The effect of prolactin on casein kinase II, MAP kinase and PKC in rabbit mammary cells and Nb-2 rat lymphoid cells

Prolactin induces milk protein gene expression in rabbit primary mammary cells without any concomitant cell multiplication. Prolactin or other lactogenic hormones is the major inducer of cell division in the rat lymphoid Nb-2 cells. In Nb-2 cells, prolactin also rapidly induces the expression of the c-myc gene, and beta-actin and stathmin gene expression is induced more slowly. The possible involvement of casein kinase II (CKII), mitogen-activated protein kinase (MAPK) and protein kinase C (PKC) in these process is not well known. The present work was undertaken to evaluate the effect of prolactin on these protein kinases and to determine the possible involvement of these enzymes in the activity of several genes under the control of the hormone. In rabbit mammary cells, prolactin did not alter CKII activity but did transiently stimulate MAP kinase activity. Prolactin also stimulated Ca2+-independent PKC. This effect was visible after 10 min and was maintained for at least 24 hr. Staurosporine, an inhibitor of PKC and of several tyrosine kinases altered Ca2+-independent PKC only moderately. In contrast, GF 109203X, a potent and specific inhibitor of PKC, abrogated almost all PKC activity. Staurosporine, but not GF 109203X, prevented the induction of the casein gene by prolactin. In Nb-2 cells, prolactin induced a slow stimulation of CKII activity. The hormone did not induce MAP kinase activity. Prolactin stimulated Ca2+-independent PKC over periods of 24 hr. GF 109203X, but not staurosporine, inhibited PKC activity, whereas staurosporine but not GF 109203X, inhibited the induction of Nb-2 cell multiplication and the accumulation of c-myc, beta-actin and stathmin mRNAs. From these data, it can be concluded that (1) the stimulation of CKII by prolactin in Nb-2 cells is concomitant with cell multiplication: (2) MAPK stimulation is not necessary for prolactin to induce Nb-2 cell multiplication; and (3) PKC is stimulated in mammary and Nb-2 cells, but this stimulation is not required for prolactin to stimulate casein, c-myc, beta-actin and stathmin gene expression and Nb-2 cell division. (C) 1996 by Elsevier Science Inc.