title: Carboxyl-methylation of Rab3D in the rat pancreatic acinar tumor cell line AR42J.
abstract: Rab3D is a small GTPase implicated in regulated exocytosis, and is a marker of secretory granules in exocrine cells. We have previously shown that rab3D undergoes reversible carboxyl-methylation in adult rat pancreatic acinar cells, and that carboxyl-methylation of rab3D is developmentally regulated concomitantly with the maturation of the regulated secretory apparatus in rat pancreas. We also observed that dexamethasone treatment of the rat pancreatic acinar tumor cell line, AR42J, led to a significant increase in the size of the unmethylated pool of a rab3-like protein. The current study was designed to further characterize this rab3-like protein. Here we show that AR42J cells express rab3D, and that the protein focuses on 2D gels as two spots with pI values of 4.9 and 5.0. Treatment of AR42J cells with N-acetyl-S-geranylgeranyl-l-cysteine, an inhibitor of carboxyl-methylation, led to a decrease in the basic form of rab3D and a proportional increase in the acidic form. In contrast, N-acetyl-S-farnesyl-l-cysteine, which inhibits carboxyl-methylation of farnesylated proteins, had no effect. Lovastatin, an inhibitor of geranylgeranylation, also induced an accumulation of the acidic form of rab3D. Taken together, these data indicate that rab3D can undergo reversible carboxyl-methylation in AR42J cells by a geranylgeranyl-specific methyltransferase. The 2D gel and immunoblotting analyses indicated that dexamethasone treatment of AR42J cells led to an increase in the proportion of the unmethylated form of rab3D concurrent to inducing a regulated secretory pathway, similar to the rab3D profile change in developing rat pancreas. Our data, along with previous studies done on developing rat pancreas, indicate that the tumor cell line AR42J represents a good model system for studying the regulated secretory pathway, and that carboxyl-methylation of rab3D may play a role in the acquisition of stimulus-secretion coupling.
authors.affiliation: Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520, USA.
authors.forename: X
authors.initials: X
authors.lastname: Qiu
authors.forename: J A
authors.initials: JA
authors.lastname: Valentijn
authors.forename: J D
authors.initials: JD
authors.lastname: Jamieson
mesh_terms: D000111:Acetylcysteine / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D000918:Antibody Specificity; D003545:Cysteine / Q000031:analogs & derivatives / Q000494:pharmacology; D003907:Dexamethasone / Q000494:pharmacology; D004224:Diterpenes / Q000494:pharmacology; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors / Q000494:pharmacology; D015151:Immunoblotting; D007525:Isoelectric Focusing; D008148:Lovastatin / Q000494:pharmacology; D008745:Methylation / Q000187:drug effects; D010179:Pancreas / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D010190:Pancreatic Neoplasms / Q000378:metabolism*; D020033:Protein Isoforms / Q000378:metabolism; D011496:Protein Methyltransferases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D017368:Protein Prenylation / Q000187:drug effects; D051381:Rats; D013347:Subcellular Fractions / Q000737:chemistry; D014407:Tumor Cells, Cultured; D020692:rab3 GTP-Binding Proteins / Q000378:metabolism*; D020826:rab3A GTP-Binding Protein / Q000378:metabolism
chemical_list: D004224:Diterpenes; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors; C095716:N-acetyl-S-geranylgeranyl-cysteine; D020033:Protein Isoforms; D003907:Dexamethasone; D008148:Lovastatin; D011496:Protein Methyltransferases; C492131:RAB3B protein, human; C492134:RAB3D protein, human; C492132:Rab3b protein, rat; C486479:Rab3c protein, mouse; C486480:Rab3c protein, rat; C492133:Rab3d protein, rat; D020692:rab3 GTP-Binding Proteins; D020826:rab3A GTP-Binding Protein; D003545:Cysteine; C068268:N-acetyl-S-farnesylcysteine; D000111:Acetylcysteine