Vanadate disrupts mammary gland development in whole organ culture

Protein tyrosine kinases and phosphatases are signaling molecules involved in all aspects of development, including proliferation, differentiation, an d apoptosis. How disruption of protein tyrosine phosphatase affects mammary gland development is not entirely clear. We examined the effects of sodium vanadate, which is known to primarily inhibit tyrosine phosphatases, in mo use mammary gland development in whole organ culture. Mammary epithelial di fferentiation was effectively inhibited by vanadate in a dose-dependent man ner as indicated by lack of epithelial alveoli compared to the contralatera l nontreated gland controls. Mammary glands in the differentiation medium a fter four days in the presence of vanadate did not differentiate into alveo li. Instead, they exhibited prominent terminal end buds and lost the distin ctive epithelial structures. The inhibitory effect of vanadate on mammary e pithelial cell differentiation was irreversible after one day of treatment. Immunohistochemical staining for PCNA (Proliferating Cell Nuclear Antigen) showed that vanadate-treated glands exhibited elevated proliferation signa ls in the differentiation medium. Expression of beta -casein protein in the vanadate-treated glands decreased dramatically and progressively. Short-te rm exposure (up to 72 hours) of mammary glands to vanadate resulted in an i ncrease in mammary epithelial cell density and loss of organization of the mammary structures. TUNEL assay of mammary glands with prolonged exposure t o vanadate revealed widespread apoptosis. Furthermore, some cells were stil l proliferating or expressing beta -casein after prolonged exposure to vana date. Taken together, these data indicate that vanadate treatment blocks ma mmary epithelial cell differentiation and promotes abnormal proliferation a nd apoptosis, likely through the inhibition of protein tyrosine phosphatase -mediated signaling. (C) 2001 Wiley-Liss, Inc.