Cloning of canine Ku80 and its localization and accumulation at DNA damage sites

The Role of Ku70 as a Cytosolic DNA Sensor in Innate Immunity and Beyond

Human Ku70 is a well-known endogenous nuclear protein involved in the non-homologous end joining pathway to repair double-stranded breaks in DNA. However, Ku70 has been studied in multiple contexts and grown into a multifunctional protein. In addition to the extensive functional study of Ku70 in DNA repair process, many studies have emphasized the role of Ku70 in various other cellular processes, including apoptosis, aging, and HIV replication. In this review, we focus on discussing the role of Ku70 in inducing interferons and proinflammatory cytokines as a cytosolic DNA sensor. We explored the unique structure of Ku70 binding with DNA; illustrated, with evidence, how Ku70, as a nuclear protein, responds to extracellular DNA stimulation; and summarized the mechanisms of the Ku70-involved innate immune response pathway. Finally, we discussed several new strategies to modulate Ku70-mediated innate immune response and highlighted some potential physiological insights based on the role of Ku70 in innate immunity.

Inhibition of Crandell-Rees Feline Kidney cell proliferation by X-ray-induced senescence

Radioresistance and radiotoxicity have been reported following cancer treatments in felines. Optimizing radiation doses to induce cytotoxic effects to only cancer cells and not normal cells is critical in achieving effective radiation therapy; however, the mechanisms of radiation resistance, radiotoxicity, and DNA damage response (DDR) in feline cells have not yet been elucidated. A DNA double-strand break (DSB) is the most toxic type of DNA damage induced by X-rays and heavy ion beams used in treating cancers. Crandell-Rees Feline Kidney (CRFK) cells is one of the most widely used cat cells in life science research. Here, we report that DSB-triggered senescence induced by X-rays is important in inhibiting the proliferation of CRFK cells. We demonstrated through cell proliferation assay that X-rays at doses 2 Gy and 10 Gy are toxic to CRFK cells that irradiating CRFK cells inhibits their proliferation. In X-irradiated CRFK cells, a dose-dependent increase in DSB-triggered senescence was detected according to morphological changes and using senescence-associated β galactosidase staining assay. Moreover, our data indicated that in CRFK cells, the major DDR pathway, which involves the phosphorylation of H2AX at Ser139, was normally activated by ATM kinases. Our findings are useful in the understanding of X-rays-induced cellular senescence and in elucidating biological effects of radiation, e.g., toxicity, in feline cells. Furthermore, our findings suggest that the CRFK cell line is an excellent matrix for elucidating radioresistance and radiotoxicity in cat cells.

The Ku complex: recent advances and emerging roles outside of non-homologous end-joining

Since its discovery in 1981, the Ku complex has been extensively studied under multiple cellular contexts, with most work focusing on Ku in terms of its essential role in non-homologous end-joining (NHEJ). In this process, Ku is well-known as the DNA-binding subunit for DNA-PK, which is central to the NHEJ repair process. However, in addition to the extensive study of Ku's role in DNA repair, Ku has also been implicated in various other cellular processes including transcription, the DNA damage response, DNA replication, telomere maintenance, and has since been studied in multiple contexts, growing into a multidisciplinary point of research across various fields. Some advances have been driven by clarification of Ku's structure, including the original Ku crystal structure and the more recent Ku-DNA-PKcs crystallography, cryogenic electron microscopy (cryoEM) studies, and the identification of various post-translational modifications. Here, we focus on the advances made in understanding the Ku heterodimer outside of non-homologous end-joining, and across a variety of model organisms. We explore unique structural and functional aspects, detail Ku expression, conservation, and essentiality in different species, discuss the evidence for its involvement in a diverse range of cellular functions, highlight Ku protein interactions and recent work concerning Ku-binding motifs, and finally, we summarize the clinical Ku-related research to date.

Feline XLF accumulates at DNA damage sites in a Ku-dependent manner

Resistance to radiotherapy and chemotherapy is a common problem in the treatment of cancer in humans and companion animals, including cats. There is thus an urgent need to develop new treatments. Molecularly targeted therapies hold the promise of high specificity and significant cancer‐killing effects. Accumulating evidence shows that DNA double‐strand break (DSB) repair proteins, which function in Ku‐dependent non‐homologous DNA‐end joining (NHEJ), are potential target molecules for next‐generation cancer therapies. Although cancer radioresistance in cats has been previously described, there are no reports on feline Ku‐dependent NHEJ. Here, we cloned and sequenced feline XLFcDNA and characterized X‐ray repair cross‐complementing protein 4‐like factor (XLF), which is one of the core NHEJ proteins. We demonstrated that feline XLF localizes to the nuclei of feline cells and that feline XLF immediately accumulates at laser‐induced DSB sites in a Ku‐dependent manner. Amino acid sequence alignment analysis showed that feline XLF has only 80.9% identity with human XLF protein, while the predicted nuclear localization signal and putative 14‐3‐3‐binding motif are perfectly conserved among human, cat, dog, chimpanzee, and mouse. These findings are consistent with the hypothesis that regulation of subcellular localization is important for the function of XLF. Furthermore, these findings may be useful in clarifying the mechanisms underlying feline Ku‐dependent DSB repair and feline cell radioresistance, and possibly facilitate the development of new molecularly targeted therapies that target common proteins in human and feline cancers.