O-GlcNAcylation Enhances Double-Strand Break Repair, Promotes Cancer Cell Proliferation, and Prevents Therapy-Induced Senescence in Irradiated Tumors

Abstract

The metabolic reprogramming associated with characteristic increases in glucose and glutamine metabolism in advanced cancer is often ascribed to answering a higher demand for metabolic intermediates required for rapid tumor cell growth. Instead, recent discoveries have pointed to an alternative role for glucose and glutamine metabolites as cofactors for chromatin modifiers and other protein posttranslational modification enzymes in cancer cells. Beyond epigenetic mechanisms regulating gene expression, many chromatin modifiers also modulate DNA repair, raising the question whether cancer metabolic reprogramming may mediate resistance to genotoxic therapy and genomic instability. Our prior work had implicated N-acetyl-glucosamine (GlcNAc) formation by the hexosamine biosynthetic pathway (HBP) and resulting protein O-GlcNAcylation as a common means by which increased glucose and glutamine metabolism can drive double-strand break (DSB) repair and resistance to therapyinduced senescence in cancer cells. We have examined the effects of modulating O-GlcNAcylation on the DNA damage response (DDR) in MCF7 human mammary carcinoma in vitro and in xenograft tumors. Proteomic profiling revealed deregulated DDR pathways in cells with altered O-GlcNAcylation. Promoting protein O-GlcNAc modification by targeting O-GlcNAcase or simply treating animals with GlcNAc protected tumor xenografts against radiation. In turn, suppressing protein O-GlcNAcylation by blocking O-GlcNAc transferase activity led to delayed DSB repair, reduced cell proliferation, and increased cell senescence in vivo. Taken together, these findings confirm critical connections between cancer metabolic reprogramming, DDR, and senescence and provide a rationale to evaluate agents targeting O-GlcNAcylation in patients as a means to restore tumor sensitivity to radiotherapy. Implications: The finding that the HBP, via its impact on protein O-GlcNAcylation, is a key determinant of the DDR in cancer provides a mechanistic link between metabolic reprogramming, genomic instability, and therapeutic response and suggests novel therapeutic approaches for tumor radiosensitization.

Fueling the fire: emerging role of the hexosamine biosynthetic pathway in cancer

“…4) [105]. A recent report shows that reducing OGT expression in breast cancer cells was associated with defects in double-stand break repair, reduced cell proliferation, and increased cell senescence in vivo [106]. Conversely, promoting O-GlcNAcylation by targeting OGA protected tumor xenografts from radiation, thus implicating O-GlcNAcylation as a key player in the DNA damage response in cancer cells and as a potential regulator of tumor radiosensitization.…”

Interplay between Cellular Metabolism and the DNA Damage Response in Cancer

“…Its activity then promotes DSB repair by enhancing H2K27 trimethylation, an important determinant in NHEJ repair. Metabolic rewiring thus protects cancer cells against radiotherapy, increasing DNA repair and limiting senescence [187].…”

O-GlcNAc: Regulator of Signaling and Epigenetics Linked to X-linked Intellectual Disability

“…To maintain genome integrity, the cell cycle is regulated by the DDR pathway following DNA damage stress, with O-GlcNAc involved by modifying the arrangement of histones and kinases (Hanover et al, 2018;Liu and Li, 2018). Blocking O-GlcNAc transferase activity leads to delayed DSB repair, reduced cell proliferation, and increased cell senescence in vivo, while increased O-GlcNAc promotes DSB repair and hyper-proliferation in vivo and in vitro (Efimova et al, 2019). These findings suggest O-GlcNAc is necessary to protect the genome and for proper cell cycle progression.…”

“…In addition, one report has suggested OGT transfers GlcNAc onto H2AXS139, the same site as γ-phosphorylation (Chen and Yu, 2016). The authors suggest O-GlcNAc inhibits the DDR, though other studies suggest O-GlcNAc activates the DDR pathway (Efimova et al, 2019;Na et al, 2020).…”