However, a role of p53 in regulation of T-cell responses or apoptosis has been poorly Ponatinib defined. TCR-mediated signaling in the absence of CD28 costimulation induces both apoptosis and proliferation of naïve T cells from WT mice. In this report we show that, in response to TCR stimulation, T cells from naïve p53-deficient mice exhibited higher proliferation and

drastically reduced apoptosis than WT T cells. CD28 costimulation enhanced the proliferation of TCR-stimulated WT and p53−/− T cells, suggesting that p53 uncouples CD28-mediated antiapoptotic and proliferative signals. To evaluate the physiological significance of these findings, we transplanted OVA expressing-EG.7 tumor cells into WT and p53−/− mice. Unlike WT mice, p53−/− mice exhibited a robust tumor-resistant phenotype and developed cytotoxic T-cell responses against OVA. Collectively, these data support the hypothesis that p53 is an essential factor in negative regulation of T-cell responses and have implication for immunomodulation during treatment of cancers and other inflammatory conditions. Transformation related protein 53 (Trp53 or p53) is a member of the p53 transcription factor family that regulates LDE225 ic50 DNA repair,

genomic integrity, DNA replication, cell proliferation and apoptosis 1–3. It contains an N-terminal transactivation domain, a C-terminal tetramerization domain and a central DNA binding domain. Under normal conditions p53 is expressed at low levels in a variety of cell types. Exposure of cells to ionizing radiation, DNA damage, or certain cellular or physiological stresses leads Exoribonuclease to stabilization and activation of p53 and its pathway 2. Once activated, p53 binds to target

DNA and initiates transcription of target genes that directly or indirectly inhibit the cell cycle or induce cell death 4, 5. Lack of p53 expression or function is related to development of a vast variety of tumor types and a role for p53 in apoptosis of cells has been the subject of numerous studies for many years. Traditionally, increased expression p53 has been reported in conditions that favor tumoroigenesis, e.g. ionizing radiations. However, p53 expression is also upregulated during inflammation and infections. Synovia from rheumatoid arthritis patients exhibit dominant negative mutations of p53 and expression of p53 is also upregulated in the joints of these patients 6. This increased level of p53 in arthritic synovium joints can be seen in the early stages of disease development 7. Further, lymphocytes from rheumatoid arthritis patients express lower levels of p53 mRNA and protein, and have an impaired ability to induce p53 expression after exposure to gamma radiation, which correlated with increased survival of CD4+ and CD8+ T cells after exposure to gamma radiation 8.