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.