Methylation Of SREBP1a By PRMT5 Is Crucial For De Novo Lipogenesis And Proliferation Of Hepatocellular Cancer Cells

As other types of malignant tumor,highly activated de novo lipogenesis is a key characterisitic of hepatocellular carcinoma.Transcription factor SREBP directly transcripts lipogenic enzymes including FASN,ACC,ACLY,SCD1,HMGCR and others to subsequently induce de novo lipogensis in tumor,as well as influences the differentiation and growth of cancer cells.We did researches in vivo and in vitro to find the underlying mechanisms of protein arginine methyltransferase member — —PRMT5 in reprogramming de novo lipogenesis to support malignant growth of hepatic cancer cells via a key SREBP——nSREBP1a.By LC-MS/MS analysis,immunocoprecipitation,GST pull down,fluorescent protein positioning experiment technology,in vivo and in vitro methylation analysis and western immunoblotting analysis,we made sure that enzymatic protein PRMT5 directly interacted with nSREBP1 a,as well as symmetry dimethylated nSREBP1 a on its 321 R,and inhibited its phosphorylation of 430 S by GSK3 and subsequently ubiquitination,then increased its protein stablity and downstream gene expression through inhibiting its proteasome-degradation.By oil red O staining,triglyceride metabolismdetection,metabolic MS analysis,cell proliferation in vitro assay and subcutaneous xenograft tumor model building,we found PRMT5 induced de novo lipogeneis in vivo as well as promoted the growth of HEPG2 cells both in vivo and in vitro via increasing the protein stability as well as the transcriptional activity of nSREBP1 a.We also found EGF/EGFR activation could promoted the interaction of nSREBP1 a and PRMT5,as well as promoted the arginine dimethylation level of nSREBP1 a.We found in primary HCC tumor tissues,the dimethylation level of 321 R on nSREBP1 a was higher than controlled normal liver tissues.We also found a positive correlation between the methylation level of 321 R on nSREBP1 a with the size of primary hepatic tumor,but a negative correlation between the methylation level of 321 R on nSREBP1 a with overall survival of HCC patients,which indicated that specific methylation on 321 R of nSREBP1 a by PRMT5 was essential for hepatic cancer cells growth and tumorigenesis.Our research data indicated PRMT5 worked as a key regulator of de novo lipogeneis of hepatic cancer cells through nSREBP1 a dimethylation,and then influenced the proliferation and progression of hepatic cancer cells,which depended EGF/EGFR pathway activation.All these data proved an insight into the mechanisms of dysregulation lipid mechanism in cancer,as well as a rationale for the applying the regulation of PRMT5 to nSREBP1 a as a potential target pathway for therapeutic intervention for the therapy of some types of cancer with de novo lipogenesis.