Defects in the Fanconi Anemia Pathway in Head and Neck Cancer Cells Stimulate Tumor Cell Invasion through DNA-PK and Rac1 Signaling

FANCD2 expression affects platinum response and further characteristics of high grade serous ovarian cancer in cells with different genetic backgrounds

High-grade serous ovarian cancer (HGSOC) is the most prevalent subtype of ovarian cancer and demonstrates 5-year survival of just 40%. One of the major causes of mortality is the development of tumour resistance to platinum-based chemotherapy, which can be modulated by dysregulation of DNA damage repair pathways. We therefore investigated the contribution of the DNA interstrand crosslink repair protein FANCD2 to chemosensitivity in HGSOC. Increased FANCD2 protein expression was observed in some cell line models of platinum resistant HGSOC compared with paired platinum sensitive models. Knockdown of FANCD2 in some cell lines, including the platinum resistant PEO4, led to increased carboplatin sensitivity. Investigation into mechanisms of FANCD2 regulation showed that increased FANCD2 expression in platinum resistant cells coincides with increased expression of mTOR. Treatment with mTOR inhibitors resulted in FANCD2 depletion, suggesting that mTOR can mediate platinum sensitivity via regulation of FANCD2. Tumours from a cohort of HGSOC patients showed varied nuclear and cytoplasmic FANCD2 expression, however this was not significantly associated with clinical characteristics. Knockout of FANCD2 was associated with increased cell migration, which may represent a non-canonical function of cytoplasmic FANCD2. We conclude that upregulation of FANCD2, possibly mediated by mTOR, is a potential mechanism of chemoresistance in HGSOC and modulation of FANCD2 expression can influence platinum sensitivity and other tumour cell characteristics.

The DNA-dependent protein kinase catalytic subunit exacerbates endotoxemia-induced myocardial microvascular injury by disrupting the MOTS-c/JNK pathway and inducing profilin-mediated lamellipodia degradation

Rationale: The DNA-dependent protein kinase catalytic subunit (DNA-PKcs) promotes pathological mitochondrial fission during septic acute kidney injury. The mitochondrial open reading frame of the 12S rRNA type-c (MOTS-c) is a mitochondria-derived peptide that exhibits anti-inflammatory properties during cardiovascular illnesses. We explored whether endotoxemia-induced myocardial microvascular injury involved DNA-PKcs and MOTS-c dysregulation. Methods: To induce endotoxemia in vivo, endothelial cell-specific DNA-PKcs-knockout mice were injected intraperitoneally with a single dose of lipopolysaccharide (10 mg/kg) and evaluated after 72 h. Results: Lipopolysaccharide exposure increased DNA-PKcs activity in cardiac microvascular endothelial cells, while pharmacological inhibition or endothelial cell-specific genetic ablation of DNA-PKcs reduced lipopolysaccharide-induced myocardial microvascular dysfunction. Proteomic analyses showed that endothelial DNA-PKcs ablation primarily altered mitochondrial protein expression. Verification assays confirmed that DNA-PKcs drastically repressed MOTS-c transcription by inducing mtDNA breaks via pathological mitochondrial fission. Inhibiting MOTS-c neutralized the endothelial protective effects of DNA-PKcs ablation, whereas MOTS-c supplementation enhanced endothelial barrier function and myocardial microvascular homeostasis under lipopolysaccharide stress. In molecular studies, MOTS-c downregulation disinhibited c-Jun N-terminal kinase (JNK), allowing JNK to phosphorylate profilin-S173. Inhibiting JNK or transfecting cells with a profilin phosphorylation-defective mutant improved endothelial barrier function by preventing F-actin depolymerization and lamellipodial degradation following lipopolysaccharide treatment. Conclusions: DNA-PKcs inactivation during endotoxemia could be a worthwhile therapeutic strategy to restore MOTS-c expression, prevent JNK-induced profilin phosphorylation, improve F-actin polymerization, and enhance lamellipodial integrity, ultimately ameliorating endothelial barrier function and reducing myocardial microvascular injury.

DNA-dependent protein kinase catalytic subunit (DNA-PKcs) drives angiotensin II-induced vascular remodeling through regulating mitochondrial fragmentation

BACKGROUND

DNA-dependent protein kinase catalytic subunit (DNA-PKcs) is a novel instigator for mitochondrial dysfunction, and plays an important role in the pathogenesis of cardiovascular diseases. However, the role and mechanism of DNA-PKcs in angiotensin II (Ang II)-induced vascular remodeling remains obscure.

METHODS

Rat aortic smooth muscle cells (SMC) and VSMC-specific DNA-PKcs knockout (DNA-PKcsΔVSMC) mice were employed to examine the role of DNA-PKcs in vascular remodeling and the underlying mechanisms. Blood pressure of mice was monitored using the tail-cuff and telemetry methods. The role of DNA-PKcs in vascular function was evaluated using vascular relaxation assessment.

RESULTS

In the tunica media of remodeled mouse thoracic aortas, and renal arteries from hypertensive patients, elevated DNA-PKcs expression was observed along with its cytoplasmic translocation from nucleus, suggesting a role for DNA-PKcs in vascular remodeling. We then infused wild-type (DNA-PKcsfl/fl) and DNA-PKcsΔVSMC mice with Ang II for 14 days to establish vascular remodeling, and demonstrated that DNA-PKcsΔVSMC mice displayed attenuated vascular remodeling through inhibition of dedifferentiation of VSMCs. Moreover, deletion of DNA-PKcs in VSMCs alleviated Ang II-induced vasodilation dysfunction and hypertension. Mechanistic investigations denoted that Ang II-evoked rises in cytoplasmic DNA-PKcs interacted with dynamin-related protein 1 (Drp1) at its TQ motif to phosphorylate Drp1S616, subsequently promoting mitochondrial fragmentation and dysfunction, as well as reactive oxygen species (ROS) production. Treatment of irbesartan, an Ang II type 1 receptor (AT1R) blocker, downregulated DNA-PKcs expression in VSMCs and aortic tissues following Ang II administration.

CONCLUSION

Our data revealed that cytoplasmic DNA-PKcs in VSMCs accelerated Ang II-induced vascular remodeling by interacting with Drp1 at its TQ motif and phosphorylating Drp1S616 to provoke mitochondrial fragmentation. Maneuvers targeting DNA-PKcs might be a valuable therapeutic option for the treatment of vascular remodeling and hypertension.

TGFβ pathway is required for viable gestation of Fanconi anemia embryos

Overexpression of the TGFβ pathway impairs the proliferation of the hematopoietic stem and progenitor cells (HSPCs) pool in Fanconi anemia (FA). TGFβ promotes the expression of NHEJ genes, known to function in a low-fidelity DNA repair pathway, and pharmacological inhibition of TGFβ signaling rescues FA HSPCs. Here, we demonstrate that genetic disruption of Smad3, a transducer of the canonical TGFβ pathway, modifies the phenotype of FA mouse models deficient for Fancd2. We observed that the TGFβ and NHEJ pathway genes are overexpressed during the embryogenesis of Fancd2-/- mice and that the Fancd2-/-Smad3-/- double knockout (DKO) mice undergo high levels of embryonic lethality due to loss of the TGFβ-NHEJ axis. Fancd2-deficient embryos acquire extensive genomic instability during gestation which is not reversed by Smad3 inactivation. Strikingly, the few DKO survivors have activated the non-canonical TGFβ-ERK pathway, ensuring expression of NHEJ genes during embryogenesis and improved survival. Activation of the TGFβ-NHEJ axis was critical for the survival of the few Fancd2-/-Smad3-/- DKO newborn mice but had detrimental consequences for these surviving mice, such as enhanced genomic instability and ineffective hematopoiesis.

IQGAP1 and RNA Splicing in the Context of Head and Neck via Phosphoproteomics

IQGAP1 (IQ motif-containing GTPase-activating protein 1) scaffolds several signaling pathways in mammalian cells that are implicated in carcinogenesis, including the RAS and PI3K pathways that involve multiple protein kinases. IQGAP1 has been shown to promote head and neck squamous cell carcinoma (HNSCC); however, the underlying mechanism(s) remains unclear. Here, we report a mass spectrometry-based analysis identifying differences in phosphorylation of cellular proteins in vivo and in vitro in the presence or absence of IQGAP1. By comparing the esophageal phosphoproteome profiles between Iqgap1+/+ and Iqgap1-/- mice, we identified RNA splicing as one of the most altered cellular processes. Serine/arginine-rich splicing factor 6 (SRSF6) was the protein with the most downregulated levels of phosphorylation in Iqgap1-/- tissue. We confirmed that the absence of IQGAP1 reduced SRSF6 phosphorylation both in vivo and in vitro. We then expanded our analysis to human normal oral keratinocytes. Again, we found factors involved in RNA splicing to be highly altered in the phosphoproteome profile upon genetic disruption of IQGAP1. Both the Clinical Proteomic Tumor Analysis Consortium (CPTAC) and the Cancer Genome Atlas (TCGA) data sets indicate that phosphorylation of splicing-related proteins is important in HNSCC prognosis. The Biological General Repository for Interaction Datasets (BioGRID) repository also suggested multiple interactions between IQGAP1 and splicing-related proteins. Based on these collective observations, we propose that IQGAP1 regulates the phosphorylation of splicing proteins, which potentially affects their splicing activities and, therefore, contributes to HNSCC. Raw data are available from the MassIVE database with identifier MSV000087770.

DNA-PKcs interacts with and phosphorylates Fis1 to induce mitochondrial fragmentation in tubular cells during acute kidney injury

The catalytic subunit of DNA-dependent protein kinase (DNA-PKcs) regulates cell death. We sought to determine whether DNA-PKcs played a role in the tubular damage that occurs during acute kidney injury (AKI) induced by LPS injection (to mimic sepsis), cisplatin administration, or renal ischemia/reperfusion injury. Although DNA-PKcs normally localizes to the nucleus, we detected cytoplasmic DNA-PKcs in mouse kidney tissues and urinary sediments of human patients with septic AKI. Increased cytoplasmic amounts of DNA-PKcs correlated with renal dysfunction. Tubule cell-specific DNA-PKcs deletion attenuated AKI-mediated tubular cell death and changes in the abundance of various proteins with mitochondrial functions or roles in apoptotic pathways. DNA-PKcs interacted with Fis1 and phosphorylated it at Thr³⁴ in its TQ motif, which increased the affinity of Fis1 for Drp1 and induced mitochondrial fragmentation. Knockin mice expressing a nonphosphorylatable T34A mutant exhibited improved renal function and histological features and reduced mitochondrial fragmentation upon induction of AKI. Phosphorylation of Thr³⁴ in Fis1 was detectable in urinary sediments of human patients with septic AKI and correlated with renal dysfunction. Our findings provide insight into the role of cytoplasmic DNA-PKcs and phosphorylated Fis1 in AKI development.

Jak HPV wysokiego ryzyka indukuje optymalne środowisko dla własnej replikacji w różnicującym się nabłonku

Wirusy brodawczaka ludzkiego (HPV) są często czynnikami wywołującymi niegroźne dla człowieka infekcje, ale przetrwałe zakażenie niektórymi typami HPV jest poważnym zagrożeniem dla zdrowia, ponieważ jest związane z wieloma nowotworami, w tym z rakiem szyjki macicy oraz rosnącą liczbą nowotworów głowy i szyi. Cykl replikacyjny HPV jest ściśle zależny od różnicowania komórek wielowarstwowego nabłonka, co oznacza, że genom wirusa musi być replikowany za pomocą różnych mechanizmów na różnych etapach różnicowania komórek. Ustanowienie infekcji i utrzymywanie genomu wirusa zachodzi w proliferujących komórkach nabłonka, gdzie dostępność czynników replikacji jest optymalna dla wirusa. Jednak produktywna faza cyklu rozwojowego wirusa, w tym produktywna replikacja, późna ekspresja genów i wytwarzanie wirionów, zachodzi w wyniku różnicowania się nabłonka w komórkach, które prawidłowo opuszczają cykl komórkowy. Wirus wykorzystuje wiele szlaków sygnalizacyjnych komórki, w tym odpowiedź na uszkodzenia DNA (DDR, DNA damage response) do realizacji produktywnej replikacji własnego genomu. Zrozumienie mechanizmów związanych z cyklem replikacyjnym HPV jest potrzebne do ustalenia właściwego podejścia terapeutycznego do zwalczania chorób powodowanych przez HPV.

Abnormal migration behavior linked to Rac1 signaling contributes to primordial germ cell exhaustion in Fanconi anemia pathway-deficient Fancg-/- embryos

Fanconi anemia (FA) is a rare human genetic disorder characterized by bone marrow failure, predisposition to cancer and developmental defects including hypogonadism. Reproductive defects leading to germ cell aplasia are the most consistent phenotypes seen in FA mouse models. We examined the role of the nuclear FA core complex gene Fancg in the development of primordial germ cells (PGCs), the embryonic precursors of adult gametes, during fetal development. PGC maintenance was severely impaired in Fancg^−/− embryos. We observed a defect in the number of PGCs starting at E9.5 and a strong attrition at E11.5 and E13.5. Remarkably, we observed a mosaic pattern reflecting a portion of testicular cords devoid of PGCs in E13.5 fetal gonads. Our in vitro and in vivo data highlight a potential role of Fancg in the proliferation and in the intrinsic cell motility abilities of PGCs. The random migratory process is abnormally activated in Fancg^−/− PGCs, altering the migration of cells. Increased cell death and PGC attrition observed in E11.5 Fancg^−/− embryos are features consistent with delayed migration of PGCs along the migratory pathway to the genital ridges. Moreover, we show that an inhibitor of RAC1 mitigates the abnormal migratory pattern observed in Fancg^−/− PGCs.

Overexpression of HPRT1 is associated with poor prognosis in head and neck squamous cell carcinoma

Hypoxanthine phosphoribosyltransferase (HPRT1), as a salvage pathway enzyme, plays a crucial role in modulating the cell cycle and has been reported to be overexpressed in multiple cancers. Nevertheless, the relationship between the HPRT1 gene and head and neck squamous cell carcinomas (HNSCCs) has not been investigated so far. In this study, we first evaluated the expression and clinical value of HPRT1 mRNA and protein in tumor and healthy control tissues. Then, we examined mutations of the HPRT1 gene and their association with survival outcomes of patients with HNSCC. We also performed functional analyses of HPRT1 coexpressed genes and examined the association between HPRT1 expression and drug sensitivity. Both HPRT1 mRNA and protein were significantly higher in HNSCC compared with normal tissues, and up‐regulation of HPRT1 was also correlated with age, sex, pathological stage and histological grades of patients with HNSCC. Moreover, HPRT1 and its associated genes were observed to be enriched for several cancer‐related pathways, including DNA replication and cell cycle. Finally, patients exhibiting overexpression of the HPRT1 gene may be resistant to abiraterone and sensitive to several drugs, including tozasertib and teniposide. This study demonstrated that the elevated expression of HPRT1 gene is correlated with the progression of HNSCC; thus, this gene may serve as a useful indicator for the early detection, risk stratification and targeted therapy of patients with HNSCC.

Generating New FANCA-Deficient HNSCC Cell Lines by Genomic Editing Recapitulates the Cellular Phenotypes of Fanconi Anemia

Fanconi anemia (FA) patients have an exacerbated risk of head and neck squamous cell carcinoma (HNSCC). Treatment is challenging as FA patients display enhanced toxicity to standard treatments, including radio/chemotherapy. Therefore, better therapies as well as new disease models are urgently needed. We have used CRISPR/Cas9 editing tools in order to interrupt the human FANCA gene by the generation of insertions/deletions (indels) in exon 4 in two cancer cell lines from sporadic HNSCC having no mutation in FA-genes: CAL27 and CAL33 cells. Our approach allowed efficient editing, subsequent purification of single-cell clones, and Sanger sequencing validation at the edited locus. Clones having frameshift indels in homozygosis did not express FANCA protein and were selected for further analysis. When compared with parental CAL27 and CAL33, FANCA-mutant cell clones displayed a FA-phenotype as they (i) are highly sensitive to DNA interstrand crosslink (ICL) agents such as mitomycin C (MMC) or cisplatin, (ii) do not monoubiquitinate FANCD2 upon MMC treatment and therefore (iii) do not form FANCD2 nuclear foci, and (iv) they display increased chromosome fragility and G2 arrest after diepoxybutane (DEB) treatment. These FANCA-mutant clones display similar growth rates as their parental cells. Interestingly, mutant cells acquire phenotypes associated with more aggressive disease, such as increased migration in wound healing assays. Therefore, CAL27 and CAL33 cells with FANCA mutations are phenocopies of FA-HNSCC cells.

Human Papillomavirus Oral- and Sero- Positivity in Fanconi Anemia

Simple Summary

People with Fanconi anemia (FA) are genetically susceptible to gynecological cancers and cancers of the head and neck. There are known associations between oral infection with human papillomavirus (HPV) and development of head and neck cancers. This study sought to measure how common oral HPV positivity is in a large sample of people with FA followed over 8 years, while also evaluating serum titers to ascertain natural exposure to HPV, and how well people with FA who were vaccinated responded to HPV vaccination. We found that oral HPV positivity is significantly higher in individuals with FA compared to family and unrelated controls, but that response to HPV vaccination between FA and controls is similar. Common risk factors associated with HPV in the general population did not predict oral DNA positivity in FA, unlike unrelated controls. Future mechanistic and vaccinations studies are needed to understand this phenomenon.

Abstract

High-risk human papillomavirus (HPV) is prevalent and known to cause 5% of all cancers worldwide. The rare, cancer prone Fanconi anemia (FA) population is characterized by a predisposition to both head and neck squamous cell carcinomas and gynecological cancers, but the role of HPV in these cancers remains unclear. Prompted by a patient-family advocacy organization, oral HPV and HPV serological studies were simultaneously undertaken. Oral DNA samples from 201 individuals with FA, 303 unaffected family members, and 107 unrelated controls were tested for 37 HPV types. Serum samples from 115 individuals with FA and 55 unrelated controls were tested for antibodies against 9 HPV types. Oral HPV prevalence was higher for individuals with FA (20%) versus their parents (13%; p = 0.07), siblings (8%, p = 0.01), and unrelated controls (6%, p ≤ 0.001). A FA diagnosis increased HPV positivity 4.84-fold (95% CI: 1.96–11.93) in adjusted models compared to unrelated controls. Common risk factors associated with HPV in the general population did not predict oral positivity in FA, unlike unrelated controls. Seropositivity and anti-HPV titers did not significantly differ in FA versus unrelated controls regardless of HPV vaccination status. We conclude that individuals with FA are uniquely susceptible to oral HPV independent of conventional risk factors.

Inherited DNA Repair Defects Disrupt the Structure and Function of Human Skin

Squamous cell carcinoma (SCC) is a global public health burden originating in epidermal stem and progenitor cells (ESPCs) of the skin and mucosa. To understand how genetic risk factors contribute to SCC, studies of ESPC biology are imperative. Children with Fanconi anemia (FA) are a paradigm for extreme SCC susceptibility caused by germline loss-of-function mutations in FA DNA repair pathway genes. To discover epidermal vulnerabilities, patient-derived pluripotent stem cells (PSCs) conditional for the FA pathway were differentiated into ESPCs and PSC-derived epidermal organotypic rafts (PSC-EORs). FA PSC-EORs harbored diminished cell-cell junctions and increased proliferation in the basal cell compartment. Furthermore, desmosome and hemidesmosome defects were identified in the skin of FA patients, and these translated into accelerated blistering following mechanically induced stress. Together, we demonstrate that a critical DNA repair pathway maintains the structure and function of human skin and provide 3D epidermal models wherein SCC prevention can now be explored.

The modulation relationship of genomic pattern of intratumor heterogeneity and immunity microenvironment heterogeneity in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the fifth most common cancer in the world, with the second highest mortality rate among all cancer types. Growing evidence has demonstrated the notable effects of intratumor heterogeneity (ITH) and tumor immune microenvironment heterogeneity (TIMH) on the biological processes involved in HCC. However, the interactive mechanisms between ITH and TIMH is still unclear. The present study systematically screened the mRNA expression, simple nucleotide variation data and clinical data of samples from The Cancer Genome Atlas (TCGA). The mutant-allele tumor heterogeneity (MATH) score was used to represent ITH, and TCGA cohort was divided into two groups according to the MATH score. Next, different immune-related signaling pathways and enriched immune-related genes were identified using Gene Set Enrichment Analysis of these two groups, and the results revealed that interleukin-1α (IL1A) and serine/threonine-protein kinase PAK4 were associated with prognosis. Furthermore, CIBERSORT was utilized to calculate the fractions of 22 types of leukocytes to represent TIMH, and the fractions of M1 and M2 macrophages were confirmed to be associated with prognosis. Therefore, PAK4, interleukin-1α (IL1A), and M1/M2 ratio were selected as the key factors involved in the interaction between ITH and TIMH. Afterwards, microRNAs (miRNAs) that were linearly related to the M1/M2 ratio and the potential target genes of the miRNAs were screened. Finally, the regulatory network between PAK4, IL1A, and the M1/M2 ratio was established, bridged by the above miRNAs and the target genes. In addition, PAK4, heat shock protein 105 kDa and miRNA-1911 were demonstrated to be a key factor involved in immune response via Weighted Correlation Network Analysis in HCC.

Ovarian cancer-derived copy number alterations signatures are prognostic in chemoradiotherapy-treated head and neck squamous cell carcinoma

DNA copy number alterations (CNAs) are frequent in cancer, and recently developed CNA signatures revealed their value in molecular tumor stratification for patient prognosis and platinum resistance prediction in ovarian cancer. Head and neck squamous cell carcinoma (HNSCC) is also characterized by high CNAs. In this study, we determined CNA in 173 human papilloma virus-negative HNSCC from a Dutch multicenter cohort by low-coverage whole genome sequencing and tested the prognostic value of seven cancer-derived CNA signatures for these cisplatin- and radiotherapy-treated patients. We find that a high CNA signature 1 (s1) score is associated with low values for all other signatures and better patient outcomes in the Dutch cohorts and The Cancer Genome Atlas HNSCC data set. High s5 and s7 scores are associated with increased distant metastasis rates and high s6 scores with poor overall survival. High cumulative cisplatin doses result in improved outcomes in chemoradiotherapy-treated HNSCC patients. Here we find that tumors high in s1 or low in s6 are most responsive to a change in cisplatin dose. High s5 values, however, significantly increase the risk for metastasis in patients with low cumulative cisplatin doses. Together this suggests that the processes causing these CNA signatures affect cisplatin response in HNSCC. In conclusion, CNA signatures derived from a different cancer type were prognostic and associated with cisplatin response in HNSCC, suggesting they represent underlying molecular processes that define patient outcome.

Combining PARP and DNA-PK Inhibitors With Irradiation Inhibits HPV-Negative Head and Neck Cancer Squamous Carcinoma Growth

Novel targeted agents to inhibit DNA repair pathways to sensitize tumors to irradiation (IR) are being investigated as an alternative to chemoradiation for locally advanced human papilloma virus negative (HPV-negative) head and neck squamous cell carcinoma (HNSCC). Two well-characterized targets that, when inhibited, exhibit potent IR sensitization are PARP1 and DNA-PKcs. However, their cooperation in sensitizing HPV-negative HNSCC to IR remains to be explored given that PARP1 and DNA-Pk_CS bind to unresected stalled DNA replication forks and cooperate to recruit XRCC1 to facilitate double-strand break repair. Here, we show that the combination of the DNA-PK inhibitor NU7441 and the PARP inhibitor olaparib significantly decrease proliferation (61–78%) compared to no reduction with either agent alone (p < 0.001) in both SCC1 and SCC6 cell lines. Adding IR to the combination further decreased cell proliferation (91–92%, p < 0.001) in SCC1 and SCC6. Similar results were observed using long-term colony formation assays [dose enhancement ratio (DER) 2.3–3.2 at 4Gy, p < 0.05]. Reduced cell survival was attributed to increased apoptosis and G2/M cell cycle arrest. Kinomic analysis using tyrosine (PTK) and serine/threonine (STK) arrays reveals that combination treatment results in the most potent inhibition of kinases involved in the CDK and ERK pathways compared to either agent alone. In vivo, a significant delay of tumor growth was observed in UM-SCC1 xenografts receiving IR with olaparib and/or NU7441, which was similar to the cisplatin-IR group. Both regimens were less toxic than cisplatin-IR as assessed by loss of mouse body weight. Taken together, these results demonstrate that the combination of NU7441 and olaparib with IR enhances HPV-negative HNSCC inhibition in both cell culture and in mice, suggesting a potential innovative combination for effectively treating patients with HPV-negative HNSCC.

DNA-PK in human malignant disorders: Mechanisms and implications for pharmacological interventions

The DNA-PK holoenzyme is a fundamental element of the DNA damage response machinery (DDR), which is responsible for cellular genomic stability. Consequently, and predictably, over the last decades since its identification and characterization, numerous pre-clinical and clinical studies reported observations correlating aberrant DNA-PK status and activity with cancer onset, progression and responses to therapeutic modalities. Notably, various studies have established in recent years the role of DNA-PK outside the DDR network, corroborating its role as a pleiotropic complex involved in transcriptional programs that operate biologic processes as epithelial to mesenchymal transition (EMT), hypoxia, metabolism, nuclear receptors signaling and inflammatory responses. In particular tumor entities as prostate cancer, immense research efforts assisted mapping and describing the overall signaling networks regulated by DNA-PK that control metastasis and tumor progression. Correspondingly, DNA-PK emerges as an obvious therapeutic target in cancer and data pertaining to various pharmacological approaches have been published, largely in context of combination with DNA-damaging agents (DDAs) that act by inflicting DNA double strand breaks (DSBs). Currently, new generation inhibitors are tested in clinical trials. Several excellent reviews have been published in recent years covering the biology of DNA-PK and its role in cancer. In the current article we are aiming to systematically describe the main findings on DNA-PK signaling in major cancer types, focusing on both preclinical and clinical reports and present a detailed current status of the DNA-PK inhibitors repertoire.

Drug Sensitivity Prediction Models Reveal a Link between DNA Repair Defects and Poor Prognosis in HNSCC

Head and neck squamous cell carcinoma (HNSCC) is characterized by the frequent manifestation of DNA crosslink repair defects. We established novel expression-based DNA repair defect markers to determine the clinical impact of such repair defects. Using hypersensitivity to the DNA crosslinking agents, mitomycin C and olaparib, as proxies for functional DNA repair defects in a panel of 25 HNSCC cell lines, we applied machine learning to define gene expression models that predict repair defects. The expression profiles established predicted hypersensitivity to DNA-damaging agents and were associated with mutations in crosslink repair genes, as well as downregulation of DNA damage response and repair genes, in two independent datasets. The prognostic value of the repair defect prediction profiles was assessed in two retrospective cohorts with a total of 180 patients with advanced HPV-negative HNSCC, who were treated with cisplatin-based chemoradiotherapy. DNA repair defects, as predicted by the profiles, were associated with poor outcome in both patient cohorts. The poor prognosis association was particularly strong in normoxic tumor samples and was linked to an increased risk of distant metastasis. In vitro, only crosslink repair-defective HNSCC cell lines are highly migratory and invasive. This phenotype could also be induced in cells by inhibiting rad51 in repair competent and reduced by DNA-PK inhibition. In conclusion, DNA crosslink repair prediction expression profiles reveal a poor prognosis association in HNSCC. SIGNIFICANCE: This study uses innovative machine learning-based approaches to derive models that predict the effect of DNA repair defects on treatment outcome in HNSCC.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/79/21/5597/F1.large.jpg.

Holding All the Cards-How Fanconi Anemia Proteins Deal with Replication Stress and Preserve Genomic Stability

Fanconi anemia (FA) is a hereditary chromosomal instability disorder often displaying congenital abnormalities and characterized by a predisposition to progressive bone marrow failure (BMF) and cancer. Over the last 25 years since the discovery of the first linkage of genetic mutations to FA, its molecular genetic landscape has expanded tremendously as it became apparent that FA is a disease characterized by a defect in a specific DNA repair pathway responsible for the correction of covalent cross-links between the two complementary strands of the DNA double helix. This pathway has become increasingly complex, with the discovery of now over 20 FA-linked genes implicated in interstrand cross-link (ICL) repair. Moreover, gene products known to be involved in double-strand break (DSB) repair, mismatch repair (MMR), and nucleotide excision repair (NER) play roles in the ICL response and repair of associated DNA damage. While ICL repair is predominantly coupled with DNA replication, it also can occur in non-replicating cells. DNA damage accumulation and hematopoietic stem cell failure are thought to contribute to the increased inflammation and oxidative stress prevalent in FA. Adding to its confounding nature, certain FA gene products are also engaged in the response to replication stress, caused endogenously or by agents other than ICL-inducing drugs. In this review, we discuss the mechanistic aspects of the FA pathway and the molecular defects leading to elevated replication stress believed to underlie the cellular phenotypes and clinical features of FA.

Sphingosine-1-phosphate induced epithelial-mesenchymal transition of hepatocellular carcinoma via an MMP-7/ syndecan-1/TGF-β autocrine loop

Sphingosine-1-phosphate (S1P) induces epithelial–mesenchymal transition (EMT) in hepatocellular carcinoma (HCC). However, its underlying mechanism remains largely unknown. In the present study, we investigated the correlation between S1P and syndecan-1 in HCC, the molecular mechanism involved, as well as their roles in EMT of HCC. Results revealed a high serum S1P level presents in patients with HCC, which positively correlated with the serum syndecan-1 level. A significant inverse correlation existed between S1P₁ and syndecan-1 in HCC tissues. S1P elicits activation of the PI3K/AKT signaling pathways via S1P₁, which triggers HPSE, leading to increases in expression and activity of MMP-7 and leading to shedding and suppression of syndecan-1. The loss of syndecan-1 causes an increase in TGF-β1 production. The limited chronic increase in TGF-β1 can convert HCC cells into a mesenchymal phenotype via establishing an MMP-7/Syndecan-1/TGF-β autocrine loop. Finally, TGF-β1 and syndecan-1 are essential for S1P-induced epithelial to mesenchymal transition. Taken together, our study demonstrates that S1P induces advanced tumor phenotypes of HCC via establishing an MMP-7/syndecan-1/TGF-β1 autocrine loop, and implicates targetable S1P₁-PI3K/AKT-HPSE-MMP-7 signaling axe in HCC metastasis.

Lipidomic Profiling Links the Fanconi Anemia Pathway to Glycosphingolipid Metabolism in Head and Neck Cancer Cells

Purpose: Mutations in Fanconi anemia (FA) genes are common in sporadic squamous cell carcinoma of the head and neck (HNSCC), and we have previously demonstrated that FA pathway depletion in HNSCC cell lines stimulates invasion. The goal of our studies was to use a systems approach in order to define FA pathway-dependent lipid metabolism and to extract lipid-based signatures and effectors of invasion in FA-deficient cells.Experimental Design: We subjected FA-isogenic HNSCC keratinocyte cell lines to untargeted and targeted lipidomics analyses to discover novel biomarkers and candidate therapeutic targets in FA-deficient cells. Cellular invasion assays were carried out in the presence and absence of N-butyldeoxynojirimycin (NB-DNJ), a biosynthetic inhibitor of the newly identified class of gangliosides, to investigate the requirement of ganglioside upregulation in FA-deficient HNSCC cells.Results: The most notable element of the lipid profiling results was a consistent elevation of glycosphingolipids, and particularly the accumulation of gangliosides. Conversely, repression of this same class of lipids was observed upon genetic correction of FA patient-derived HNSCC cells. Functional studies demonstrate that ganglioside upregulation is required for HNSCC cell invasion driven by FA pathway loss. The motility of nontransformed keratinocytes in response to FA loss displayed a similar dependence, thus supporting early and late roles for the FA pathway in controlling keratinocyte invasion through lipid regulation.Conclusions: Elevation of glycosphingolipids including the ganglioside GM3 in response to FA loss stimulates invasive characteristics of immortalized and transformed keratinocytes. An inhibitor of glycosphingolipid biosynthesis NB-DNJ attenuates invasive characteristics of FA-deficient HNSCC cells. Clin Cancer Res; 24(11); 2700-9. ©2018 AACR.

Risk of Human Papillomavirus Infection in Cancer-Prone Individuals: What We Know

Human papillomavirus (HPV) infections cause a significant proportion of cancers worldwide, predominantly squamous cell carcinomas (SCC) of the mucosas and skin. High-risk HPV types are associated with SCCs of the anogenital and oropharyngeal tract. HPV oncogene activities and the biology of SCCs have been intensely studied in laboratory models and humans. What remains largely unknown are host tissue and immune-related factors that determine an individual's susceptibility to infection and/or carcinogenesis. Such susceptibility factors could serve to identify those at greatest risk and spark individually tailored HPV and SCC prevention efforts. Fanconi anemia (FA) is an inherited DNA repair disorder that is in part characterized by extreme susceptibility to SCCs. An increased prevalence of HPV has been reported in affected individuals, and molecular and functional connections between FA, SCC, and HPV were established in laboratory models. However, the presence of HPV in some human FA tumors is controversial, and the extent of the etiological connections remains to be established. Herein, we discuss cellular, immunological, and phenotypic features of FA, placed into the context of HPV pathogenesis. The goal is to highlight this orphan disease as a unique model system to uncover host genetic and molecular HPV features, as well as SCC susceptibility factors.

Human Papillomavirus and the DNA Damage Response: Exploiting Host Repair Pathways for Viral Replication

High-risk human papillomaviruses (HPVs) are the causative agents of cervical and other genital cancers. In addition, HPV infections are associated with the development of many oropharyngeal cancers. HPVs activate and repress a number of host cellular pathways to promote their viral life cycles, including those of the DNA damage response. High-risk HPVs activate the ataxia telangiectasia-mutated (ATM) and ATM and Rad3-related (ATR) DNA damage repair pathways, which are essential for viral replication (particularly differentiation-dependent genome amplification). These DNA repair pathways are critical in maintaining host genomic integrity and stability and are often dysregulated or mutated in human cancers. Understanding how these pathways contribute to HPV replication and transformation may lead to the identification of new therapeutic targets for the treatment of existing HPV infections.

The Role of the Core Non-Homologous End Joining Factors in Carcinogenesis and Cancer

DNA double-strand breaks (DSBs) are deleterious DNA lesions that if left unrepaired or are misrepaired, potentially result in chromosomal aberrations, known drivers of carcinogenesis. Pathways that direct the repair of DSBs are traditionally believed to be guardians of the genome as they protect cells from genomic instability. The prominent DSB repair pathway in human cells is the non-homologous end joining (NHEJ) pathway, which mediates template-independent re-ligation of the broken DNA molecule and is active in all phases of the cell cycle. Its role as a guardian of the genome is supported by the fact that defects in NHEJ lead to increased sensitivity to agents that induce DSBs and an increased frequency of chromosomal aberrations. Conversely, evidence from tumors and tumor cell lines has emerged that NHEJ also promotes chromosomal aberrations and genomic instability, particularly in cells that have a defect in one of the other DSB repair pathways. Collectively, the data present a conundrum: how can a single pathway both suppress and promote carcinogenesis? In this review, we will examine NHEJ's role as both a guardian and a disruptor of the genome and explain how underlying genetic context not only dictates whether NHEJ promotes or suppresses carcinogenesis, but also how it alters the response of tumors to conventional therapeutics.

Cancer Stem Cells and Radioresistance: Rho/ROCK Pathway Plea Attention

Radiation is the most potent mode of cancer therapy; however, resistance to radiation therapy results in tumor relapse and subsequent fatality. The cancer stem cell (CSC), which has better DNA repair capability, has been shown to contribute to tumor resistance and is an important target for treatment. Signaling molecules such as Notch, Wnt, and DNA repair pathways regulate molecular mechanisms in CSCs; however, none of them have been translated into therapeutic targets. The RhoGTPases and their effector ROCK-signaling pathway, though important for tumor progression, have not been well studied in the context of radioresistance. There are reports that implicate RhoA in radioresistance. ROCK2 has also been shown to interact with BRCA2 in the regulation of cell division. Incidentally, statins (drug for cardiovascular ailment) are functional inhibitors of RhoGTPases. Studies suggest that patients on statins have a better prognosis in cancers. Data from our lab suggest that ROCK signaling regulates radioresistance in cervical cancer cells. Collectively, these findings suggest that Rho/ROCK signaling may be important for radiation resistance. In this review, we enumerate the role of Rho/ROCK signaling in stemness and radioresistance and highlight the need to explore these molecules for a better understanding of radioresistance and development of therapeutics.

DNA-PkCS expression in oropharyngeal squamous cell carcinoma: Correlations with human papillomavirus status and recurrence after transoral robotic surgery

BACKGROUND

Human papillomavirus (HPV)-positive oropharyngeal squamous cell carcinoma (SCC) has improved clinical outcomes compared to HPV-negative disease. However, the biology underlying differences in prognosis remains unclear.

METHODS

We characterized the expression of DNA-protein kinase catalytic subunit (DNA-Pk_CS ), a key DNA repair protein also associated with tumor progression, in 29 cases of oropharyngeal SCCs and correlated our findings with HPV status and disease recurrence. In addition, we assessed therapeutic response, migration, and invasion in head and neck cancer cell lines upon DNA-Pk_CS knockdown.

RESULTS

DNA-Pk_CS expression was significantly decreased in HPV-positive compared to HPV-negative oropharyngeal SCC samples. Within the HPV-positive subgroup, DNA-Pk_CS expression was inversely related to HPV E6 and E7 expression and trended toward significance as a predictor of recurrence. DNA-Pk_CS knockdown in cell lines resulted in increased sensitivity to cisplatin and radiotherapy and reduced cell migration and invasion.

CONCLUSION

These results suggest DNA-Pk_CS should be further studied as a potential marker of tumor progression in HPV-positive oropharyngeal SCCs. © 2016 Wiley Periodicals, Inc. Head Neck 39: 206-214, 2017.