Hong Min, Lin Meng-yin, Huang Jen-ming, Baumeister Peter, Hakre Shweta, Roy Ananda L, Lee Amy S
Department of Biochemistry and Molecular Biology and the University of Southern California/Norris Comprehensive Cancer Center, Keck School of Medicine of the University of Southern California, Los Angeles, California 90089-9176, USA.
J Biol Chem. 2005 Apr 29;280(17):16821-8. doi: 10.1074/jbc.M413753200. Epub 2005 Jan 21.
TFII-I is a signal-induced multi-functional transcription factor that has recently been implicated as a regulatory component of the endoplasmic reticulum (ER) stress response. TFII-I acts through ER stress-induced binding to the ER stress element, which is highly conserved in promoters of ER stress-inducible genes such as Grp78/BiP. Interestingly, its tyrosine phosphorylation sites are required for its activation of the Grp78 promoter. Toward understanding the link between TFII-I, the tyrosine kinase signaling pathway, and Grp78 activation, we discovered that Tg stress induces a dramatic increase of TFII-I phosphorylation at Tyr248 and localization of this form of TFII-I to the nucleus. Chromatin immunoprecipitation analysis further reveals enhanced TFII-I binding to the Grp78 promoter in vivo upon ER stress. Previously, we reported that genistein, a general inhibitor of tyrosine kinase, could suppress ER stress induction of Grp78 by inhibiting complex formation on the ER stress element; however, the mechanism is not known. Consistent with TFII-I being a target of genistein suppression, we observed that genistein could suppress Tg stress-induced phosphorylation of TFII-I. We further demonstrate that c-Src, which is one of kinases identified to mediate phosphorylation of TFII-I at Tyr248, is activated by Tg stress and is able to stimulate the Grp78 promoter activity. Lastly, using stable cell lines with suppressed TFII-I levels, we show that TFII-I is required for optimal induction of Grp78 by ER stress. Our studies provide a molecular link that connects the c-Src tyrosine kinase transduction pathway to ER stress-induced transcriptional activation of Grp78 mediated by TFII-I.
TFII-I是一种信号诱导的多功能转录因子，最近被认为是内质网（ER）应激反应的调节成分。TFII-I通过内质网应激诱导与内质网应激元件结合发挥作用，该元件在内质网应激诱导基因（如Grp78/BiP）的启动子中高度保守。有趣的是，其酪氨酸磷酸化位点是其激活Grp78启动子所必需的。为了理解TFII-I、酪氨酸激酶信号通路和Grp78激活之间的联系，我们发现Tg应激诱导Tyr248位点的TFII-I磷酸化显著增加，并使这种形式的TFII-I定位于细胞核。染色质免疫沉淀分析进一步揭示，内质网应激时体内TFII-I与Grp78启动子的结合增强。此前，我们报道过染料木黄酮，一种酪氨酸激酶的通用抑制剂，可以通过抑制内质网应激元件上的复合物形成来抑制Grp78的内质网应激诱导；然而，其机制尚不清楚。与TFII-I是染料木黄酮抑制的靶点一致，我们观察到染料木黄酮可以抑制Tg应激诱导的TFII-I磷酸化。我们进一步证明，c-Src是已确定介导TFII-I在Tyr248位点磷酸化的激酶之一，被Tg应激激活，并能够刺激Grp78启动子活性。最后，使用TFII-I水平被抑制的稳定细胞系，我们表明TFII-I是内质网应激最佳诱导Grp78所必需的。我们的研究提供了一个分子联系，将c-Src酪氨酸激酶转导通路与内质网应激诱导的由TFII-I介导的Grp78转录激活联系起来。
