PMP22蛋白抑制细胞凋亡促进胃癌细胞耐药的机制

Drug resistance is the major obstacle to further enhancement of the cure rate for cancer patients , including gastric cancer (GC). In previous studies we have observed that PMP22 is a key factor in regulation cell self-renewal and is linked to drug resistance in gastric cancer. However, the mechanistic insights causing PMP22-mediated chemoresistance, an urgent need in clinic treatment for GC patients, remains unsolved. During the early stage of this research project, we have found that that PMP22 up-regulated the transcription activity of STAT pathway, but down-regulated the transcription activity of p53 pathway. In addition, PMP22 was found to increase the expression level of DNp73, the dominant negative isoform of p73 protein. Since DNp73 proteins can be translated via an intragenic promoter located in intron 3 (P2p73) which contains STAT3-binding site, and that DNp73 acts as trans-repressors of p53-dependent transcription, we hypothesize that PMP22 actives STATs pathway resulting in DNp73 expression and inhibition of apoptosis by repressing p53. To further elucidate the exact mechanism underlying PMP22-induced drug resistance, we aim to identify novel therapeutic targets for GC by screening the interaction proteins and downstream kinases of PMP22. We will focus on detection and confirmation of potential new motifis for phosphorylation motifs and its nuclear localization of STAT3 proteins. In addition to confirmation of STAT3 binding onto the P2p73 promoter, we will further identify the potential co-activitors that could be recruited together with STAT3 for target gene transcription, and compare the relative abundance of p53 and DNp73 on p53-targeted and apoptosis-related gene promotors. Finally, to generate effective therapeutic targets for GC, based on our preliminary studies, we will test and verify the our newly designed drug combination which include the drugs which bind PMP22 or Nano antibodies of PMP22 with cisplatin. All these experiments will be conducted at cellular and animal levels. We believe that the success of conduction of this project will generate critical new information for identifying effective drugs of drug-combinations that can overcome the chemoresistance and significantly enhance the care rate for GC patients.

化疗耐药是肿瘤有效治疗的主要障碍。PMP22蛋白调控胃癌细胞自我更新与化疗耐受，但机制尚不清楚。本课题前期发现PMP22蛋白增强STAT信号通路、抑制P53信号通路活性，并上调p73蛋白的显性失活型DNp73表达水平。鉴于DNp73启动子存在STAT3结合序列，且DNp73抑制p53活性，提示PMP22蛋白可能通过STAT信号通路上调DNp73表达、进而抑制P53蛋白活性，从而抑制细胞凋亡，诱导胃癌细胞耐药。本课题将筛选PMP22蛋白的互作蛋白及下游激酶、检测STAT3蛋白磷酸化与核内定位、确认STAT3蛋白与DNp73基因启动子的结合及转录激活机制，并比较凋亡相关基因启动子上DNp73与p53的丰度，从而阐明PMP22促进胃癌耐药的作用机制；并以PMP22蛋白为靶点，在细胞与动物水平评价不同药物或纳米抗体增强胃癌细胞药物敏感性的效果及副作用，为临床克服肿瘤化疗耐受提供新的思路与治疗方案。

化疗耐药是肿瘤有效治疗的主要障碍。PMP22蛋白在顺铂耐受的胃癌细胞中表达上升，调控胃癌细胞自我更新与化疗耐受，但机制尚不清楚。本项目通过鉴定相互作用蛋白，发现PMP22蛋白与TFRC蛋白相互作用，并结合EGFR；通过筛选转录因子报告基因，发现PMP22蛋白上调STAT3蛋白转录活性；通过筛选下游靶基因，发现DNp73表达上升而凋亡相关基因表达下降。最终阐明PMP22蛋白通过促进STAT3转录因子结合TP73基因的基因内启动子P2p73上，上调显性失活型DNp73的转录，DNp73蛋白继而与p53蛋白竞争性结合，抑制凋亡相关基因的转录，从而诱导胃癌细胞耐药的机制。本项目为顺铂耐药的胃癌患者提供了新的治疗靶点与思路，将顺铂与STAT3抑制剂或PMP22抑制剂联用，可能能够增强胃癌的敏感性。并且由于PMP22与EGFR结合，提示PMP22蛋白可能也参与胃癌的EGFR-TKI耐药，可能作为EGFR-TKI治疗抵抗患者的辅助治疗靶点，我们将对此继续深入研究。同时我们也发现PMP22蛋白调控的治疗抵抗可能不是广谱的，在纳武单抗治疗后的耐药肿瘤组织中未检测到PMP22蛋白阳性的肿瘤细胞，提示PMP22蛋白作为耐药治疗靶点具有一定的适用范围。