Deficiency of small GTPase Rac2 affects T cell activation

Rac2 is a hematopoietic-specific GTPase acting as a molecular switch to mediate both transcriptional activation and cell morphological changes. We have examined the effect of Rac2 deficiency during T cell activation. In Rac2^-/- T cells, proliferation was reduced upon stimulation with either plate-bound anti-CD3 or T cell receptor-specific antigen. This defect is accompanied with decreased activation of mitogen activated protein kinase extracellular signal-regulated kinase (ERK) 1/2 and p38, and reduced Ca²⁺ mobilization. TCR stimulation-induced actin polymerization is also reduced. In addition, anti-CD3 cross-linking-induced T cell capping is reduced compared with wild-type T cells. These results indicate that Rac2 is important in mediating both transcriptional and cytoskeletal changes during T cell activation. The phenotypic similarity of Rac2^-/- to Vav^-/- cells implicates Rac2 as a downstream mediator of Vav signaling.