PROTEIN-KINASE-C ISOENZYME EXPRESSION IN NORMAL MOUSE MAMMARY EPITHELIAL-CELLS GROWN IN PRIMARY CULTURE

Mammary epithelial cells isolated from midpregnant BALB/c mice were gr own within collagen gels and maintained in serum-free media containing 10 ng/ml epidermal growth factor (EGF) for an 8-day culture period, W estern blot and scanning densitometric image analysis showed the prese nce of protein kinase C (PKC) or (82 kDa), delta (75 kDa), eta (90 and 78 kDa), and zeta (82, 74, and 65 kDa), whereas PKC beta, gamma, and theta were not detected in either the cytosolic or membrane fractions in these cells. Cytosolic end membrane levels of PKC alpha and 82 kDa PKC zeta band progressively increased throughout the 8-day culture per iod, During this same time, cytosolic PKC delta levels decreased, whil e membrane levels of PKC delta showed no change. Cytosolic and membran e levels of PKC eta and the 74- and 65-kDa PKC zeta bands displayed so me fluctuations but remained relatively constant during the 8-day cult ure period. Other studies showed that 24-hr treatment with 100 nM of p horbol 12-myristate 13-acetate (PMA), resulted in the downregulation o f PKC alpha, delta, and eta, and the 82-kDa PKC zeta band. However, PM A treatment had no effect on cytosolic and membrane levels of the 74- and 65-kDa PKC zeta bands. Since PKC activation is associated with hor mone- and growth factor-dependent mammary epithelial cell proliferatio n, these findings suggest that increases and/or decreases in the relat ive levels of the different PKC isoenzymes in proliferating cells may indicate their possible role in mediating or regulating EGF-dependent mitogenesis.