Functional significance of MMP-9 in tumor necrosis factor-induced proliferation and branching morphogenesis of mammary epithelial cells

Tissue remodeling is a key process involved in normal mammary gland develop ment, with matrix metalloproteinases (MMPs) playing an important role in th is process. Our laboratory has demonstrated that tumor necrosis factor (TNF ) stimulates branching morphogenesis of mammary epithelial cells (MEC) with in a reconstituted basement membrane. Studies were therefore undertaken to determine whether MMPs might mediate the effects of TNF. Using a primary cu lture model in which rat MEC grow three-dimensionally within a reconstitute d basement membrane, we found that TNF stimulated secretion of MMP-9 but no t MMP-2. To determine whether MMP-9 was involved in TNF-induced proliferati on and branching morphogenesis, we used a peptide containing the prodomain sequence of MMPs and two MMP inhibitors. Both the prodomain peptide (5 x 10 (-4)-10(-8) M), as well as BB-94 (10(-8)-10(-5) M) and CGS 27023A (10(-6)-1 0(-5) M), inhibited TNF-induced proliferation and branching morphogenesis i n a concentration-dependent manner. Finally, to verify the specific require ment for MMP-9, we demonstrated that an MMP-9 neutralizing antibody blocked TNF-induced proliferation and branching morphogenesis. Together, these dat a suggest that TNF-regulated MMP-9 may play a role in the controlled invasi on of the fad pad that occurs during normal mammary gland development and t hat misregulation of MMP-9 may contribute to the invasiveness of breast can cer.