggest that TRB3 may function as an antagonist to replace the p300 from CHOP, and control its transcriptional effect. Moreover, transactivational activity of ATF4 is also suppressed by TRB3 probably by the decrease in its stability and by the dissociation of p300 from ATF4.It is well known that some products necessary for cell survival are the downstream targets of ATF4, suggesting that the downregulation of ATF4 by TRB3 may greatly contribute the apoptosis according to the ER stress. Less