Non-canonical Notch signaling drives activation and differentiation of peripheral CD4+ T cells

Cleavage of the Notch receptor via a gamma-secretase, results in the release of the active intracellular domain of Notch that migrates to the nucleus and interacts with RBP-J kappa, resulting in the activation of downstream target genes. This canonical Notch signaling pathway has been documented to influence T cell development and function. However, the mechanistic details underlying this process remain obscure. In addition to RBP-J kappa, the intra-cellular domain of Notch also interacts with other proteins in the cytoplasm and nucleus, giving rise to the possibility of an alternate, RBP-J kappa independent Notch pathway. However, the contribution of such RBP-J kappa independent, "non-canonical" Notch signaling in regulating peripheral T cell responses is unknown. In this report, we specifically demonstrate the requirement of Notch1 for regulating signal strength and signaling events distal to the T cell receptor in peripheral CD4(+)T cells. By using mice with a conditional deletion in Notch1 or RBP-J kappa, we show that Notch1 regulates activation and proliferation of CD4(+)T cells independently of RBP-J kappa. Furthermore, differentiation to T(H)1 and iTreg lineages although Notch dependent, is RBP-J kappa independent. Our striking observations demonstrate that many of the cell-intrinsic functions of Notch occur independently of RBP-J kappa. Such non-canonical regulation of these processes likely occurs through NF-kappa B. This reveals a previously unknown, novel role of non-canonical Notch signaling in regulating peripheral T cell responses.