The pseudorabies virus US3 protein kinase possesses anti-apoptotic activity that protects cells from apoptosis during infection and after treatment with sorbitol or staurosporine.

Most large DNA viruses, like herpesviruses, encode anti-apoptotic proteins to interfere with the apoptotic cellular response to infection. Previous studies have shown that the US3 protein kinase of herpes simplex virus, in contrast to US3 of bovine herpes virus 1, is very potent in protecting cells from apoptosis induced by the virus itself or by a broad range of exogenous apoptotic stimuli. Here, we demonstrate that US3 of the swine alphaherpesvirus pseudorabies virus (PRV) suppresses PRV-induced apoptosis in swine-testicle (ST) cells at late stages in infection, and that it protects ST cells from apoptosis induced by either sorbitol or staurosporine. Interestingly, PRV US3 encodes a short and a long isoform, the latter of which contains a functional mitochondrial localization sequence. Transient transfections showed that the PRV US3 long isoform is more efficient in protecting ST cells from PRV- or staurosporine-induced apoptosis, suggesting a potential advantage for the mitochondrial localization of PRV US3 in implementing its anti-apoptotic function.