Malignant melanoma cells acquire resistance to DNA interstrand cross-linking chemotherapeutics by p53-triggered upregulation of DDB2/XPC-mediated DNA repair

MDM2 is an important prognostic and predictive factor for platin-pemetrexed therapy in malignant pleural mesotheliomas and deregulation of P14/ARF (encoded by CDKN2A) seems to contribute to an MDM2-driven inactivation of P53

Background:

Malignant pleural mesothelioma (MPM) is a highly aggressive tumour that is first-line treated with a combination of cisplatin and pemetrexed. Until now, predictive and prognostic biomarkers are lacking, making it a non-tailored therapy regimen with unknown outcome. P53 is frequently inactivated in MPM, but mutations are extremely rare. MDM2 and P14/ARF are upstream regulators of P53 that may contribute to P53 inactivation.

Methods:

A total of 72 MPM patients were investigated. MDM2 immunoexpression was assessed in 65 patients. MDM2 and P14/ARF mRNA expression was analysed in 48 patients of the overall collective. The expression results were correlated to overall survival (OS) and progression-free survival (PFS).

Results:

OS and PFS correlated highly significantly with MDM2 mRNA and protein expression, showing a dismal prognosis for patients with elevated MDM2 expression (for OS: Score (logrank) test: P⩽0.002, and for PFS: Score (logrank) test; P<0.007). MDM2 was identified as robust prognostic and predictive biomarker for MPM on the mRNA and protein level. P14/ARF mRNA expression reached no statistical significance, but Kaplan–Meier curves distinguished patients with low P14/ARF expression and hence shorter survival from patients with higher expression and prolonged survival.

Conclusions:

MDM2 is a prognostic and predictive marker for a platin–pemetrexed therapy of patients with MPMs. Downregulation of P14/ARF expression seems to contribute to MDM2-overexpression-mediated P53 inactivation in MPM patients.

MicroRNAs Used in Combination with Anti-Cancer Treatments Can Enhance Therapy Efficacy

MicroRNAs (miRNAs), a recently discovered class of small non-coding RNAs, constitute a promising approach to anti-cancer treatments when they are used in combination with other agents. MiRNAs are evolutionarily conserved non-coding RNAs that negatively regulate gene expression by binding to the complementary sequence in the 3'-untranslated region (UTR) of target genes. MiRNAs typically suppress gene expression by direct association with target transcripts, thus decreasing the expression levels of target proteins. The delivery to cells of synthetic miRNAs that mimic endogenous miRNA targeting genes involved in the DNA-Damage Response (DDR) can perturb the process, making cells more sensitive to chemotherapy or radiotherapy. This review examines how cells respond to combined therapy and it provides insights into the role of miRNAs in targeting the DDR repair pathway when they are used in combination with chemical compounds or ionizing radiation to enhance cellular sensitivity to treatments.

Attenuated NER expressions of XPF and XPC associated with smoking are involved in the recurrence of bladder cancer

The varied NER genes and smoking are two important risk factors of bladder cancer, but the mechanism of the NER protein and smoking in cancer progression, however, remains unclear. In this report, we compared the expressions of NER genes in 79 bladder cancer tissues with or without any recurrence by real-time PCR and then analyzed the varied NER genes by immunochemistry in 219 bladder cancer tissue samples. Based on the clinical data, we analyzed the clinical value of varied NER genes and smoking in 219 bladder cancers by the Kaplan-Meier method and Cox proportional hazards regression. We found the expressions of the NER gene XPF and XPC were significantly lower in bladder cancer tissues with a recurrence compared with those without a recurrence at mRNA level. Also, the patients with the XPF and XPC defect had a statistically significant lower median recurrence-free survival time than those without the XPF and XPC defect, and smoking can make this difference more remarkable. Our results suggest that XPF and XPC expression may be a potential predictive factor for bladder cancer, and smoking can not only influence the recurrence of bladder cancer as a single factor but also aggravate the results of the XPF defect and XPC defect.

JWA reverses cisplatin resistance via the CK2-XRCC1 pathway in human gastric cancer cells

Gastric cancer is the third most common malignancy in China, with a median 5-year survival of only 20%. Cisplatin has been used in first-line cancer treatment for several types of cancer including gastric cancer. However, patients are often primary resistant or develop acquired resistance resulting in relapse of the cancer and reduced survival. Recently, we demonstrated that the reduced expression of base excision repair protein XRCC1 and its upstream regulator JWA in gastric cancerous tissues correlated with a significant survival benefit of adjuvant first-line platinum-based chemotherapy as well as XRCC1 playing an important role in the DNA repair of cisplatin-resistant gastric cancer cells. In the present study, we demonstrated the role of JWA in cisplatin-induced DNA lesions and aquired cisplatin resistance in five cell-culture models: gastric epithelial cells GES-1, cisplatin-sensitive gastric cancer cell lines BGC823 and SGC7901, and the cisplatin-resistant gastric cancer cell lines BGC823/DDP and SGC7901/DDP. Our results indicated that JWA is required for DNA repair following cisplatin-induced double-strand breaks (DSBs) via XRCC1 in normal gastric epithelial cells. However, in gastric cancer cells, JWA enhanced cisplatin-induced cell death through regulation of DNA damage-induced apoptosis. The protein expression of JWA was significantly decreased in cisplatin-resistant cells and contributed to cisplatin resistance. Interestingly, as JWA upregulated XRCC1 expression in normal cells, JWA downregulated XRCC1 expression through promoting the degradation of XRCC1 in cisplatin-resistant gastric cancer cells. Furthermore, the negative regulation of JWA to XRCC1 was blocked due to the mutation of 518S/519T/523T residues of XRCC1, and indicating that the CK2 activated 518S/519T/523T phosphorylation is a key point in the regulation of JWA to XRCC1. In conclusion, we report for the first time that JWA regulated cisplatin-induced DNA damage and apoptosis through the CK2—P-XRCC1—XRCC1 pathway, indicating a putative drug target for reversing cisplatin resistance in gastric cancer.

Heme oxygenase-1 plays a crucial role in chemoresistance in acute myeloid leukemia

OBJECTIVES

The heme oxygenase-1 (HO-1) gene may contribute to the development of acquired chemoresistance in solid tumor cells, but its function in acute myeloid leukemia (AML) remains unclear. Therefore, we investigated whether the expressions of HO-1 mRNA and protein were associated with AML chemoresistance.

METHODS

Bone marrow or peripheral blood was obtained from newly diagnosed (n = 26), relapsed (n = 10), and completely remitted (n = 18) patients with AML (M3 exclusion) and healthy donors (n = 10). Small interfering RNA was used to stably silence HO-1 gene expression in AML cell lines. The expressions of HO-1, hypoxia inducible factor-1ɑ (HIF-1ɑ), glucose transporter-1 (GLUT1) mRNA and proteins were measured by quantitative real-time PCR and Western blot. Cell viability was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Apoptosis induction was analyzed by flow cytometry.

RESULTS

The drug-resistant AML cell line HL-60R was significantly less sensitive to cytarabine and daunorubicin than HL-60 cells. HO-1 mRNA and proteins were highly expressed in HL-60R cells. However, down-regulating HO-1 significantly enhanced the sensitivity of HL-60R to chemotherapy, and the expressions of HIF-1ɑ and GLUT1 mRNA and proteins decreased. Meanwhile, the expressions of caspase-3 and caspase-8 proteins increased, while that of bcl-2 decreased. Overexpressions of HO-1, HIF-1ɑ, and GLUT1 were associated with poor response of AML to chemotherapy. Conclusions Overexpressions of HO-1, HIF-1ɑ, and GLUT1 might be involved in the chemoresistance of AML. HO-1 is a potential target to overcome the drug resistance of AML.

Translesion polymerase η is upregulated by cancer therapeutics and confers anticancer drug resistance

DNA repair processes are a key determinant of the sensitivity of cancer cells to DNA-damaging chemotherapeutics, which may induce certain repair genes as a mechanism to promote resistance. Here, we report the results of a screen for repair genes induced in cancer cells treated with DNA crosslinking agents, which identified the translesion polymerase η (PolH) as a p53-regulated target acting as one defense against interstrand crosslink (ICL)-inducing agents. PolH was induced by fotemustine, mafosfamide, and lomustine in breast cancer, glioma, and melanoma cells in vitro and in vivo, with similar inductions observed in normal cells such as lymphocytes and diploid fibroblasts. PolH contributions to the protection against ICL-inducing agents were evaluated by its siRNA-mediated attenuation in cells, which elevated sensitivity to these drugs in all tumor cell models. Conversely, PolH overexpression protected cancer cells against these drugs. PolH attenuation reduced repair of ICL lesions as measured by host cell reactivation assays and enhanced persistence of γH2AX foci. Moreover, we observed a strong accumulation of PolH in the nucleus of drug-treated cells along with direct binding to damaged DNA. Taken together, our findings implicated PolH in ICL repair as a mechanism of cancer drug resistance and normal tissue protection.

Histone deacetylase 2 controls p53 and is a critical factor in tumorigenesis

Histone deacetylase 2 (HDAC2) regulates biological processes by deacetylation of histones and non-histone proteins. HDAC2 is overexpressed in numerous cancer types, suggesting general cancer-relevant functions of HDAC2. In human tumors the TP53 gene encoding p53 is frequently mutated and wild-type p53 is often disarmed. Molecular pathways inactivating wild-type p53 often remain to be defined and understood. Remarkably, current data link HDAC2 to the regulation of the tumor suppressor p53 by deacetylation and to the maintenance of genomic stability. Here, we summarize recent findings on HDAC2 overexpression in solid and hematopoietic cancers with a focus on mechanisms connecting HDAC2 and p53 in vitro and in vivo. In addition, we present an evidence-based model that integrates molecular pathways and feedback loops by which p53 and further transcription factors govern the expression and the ubiquitin-dependent proteasomal degradation of HDAC2 and of p53 itself. Understanding the interactions between p53 and HDAC2 might aid in the development of new therapeutic approaches against cancer.

Chromatin retention of DNA damage sensors DDB2 and XPC through loss of p97 segregase causes genotoxicity

DNA damage recognition subunits like DDB2 and XPC protect the human skin from ultraviolet (UV) light-induced genome instability and cancer, as demonstrated by the devastating inherited syndrome xeroderma pigmentosum. Here, we show that the beneficial DNA repair response triggered by these two genome caretakers critically depends on a dynamic spatiotemporal regulation of their homeostasis. The prolonged retention of DDB2 and XPC in chromatin, due to a failure to readily remove both recognition subunits by the ubiquitin-dependent p97/VCP/Cdc48 segregase complex, leads to impaired DNA excision repair of UV lesions. Surprisingly, the ensuing chromosomal aberrations in p97-deficient cells are alleviated by a concomitant down regulation of DDB2 or XPC. Also, genome instability resulting from an excess of DDB2 persisting in UV-irradiated cells is prevented by concurrent p97 over-expression. Our findings demonstrate that DNA damage sensors and repair initiators acquire unexpected genotoxic properties if not controlled by timely extraction from chromatin.

Investigating the different mechanisms of genotoxic and non-genotoxic carcinogens by a gene set analysis

Based on the process of carcinogenesis, carcinogens are classified as either genotoxic or non-genotoxic. In contrast to non-genotoxic carcinogens, many genotoxic carcinogens have been reported to cause tumor in carcinogenic bioassays in animals. Thus evaluating the genotoxicity potential of chemicals is important to discriminate genotoxic from non-genotoxic carcinogens for health care and pharmaceutical industry safety. Additionally, investigating the difference between the mechanisms of genotoxic and non-genotoxic carcinogens could provide the foundation for a mechanism-based classification for unknown compounds. In this study, we investigated the gene expression of HepG2 cells treated with genotoxic or non-genotoxic carcinogens and compared their mechanisms of action. To enhance our understanding of the differences in the mechanisms of genotoxic and non-genotoxic carcinogens, we implemented a gene set analysis using 12 compounds for the training set (12, 24, 48 h) and validated significant gene sets using 22 compounds for the test set (24, 48 h). For a direct biological translation, we conducted a gene set analysis using Globaltest and selected significant gene sets. To validate the results, training and test compounds were predicted by the significant gene sets using a prediction analysis for microarrays (PAM). Finally, we obtained 6 gene sets, including sets enriched for genes involved in the adherens junction, bladder cancer, p53 signaling pathway, pathways in cancer, peroxisome and RNA degradation. Among the 6 gene sets, the bladder cancer and p53 signaling pathway sets were significant at 12, 24 and 48 h. We also found that the DDB2, RRM2B and GADD45A, genes related to the repair and damage prevention of DNA, were consistently up-regulated for genotoxic carcinogens. Our results suggest that a gene set analysis could provide a robust tool in the investigation of the different mechanisms of genotoxic and non-genotoxic carcinogens and construct a more detailed understanding of the perturbation of significant pathways.

Challenging resistance mechanisms to therapies for metastatic melanoma

Melanoma is the most aggressive form of skin cancer and, if spread outside the epidermis, has a dismal prognosis. Before the approval of the anti-cytotoxic T lymphocyte-associated antigen 4 (CTLA-4) monoclonal antibody ipilimumab and the BRAF inhibitors vemurafenib and dabrafenib, no other agents had demonstrated better results in terms of overall survival than the DNA-methylating compound dacarbazine (or its oral analog temozolomide). However, most patients with metastatic melanoma do not obtain long-lasting clinical benefit from ipilimumab and responses to BRAF inhibitors are short lived. Thus, combination therapies with inhibitors of DNA repair (e.g., poly(ADP-ribose) polymerase [PARP] inhibitors), novel immunomodulators (monoclonal antibodies against programmed death-1 [PD-1] or its ligand PD-L1), targeted therapies (mitogen-activated protein kinase [MAPK]/extracellular signal-regulated kinase [ERK] kinase [MEK] or phosphatidylinositol 3-kinase [PI3K]/AKT/mammalian target of rapamycin [mTOR] inhibitors) or antiangiogenic agents are currently being investigated to improve the efficacy of antimelanoma therapies. This review discusses the implications of simultaneously targeting key regulators of melanoma cell proliferation/survival and immune responses to counteract resistance.

Transcriptional regulation of human DNA repair genes following genotoxic stress: trigger mechanisms, inducible responses and genotoxic adaptation

DNA repair is the first barrier in the defense against genotoxic stress. In recent years, mechanisms that recognize DNA damage and activate DNA repair functions through transcriptional upregulation and post-translational modification were the focus of intensive research. Most DNA repair pathways are complex, involving many proteins working in discrete consecutive steps. Therefore, their balanced expression is important for avoiding erroneous repair that might result from excessive base removal and DNA cleavage. Amelioration of DNA repair requires both a fine-tuned system of lesion recognition and transcription factors that regulate repair genes in a balanced way. Transcriptional upregulation of DNA repair genes by genotoxic stress is counteracted by DNA damage that blocks transcription. Therefore, induction of DNA repair resulting in an adaptive response is only visible through a narrow window of dose. Here, we review transcriptional regulation of DNA repair genes in normal and cancer cells and describe mechanisms of promoter activation following genotoxic exposures through environmental carcinogens and anticancer drugs. The data available to date indicate that 25 DNA repair genes are subject to regulation following genotoxic stress in rodent and human cells, but for only a few of them, the data are solid as to the mechanism, homeostatic regulation and involvement in an adaptive response to genotoxic stress.