Foxp3 transcription factor is pro-apoptotic and lethal to developing regulatory T cells unless counterbalanced by cytokine survival signals

• Published in: Immunity (Cambridge, Mass.) Mass.), 2013-06, Vol.38 (6), p.1116-1128
• Main Authors: Tai, Xuguang, Erman, Batu, Alag, Amala, Mu, Jie, Kimura, Motoko, Katz, Gil, Guinter, Terry, McCaughtry, Tom, Etzensperger, Ruth, Feigenbaum, Lionel, Singer, Dinah S., Singer, Alfred
• Format: Article
• Language: English
• ISSN: 1074-7613; 1097-4180
• DOI: 10.1016/j.immuni.2013.02.022

Immune tolerance requires regulatory T (Treg) cells to prevent autoimmune disease, with the transcription factor Foxp3 functioning as the critical regulator of Treg cell development and function. We report here that Foxp3 was lethal to developing Treg cells in the thymus because it induced a unique pro-apoptotic protein signature (Puma ++ p-Bim ++ p-JNK ++ DUSP6 - ) and repressed expression of pro-survival Bcl-2 molecules. However, Foxp3 lethality was prevented by common gamma chain (γc)-dependent cytokine signals that were present in the thymus in limiting amounts sufficient to support only ~1 million Treg cells. Consequently, most newly arising Treg cells in the thymus were deprived of this signal and underwent Foxp3-induced death, with Foxp3 + CD25 - Treg precursor cells being the most susceptible. Thus, we identify Foxp3 as a pro-apoptotic protein that requires developing Treg cells to compete with one another for limiting amounts of γc-dependent survival signals in the thymus.