An accumulating body of evidence suggests that factors which regulate normal growth and cellular differentiation are fundamentally involved in the processes of malignant transformation and metastatic progression in human breast cancer. Transforming growth factor beta (TGF-beta) is one such protein, and evidence suggests that it may play a central role in mammary neoplasia. Several studies suggest that TGF-beta may act as a negative autocrine growth factor which mediates the effects of hormonal therapy on breast cancer. On the other hand, some observations support a view of TGF-beta which favors net progression of the malignant phenotype. These studies reported that TGF-beta1 MRNA was increased in transformed as opposed to normal breast epithelium, and that TGF-beta increased the metastatic potential of mammary tumor cells. The overall goals of this research proposal are to study the impact of TGF-beta as regards the malignant behavior of human breast cancer, and to examine the molecular basis of hormonal regulation of TGF-beta expression. We have performed a retrospective immunohistochemical analysis of archived breast tumors, and have observed an association between intense staining with an anti-TGF-beta1 antibody and disease progression. This association was statistically significant, and independent of stage, axillary node involvement, estrogen receptor content, and menopausal status. The intensity of immunoreactivity with antibodies specific from TGF-beta2 or beta3 was not associated with clinical outcome. We will expand this analysis in order to determine if overexpression of TGF-beta1 is a clinically useful prognostic indicator in breast cancer. We will continue to examine specimens from expression of TGF-beta2 and -beta3 in order to test the hypothesis that the in vivo impact of TGF-beta expression may be isoform specific. In a parallel series of experiments, we will generate by stable transfection clones of a human breast cancer cell line (MDA-MB-231) which produce altered levels of TGF-beta1. Specifically, we will transfect cells with one of three expression plasmids containing the TGF-beta1 CDNA. One plasmid directs transcription from an unmodified CDNA sequence. Another encodes a double cysteine-to-serine mutation, which results in the secretion of active, rather than latent, TGF-beta1. The third incorporates a dominant negative mutation of the TGF-beta1 CDNA which has been shown to abolish endogenous TGF-beta secretion. The tumorigenic and metastatic properties of these cells in nude mice will then be studies. We also propose to study hormonal regulation of TGF-beta MRNA expression by breast cancer cell lines. In these experiments, we will determine the molecular mechanisms which underlie down-regulation of TGF-beta2 and -beta3 by estradiol, and up-regulation of TGF-beta1 by anti-estrogens. Experimental approaches will include determination of rates of RNA transcription and degradation, polysome distribution of TGF-beta MRNAS, and analysis of the effect of protease inhibitors on tamoxifen-induced activation of TGF-beta from its latent form.
| Tobin, Stephen W; Douville, Karen; Benbow, Ulrike et al. (2002) Consequences of altered TGF-beta expression and responsiveness in breast cancer: evidence for autocrine and paracrine effects. Oncogene 21:108-18 |
| Arrick, B A; Grendell, R L; Griffin, L A (1994) Enhanced translational efficiency of a novel transforming growth factor beta 3 mRNA in human breast cancer cells. Mol Cell Biol 14:619-28 |
