Glucose-dependent Insulinotropic Polypeptide Activates the Raf-Mek1/2-ERK1/2 Module via a Cyclic AMP/cAMP-dependent Protein Kinase/Rap1-mediated Pathway

• Published in: The Journal of biological chemistry Vol. 277; no. 40; pp. 37088 - 37097
• Main Authors: Ehses, Jan A., Pelech, Steven L., Pederson, Raymond A., McIntosh, Christopher H.S.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 04-10-2002; American Society for Biochemistry and Molecular Biology
• Subjects: Animals; Cell Line; CHO Cells; Cricetinae; Cyclic AMP - physiology; Cyclic AMP-Dependent Protein Kinases - classification; Cyclic AMP-Dependent Protein Kinases - genetics; Cyclic AMP-Dependent Protein Kinases - metabolism; Gastric Inhibitory Polypeptide - pharmacology; Glucose - pharmacology; MAP Kinase Kinase 1; MAP Kinase Kinase 2; MAP Kinase Signaling System; Mitogen-Activated Protein Kinase 1 - metabolism; Mitogen-Activated Protein Kinase 3; Mitogen-Activated Protein Kinase Kinases - metabolism; Mitogen-Activated Protein Kinases - metabolism; Protein-Serine-Threonine Kinases - metabolism; Protein-Tyrosine Kinases - metabolism; Proto-Oncogene Proteins c-raf - metabolism; rap1 GTP-Binding Proteins - metabolism; Rats; Recombinant Proteins - metabolism; Transfection
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M205055200

The gastrointestinal hormone, glucose-dependent insulinotropic polypeptide (GIP), is one of the most important regulators of insulin secretion following ingestion of a meal. GIP stimulates insulin secretion from the pancreatic β-cell via its G protein-coupled receptor activation of adenylyl cyclase and other signal transduction pathways, but there is little known regarding subsequent protein kinase pathways that are activated. A screening technique was used to determine the relative abundance of 75 protein kinases in CHO-K1 cells expressing the GIP receptor and in two pancreatic β-cell lines (βTC-3 and INS-1 (832/13) cells). This information was used to identify kinases that are potentially regulated following GIP stimulation, with a focus on GIP regulation of the ERK1/2 MAPK pathway. In CHO-K1 cells, GIP induced phosphorylation of Raf-1 (Ser-259), Mek1/2 (Ser-217/Ser-221), ERK1/2 (Thr-202 and Tyr-204), and p90 RSK (Ser-380) in a concentration-dependent manner. Activation of ERK1/2 was maximal at 4 min and was cAMP-dependent protein kinase-dependent and protein kinase C-independent. Studies using a β-cell line (INS-1 clone 832/13) corroborated these findings, and it was also demonstrated that the ERK1/2 module could be activated by GIP in the absence of glucose. Finally, we have shown that GIP regulation of the ERK1/2 module is via Rap1 but does not involve Gβγ subunits nor Src tyrosine kinase, and we propose that cAMP-based regulation occurs via B-Raf in both CHO-K1 and β-cells. These results establish the importance of GIP in the cellular regulation of the ERK1/2 module and identify a role for cAMP in coupling its G protein-coupled receptors to ERK1/2 activity in pancreatic β-cells.