TNF-α represses connexin43 expression in hacat keratinocytes via activation of JNK signaling

We used both pharmacological and gene knockout approaches to elucidate the specific roles played by the Jun‐N‐terminal kinase (JNK) and NFκB pathways downstream of TNF‐α in the context of connexin43 (Cx43) gene expression. We demonstrate that TNF‐α reduces the expression of Cx43 in HaCat cell lines at the protein and mRNA levels, and transcriptionally. We also demonstrate that TNF‐α decreases gap junctional intercellular communication (GJIC) between HaCat cells. Using pharmacological inhibitors of the NFκB signaling pathway, we determined that the NFκB signaling cascade is not implicated in TNF‐α effect on Cx43 expression and in the subsequent decrease of GJIC. Conversely, in NFκB essential modulator (NEMO−) fibroblasts, lack of NFκB activation did not influence both the effect of TNF‐α on Cx43 expression and on GJIC. In contrast, pharmacologic inhibition of JNK abolishes TNF‐α‐driven repression of Cx43 gene expression and GJIC between HaCat cells. Using JNK 1−/−‐JNK 2−/− (JNK−/−) fibroblasts, we demonstrate that similar regulatory mechanisms take place in fibroblasts. Together, these results identify JNK and not NFκB, as a critical mediator of TNF‐α repressory effect on Cx43 gene expression. J. Cell. Physiol. 216: 438–444, 2008. © 2008 Wiley‐Liss, Inc.