title: Regulation of G protein signaling by the 70kDa heat shock protein.
abstract: G protein-coupled receptors (GPCRs) transduce extracellular signals to the interior of the cell by activating membrane-bound guanine nucleotide-binding regulatory proteins (G proteins). An increasing number of proteins have been reported to bind to and regulate GPCRs. We report a novel regulation of the alpha(2A) adrenergic receptor (α(2A)-R) by the ubiquitous stress-inducible 70kDa heat shock protein, hsp70. Hsp70, but not hsp90, attenuated G protein-dependent high affinity agonist binding to the α(2A)-R in Sf9 membranes. Antagonist binding was unchanged, suggesting that hsp70 uncouples G proteins from the receptor. As hsp70 did not bind G proteins but complexed with the α(2A)-R in intact cells, a direct interaction with the receptor seems likely. In the presence of hsp70, α(2A)-R-catalyzed [(35)S]GTPγS binding was reduced by approximately 70%. In contrast, approximately 50-fold higher concentrations of hsp70 were required to reduce agonist binding to the stress-inducible 5-hydroxytryptamine(1A) receptor (5-HT(1A)-R). In heat-stressed CHO cells, the α(2A)-R was significantly uncoupled from G proteins, coincident with an increased localization of hsp70 at the membrane. The contrasting effect of hsp70 on the α(2A)-R compared to the 5-HT(1A)-R suggests that during stress, upregulation of hsp70 may attenuate signaling from specific GPCRs as part of the stress response to foster survival.
authors.affiliation: Universiti Malaysia Sarawak, 93150 Kuching, Sarawak, Malaysia. kslim@fmhs.unimas.my
authors.forename: William K
authors.initials: WK
authors.lastname: Lim
authors.forename: Kimon C
authors.initials: KC
authors.lastname: Kanelakis
authors.forename: Richard R
authors.initials: RR
authors.lastname: Neubig
mesh_terms: D058647:Adrenergic alpha-2 Receptor Agonists / Q000378:metabolism; D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism / Q000494:pharmacology*; D047468:Immunoprecipitation; D011485:Protein Binding; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D018341:Receptors, Adrenergic, alpha-2 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects*; D013696:Temperature; D014162:Transfection
chemical_list: D058647:Adrenergic alpha-2 Receptor Agonists; D018840:HSP70 Heat-Shock Proteins; D021122:Protein Subunits; D018341:Receptors, Adrenergic, alpha-2; D016244:Guanosine 5'-O-(3-Thiotriphosphate)