title: G protein-coupled receptors (GPCRs) That Signal via Protein Kinase A (PKA) Cross-talk at Insulin Receptor Substrate 1 (IRS1) to Activate the phosphatidylinositol 3-kinase (PI3K)/AKT Pathway.
abstract: G protein-coupled receptors (GPCRs) activate PI3K/v-AKT thymoma viral oncoprotein (AKT) to regulate many cellular functions that promote cell survival, proliferation, and growth. However, the mechanism by which GPCRs activate PI3K/AKT remains poorly understood. We used ovarian preantral granulosa cells (GCs) to elucidate the mechanism by which the GPCR agonist FSH via PKA activates the PI3K/AKT cascade. Insulin-like growth factor 1 (IGF1) is secreted in an autocrine/paracrine manner by GCs and activates the IGF1 receptor (IGF1R) but, in the absence of FSH, fails to stimulate YXXM phosphorylation of IRS1 (insulin receptor substrate 1) required for PI3K/AKT activation. We show that PKA directly phosphorylates the protein phosphatase 1 (PP1) regulatory subunit myosin phosphatase targeting subunit 1 (MYPT1) to activate PP1 associated with the IGF1R-IRS1 complex. Activated PP1 is sufficient to dephosphorylate at least four IRS1 Ser residues, Ser318, Ser346, Ser612, and Ser789, and promotes IRS1 YXXM phosphorylation by the IGF1R to activate the PI3K/AKT cascade. Additional experiments indicate that this mechanism also occurs in breast cancer, thyroid, and preovulatory granulosa cells, suggesting that the PKA-dependent dephosphorylation of IRS1 Ser/Thr residues is a conserved mechanism by which GPCRs signal to activate the PI3K/AKT pathway downstream of the IGF1R.
authors.affiliation: From the School of Molecular Biosciences, Washington State University, Pullman, Washington 99164 and.
authors.forename: Nathan C
authors.initials: NC
authors.lastname: Law
authors.affiliation: the Division of Endocrinology, Dept. of Medicine, Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts 02115.
authors.forename: Morris F
authors.initials: MF
authors.lastname: White
authors.affiliation: From the School of Molecular Biosciences, Washington State University, Pullman, Washington 99164 and mehd@wsu.edu.
authors.forename: Mary E
authors.initials: ME
authors.lastname: Hunzicker-Dunn
mesh_terms: D000818:Animals; D001943:Breast Neoplasms / Q000378:metabolism / Q000473:pathology; D002478:Cells, Cultured; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D005260:Female; D006107:Granulosa Cells / Q000166:cytology / Q000378:metabolism; D006801:Humans; D055504:Insulin Receptor Substrate Proteins / Q000378:metabolism*; D006080:Ovarian Follicle / Q000166:cytology / Q000378:metabolism; D058539:Phosphatidylinositol 3-Kinase / Q000378:metabolism*; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism*; D015398:Signal Transduction; D013964:Thyroid Neoplasms / Q000378:metabolism / Q000473:pathology
chemical_list: D055504:Insulin Receptor Substrate Proteins; D043562:Receptors, G-Protein-Coupled; D058539:Phosphatidylinositol 3-Kinase; D051057:Proto-Oncogene Proteins c-akt; D017868:Cyclic AMP-Dependent Protein Kinases
keywords: G protein-coupled receptor (GPCR); PI3K; PKA; insulin receptor substrate 1 (IRS1); insulin-like growth factor (IGF)