A novel Ku70 function in colorectal homeostasis separate from nonhomologous end joining

Ku70 senses cytosolic DNA and assembles a tumor-suppressive signalosome

The innate immune response contributes to the development or attenuation of acute and chronic diseases, including cancer. Microbial DNA and mislocalized DNA from damaged host cells can activate different host responses that shape disease outcomes. Here, we show that mice and humans lacking a single allele of the DNA repair protein Ku70 had increased susceptibility to the development of intestinal cancer. Mechanistically, Ku70 translocates from the nucleus into the cytoplasm where it binds to cytosolic DNA and interacts with the GTPase Ras and the kinase Raf, forming a tripartite protein complex and docking at Rab5+Rab7+ early-late endosomes. This Ku70-Ras-Raf signalosome activates the MEK-ERK pathways, leading to impaired activation of cell cycle proteins Cdc25A and CDK1, reducing cell proliferation and tumorigenesis. We also identified the domains of Ku70, Ras, and Raf involved in activating the Ku70 signaling pathway. Therapeutics targeting components of the Ku70 signalosome could improve the treatment outcomes in cancer.

The DNA Damage Response and Inflammation in Cancer

Genomic stability in normal cells is crucial to avoid oncogenesis. Accordingly, multiple components of the DNA damage response (DDR) operate as bona fide tumor suppressor proteins by preserving genomic stability, eliciting the demise of cells with unrepairable DNA lesions, and engaging cell-extrinsic oncosuppression via immunosurveillance. That said, DDR sig-naling can also favor tumor progression and resistance to therapy. Indeed, DDR signaling in cancer cells has been consistently linked to the inhibition of tumor-targeting immune responses. Here, we discuss the complex interactions between the DDR and inflammation in the context of oncogenesis, tumor progression, and response to therapy.

SIGNIFICANCE

Accumulating preclinical and clinical evidence indicates that DDR is intimately connected to the emission of immunomodulatory signals by normal and malignant cells, as part of a cell-extrinsic program to preserve organismal homeostasis. DDR-driven inflammation, however, can have diametrically opposed effects on tumor-targeting immunity. Understanding the links between the DDR and inflammation in normal and malignant cells may unlock novel immunotherapeutic paradigms to treat cancer.

T Cell Aging in Patients with Colorectal Cancer-What Do We Know So Far?

Simple Summary

This review describes the role of T cell aging in colorectal cancer development. T cells are important mediators in cancer immunity. Aging affects T cells, leading to various dysfunctions which can impede antitumor immunity. While some hallmarks of T cell aging have been observed in colorectal cancer patients, the functional role of such cells is not clear. Therefore, understanding how aged T cells influence overall patient outcome could potentially help in the pursue to develop new therapies for the elderly.

Abstract

Colorectal cancer (CRC) continues to be one of the most frequently diagnosed types of cancers in the world. CRC is considered to affect mostly elderly patients, and the number of diagnosed cases increases with age. Even though general screening improves outcomes, the overall survival and recurrence-free CRC rates in aged individuals are highly dependent on their history of comorbidities. Furthermore, aging is also known to alter the immune system, and especially the adaptive immune T cells. Many studies have emphasized the importance of T cell responses to CRC. Therefore, understanding how age-related changes affect the outcome in CRC patients is crucial. This review focuses on what is so far known about age-related T cell dysfunction in elderly patients with colorectal cancer and how aged T cells can mediate its development. Last, this study describes the advances in basic animal models that have potential to be used to elucidate the role of aged T cells in CRC.

Fusobacterium nucleatum Caused DNA Damage and Promoted Cell Proliferation by the Ku70/p53 Pathway in Oral Cancer Cells

Bacterial infection influences genomic stability and integrity by causing DNA damage, which increases the possibility of tumor initiation and development. We aimed to investigate whether Fusobacterium nucleatum, one of the periodontal pathogens, promoted oral squamous cell carcinoma (OSCC) by causing DNA double-strand break (DSB). Tca8113 tongue squamous cell carcinoma cells were infected with F. nucleatum. The expression of γH2AX was detected by western blots and immunofluorescence. The proliferation and cell cycle alterations were tested by CCK8 and flow cytometry, respectively. The expression levels of Ku70, p53, and p27 were evaluated by quantitative real-time polymerase chain reaction and western blots. A plasmid was used for the overexpression of Ku70 to verify the possible relationship between Ku70 and p53. We confirmed the presence of DSBs in the response to F. nucleatum by detecting the expression of γH2AX. The cell proliferation ability was increased with an accelerated cell cycle while the expression of p27 was decreased. Meanwhile, the expression of Ku70 and wild p53 was downregulated. When Ku70 was overexpressed, the expression of wild p53 in response to F. nucleatum infection was upregulated and cell proliferation was accordingly inhibited. We concluded that F. nucleatum infection promoted the proliferation ability of Tca8113 by causing DNA damage via the Ku70/p53 pathway.

Rapid generation and selection of Cas9-engineering TRP53 R172P mice that do not have off-target effects

BACKGROUND

Genetic mutations cause severe human diseases, and suitable animal models to study the regulatory mechanisms involved are required. The CRISPR/Cas9 system is a powerful, highly efficient and easily manipulated tool for genetic modifications. However, utilization of CRISPR/Cas9 to introduce point mutations and the exclusion of off-target effects in mice remain challenging. TP53-R175 is one of the most frequently mutated sites in human cancers, and it plays crucial roles in human diseases, including cancers and diabetes.

RESULTS

Here, we generated TRP53-R172P mutant mice (C57BL/6 J, corresponding to TP53-R175P in humans) using a single microinjection of the CRISPR/Cas9 system. The optimal parameters comprised gRNA selection, donor designation (silent mutations within gRNA region), the concentration of CRISPR components and the cellular sites of injection. TRP53-R172P conversion was genetically and functionally confirmed. Combination of TA cloning and Sanger sequencing helped identify the correctly targeted mice as well as the off-target effects in the engineered mice, which provide us a strategy to select the on-target mice without off-target effects quickly and efficiently.

CONCLUSIONS

A single injection of the this optimized CRISPR/Cas9 system can be applied to introduce particular mutations in the genome of mice without off-target effects to model various human diseases.

β-Barrel outer membrane proteins suppress mTORC2 activation and induce autophagic responses

The outer membranes of Gram-negative bacteria and mitochondria contain proteins with a distinct β-barrel tertiary structure that could function as a molecular pattern recognized by the innate immune system. Here, we report that purified outer membrane proteins (OMPs) from different bacterial and mitochondrial sources triggered the induction of autophagy-related endosomal acidification, LC3B lipidation, and p62 degradation. Furthermore, OMPs reduced the phosphorylation and therefore activation of the multiprotein complex mTORC2 and its substrate Akt in macrophages and epithelial cells. The cell surface receptor SlamF8 and the DNA-protein kinase subunit XRCC6 were required for these OMP-specific responses in macrophages and epithelial cells, respectively. The addition of OMPs to mouse bone marrow-derived macrophages infected with Salmonella Typhimurium facilitated bacterial clearance. These data identify a specific cellular response mediated by bacterial and mitochondrial OMPs that can alter inflammatory responses and influence the killing of pathogens.

DNA damage response and repair in colorectal cancer: Defects, regulation and therapeutic implications

DNA damage response, a key factor involved in maintaining genome integrity and stability, consists of several kinase-dependent signaling pathways, which sense and transduce DNA damage signal. The severity of damage appears to determine DNA damage responses, which can include cell cycle arrest, damage repair and apoptosis. A number of recent studies have demonstrated that defection in signaling through this network is thought to be an underlying mechanism behind the development and progression of various types of human malignancies, including colorectal cancer. In this review, colorectal cancer and its molecular pathology as well as DNA damage response is briefly introduced. Finally, the involvement of key components of this network in the initiation/progression, prognosis, response to treatment and development of drug resistance is comprehensively discussed.

Detection of Infiltrating Mast Cells Using a Modified Toluidine Blue Staining

Mast cells are part of the immune system and characteristically contain histamine- and heparin-rich basophilic granules. While these cells are usually associated with allergy and anaphylaxis, they also promote wound healing and angiogenesis and confer protection against pathogens. The presence of these cells is sometimes indicative of a poor prognosis, especially in skin cancer, pancreatic cancer, and lymphoma. Toluidine blue staining of acid-fast granules is an established method for the identification and quantification of mast cells. Generating detailed information on the location of mast cells within tissues is problematic using this technique and often requires serial sections from adjacent tissue to be separately stained with hematoxylin and eosin (H&E). Staining serial sections is not always possible, particularly if the sample is very small or rare. In such cases, a method of simultaneously identifying and localizing mast cells in a tissue would be advantageous. Toluidine blue and H&E are not commonly combined because H&E includes repetitive washes in water, which may affect the efficacy of the aqueous-soluble toluidine blue. We have developed and tested a novel staining technique that integrates toluidine blue between hematoxylin and eosin in one simple procedure. This protocol works on both frozen and formalin-fixed, paraffin-embedded tissue and readily allows for the identification of purple-stained mast cells against a clean H&E background. This facilitates a more accurate localization and proper counting of mast cells in normal and affected tissue.

Proteomic analysis of pancreatic cancer stem cells: Functional role of fatty acid synthesis and mevalonate pathways

Recently, we have shown that the secretome of pancreatic cancer stem cells (CSCs) is characterized by proteins that participate in cancer differentiation, invasion, and metastasis. However, the differentially expressed intracellular proteins that lead to the specific characteristics of pancreatic CSCs have not yet been identified, and as a consequence the deranged metabolic pathways are yet to be elucidated. To identify the modulated proteins of pancreatic CSCs, iTRAQ-based proteomic analysis was performed to compare the proteome of Panc1 CSCs and Panc1 parental cells, identifying 230 modulated proteins. Pathway analysis revealed activation of glycolysis, the pentose phosphate pathway, the pyruvate-malate cycle, and lipid metabolism as well as downregulation of the Krebs cycle, the splicesome and non-homologous end joining. These findings were supported by metabolomics and immunoblotting analysis. It was also found that inhibition of fatty acid synthase by cerulenin and of mevalonate pathways by atorvastatin have a greater anti-proliferative effect on cancer stem cells than parental cells. Taken together, these results clarify some important aspects of the metabolic network signature of pancreatic cancer stem cells, shedding light on key and novel therapeutic targets and suggesting that fatty acid synthesis and mevalonate pathways play a key role in ensuring their viability.

BIOLOGICAL SIGNIFICANCE

To better understand the altered metabolic pathways of pancreatic cancer stem cells (CSCs), a comprehensive proteomic analysis and metabolite profiling investigation of Panc1 and Panc1 CSCs were carried out. The findings obtained indicate that Panc1 CSCs are characterized by upregulation of glycolysis, pentose phosphate pathway, pyruvate-malate cycle, and lipid metabolism and by downregulation of Krebs cycle, spliceosome and non-homologous end joining. Moreover, fatty acid synthesis and mevalonate pathways are shown to play a critical contribution to the survival of pancreatic cancer stem cells. This study is helpful for broadening the knowledge of pancreatic cancer stem cells and could accelerate the development of novel therapeutic strategies.

High Expression of XRCC6 Promotes Human Osteosarcoma Cell Proliferation through the β-Catenin/Wnt Signaling Pathway and Is Associated with Poor Prognosis

Increasing evidences show that XRCC6 (X-ray repair complementing defective repair in Chinese hamster cells 6) was upregulated and involved in tumor growth in several tumor types. However, the correlation of XRCC6 and human osteosarcoma (OS) is still unknown. This study was conducted with the aim to reveal the expression and biological function of XRCC6 in OS and elucidate the potential mechanism. The mRNA expression level of XRCC6 was measured in osteosarcoma cells and OS samples by quantitative transcription-PCR (qRT-PCR). The expression of XRCC6 protein was measured using Western blot and immunohistochemical staining in osteosarcoma cell lines and patient samples. Cell Counting Kit 8 (CCK8), colony-forming and cell cycle assays were used to test cell survival capacity. We found that XRCC6 was overexpressed in OS cells and OS samples compared with the adjacent non-tumorous samples. High expression of XRCC6 was correlated with clinical stage and tumor size in OS. Reduced expression of XRCC6 inhibits OS cell proliferation through G2/M phase arrest. Most importantly, further experiments demonstrated that XRCC6 might regulate OS growth through the β-catenin/Wnt signaling pathway. In conclusion, these findings indicate that XRCC6 exerts tumor-promoting effects for OS through β-catenin/Wnt signaling pathway. XRCC6 may serve as a novel therapeutic target for OS patients.

Genetic predisposition for beta cell fragility underlies type 1 and type 2 diabetes

Type 1 (T1D) and type 2 (T2D) diabetes share pathophysiological characteristics, yet mechanistic links have remained elusive. T1D results from autoimmune destruction of pancreatic beta cells, whereas beta cell failure in T2D is delayed and progressive. Here we find a new genetic component of diabetes susceptibility in T1D non-obese diabetic (NOD) mice, identifying immune-independent beta cell fragility. Genetic variation in Xrcc4 and Glis3 alters the response of NOD beta cells to unfolded protein stress, enhancing the apoptotic and senescent fates. The same transcriptional relationships were observed in human islets, demonstrating the role of beta cell fragility in genetic predisposition to diabetes.

Association between the XRCC6 polymorphisms and cancer risks: a systematic review and meta-analysis

A number of studies have been carried out to investigate the association of X-ray repair complementing defective repair in Chinese hamster cells 6 (XRCC6) polymorphisms and cancer risks, and the results remained inconsistent and inconclusive.To assess the effect of XRCC6 polymorphisms on cancer susceptibility, we conducted a meta-analysis, up to May 23rd 2014, 6267 cases with different types of tumor and 7536 controls from 20 published case-control studies. Summary odds ratios and corresponding 95% confidence intervals for XRCC6 polymorphism and cancer risk were estimated using fixed- or random-effects models when appropriate. Heterogeneity was assessed by chi-squared-based Q-statistic test, and the sources of heterogeneity were explored by subgroup analyses, logistic meta-regression analyses and Galbraith plot. Publication bias was evaluated by Begg funnel plot and Egger test. Sensitivity analyses were also performed.The rs2267437 polymorphism was associated with a significant increase in risks of overall cancers, breast cancer, renal cell carcinoma and hepatocellular carcinoma, and it could increase the cancer risk in Asian population; the rs5751129 polymorphism could increase the cancer risk in overall cancers; the rs132770 polymorphism was associated with the increased renal cell carcinoma risk; furthermore, the rs132793 polymorphism could decrease breast cancer risk and increase risks in "other cancers".Overall, the results provided evidences that the single nucleotide polymorphisms in XRCC6 promoter region might play different roles in various cancers, indicating different cancers have different tumorigenesis mechanisms. Our studies may perhaps supplement for the disease monitoring of cancers in the future, and additional studies to determine the exact molecular mechanism might provide us with interventions to protect the susceptible subgroups.

Cutting edge: STING mediates protection against colorectal tumorigenesis by governing the magnitude of intestinal inflammation

Stimulator of IFN genes (STING) is a cytoplasmic innate immune sensor for cyclic dinucleotides that also serves a dual role as an adaptor molecule for a number of intracellular DNA receptors. Although STING has important functions in the host defense against pathogens and autoimmune diseases, its physiological role in cancer is unknown. In this study, we show that STING-deficient mice are highly susceptible to colitis-associated colorectal cancer. Colons of STING-deficient mice exhibit significant intestinal damage and overt proliferation during early stages of tumorigenesis. Moreover, STING-deficient mice fail to restrict activation of the NF-κB- and STAT3-signaling pathways, which leads to increased levels of the proinflammatory cytokines IL-6 and KC. Therefore, our results identified an unexpected and important role for STING in mediating protection against colorectal tumorigenesis.