Bradley A. Arrick

Regulation of growth of normal ovarian epithelial cells and ovarian cancer cell lines by transforming growth factor-β

OBJECTIVE The purpose of this study was to study the role of transforming growth factor-beta in regulation of proliferation of normal and malignant ovarian epithelial cells. STUDY DESIGN We examined production of and responsiveness to transforming growth factor-beta in primary monolayer cultures of epithelial cells from five normal human ovaries and in five ovarian cancer cell lines. RESULTS In normal ovarian epithelial cells, proliferation always was inhibited by transforming growth factor-beta (greater than 40%) (p less than 0.01). Among the cancer cell lines, proliferation of one was markedly inhibited (greater than 95%) (p less than 0.01), two were only modestly inhibited (15% to 20%) (p less than 0.05), and two were unaffected. In addition, we found that all of the normal ovarian epithelial cells and four of five ovarian cancer cell lines produce transforming growth factor-beta ribonucleic acid and protein. CONCLUSIONS These data suggest that transforming growth factor-beta may act as an autocrine growth inhibitory factor for normal ovarian epithelium in vivo. Because most of the ovarian cancer cell lines are relatively resistant to the growth inhibitory effect of transforming growth factor-beta and because one cell line does not produce transforming growth factor-beta, it is possible that loss of the transforming growth factor-beta pathway may play a role in the development of some ovarian cancers.

Consequences of altered TGF-β expression and responsiveness in breast cancer: evidence for autocrine and paracrine effects

To characterize the impact of increased production of TGF-β in a xenograft model of human breast cancer, TGF-β-responsive MDA-231 cells were genetically modified by stable transfection so as to increase their production of active TGF-β1. Compared with control cells, cells that produced increased amounts of TGF-β proliferated in vitro more slowly. In vivo, however, tumors derived from these cells exhibited increased proliferation and grew at an accelerated pace. To evaluate the role of autocrine TGF-β signaling, cells were also transfected with a dominant-negative truncated type II TGF-β receptor (TβRII). Disruption of autocrine TGF-β signaling in the TGF-β-overexpressing cells reduced their in vivo growth rate. Co-inoculation of Matrigel with the TGF-β-overexpressing cells expressing the truncated TβRII compensated for their diminished in vivo growth capacity, compared with the TGF-β-overexpressing cells with an intact autocrine loop. Tissue invasion by the tumor was a distinctive feature of the TGF-β-overexpressing cells, whether or not the autocrine loop was intact. Furthermore, tumors derived from TGF-β-overexpressing cells, irrespective of the status of the autocrine TGF-β-signaling pathway, had a higher incidence of lung metastasis. Consistent with the suggestion that TGF-βs enhancement of invasion and metastasis is paracrine-based, we observed no significant differences among the cell clones in an in vitro invasion assay. Thus, in this experimental model system in vitro assays of cell proliferation and invasion do not accurately reflect in vivo observations, perhaps due to autocrine and paracrine effects of TGF-β that influence the important in vivo-based phenomena of tumor growth, invasion, and metastasis.

Growth regulation by transforming growth factor-β

The name transforming growth factor-s (TGF-s) has come to represent a family of highly homologous polypeptides with a wide range of biological activities. The first member of this gene family was identified nearly a decade ago as one of two essential factors, called TGF-α and TGF-s present in the conditioned medium of a murine sarcoma virus-transformed cell line, which together stimulated the anchorage-independent growth of non-transformed fibroblast cell lines [1]. Several members of the TGF-s family have since been identified, of which TGF-sl, s2, and s3 are produced by mammalian cells. These three forms of TGF-s have similar biological activities in the majority of assay systems, though differences in relative potency are sometimes evident. For simplicity, we will use the name TGF-s to refer to the TGF-s family as a whole, unless otherwise specified. It should, however, be pointed out that most studies have evaluated only the biological activities of TGF-sl. Finally, a number of proteins have been identified that exhibit structural similarities to TGF-s, though with a more distant relationship than the individual TGF-s isoforms. Together with TGF-s, they constitute the TGF-s superfamily. As yet little is known about the effects of these factors on cell proliferation, and they will not be discussed here.