PAK6- A novel kinase in the maintenance of T cell anergy

Abstract

Abstract Costimulation of T cells through the antigen receptor and the CD28 receptor engages an ‘effector’ gene expression program and a burst of proliferation. Conversely, antigen receptor engagement in the absence of costimulation induces a hypo-responsive state, referred to as anergy, that is associated with active silencing of effector genes. Our ATAC-seq analysis of CD28-dependent chromatin remodeling in anergic and effector CD4+ T cells has identified p21-activated kinase 6 (PAK6) as a gene that becomes accessible in anergic but not effector T cells. PAK6 is a member of a family of kinases comprised of two groups, group I (PAK1-3) and group II (PAK4-6). PAK6 and other group II members lack a regulatory domain that is present in group I, causing it to function differently. Previous studies by others have shown that PAK2, a group I PAK, was a positive regulator of CD3/CD28 T cell activation. Here, we demonstrate that PAK6 has the opposite role in T cell activation as PAK2, where it inhibits IL2 secretion, a hallmark characteristic of T cell anergy. Knockdown of PAK6 in anergic and effector T cells, using a CRISPR/CAS9 approach, resulted in a 50% increase in IL2 secretion, and 5-fold more cell expansion in anergic cultures upon restimulation with CD3/CD28. This suggests that PAK6 may be involved in a signaling pathway which inhibits cellular proliferation or promotes apoptosis. The highest level of PAK6 expression was observed upon re-stimulation of anergic cells, suggesting that PAK6 may be involved in the maintenance of T cell anergy. This study identifies a novel role for PAK6 in T cell anergy and a potential new target for regulating T cell function in autoimmune diseases.