Changes in protein kinase C activity, subcellular distribution and protein phosphorylation during the lactogenic cycle in the rat mammary tissue

Direct and indirect evidence emphasizes the participation of classical protein kinase C (cPKC) in the development and function of the mammary gland. This work shows that there are changes not only in total cPKC activity during the lactogenic cycle, but also in the relative amounts of the soluble and particulate cPKC activities and that the time-course of these two events are not the same. The time-course of translocation from the cytoplasm to the plasma membrane suggests that the soluble and particulate forms of the enzyme may be associated with growth and differentiation of the tissue, respectively. Phosphorylation patterns also show characteristic and significant differences throughout the development of the gland. These results suggest that both total mammary cPKC activity and its subcellular forms change in accordance with the proliferative and differentiative stages of the mammary gland, and that the enzyme translocation occurs during the transition from pregnancy to lactation.