Deficiency Of Histone Methyltransferase SETD2 In Liver Leads To Abnormal Lipid Metabolism And Hepatocarcinoma

SETD2 is the primary methyltransferase catalyzing H3K36 trimethylation(H3K36me3)in mammalian cells.H3K36me3 is one of the most conserved epigenetic markers from yeast to mammalian.It is mainly localized on the transcribed regions of genes and plays important roles in maintaining transcription fidelity,RNA alternative splicing and DNA damage repair.Many studies have found that SETD2 is frequently mutated in a variety of cancers and acts as a tumor suppressor.In our study,we first analyzed the TCGA cancer databases,and found that SETD2 is frequently mutated in hepatocarcinoma(HCC),with a mutation rate around 4-5%.Meanwhile,SETD2 mutation is associated with worse overall survival rate.To study the function of SETD2 in HCC development,we constructed a mouse model with liver-specific Setd2 knockout,and found that Setd2 depletion caused spontaneous hepatocarcinogenesis in mice.Also,Setd2 depletion significantly increased the tumor numbers and tumor size in the DEN-induced HCC mouse model.In the study of molecular mechanism of Setd2 repressing HCC,we found that liver-specific Setd2 deficiency inhibited the activation of p53 signal pathway under DEN treatment.In addition,according to the tissues transcriptome sequencing and H3K36me3 ChIP-seq analysis,we found that Setd2 is closely related to the homeostasis of lipid metabolism in liver.The results of gene expression detection showed that Setd2 depletion inhibited the expression of cholesterol metabolism genes,such as Abcal,Abcg5/8,Cyp7al and so on.Furthermore,in p53 wild-type cells,SETD2 gene silencing resulted in the down-regulation of p53 protein level.However,in p53 mutant cells,in which p53 target genes could not response to the upstream signals,SETD2 knockdown still led to ABCA1 down-regulation.Then ChIP-qPCR results showed that SETD2 directly regulates the expression of ABCAl through tri-methylating H3K36.The normal expression of ABCA1 is essential to maintain the lipid homeostasis in vivo.Through the determination of lipid content,the level of liver fat and serum cholesterol were significantly increased in live-specific Setd2 knockout mice.In addition,high-fat diet significantly promoted the development of liver cancer associated with Setd2 deficiency.By H3K27ac ChIP-seq analysis,we predicted that c-Jun/AP-1 was activated in Setd2 deficient HCC.In liver cells and tissues,we demonstrated that Setd2 deletion induced c-Jun/AP-1 overexpression by increasing lipid accumulation.c-Jun plays a role of oncogene in HCC.In Setd2 deficient cells,c-Jun up-regulation inhibits DNA damage response signal pathway and ATM phosphorylation,and then inhibits the expression of p53,finally promotes the development of cancer.Taken together,our study shown that Setd2 deletion is one of the driving factors for liver cancer,and revealed the mechanisms of Setd2 regulating cholesterol homeostasis and c-Jun/AP-1 signal transduction,which provides a new therapeutic strategy for HCC patients with SETD2 mutation.