| Activin is a member of the transforming growth factor beta (TGFβ) superfamily of growth factors, which exerts growth controlling influences throughout the body. Members of the TGFβ superfamily have been associated with mammary gland development and breast oncogenesis, but activin has not been rigorously studied in this context. We hypothesize that activin signaling components are involved in post-natal mammary development, and when activin signaling is disrupted or lost, malignant progression is potentiated. During mammary development, mRNA abundance of activin signaling components is greatest in nonparous tissue, and then decreases, whereas protein immunoreactivity for activin signaling components increases during lactation and decreases during involution. Smad 3, but not Smad 2, is detected in epithelial cell nuclei during all points in development, indicating that activin signaling is mediated by Smad 3 at these times. Examination of breast cancers sub-stratified by pathologic grade, revealed that the activin βA-subunit is present in all tissues examined. The βB-subunit, activin type II receptors, and Smads are less evident in high grade cancers. Correlations are made in breast cancers between a decrease in nuclear Smad 3 abundance and high tumor grade, high architectural grade, larger tumor size, and hormone receptor negativity. Investigation of the mechanistic action of activin and Smad 3 signaling in breast cancer T47D cells, finds Smad 3 to induce a redistribution of cells into the G1 phase of the cell cycle, and dominant negative (DN) Smad 3 to shift the cellular distribution into S-phase. Activin treatment also mediates a redistribution of cells into the G1 phase, and this affect is additive in cells transduced with Smad 3. A method utilizing whole tumor culture for the study of breast cancer was also developed. Whole tumor and normal tissue are transduced with adenobetagalactosidease, and these tissues stain positively for nuclear betagalactosidase, demonstrating their viability through the ability to take up the betagalactosidase gene in culture, and then express the betagalactosidase protein. Taken together, the results of these studies demonstrate the potential for the activin signaling pathway to serve in a tumor suppressant capacity, and for whole tumor culture to provide an additional means for studying cancer biology. |
