DNA-PKcs Ser2056 auto-phosphorylation is affected by an O-GlcNAcylation/phosphorylation interplay

OGT and OGA: Sweet guardians of the genome

The past 4 decades have witnessed tremendous efforts in deciphering the role of O-GlcNAcylation in a plethora of biological processes. Chemists and biologists have joined hand in hand in the sweet adventure to unravel this unique and universal yet uncharted post-translational modification, and the recent advent of cutting-edge chemical biology and mass spectrometry tools has greatly facilitated the process. Compared with O-GlcNAc, DNA damage response (DDR) is a relatively intensively studied area that could be traced to before the elucidation of the structure of DNA. Unexpectedly, yet somewhat expectedly, O-GlcNAc has been found to regulate various DDR pathways: homologous recombination, nonhomologous end joining, base excision repair, and translesion DNA synthesis. In this review, we first cover the recent structural studies of the O-GlcNAc transferase and O-GlcNAcase, the elegant duo that "writes" and "erases" O-GlcNAc modification. Then we delineate the intricate roles of O-GlcNAc transferase and O-GlcNAcase in DDR. We envision that this is only the beginning of our full appreciation of how O-GlcNAc regulates the blueprint of life-DNA.

Review: Protein O-GlcNAcylation regulates DNA damage response: A novel target for cancer therapy

The DNA damage response (DDR) safeguards the stable genetic information inheritance by orchestrating a complex protein network in response to DNA damage. However, this mechanism can often hamper the effectiveness of radiotherapy and DNA-damaging chemotherapy in destroying tumor cells, causing cancer resistance. Inhibiting DDR can significantly improve tumor cell sensitivity to radiotherapy and DNA-damaging chemotherapy. Thus, DDR can be a potential target for cancer treatment. Post-translational modifications (PTMs) of DDR-associated proteins profoundly affect their activity and function by covalently attaching new functional groups. O-GlcNAcylation (O-linked-N-acetylglucosaminylation) is an emerging PTM associated with adding and removing O-linked N-acetylglucosamine to serine and threonine residues of proteins. It acts as a dual sensor for nutrients and stress in the cell and is sensitive to DNA damage. However, the explanation behind the specific role of O-GlcNAcylation in the DDR remains remains to be elucidated. To illustrate the complex relationship between O-GlcNAcylation and DDR, this review systematically describes the role of O-GlcNAcylation in DNA repair, cell cycle, and chromatin. We also discuss the defects of current strategies for targeting O-GlcNAcylation-regulated DDR in cancer therapy and suggest potential directions to address them.

Autophosphorylation and Self-Activation of DNA-Dependent Protein Kinase

The DNA-dependent protein kinase catalytic subunit (DNA-PKcs), a member of the phosphatidylinositol 3-kinase-related kinase family, phosphorylates serine and threonine residues of substrate proteins in the presence of the Ku complex and double-stranded DNA. Although it has been established that DNA-PKcs is involved in non-homologous end-joining, a DNA double-strand break repair pathway, the mechanisms underlying DNA-PKcs activation are not fully understood. Nevertheless, the findings of numerous in vitro and in vivo studies have indicated that DNA-PKcs contains two autophosphorylation clusters, PQR and ABCDE, as well as several autophosphorylation sites and conformational changes associated with autophosphorylation of DNA-PKcs are important for self-activation. Consistent with these features, an analysis of transgenic mice has shown that the phenotypes of DNA-PKcs autophosphorylation mutations are significantly different from those of DNA-PKcs kinase-dead mutations, thereby indicating the importance of DNA-PKcs autophosphorylation in differentiation and development. Furthermore, there has been notable progress in the high-resolution analysis of the conformation of DNA-PKcs, which has enabled us to gain a visual insight into the steps leading to DNA-PKcs activation. This review summarizes the current progress in the activation of DNA-PKcs, focusing in particular on autophosphorylation of this kinase.