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Role of atypical protein kinase C isozymes and NF‐κB in IL‐1β‐induced expression of cyclooxygenase‐2 in human myometrial smooth muscle cells

Increased myometrial expression of cyclooxygenase‐2 (Cox‐2) at term results from elevated local levels of inflammatory cytokines, and its inhibition provides a potential route for intervention in human pre‐term labor. We have identified a role for atypical protein kinase C (PKC) isozymes in IL‐1β‐induced Cox‐2 expression in human myometrial smooth muscle cells (HMSMC). The PKC inhibitor GF109203X (10 µM) inhibited IL‐1β‐induced Cox‐2 protein and RNA expression, which were also reduced by MAPK and nuclear factor κB (NF‐κB) inhibitors. GF109203X did not affect MAPK activities, and neither did it replicate the effect of p38 MAPK inhibition on Cox‐2 mRNA stability, suggesting that PKC operates through an independent mechanism. The effect of GF109203X remained intact after depletion of conventional and novel PKC isozymes by phorbol ester pre‐treatment. In contrast LY379196 (10 µM), which at micromolar concentrations inhibits all but atypical PKCs, did not affect Cox‐2 expression. A peptide corresponding to the pseudosubstrate sequence of atypical PKCs blocked Cox‐2 protein expression, whereas the sequence from conventional PKCs was ineffective. GF109203X did not affect NF‐κB binding to nuclear proteins, but strongly reduced NF‐κB‐dependent transcription in luciferase reporter assays. Our findings indicate that IL‐1β‐induced Cox‐2 expression in HMSMC in culture requires p38‐MAPK‐mediated mRNA stabilization and an independent activation of Cox‐2 transcription which is dependent on the action of atypical PKCs, probably through direct stimulation of the transactivating activity of NF‐κB. J. Cell. Physiol. 210: 637–643, 2007. © 2006 Wiley‐Liss, Inc.