title: The rho guanosine 5'-triphosphatase, cell division cycle 42, is required for insulin-induced actin remodeling and glucagon-like peptide-1 secretion in the intestinal endocrine L cell.
abstract: Rho GTPases, such as cell division cycle 42 (Cdc42) and ras-related C3 botulinum toxin substrate 1 (Rac1), have been identified as regulators of F-actin dynamics and hormone release from endocrine cells; however, their role in secretion of the incretin hormone, glucagon-like peptide-1 (GLP-1), from the enteroendocrine L cell is unknown. Insulin induced a 1.4-fold increase in L cell GLP-1 release; however, secretion was potentiated to 2.1-fold in the presence of the F-actin depolymerizing agent, latrunculin B, suggesting that F-actin functions as a permissive barrier. In murine GLUTag L cells, insulin stimulated F-actin depolymerization and Cdc42 activation simultaneously, and these events occurred prior to detectable increases in insulin-induced GLP-1 release. After insulin treatment, Cdc42-dependent p21-activated kinase-1 (PAK1) activation was also detected, and transfection of small-interfering RNA against Cdc42 or of dominant-negative Cdc42(T17N) impaired insulin-stimulated PAK1 activation, actin remodeling, and GLP-1 secretion. Overexpression of kinase-dead PAK1(K299R) or PAK1 small interfering RNA similarly attenuated insulin-induced GLP-1 secretion. Knockdown or inhibition of Cdc42 and PAK1 activities also prevented activation of MAPK/ERK (MEK)-1/2-ERK1/2 by insulin, which was previously identified as a critical pathway for insulin-regulated GLP-1 release. Taken together, these data identify a novel signaling pathway in the endocrine L cell, whereby Cdc42 regulates actin remodeling, activation of the cannonical 1/2-ERK1/2 pathway and PAK1, and GLP-1 secretion in response to insulin.
authors.affiliation: Department of Physiology, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Gareth E
authors.initials: GE
authors.lastname: Lim
authors.forename: Molie
authors.initials: M
authors.lastname: Xu
authors.forename: Jane
authors.initials: J
authors.lastname: Sun
authors.forename: Tianru
authors.initials: T
authors.lastname: Jin
authors.forename: Patricia L
authors.initials: PL
authors.lastname: Brubaker
mesh_terms: D000199:Actins / Q000378:metabolism*; D000818:Animals; D002460:Cell Line; D045744:Cell Line, Tumor; D003599:Cytoskeleton / Q000187:drug effects / Q000378:metabolism; D019858:Enteroendocrine Cells / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D052216:Glucagon-Like Peptide 1 / Q000378:metabolism*; D006801:Humans; D015151:Immunoblotting; D047468:Immunoprecipitation; D007328:Insulin / Q000494:pharmacology*; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D034622:RNA Interference; D015398:Signal Transduction / Q000187:drug effects; D013997:Time Factors; D020764:cdc42 GTP-Binding Protein / Q000235:genetics / Q000378:metabolism*; D054462:p21-Activated Kinases / Q000235:genetics / Q000378:metabolism; D020741:rho GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D000199:Actins; D007328:Insulin; D052216:Glucagon-Like Peptide 1; C515903:PAK1 protein, human; D054462:p21-Activated Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D020764:cdc42 GTP-Binding Protein; D020741:rho GTP-Binding Proteins