Nrf2和ATF4相互作用在蛋白酶体抑制剂竞争性诱导甲状腺癌细胞ORP150和CHOP表达中的作用及机制研究

Owing to the growing incidences of thyroid cancer worldwide, it has become one of the emerging concerns in cancer studies. In addition, it is a research focus in endocrine tumors. Conventional chemoradiotherapy is very limited in its efficacy in treating thyroid cancer which is resistance from traditional therapy of 'surgery+iodine131+thyroxine'. The era of molecular targeted therapy of thyroid cancer has coming gradually.Proteasome inhibitors represent a novel class of anticancer drugs with very promising clinical activity, while the mechanisms underlying their antitumoral effects remain largely unclarified. Our research group had reported that in thyroid cancer cells，proteasome inhibitors could competitively induce the expression of ORP150 and CHOP,which belong to antiapoptotic protein and proapoptotic protein respectively although the mechanisms remain unclear. Recently, we demonstrated that the extent of ATF4 recruitment to the CHOP promoter was ascribed to the differential induction of CHOP by proteasome inhibitors in a panel of thyroid cancer cells. In addition, we reported that Nrf2 inhibited ATF4 recruitment to the CHOP promoter by direct interaction with ATF4, therefore suppressed CHOP induction mediated by proteasome inhibitors. The interaction between ATF4 and Nrf2 might ascribe to competitive induction of ORP150 and CHOP by proteasome inhibitors. The current project aims to elucidate this hypothesis on the basis of previous work,which will be beneficial to understanding the antitumor mechanism of proteasome inhibitors and provide evidence for its molecular targeted therapy as novel antitumor drug.

由于甲状腺癌在全球发病率逐年上升而成为备受关注的肿瘤之一，也是内分泌系统肿瘤的研究热点，常规放化疗对传统"手术+碘131+甲状腺素"方案治疗无效的甲状腺癌作用显得十分有限，甲状腺癌分子靶向治疗时代已悄然而至。蛋白酶体抑制剂是一类非常有前景的新型肿瘤靶向治疗药物，但其作用机制远未阐明。本课题组报道了蛋白酶体抑制剂在甲状腺肿瘤细胞中竞争性诱导抗凋亡蛋白ORP150和促凋亡蛋白CHOP的表达，但机制尚未阐明。最近本课题组发现ATF4募集到CHOP基因启动子的程度与蛋白酶体抑制剂差异性诱导CHOP表达密切相关，并且Nrf2通过与ATF4相互作用抑制ATF4募集到CHOP基因启动子。Nrf2和ATF4的相互作用可能介导蛋白酶体抑制剂竞争性诱导ORP150和CHOP的表达。本项目拟在这些前期工作基础上阐明这一科学假设，将有助于对蛋白酶体抑制剂抗肿瘤机制的理解，为其成为新型肿瘤靶向治疗药物提供依据。

蛋白酶体抑制剂增加ORP150的表达，并且ORP150敲低增加甲状腺癌细胞对蛋白酶体抑制剂的反应性，提示ORP150的表达上调限制了了蛋白酶体抑制剂对甲状腺癌的治疗效果。机制上本项目发现蛋白酶体抑制剂在转录激活水平增加ORP150的表达，主要表现在蛋白酶体抑制剂通过ORP150基因启动子的-421/-307和-243/+53两个上游序列调节ORP150的转录激活。进一步我们发现Nrf2可以直接结合-421/-307序列并直接转录激活ORP150的表达，而Nrf2还可以通过募集ATF4到-243/+53序列而间接转录激活ORP150的表达。该项目明确了Nrf2在ORP150转录激活的作用及其作用序列，明确了Nrf2及其与ATF4相互作用在蛋白酶体抑制剂上调ORP150中的作用。本项目为临床更合理应用蛋白酶体抑制剂提供了新的潜在靶点。