Regulation of Notch activation in CD4+ T cells

Abstract

Abstract Notch signaling provides an important cue in the mammalian developmental process. It is a key player in T cell development and function. Mature T cells express Notch receptors 1, 2 and 3. Data from our lab and others indicate that T cell receptor (TCR) signaling activates Notch. Conventional ligand dependent Notch signaling involves, interaction of the Notch receptor with ligands such as Delta like ligand (DLL) 1,3, 4 or Jagged (JAG) 1, 2. However, in T cells it is unclear whether TCR induced activation of Notch is dependent upon engagement of Notch receptor with ligand. In-vitro stimulation of purified CD4+T cells, using antibodies against CD3 and costimulatory molecule CD28, results in activation of Notch. This occurs in absence of APC or any apparent ligand presenting cell. Thus, the mechanism that drives Notch activation during TCR stimulation is unclear. When naïve CD4+ T cells were cultured with bone marrow derived dendritic cells pulsed with antigen, we observed activation of Notch in the apparent absence of ligand on APC or activated T cells. However, when we examined ligand expression on naïve CD4+ T cell, activated by anti-CD3/CD28, we found resting T cells express constitutively low levels of DLL1 which increases with activation and is maintained through activated state. Additionally, DLL4 and JAG1 are expressed only after T cell activation and maintained only for 24hrs after activation. This upregulation is completely dependent upon signaling through CD28. However, whether the expression of ligand is sufficient to activate Notch remains unclear. Our preliminary data thus suggests that TCR mediated signaling in the absence of ligand may be is sufficient to activate Notch.