G protein-mediated mitogen-activated protein kinase activation by two dopamine D2 receptors

Two isoforms of dopamine D2 receptor, D2L (long) and D2S (short), differ by the insertion of 29 amino acids specific to D2L within the putative third intracellular loop of the receptor, which appears to be important in select ivity for G-protein coupling. We have generated D2L- and D2S-expressing Chi nese hamster ovary (CHO) cells, and regulation of the mitogen-activated pro tein kinase (MAPK) pathway was examined in these cells. Both D2L and D2S me diated a rapid and transient activation of MAPK with dominant activation of p42-kDa MAPK. Pertussis toxin treatment completely abrogated stimulation o f MAPK mediated by D2L and D2S, demonstrating that both receptors couple to pertussis toxin-sensitive G proteins in this signaling. Stimulation of MAP K mediated by both D2L and D2S receptor was markedly attenuated by coexpres sion of the C-terminus of beta-adrenergic receptor kinase (beta ARKct), whi ch selectively inhibits G beta gamma-mediated signal transduction. Further analysis of D2L- and D2S-mediated MAPK activation demonstrated that D2L-med iated MAPK activation was not significantly affected by PKC depletion or pa rtially affected by genistein. In contrast, D2S-mediated MAPK activation wa s potentially inhibited by PHC depletion and genistein was capable of compl etely inhibiting D2S-mediated MAPK activation. Together, these results sugg est that D2L- and D2S-mediated MAPK activation is predominantly G beta gamm a subunit-mediated signaling and that protein kinase C and tyrosine phospho rylations are involved in these signaling pathways. (C) 1999 Academic Press .