PT  - JOURNAL ARTICLE
AU  - Stuart J. Mundell
AU  - Giordano Pula
AU  - Julia C. A. More
AU  - David E. Jane
AU  - Peter J. Roberts
AU  - Eamonn Kelly
TI  - Activation of Cyclic AMP-Dependent Protein Kinase Inhibits the Desensitization and Internalization of Metabotropic Glutamate Receptors 1a and 1b
AID  - 10.1124/mol.65.6.1507
DP  - 2004 Jun 01
TA  - Molecular Pharmacology
PG  - 1507--1516
VI  - 65
IP  - 6
4099  - http://molpharm.aspetjournals.org/content/65/6/1507.short
4100  - http://molpharm.aspetjournals.org/content/65/6/1507.full
SO  - Mol Pharmacol2004 Jun 01; 65
AB  - In this study, we characterized the effects of activation of cyclic AMP-dependent protein kinase (PKA) on the internalization and functional coupling of the metabotropic glutamate receptor (mGluR1) splice variants mGluR1a and mGluR1b. Using an enzyme-linked immunosorbent assay technique to assess receptor internalization, we found that the glutamate-induced internalization of mGluR1a or mGluR1b transiently expressed in human embryonic kidney (HEK) 293 cells was inhibited by coactivation of endogenous β2-adrenoceptors with isoprenaline or by direct activation of adenylyl cyclase with forskolin. The PKA inhibitor N-(2-[p-bromocinnamylamino]ethyl)-5-isoquinolinesulfonamide hydrochloride (H89) blocked the effects of both isoprenaline and forskolin. The heterologous internalization of the mGluR1 splice variants triggered by carbachol was also inhibited by isoprenaline and forskolin in a PKA-sensitive fashion, whereas the constitutive (agonist-independent) internalization of mGluR1a was inhibited only modestly by PKA activation. Using inositol phosphate (IP) accumulation in cells prelabeled with [3H]inositol to assess receptor coupling, PKA activation increased basal IP accumulation in mGluR1a receptor-expressing cells and also increased glutamate-stimulated IP accumulation in both mGluR1a- and mGluR1b-expressing cells, but only at short times of glutamate addition. Furthermore, PKA activation completely blocked the carbachol-induced heterologous desensitization of glutamate-stimulated IP accumulation in both mGluR1a- and mGluR1b-expressing cells. In coimmunoprecipitation experiments, the ability of glutamate to increase association of GRK2 and arrestin-2 with mGluR1a and mGluR1b was inhibited by PKA activation with forskolin. Together, these results indicate that PKA activation inhibits the agonist-induced internalization and desensitization of mGluR1a and mGluR1b, probably by reducing their interaction with GRK2 and nonvisual arrestins.