Regulation of rat placental lactogen (rPL)-II secretion: cAMP inhibits rPL-II secretion in vitro

Abstract

We examined whether epidermal growth factor (EGF), interleukin (IL)-1, IL-6 and cAMP analogs, which regulate mouse placental lactogen II secretion, affect rat placental lactogen (rPL)-II secretion using a rat choriocarcinoma cell line, Rcho-1. EGF, IL-1 and IL-6 did not affect rPL-II secretion, but 8-bromo-cAMP and forskolin inhibited rPL-II secretion by the 8th day of culture. The effects were dose dependent and the lowest concentrations of 8-bromo-cAMP and forskolin that significantly inhibited rPL-II secretion were 125 and 5 mumol/l, respectively. Cholera toxin also inhibited rPL-II secretion. The reverse hemolytic plaque assay for rPL-II indicated that the cells releasing rPL-II in the culture were giant cells and that 8-bromo-cAMP decreased the number of rPL-II-releasing cells. Western blot analysis of rPL-II yielded a single band at approximately 24.5 K, and 8-bromo-cAMP treatment significantly reduced the band intensity. Northern blot analysis of rPL-II indicated that 8-bromo-cAMP also reduced rPL-II gene expression. These findings suggest that the increase of intracellular cAMP accumulation results in inhibition of rPL-II secretion by decreasing rPL-II gene expression and inhibiting giant cell differentiation.

Placental lactogen-I gene activation in differentiating trophoblast cells: extrinsic and intrinsic regulation involving mitogen-activated protein kinase signaling pathways

“…Rcho-1 trophoblast cells have also been utilized to investigate modulatory roles of growth factors and cytokines on trophoblast cell proliferation (Verstuyf et al 1993, Hamlin & Soares 1995. Attempts to identify extracellular signals controlling trophoblast cell differentiation with the Rcho-1 trophoblast cell model have been limited (Yamaguchi et al 1995a, Yamamoto et al 1997.…”