The Ubiquitination And Degradation Mechanism Of Methyltransferase MGMT

Double-stranded DNA is an important carrier for storing and transmitting genetic information.Radiation,endogenous and exogenous substances in the environment cause many types of DNA damage.If the organism fails to repair these damages in time,three reactions may occur: cell senescence,cell apoptosis,and cell carcinogenesis.DNA methylation(or alkylation)is a common type of DNA damage.Its repair pathway involves the participation of a variety of DNA repair enzymes,mainly including three repair pathways: base excision repair,a direct reversal of methyltransferase MGMT,demethylation of the ALKB family of demethylases.Alkylating agents are an effective chemotherapy method for cancer treatment.The main mechanism is to cause the alkylation of DNA bases,affect cell proliferation,and even lead to cell death.For example,the alkylated drug TMZ methylates DNA at the N7 of guanine,O3 of adenine,and O6 of guanine.The cytotoxicity of this drug is mainly the DNA damage induced by O6-methylguanine.Studies have shown that the methyltransferase MGMT can transfer the modified methylation group at the O6 position of DNA guanine to its Cys145 active site to repair DNA damage.The high expression of MGMT in tumor cells is a key factor for tumor resistance to TMZ therapy and the main reason for clinical treatment failure.MGMT protein is abnormally highly expressed in a variety of tumor cells,and its regulatory mechanism is still unclear.In this paper,the degradation mechanism of MGMT protein has been deeply studied.Through immunoprecipitation and Pull-down experiments,we identified LMO7 as the E3 ubiquitin ligase of MGMT.Besides,we demonstrate that the 305-638 domain in LMO7,binding to MGMT,is shown to promote the ubiquitination and degradation of MGMT.Next,our research shows that in non-small cell lung cancer,E3 ubiquitin ligase LMO7 acts as a negative regulator of MGMT and affects the stability of MGMT protein.At the same time,under the stimulation of the alkylating agent TMZ,LMO7 significantly accelerates the ubiquitination and degradation of MGMT.In addition,the down-regulation of MGMT by LMO7 results in nonsmall cell lung cancer being sensitive to alkylating agents.In summary,our study identifies LMO7 as the E3 ubiquitin ligase of the methyltransferase MGMT and reveals the ubiquitination and degradation mechanism of MGMT.Our results reveal insights into the potential prospects of LMO7 and MGMT as tumor treatment targets for non-small cell lung cancer treatment.