SELECTIVE-INHIBITION OF MOUSE PLACENTAL-LACTOGEN-II SECRETION BY TUMOR-NECROSIS-FACTOR-ALPHA

The placental members of the prolactin-GH-placental lactogen (PL) gene family of the mouse include mPL-I, mPL-II, proliferin (PLF) and proli ferin-related protein (PRP). The aim of the present study was to asses s the effects of tumour necrosis factor-alpha (TNF-alpha) on the secre tion of these proteins in primary cultures of placental cells from day s 7, 9 and 12 of pregnancy. The effects of epidermal growth factor (EG F) on the secretion of PLF and PRP were also determined. EGF has previ ously been shown to stimulate mPL-I and inhibit mPL-II secretion. Incu bation of placental cells from day 7 of pregnancy for 5 days with 10 n mol human (h)TNF-alpha/1 did not affect the mPL-II concentration of th e medium, but similar treatment of cells from days 9 or 12 of pregnanc y resulted in a significant reduction in the mPL-II concentration of t he medium by the second or third day of culture. The intracellular con centration of mPL-II, the number of cells that released mPL-II as asse ssed by reverse haemolytic plaque assay, and steady-state levels of mP L-II mRNA as assessed by Northern analysis were also reduced by hTNF-a lpha treatment. The lowest concentration of hTNF-alpha that significan tly inhibited mPL-II secretion by cells from day 12 of pregnancy was 0 .01 nmol/l. hTNF-alpha treatment did not affect the secretion of mPL-I , PLF or PRP, as assessed by the concentrations of these proteins in t he medium during a 5-day incubation. Incubation of the cells with 20 n g EGF/ml also did not affect the PLF or PRP concentration of the mediu m during 5 days of culture. To determine whether the effect of hTNF-al pha on mPL-II secretion was mediated by interleukin-6 (IL-6), the IL-6 concentration of the medium of control and hTNF-alpha-treated cells w as determined. Bioactive and immunoreactive IL-6 could not be detected in medium from either treatment group. The presence of binding sites for hTNF-alpha was assessed in cells from day 12 of pregnancy. Scatcha rd analysis detected a single class of binding sites having a K-d of 1 .6 +/- 0.34 nmol/l, with about 1350 sites per cell. The results of thi s study demonstrate that hTNF-alpha inhibits the secretion of mPL-II b y placental cells from days 9 and 12 of pregnancy, suggesting that TNF -alpha may be one of the factors that regulate the production of this hormone in vivo.