DNA‐PKcs, but not Toll‐like receptor 9, is required for activation of Akt by CpG‐DNA

Abstract

CpG-DNA and its related synthetic CpG oligodeoxynucleotides (CpG-ODNs) play an important role in immune cell survival. It has been suggested that Akt is one of the CpG-DNA responsive serine/threonine kinases; however, the target protein of CpG-DNA that leads to Akt activation has not been elucidated. Here, we report that stimulation of bone marrow-derived macrophages (BMDMs) from mice lacking the catalytic subunit of DNA-dependent protein kinase (DNA-PKcs) or mice harboring a point mutation in DNA-PKcs gene results in defective phosphorylation and activation of Akt by CpGDNA. Unexpectedly, loss of the Toll-like receptor 9 has a minimal effect on Akt activation in response to CpG-DNA. Further in vitro analysis using purified DNA-PK and recombinant Akt proteins reveals that DNA-PK directly induces phosphorylation and activation of Akt. In addition, in BMDMs, DNA-PKcs associates with Akt upon CpG-DNA stimulation and triggers transient nuclear translocation of Akt. Thus, our findings establish a novel role for DNAPKcs in CpG-DNA signaling and define a CpG-DNA/DNAPKcs/Akt pathway.