Prolactin stimulation of protein kinase C in isolated mouse mammary gland nuclei.

Prolactin (PRL) was found to stimulate protein kinase C (PKC) activity in a transient fashion in isolated nuclei derived from the mammary glands of 12-14 day pregnant mice. PKC activation was time and dose dependent and was blocked by staurosporine. With 10 ng/ml PRL a maximum stimulation of PKC occurred at 3 min, whereas with 50 ng/ml the effect was maximal at 2 min. After 5 min, the effect of PRL on PKC activity was no longer detected. Specificity of the PRL effect on PKC was established by showing that bovine growth hormone and insulin at 10 ng/ml had no effect on PKC activity. Multiple proteins in the nuclear preparations were shown to be phosphorylated by the addition of PKC derived from rat brain tissue. These studies have important implications regarding the possible direct effects of prolactin in the nucleus of mammary cells.