IL-32θ downregulates CCL5 expression through its interaction with PKCδ and STAT3

Interleukin-32 (IL-32) exists in several isoforms and plays an important role in inflammatory response. Recently, we identified a new isoform, IL-32 theta, and performed a microarray analysis to identify IL-32 theta-regulated genes in THP-1 myelomonocytic cells. Upon stimulating IL-32 theta-expressing THP-1 cells with phorbol myristate acetate (PMA), we found that the CCL5 transcript level was significantly reduced. We confirmed the downregulation of CCL5 protein expression by using an enzyme-linked immunosorbent assay (ELISA). Because STAT3 phosphorylation on Ser727 by PKC delta is reported to suppress CCL5 protein expression, we examined whether IL-32 theta-mediated STAT3 Ser727 phosphorylation occurs through an interaction with PKC delta. In this study, we first demonstrate that IL-32 theta interacts with PKC delta and STAT3 using co-immunoprecipitation (Co-IP) and pulldown assay. Moreover, STAT3 was rarely phosphorylated on Ser727 in the absence of IL-32 theta, leading to the binding of STAT3 to the CCL5 promoter. These results indicate that IL-32 theta, through its interaction with PKC delta, downregulates CCL5 expression by mediating the phosphorylation of STAT3 on Ser727 to render it transcriptionally inactive. Therefore, similar to what we have reported for IL-32 alpha and IL-32 beta, our data from this study suggests that the newly identified IL-32 theta isoform also acts as an intracellular modulator of inflammation. (C) 2014 Elsevier Inc All rights reserved.