The Function And Mechanism Study Of SMYD5-catalyzed Histone H3 Lysine 36 Trimethylation At Promoters

Histone modification,one of the most important epigenetic information carriers,functions in regulating gene expression.H3K36me3 is widely enriched in the genome and participates in various biological processes,including DNA damage,transcription activation,RNA splicing,m~6A modification,etc.In mammalian cells,H3K36me3 is mainly distributed in the gene body regions.The enrichment gradually increases from 5’ends to 3’ends.H3K36me3 is mainly catalyzed by SETD2.When we perform CUT&Tag to analyze the distribution of H3K36me3,we find a high enrichment of H3K36me3 at promoter regions,which is not detected by Ch IP-seq.Through CRISPR/Cas9 knockout screening,we identify SMYD5 as the methyltransferase to catalyze H3K36me3 at promoter regions.A further mechanistic study finds that SMYD5 is recruited to chromatin by RNA Polymerase II to participate in the regulation of gene expression.Biochemistry studies have demonstrated that the enzyme activity of SMYD5 is dependent on its C-terminal glutamic acid-rich domain.Overexpression of full-length SMYD5 can rescue the enrichment of H3K36me3 at promoters in Smyd5 knockout cells,while the C-terminal domain-truncated SMYD5 cannot restore this enrichment.In addition,elevated Smyd5 expression is detected in liver hepatocellular carcinoma.In mice liver tumor models,the tumorigenesis of liver tumor can be effectively reduced by knocking down Smyd5,and relapsed by overexpressing full-length SMYD5,but not C-terminal domain-truncated SMYD5.In this study,we reveal the enrichment of H3K36me3 at the promoter regions and identify SMYD5 as the responsible methyltransferase.These data provide a new idea for further exploring the function of H3K36me3 and understanding the abnormal H3K36me3 in tumorigenesis.