A Study On Epigrnetic Regulation And Molecular Mechanisms Of ASPP2 In Cancers

According to the latest statistics of the World Health Organization in 2015,cancer is the first or second leading cause of death among those aged < 70 years in 91 of 172 countries,and it ranks third or fourth in an additional 22 countries.The incidence and mortality of malignant tumors in China have increased year by year,and have surpassed cardiovascular and cerebrovascular diseases to become the number one cause of death among Chinese residents.Therefore,revealing the molecular mechanisms of malignant tumors will provide a key target for effective treatment of tumors and is a top priority for improving people's health.Epigenetic regulation refers to the mechanisms that alert gene expression without changing the gene sequence,and is heritable and reversible.This mechanism is widely involved in the regulation of many characteristic changes of malignant tumors,and is closely related to its occurrence,development and drug resistance,so it has attracted much attention.Revealing the epigenetic regulation mechanism is expected to provide potential molecular markers for early detection,disease monitoring and prognosis of cancer patients.ASPP2(Apoptosis Stimulating Proteins of p53-2)belongs to the ASPP family and has tumour suppresser activity such as promoting apoptosis and inhibiting cell migration and growth.Studies have shown that ASPP2 is down-regulated in breast cancer,liver cancer and other malignant tumors,and the decreased ASPP2 is associated with tumor stage and poor prognosis,suggesting that this gene may be an important target for tumor therapy.Renal cell carcinoma and cervical cancer are important tumor types in the urinary system and reproductive system,respectively,and patients with advanced stage have a poor prognosis due to lack of effective treatment strategies.Notably,the expression,regulation and mechanism of ASPP2 in renal and cervical cancer have not been reported.As such,this study will systematically investigate these points in order to find new clues on the mechanisms of tumorigenesis and treatment strategies in those tumours.First of all,RT-PCR and immunohistochemistry combined with TCGA database analysis was applied to reveal the expression of ASPP2 in in renal and cervical cancers.The results show that ASPP2 mRNA and protein levels were significantly reduced in renal cancer cell lines and tissues.mRNA levels were positively correlated with its protein products,and ASPP2 downregualtion is associated with high stage and poor prognosis in renal cell carcinoma patients.Similar results were obtained in cervical cancers.It was found that the mRNA expression level of ASPP2 was significantly down-regulated in cervical cancer tissues compared with the matched ajecent controls.The expression of ASPP2 in cervical cancers is correlated with poor prognosis.Next,this thesis further studied the molecular mechanisms of ASPP2 down-regulation in the above tumors.The results show that ASPP2 downregualtion in renal cell carcinoma cells was mainly due to HDAC1-mediated histone deacetylation,but not DNA methylation at ASPP2 promoter.Further mechanisms study revealed that histone acetylation can affect the binding ability of the transcription factor E2F1 to the ASPP2 promoter,and thus play a role in promoting the expression of ASPP2.In addition,the study also found that MiR-205 can directly target ASPP2 in cervical cancer cells,inhibiting the mRNA and protein expression of ASPP2.The expression level of MiR-205 is negatively correlated with ASPP2 in tumor tissues,suggesting that miR-205 may be an important factor mediating the inactivation of ASPP2 in vivo in tumor tissues.Furthermore,in this thesis,the biological function of ASPP2 in renal and cervical cancer was also explored by in vitro cell model and in vivo animal experiments.The results demenstrate that ASPP2 increases the chemosensitivity of tumor cells and xenograft tumors by promoting chemotherapeutic drugs induced apoptosis in both renal and cervical cancers.In addition,ASPP2 also has the effect of inhibiting tumor cell proliferation and xenograft tumor growth.Wound healing and cell migration assay have shown that ASPP2 can inhibit the migration of cancer cells.Hypoxia is a featured tumor microenviroment conditions.The expression levels of ASPP2 and MiR-205 were detected under such conditions,and MiR-205 expression was found to be increased by hypoxia,while ASPP2 was decreased.In addition,MiR-205 exhibited a negative association with ASPP2.Restoration of ASPP2 expression reversed epithelial-mesenchymal transition and cell migration induced by hypoxia,suggesting that MiR-205/ASPP2 plays an important regulatory role in hypoxia-induced cell metastasis.In summary,this thesis first discovered the down-regulation of ASPP2 expression in renal and cervical cancer and also found that its correlation with poor tumor prognosis.It also revealed the molecular mechanism of epigenetic regulation of ASPP2 down-regulation.Functional studies show that ASPP2 promotes tumor cell apoptosis and inhibits cell growth and migration.These new findings not only deepen people's understanding of the regulation mechanisms and biological effects of the tumor suppressor gene ASPP2,but also provide new perspectives and clues for improving the chemotherapy effect and inhibiting the metastasis of renal and cervical cancer.