Characterization of the in vivo function of RGC-32 in T-cells

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 develop normally and do not spontaneously develop overt tumors. To assess the effect of RGC-32 deficiency on cell cycle activation in T cells we determined the proliferation rate of CD4 and CD8 from spleens of RGC-32-/- mice compared to wild type (WT) mice. CD4 T cells from RGC-32-/- mice display a significant increase in 3H-thymidine incorporation when compared with WT mice after stimulation with anti-CD3/anti-CD28. In addition, both CD4 and CD8 T cells from RGC-32-/- 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. Furthermore, Akt and FOXO1 phosphorylation induced in CD4 from RGC-32-/- were significantly higher indicating that RGC-32 inhibits cell cycle activation by suppressing FOXO1 activation. To further examine the effect of RGC-32 on T cell functions we investigated the effect of RGC-32 on T regulatory (Treg) cells differentiation. A significantly lower percentage of CD4+ FoxP3+ Treg cells was found in unstimulated cells from RGC-32-/- compared to WT mice. Significantly fewer CD4+ FoxP3+ Treg cells are induced by TGF-β in RGC-32-/- compared to WT mice. Thus, RGC-32 is involved in controlling cell cycle in vivo, and in addition seems to play a role in the differentiation of Treg cells.