c-Myc suppression of DNA double-strand break repair

LRRC45 promotes lung cancer proliferation and progression by enhancing c-MYC, slug, MMP2, and MMP9 expression

BACKGROUND

The leucine-rich repeat-containing (LRRC) superfamily members are known for their significant roles in tumorigenesis and cellular proliferation. However, the specific regulatory role of LRRC45 in lung cancer remains unexplored. This study investigated the impact and underlying mechanisms of LRRC45 on the proliferative, migratory, and invasive capacities of lung adenocarcinoma (LUAD) cells, potentially identifying new targets for therapeutic intervention.

MATERIAL AND METHODS

The importance of LRRC45 in lung cancer was analyzed using the online databases of UCSC Xena, TCGA, TISIDB, and UALCAN, whereas to detect target gene expression, we used the qRT-PCR, Western blot, and immunofluorescence confocal. The cell growth was monitored by colony formation assay and migration was examined by cell migration assay. Finally, a xenograft mouse tumor model using A549 ​cells was used to explore the in vivo effect of LRRC45 in lung cancer.

RESULTS

Inhibition of LRRC45 expression led to a notable decrease in proliferation, migration, and invasion of A549 and H1299 ​cells. LRRC45 silencing significantly reduced the tumor volume and improved the mice's survival. Additionally, inhibition of LRRC45 expression dramatically suppressed c-MYC, Slug, MMP2, and MMP9 expression. Overexpression of c-MYC and/or Slug in the LRRC45-deficient cells can partially or totally restore the LRRC45 deficiency-suppressed growth. Moreover, the overexpression of MMP2 and/or MMP9 could partially or totally restore LRRC45 deficiency-reduced cell metastasis.

CONCLUSIONS

LRRC45 could promote the proliferative, migrative, and invasive capacities of lung cancer cells by increasing c-MYC, Slug, MMP2, and MMP9 expression, indicating the therapeutic implications and potential significance of these pathways in lung cancer.

Synergistic Effect of Ubiquitin-Specific Protease 14 and Poly(ADP-Ribose) Glycohydrolase Co-Inhibition in BRCA1-Mutant, Poly(ADP-Ribose) Polymerase Inhibitor-Resistant Triple-Negative Breast Cancer Cells

Purpose

The clinical benefits of poly(ADP-ribose) polymerase (PARP) inhibitors are limited to triple-negative breast cancer (TNBC) with BRCA deficiency due to primary and acquired resistance. Thus, there is a pressing need to develop alternative treatment regimens to target BRCA-mutated TNBC tumors that are resistant to PARP inhibition. Similar to PARP, poly(ADP-ribose) glycohydrolase (PARG) plays a role in DNA replication and repair. However, there are conflicting reports on the vulnerability of BRCA1-deficient tumor cells to PARG inhibition. This study aims to investigate the synergistically lethal effect of the PARG inhibitor COH34 and the ubiquitin-specific protease (USP) 14 inhibitor IU1-248 and the underlying mechanisms in BRCA1-mutant, PARP inhibitor-resistant TNBC cells.

Methods

The cytotoxicity of PARG inhibition alone or in combination with USP14 inhibition in the BRCA-mutant, PARP inhibitor-resistant TNBC cell lines, HCC1937 and SUM149PT, was analyzed using cell viability and proliferation assays and flow cytometry. The molecular mechanisms underlying the synergistic effects of IU1-248 and COH34 were evaluated by immunofluorescence staining, DNA repair reporter assays and Western blot analysis.

Results

It was found that HCC1937 and SUM149PT cells exhibited moderate responsiveness to PARG inhibition alone. To the best of our knowledge, this research is the first to demonstrate that the combination of IU1-248 and COH34 produces synergistic effects against TNBC cells in the same setting. Mechanistically, the blockade of USP14 by IU1-248 was shown to increase DNA damage and promote error-prone non-homologous end joining (NHEJ), as evidenced by the accumulation of γH2AX and 53BP1 in the nucleus and the activation of a reporter assay. Additionally, it was demonstrated that the inhibition of NHEJ repair activity attenuates the synergistic effects of concomitant PARG and USP14 inhibition. IU1-248 promotes NHEJ repair through the downregulation of the expression of c-Myc.

Conclusion

USP14 inhibition may be a plausible strategy for expanding the utility of PARG inhibitors in TNBC in BRCA-mutant, PARP inhibitor-resistant settings.

Chia Seed (Salvia hispanica) Attenuates Chemically Induced Lung Carcinomas in Rats through Suppression of Proliferation and Angiogenesis

In 2022, 2.5 million cases of lung cancer were diagnosed, resulting in 1.8 million deaths. These statistics have motivated us to introduce a new natural product which is feasible in lung cancer therapies. This comprehensive study was performed to study the effects of chia seed extracts (70% ethanol and petroleum ether) on lung cancer in vitro and in vivo models. The invitro cytotoxicity activity of the chia extracts was studied in lung cancer cell lines (A549 cells). After 48 h, chia alcohol and ether extracts showed more inhibitory influence (IC50, 16.08, and 14.8 µg/mL, respectively) on A549 cells compared to Dox (IC50, 13.6 µg/mL). In vivo, administration of chia alcohol and ether extracts (500 mg/kg/day, orally for 20 weeks) recovered 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)-induced lung cancer, as a significant reduction in the lung cancer biomarkers, including the relative weight of the lung (20.0 and 13.33%), ICAM(31.73 and 15.66%), and c-MYC (80 and 96%) and MMP9(60 and 69%) expression genes, and improvement in these changes were observed by histopathological examinations of the lung tissues compared to the lung control. Chia seeds fought lung cancer via suppression of proliferation, angiogenesis, inflammation, and activation apoptosis. These activities may be attributed to the chemical composition of chia, which is identified by LC-Mass, such as caffeic acid, vanillic acid, kaempferol-3-O-glucuronide, and taxifolin. Finally, we can conclude that chia seeds have an anti-lung cancer effect with a good safety margin.

(-)-Epigallocatechin-3-gallate induced apoptosis by dissociation of c-FLIP/Ku70 complex in gastric cancer cells

Anti-cancer properties of (-)-epigallocatechin-3-gallate (EGCG) are mediated via apoptosis induction, as well as inhibition of cell proliferation and histone deacetylase. Accumulation of stabilized cellular FLICE-inhibitory protein (c-FLIP)/Ku70 complex in the cytoplasm inhibits apoptosis through interruption of extrinsic apoptosis pathway. In this study, we evaluated the anti-cancer role of EGCG in gastric cancer (GC) cells through dissociation of c-FLIP/Ku70 complex. MKN-45 cells were treated with EGCG or its antagonist MG149 for 24 h. Apoptosis was evaluated by flow cytometry and quantitative RT-PCR. Protein expression of c-FLIP and Ku70 was analysed using western blot and immunofluorescence. Dissociation of c-FLIP/Ku70 complex as well as Ku70 translocation were studied by sub-cellular fractionation and co-immunoprecipitation. EGCG induced apoptosis in MKN-45 cells with substantial up-regulation of P53 and P21, down-regulation of c-Myc and Cyclin D1 as well as cell cycle arrest in S and G2/M check points. Moreover, EGCG treatment suppressed the expression of c-FLIP and Ku70, decreased their interaction while increasing the Ku70 nuclear content. By dissociating the c-FLIP/Ku70 complex, EGCG could be an alternative component to the conventional HDAC inhibitors in order to induce apoptosis in GC cells. Thus, its combination with other cancer therapy protocols could result in a better therapeutic outcome.

Discovery and Characterization of ZL-2201, a Potent, Highly Selective, and Orally Bioavailable Small-molecule DNA-PK Inhibitor

DNA-dependent protein kinase (DNA-PK), a driver of the non-homologous end-joining (NHEJ) DNA damage response pathway, plays an instrumental role in repairing double-strand breaks (DSB) induced by DNA-damaging poisons. We evaluate ZL-2201, an orally bioavailable, highly potent, and selective pharmacologic inhibitor of DNA-PK activity, for the treatment of human cancerous malignancies. ZL-2201 demonstrated greater selectivity for DNA-PK and effectively inhibited DNA-PK autophosphorylation in a concentration- and time-dependent manner. Initial data suggested a potential correlation between ataxia-telangiectasia mutated (ATM) deficiency and ZL-2201 sensitivity. More so, ZL-2201 showed strong synergy with topoisomerase II inhibitors independent of ATM status in vitro. In vivo oral administration of ZL-2201 demonstrated dose-dependent antitumor activity in the NCI-H1703 xenograft model and significantly enhanced the activity of approved DNA-damaging agents in A549 and FaDu models. From a phosphoproteomic mass spectrometry screen, we identified and validated that ZL-2201 and PRKDC siRNA decreased Ser108 phosphorylation of MCM2, a key DNA replication factor. Collectively, we have characterized a potent and selective DNA-PK inhibitor with promising monotherapy and combinatory therapeutic potential with approved DNA-damaging agents. More importantly, we identified phospho-MCM2 (Ser108) as a potential proximal biomarker of DNA-PK inhibition that warrants further preclinical and clinical evaluation.

Significance

ZL-2201, a potent and selective DNA-PK inhibitor, can target tumor models in combination with DNA DSB-inducing agents such as radiation or doxorubicin, with potential to improve recurrent therapies in the clinic.

Role of c-Myc in lung cancer: Progress, challenges, and prospects

Lung cancer remains the leading cause of cancer-related deaths worldwide. Despite the recent advances in cancer therapies, the 5-year survival of non-small cell lung cancer (NSCLC) patients hovers around 20%. Inherent and acquired resistance to therapies (including radiation, chemotherapies, targeted drugs, and combination therapies) has become a significant obstacle in the successful treatment of NSCLC. c-Myc, one of the critical oncoproteins, has been shown to be heavily associated with the malignant cancer phenotype, including rapid proliferation, metastasis, and chemoresistance across multiple cancer types. The c-Myc proto-oncogene is amplified in small cell lung cancers (SCLCs) and overexpressed in over 50% of NSCLCs. c-Myc is known to actively regulate the transcription of cancer stemness genes that are recognized as major contributors to tumor progression and therapeutic resistance; thus, targeting c-Myc either directly or indirectly in mitigation of the cancer stemness phenotype becomes a promising approach for development of a new strategy against drug resistant lung cancers. This review will summarize what is currently known about the mechanisms underlying c-Myc regulation of cancer stemness and its involvement in drug resistance and offer an overview on the current progress and future prospects in therapeutically targeting c-Myc in both SCLC and NSCLC.

In Silico, In Vitro, and In Vivo Investigations on Adapalene as Repurposed Third Generation Retinoid against Multiple Myeloma and Leukemia

The majority of hematopoietic cancers in adults are incurable and exhibit unpredictable remitting-relapsing patterns in response to various therapies. The proto-oncogene c-MYC has been associated with tumorigenesis, especially in hematological neoplasms. Therefore, targeting c-MYC is crucial to find effective, novel treatments for blood malignancies. To date, there are no clinically approved c-MYC inhibitors. In this study, we virtually screened 1578 Food and Drug Administration (FDA)-approved drugs from the ZINC15 database against c-MYC. The top 117 compounds from PyRx-based screening with the best binding affinities to c-MYC were subjected to molecular docking studies with AutoDock 4.2.6. Retinoids consist of synthetic and natural vitamin A derivatives. All-trans-retinoic acid (ATRA) were highly effective in hematological malignancies. In this study, adapalene, a third-generation retinoid usually used to treat acne vulgaris, was selected as a potent c-MYC inhibitor as it robustly bound to c-MYC with a lowest binding energy (LBE) of -7.27 kcal/mol, a predicted inhibition constant (pKi) of 4.69 µM, and a dissociation constant (Kd value) of 3.05 µM. Thus, we examined its impact on multiple myeloma (MM) cells in vitro and evaluated its efficiency in vivo using a xenograft tumor zebrafish model. We demonstrated that adapalene exerted substantial cytotoxicity against a panel of nine MM and two leukemic cell lines, with AMO1 cells being the most susceptible one (IC50 = 1.76 ± 0.39 µM) and, hence, the focus of this work. Adapalene (0.5 × IC50, 1 × IC50, 2 × IC50) decreased c-MYC expression and transcriptional activity in AMO1 cells in a dose-dependent manner. An examination of the cell cycle revealed that adapalene halted the cells in the G2/M phase and increased the portion of cells in the sub-G0/G1 phase after 48 and 72 h, indicating that cells failed to initiate mitosis, and consequently, cell death was triggered. Adapalene also increased the number of p-H3(Ser10) positive AMO1 cells, which is a further proof of its ability to prevent mitotic exit. Confocal imaging demonstrated that adapalene destroyed the tubulin network of U2OS cells stably transfected with a cDNA coding for α-tubulin-GFP, refraining the migration of malignant cells. Furthermore, adapalene induced DNA damage in AMO1 cells. It also induced apoptosis and autophagy, as demonstrated by flow cytometry and western blotting. Finally, adapalene impeded tumor growth in a xenograft tumor zebrafish model. In summary, the discovery of the vitamin A derivative adapalene as a c-MYC inhibitor reveals its potential as an avant-garde treatment for MM.

Identification of biomarkers of response to preoperative talazoparib monotherapy in treatment naïve gBRCA+ breast cancers

Germline mutations in BRCA1 or BRCA2 exist in ~2–7% of breast cancer patients, which has led to the approval of PARP inhibitors in the advanced setting. We have previously reported a phase II neoadjuvant trial of single agent talazoparib for patients with germline BRCA pathogenic variants with a pathologic complete response (pCR) rate of 53%. As nearly half of the patients treated did not have pCR, better strategies are needed to overcome treatment resistance. To this end, we conducted multi-omic analysis of 13 treatment naïve breast cancer tumors from patients that went on to receive single-agent neoadjuvant talazoparib. We looked for biomarkers that were predictive of response (assessed by residual cancer burden) after 6 months of therapy. We found that all resistant tumors exhibited either the loss of SHLD2, expression of a hypoxia signature, or expression of a stem cell signature. These results indicate that the deep analysis of pre-treatment tumors can identify biomarkers that are predictive of response to talazoparib and potentially other PARP inhibitors, and provides a framework that will allow for better selection of patients for treatment, as well as a roadmap for the development of novel combination therapies to prevent emergence of resistance.

Function of BCLAF1 in human disease

Originally identified as a regulator of apoptosis and transcription, B-cell lymphoma-2-associated transcription factor 1 (BCLAF1) has since been shown to be associated with a multitude of biological processes, such as DNA damage response, splicing and processing of pre-mRNA, T-cell activation, lung development, muscle cell proliferation and differentiation, autophagy, ischemia-reperfusion injury, and viral infection. In recent years, an increasing amount of evidence has shown that BCLAF1 acts as either a tumor promoter or tumor suppressor in tumorigenesis depending on the cellular context and the type of cancer. Even in the same tumor type, BCLAF1 may have opposite effects. In the present review, the subcellular localization, structural features, mutations within BCLAF1 will be described, then the regulation of BCLAF1 and its downstream targets will be analyzed. Furthermore, the different roles and possible mechanisms of BCLAF1 in tumorigenesis will also be highlighted and discussed. Finally, BCLAF1 may be considered as a potential target for cancer therapy in the future.

The MYC oncogene - the grand orchestrator of cancer growth and immune evasion

The MYC proto-oncogenes encode a family of transcription factors that are among the most commonly activated oncoproteins in human neoplasias. Indeed, MYC aberrations or upregulation of MYC-related pathways by alternate mechanisms occur in the vast majority of cancers. MYC proteins are master regulators of cellular programmes. Thus, cancers with MYC activation elicit many of the hallmarks of cancer required for autonomous neoplastic growth. In preclinical models, MYC inactivation can result in sustained tumour regression, a phenomenon that has been attributed to oncogene addiction. Many therapeutic agents that directly target MYC are under development; however, to date, their clinical efficacy remains to be demonstrated. In the past few years, studies have demonstrated that MYC signalling can enable tumour cells to dysregulate their microenvironment and evade the host immune response. Herein, we discuss how MYC pathways not only dictate cancer cell pathophysiology but also suppress the host immune response against that cancer. We also propose that therapies targeting the MYC pathway will be key to reversing cancerous growth and restoring antitumour immune responses in patients with MYC-driven cancers.

Tumor Suppressor FBXW7 and Its Regulation of DNA Damage Response and Repair

The proper DNA damage response (DDR) and repair are the central molecular mechanisms for the maintenance of cellular homeostasis and genomic integrity. The abnormality in this process is frequently observed in human cancers, and is an important contributing factor to cancer development. FBXW7 is an F-box protein serving as the substrate recognition component of SCF (SKP1-CUL1-F-box protein) E3 ubiquitin ligase. By selectively targeting many oncoproteins for proteasome-mediated degradation, FBXW7 acts as a typical tumor suppressor. Recent studies have demonstrated that FBXW7 also plays critical roles in the process of DDR and repair. In this review, we first briefly introduce the processes of protein ubiquitylation by SCF^FBXW7 and DDR/repair, then provide an overview of the molecular characteristics of FBXW7. We next discuss how FBXW7 regulates the process of DDR and repair, and its translational implication. Finally, we propose few future perspectives to further elucidate the role of FBXW7 in regulation of a variety of biological processes and tumorigenesis, and to design a number of approaches for FBXW7 reactivation in a subset of human cancers for potential anticancer therapy.

DNA damage triggers an interplay between wtp53 and c-Myc affecting lymphoma cell proliferation and Kaposi sarcoma herpesvirus replication

The induction of DNA damage together with the interference with DNA repair represents a promising strategy in cancer treatment. Here we show that the PARP-1/2/3 inhibitor AZD2461 in combination with the CHK1 inhibitor UCN-01 altered the DNA damage response and reduced cell proliferation in PEL cells, an aggressive B cell lymphoma highly resistant to chemotherapies. AZD2461/UCN-01 combination activated p53/p21 and downregulated c-Myc in these cells, leading to a reduced expression level of RAD51, molecule involved in DNA repair. The effect of AZD2461/UCN-01 on c-Myc and p53/p21 was inter-dependent and, besides impairing cell proliferation, contributed to the activation of the replicative cycle of KSHV, carried in a latent state in PEL cells. Finally, we found that the pharmacological or genetic inhibition of p21 counteracted the viral lytic cycle activation and further reduced PEL cell proliferation, suggesting that it could induce a double beneficial effect in this setting. This study unveils that, therapeutic approaches, based on the induction of DNA damage and the reduction of DNA repair, could be used to successfully treat this malignant lymphoma.

PRMT1 Confers Resistance to Olaparib via Modulating MYC Signaling in Triple-Negative Breast Cancer

Treatment of triple-negative breast cancer (TNBC) remains an unmet clinical need owing to its lack of an efficient therapeutic target. The targeting of DNA repair by poly(ADP-ribose) polymerase (PARP) inhibitors has shown benefit for patients with the BRCA variation. However, sensitivities to the PARP inhibitors were reported regardless of BRCA status. Thus, exploring the underlying mechanisms is imperative. Herein, we identified that breast cancer cells with an elevated expression of protein arginine methyl transferase 1 (PRMT1) was associated with therapeutic sensitivity to the PARP inhibitor olaparib. The results of cell viability and colony formation assays indicated that the suppression of PRMT1 by small hairpin RNA or by the chemical inhibitor increased sensitivity to olaparib in human TNBC MDA-MB-231 and BT549 cells. Bioinformatic analysis revealed that PRMT1 expression was significantly associated with the MYC signature, and TNBC cells with higher PRMT1 and the MYC signature were associated with therapeutic sensitivity to olaparib. Mechanistic studies further demonstrated that knockdown of PRMT1 reduced the c-Myc protein level and downregulated the expression of MYC downstream targets, whereas overexpression of PRMT1 enhanced c-Myc protein expression. Moreover, the overexpression of PRMT1 promoted c-Myc protein stability, and the inhibition of PRMT1 downregulated c-Myc protein stability. Accordingly, the knockdown of PRMT1 inhibited homologous recombination gene expression. These data indicate that PRMT1 is instrumental in regulating DNA repair, at least in part, by modulating c-Myc signaling. Our data highlighted the PRMT1/c-Myc network as a potential therapeutic target in patients with TNBC.

Low-Dose Radiation Can Cause Epigenetic Alterations Associated With Impairments in Both Male and Female Reproductive Cells

Humans are regularly and continuously exposed to ionizing radiation from both natural and artificial sources. Cumulating evidence shows adverse effects of ionizing radiation on both male and female reproductive systems, including reduction of testis weight and sperm count and reduction of female germ cells and premature ovarian failure. While most of the observed effects were caused by DNA damage and disturbance of DNA repairment, ionizing radiation may also alter DNA methylation, histone, and chromatin modification, leading to epigenetic changes and transgenerational effects. However, the molecular mechanisms underlying the epigenetic changes and transgenerational reproductive impairment induced by low-dose radiation remain largely unknown. In this study, two different types of human ovarian cells and two different types of testicular cells were exposed to low dose of ionizing radiation, followed by bioinformatics analysis (including gene ontology functional analysis and Ingenuity Pathway Analysis), to unravel and compare epigenetic effects and pathway changes in male and female reproductive cells induced by ionizing radiation. Our findings showed that the radiation could alter the expression of gene cluster related to DNA damage responses through the control of MYC. Furthermore, ionizing radiation could lead to gender-specific reproductive impairment through deregulation of different gene networks. More importantly, the observed epigenetic modifications induced by ionizing radiation are mediated through the alteration of chromatin remodeling and telomere function. This study, for the first time, demonstrated that ionizing radiation may alter the epigenome of germ cells, leading to transgenerational reproductive impairments, and correspondingly call for research in this new emerging area which remains almost unknown.

MYC: a multipurpose oncogene with prognostic and therapeutic implications in blood malignancies

MYC oncogene is a transcription factor with a wide array of functions affecting cellular activities such as cell cycle, apoptosis, DNA damage response, and hematopoiesis. Due to the multi-functionality of MYC, its expression is regulated at multiple levels. Deregulation of this oncogene can give rise to a variety of cancers. In this review, MYC regulation and the mechanisms by which MYC adjusts cellular functions and its implication in hematologic malignancies are summarized. Further, we also discuss potential inhibitors of MYC that could be beneficial for treating hematologic malignancies.

Chromosomal Instability in Acute Myeloid Leukemia

Chromosomal instability (CIN), the increasing rate in which cells acquire new chromosomal alterations, is one of the hallmarks of cancer. Many studies highlighted CIN as an important mechanism in the origin, progression, and relapse of acute myeloid leukemia (AML). The ambivalent feature of CIN as a cancer-promoting or cancer-suppressing mechanism might explain the prognostic variability. The latter, however, is described in very few studies. This review highlights the important CIN mechanisms in AML, showing that CIN signatures can occur largely in all the three major AML types (de novo AML, secondary-AML, and therapy-related-AML). CIN features in AML could also be age-related and reflect the heterogeneity of the disease. Although most of these abnormalities show an adverse prognostic value, they also offer a strong new perspective on personalized therapy approaches, which goes beyond assessing CIN in vitro in patient tumor samples to predict prognosis. Current and emerging AML therapies are exploring CIN to improve AML treatment, which includes blocking CIN or increasing CIN beyond the limit threshold to induce cell death. We argue that the characterization of CIN features, not included yet in the routine diagnostic of AML patients, might provide a better stratification of patients and be extended to a more personalized therapeutic approach.

Combining Radiation Therapy with ALK Inhibitors in Anaplastic Lymphoma Kinase-Positive Non-Small Cell Lung Cancer (NSCLC): A Clinical and Preclinical Overview

Over the past years, the identification of genetic alterations in oncogenic drivers in non-small cell lung cancer (NSCLC) has significantly and favorably transformed the outcome of patients who can benefit from targeted therapies such as tyrosine kinase inhibitors. Among these genetic alterations, anaplastic lymphoma kinase (ALK) rearrangements were discovered in 2007 and are present in 3-5% of patients with NSCLC. In addition, radiotherapy remains one of the cornerstones of NSCLC treatment. Moreover, improvements in the field of radiotherapy with the use of hypofractionated or ablative stereotactic radiotherapy have led to a better outcome for localized or oligometastatic NSCLC. To date, the effects of the combination of ALK inhibitors and radiotherapy are unclear in terms of safety and efficacy but could potently improve treatment. In this manuscript, we provide a clinical and preclinical overview of combining radiation therapy with ALK inhibitors in anaplastic lymphoma kinase-positive non-small cell lung cancer.

Exploiting MYC-induced PARPness to target genomic instability in multiple myeloma

Multiple Myeloma (MM) is a hematologic malignancy strongly characterized by genomic instability, which promotes disease progression and drug resistance. Since we previously demonstrated that LIG3-dependent repair is involved in the genomic instability, drug resistance and survival of MM cells, we here investigated the biological relevance of PARP1, a driver component of Alternative-Non Homologous End Joining (Alt-NHEJ) pathway, in MM. We found a significant correlation between higher PARP1 mRNA expression and poor prognosis of MM patients. PARP1 knockdown or its pharmacological inhibition by Olaparib impaired MM cells viability in vitro and was effective against in vivo xenografts of human MM. Anti-proliferative effects induced by PARP1-inhibition were correlated to increase of DNA double-strand breaks, activation of DNA Damage Response (DDR) and finally apoptosis. Importantly, by comparing a gene expression signature of PARP inhibitors (PARPi) sensitivity to our plasma cell dyscrasia (PC) gene expression profiling (GEP), we identified a subset of MM patients which could benefit from PARP inhibitors. In particular, Gene Set Enrichment Analysis (GSEA) suggested that high MYC expression correlates to PARPi sensitivity in MM. Indeed, we identified MYC as promoter of PARP1-mediated repair in MM and, consistently, we demonstrate that cytotoxic effects induced by PARP inhibition are mostly detectable on MYC-proficient MM cells. Taken together, our findings indicate that MYC-driven MM cells are addicted to PARP1 Alt-NHEJ repair, which represents therefore a druggable target in this still incurable disease.

Emerging functions of PRKDC in the initiation and progression of cancer

The DNA-dependent protein kinase catalytic subunit (DNA-PKcs) is encoded by the protein kinase, DNA-activated, catalytic polypeptide (PRKDC) gene. DNA-PKcs plays a major role in nonhomologous end joining DNA repair, and it has been identified to be an important factor in tumor progression and metastasis. DNA-PKcs may have opposite effects in diseases, depending on the cell and tissue types. In this review, we discuss its role in various tumors. High levels of DNA-PKcs are directly associated with prognosis, neoplasm recurrence rates, and overall survival. Our results suggest that DNA-PKcs may serve as a therapeutic target for advanced malignancies.

The prognostic role of c-MYC amplification in schistosomiasis-associated colorectal cancer

OBJECTIVE

The purpose of this study was to explore the prognostic role of c-MYC amplification in colorectal cancer, particularly in schistosomiasis-associated colorectal cancer.

METHODS

Three hundred and fifty four cases of colorectal cancer, which were from Qingpu Branch of Zhongshan Hospital affiliated to Fudan University, were retrospectively analyzed in a tissue microarray (TMA) format, with fluorescence in situ hybridization (FISH) assay and immunohistochemistry (IHC).

RESULTS

c-MYC gene amplification was found in 14.1% (50 out of 354) of patients with colorectal cancer and was correlated with old age (P = 0.028), positive lymph node metastasis (P = 0.004) and advanced stage tumors (P = 0.002). The overexpression of c-MYC was closely associated with the amplification status (P = 0.023). Kaplan-Meier survival curves for overall survival (OS) showed a statistically significant difference for patients with c-MYC amplification in full cohort of colorectal cancer, stage III-IV set and patients with lymph node metastasis (P = 0.002, 0.034, 0.012, respectively). Further analysis found c-MYC amplification associated with poorer survival in the subgroup of colorectal cancer with schistosomiasis (CRC-S, P < 0.001), but not in colorectal cancer without schistosomiasis (CRC-NS, P = 0.155). By multivariate analysis, c-MYC amplification was an independent poor-prognostic factor in CRC-S set (P = 0.046).

CONCLUSIONS

Our study firstly found c-MYC amplification could predict poor prognosis in schistosomiasis-associated colorectal cancer, but not in colorectal cancer without schistosomiasis.

Apoptosis Induction byHistone Deacetylase Inhibitors in Cancer Cells: Role of Ku70

Histone deacetylases (HDACs) are a group of enzymes that regulate gene transcription by controlling deacetylation of histones and non-histone proteins. Overexpression of HDACs is found in some types of tumors and predicts poor prognosis. Five HDAC inhibitors are approved for the treatment of cutaneous T-cell lymphoma, peripheral T-cell lymphoma, and multiple myeloma. Treatment with HDAC inhibitors regulates gene expression with increased acetylated histones with unconfirmed connection with therapy. Apoptosis is a key mechanism by which HDAC inhibitors selectively kill cancer cells, probably due to acetylation of non-histone proteins. Ku70 is a protein that repairs DNA breaks and stabilizes anti-apoptotic protein c-FLIP and proapoptotic protein Bax, which is regulated by acetylation. HDAC inhibitors induce Ku70 acetylation with repressed c-FLIP and activated Bax in cancer cells. Current studies indicate that Ku70 is a potential target of HDAC inhibitors and plays an important role during the induction of apoptosis.

MYC status as a determinant of synergistic response to Olaparib and Palbociclib in ovarian cancer

Background

While PARP inhibitors and CDK4/6 inhibitors, the two classes of FDA-approved agents, have shown promising clinical benefits, there is an urgent need to develop new therapeutic strategies to improve clinical response. Meanwhile, extending the utility of these inhibitors beyond their respective molecularly defined cancer types is challenging and will likely require biomarkers predictive of treatment response especially when used in a combination drug development setting.

Methods

The effects of PARP inhibitor Olaparib and CDK4/6 inhibitor Palbociclib on ovarian cancer cells lines including those of high-grade serous histology were examined in vitro and in vivo. We investigated the molecular mechanism underlying the synergistic effects of drug combination.

Findings

We show for the first time that combining PARP and CDK4/6 inhibition has synergistic effects against MYC overexpressing ovarian cancer cells both in vitro and in vivo. Mechanistically, we find that Palbociclib induces homologous recombination (HR) deficiency through downregulation of MYC-regulated HR pathway genes, causing synthetic lethality with Olaparib. We further demonstrate that MYC expression determines sensitivity to combinatorial treatment with Olaparib and Palbociclib.

Interpretation

Our data provide a rationale for clinical evaluation of therapeutic synergy of these two classes of inhibitors in ovarian cancer patients whose tumors show high MYC expression and who do not respond to PARP inhibitors or CDK4/6 inhibitors monotherapies.

Fund

This work was supported by the National Natural Science Foundation of China [81672575, 81874111, 81472447 to HC; 81572586 and 81372853 to PL], and the Liaoning Provincial Key Basic Research Program for Universities [LZ2017002 to HC].

Deciphering the Combined Effects of Environmental Stressors on Gene Transcription: A Conceptual Approach

The use of classical mixture toxicity models to predict the combined effects of environmental stressors based on toxicogenomics (OMICS) data is still in its infancy. Although several studies have made attempts to implement mixture modeling in OMICS analysis to understand the low-dose interactions of stressors, it is not clear how interactions occur at the molecular level and how results generated from such approaches can be better used to inform future studies and cumulative hazard assessment of multiple stressors. The present work was therefore conducted to propose a conceptual approach for combined effect assessment using global gene expression data, as illustrated by a case study on assessment of combined effects of gamma radiation and depleted uranium (DU) on Atlantic salmon ( Salmo salar). Implementation of the independent action (IA) model in reanalysis of a previously published microarray gene expression dataset was performed to describe gene expression patterns of combined effects and identify key gene sets and pathways that were relevant for understanding the interactive effects of these stressors. By using this approach, 3120 differentially expressed genes (DEGs) were found to display additive effects, whereas 279 (273 synergistic, 6 antagonistic) were found to deviate from additivity. Functional analysis further revealed that multiple toxicity pathways, such as oxidative stress responses, cell cycle regulation, lipid metabolism, and immune responses were enriched by DEGs showing synergistic gene expression. A key toxicity pathway of DNA damage leading to enhanced tumorigenesis signaling is highlighted and discussed in detail as an example of how to take advantage of the approach. Furthermore, a conceptual workflow describing the integration of combined effect modeling, OMICS analysis, and bioinformatics is proposed. The present study presents a conceptual framework for utilizing OMICS data in combined effect assessment and may provide novel strategies for dealing with data analysis and interpretation of molecular responses of multiple stressors.

Activation of nuclear β-catenin/c-Myc axis promotes oxidative stress injury in streptozotocin-induced diabetic cardiomyopathy

Myocardial oxidative stress injury plays a crucial role in the pathogenesis of diabetic cardiomyopathy (DCM). Wnt/β-catenin signaling has been reported to involve in various heart diseases. However, the underlying mechanism associated with β-catenin in DCM remains elusive. This study intended to explore the effect of β-catenin on oxidative damage of DCM by establishing streptozotocin (STZ)-induced diabetic mouse model and hydrogen peroxide (H₂O₂)-treated myocardial cell model. Cardiac oxidative stress in DCM was detected by measurements of lipid peroxidation and anti-oxidative enzyme activities as well as DHE staining. Nuclear β-catenin activity and oxidative damage degree were measured by western blotting, qPCR, MTT assay and TUNEL staining. Cardiac function and morphology were evaluated by echocardiography and histopathology. Under diabetic oxidative stress or H₂O₂ stimulation, nuclear β-catenin accumulation upregulated downstream c-Myc and further facilitated DNA damage and p53-mediated apoptosis as well as cell viability reduction, followed by phenotypic changes of cardiac dysfunction, interstitial fibrosis deposition and myocardial atrophy. Conversely, through directly inhibiting nuclear β-catenin/c-Myc axis, not only did siRNA knockdown of β-catenin or c-Myc attenuate cell injury in H₂O₂-stimulated cardiomyocytes, but also diabetic cardiac-specific β-catenin-knockout mice displayed the same prevention of heart injury as insulin-treated diabetic mice. The present study demonstrated that activated nuclear β-catenin/c-Myc axis was responsible for oxidative cardiac impairment of DCM. Therefore, repressing functional nuclear β-catenin may provide a hopeful therapeutic strategy for DCM.

Shp2 regulates migratory behavior and response to EGFR-TKIs through ERK1/2 pathway activation in non-small cell lung cancer cells

In the clinical treatment of lung cancer, therapy failure is mainly caused by cancer metastasis and drug resistance. Here, we investigated whether the tyrosine phosphatase Shp2 is involved in the development of metastasis and drug resistance in non-small cell lung cancer (NSCLC). Shp2 was overexpressed in a subset of lung cancer tissues, and Shp2 knockdown in lung cancer cells inhibited cell proliferation and migration, downregulated c-Myc and fibronectin expression, and upregulated E-cadherin expression. In H1975 cells, which carry double mutations (L858R + T790M) in epidermal growth factor receptor (EGFR) that confers resistance toward the tyrosine kinase inhibitor gefitinib, Shp2 knockdown increased cellular sensitivity to gefitinib; conversely, in H292 cells, which express wild-type EGFR and are sensitive to gefitinib, Shp2 overexpression increased cellular resistance to gefitinib. Moreover, by overexpressing Shp2 or using U0126, a small-molecule inhibitor of extracellular signal-regulated kinase 1/2 (ERK1/2), we demonstrated that Shp2 inhibited E-cadherin expression and enhanced the expression of fibronectin and c-Myc through activation of the ERK1/2 pathway. Our findings reveal that Shp2 is overexpressed in clinical samples of NSCLC and that Shp2 knockdown reduces the proliferation and migration of lung cancer cells, and further suggest that co-inhibition of EGFR and Shp2 is an effective approach for overcoming EGFR T790M mutation acquired resistance to EGFR tyrosine kinase inhibitors (TKIs). Thus, we propose that Shp2 could serve as a new biomarker in the treatment of NSCLC.

New Insight into microRNA Functions in Cancer: Oncogene-microRNA-Tumor Suppressor Gene Network

Tumorigenesis is a multi-step and complex process with multi-factors involved. Deregulated oncogenes and tumor suppressor genes (TSGs) induced by genetic and epigenetic factors are considered as the driving force in the development and progression of cancer. Besides, microRNAs (miRNAs) act vital roles in tumorigenesis through regulating some oncogenes and TSGs. Interestingly, miRNAs are also regulated by oncogenes and TSGs. Considering the entangled regulation, here we propose a new insight into these regulation relationships in cancer: oncogene–miRNA–TSG network, which further emphasizes roles of miRNA, as well as highlights the network regulation among oncogene, miRNA, and TSG during tumorigenesis. The oncogene–miRNA–TSG network demonstrates that oncogenes and TSGs not only show functional synergy, but also there are regulatory relationships among oncogenes and TSGs during tumorigenesis, which could be mediated by miRNAs. In view of the oncogene–miRNA–TSG network involved in many oncogenes, miRNAs, and TSGs, as well as occurring in various tumor types, the anomaly of this network may be a common event in cancers and participates in tumorigenesis. This hypothesis broadens horizons of molecular mechanisms underlying tumorigenesis, and may provide a new promising venue for the prediction, diagnosis, and even therapy of cancer.

The Dual Roles of MYC in Genomic Instability and Cancer Chemoresistance

Cancer is associated with genomic instability and aging. Genomic instability stimulates tumorigenesis, whereas deregulation of oncogenes accelerates DNA replication and increases genomic instability. It is therefore reasonable to assume a positive feedback loop between genomic instability and oncogenic stress. Consistent with this premise, overexpression of the MYC transcription factor increases the phosphorylation of serine 139 in histone H2AX (member X of the core histone H2A family), which forms so-called γH2AX, the most widely recognized surrogate biomarker of double-stranded DNA breaks (DSBs). Paradoxically, oncogenic MYC can also promote the resistance of cancer cells to chemotherapeutic DNA-damaging agents such as cisplatin, clearly implying an antagonistic role of MYC in genomic instability. In this review, we summarize the underlying mechanisms of the conflicting functions of MYC in genomic instability and discuss when and how the oncoprotein exerts the contradictory roles in induction of DSBs and protection of cancer-cell genomes.

Genomic analysis-integrated whole-exome sequencing of neuroblastomas identifies genetic mutations in axon guidance pathway

Neuroblastoma (NB) is a childhood solid malignant tumor originating from precursor cells of the peripheral nervous system. We have previously established a risk classification system based on DNA copy number profiles. To further explore the pathogenesis of NBs in distinct risk groups, we performed whole-exome sequencing analysis of 57 primary and 7 recurrent/metastatic tumors with unique chromosomal aberration profiles as categorized by our genomic sub-grouping system. Overall, a low frequency of somatic mutations was found. Besides ALK (4/64, 6.3%), SEMA6C, SLIT1 and NRAS, genes involved in the axon guidance pathway, were identified as recurrently mutated in 6 of 64 tumors (9.4%). Pathway enrichment analysis revealed enrichment of 25 mutated genes in the mitogen-activated protein kinase (MAPK) pathway, 13 genes in the Wnt pathway, and 12 genes in the axon guidance pathway. Genomic analyses demonstrated that primary and matched recurrent or metastatic tumors obtained from sporadic and monozygotic twin NBs were clonally related with variable extents of genetic heterogeneity. Monozygotic twin NBs displayed different evolutionary trajectories. These results indicate the involvement of the axon guidance, MAPK and Wnt pathways in NB and demonstrate genomic diversity with NB progression.

BRCA1 alterations with additional defects in DNA damage response genes may confer chemoresistance to BRCA-like breast cancers treated with neoadjuvant chemotherapy

The BRCA-like phenotype is a feature that some sporadic breast cancers share with those occurring in BRCA1 or BRCA2 mutation carriers. As tumors with the phenotype have defects in the DNA damage response pathway, which may increase sensitivity to drugs such as DNA cross-linking agents and PARP inhibitors, a method to identify this phenotype is important. The prediction of chemoresistance, which frequently develops in these tumors, is also crucial for improving therapy. We examined genomic aberrations and BRCA1 promoter methylation in tumors of 73 breast cancer (20 HR-/HER2- and 53 HR+/HER2-) patients, who received neoadjuvant chemotherapy with anthracycline, cyclophosphamide, and taxane, using SNP array CGH and quantitative PCR. The methylation and/or loss or uniparental disomy (UPD) of BRCA1 (BRCA1 alterations) and the loss or UPD of BRCA2 (BRCA2 alterations) were detected in 27 (37%) and 21 (29%), respectively, of the 73 tumors. Tumors with BRCA1 or BRCA2 alterations were associated with a higher number of genomic aberrations (P < 0.001 and P < 0.001) and higher percentage of TP53 alterations (P < 0.001 and P < 0.001) than those without. Overall survival (OS) rates were similar between patients with or without BRCA1 or BRCA2 alterations. However, when 27 patients with BRCA1-altered tumors were classified into those with or without the loss or UPD of PALB2, PAGR1, RAD51B, FANCM, MLL4, or ERCC1/2 in tumors, patients with additional defects in DNA damage response genes had worse OS (P = 0.037, 0.045, 0.038, 0.044, 0.041, or 0.019) than those without. These defects may confer chemoresistance and predict poor outcomes in patients with BRCA1-altered breast cancer.

Relationship of immunohistochemistry, copy number aberrations and epigenetic disorders with BRCAness pattern in hereditary and sporadic breast cancer

The study aims to identify the relevance of immunohistochemistry (IHC), copy number aberrations (CNA) and epigenetic disorders in BRCAness breast cancers (BCs). We studied 95 paraffin included BCs, of which 41 carried BRCA1/BRCA2 germline mutations and 54 were non hereditary (BRCAX/Sporadic). Samples were assessed for BRCA1ness and CNAs by Multiplex Ligation-dependent Probe Amplification (MLPA); promoter methylation (PM) was assessed by methylation-specific-MLPA and the expression of miR-4417, miR-423-3p, miR-590-5p and miR-187-3p by quantitative RT-PCR. IHC markers Ki67, ER, PR, HER2, CK5/6, EGFR and CK18 were detected with specific primary antibodies (DAKO, Denmark). BRCAness association with covariates was performed using multivariate binary logistic regression (stepwise backwards Wald option). BRCA1/2 mutational status (p = 0.027), large tumor size (p = 0.041) and advanced histological grade (p = 0.017) among clinic-pathological variables; ER (p < 0.001) among IHC markers; MYC (p < 0.001) among CNA; APC (p = 0.065), ATM (p = 0.014) and RASSF1 (p = 0.044) among PM; and miR-590-5p (p = 0.001), miR-4417 (p = 0.019) and miR-423 (p = 0.013) among microRNA expression, were the selected parameters significantly related with the BRCAness status. The logistic regression performed with all these parameters selected ER+ as linked with the lack of BRCAness (p = 0.001) and MYC CNA, APC PM and miR-590-5p expression with BRCAness (p = 0.014, 0.045 and 0.007, respectively). In conclusion, the parameters ER expression, APC PM, MYC CNA and miR-590-5p expression, allowed detection of most BRCAness BCs. The identification of BRCAness can help establish a personalized medicine addressed to predict the response to specific treatments.

A new phosphorylated form of Ku70 identified in resistant leukemic cells confers fast but unfaithful DNA repair in cancer cell lines

Ku70-dependent canonical nonhomologous end-joining (c-NHEJ) DNA repair system is fundamental to the genome maintenance and B-cell lineage. c-NHEJ is upregulated and error-prone in incurable forms of chronic lymphocytic leukemia which also displays telomere dysfunction, multiple chromosomal aberrations and the resistance to DNA damage-induced apoptosis. We identify in these cells a novel DNA damage inducible form of phospho-Ku70. In vitro in different cancer cell lines, Ku70 phosphorylation occurs in a heterodimer Ku70/Ku80 complex within minutes of genotoxic stress, necessitating its interaction with DNA damage-induced kinase pS2056-DNA-PKcs and/or pS1981-ATM. The mutagenic effects of phospho-Ku70 are documented by a defective S/G2 checkpoint, accelerated disappearance of γ-H2AX foci and kinetics of DNA repair resulting in an increased level of genotoxic stress-induced chromosomal aberrations. Together, these data unveil an involvement of phospho-Ku70 in fast but inaccurate DNA repair; a new paradigm linked to both the deregulation of c-NHEJ and the resistance of malignant cells.

ZNF281 contributes to the DNA damage response by controlling the expression of XRCC2 and XRCC4

ZNF281 is a zinc-finger factor involved in the control of cellular stemness and epithelial-mesenchymal transition (EMT). Here, we report that ZNF281 expression increased after genotoxic stress caused by DNA-damaging drugs. Comet assays demonstrated that DNA repair was delayed in cells silenced for the expression of ZNF281 and treated with etoposide. Furthermore, the expression of 10 DNA damage response genes was downregulated in cells treated with etoposide and silenced for ZNF281. In line with this finding, XRCC2 and XRCC4, two genes that take part in homologous recombination and non-homologous end joining, respectively, were transcriptionally activated by ZNF281 through a DNA-binding-dependent mechanism, as demonstrated by luciferase assays and Chromatin crosslinking ImmunoPrecipitation experiments. c-Myc, which also binds to the promoters of XRCC2 and XRCC4, was unable to promote their transcription or to modify ZNF281 activity. Of interest, bioinformatic analysis of 1971 breast cancer patients disclosed a significant correlation between the expression of ZNF281 and that of XRCC2. In summary, our data highlight, for the first time, the involvement of ZNF281 in the cellular response to genotoxic stress through the control exercised on the expression of genes that act in different repair mechanisms.

The Role of miR-34a in Tritiated Water Toxicity in Human Umbilical Vein Endothelial Cells

In this work, we investigated the toxic effects of tritiated water (HTO) on the cardiovascular system. We examined the role of microRNA-34a (miR-34a) in DNA damage and repair in human umbilical vein endothelial cells (HUVECs) exposed to HTO. Cell proliferation capacity was evaluated by cell counting, and miR-34a expression was detected using quantitative PCR (QT-PCR). The Comet assay and γ-H2AX immunostaining were used to measure DNA double-strand breaks (DSBs). Reverse transcription polymerase chain reaction was used to measure the expression level of c-myc messenger RNA (mRNA). The cells exposed to HTO showed significantly lower proliferation than the control cells over 3 days. The DNA damage in the HTO group was more severe than that in the control group, at each time point examined. The expression of miR-34a mimics caused increased DNA DSBs whereas that of the miR-34a inhibitor caused decreased DNA DSBs. The proliferation viability was the opposite for the miR-34a mimics and inhibitor groups. The expression levels of c-myc mRNA in cells transfected with miR-34a mimics were lower than that in cells transfected with the miR-34a-5p inhibitor, at 0.5 hours and 2 hours after transfection. In summary, miR-34a mediates HTO toxicity in HUVECs by downregulating the expression of c-myc.

Effects of Low-Dose Bisphenol A on DNA Damage and Proliferation of Breast Cells: The Role of c-Myc

BACKGROUND

Humans are exposed to low-dose bisphenol A (BPA) through plastic consumer products and dental sealants containing BPA. Although a number of studies have investigated the mammary gland effects after high-dose BPA exposure, the study findings differ. Furthermore, there has been a lack of mechanistic studies.

OBJECTIVE

The objective of this study was to investigate the effect and the mechanism of low-dose BPA in mammary gland cells.

METHODS

We evaluated DNA damage following BPA exposure using the comet assay and immunofluorescence staining, and used cell counting and three-dimensional cultures to evaluate effects on proliferation. We examined the expressions of markers of DNA damage and cell-cycle regulators by immunoblotting and performed siRNA-mediated gene silencing to determine the role of c-Myc in regulating BPA's effects.

RESULTS

Low-dose BPA significantly promoted DNA damage, up-regulated c-Myc and other cell-cycle regulatory proteins, and induced proliferation in parallel in estrogen receptor-α (ERα)-negative mammary cells. Silencing c-Myc diminished these BPA-induced cellular events, suggesting that c-Myc is essential for regulating effects of BPA on DNA damage and proliferation in mammary cells.

CONCLUSIONS

Low-dose BPA exerted c-Myc-dependent genotoxic and mitogenic effects on ERα-negative mammary cells. These findings provide significant evidence of adverse effects of low-dose BPA on mammary cells.

Cathepsin L suppression increases the radiosensitivity of human glioma U251 cells via G2/M cell cycle arrest and DNA damage

AIM

Cathepsin L is a lysosomal cysteine protease that plays important roles in cancer tumorigenesis, proliferation and chemotherapy resistance. The aim of this study was to determine how cathepsin L regulated the radiosensitivity of human glioma cells in vitro.

METHODS

Human glioma U251 cells (harboring the mutant type p53 gene) and U87 cells (harboring the wide type p53 gene) were irradiated with X-rays. The expression of cathepsin L was analyzed using Western blot and immunofluorescence assays. Cell survival and DNA damage were evaluated using clonogenic and comet assays, respectively. Flow cytometry was used to detect the cell cycle distribution. Apoptotic cells were observed using Hoechst 33258 staining and fluorescence microscopy.

RESULTS

Irradiation significantly increased the cytoplasmic and nuclear levels of cathepsin L in U251 cells but not in U87 cells. Treatment with the specific cathepsin L inhibitor Z-FY-CHO (10 μmol/L) or transfection with cathepsin L shRNA significantly increased the radiosensitivity of U251 cells. Both suppression and knockdown of cathepsin L in U251 cells increased irradiation-induced DNA damage and G2/M phase cell cycle arrest. Both suppression and knockdown of cathepsin L in U251 cells also increased irradiation-induced apoptosis, as shown by the increased levels of Bax and decreased levels of Bcl-2.

CONCLUSION

Cathepsin L is involved in modulation of radiosensitivity in human glioma U251 cells (harboring the mutant type p53 gene) in vitro.

Elevated expression of CCAT2 is associated with poor prognosis in esophageal squamous cell carcinoma

BACKGROUND AND OBJECTIVES

CCAT2, a novel long non-coding RNAs (lncRNAs), is found to promote the metastasis and invasion of colon, lung, and breast cancers. This study aimed to investigate the level of CCAT2 in esophageal squamous cell carcinoma (ESCC) and to elucidate its clinical significance.

METHODS

The expression level of CCAT2 and the status of MYC amplification were examined in 229 ESCC samples using quantitative real- time PCR.

RESULTS

CCAT2 was upregulated in ESCC tissues, especially in cases with lymph node metastasis (LNM), advanced TNM stages, and MYC amplification. Furthermore, the level of CCAT2 was positively correlated with TNM stages, LNM, and the number of positive lymph nodes. High CCAT2 expression and MYC amplification were significantly associated with TNM stages and LNM. Survival analyses revealed that high CCAT2 expression and MYC amplification were significantly associated with poorer overall survival in ESCC patients. Furthermore, patients with high CCAT2 expression and MYC amplification had a 2.199-fold increased risk of death compared with those with low CCAT2 expression and MYC non-amplification.

CONCLUSIONS

Our study provides the first evidence associating CCAT2 expression and poor survival in ESCC. CCAT2 may be a prognostic biomarker and therapeutic target for ESCC.

Immunohistochemical, genetic and epigenetic profiles of hereditary and triple negative breast cancers. Relevance in personalized medicine

This study aims to identify the profile of immunohistochemical (IHC) parameters, copy number aberrations (CNAs) and epigenetic alterations [promoter methylation (PM) and miR expression] related to hereditary (H) and triple negative (TN) breast cancer (BC). This profile could be of relevance for guiding tumor response to treatment with targeting therapy. The study comprises 278 formalin fixed paraffin-embedded BCs divided into two groups: H group, including 88 hereditary BC (HBC) and 190 non hereditary (NHBC), and TN group, containing 79 TNBC and 187 non TNBC (NTNBC). We assessed IHC parameters (Ki67, ER, PR, HER2, CK5/6, CK18 and Cadherin-E), CNA of 20 BC related genes, and PM of 24 tumor suppressor genes employing MLPA/MS-MLPA (MRC Holland, Amsterdam). MiR-4417, miR-423-3p, miR-590-5p and miR-187-3p expression was assessed by quantitative RT-PCR (Applied Biosystems). Binary logistic regression was applied to select the parameters that better differentiate the HBC or TN groups. For HBC we found that, ER expression, ERBB2 CNA and PM in RASSF1 and TIMP3 were associated with NHBC whereas; MYC and AURKA CNA were linked to HBC. For TNBC, we found that CDC6 CNA, GSTP1 and RASSF1 PM and miR-423-3p hyperexpression were characteristic of NTNBC, while MYC aberrations, BRCA1 hypermethylation and miR-590-5p and miR-4417 hyperexpression were more indicative of TNBC. The selected markers allow establishing BC subtypes, which are characterized by showing similar etiopathogenetic mechanisms, some of them being molecular targets for known drugs or possible molecular targets. These results could be the basis to implement a personalized therapy.

The involvement of c-Myc in the DNA double-strand break repair via regulating radiation-induced phosphorylation of ATM and DNA-PKcs activity

Deregulation of c-Myc often occurs in various human cancers, which not only contributes to the genesis and progression of cancers but also affects the outcomes of cancer radio- or chemotherapy. In this study, we have investigated the function of c-Myc in the repair of DNA double-strand break (DSB) induced by γ-ray irradiation. A c-Myc-silenced Hela-630 cell line was generated from HeLa cells using RNA interference technology. The DNA DSBs were detected by γ-H2AX foci, neutral comet assay and pulsed-field gel electrophoresis. We found that the capability of DNA DSB repair in Hela-630 cells was significantly reduced, and the repair kinetics of DSB was delayed as compared to the control Hela-NC cells. Silence of c-myc sensitized the cellular sensitivity to ionizing radiation. The phosphorylated c-Myc (Thr58/pSer62) formed the consistent co-localisation foci with γ-H2AX as well as the phosphorylated DNA-PKcs/S2056 in the irradiated cells. Moreover, depression of c-Myc largely attenuated the ionizing radiation-induced phosphorylation of the ataxia telangiectasia mutated (ATM) and decreased the in vitro kinase activity of DNA-PKcs. Taken together, our results demonstrated that c-Myc protein functions in the process of DNA double-strand break repair, at least partially, through affecting the ATM phosphorylation and DNA-PKcs kinase activity. The overexpression of c-Myc in tumours can account for the radioresistance of some tumour cell types.

MYC impairs resolution of site-specific DNA double-strand breaks repair

Although it is established that when overexpressed, the MYC family proteins can cause DNA double-stand breaks (DSBs) and genome instability, the mechanisms involved remain unclear. MYC induced genetic instability may result from increased DNA damage and/or reduced DNA repair. Here we show that when overexpressed, MYC proteins induce a sustained DNA damage response (DDR) and reduce the wave of DSBs repair. We used a cell-based DSBs system whereby, upon induction of an inducible restriction enzyme AsiSI, hundreds of site-specific DSBs are generated across the genome to investigate the role of MYC proteins on DSB. We found that high levels of MYC do not block accumulation of γH2AX at AsiSI sites, but delay its clearance, indicating an inefficient repair, while the initial recognition of DNA damage is largely unaffected. Repair of both homologous and nonhomologous repair-prone segments, characterized by high or low levels of recruited RAD51, respectively, was delayed. Collectively, these data indicate that high levels of MYC proteins delay the resolution of DNA lesions engineered to occur in cell cultures.

c-MYC is a radiosensitive locus in human breast cells

Ionising radiation is a potent human carcinogen. Epidemiological studies have shown that adolescent and young women are at increased risk of developing breast cancer following exposure to ionising radiation compared with older women, and that risk is dose-dependent. Although it is well understood which individuals are at risk of radiation-induced breast carcinogenesis, the molecular genetic mechanisms that underlie cell transformation are less clear. To identify genetic alterations potentially responsible for driving radiogenic breast transformation, we exposed the human breast epithelial cell line MCF-10A to fractionated doses of X-rays and examined the copy number and cytogenetic alterations. We identified numerous alterations of c-MYC that included high-level focal amplification associated with increased protein expression. c-MYC amplification was also observed in primary human mammary epithelial cells following exposure to radiation. We also demonstrate that the frequency and magnitude of c-MYC amplification and c-MYC protein expression is significantly higher in breast cancer with antecedent radiation exposure compared with breast cancer without a radiation aetiology. Our data also demonstrate extensive intratumor heterogeneity with respect to c-MYC copy number in radiogenic breast cancer, suggesting continuous evolution at this locus during disease development and progression. Taken together, these data identify c-MYC as a radiosensitive locus, implicating this oncogenic transcription factor in the aetiology of radiogenic breast cancer.

Identification of synthetic lethality of PRKDC in MYC-dependent human cancers by pooled shRNA screening

Background

MYC family members are among the most frequently deregulated oncogenes in human cancers, yet direct therapeutic targeting of MYC in cancer has been challenging thus far. Synthetic lethality provides an opportunity for therapeutic intervention of MYC-driven cancers.

Methods

A pooled kinase shRNA library screen was performed and next-generation deep sequencing efforts identified that PRKDC was synthetically lethal in cells overexpressing MYC. Genes and proteins of interest were knocked down or inhibited using RNAi technology and small molecule inhibitors, respectively. Quantitative RT-PCR using TaqMan probes examined mRNA expression levels and cell viability was assessed using CellTiter-Glo (Promega). Western blotting was performed to monitor different protein levels in the presence or absence of RNAi or compound treatment. Statistical significance of differences among data sets were determined using unpaired t test (Mann–Whitney test) or ANOVA.

Results

Inhibition of PRKDC using RNAi (RNA interference) or small molecular inhibitors preferentially killed MYC-overexpressing human lung fibroblasts. Moreover, inducible PRKDC knockdown decreased cell viability selectively in high MYC-expressing human small cell lung cancer cell lines. At the molecular level, we found that inhibition of PRKDC downregulated MYC mRNA and protein expression in multiple cancer cell lines. In addition, we confirmed that overexpression of MYC family proteins induced DNA double-strand breaks; our results also revealed that PRKDC inhibition in these cells led to an increase in DNA damage levels.

Conclusions

Our data suggest that the synthetic lethality between PRKDC and MYC may in part be due to PRKDC dependent modulation of MYC expression, as well as MYC-induced DNA damage where PRKDC plays a key role in DNA damage repair.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2407-14-944) contains supplementary material, which is available to authorized users.

Cancer subclonal genetic architecture as a key to personalized medicine

The future of personalized oncological therapy will likely rely on evidence-based medicine to integrate all of the available evidence to delineate the most efficacious treatment option for the patient. To undertake evidence-based medicine through use of targeted therapy regimens, identification of the specific underlying causative mutation(s) driving growth and progression of a patient's tumor is imperative. Although molecular subtyping is important for planning and treatment, intraclonal genetic diversity has been recently highlighted as having significant implications for biopsy-based prognosis. Overall, delineation of the clonal architecture of a patient's cancer and how this will impact on the selection of the most efficacious therapy remain a topic of intense interest.

Clinicopathologic and prognostic significance of c-MYC copy number gain in lung adenocarcinomas

BACKGROUND

c-MYC copy number gain (c-MYC gain) has been associated with aggressive behaviour in several cancers. However, the role of c-MYC gain has not yet been determined in lung adenocarcinomas classified by genetic alterations in epidermal growth factor receptor (EGFR), KRAS, and anaplastic lymphoma kinase (ALK) genes. We investigated the clinicopathologic and prognostic significance of c-MYC gain for disease-free survival (DFS) and overall survival (OS) according to EGFR, KRAS, and ALK gene status and stages in lung adenocarcinomas.

METHODS

In 255 adenocarcinomas resected in Seoul National University Bundang Hospital from 2003 to 2009, fluorescence in situ hybridisation (FISH) with c-MYC probe and centromeric enumeration probe 8 (CEP8) was analysed using tissue microarray containing single representative core per each case. EGFR (codon 18 to 21) and KRAS (codon 12, 13, and 61) mutations were analysed by polymerase chain reaction and direct sequencing method from formalin-fixed, paraffin-embedded tissue sections. ALK rearrangement was determined by FISH method. c-MYC gain was defined as >2 copies per nucleus, chromosome 8 gain as ⩾3 copies per nucleus, and gain of c-MYC:CEP8 ratio (hereafter, c-MYC amplification) as ⩾2.

RESULTS

We observed c-MYC gain in 20% (51 out of 255), chromosome 8 gain in 5.5% (14 out of 255), c-MYC amplification in 2.4% (6 out of 255), EGFR mutation in 49.4% (118 out of 239), KRAS mutation in 5.7% (7 out of 123), and ALK rearrangement in 4.9% (10 out of 205) of lung adenocarcinomas. c-MYC gain was observed in 19% (22 out of 118) of patients with lung adenocarcinomas with an EGFR mutation, but not in any patients with a KRAS mutation, or an ALK rearrangement. c-MYC gain (but not chromosome 8 gain or c-MYC amplification) was an independent poor-prognostic factor in the full cohort of lung adenocarcinoma (P=0.022, hazard ratio (HR)=1.71, 95% confidence interval (CI), 1.08-2.69 for DFS; P=0.032, HR=2.04, 95% CI, 1.06-3.91 for OS), as well as in stage I subgroup (P=0.023, HR=4.70, 95% CI, 1.24-17.78 for DFS; P=0.031, HR=4.65, 95% CI, 1.15-18.81 for OS), and in EGFR-mutant subgroup (P=0.022; HR=2.14; 95% CI, 1.11-4.10 for DFS).

CONCLUSIONS

c-MYC gain (but not chromosome 8 gain or c-MYC amplification) was an independent poor-prognostic factor for DFS and OS in lung adenocarcinomas, both in full cohort and stage I cancer, and possibly for DFS in EGFR-mutant adenocarcinomas. Additional studies are required to determine if patients with lung adenocarcinoma with c-MYC gain are candidates for additional first-line treatment to mitigate their increased risk for disease progression and death.

Role of Ku70 in deubiquitination of Mcl-1 and suppression of apoptosis

Mcl-1 is a unique antiapoptotic Bcl2 family member with a short half-life due to its rapid turnover through ubiquitination. We discovered that Ku70, a DNA double-strand break repair protein, functions as a deubiquitinase to stabilize Mcl-1. Ku70 knockout in mouse embryonic fibroblast (MEF) cells or depletion from human lung cancer H1299 cells leads to the accumulation of polyubiquitinated Mcl-1 and a reduction in its half-life and protein expression. Conversely, expression of exogenous Ku70 in Ku70(-/-) MEF cells restores Mcl-1 expression. Subcellular fractionation indicates that Ku70 extensively colocalizes with Mcl-1 in mitochondria, endoplasmic reticulum and nucleus in H1299 cells. Ku70 directly interacts with Mcl-1 via its C terminus (that is, aa 536-609), which is required and sufficient for deubiquitination and stabilization of Mcl-1, leading to suppression of apoptosis. Purified Ku70 protein directly deubiquitinates Mcl-1 by removing K48-linked polyubiquitin chains. Ku70 knockdown not only promotes Mcl-1 turnover but also enhances antitumor efficacy of the BH3-mimetic ABT-737 in human lung cancer xenografts. These findings identify Ku70 as a novel Mcl-1 deubiquitinase that could be a potential target for cancer therapy by manipulating Mcl-1 deubiquitination.

c-MYC-induced genomic instability

MYC dysregulation initiates a dynamic process of genomic instability that is linked to tumor initiation. Early studies using MYC-carrying retroviruses showed that these viruses were potent transforming agents. Cell culture models followed that addressed the role of MYC in transformation. With the advent of MYC transgenic mice, it became obvious that MYC deregulation alone was sufficient to initiate B-cell neoplasia in mice. More than 70% of all tumors have some form of c-MYC gene dysregulation, which affects gene regulation, microRNA expression profiles, large genomic amplifications, and the overall organization of the nucleus. These changes set the stage for the dynamic genomic rearrangements that are associated with cellular transformation.

The DNA double-strand break response is abnormal in myeloblasts from patients with therapy-related acute myeloid leukemia

The complex chromosomal aberrations found in therapy-related acute myeloid leukemia (t-AML) suggest that the DNA double-strand break (DSB) response may be altered. In this study we examined the DNA DSB response of primary bone marrow cells from t-AML patients and performed next-generation sequencing of 37 canonical homologous recombination (HR) and non-homologous end-joining (NHEJ) DNA repair genes, and a subset of DNA damage response genes using tumor and paired normal DNA obtained from t-AML patients. Our results suggest that the majority of t-AML patients (11 of 15) have tumor-cell intrinsic, functional dysregulation of their DSB response. Distinct patterns of abnormal DNA damage response in myeloblasts correlated with acquired genetic alterations in TP53 and the presence of inferred chromothripsis. Furthermore, the presence of trisomy 8 in tumor cells was associated with persistently elevated levels of DSBs. Although tumor-acquired point mutations or small indels in canonical HR and NHEJ genes do not appear to be a dominant means by which t-AML leukemogenesis occurs, our functional studies suggest that an abnormal response to DNA damage is a common finding in t-AML.

Myc-dependent genome instability and lifespan in Drosophila

The Myc family of transcription factors are key regulators of cell growth and proliferation that are dysregulated in a large number of human cancers. When overexpressed, Myc family proteins also cause genomic instability, a hallmark of both transformed and aging cells. Using an in vivo lacZ mutation reporter, we show that overexpression of Myc in Drosophila increases the frequency of large genome rearrangements associated with erroneous repair of DNA double-strand breaks (DSBs). In addition, we find that overexpression of Myc shortens adult lifespan and, conversely, that Myc haploinsufficiency reduces mutation load and extends lifespan. Our data provide the first evidence that Myc may act as a pro-aging factor, possibly through its ability to greatly increase genome instability.