Human breast cancer cells contain a phosphoramidon-sensitive metalloproteinase which can process exogenous big endothelin-1 to endothelin-1: a proposed mitogen for human breast fibroblasts

Abstract

SaryEndothei-1 (ET-I) levels are elvated in human breast tumours compared with normal and benign tissues, and in the presence of insuin-hlke growth factor I (IGF-I) ET-I is a potent mitogen for human breast fibroblasts. In this study we have examied the ability of intact human breast cancer cell lines to process exogenously added big ET-I (1 -38) to the active mature ET-I peptide by using a specific radioimmu assay. In both hormome-dpendent (MCF-7, T47-D) and hormone-independent (MDA-MB-231) breast cancer cell lnes the putative endothehn-converting enzyme (ECE) exhibited apparent Mxichalis-Menten kinetics when converting added big ET-I to ET-I. Both basal ET-I production and exogenously added big ET-I to ET-I convesion were greatly reduced m all three cel lines in response to the metalloproteinase inhibitor phosphoramidon but were insensitive to other classes of protease inhibitors. Inhibition was also observed when cells were incubated in the presence of the divalent cation chelators 1,10-phenanthrohn and EDTA. In MCF-7 cells the optimal pH for the ECE activity using a saponin cell permeabilisation procedure was found to reside within a narrow range of 6.2-726. Our results indicate that human breast cancer cells contain a neutral phosphoramidon-sensitive metalloproteinase which can process big ET-i to ET-I. In the breast this converson could contnbute substantially to the local extracellular kvels of this proposed paracrie breast fibroblast mitogen.

Serum big endothelin-1 levels in female patients with breast cancer

“…It was suggested that because of its long half-life, big ET-1 reflects the activity of endothelin system with greater sensitivity than does ET-1 itself [13]. Human breast cancer cells contain endothelin converting enzyme, which converts big ET-1 to ET-1 [9]. In a few studies [4,7] the levels of ET-1 were higher in breast cancer tissues than in healthy breast tissues; however, to our knowledge, the clinical significance of serum big ET-1 levels has not been evaluated in breast cancer patients.…”

“…ET-1 and its receptors ETA and ETB are overexpressed in breast carcinoma [8]. ET-1 released from breast cancer cell binds ETA receptors on breast fibroblasts [3,9]. In vivo and in vitro studies have shown that breast fibroblasts stimulate breast cancer cells by paracrine manner [10][11][12].…”

A causal role for endothelin-1 in the pathogenesis of osteoblastic bone metastases

“…Breast cancer cells can convert preproET-1 to ET-1 (19,20). Thus, substantial data implicate ET-1 in the pathogenesis of osteoblastic metastases, but a causal role for ET-1 in bone metastasis has not been directly tested.…”

Prostaglandin E2 production and metabolism in human breast cancer cells and breast fibroblasts. Regulation by inflammatory mediators

“…The antisera employed was raised to the methyl oxime of PGE2. At the end of each experiment aliquots of the culture media were derivatised at room temperature overnight with equal volumes of methyloximating reagent (Kelly et al, 1986) Endothelin immunoradiometric assay The production of ET-1 by MCF-7 cells was measured using a specific solid phase-based sandwich assay in 96-well microtitre plates as previously described (Patel and Schrey, 1995). The sensitivity of the assay is 0.5pmoll1' with percentage cross-reactivities for ET-1, big ET-1, ET-2 and ET-3 being 100, 0.01, 100 and 50 respectively.…”