title: PRMT1 promotes glucose toxicity-induced β cell dysfunction by regulating the nucleo-cytoplasmic trafficking of PDX-1 in a FOXO1-dependent manner in INS-1 cells.
abstract: Protein N-arginine methyltransferase-1 (PRMT1), the major asymmetric arginine methyltransferase, plays important roles in various cellular processes. Previous reports have demonstrated that levels and activities of PRMT1 can vary in animals with type 2 diabetes mellitus. The aim of this study was to assess the expression and mechanism of action of PRMT1 during glucose toxicity-induced β cell dysfunction. Liposome-mediated gene transfection was used to transfect INS-1 cells with siPRMT1, which inhibits PRMT1 expression, and pALTER-FOXO1, which overexpresses forkhead box protein O1 (FOXO1). The cells were then cultured in media containing 5.6 or 25 mmol/L glucose with or without the small molecule PRMT1 inhibitor AMI-1 for 48 h. The protein levels of PRMT1, the arginine methylated protein α-metR, FOXO1, Phospho-FOXO1, pancreas duodenum homeobox-1 (PDX-1), and the intracellular localization of PDX-1 and FOXO1 were then measured by western blotting. FOXO1 methylation was detected by immunoprecipitated with anti-PRMT1 antibody and were immunoblotted with α-metR. The levels of insulin mRNA were measured by real-time fluorescence quantitative PCR. Glucose-stimulated insulin secretion (GSIS) and intracellular insulin content were measured using radioimmunoassays. Intracellular Ca(2+) ([Ca(2+)]i) was detected using Fura-2 AM. Intracellular cAMP levels were measured using ELISA. Chronic exposure to high glucose impaired insulin secretion, decreased insulin mRNA levels and insulin content, increased intracellular [Ca(2+)]i and cAMP levels, and abolishes their responses to glucose. Inhibiting PRMT1 expression improved insulin secretion, increased mRNA levels and insulin content by regulating the intracellular translocation of PDX-1 and FOXO1, decreasing the methylation of FOXO1, and reducing intracellular [Ca(2+)]i and cAMP concentrations. Transient overexpression of constitutively active FOXO1 in nuclear reversed the AMI-1-induced improvement of β cell function without changing arginine methylation. It is concluded therefore that PRMT1 regulates GSIS in INS-1 cells, through enhanced methylation-induced nuclear localization of FOXO1, which subsequently suppresses the nuclear localization of PDX-1. Our results suggest a novel mechanism that might contribute to the deficient insulin secretion observed under conditions of chronically hyperglycemia.
authors: Department of Endocrinology and Metabolism, The Second Affiliated Hospital of Chongqing Medical University, 76 Linjiang Road, Yuzhong District, Chongqing, 400010, China.
authors: Lixia
authors: L
authors: Lv
authors: Hewen
authors: H
authors: Chen
authors: Jiaying
authors: J
authors: Sun
authors: Di
authors: D
authors: Lu
authors: Chen
authors: C
authors: Chen
authors: Dongfang
authors: D
authors: Liu
mesh_terms: D020013:Calcium Signaling / Q000187:drug effects / Q000235:genetics; D002460:Cell Line; D000242:Cyclic AMP / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors / Q000235:genetics*; D020868:Gene Silencing; D005947:Glucose / Q000633:toxicity*; D018398:Homeodomain Proteins / Q000235:genetics*; D006801:Humans; D007328:Insulin / Q000096:biosynthesis; D050417:Insulin-Secreting Cells / Q000187:drug effects*; D008081:Liposomes; D010182:Pancreatic Diseases / Q000235:genetics*; D011484:Protein-Arginine N-Methyltransferases / Q000037:antagonists & inhibitors / Q000235:genetics*; D012333:RNA, Messenger / Q000096:biosynthesis; D012097:Repressor Proteins / Q000037:antagonists & inhibitors / Q000235:genetics*; D015534:Trans-Activators / Q000235:genetics*; D014162:Transfection
chemical_list: D004791:Enzyme Inhibitors; C085126:FOXO1 protein, human; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors; D018398:Homeodomain Proteins; D007328:Insulin; D008081:Liposomes; D012333:RNA, Messenger; D012097:Repressor Proteins; D015534:Trans-Activators; C084010:pancreatic and duodenal homeobox 1 protein; D000242:Cyclic AMP; C099988:PRMT1 protein, human; D011484:Protein-Arginine N-Methyltransferases; D005947:Glucose