Id1 potentiates NF-κB activation upon T cell receptor signaling

E2A and HEB are basic helix-loop-helix transcription factors that play important roles in T cell development. Expression of Id1, one of their inhibitors, severely impairs T cell development in transgenic mice. Aberrant activation of NF-kappa B transcription factors has been shown to contribute to the developmental defects, but it is not clear whether NF-kappa B activation is directly due to Id1 expression or is secondary to an abnormal thymic environment in Id1 transgenic mice. Here, by using a T cell line model, we demonstrate that Id1 expression stimulates basal levels of NF-kappa B activity and further enhances NF-kappa B activation upon T cell receptor (TCR) signaling achieved by anti-CD3 and anti-CD28 stimulation. Activation of NF-kappa B is partially mediated by the classical pathway involving the interaction between the regulatory subunit, NF-kappa B essential modulator (NEMO), and the catalytic subunit, I kappa B kinase beta. However, a NEMO-independent pathway also appears to be at play. Id1-potentiated activation of NF-kappa B leads to overproduction of cytokines such as tumor necrosis factor alpha and interferon-gamma in a T cell line as well as in thymocytes. Among members of the NF-kappa B family, c-Rel appears to be preferentially activated by Id1, especially during TCR stimulation. Consistently, c-rel deficiency diminishes tumor necrosis factor alpha and interferon-gamma expression induced by Id1 and TCR signaling.