Enhanced endothelin ETB receptor down-regulation in human tumor cells

The characteristics of specific binding of human [I-125]Tyr(13)-endothelin-(1-21), [I-125]-Tyr(13)-Suc-[Glu(9),Ala(11,15)]-endothelin-(8-21), ([I-125]IRL-1620) and endothelin ETA receptor antagonist [I-125]Tyr(3)-(N-[(hexahydro-1H-azepin-1-yl)carbonyl]-L-Leu]-1Me)-D-Trp ([I-125]PD151242) (number of sites and their affinity) and proliferation responses to exogenous endothelin receptor agonists (endothelin-1 and the endothelin ETB receptor-selective, truncated N-acetyl-[Ala(11,15)]-endothelin-(6-21) analogue BQ3020) were determined in cultured human fibroblasts and in tumorigenic HeLa cells. The cells were pre-incubated with equimolar concentrations of human endothelin-1 or its truncated analogue BQ3020. After pre-incubation (2 h), both peptides induced down-regulation of surface-membrane endothelin-1 receptors. This process was specific for endothelin ETB receptors and was much more intensive in tumorigenic cells. BQ3020, acting mostly through its C-terminus, induced nearly maximal endothelin ETB receptor down-regulation in HeLa cells. Staurosporine, a wide spectrum protein kinase inhibitor, significantly reduced, and N-[N-[N-[2,6-dimethyl-lpiperidinyl)carbonyl]-4-Me-L-Leu]-1-(methoxycarbonyl)-D-tryptophanyl]-D-norleucine (BQ788), an endothelin ETB receptor antagonist, attenuated the down-regulation of endothelin receptors induced by endothelin receptor agonists. The down-regulation of endothelin ETB receptors was prevented by pre-incubation of the cells with the lysosomal enzyme blocker chloroquine. The endothelin-1-induced cell proliferation was attenuated by pre-incubation of the cells with the non-selective endothelin receptor antagonist Ac-D-10,11-dihydro-5H-dibenzo[a,d] cyclohepteneglycine-3,3-D-diphenyl-Ala-Leu-Asp-Ile-Trp (PD142893) and it was only partially reduced by the endothelin ET, receptor-selective endothelin antagonist PD151242. (C) 2000 Elsevier Science B.V. All rights reserved.