An important feature of the mammary gland is the regenerative capacity of its epithelium which is demonstrated upon successive cycles of lactation and involution. Pregnant mice expressing a whey-acidic protein (WAP) promoter-driven transforming growth factor-beta 1 (TGF beta 1) cDNA are unable either to generate a secretory mammary epithelium or to lactate. Here we investigate whether ectopic TGF beta 1 induces this phenotype by affecting the transgenic epithelium directly or in trans. Reciprocal transplantation of mammary tissue between normal and transgenic hosts resulted in the development of the respective phenotypes of the transplants within the same mammary fat pad. When isolated mammary epithelial cells from both were mixed before implantation so that transgenic and normal epithelium would develop together more proximately, both phenotypes were simultaneously observed in the resultant chimeric mammary outgrowths. Since no trans effect was detectable, we hypothesize that early expression of the transgene results in compromised lobular progenitor cells through an intracrine mechanism. Consistent with this posit, WAP promoter-driven protein expression was detected in individual cells of the subtending ducts of immature females at estrus. Transplantation of WAP-TGF beta 1 mammary gland into nonpregnant hosts revealed that transgenic implants, even those from young postpubertal virgin females, had a diminished ability to repopulate epithelium-free mammary fat pads. Accordingly, the ectopic expression of WAP-TGF beta 1 not only impairs lobular progenitors, but also promotes an early senescence of the regenerative capacity of the mammary ductal epithelium. This leads us to propose that mammary epithelial stem cells give rise to two functionally distinct progenitor cells in the mammary gland epithelium: one capable of producing daughters committed to ductal formation, the other capable only of producing daughters committed to lobular function.

Transforming growth factor‐beta 1 (TGF‐beta 1) possesses highly potent, diverse and often opposing cell‐specific activities, and has been implicated in the regulation of a variety of physiologic and developmental processes. To determine the effects of in vivo overexpression of TGF‐beta 1 on mammary gland function, transgenic mice were generated harboring a fusion gene consisting of the porcine TGF‐beta 1 cDNA placed under the control of regulatory elements of the pregnancy‐responsive mouse whey‐acidic protein (WAP) gene. Females from two of four transgenic lines were unable to lactate due to inhibition of the formation of lobuloalveolar structures and suppression of production of endogenous milk protein. In contrast, ductal development of the mammary glands was not overtly impaired. There was a complete concordance in transgenic mice between manifestation of the lactation‐deficient phenotype and expression of RNA from the WAP/TGF‐beta 1 transgene, which was present at low levels in the virgin gland, but was greatly induced at mid‐pregnancy. TGF‐beta 1 was localized to numerous alveoli and to the periductal extracellular matrix in the mammary gland of transgenic females late in pregnancy by immunohistochemical analysis. Glands reconstituted from cultured transgenic mammary epithelial cells duplicated the inhibition of lobuloalveolar development observed in situ in the mammary glands of pregnant transgenic mice. Results from this transgenic model strongly support the hypothesis that TGF‐beta 1 plays an important in vivo role in regulating the development and function of the mammary gland.

Breast tumors are usually classified according to their response to estrogens as hormone-dependent or -independent. In this work, we investigated the role of the proinflammatory cytokine TNF-a on the estrogen-receptor-positive T47D breast ductal tumor cells. We have found that TNF-a exerts a mitogenic effect, inducing cyclin D1 expression and activation of the transcription factor NF-jB. Importantly, activation of NF-jB was required for estrogen-induced proliferation and cyclin D1 expression. TNF-a enhanced the estrogen response by increasing the levels and availability of NF-jB. Chromatin immunoprecipitation analysis suggested that the action of estrogens is mediated by a protein complex that contains the activated estrogen receptor, the nuclear receptor coactivator RAC3 and a member of the NF-jB family. Finally, our results demonstrate that activation of this transcription factor could be one of the key signals for estrogen-mediated response.