The multifaceted functions of DNA-PKcs: implications for the therapy of human diseases

Abstract

The DNA-dependent protein kinase (DNA-PK), catalytic subunit, also known as DNA-PKcs, is complexed with the heterodimer Ku70/Ku80 to form DNA-PK holoenzyme, which is well recognized as initiator in the nonhomologous end joining (NHEJ) repair after double strand break (DSB). During NHEJ, DNA-PKcs is essential for both DNA end processing and end joining. Besides its classical function in DSB repair, DNA-PKcs also shows multifaceted functions in various biological activities such as class switch recombination (CSR) and variable (V) diversity (D) joining (J) recombination in B/T lymphocytes development, innate immunity through cGAS-STING pathway, transcription, alternative splicing, and so on, which are dependent on its function in NHEJ or not. Moreover, DNA-PKcs deficiency has been proven to be related with human diseases such as neurological pathogenesis, cancer, immunological disorder, and so on through different mechanisms. Therefore, it is imperative to summarize the latest findings about DNA-PKcs and diseases for better targeting DNA-PKcs, which have shown efficacy in cancer treatment in preclinical models. Here, we discuss the multifaceted roles of DNA-PKcs in human diseases, meanwhile, we discuss the progresses of DNA-PKcs inhibitors and their potential in clinical trials. The most updated review about DNA-PKcs will hopefully provide insights and ideas to understand DNA-PKcs associated diseases.

Keywords: DNA damage; DNA‐PKcs; V(D)J recombination; class switch recombination; innate immunity.

FIGURE 1

The functional domains and phosphorylation sites of DNA‐PKcs. (A) DNA‐PKcs contains a N‐terminal HEAT (Huntingtin, elongation, factor 3, protein phosphatase 2A, TOR1) repeats domain and a C‐terminal kinase domain surrounded by FAT (FRAP‐ATM‐TRRAP) and FATC (FATC‐terminal) domains. And the modification site of DNA‐PKcs. (B) The structure of DNA‐PKcs with functional domains and phosphorylation sites as depicted. (C) The history of key events in DNA‐PKcs discovery.

FIGURE 2

The DSB repair of NHEJ and HR. (A) The function of DNA‐PKcs in NHEJ pathway. In NHEJ, DNA‐PKcs and Ku70/Ku80 form a complex to bind to the site of DNA breaks and complete the repair of DNA breaks through the involvement of multiple factors such as 53BP1 and so on. This process usually occurs in G0/G1 phase. (B) In HR, MRN, ATM, and CtIP form a trimer, followed by the participation of EXO1, RAD51, and so on, to complete the repair of DNA. HR usually occurs in S/G2 phase. DSBs, double strand breaks; NHEJ, nonhomologous end joining; HR, homologous recombination; XRCC4, the X‐ray cross complementing protein 4; XLF, the XRCC4‐like factor; RAGs, recombination‐activation genes; BRCA1/2, breast cancer susceptibility genes1/2.

FIGURE 3

The regulation of DNA‐PKcs in immune cells. The regulation of DNA‐PKcs in immune cells. In DCs, DNA‐PKcs regulates inflammation via IKK‐NF‐κB, but whether the PARP‐1 is involved the regulation of DNA‐PKcs for DCs is uncertain. In NK, DNA‐PKcs regulates inflammation, cytotoxic lysis and development via AKT and other pathways. In macrophages, DNA‐PKcs regulates inflammation, infection and proliferation. In neutrophil cells, DNA‐PKcs regulates myeloid differentiation, but the mechanisms need exploration. In mast cells, DNA‐PKcs regulates histamine release under ultraviolet radiation. For B cells, DNA‐PKcs regulates cell growth, development, differentiation, and immunoglobulin diversity via V(D)J and CSR. For T cells, DNA‐PKcs regulates cell action, immune response, tumor, and so on via ATM/ATR/DNA‐PKcs and other pathways. DCs, dendric cells; NK cells, natural killer cells; V(D)J, variable (V) diversity (D) and joining (J); CSR, class switch recombination. Created with BioRender.com (https://www.biorender.com).

FIGURE 4

DNA‐PKcs in V(D)J recombination. (A) NHEJ pathway in V(D)J. the process as four steps: (1) RAG‐1/2 proteins combine HMG1 or HMG2 to form RAG complex, then the RAG complex open free hairpins. (2) The KU complex recognizes the DSBs, recruits the DNA‐PKcs, and together tether the break DNA ends. (3) Nucleases and polymerases participate in the processing of the DNA ends123. (4) The ligation of the processed DNA ends, conducted by XLF, DNA ligase IV, and XRCC4 in NHEJ. (B) The influence of DNA‐PKcs on B cells development and differentiation. DSBs, double strand breaks; RAGs, recombination‐activation genes; XRCC4, the X‐ray cross complementing protein 4; XLF, the XRCC4‐like factor. Created with BioRender.com (https://www.biorender.com).

FIGURE 5

DNA‐PKcs in diseases and targeted therapies. (A) The function of DNA‐PKcs in immune‐related diseases. (B) The function of DNA‐PKcs in senescence. (C) The function of DNA‐PKcs in nervous system diseases. (D) The function of DNA‐PKcs in cancers. (E) The function of DNA‐PKcs in other diseases, such as cardiovascular disease and kidney diseases. RA, rheumatoid arthritis; APECED, autoimmune‐polyendocrinopathy‐candidiasis‐ectodermal dystrophy; PD‐L1, programmed cell death 1 ligand 1; EMT, epithelial–mesenchymal cell transformation; TME, tumor microenvironment; TBC1D15, TBC domain family member 15; ROS, reactive oxygen species; MSI, microsatellite instability. Created with BioRender.com (https://www.biorender.com).