RGC-32 is a novel regulator of the T-lymphocyte cell cycle.

Abstract We have previously shown that RGC-32 is involved in cell cycle regulation in vitro . To define the in vivo role of RGC-32, we generated RGC-32 knockout mice. These mice developed normally and did not spontaneously develop overt tumors. To assess the effect of RGC-32 deficiency on cell cycle activation in T cells, we determined the proliferative rates of CD4 + and CD8 + T cells from the spleens of RGC-32 −/− mice, as compared to wild-type (WT, RGC-32 +/+ ) control mice. After stimulation with anti-CD3/anti-CD28, CD4 + T cells from RGC-32 −/− mice displayed a significant increase in [ 3 H]-thymidine incorporation when compared to WT mice. In addition, both CD4 + and CD8 + T cells from RGC-32 −/− mice displayed a significant increase in the proportion of proliferating Ki67 + cells, indicating that in T cells, RGC-32 has an inhibitory effect on cell cycle activation induced by T-cell receptor/CD28 engagement. Furthermore, Akt and FOXO1 phosphorylation induced in stimulated CD4 + T-cells from RGC-32 −/− mice were significantly higher, indicating that RGC-32 inhibits cell cycle activation by suppressing FOXO1 activation. We also found that IL-2 mRNA and protein expression were significantly increased in RGC-32 −/− CD4 + T cells when compared to RGC-32 +/+ CD4 + T cells. In addition, the effect of RGC-32 on the cell cycle and IL-2 expression was inhibited by pretreatment of the samples with LY294002, indicating a role for phosphatidylinositol 3-kinase (PI3K). Thus, RGC-32 is involved in controlling the cell cycle of T cells in vivo , and this effect is mediated by IL-2 in a PI3K-dependent fashion.