Deficiency in Epithelium RAD50 Aggravates UC via IL-6-Mediated JAK1/2-STAT3 Signaling and Promotes Development of Colitis-Associated Cancer in Mice

Abstract Background Ulcerative colitis (UC) is one of the most important risk factors for developing colitis-associated cancer (CAC). Persistent DNA damage increases CAC risk and has been observed in patients with UC. We aimed to identify the regulatory role of RAD50, a DNA double-strand breaks (DSBs) sensor, in UC progression to CAC. Methods DSBs and RAD50 expression in inflammatory bowel disease (IBD) and CAC cell and mouse models were assessed. Mice with intestinal epithelial RAD50 deletion (RAD50IEC-KO) were used to examine the role of RAD50 in colitis and CAC. Results Along with the increased γ-H2AX expression in colitis and CAC models, RAD50 expression was reduced in human IBD and CAC as well as in mouse models. Furthermore, RAD50IEC-KO sensitizes mice to dextran sulfate sodium (DSS)-induced acute and chronic experimental colitis. RNA-seq analyses revealed that RAD50IEC-KO activated the cytokine-cytokine receptor response, which was amplified through the Janus kinase-signal transducer and activator of transcription (JAK-STAT) pathway. RAD50 directly interacts with STAT3 and subsequently inhibits its phosphorylation, which may disrupt the IL-6-JAK1/2-STAT3-IL-6 feed-forward loop. Pharmacological STAT3 inhibition relieves colitis in RAD50IEC-KO mice. Severe DSBs, increased cell proliferation, and extended inflammatory response were identified in RAD50-deficient cells, which promoted azoxymethane (AOM)-DSS-induced colon tumor development in RAD50IEC-KO mice. Conclusions RAD50 exerts anti-IL-6-related inflammatory effects in colitis and suppresses CAC. Increasing RAD50 level in colon tissues may be promising for treating patients with UC and CAC.