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Article: Cytosolic protein kinase A mediates the growth hormone (GH)-releasing action of GH-releasing factor in purified rat somatotrophs

TitleCytosolic protein kinase A mediates the growth hormone (GH)-releasing action of GH-releasing factor in purified rat somatotrophs
Authors
Issue Date1995
PublisherS Karger AG. The Journal's web site is located at http://www.karger.com/NEN
Citation
Neuroendocrinology, 1995, v. 61 n. 5, p. 590-600 How to Cite?
AbstractThe growth hormone (GH)-releasing action of GH-releasing factor (GRF) is known to be cAMP-dependent. However, definitive proof for the involvement of the cAMP-dependent enzyme protein kinase A (PKA) is still lacking. In this study, we characterized the PKA system in purified rat somatotrophs and examined its role in mediating GRF-stimulated GH release under static incubation conditions. PKA enzyme activity was detected only in the cytosolic, but not the particulate fraction of rat somatotrophs. This cytosolic PKA activity exhibited the characteristic cAMP dependence (with ED50 of 0.1 μM), ability to phosphorylate kemptide (a synthetic peptide with a PKA phosphorylation site), and susceptibility to inhibition by the bovine heat-stable PKA inhibitor. GRF treatment (1 pM-1 nM) stimulated the cytosolic PKA activity and GH release from rat somatotrophs in a dose-dependent manner. Time-course studies also demonstrated that activation of cAMP synthesis and PKA activity preceded the GH response to GRF. Stimulation of cytosolic PKA activity in rat somatotrophs by the adenylate cyclase activator forskolin (10 nM-1 μM) and membrane permeant cAMP analog db.cAMP (5 μM-0.5 mM) mimicked the GH-releasing effect of GRF. In contrast, Rp.cAMP, a cAMP antagonist for PKA regulatory subunits, blocked both the cytosolic PKA activity as well as GRF-induced GH release. Similar inhibitions were also observed when an inhibitor for PKA catalytic subunits, H89, was used. Somatostatin (SRIF) (1 nM), the physiological GH-release inhibitor, suppressed the GH response to GRF without affecting the basal or GRF-stimulated PKA activity. SRIF at a higher dose (10 nM) abolished the GH-releasing effect of GRF. In this case, SRIF also induced a small but significant inhibition of GRF-stimulated PKA activity. Taken together, the present study provides direct evidence that PKA enzyme activity is localized only in the cytosol of rat somatotrophs and constitutes an essential component of the signal transduction mechanism for GRF-stimulated GH release. This cytosolic PKA system, however, does not appear to be a major target for the GH-release inhibiting action of SRIF.
Persistent Identifierhttp://hdl.handle.net/10722/178576
ISSN
2015 Impact Factor: 2.583
2015 SCImago Journal Rankings: 1.479
ISI Accession Number ID

 

DC FieldValueLanguage
dc.contributor.authorWong, AOLen_US
dc.contributor.authorMoor, BCen_US
dc.contributor.authorHawkins, CEen_US
dc.contributor.authorNarayanan, Nen_US
dc.contributor.authorKraicer, Jen_US
dc.date.accessioned2012-12-19T09:48:29Z-
dc.date.available2012-12-19T09:48:29Z-
dc.date.issued1995en_US
dc.identifier.citationNeuroendocrinology, 1995, v. 61 n. 5, p. 590-600en_US
dc.identifier.issn0028-3835en_US
dc.identifier.urihttp://hdl.handle.net/10722/178576-
dc.description.abstractThe growth hormone (GH)-releasing action of GH-releasing factor (GRF) is known to be cAMP-dependent. However, definitive proof for the involvement of the cAMP-dependent enzyme protein kinase A (PKA) is still lacking. In this study, we characterized the PKA system in purified rat somatotrophs and examined its role in mediating GRF-stimulated GH release under static incubation conditions. PKA enzyme activity was detected only in the cytosolic, but not the particulate fraction of rat somatotrophs. This cytosolic PKA activity exhibited the characteristic cAMP dependence (with ED50 of 0.1 μM), ability to phosphorylate kemptide (a synthetic peptide with a PKA phosphorylation site), and susceptibility to inhibition by the bovine heat-stable PKA inhibitor. GRF treatment (1 pM-1 nM) stimulated the cytosolic PKA activity and GH release from rat somatotrophs in a dose-dependent manner. Time-course studies also demonstrated that activation of cAMP synthesis and PKA activity preceded the GH response to GRF. Stimulation of cytosolic PKA activity in rat somatotrophs by the adenylate cyclase activator forskolin (10 nM-1 μM) and membrane permeant cAMP analog db.cAMP (5 μM-0.5 mM) mimicked the GH-releasing effect of GRF. In contrast, Rp.cAMP, a cAMP antagonist for PKA regulatory subunits, blocked both the cytosolic PKA activity as well as GRF-induced GH release. Similar inhibitions were also observed when an inhibitor for PKA catalytic subunits, H89, was used. Somatostatin (SRIF) (1 nM), the physiological GH-release inhibitor, suppressed the GH response to GRF without affecting the basal or GRF-stimulated PKA activity. SRIF at a higher dose (10 nM) abolished the GH-releasing effect of GRF. In this case, SRIF also induced a small but significant inhibition of GRF-stimulated PKA activity. Taken together, the present study provides direct evidence that PKA enzyme activity is localized only in the cytosol of rat somatotrophs and constitutes an essential component of the signal transduction mechanism for GRF-stimulated GH release. This cytosolic PKA system, however, does not appear to be a major target for the GH-release inhibiting action of SRIF.en_US
dc.languageengen_US
dc.publisherS Karger AG. The Journal's web site is located at http://www.karger.com/NENen_US
dc.relation.ispartofNeuroendocrinologyen_US
dc.rightsNeuroendocrinology. Copyright © S Karger AG.-
dc.subject.meshAnimalsen_US
dc.subject.meshCyclic Amp - Pharmacologyen_US
dc.subject.meshCyclic Amp-Dependent Protein Kinases - Metabolismen_US
dc.subject.meshCytosol - Enzymologyen_US
dc.subject.meshEnzyme Activation - Drug Effectsen_US
dc.subject.meshGrowth Hormone - Secretionen_US
dc.subject.meshGrowth Hormone-Releasing Hormone - Pharmacologyen_US
dc.subject.meshKineticsen_US
dc.subject.meshMaleen_US
dc.subject.meshPituitary Gland - Enzymology - Secretionen_US
dc.subject.meshRatsen_US
dc.subject.meshRats, Sprague-Dawleyen_US
dc.titleCytosolic protein kinase A mediates the growth hormone (GH)-releasing action of GH-releasing factor in purified rat somatotrophsen_US
dc.typeArticleen_US
dc.identifier.emailWong, AOL: olwong@hkucc.hku.hken_US
dc.identifier.authorityWong, AOL=rp00806en_US
dc.description.naturelink_to_subscribed_fulltexten_US
dc.identifier.doi10.1159/000126884-
dc.identifier.pmid7617138-
dc.identifier.scopuseid_2-s2.0-0029043788en_US
dc.identifier.hkuros9707-
dc.identifier.volume61en_US
dc.identifier.issue5en_US
dc.identifier.spage590en_US
dc.identifier.epage600en_US
dc.identifier.isiWOS:A1995QY53600015-
dc.publisher.placeSwitzerlanden_US
dc.identifier.scopusauthoridWong, AOL=7403147570en_US
dc.identifier.scopusauthoridMoor, BC=6701600835en_US
dc.identifier.scopusauthoridHawkins, CE=7202253904en_US
dc.identifier.scopusauthoridNarayanan, N=7004293248en_US
dc.identifier.scopusauthoridKraicer, J=7006871335en_US

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