title: Isoprenylcysteine carboxyl methyltransferase facilitates glucose-induced Rac1 activation, ROS generation and insulin secretion in INS 832/13 β-cells.
abstract: Isoprenylcysteine carboxyl methyltransferase (ICMT) catalyzes the post-translational methylation of C-terminal cysteines of isoprenylated proteins, including small G-proteins and the γ-subunits of heterotrimeric G-proteins. It is widely felt that carboxymethylation promotes efficient membrane association of the methylated proteins and specific protein-protein interactions. In the current study, we tested the hypothesis that ICMT-mediated carboxymethylation of specific proteins (e.g., Rac1) plays a regulatory role in glucose-stimulated insulin secretion (GSIS). Western blot analysis indicated that lCMT is expressed and predominantly membrane associated in INS 832/13 β-cells. siRNA-mediated knockdown of endogenous expression of ICMT markedly attenuated glucose, but not KCl-induced insulin secretion. These findings were further supported by pharmacological observations, which suggested a marked reduction in glucose-, but not KCl-stimulated insulin secretion by acetyl farnesyl cysteine (AFC), a selective inhibitor of ICMT. In addition, glucose-induced Rac1 activation, a hallmark signaling step involved in glucose-stimulated insulin secretion, was markedly inhibited following pharmacological (AFC) or molecular biological (siRNA-ICMT) inhibition of ICMT. Lastly, we also noticed a marked reduction in glucose-induced acute increase in the generation of reactive oxygen species in INS 832/13 cells pre-treated with AFC or transfected with siRNA-ICMT. Together, these data suggest that ICMT regulates glucose-induced Rac1 activation, generation of reactive oxygen species and insulin secretion in pancreatic β-cells.
authors.affiliation: Department of Pharmaceutical Sciences, Eugene Applebaum College of Pharmacy and Health Science, Wayne State University, Detroit, MI, USA.
authors.forename: Bhavaani
authors.initials: B
authors.lastname: Jayaram
authors.forename: Ismail
authors.initials: I
authors.lastname: Syed
authors.forename: Alka
authors.initials: A
authors.lastname: Singh
authors.forename: Wasanthi
authors.initials: W
authors.lastname: Subasinghe
authors.forename: Chandrashekara N
authors.initials: CN
authors.lastname: Kyathanahalli
authors.forename: Anjaneyulu
authors.initials: A
authors.lastname: Kowluru
mesh_terms: D000818:Animals; D002460:Cell Line; D004721:Endoplasmic Reticulum / Q000378:metabolism; D005947:Glucose / Q000494:pharmacology*; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000378:metabolism*; D011189:Potassium Chloride / Q000494:pharmacology; D011496:Protein Methyltransferases / Q000502:physiology*; D034741:RNA, Small Interfering / Q000235:genetics; D051381:Rats; D017382:Reactive Oxygen Species / Q000378:metabolism*; D020830:rac1 GTP-Binding Protein / Q000378:metabolism*
chemical_list: D007328:Insulin; D034741:RNA, Small Interfering; D017382:Reactive Oxygen Species; D011189:Potassium Chloride; D011496:Protein Methyltransferases; C056501:protein-S-isoprenylcysteine O-methyltransferase; C499134:Rac1 protein, rat; D020830:rac1 GTP-Binding Protein; D005947:Glucose