Ca2+ mobilization by the LH receptor expressed in Xenopus oocytes independent of 3',5'-cyclic adenosine monophosphate formation: evidence for parallel activation of two signaling pathways.
The cDNAs encoding the murine LH receptor (LHR) and the human beta 2-adrenoceptor (h beta 2AR) were cloned and RNAs complementary to their sense strands (cRNAs) were injected into defolliculated Xenopus oocytes. This led to expression, respectively, of LH- and isoproterenol-stimulable adenylyl cyclase activities, indicating that functionally active receptor cDNAs had been cloned. In oocytes injected with LHR cRNA, but not in control or h beta 2AR cRNA-injected oocytes, human CG and LH increased a Ca(2+)-activated Cl- current, as measured by the two-microelectrode voltage-clamp method. This effect was not seen with isoproterenol in control or h beta 2AR cRNA-injected oocytes, it was also not observed in response to forskolin or (Bu)2cAMP. The response to human CG could be obtained in the absence of extracellular Ca2+ but was abolished by injection of EGTA, indicating that it was caused by mobilization of Ca2+ from intracellular stores. The response was unaffected by overnight treatment with 1 microgram/ml pertussis toxin. The experiments show that a glycoprotein hormone receptor can be expressed as a functionally active molecule in Xenopus oocytes, and that the LHR has the ability of activating two separate intracellular signaling pathways: one forming the second messenger cAMP, and the other mobilizing Ca2+ from intracellular stores. It is proposed that the latter is secondary to a primary activation of phospholipase C by the LHR, which elevates intracellular Ca2+ via intermediary elevation of inositol phosphates, presumably (1,4,5)inositol trisphosphate.
Gudermann
T
T
Department of Cell Biology, Baylor College of Medicine, Houston, Texas 77030.
Nichols
C
C
Levy
F O
FO
Birnbaumer
M
M
Birnbaumer
L
L
D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002712:Chlorides / Q000378:metabolism; D003001:Cloning, Molecular; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism*; D004533:Egtazic Acid / Q000494:pharmacology; D006801:Humans; D007545:Isoproterenol / Q000494:pharmacology; D051379:Mice; D009865:Oocytes / Q000378:metabolism; D011943:Receptors, Adrenergic, beta / Q000235:genetics / Q000378:metabolism; D011974:Receptors, LH / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D014158:Transcription, Genetic; D014981:Xenopus
D002712:Chlorides; D011943:Receptors, Adrenergic, beta; D011974:Receptors, LH; D005576:Colforsin; D004533:Egtazic Acid; D000242:Cyclic AMP; D000262:Adenylyl Cyclases; D007545:Isoproterenol; D002118:Calcium