The embryonic pregnancy signal oestradiol influences gene expression at the level of translational initiation in porcine endometrial cells.

Contents In the pig, conceptus-derived oestrogens (days 11 and 12 of pregnancy) seem to be a critical component of the signalling mechanism for maternal recognition of pregnancy. Embryonic oestrogens can mediate effects on endometrial function by interactions with epithelial and stromal oestrogen receptors (ER). Recent data demonstrate that cell membrane ER interacts with the phosphatidylinositol 3-kinase/Akt pathway in several types of cells. The protein kinase Akt is involved in the control of cell growth, survival and proliferation. One distinct function of the Akt signalling cascade is its ability to phosphorylate the eukaryotic initiation factor-4E (eIF-4E)binding protein 1 (4E-BP1). This phosphorylation suppresses the inhibitory effect of 4E-BP1 on the translation initiation factor eIF4E and in such a way potentially stimulates gene expression at the level of translational initiation. The aim of the present study was to examine if embryonic oestradiol (E2) transmits its effect by such a mechanism. Endometrial cells of cyclic gilts (day 13 of the oestrous cycle, n ¼ 4) were cultured and supplemented with vehicle (control), E2 (50 and 100 pM/l) or with the selective ER modulator raloxifen (10 and 1000 nM/ l), and incubated for 24 h. The cell viability was detected by MTT assay, the abundance and phosphorylation of Akt, 4EBP1 and ERa was analysed by Western blotting. Incubation with E2 or raloxifen did not alter endometrial cell viability. The phosphorylation of Akt at Ser 473 seems to be increased by E2 (p 0.05). Raloxifen (1000 nM/l) induced a band shift in 4E-BP1 to the highest electrophoretic mobility which reflects a decrease in phosphorylation (p < 0.05), whereas an influence of E2 on 4E-BP1 phosphorylation could not be detected. The decrease (p < 0.05) of the abundance of the 80 kDa ERa form both by E2 and raloxifen indicates that the E2-stimulated Akt phosphorylation and the inhibition of 4E-BP1 phosphorylation by raloxifen is an E2 ER-transmitted process. Therefore, embryonic oestrogens can potentially transmit their effect by influencing signalling cascades which modulate gene expression at the level of translational initiation.