G-ALPHA-Q FAMILY MEMBERS COUPLE PARATHYROID-HORMONE (PTH) PTH-RELATEDPEPTIDE AND CALCITONIN RECEPTORS TO PHOSPHOLIPASE-C IN COS-7 CELLS/

The PTH/PTH-related peptide (PTHrP) receptor and the calcitonin recept or mediate the action of their physiological ligands by activating two different effecters, adenylyl cyclase and phospholipase C. Whereas re gulation of adenylyl cyclase via both receptors is thought to involve the G protein G(s), it is not known whether activation of phospholipas e C results from coupling of the receptors to G(q) family members or w hether beta gamma-subunits released from receptor-activated G(s) lead to phospholipase C activation. To elucidate the mechanism of this type of dual signaling, we reconstituted the signal transduction of the PT H/PTHrP and the calcitonin receptor in COS-7 and HEK293 cells. In COS- 7 cells expressing the receptor alone, addition of the respective liga nds resulted in the accumulation of cAMP and inositol phosphates. When cells were cotransfected with the cDNAs of receptor and different alp ha-subunits of the G(q) family (G alpha(q), G alpha(11), G alpha(14), G alpha(15), and G alpha(16)), a severalfold increase in the ligand-de pendent inositol phosphate production could be observed, indicating th at the receptors functionally interacted with all alpha-subunits of th e G alpha(q) family. Additionally, whereas PTH treatment of HEK293 cel ls coexpressing both the PTH/PTHrP receptor and G alpha(q), increased both second messengers, the same treatment in cells expressing the PTH /PTHrP receptor alone increased only cAMP. Under all conditions tested , activation of phospholipase C via the PTH/PTHrP and calcitonin recep tor required higher ligand concentrations than receptor-mediated adeny lyl cyclase activation. Our data strongly support the idea that dual s ignaling of the PTH/PTHrP and calcitonin receptors is due to the activ ation of different G proteins belonging to the G(s) and G(q) families.