Potentiation response of cultured human uterine leiomyoma cells to variousgrowth factors by endothelin-l: role of protein kinase C

Objective: Factors responsible for the abnormal proliferation of myometrial cells that accompanies leiomyoma formation are unknown, although steroid h ormones and peptide growth factors have been implicated. We hypothesized th at endothelin-1 (ET-1) is a physiological regulator of tumor growth. Design: In this study, we investigated the role of ET-1 on growth of human leiomyoma cells and its synergistic effect with growth factors, as well as the signaling pathway involved in this interaction. Methods: Leiomyoma cell proliferation was assayed by [H-3]thymidine incorpo ration and cell number. Protein kinase C (PKC) isoforms were analyzed by We stern blot using specific antibodies. Results: ET-1 on its own was unable to stimulate DNA synthesis but potentia ted the leiomyoma cell growth effects of basic fibroblast growth factor (bF GF), epidermal growth factor (EGF), IGF-I and IGF-II, The failure of a prot ein tyrosine kinase (PTK) inhibitor, tyrphostin 51, to affect the potentiat ing effect of ET-1, supports the hypothesis of non-involvement of PTK in th is process. The inhibition of PKC by calphostin C or its down-regulation by phorbol 12,13-dibutyrate (PDB) eliminated the potentiating effect of ET-1, but did not block cell proliferation induced by the growth factors alone. Five PKC isoforms (alpha, beta1, epsilon, delta and xi) were detected in le iomyoma cells, but only phorbol ester-sensitive PKC isoforms (PK alpha, eps ilon and delta) contribute to the potentiating effect of leiomyoma cell gro wth by ET-1. Conclusions: We have demonstrated that ET-1 potentiates leiomyoma cell prol iferation to growth factors through a PKC-dependent pathway. These findings suggest a possible involvement of ET-1 in the pathogenesis of leiomyomas.