Inhibition of phorbol ester-induced PGF 2α secretion by IFN-τ is not through regulation of protein kinase C

Abstract

Inhibitory effect of IFN-τ on phorbol ester (PdBu)-induced PGF 2α 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 PGF 2α secretion in response to PdBu. Therefore, PdBu induction of PGF 2α secretion is through activation of PKC. The α, ɛ, ι and λ isotypes of the PKC family were identified by Western blotting. Cells were then treated with medium alone (control), PdBu or PdBu + IFN-τ for 3 or 6 h. The PdBu-induced secretion of PGF 2α was suppressed by IFN-τ. At 3 and 6 h, PKCα and PKCɛ were detected both in the cytosolic and membrane fractions of unstimulated cells. There was a clear reduction of PKCα in the cytoplasm induced by PdBu and PdBu + IFN-τ at 3 and 6 h. The total abundance (cytoplasm and membrane fractions) of PKCα was lower in the PdBu + IFN-τ than PdBu alone. These temporal responses indicate a PKCα responsiveness of BEND cells to PdBu and PDBu + INF-τ with some evidence that IFN-τ causes a slight but detectable reduction in PKCα when added with PdBu. However, IFN-τ-induced decrease in the total abundance of PKCα was not enough to affect negatively the translocation of the PKCα to the membrane. Therefore, IFN-τ's ability to suppress secretion of PGF 2α is unlikely due to an interference with the PdBu-induced activity of PKC.