IDH1 R132H/Q Mutant Promotes Tumorigenesis Through Downregulating P53

In recent years,a series ofmutations of isocitrate dehydrogenase 1(IDH1)Arg132 site,IDH1 R132H/Q/C/L,have been widely detected in glioma,acute myeloid leukemia,sarcoma,intrahepatic cholangiocarcinoma and other tumors,indicating the correlation of these mutations with the occurrence and development of various tumors.Interestingly,these mutants exhibit gain of function to convert α-KG to 2-HG.Because of its high similarity with α-KG in structure,2-HG can competitively inhibit a series of dioxygenase-catalyzed reactions with α-KG as a substrate.Mechanistically,as an oncometabolite,2-HG have been found to promote tumorigenesis by promoting DNA and histone methylation and facilitating HIF1α expression.However,it is unclear whether 2-HG promotes tumorigenesis by regulating p53,a well-known tumor suppressor.In this work,we constructed the liver conditional knock-in mice of IDH1 R132Q,isolated hepatocytes and MEFs and detected p53 expression in these cells.p53 protein level was dramatically downregulated in both mice hepatocytes and MEFs harbouring IDH1 R132Q mutant,which is further confirmed by overexpressing IDH1 R132H,another 2-HG producing mutant of IDH1,in tumor cell lines.Additionally,p53 was downregulated by treatment of tumor cells with permeable TFMB-2-HG and octyl-2HG,demonstrating that IDH1 R132H/Q caused downregulation of p53 depends on the function of these mutants to produce 2-HG.We also found that p53 mRNA level was decreased in mice hepatocytes and MEFs containing IDH1 R132H/Q mutant.Next we explored the mechanism by which DH1 R132H/Q mutant downregulates p53 mRNA level and found that 2-HG produced by IDH1 R132H/Q mutant inhibited the hydroxylation-mediated ubiquitination and degradation of HIF2α,thereby increasing HIF2α protein level.Increased HIF2α in turn drove the transcription of miR-380-5p.Because miR-380-5p can bind to 3’ UTR of p53 mRNA and promote its degradation,IDH1 R132H/Q mutant eventually downregulates p53 by 2-HG mediated upregulation of HIF2a.Finally,we determined the biological significance of IDH1 R132H/Q mutant regulation of p53.Expression of IDH1 R132Q mutant promoted cell proliferation and such effect was abolished by further expression of p53,indicating that this mutant promotes cell proliferation partially by downregulation of p53.In clinical glioma samples with IDH1 R132H mutation,p53 expression is significant lower than in glioma samples without IDH1 mutation.This observation confirmed our finding that IDH1 mutation may promote tumorigenesis by downregulating p53.In this study we revealed a novel mechanism by which IDH1 R132H/Q mutant promotes tumorigenesis,and thus provide a new clue based on p53 for treatment of tumor with these mutations.