Paracrine regulation of ovarian cancer by endothelin

Previous studies have demonstrated that endothelin (ET) isoforms (ET-1, ET-2 and ET-3) can act in an autocrine manner in ovarian cancer while in breast cancer their role has been proposed to be that of a paracrine mitogen. To explore the possibility that endothelin isoforms might function not only as autocrine regulators but also as paracrine mitogens in ovarian cancers, we investigated their effects on the growth of ovarian fibroblasts derived from ovarian carcinomas, the interaction between ovarian carcinoma and fibroblast cells and the location of the isoform expression in primary ovarian tumours. ET-1, ET-2 and ET-3 stimulated the growth of three ovarian fibroblast cell lines at concentrations ranging from 10(-12) M to 10(-7) M. Inhibition of 125I-ET binding by the ETA receptor antagonist BQ123 and the ETB receptor antagonist BQ788 suggested the presence of both types of ET receptors in fibroblast cells. In the absence of ET-1, neither BQ 123 nor BQ 788 inhibited growth. However, both antagonists inhibited ET-1 stimulated growth suggesting the involvement of both receptor types in ET-1 growth regulation. In contrast to carcinoma cells which secrete measurable levels of ET-1, fibroblast cell lines did not secrete detectable protein. Co-culture experiments (using porous membrane insert wells) of fibroblasts with carcinoma cells demonstrated that growth of both populations of cells was increased compared with either grown in isolation. In this system, growth of the fibroblast cell line was partially inhibited by both BQ123 and BQ788, whilst growth of the PE014 carcinoma cell line was inhibited by only BQ123. RT-PCR measurements detected the presence of the ETA receptor subtype in 10/10 primary ovarian cancers but the presence of ETB receptor in only 6/10 cancers. Using specific antibodies, ET-1 was found in 11/15, ET-2 in 5 of 7 and ET-3 in 5/7 primary ovarian cancers predominantly in the epithelial cells but with some stromal expression. These data indicate that the ET isoforms may stimulate growth of the fibroblast population within an ovarian cancer in addition to stimulating the epithelial cells and since the ETs are expressed in the majority of ovarian cancers, this paracrine effect may contribute to the overall growth of the tumour.