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 mammar y gland. This work shows that there are changes not only in total cPKC activity during the lactogenic cycle, but also in the relative amount s of the soluble and particulate cPKC activities and that the time-cou rse of these two events are not the same. The time-course of transloca tion from the cytoplasm to the plasma membrane suggests that the solub le and particulate forms of the enzyme may be associated with growth a nd differentiation of the tissue, respectively. Phosphorylation patter ns also show characteristic and significant differences throughout the development of the gland. These results suggest that both total mamma ry cPKC activity and its subcellular forms change in accordance with t he proliferative and differentiative stages of the mammary gland, and that the enzyme translocation occurs during the transition from pregna ncy to lactation.