Role of group A p21-activated kinases in the anti-apoptotic activity of the pseudorabies virus US3 protein kinase

The alphaherpesvirus US3 kinase is a conserved multifunctional serine/threonine kinase that plays a role in several processes, including modulation of the actin cytoskeleton, egress of virus particles from the nucleus and inhibition of apoptosis. However, the mechanisms used by the US3 protein to exert its functions remain poorly understood. Recently, we identified the group A p21-activated kinases PAK1 and PAK2 as important effectors in the US3-mediated cytoskeletal rearrangements. Here, we investigated if group A PAKs are also involved in the anti-apoptotic properties of US3. Infection experiments using a group A PAK inhibitor pointed at a moderate role for group A PAKs in the anti-apoptotic properties of US3. Furthermore, infection assays using wild type and US3null PRV in wild type MEF, PAK1(-/-) MEF and PAK2(-/-) MEF indicated that PAK2 does not play a role in US3-mediated inhibition of apoptosis during infection, whereas PAK1 plays a significant, yet limited role. Experiments in US3-transfected MEF using staurosporine as apoptosis trigger confirmed these observations. These results show that PAK1 plays a significant, yet limited, role in the anti-apoptotic activity of US3.