Abstract
Rab GTPases control membrane traffic and receptor-mediated endocytosis. Within this context, Rab5a plays an important role in the spatial regulation of intracellular transport and signal transduction processes. Here, we report a previously uncharacterized role for Rab5a in the regulation of T-cell motility. We show that Rab5a physically associates with protein kinase Cϵ (PKCϵ) in migrating T-cells. After stimulation of T-cells through the integrin LFA-1 or the chemokine receptor CXCR4, Rab5a is phosphorylated on an N-terminal Thr-7 site by PKCϵ. Both Rab5a and PKCϵ dynamically interact at the centrosomal region of migrating cells, and PKCϵ-mediated phosphorylation on Thr-7 regulates Rab5a trafficking to the cell leading edge. Furthermore, we demonstrate that Rab5a Thr-7 phosphorylation is functionally necessary for Rac1 activation, actin rearrangement, and T-cell motility. We present a novel mechanism by which a PKCϵ-Rab5a-Rac1 axis regulates cytoskeleton remodeling and T-cell migration, both of which are central for the adaptive immune response.