Glucagon-like peptide 1 induces pancreatic beta-cell proliferation via transactivation of the epidermal growth factor receptor.
We previously provided evidence that glucagon-like peptide 1 (GLP-1) induces pancreatic beta-cell growth nonadditively with glucose in a phosphatidylinositol (PI) 3-kinase- and protein kinase C zeta-dependent manner. However, the exact mechanism by which the GLP-1 receptor (GLP-1R), a member of the G protein-coupled receptor (GPCR) superfamily, activates the PI 3-kinase signaling pathway to promote beta-cell growth remains unknown. We hypothesized that the GLP-1R could activate PI 3-kinase and promote beta-cell proliferation through transactivation of the epidermal growth factor (EGF) receptor (EGFR), an event possibly linked to GPCRs via activation of c-Src and the production of putative endogenous EGF-like ligands. Both the c-Src inhibitor PP1 and the EGFR-specific inhibitor AG1478 blocked GLP-1-induced [(3)H]thymidine incorporation in INS(832/13) cells as well as in isolated rat islets, while only AG1478 inhibited the proliferative action of betacellulin (BTC), an EGFR agonist. Both compounds also suppressed GLP-1-induced PI 3-kinase activation. A time-dependent increase in tyrosine phosphorylation of the EGFR in response to GLP-1 was observed in INS(832/13) cells. This transactivation of the EGFR was sensitive to both the pharmacological agents PP1 and AG1478. The action of GLP-1 and BTC on INS cell proliferation was found to be not additive. Overexpression of a dominant-negative EGFR in INS cells with a retroviral expression vector curtailed GLP-1-induced beta-cell proliferation. GLP-1 treatment of INS cells caused a decrease in cell surface-associated BTC, as shown by FACS analysis. Also, the metalloproteinase inhibitor GM6001 and an anti-BTC neutralizing antibody suppressed the GLP-1 proliferative effect. Finally, coculturing the prostatic cancer cell line LNCaP that lacks GLP-1 responsiveness with INS cells increased LNCaP cell proliferation in the presence of GLP-1, thus revealing that INS cells secrete a growth factor in response to GLP-1. GM6001 and an anti-BTC neutralizing antibody suppressed increased LNCaP cell proliferation in the presence of GLP-1 in the coculture experiments. The results are consistent with a model in which GLP-1 increases PI 3-kinase activity and enhances beta-cell proliferation via transactivation of the EGFR that would require the proteolytic processing of membrane-anchored BTC or other EGF-like ligands.
Buteau
Jean
J
Molecular Nutrition Unit, Departments of Nutrition and Biochemistry, University of Montreal, the Centre de Recherche du CHUM and Institut du Cancer, Montreal, Quebec, Canada.
Foisy
Sylvain
S
Joly
Erik
E
Prentki
Marc
M
D000818:Animals; D000906:Antibodies / Q000494:pharmacology; D066259:Betacellulin; D000081247:CSK Tyrosine-Protein Kinase; D002455:Cell Division / Q000502:physiology; D002460:Cell Line; D018920:Coculture Techniques; D004151:Dipeptides / Q000494:pharmacology; D066246:ErbB Receptors / Q000235:genetics* / Q000502:physiology; D005799:Genes, Dominant; D005934:Glucagon / Q000494:pharmacology*; D052216:Glucagon-Like Peptide 1; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins / Q000276:immunology / Q000378:metabolism; D007515:Islets of Langerhans / Q000166:cytology* / Q000378:metabolism; D008297:Male; D010446:Peptide Fragments / Q000494:pharmacology*; D011471:Prostatic Neoplasms / Q000473:pathology; D011498:Protein Precursors / Q000494:pharmacology*; D011505:Protein-Tyrosine Kinases / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D015533:Transcriptional Activation / Q000502:physiology*; D019061:src-Family Kinases
D000906:Antibodies; C587851:BTC protein, human; D066259:Betacellulin; C587853:Btc protein, rat; D004151:Dipeptides; D036341:Intercellular Signaling Peptides and Proteins; C078131:N-(2(R)-2-(hydroxamidocarbonylmethyl)-4-methylpentanoyl)-L-tryptophan methylamide; D010446:Peptide Fragments; D011498:Protein Precursors; D052216:Glucagon-Like Peptide 1; D005934:Glucagon; D066246:ErbB Receptors; D011505:Protein-Tyrosine Kinases; D000081247:CSK Tyrosine-Protein Kinase; D019061:src-Family Kinases; C000631346:CSK protein, human