DNA‐PKcs, but not TLR9, is required for activation of Akt by CpG‐DNA

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 ex vivo stimulation of bone marrow‐derived macrophages (BMDMs) from mice lacking the catalytic subunit of DNA‐dependent protein kinase (DNA‐PKcs) results in defective phosphorylation and activation of Akt by CpG‐DNA. 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 DNA‐PKcs in CpG‐DNA signaling and define a CpG‐DNA/DNA‐PKcs/Akt pathway.