Expression of a functional endothelin (ET(A)) receptor in human meningiomas

Abstract

Endothelin (ET) receptor subtypes (ET(A) and ET(B)) in human meningiomas were characterized using quantitative receptor autoradiography. A single class of high-affinity 125I-ET-1 binding sites was localized in all meningioma tissue studied (dissociation constant: 2.4 ± 0.3 nM, maximum binding capacity: 319 ± 66 fmol/mg (mean ± standard error of the mean for 13 tumors)). Unlabeled ET-1 showed a strong affinity for 125I-ET-1 binding to tissue sections of the tumors with a 50% inhibiting concentration (IC50) of 2.9 ± 0.7 x 10-9 M, whereas ET-3 showed a much lower affinity (IC50: 8.4 ± 2.5 x 10-6 M). Sarafotoxin S6c, a selective agonist for the ET(B) receptor, could not compete for 125I-ET-1 binding to meningiomas. Endothelin-1 significantly stimulated deoxyribonucleic acid (DNA) synthesis in a dose-dependent manner in cultured human meningioma cells. In contrast, no significant stimulation of DNA synthesis occurred with an S6c concentration up to 10-7 M. Pretreatment of the meningioma cells with pertussis toxin, a bacterial toxin that adds adenosine 5'-diphosphate-ribose to the α subunit of guanine nucleotide binding (G) proteins such as G(i) or G(o), induced a concentration-dependent reduction in ET-stimulated DNA synthesis in meningioma cells, but did not affect the epidermal growth factor-induced DNA synthesis. These observations suggest that the ET(A) receptor is predominantly expressed in human meningioma tissue and that ET may act as a growth factor on the meningioma cells by interacting with the ET(A) receptor and by pertussis toxin-sensitive mechanisms.