Downmodulation of tumor suppressor p53 by T cell receptor signaling is critical for antigen-specific CD4(+) T cell responses.

Antigen specificity is critical in immune response and requires integration of antigen-specific signals with antigen-nonspecific signals such as those provided by cytokines. The mechanism integrating these pathways is incompletely understood. We report here that antigen-specific proliferative responses of CD4(+) T cells required downmodulation of tumor suppressor p53. In the absence of T cell receptor (TCR) signal, IL-2 induced sustained increase in p53 protein, which prevented proliferative responses despite strong signaling through the IL-2 receptor. In contrast, TCR signaling resulted in early termination of p53 protein expression by decreasing p53 mRNA as well as strong transcriptional induction of the p53-regulating protein Mdm2. Downmodulation of p53 in response to antigen stimulation was in fact critical for antigen-specific T cell proliferation, and preventing p53 degradation by inhibiting Mdm2 resulted in sustained p53 protein and prevented antigen-specific T cell proliferation. It is thus termination of p53 by TCR signaling that allows proliferative responses, enforcing antigen specificity.