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J Exp Med. 2008 Mar 17;205(3):565-74. doi: 10.1084/jem.20071477. Epub 2008 Feb 18.

The AKT-mTOR axis regulates de novo differentiation of CD4+Foxp3+ cells.

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  • 1Section on Immunology and Immunogenetics, Joslin Diabetes Center, Boston, MA 02215, USA.

Abstract

CD4(+)Foxp3(+) regulatory T (T reg) cells play an essential role in maintaining immunological tolerance via their suppressive function on conventional CD4(+) T (Tconv) cells. Repertoire studies suggest that distinct T cell receptor signaling pathways lead to T reg differentiation, but the signals that regulate T reg specification are largely unknown. We identify AKT as a strong repressor of entry into the T reg phenotype in vitro and in vivo. A constitutively active allele of AKT substantially diminished TGF-beta-induced Foxp3 expression in a kinase-dependent manner and via a rapamycin-sensitive pathway, implicating the AKT-mammalian target of rapamycin axis. The observed impairment in Foxp3 induction was part of a broad dampening of the typical T reg transcriptional signature. Expression of active AKT at a stage before Foxp3 turn on during normal T reg differentiation in the thymus selectively impaired differentiation of CD4(+)Foxp3(+) cells without any alteration in the positive selection of Tconv. Activated AKT, in contrast, did not affect established Foxp3 expression in T reg cells. These results place AKT at a nexus of signaling pathways whose proper activation has a strong and broad impact on the onset of T reg specification.

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