ET(A) AND ET(B) RECEPTORS COOPERATE IN DNA-SYNTHESIS VIA OPPOSING REGULATIONS OF CAMP IN HUMAN LUNG-CELL LINE

We investigated the contribution of endothelin type A (ET(A)) and ET(B ) receptors on ET-induced DNA synthesis in CCD-18Lu cells, a human lun g cell line possessing both ET(A) and ET(B) (ET(A)/ET(B) ratio: 9:1). ET-1 (0.05-2 nM) potently induced [H-3]thymidine incorporation by 2- t o 14-fold over the basal level. An ET(A)-selective antagonist, FR13931 7, inhibited 0.2 nM ET-1-induced DNA synthesis dose dependently, showi ng complete inhibition at 1 mu M. ET-3 was inactive up to 2 nM. In con trast, ET(B)-selective antagonists, 100 nM of BQ-788 or IRL 2500, part ially (30-60%) inhibited 0.2 nM ET-1-induced DNA synthesis. Stimulatio n of either ET(A) or ET(B) evoked the increases in intracellular Ca2concentration ([Ca2+](i)). ET(B)-mediated but not ET-1-induced [Ca2+]( i) increase was pertussis toxin (PTX) sensitive. Adenosine 3',5'-cycli c monophosphate (cAMP) formation via ET(A) was observed in PTX-treated cells, whereas the inhibition of isoproterenol-stimulated cAMP format ion via ET(B) was observed in PTX-untreated cells. Like the ET(B)-sele ctive antagonists, PTX treatment or dibutyryl cAMP partially (50-70%) inhibited ET-1-induced DNA synthesis. These data suggest that 1) ET-1 induces DNA synthesis predominantly through ET(A), via PTX-insensitive G protein; 2) ET(A)-mediated cAMP formation inhibits DNA synthesis; a nd 3) stimulation of ET(B) coupling to G(i) protein modulates ET(A)-me diated DNA synthesis by inhibiting cAMP formation.