DNA-PKcs Inhibition Extends Allogeneic Skin Graft Survival and Suppresses EGR1 and NFκB-mediated IL6 Production

Abstract Organ transplantation is the only option for patients in end-stage organ failure. Therefore; it is imperative that immunological mechanisms that foster graft rejection be elucidated to develop more effective immunosuppressants for transplant patients. In recent studies, the double-strand DNA break repair kinase, DNA-dependent protein kinase catalytic subunit(DNA-PKcs) has been implicated as a signaling molecule necessary for both B and T cell activity highlighting its potential role in graft rejection. In this study, we performed a phospho-proteomic screen to identify immunological targets of DNA-PKcs and a murine allogeneic skin graft study using DNA-PKcs inhibitors to investigate its effects on graft rejection. We identified a mechanism whereby DNA-PKcs is required for the protein stability of EGR1, a transcription factor known to promote NFκB expression. In primary splenocytes, DNA-PKcs inhibition abrogated EGR1 expression causing a decrease in NFκB-p65 levels and a reduction in the levels of the pro-inflammatory cytokine IL6 which can promote maturation of plasma cells. DNA-PKcs inhibition significantly reduced skin graft necrosis and extended graft survival compared to controls. DNA-PKcs inhibition reduced the infiltration of CD3+ lymphocytes into the grafts and the level of circulating CD19+ CD138+ lymphocytes. Additionally, DNA-PKcs inhibition reduced the production of donor-specific IgG and IgM antibodies. These results highlight a novel function for DNA-PKcs in the immune system and support further investigations into the use DNA-PKcs inhibitors in transplant therapy.