Abstract
Abstract
Mammary epithelial cells isolated from midpregnant BALB/c mice were grown within collagen gels and maintained in serum-free media containing 10 ng/ml epidermal growth factor (EGF) for an 8-day culture period. Western blot and scanning densitometric image analysis showed the presence of protein kinase C (PKC) α (82 kDa), δ (75 kDa), η (90 and 78 kDa), and ζ (82, 74, and 65 kDa), whereas PKCβ, γ, and θ were not detected in either the cytosolic or membrane fractions in these cells. Cytosolic and membrane levels of PKCα and 82 kDa PKC° band progressively increased throughout the 8-day culture period. During this same time, cytosolic PKC° levels decreased, while membrane levels of PKC° showed no change. Cytosolic and membrane levels of PKCη and the 74- and 65-kDa PKCζ bands displayed some fluctuations but remained relatively constant during the 8-day culture period. Other studies showed that 24-hr treatment with 100 nM of phorbol 12-myristate 13-acetate (PMA), resulted in the downregulation of PKCα, δ, and η, and the 82-kDa PKC° band. However, PMA treatment had no effect on cytosolic and membrane levels of the 74- and 65-kDa PKC° bands. Since PKC activation is associated with hormone- and growth factor-dependent mammary epithelial cell proliferation, these findings suggest that increases and/or decreases in the relative levels of the different PKC isoenzymes in proliferating cells may indicate their possible role in mediating or regulating EGF-dependent mitogenesis.
Get full access to this article
View all access options for this article.