DNA-PK

DNA-PK (DNA-dependent protein kinase) is a nuclear serine/threonine protein kinase composed of a large catalytic subunit (DNA-PKcs) and a heterodimeric DNA-targeting subunit Ku. DNA-PK is a major component of the nonhomologous end-joining (NHEJ) pathway of DNA double-strand breaks repair. DNA-PK specifically requires association with DNA for its kinase activity, plays important roles in the regulation of different DNA transactions, including transcription, replication and DNA repair, as well as in the maintenance of telomeres.

The assembly of DNA-PK at DSB ends serves as a platform to recruit Artemis, DNA ligase IV and other NHEJ factors that are involved in end-processing and ligation. Within the DNA-PK complex, Ku proteins confer high affinity to DSB ends, and function as early sensors. The subsequent recruitment of DNA-PKcs to DSBs via the Ku proteins triggers the activation of DNA-PKcs, a member of the phosphatidylinositol 3-kinase-related kinase (PIKK) family. Upon activation, DNA-PKcs phosphorylates a number of substrates, including H2AX, XRCC4, Artemis and most importantly, DNA-PKcs itself. Autophosphorylation of DNA-PKcs occurs at numerous Ser/Thr residues throughout the kinase, and has been shown to mediate NHEJ.