BRCA1 Silencing GPX3 Expression By DNA Methylation Regulate Platinum Therapy Sensitivity In Breast Cancer

Objective: Cancer is a critical public health issue,and chemotherapy is an important component of cancer treatment.However,secondary drug resistance is a significant obstacle to the treatment of cancer.Mutations in the breast cancer susceptibility gene(BRCA1)make cancer more sensitive to chemotherapy drugs that damage DNA,such as platinum.Glutathione peroxidase 3(GPX3)is a vital antioxidant,it also contributes to chemotherapy resistance and tumor progression by regulating ROS levels.The relationship between BRCA1 and GPX3 and how they affect chemotherapy sensitivity in cancer is unknown.Method and Results:(1)The analysis of the transcriptome,clinical,and proteomic data from TCGA,GTEx,HAP,and CPTAC revealed that the expression of GPX3 was down-regulated in a variety of tumor tissues as compared to normal tissues.However,GPX3 expression is associated with lymph node metastases,higher N and T stages,and a worse prognosis for breast,colon,and other malignancies.With the aid of bioinformatics techniques,GPX3 is predicted to be essential in thyroid metabolic health,antioxidants,and the development of immunosuppressive tumor microenvironments.In ovarian,breast,colon,and stomach cancer cells,GPX3 has been discovered to influence the cancer cells’ susceptibility to platinum-based chemotherapy and to affect the proliferation and metastasis of cancer cells in oxidized settings.(2)Downregulation of GPX3 dramatically increased breast cancer cell death,ROS levels,and DNA damage brought on by oxidizing agents and platinum treatments both in vivo and in vitro.Oxidants can reverse the regulation of β-catenin phosphorylated protein levels by GPX3,subcellular location,and production of downstream components.Western Bolt results demonstrated that GPX3 controlled ROS levels to influence the phosphorylation of Akt and GSK3 b.GPX3 knockdown resulted in lowered antioxidant capacity of breast cancer cells,while activation of β-catenin led to further decreased DNA damage repair ability of breast cancer cells,considerably increasing cell sensitivity to oxidants and platinum.(3)High-throughput sequencing revealed that BRCA1 positively regulated GPX3 expression in vitro,controlling the sensitivity of breast cancer to platinum and oxidants.This conclusion is further supported by the findings that overexpression of GPX3 reverses the phenotypic and molecular effects of BRCA1.Histone modification and DNA methylation control the epigenetic regulation of GPX3.Decitabine can lessen GPX3 promoter methylation and restore GPX3 expression,according to MS-PCR.Furthermore,it was discovered that GPX3 expression and methylation levels are controlled by BRCA1.RT-PCR and bioinformatics studies suggested that BRCA1 and DNMT1 were closely related.The Ch IP experiment revealed that DNMT1 directly binds to the Cp G island chromatin of the GPX3 promoter whereas the Co-IP assay revealed that BRCA1 interacts with DNMT1.Conclusion:(1)Clinical data showed that GPX3 was down-regulated in tumor tissues,but GPX3 was associated with lymph node metastasis and poor prognosis in cancer patients.In vitro experiments have shown that GPX3 enhances the metastasis of cancer cells in an oxidative environment and down-regulates GPX3 to increase the sensitivity of cancer cells to oxidants and cisplatin.(2)Regulation of ROS levels by GPX3 affects phosphorylation of Akt,GSK3 b,and β-catenin,and regulates CDK4/6-Cyclin D1 signaling and sensitivity to platinum-based chemotherapy in a β-catenin-activation-dependent manner.(3)BRCA1 directly interacts with DNMT1 to protect GPX3 promoter Cp G island from methylation silencing and participate in platinum-based chemotherapy resistance.