Receptor-mediated regulation of the TRPM7 channel through its endogenous protein kinase domain.
TRPM7 is a ubiquitously expressed and constitutively active divalent cation-selective ion channel, whose basal activity is regulated by intracellular levels of Mg(2+) and Mg.ATP. We have investigated receptor-mediated mechanisms that may actively regulate TRPM7 activity. We here report that TRPM7 currents are suppressed by intracellular GTPgammaS, suggesting the involvement of heterotrimeric G proteins. TRPM7 currents are also inhibited by stimulating endogenous muscarinic receptors, which is mediated by G(i) because the inhibitory effect is blunted by pertussis toxin. Conversely, stimulation of endogenous G(s)-coupled beta-adrenergic receptors potentiates TRPM7 currents, whereas G(q)-coupled thrombin receptors have little effect. Consistent with the involvement of G(s)/G(i) in controlling adenylyl cyclase activity, elevations of intracellular cAMP levels enhance TRPM7 activity and prevent receptor-mediated modulation of TRPM7 activity by muscarinic and adrenergic agonists. This cAMP-dependent effect requires the functional integrity of both protein kinase A (PKA) and the endogenous kinase domain of TRPM7 because cAMP-mediated effects are abolished when treating cells with the PKA inhibitors H89 or KT5720 as well as in cells expressing phosphotransferase-deficient TRPM7 constructs. These mutant channels are also much less susceptible to GTPgammaS-mediated inhibition, suggesting that the main regulatory effect occurs through G(i)- and G(s)-mediated changes in cAMP. Taken together, our results demonstrate that TRPM7 activity is up- and down-regulated through its endogenous kinase in a cAMP- and PKA-dependent manner.
Takezawa
Ryuichi
R
Laboratory of Cell and Molecular Signaling, Center for Biomedical Research, The Queen's Medical Center and John A. Burns School of Medicine, University of Hawaii, Honolulu, HI 96813, USA.
Schmitz
Carsten
C
Demeuse
Philippe
P
Scharenberg
Andrew M
AM
Penner
Reinhold
R
Fleig
Andrea
A
D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D000242:Cyclic AMP / Q000502:physiology; D019204:GTP-Binding Proteins / Q000378:metabolism; D006801:Humans; D007473:Ion Channels / Q000502:physiology*; D008565:Membrane Proteins / Q000502:physiology*; D018408:Patch-Clamp Techniques; D037342:Pertussis Toxin / Q000494:pharmacology; D011494:Protein Kinases / Q000378:metabolism* / Q000502:physiology*; D017346:Protein Serine-Threonine Kinases; D011956:Receptors, Cell Surface / Q000378:metabolism / Q000502:physiology*; D050053:TRPM Cation Channels; D010738:Type C Phospholipases / Q000378:metabolism
D007473:Ion Channels; D008565:Membrane Proteins; D011956:Receptors, Cell Surface; D050053:TRPM Cation Channels; D000242:Cyclic AMP; D037342:Pertussis Toxin; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; C486583:TRPM7 protein, human; D010738:Type C Phospholipases; D019204:GTP-Binding Proteins; D002118:Calcium