Hormonal induction and roles of Disabled-2 in lactation and involution

Disabled-2 (Dab2) is a widely expressed endocytic adaptor that was first isolated as a 96 KDa phospho-protein, p96, involved in MAPK signal transduction. Dab2 expression is lost in several cancer types including breast cancer, and Dab2 is thought to have a tumor suppressor function. In mammary epithelia, Dab2 was induced upon pregnancy and further elevated during lactation. We constructed mutant mice with a mosaic Dab2 gene deletion to bypass early embryonic lethality and to investigate the roles of Dab2 in mammary physiology. Loss of Dab2 had subtle effects on lactation, but Dab2-deficient mammary glands showed a strikingly delayed cell clearance during involution. In primary cultures of mouse mammary epithelial cells, Dab2 proteins were also induced by estrogen, progesterone, and/or prolactin. Dab2 null mammary epithelial cells were refractory to growth suppression induced by TGF-beta. However, Dab2 deletion did not affect Smad2 phosphorylation; rather TGF-beta-stimulated MAPK activation was enhanced in Dab2-deficient cells. We conclude that Dab2 expression is induced by hormones and Dab2 plays a role in modulating TGF-beta signaling to enhance apoptotic clearance of mammary epithelial cells during involution.