Enhanced cell cycle activation in response to stimulation in RGC-32-/- T lymphocytes (115.3)

Abstract

Abstract We have previously identified Response Gene to Complement (RGC)-32 as a factor induced by complement activation, growth factors and cytokines. To study the in vivo function of RGC-32, we have generated mice carrying a null allele of the gene. Mice lacking RGC-32 were generated by replacing most of the second exon of the RGC-32 gene with sequences encoding neomycin resistance. These mice develop normally, have a similar size as wild type (WT) mice and a normal life span. Although RGC-32 was found to be involved in cell cycle regulation in vitro and is considered a tumor suppressor gene, RGC-32-/- mice do not spontaneously develop overt tumors. Little is known about the roles played by RGC-32 in T-cell proliferation. The effect of the lack of RGC-32 on cell cycle activation was investigated in CD4 cells isolated from spleen. Proliferation of anti-CD3/anti-CD28 stimulated CD4 cells from RGC-32-/- mice measured by [3H]-thymidine incorporation was significantly increased when compared with WT mice. In addition, by flow cytometry, both CD4 and CD8 T-cells from RGC-32-/- mice displayed a significant increase in the percentage of proliferating Ki-67 cells upon TCR stimulation. Furthermore, Akt phosphorylation was induced significantly in CD4 cells of RGC-32-/- when compared with WT mice. Our data indicate that in T-cells, RGC-32 plays an important role in inhibiting cell cycle activation by suppressing Akt activation.