| First Author | Seyedabadi M | Year | 2012 |
| Journal | FEBS J | Volume | 279 |
| Issue | 4 | Pages | 650-60 |
| PubMed ID | 22177524 | Mgi Jnum | J:200487 |
| Mgi Id | MGI:5508716 | Doi | 10.1111/j.1742-4658.2011.08459.x |
| Citation | Seyedabadi M, et al. (2012) Ser/ Thr residues at alpha3/beta5 loop of Galphas are important in morphine-induced adenylyl cyclase sensitization but not mitogen-activated protein kinase phosphorylation. FEBS J 279(4):650-60 |
| abstractText | The signaling switch of beta2-adrenergic and mu(1) -opioid receptors from stimulatory G-protein (G(alphas) ) to inhibitory G-protein (G(alphai) ) (and vice versa) influences adenylyl cyclase (AC) and extracellular-regulated kinase (ERK)1/2 activation. Post-translational modifications, including dephosphorylation of G(alphas) , enhance opioid receptor coupling to G(alphas) . In the present study, we substituted the Ser/Thr residues of G(alphas) at the alpha3/beta5 and alpha4/beta6 loops aiming to study the role of G(alphas) lacking Ser/Thr phosphorylation with respect to AC sensitization and mitogen-activated protein kinase activation. Isoproterenol increased the cAMP concentration (EC(50) = 22.8 +/- 3.4 mum) in G(alphas) -transfected S49 cyc- cells but not in nontransfected cells. However, there was no significant difference between the G(alphas) -wild-type (wt) and mutants. Morphine (10 mum) inhibited AC activity more efficiently in cyc- compared to G(alphas) -wt introduced cells (P < 0.05); however, we did not find a notable difference between G(alphas) -wt and mutants. Interestingly, G(alphas) -wt transfected cells showed more sensitization with respect to AC after chronic morphine compared to nontransfected cells (101 +/- 12% versus 34 +/- 6%; P < 0.001); mu1-opioid receptor interacted with G(alphas) , and both co-immunoprecipitated after chronic morphine exposure. Furthermore, mutation of T270A and S272A (P < 0.01), as well as T270A, S272A and S261A (P < 0.05), in alpha3/beta5, resulted in a higher level of AC supersensitization. ERK1/2 phosphorylation was rapidly induced by isoproterenol (by 9.5 +/- 2.4-fold) and morphine (22 +/- 2.2-fold) in G(alphas) -transfected cells; mutations of alpha3/beta5 and alpha4/beta6 did not affect the pattern or extent of mitogen-activated protein kinase activation. The findings of the present study show that G(alphas) interacts with the mu1-opioid receptor, and the Ser/Thr mutation to Ala at the alpha3/beta5 loop of G(alphas) enhances morphine-induced AC sensitization. In addition, G(alphas) was required for the rapid phosphorylation of ERK1/2 by isoproterenol but not morphine. |
