Dual Effect of Prolactin on Protein Kinase C Activity in CHO Cells Expressing Functional Prolactin Receptors

We investigated the effects of prolactin (PRL) on the protein kinase C (PKC) activity in Chinese hamster ovary (CHO-E32) cells stably transfected with rabbit mammary gland PRL receptor cDNA. These cells express a functional long form of PRL-R. A 10-min to 2-hour treatment with 5 nM PRL resulted in the translocation of PKC activity from the cytosol to the membrane. Longer treatment (10-24 h) with the same concentration of PRL decreased the PKC activity in both particulate and cytoplasmic fractions. The PRL effect was dose dependent: maximal action was obtained with 1-10 nM. The PRL-induced activation of PKC was blocked by 20 nM staurosporine, a PKC inhibitor. Two inhibitors of tyrosine kinase, herbimycin A (1.75 &mgr;M) and genistein (100 &mgr;M), had no effect on PRL-induced activation of PKC. Copyright 1996 S. Karger AG, Basel