Keratinocyte growth factor and acidic fibroblast growth factor are mitogens for primary cultures of mammary epithelium.

Mammary epithelial cells derived from the entire mammary parenchyma or only end buds were isolated by collagenase digestion of mammary glands from virgin mice. Cells were cultured within collagen gels in serum-free medium containing insulin. Keratinocyte growth factor (KGF or FGF-7) and acidic fibroblast growth factor (aFGF or FGF-1) stimulated multifold proliferation when added alone to this medium. Growth occurred as three-dimensional colonies within the collagen gel matrix. KGF stimulated growth was unaffected by adding heparin. Conversely, multifold growth stimulation by acidic FGF required heparin. Since end buds are the actively proliferating cell population of ductal glands, organ cultures of these structures were prepared. KGF stimulated 3H-thymidine incorporation in these end buds in the absence and presence of epidermal growth factor. These data suggest that acidic FGF and KGF may represent in vivo stromal factors capable of regulating mammary gland development.