DNA-PKcs

DNA-PKcs
National Center for Biotechnology Information, U.S. National Library of Medicine · Public domain · source
Name	DNA-dependent protein kinase catalytic subunit
Organism	Homo sapiens
Taxid	9606
Status	Reviewed
Length	~4128 aa
Uniprot	P09382

DNA-PKcs is a large serine/threonine protein kinase encoded by the human PRKDC gene that functions in the repair of DNA double-strand breaks and in the maintenance of genomic stability. First characterized biochemically in studies involving ionizing radiation and mammalian cell extracts, DNA-PKcs has been studied in contexts ranging from X-ray crystallography and electron microscopy to genetic models such as Mus musculus and Saccharomyces cerevisiae, and has been implicated in cancer biology and immune system development. Its discovery connected work on Ku70, Ku80, non-homologous end joining, and ionizing-radiation sensitivity in cultured human and rodent cells.

Structure and Biochemical Properties

DNA-PKcs is a ~4128–amino-acid polypeptide that adopts a large, HEAT-repeat–containing architecture characterized by a flexible solenoid and a C-terminal PI3K-like kinase domain; structural studies have employed cryo-electron microscopy, X-ray crystallography, and crosslinking coupled to mass spectrometry derived from complexes studied in laboratories such as those of Roger Kornberg and groups using instrumentation at facilities like the European Synchrotron Radiation Facility. The protein associates tightly with the DNA end–binding heterodimer comprising Ku70 and Ku80 and binds DNA ends in a manner that is modulated by ATP and metal ions such as magnesium. Biochemically, DNA-PKcs belongs to the phosphatidylinositol 3-kinase–related kinase (PIKK) family alongside ATM, ATR, and mTOR, sharing conserved motifs required for catalytic activity, substrate recognition, and interaction with regulatory proteins including XRCC4 and Ligase IV. Mutational analyses in human cell lines and genetically engineered mouse knockout models demonstrate that truncations or point mutations within the kinase domain disrupt catalytic activity and result in radiosensitivity phenotypes observed in classic studies by investigators at institutions such as Cold Spring Harbor Laboratory and Lawrence Berkeley National Laboratory.

Role in DNA Double-Strand Break Repair

DNA-PKcs is central to the classical non-homologous end joining (C-NHEJ) pathway, cooperating with Ku70, Ku80, Artemis, XRCC4, and DNA ligase IV to detect, process, and ligate DNA double-strand breaks generated by agents like ionizing radiation, etoposide, and during programmed recombination events such as V(D)J recombination in developing B cell and T cell lineages. In DSB repair pathway choice, DNA-PKcs activity influences competition with homologous recombination factors including BRCA1, BRCA2, RAD51, and MRE11, and cross-talk with damage sensors such as ATM and CHK2 modulates cell-cycle–dependent repair outcomes delineated in studies from groups at Dana-Farber Cancer Institute and Harvard Medical School. Loss-of-function alleles produce severe combined immunodeficiency–like phenotypes in model organisms and radiosensitivity syndromes reported in clinical genetics literature from centers like Mayo Clinic.

Regulation and Post-translational Modifications

DNA-PKcs is regulated by autophosphorylation at multiple sites (for example, the ABCDE and PQR clusters) and by phosphorylation mediated via cross-talk with ATM and ATR kinases; mass spectrometry–based phosphoproteomic studies from consortia including The Cancer Genome Atlas have mapped numerous serine/threonine phosphorylation events. Ubiquitination, sumoylation, and acetylation have been reported in proteomic datasets generated at institutions such as Salk Institute and Broad Institute, and proteostasis is influenced by E3 ligases and deubiquitinases that intersect with pathways involving MDM2 and the ubiquitin–proteasome system. Conformational changes triggered by phosphorylation control end-processing functions mediated by nucleases such as Artemis and influence interactions with chromatin remodelers characterized in studies from Max Planck Institute laboratories.

Interactions and Protein Complexes

DNA-PKcs forms stoichiometric complexes with the Ku heterodimer, creating a DNA-bound assembly that recruits additional factors including Artemis, the XRCC4–Ligase IV complex, and the scaffold protein XLF (Cernunnos), as demonstrated by biochemical reconstitution experiments in laboratories at MIT and Stanford University. It also interacts functionally with chromatin-associated proteins such as H2AX (γ-H2AX), MDC1, 53BP1, and remodeling complexes that include subunits studied by groups at European Molecular Biology Laboratory and Whitehead Institute, integrating DSB signaling with chromatin dynamics. Proteomic surveys and yeast two-hybrid screens have uncovered broader networks linking DNA-PKcs to factors involved in transcriptional regulation (for example, components associated with p53), cell-cycle control factors such as Cyclin-dependent kinase 1 and RB1, and stress-response modules characterized at institutions like NIH.

Cellular Functions and Pathophysiological Roles

Beyond canonical DSB repair, DNA-PKcs contributes to telomere maintenance, replication stress responses, and the processing of programmed DNA lesions during antigen receptor diversification in lymphocytes, implicating it in immunodeficiency syndromes and in the etiology of lymphoid malignancies documented by oncology centers including Memorial Sloan Kettering Cancer Center and Johns Hopkins Hospital. Aberrant DNA-PKcs activity or expression is associated with tumor progression and therapeutic resistance in cancers such as glioblastoma, prostate cancer, and non-small cell lung carcinoma, prompting translational studies and clinical trials coordinated by consortia including NCI and pharmaceutical partnerships with companies like AstraZeneca and Bayer. Germline and somatic PRKDC variants are cataloged in clinical genetics resources and have been linked to radiosensitivity, chromosomal instability syndromes, and altered responses to genotoxic chemotherapies referenced in reports from American Society of Hematology meetings.

Experimental Methods and Clinical Relevance

Experimental interrogation of DNA-PKcs employs assays including in vitro kinase assays, chromatin-immunoprecipitation, laser microirradiation, γ-H2AX foci quantification, and genetics using CRISPR/Cas9 and conditional knockout mouse models developed at centers such as Broad Institute and Jackson Laboratory. Small-molecule inhibitors targeting the kinase domain (for example, compounds developed by academic–industry collaborations) are being evaluated in combination with radiotherapy and PARP inhibitors in clinical trials registered by agencies like FDA and conducted at comprehensive cancer centers including MD Anderson Cancer Center. Biomarker studies use next-generation sequencing platforms and proteomic pipelines from institutions such as Genentech and Illumina to stratify patients based on PRKDC status for precision oncology applications.

Category:DNA repair proteins