The transcription factor Bcl-3 represses the function of regulatory T cells leading to the development of colitis (BA15P.223)

Abstract

Abstract The proto-oncogene Bcl-3 (B cell leukemia-3) is a member of the IκB family of NF-κB inhibitors and was originally identified as a component of a chromosomal rearrangement in some B cell lymphomas. In contrast to other IκB proteins, Bcl-3 associates with p50 and p52 homodimers and is predominantly a nuclear protein involved in regulating nuclear NF-κB activity. To understand more about the effects of Bcl-3 on T cells, we have generated a new mouse model, where Bcl-3 is overexpressed specifically in T cells. We could show that mice overexpressing Bcl-3 solely in T cells developed spontaneous colitis accompanied by a massive cell infiltration into the colon. Interestingly, by analyzing regulatory T cells we could demonstrate that these cells were not able to suppress an inflammatory response. Due to the suppressive dysfunction, Tregs of Bcl-3 overexpressing mice expressed less CD25, Foxp3 as well as less of the co-inhibitory molecule CTLA-4. Hence, the loss of suppression of Bcl-3 overexpressing Tregs might result in the development of severe spontaneous colitis. Our data emphasize a novel pathway in the maintenance of viability and suppressive function of Tregs in the gut that critically involves Bcl-3 as a negative regulator, qualifying this protein as an interesting pharmacological target for the treatment of IBD.