title: Integrins regulate the linkage between upstream and downstream events in G protein-coupled receptor signaling to mitogen-activated protein kinase.
abstract: Receptor tyrosine kinases (RTKs) and G protein-coupled receptors (GPCRs) can both activate mitogen-activated protein kinase (MAPK), a critical intermediate in the transduction of proliferative signals. Numerous observations have demonstrated that integrin-mediated cell anchorage can regulate the efficiency of signaling from RTKs to MAPK. Recently, a relationship between integrins and GPCR signaling has also emerged; however, little is understood concerning the mechanisms involved. Here, we investigate integrin regulation of GPCR signaling to MAPK, focusing on the P2Y class of GPCRs that function through activation of phospholipase Cbeta. P2Y receptor signaling to the downstream components mitogen-activated protein kinase kinase and MAPK is highly dependent on integrin-mediated cell anchorage. However, activation of upstream events, including inositol phosphate production and generation of calcium transients, is completely independent of cell anchorage. This indicates that integrins regulate the linkage between upstream and downstream events in this GPCR pathway, just as they do in some aspects of RTK signaling. However, the P2Y pathway does not involve cross-activation of a RTK, nor a role for Shc or c-Raf; thus, it is quite distinct from the classical RTK-Ras-Raf-MAPK cascade. Rather, integrin-modulated P2Y receptor stimulation of MAPK depends on calcium and on the activation of protein kinase C.
authors.affiliation: Department of Pharmacology, School of Medicine, University of North Carolina, Chapel Hill, North Carolina 27599-7365, USA.
authors.forename: S M
authors.initials: SM
authors.lastname: Short
authors.forename: J L
authors.initials: JL
authors.lastname: Boyer
authors.forename: R L
authors.initials: RL
authors.lastname: Juliano
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism; D002448:Cell Adhesion; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D005353:Fibronectins / Q000378:metabolism; D006801:Humans; D007295:Inositol Phosphates / Q000378:metabolism; D016023:Integrins / Q000378:metabolism / Q000502:physiology*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D008954:Models, Biological; D011233:Precipitin Tests; D011493:Protein Kinase C / Q000378:metabolism; D058910:Purinergic P2 Receptor Agonists; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000378:metabolism*; D018048:Receptors, Purinergic P2 / Q000378:metabolism*; D015398:Signal Transduction; D013997:Time Factors; D014544:Uridine Triphosphate / Q000378:metabolism
chemical_list: D005353:Fibronectins; D007295:Inositol Phosphates; D016023:Integrins; D058910:Purinergic P2 Receptor Agonists; D011956:Receptors, Cell Surface; D018048:Receptors, Purinergic P2; D000255:Adenosine Triphosphate; D020794:Receptor Protein-Tyrosine Kinases; D011493:Protein Kinase C; D020928:Mitogen-Activated Protein Kinases; D002118:Calcium; D014544:Uridine Triphosphate