Growth Factor Production by Mammary Tumor Cells

Abstract

Much attention has recently been focused on the possibility that the behavior of tumorigenic cells (anchorage independent growth, loss of growth factor dependency, loss of contact inhibition, etc.) are caused by changes in the control of expression of growth factors and/or their receptors (1,2). Indeed, the transforming genes of a number of tumor cells and viruses have been identified as genes for growth factors or receptors (1,2). Our aim here is not to present a complete review of this area, but rather to compile the published data from our lab and others on the types of growth factors that have been detected in primary and established mammary cell lines and in extracts of normal and neoplastic mammary epithelium from rodent and human tissues. The list is quite long, even for human mammary tumors and tumor cell lines. It includes mammary-derived growth factor I (MDGFI), mammary-derived growth factor II (MDGFII), transforming growth factor alpha (TGFα), transforming growth factor beta (TGF/β), insulin-like growth factor I (IGFI), p; platelet-derived growth factor (PDGF), gastrin-releasing peptide (GRP), 52 K protein, epidermal growth factor (EGF), and human tumor growth factor (h. TGF). Rodent mammary tumors contain these factors and some additional ones as well. For example, 7, 12-dimethylbenz(a)anthracene-induced rat mammary cell lines produce an activity that greatly stimulates myoepithelial, but not epithelial, cell growth. Rat mammary tumors also contain a growth inhibitory activity similar to one that Grosse’s laboratory has purified from bovine mammary tissue (3).