Inhibition of phorbol ester-induced PGF2alpha secretion by IFN-tau is not through regulation of protein kinase C.

Inhibitory effect of IFN-tau on phorbol ester (PdBu)-induced PGF2alpha secretion was hypothesized to be manifested by the regulation of protein kinase C (PKC) in bovine endometrial (BEND) cells. Following 12 h stimulation with PdBu, cells were unresponsive to freshly added PdBu. Pretreatment of cells with a PKC inhibitor abolished PGF2alpha secretion in response to PdBu. Therefore, PdBu induction of PGF2alpha secretion is through activation of PKC. The alpha, epsilon, iota and lambda isotypes of the PKC family were identified by Western blotting. Cells were then treated with medium alone (control), PdBu or PdBu + IFN-tau for 3 or 6 h. The PdBu-induced secretion of PGF2alpha was suppressed by IFN-tau. At 3 and 6 h, PKCalpha and PKCepsilon were detected both in the cytosolic and membrane fractions of unstimulated cells. There was a clear reduction of PKCalpha in the cytoplasm induced by PdBu and PdBu + IFN-tau at 3 and 6 h. The total abundance (cytoplasm and membrane fractions) of PKCalpha was lower in the PdBu + IFN-tau than PdBu alone. These temporal responses indicate a PKCalpha responsiveness of BEND cells to PdBu and PDBu + INF-tau with some evidence that IFN-tau causes a slight but detectable reduction in PKCalpha when added with PdBu. However, IFN-tau-induced decrease in the total abundance of PKCalpha was not enough to affect negatively the translocation of the PKCalpha to the membrane. Therefore, IFN-tau's ability to suppress secretion of PGF2alpha is unlikely due to an interference with the PdBu-induced activity of PKC.