title: Mechanisms of extracellularly regulated kinases 1/2 activation in adrenal glomerulosa cells by lysophosphatidic acid and epidermal growth factor.
abstract: The regulation of adrenal function, including aldosterone production from adrenal glomerulosa cells, is dependent on a variety of G protein-coupled receptors (GPCRs) and receptor tyrosine kinases (RTKs). In many cell types, GPCR-mediated MAPK activation is mediated through transactivation of RTKs, in particular the epidermal growth factor (EGF) receptor (EGF-R). However, the extent to which this cross-communication between GPCRs and RTKs is operative in the adrenal glomerulosa has not been defined. Bovine adrenal glomerulosa cells express receptors for lysophosphatidic acid (LPA) and EGF. In cultured bovine adrenal glomerulosa cells, LPA, which is predominantly coupled to Gi and partially to Gq/protein kinase C alpha and epsilon, caused phosphorylation of Src (at Tyr416), proline-rich tyrosine kinase (Pyk2 at Tyr402), EGF-R, protein kinase B/Akt, extracellularly regulated signal kinases 1/2, and their dependent protein, p90 ribosomal S6 kinase. Overexpression of dominant negative mutants of Ras or EGF-R, and selective inhibition of EGF-R kinase with AG1478, significantly reduced LPA-induced ERK1/2 phosphorylation. However, this was not impaired by inhibition of matrix metalloproteinase (MMP) and heparin-binding EGF. LPA-induced ERK1/2 activation occurs predominantly through EGF-R transactivation by Gi/Src and partly through activation of protein kinase C, which acts downstream of EGF-R and Ras. In contrast, LPA-induced phosphorylation of Shc and ERK1/2 in clonal hepatocytes (C9 cells) was primarily mediated through MMP-dependent transactivation of the EGF-R. These observations in adrenal glomerulosa and hepatic cells demonstrate that LPA phosphorylates ERK1/2 through EGF-R transactivation in a MMP-dependent or -independent manner in individual target cells. This reflects the ability of GPCRs expressed in cell lines and neoplastic cells to utilize distinct signaling pathways that can elicit altered responses compared with those of native tissues.
authors.affiliation: Endocrinology and Reproduction Research Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda Maryland 20892-4510, USA. shahb@mail.nih.gov
authors.forename: Bukhtiar H
authors.initials: BH
authors.lastname: Shah
authors.forename: Albert J
authors.initials: AJ
authors.lastname: Baukal
authors.forename: Farzana B
authors.initials: FB
authors.lastname: Shah
authors.forename: Kevin J
authors.initials: KJ
authors.lastname: Catt
mesh_terms: D000818:Animals; D002417:Cattle; D002478:Cells, Cultured; D004789:Enzyme Activation / Q000187:drug effects; D004815:Epidermal Growth Factor / Q000378:metabolism / Q000494:pharmacology*; D066246:ErbB Receptors / Q000235:genetics; D066257:Heparin-binding EGF-like Growth Factor; D066298:In Vitro Techniques; D036341:Intercellular Signaling Peptides and Proteins; D008246:Lysophospholipids / Q000494:pharmacology*; D020782:Matrix Metalloproteinases / Q000378:metabolism; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism*; D008954:Models, Biological; D015533:Transcriptional Activation / Q000187:drug effects; D015384:Zona Glomerulosa / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology*
chemical_list: C587883:HBEGF protein, human; D066257:Heparin-binding EGF-like Growth Factor; D036341:Intercellular Signaling Peptides and Proteins; D008246:Lysophospholipids; D004815:Epidermal Growth Factor; D066246:ErbB Receptors; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020782:Matrix Metalloproteinases; C032881:lysophosphatidic acid