Loss of RNF40 Decreases NF-κB Activity in Colorectal Cancer Cells and Reduces Colitis Burden in Mice.

Abstract

Inflammatory bowel diseases are linked to an increased risk of developing colorectal cancer [CRC]. Previous studies suggested that the H2B ubiquitin ligase RING finger protein-20 [RNF20] inhibited inflammatory signaling mediated by the nuclear factor kappa-light-chain-enhancer of activated B cells [NF-κB]. However, the role of RNF40, the obligate heterodimeric partner of RNF20, in the context of inflammation and CRC has not been addressed. Here, we examined the effect of RNF40 loss on CRC cells in vitro and on inflammation and inflammatory signaling in vitro and in vivo. We evaluated H2Bub1 levels in human and murine colorectal tumors by immunohistochemistry. Moreover, we correlated H2Bub1 and RNF40 levels in vivo and assessed the consequences of RNF40 depletion on cellular phenotype and gene expression in CRC cells in vitro. Finally, we examined the effect of a colon-specific loss of Rnf40 in a murine model of colitis, and assessed both local and systemic inflammation-associated consequences. In vitro studies revealed that the tumorigenic phenotype of CRC cells decreased after RNF40 depletion and displayed gene expression changes related to chromosome segregation and DNA replication, as well as decreased induction of several NF-κB-associated cytokines. This effect was associated with decreased nuclear localization of NF-κB following tumor necrosis factor alpha treatment. Consistently, the colon-specific loss of Rnf40 exerted a protective local, as well as systemic, effect following acute colitis. Our findings suggest that RNF40 plays a central role in the maintenance of tumorigenic features and inflammatory signaling by promoting nuclear NF-κB activity.