CORRELATION OF TGF-BETA(1) EXPRESSION WITH MEDROXIPROGESTERONE ACETATE RESPONSIVENESS IN MOUSE MAMMARY ADENOCARCINOMAS

We investigated the expression of transforming growth factors beta(1) and alpha (TGF-beta(1), TGF-alpha) in hormone-responsive (MPA-R) and u nresponsive (MPA-U) tumor lines obtained from medroxyprogesterone acet ate (MPA)-induced mammary adenocarcinomas in BALB/c mice. The tumors w ere transplanted into MPA-treated and untreated mice. TGF-beta(1) gene expression was observed in the MPA-R lines growing in unheated animal s, but not in MPA-treated mice. TGF-beta(1) mRNA was not detected in t he MPA-U tumor lines growing in either MPA-treated or untreated animal s. In MPA-R lines the levels of TGF-beta(1) expression were inversely correlated to growth rate. High-affinity TGF-beta(1) receptors were pr esent in the MPA-R tumors. These results suggest that one of the mecha nisms by which MPA exerts its proliferative effect on MPA-R tumor line s is inhibition of the expression of TGF-beta(1). Thus, the lack of ex pression of TGF-beta(1) in MPA-U tumors may be related to the acquisit ion of autonomous growth.