【作者】 李超；

【导师】 张晓东；

【作者基本信息】 武汉大学 ， 细胞生物学， 2020， 硕士

【摘要】 结直肠癌是世界上致死率排名第四的恶性肿瘤,并且在女性肿瘤中发生率排名第二,在男性肿瘤中排名第三,结直肠癌总体发生率在所有癌症中大约占据了9%,并且发病率近年来逐步上升,对人类的生命健康产生了严重威胁。结直肠癌的发病因素至今没有具体的结论,但与遗传、饮食、年龄等因素有着密切的联系。目前常见的结直肠癌的治疗方式有放射治疗、化学治疗和免疫治疗等,但对于中期晚期患者治疗效果不佳,病人预后差,且复发风险高。所以研究新的治疗方式以及新的治疗靶点对于结直肠癌的治疗是必要的。蛋白质酪氨酸磷酸酶(PTPs)是一类作用于蛋白质酪氨酸的去磷酸酶,此类分子在细胞信号通路中起到重要的调节作用,它们表达的异常或者突变会导致细胞内环境紊乱,从而引起许多疾病例如癌症。经典型的PTPs分子包括受体型与非受体型,其中PTPN18属于非受体型酪氨酸磷酸酶。我们研究发现,PTPN18在结直肠癌组织中的m RNA表达量要高于癌旁组织,并且PTPN18表达量的升高与病人的不良预后有着密切关系,但是PTPN18对结直肠癌具体的影响与作用不得而知。因此,研究PTPN18对结直肠癌的影响以及其在结直肠癌细胞系中的作用机制有着重要意义。本研究结果显示:PTPN18过表达可以促进结直肠癌细胞系的生长增殖,而PTPN18敲除后对结直肠癌细胞系的生长增殖产生抑制。并且,我们通过裸鼠成瘤实验证明了在体内条件下PTPN18敲除后对肿瘤的发生发展也有着明显的抑制作用。PTPN18对MYC信号通路有着激活作用并且可以提高MYC下游基因CDK4的m RNA的表达,而CDK4正是一种调控细胞周期与肿瘤细胞增殖的重要蛋白。随后,我们证明了PTPN18对MYC信号通路的调节是通过对MYC的翻译后修饰途径而非调控MYC的转录。PTPN18与MYC之间具有相互作用并且提高MYC蛋白的稳定性,PTPN18蛋白表达量的提高也增加了MYC与CDK4的蛋白表达量,在肠癌细胞系中敲除PTPN18后MYC与CDK4的蛋白表达量显著降低。总之,我们的结果证明了PTPN18可以通过稳定MYC蛋白来激活MYCCDK4信号通路,从而促进结直肠癌细胞系的生长增殖。所以,PTPN18在结直肠癌中作用机制的揭示为结直肠癌的治疗提供了新的思路,也为未来结直肠癌药物的研究提供了新的靶点。更多还原

【Abstract】 Colorectal cancer is the fourth deadliest cancer in the world,and it ranks the second in female cancer incidence and the third in male cancer incidence.The overall incidence of colorectal cancer accounts for about 9% of all cancers.CRC threatens people’s life and health seriously with its increasing incidence rate.There is no certain conclusion about the cause of colorectal cancer,but it is closely related to heredity,diet,age and other factors.At present,the common treatment methods of colorectal cancer include radiotherapy,chemotherapy,immunotherapy and so on,but the treatment effect is not ideal to the middle and late stage patients with poor prognosis and high recurrence rate.Therefore,it is necessary to find new therapeutic methods and new targets for the treatment of colorectal cancer.Protein Tyr phosphatases(PTPs)are enzymes that dephosphorylate phosphor-Tyr in target proteins,which act a vital role in regulating the cell signaling.Their abnormal expression or mutation will lead to the disorder of intracellular environment,which will cause many diseases such as cancer.Classic PTPs are divided into receptor like and non-receptor like PTPs,and PTPN18 is a member of the NRPTP(non-receptor)subfamily.We found that the m RNA level of PTPN18 in CRC tissues is much higher than that in adjacent tissues,and the increased expression of PTPN18 is tightly relevant to the poor prognosis of patients.However,there are no research about PTPN18 in CRC,and the function of PTPN18 has not yet been fully understood.Therefore,it is of vital importance to find out the effect of PTPN18 on colorectal cancer and its mechanism in colorectal cancer cell lines.Our research found that PTPN18 overexpression promoted growth and tumorigenesis in CRC cells and that PTPN18 deficiency generated the opposite results in vitro.Moreover,a xenograft assay showed that PTPN18 deficiency significantly inhibited tumorigenesis in vivo.PTPN18 activated the MYC signaling pathway and enhanced CDK4 expression,which is closely relevant to the cell cycle and proliferation of cancer cells.Then,we demonstrated that PTPN18 regulated the MYC signaling pathway through post-translational modification instead of the transcription of MYC.PTPN18 can interact with MYC and improve the stability of MYC protein.The increase of PTPN18 protein expression also boosted the protein expression of MYC and CDK4.The protein expression of MYC and CDK4 was significantly decreased after the removal of PTPN18 in colorectal cancer cell lines.All in all,our results showed that PTPN18 can activate MYC-CDK4 signaling pathway by stabilizing MYC protein,thus promoting the proliferation of CRC cell lines.Therefore,the discovery of the mechanism of PTPN18 in colorectal cancer provides a new approach for the treatment of colorectal cancer and provides a novel target for the future research of CRC drugs.更多还原