The Role Of CDC20 And RRM1 In The Regulation Of Radiosensitivity In Human Colorectal Cancer

Radiotherapy is one of the most important methods for the treatment of malignant tumors.More than 50%of cancer patients will be involved in radiotherapy during the treatment process.However,due to individual differences and tumor heterogeneity,not all patients derive survival benefit from radiotherapy,while suffering serious adverse consequences.Thus,radiosensitivity has always been a topic of primary importance in the field of radiation oncology.Based on our previously established databases(dbCRSR)and GEO(Gene Expression Omnibus)databases,we identified two leading genes specifically associated with radiosensitivity in cancer cells by integrating gene co-expression and protein-protein interaction data(PPI)to identify cancer regulatory networks and candidate genes.The core of this article was as follows:Part I:CDC20 affects the radiosensitivity of tumor cells through intrinsic apoptotic pathway.Radiotherapy is an important modality for the local control of human cancers,but the radioresistance induced by the aberrant apoptotic signaling is a hallmark of cancers.Restoring the aberrant apoptotic pathways is an emerging strategy for cancer radiotherapy.In this study,we determined that targeting cell division cycle 20(CDC20)radiosensitized colorectal cancer(CRC)through the mitochondrial-dependent apoptotic signaling.CDC20 was overexpressed in CRC and upregulated after radiation.Inhibiting CDC20 activities genetically or pharmacologically suppressed the proliferation and increased radiation-induced DNA damage and intrinsic apoptosis in CRC cells.Mechanistically,knockdown of CDC20 suppressed the expression of anti-apoptotic protein Mcl-1 but not other Bcl-2 family proteins.The expression of CDC20 and Mcl-1 respond to radiation simultaneously through direct interaction evidenced by immunoprecipitation and GST pull down assays.Subsequently,decreased Mcl-1 expression inhibited the phosphorylation of downstream Chkl,which resulting in increased DNA damage through downregulating the homologous recombination repair protein Rad51 and finally caused apoptotic signaling.In addition,both CDC20 and Chkl inhibitors together with in vivo studies confirmed the radiosensitizing effect of CDC20 through inhibiting Mcl-1 and p-Chk1 expression.In summary,our results indicate that targeting CDC20 is a promising strategy to improve the cancer radiotherapy.Part II:Targeting RRM1 improves radioresistance by regulating the ferroptosis pathway induced by radiotherapy.Although radiotherapy has been successfully applied to treat many types of cancer,surviving cancer cells are usually resistant to treatment,increasing the risk of local recurrence and distant metastasis.Ribonucleotide reductase M1(RRM1)is the rate-limiting enzyme in DNA synthesis.In this paper,we report that targeting RRM1 increases the accumulation of cellular reactive oxygen species(ROS)and lipid peroxidation by disrupting the activity and expression of the antioxidant enzyme GPX4,thereby promoting ferroptosis and affects sensitivity to radiation and chemotherapeutics in human cancer cells.In response to radiation-induced DNA double-strand breaks,RRM1 in the cytoplasm translocated into the nucleus and regulates the stability of p53.Importantly,we demonstrated that RRM1 regulates the deubiquitinating enzyme USP11 and ubiquitinating enzyme MDM2 to affect the ubiquitination modification of p53.Unstable p53 inhibits the expression of GPX4 through the p21 protein.In addition,we confirmed that targeting RRM1 can also increase radiation-induced apoptosis signals and cause crosstalk between radiation-induced ferroptosis and apoptosis.Based on the collective findings,we propose that RRM1 as important negative mediators of resistance in radiotherapy could serve as useful potential targets of concurrently applied genetic therapy aimed to inhibit tumor’s antioxidant system and enhance the efficiency of radiotherapy in cancer patients.In summary,this study revealed the radiosensitization mechanism of the cytoplasmic targets CDC20 and RRM1.This study provides a powerful experimental basis for the screening of radiotherapy markers,and has important significance for the"biological precision" and clinical translational research of radiotherapy.