Inhibition of IL‐13 and IL‐13rα2 expression by IL‐32θ in human monocytic cells requires PKCδ and STAT3 association

Abstract

Interleukin (IL)‐32θ, a newly identified IL‐32 isoform, has been reported to exert pro‐inflammatory effects through the association with protein kinase C delta (PKCδ). In this study, we further examined the effects of IL‐32θ on IL‐13 and IL‐13Rα2 expression and the related mechanism in THP‐1 cells. Upon stimulating IL‐32θ‐expressing and non‐expressing cells with phorbol 12‐myristate 13‐acetate (PMA), the previous microarray analysis showed that IL‐13Rα2 and IL‐13 mRNA expression were significantly decreased by IL‐32θ. The protein expression of these factors was also confirmed to be down‐regulated. The nuclear translocation of transcription factors STAT3 and STAT6, which are necessary for IL‐13Rα2 and IL‐13 promoter activities, was suppressed by IL‐32θ. Additionally, a direct association was found between IL‐32θ, PKCδ, and signal transducer and activator of transcription 3 (STAT3), but not STAT6, revealing that IL‐32θ might act mainly through STAT3 and indirectly affect STAT6. Moreover, the interaction of IL‐32θ with STAT3 requires PKCδ, since blocking PKCδ activity eliminated the interaction and consequently limited the inhibitory effect of IL‐32θ on STAT3 activity. Interfering with STAT3 or STAT6 binding by decoy oligodeoxynucleotides (ODNs) identified that IL‐32θ had additive effects with the STAT3 decoy ODN to suppress IL‐13 and IL‐13Rα2 mRNA expression. Taken together, our data demonstrate the intracellular interaction of IL‐32θ, PKCδ, and STAT3 to regulate IL‐13 and IL‐13Rα2 synthesis, supporting the role of IL‐32θ as an inflammatory modulator.