Protein kinase C delta mediates fibroblast growth factor-2-induced interferon-tau expression in bovine trophoblast

Interferon-tau (IFNT) is the trophoblast-secreted factor responsible for establishing and maintaining pregnancy in ruminants. Several uterine- and embryo-derived factors, including fibroblast growth factor-2 (FGF2), regulate IFNT production. The objective of the present study was to decipher the intracellular signaling mechanisms employed by FGF2 to regulate IFNT production. In bovine trophoblast cells (CT1), mitogen-activated protein kinase kinase-dependent pathways mediated constitutive IFNT mRNA concentrations. However, FGF2-mediated increases in IFNT mRNA levels occurs independent of mitogen-activated protein kinase. Exposure to the pan-protein kinase C (PKC) inhibitor, calphostin C, did not affect basal IFNT mRNA levels but limited the ability of FGF2 to increase IFNT mRNA abundance. Also, supplementation with phorbol 12-myristate 13-acetate (PMA) stimulated IFNT mRNA levels to the same extent as with FGF2. PMA and FGF2 cosupplementation did not elicit an additive effect on IFNT mRNA abundance. Pharmacological antagonists for classic PKCs (Gö6976) or novel PKCs, including PKC delta (rottlerin), were used to identify the specific PKC isoform utilized by FGF2. Supplementation of CT1 cells with Gö6976 did not affect FGF2 or PMA activities, whereas rottlerin prevented FGF2- and PMA-dependent increases in IFNT mRNA abundance in CT1 cells. Rottlerin also prevented FGF2 from increasing IFNT mRNA levels in Vivot trophoblast cells and primary trophoblast outgrowths. Modifications in PRKCD phosphorylation status were evident following FGF2 and PMA treatment. Also, reducing PRKCD expression by RNA interference attenuated FGF2-dependent increases in IFNT mRNA abundance. In conclusion, these results provide evidence that FGF2 regulates IFNT production in bovine trophectoderm by acting through PRKCD.