TNF-alpha 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 NFkappaB pathways downstream of TNF-alpha in the context of connexin43 (Cx43) gene expression. We demonstrate that TNF-alpha reduces the expression of Cx43 in HaCat cell lines at the protein and mRNA levels, and transcriptionally. We also demonstrate that TNF-alpha decreases gap junctional intercellular communication (GJIC) between HaCat cells. Using pharmacological inhibitors of the NFkappaB signaling pathway, we determined that the NFkappaB signaling cascade is not implicated in TNF-alpha effect on Cx43 expression and in the subsequent decrease of GJIC. Conversely, in NFkappaB essential modulator (NEMO(-)) fibroblasts, lack of NFkappaB activation did not influence both the effect of TNF-alpha on Cx43 expression and on GJIC. In contrast, pharmacologic inhibition of JNK abolishes TNF-alpha-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 NFkappaB, as a critical mediator of TNF-alpha repressory effect on Cx43 gene expression. (c) 2008 Wiley-Liss, Inc.