NOTCH4 AND WNT-1 PROTEINS FUNCTION TO REGULATE BRANCHING MORPHOGENESIS OF MAMMARY EPITHELIAL-CELLS IN AN OPPOSING FASHION

Elongation and branching of epithelial ducts is a crucial event during the development of the mammary gland. Branching morphogenesis of the mouse mammary epithelial TAC-2 cell line was used as an assay to exami ne the role of Wnt, HGF, TGF-beta, and the Notch receptors in branchin g morphogenesis. Wnt-1 was found to induce the elongation and branchin g of epithelial tubules, like HGF and TGF-beta 2, and to strongly coop erate with either HGF or TGF-beta 2 in this activity. Wnt-1 displayed morphogenetic activity in TAC-2 cells as it induced branching even und er conditions that normally promote cyst formation. The Notch4(int-3) mammary oncoprotein, an activated form of the Notch4 receptor, inhibit ed the branching morphogenesis normally induced by HGF and TGF-beta 2. The minimal domain within the Notch4(int-3) protein required to inhib it morphogenesis consists of the CBF-1 interaction domain and the cdc1 0 repeat domain. Coexpression of Wnt-1 and Notch4(int-3) demonstrates that Wnt-1 can overcome the Notch-mediated inhibition of branching mor phogenesis. These data suggest that Wnt and Notch signaling may play o pposite roles in mammary gland development, a finding consistent with the convergence of the wingless and Notch signaling pathways found in Drosophila. (C) 1998 Academic Press.