Critical roles of translationally controlled tumor protein in the homeostasis and TCR-mediated proliferation of peripheral T cells

Translationally controlled tumor protein (TCTP) is expressed throughout T cell development and prominently induced following T cell activation. However, its function(s) during these processes is unclear. Here, we demonstrated that conditional deletion of TCTP before the β selection checkpoint resulted into a partial block of thymocyte development at the double-negative (DN) 3 stage. Deletion of TCTP in the double-positive (DP) stage did not cause any significant phenotype in the thymus except a slight increase of mature CD8 single-positive (SP) thymocytes. In contrast to the very modest phenotype observed in the thymus, a significant reduction of mature T cells was observed in the peripheral lymphoid organs of these two conditional null TCTP mutant mice. Detailed analysis revealed that the latter phenotype (peripheral T cell lymphopenia) was largely due to a decreased viability of mature TCTP-deficient (TCTP^-/-) T cells. Transgenic expression of the anti-apoptotic protein Bcl-2 rescued the partial block of early thymocyte development, but not peripheral T cell lymphopenia of T-lineage-specific TCTP^-/- mice, suggesting that the signaling networks of TCTP in these two processes are not identical. Last, we demonstrated that TCTP^-/- T cells manifested a significant defect in T cell Ag receptor (TCR)-mediated cell proliferation. Further analysis revealed that such defect was due to a marked delay in the initial cell-cycle entry of TCTP^-/- T cells following TCR stimulation. Together, these results indicate that TCTP plays a very modest role in thymocyte development, but is critical for peripheral T cell maintenance and TCR-mediated cell proliferation.