Regulation of the activation of the Fanconi anemia pathway by the p21 cyclin-dependent kinase inhibitor

The P53-P21-RB1 pathway promotes BRD4 degradation in liver cancer through USP1

Liver cancer is notoriously refractory to conventional therapeutics. Tumor progression is governed by the interplay between tumor-promoting genes and tumor-suppressor genes. BRD4, an acetyl lysine-binding protein, is overexpressed in many cancer types, which promotes activation of a pro-tumor gene network. But the underlying mechanism for BRD4 overexpression remains incompletely understood. In addition, understanding the regulatory mechanism of BRD4 protein level will shed insight into BRD4-targeting therapeutics. In this study, we investigated the potential relation between BRD4 protein level and P53, the most frequently dysregulated tumor suppressor. By analyzing the TCGA datasets, we first identify a strong negative correlation between protein levels of P53 and BRD4 in liver cancer. Further investigation shows that P53 promotes BRD4 protein degradation. Mechanistically, P53 indirectly represses the transcription of USP1, a deubiquitinase, through the P21-RB1 axis. USP1 itself is also overexpressed in liver cancer and we show USP1 deubiquitinates BRD4 in vivo and in vitro, which increases BRD4 stability. With cell proliferation assays and xenograft model, we show the pro-tumor role of USP1 is partially mediated by BRD4. With functional transcriptomic analysis, we find the USP1-BRD4 axis upholds expression of a group of cancer-related genes. In summary, we identify a functional P53-P21-RB1-USP1-BRD4 axis in liver cancer.

Ubiquitin-specific peptidase 1: assessing its role in cancer therapy

Reversible protein ubiquitination represents an essential determinator of cellular homeostasis, and the ubiquitin-specific enzymes, particularly deubiquitinases (DUBs), are emerging as promising targets for drug development. DUBs are composed of seven different subfamilies, out of which ubiquitin-specific proteases (USPs) are the largest family with 56 members. One of the well-characterized USPs is USP1, which contributes to several cellular biological processes including DNA damage response, immune regulation, cell proliferation, apoptosis, and migration. USP1 levels and activity are regulated by multiple mechanisms, including transcription regulation, phosphorylation, autocleavage, and proteasomal degradation, ensuring that the cellular function of USP1 is performed in a suitably modulated spatio-temporal manner. Moreover, USP1 with deregulated expression and activity are found in several human cancers, indicating that targeting USP1 is a feasible therapeutic approach in anti-cancer treatment. In this review, we highlight the essential role of USP1 in cancer development and the regulatory landscape of USP1 activity, which might provide novel insights into cancer treatment.

Fanconi anemia pathway regulation by FANCI in prostate cancer

Prostate cancer is one of the leading causes of death among men worldwide, and thus, research on the genetic factors enabling the formation of treatment-resistant cancer cells is crucial for improving patient outcomes. Here, we report a cell line-specific dependence on FANCI and related signaling pathways to counteract the effects of DNA-damaging chemotherapy in prostate cancer. Our results reveal that FANCI depletion results in significant downregulation of Fanconi anemia (FA) pathway members in prostate cancer cells, indicating that FANCI is an important regulator of the FA pathway. Furthermore, we found that FANCI silencing reduces proliferation in p53-expressing prostate cancer cells. This extends the evidence that inactivation of FANCI may convert cancer cells from a resistant state to an eradicable state under the stress of DNA-damaging chemotherapy. Our results also indicate that high expression of FA pathway genes correlates with poorer survival in prostate cancer patients. Moreover, genomic alterations of FA pathway members are prevalent in prostate adenocarcinoma patients; mutation and copy number information for the FA pathway genes in seven patient cohorts (N = 1,732 total tumor samples) reveals that 1,025 (59.2%) tumor samples have an alteration in at least one of the FA pathway genes, suggesting that genomic alteration of the pathway is a prominent feature in patients with the disease.

Gene therapy restores the transcriptional program of hematopoietic stem cells in Fanconi anemia

Clinical trials have shown that lentiviral-mediated gene therapy can ameliorate bone marrow failure (BMF) in nonconditioned Fanconi anemia (FA) patients resulting from the proliferative advantage of corrected FA hematopoietic stem and progenitor cells (HSPC). However, it is not yet known if gene therapy can revert affected molecular pathways in diseased HSPC. Single-cell RNA sequencing was performed in chimeric populations of corrected and uncorrected HSPC co-existing in the BM of gene therapy-treated FA patients. Our study demonstrates that gene therapy reverts the transcriptional signature of FA HSPC, which then resemble the transcriptional program of healthy donor HSPC. This includes a down-regulated expression of TGF-β and p21, typically up-regulated in FA HSPC, and upregulation of DNA damage response and telomere maintenance pathways. Our results show for the first time the potential of gene therapy to rescue defects in the HSPC transcriptional program from patients with inherited diseases; in this case, in FA characterized by BMF and cancer predisposition.

Inhibition of USP1 activates ER stress through Ubi-protein aggregation to induce autophagy and apoptosis in HCC

The deubiquitinating enzyme USP1 (ubiquitin-specific protease 1) plays a role in the progression of various tumors, emerging as a potential therapeutic target. This study aimed to determine the role of USP1 as a therapeutic target in hepatocellular carcinoma (HCC). We detected USP1 expression in the tumor and adjacent tissues of patients with HCC using immunohistochemical staining. We evaluated the effect of the USP1 inhibitor ML-323 on HCC cell proliferation and cell cycle using a CCK-8 cell-counting kit and plate cloning assays, and propidium iodide, respectively. Apoptosis was detected by annexin V-FITC/Propidium Iodide (PI) staining and caspase 3 (casp3) activity. Transmission electron microscopy and LC3B immunofluorescence were used to detect autophagy. Western blotting was used to detect the accumulation of ubiquitinated proteins, the expression of endoplasmic reticulum (ER) stress-related proteins, and the AMPK-ULK1/ATG13 signaling pathway. We demonstrated that ML-323 inhibits the growth of HCC cells and induces G1 phase cell cycle arrest by regulating cyclin expression. ML-323 treatment resulted in the accumulation of ubiquitinated proteins, induced ER stress, and triggered Noxa-dependent apoptosis, which was regulated by the Activating Transcription Factor 4(ATF4). Moreover, active ER stress induces protective autophagy by increasing AMPK phosphorylation; therefore, we inhibited ER stress using 4-Phenylbutyric acid (4-PBA), which resulted in ER stress reduction, apoptosis, and autophagy in ML-323-treated HCC cells. In addition, blocking autophagy using the AMPK inhibitor compound C (CC), chloroquine (CQ), or bafilomycin A1 (BafA1) enhanced the cytotoxic effect of ML-323. Our findings revealed that targeting USP1 may be a potential strategy for the treatment of HCC.

Revisiting the Function of p21CDKN1A in DNA Repair: The Influence of Protein Interactions and Stability

The p21CDKN1A protein is an important player in the maintenance of genome stability through its function as a cyclin-dependent kinase inhibitor, leading to cell-cycle arrest after genotoxic damage. In the DNA damage response, p21 interacts with specific proteins to integrate cell-cycle arrest with processes such as transcription, apoptosis, DNA repair, and cell motility. By associating with Proliferating Cell Nuclear Antigen (PCNA), the master of DNA replication, p21 is able to inhibit DNA synthesis. However, to avoid conflicts with this process, p21 protein levels are finely regulated by pathways of proteasomal degradation during the S phase, and in all the phases of the cell cycle, after DNA damage. Several lines of evidence have indicated that p21 is required for the efficient repair of different types of genotoxic lesions and, more recently, that p21 regulates DNA replication fork speed. Therefore, whether p21 is an inhibitor, or rather a regulator, of DNA replication and repair needs to be re-evaluated in light of these findings. In this review, we will discuss the lines of evidence describing how p21 is involved in DNA repair and will focus on the influence of protein interactions and p21 stability on the efficiency of DNA repair mechanisms.

Fanconi anemia: current insights regarding epidemiology, cancer, and DNA repair

Fanconi anemia is a genetic disorder that is characterized by bone marrow failure, as well as a predisposition to malignancies including leukemia and squamous cell carcinoma (SCC). At least 22 genes are associated with Fanconi anemia, constituting the Fanconi anemia DNA repair pathway. This pathway coordinates multiple processes and proteins to facilitate the repair of DNA adducts including interstrand crosslinks (ICLs) that are generated by environmental carcinogens, chemotherapeutic crosslinkers, and metabolic products of alcohol. ICLs can interfere with DNA transactions, including replication and transcription. If not properly removed and repaired, ICLs cause DNA breaks and lead to genomic instability, a hallmark of cancer. In this review, we will discuss the genetic and phenotypic characteristics of Fanconi anemia, the epidemiology of the disease, and associated cancer risk. The sources of ICLs and the role of ICL-inducing chemotherapeutic agents will also be discussed. Finally, we will review the detailed mechanisms of ICL repair via the Fanconi anemia DNA repair pathway, highlighting critical regulatory processes. Together, the information in this review will underscore important contributions to Fanconi anemia research in the past two decades.

Toward Targeted Therapies in Oesophageal Cancers: An Overview

Oesophageal cancer is one of the leading causes of cancer-related death worldwide. Oesophageal cancer occurs as squamous cell carcinoma (ESCC) or adenocarcinoma (EAC). Prognosis for patients with either ESCC or EAC is poor, with less than 20% of patients surviving more than 5 years after diagnosis. A major progress has been made in the development of biomarker-driven targeted therapies against breast and lung cancers, as well as melanoma. However, precision oncology for patients with oesophageal cancer is still virtually non-existent. In this review, we outline the recent advances in oesophageal cancer profiling and clinical trials based on targeted therapies in this disease.

Immunohistochemical analysis of BRCA1 and acetyl-histone H3 in squamous cell carcinoma of the mobile tongue

OBJECTIVE

The objective of this study was to evaluate the immunoexpression profiles of breast cancer 1 (BRCA1) and acetyl-histone H3 (AcH3) in squamous cell carcinoma of the mobile tongue (SCC-MT) and their correlation with epidemiologic data and the histopathological grade of tumors.

STUDY DESIGN

Incisional biopsies of 43 SCC-MT were submitted to immunohistochemistry for AcH3 and BRCA1. Samples were microscopically graded as well differentiated (n = 21) or poorly differentiated (n = 22). Both groups were submitted to statistical analysis (P < .05) regarding the percentage of positive cells.

RESULTS

Thirty-nine cases were positive for AcH3 (91%), but no difference was observed for the histologic grading (P = .27). Positivity for BRCA1 was observed in all samples regardless of their cellular locations. Most cases in the poorly differentiated group presented with less than 10% nuclear staining (P < .01) and a predominance of cytoplasmic staining (P = .034). The well-differentiated group showed nuclear staining in most of the cases, with more than 50% of cells staining positive (P < .01).

CONCLUSION

AcH3 and BRCA1 were expressed in all samples. There was a significant decrease in cytoplasmic BRCA1 expression in the poorly differentiated group, suggesting BRCA1 as a possible prognostic marker for SCC-MT.

RUNX3 Transcript Variants Have Distinct Roles in Ovarian Carcinoma and Differently Influence Platinum Sensitivity and Angiogenesis

Simple Summary

Epithelial ovarian cancer treatment is limited by missing predictive markers, frequent chemotherapy resistance and an incomplete understanding of the biology of tumors. Earlier work proved that hypermethylation of the gene RUNX3 coding for a transcription factor has prognostic value, and RUNX3 transcript variant overexpression, regulated by this epigenetic mechanism, influences cisplatin sensitivity and malignant properties of cells contrary. The present data validate RUNX3 transcript variant-specific effects for high-grade serous ovarian cancer and identify RUNX3-regulated genes and processes. Specifically, DNA damage repair and angiogenesis are influenced by RUNX3, and transcript variant 1 mediates stronger carcinogenic properties.

Abstract

The prognosis of late-stage epithelial ovarian cancer (EOC) patients is affected by chemotherapy response and the malignant potential of the tumor cells. In earlier work, we identified hypermethylation of the runt-related transcription factor 3 gene (RUNX3) as a prognostic biomarker and contrary functions of transcript variants (TV1 and TV2) in A2780 and SKOV3 cells. The aim of the study was to further validate these results and to increase the knowledge about RUNX3 function in EOC. New RUNX3 overexpression models of high-grade serous ovarian cancer (HGSOC) were established and analyzed for phenotypic (IC₅₀ determination, migration, proliferation and angiogenesis assay, DNA damage analysis) and transcriptomic consequences (NGS) of RUNX3 TV1 and TV2 overexpression. Platinum sensitivity was affected by a specific transcript variant depending on BRCA background. RUNX3 TV2 induced an increased sensitivity in BRCA1^wt cells (OVCAR3), whereas TV1 increased the sensitivity and induced a G2/M arrest under treatment in BRCA1^mut cells (A13-2-12). These different phenotypes relate to differences in DNA repair: homologous recombination deficient A13-2-12 cells show less γH2AX foci despite higher levels of Pt-DNA adducts. RNA-Seq analyses prove transcript variant and cell-line-specific RUNX3 effects. Pathway analyses revealed another clinically important function of RUNX3—regulation of angiogenesis. This was confirmed by thrombospondin1 analyses, HUVEC spheroid sprouting assays and proteomic profiling. Importantly, conditioned media (CM) from RUNX3 TV1 overexpressing A13-2-12 cells induced an increased HUVEC sprouting. Altogether, the presented data support the hypothesis of different functions of RUNX3 transcript variants related to the clinically relevant processes—platinum resistance and angiogenesis.

p21 limits S phase DNA damage caused by the Wee1 inhibitor MK1775

The Wee1 inhibitor MK1775 (AZD1775) is currently being tested in clinical trials for cancer treatment. Here, we show that the p53 target and CDK inhibitor p21 protects against MK1775-induced DNA damage during S-phase. Cancer and normal cells deficient for p21 (HCT116 p21^-/-, RPE p21^-/-, and U2OS transfected with p21 siRNA) showed higher induction of the DNA damage marker γH2AX in S-phase in response to MK1775 compared to the respective parental cells. Furthermore, upon MK1775 treatment the levels of phospho-DNA PKcs S2056 and phospho-RPA S4/S8 were higher in the p21 deficient cells, consistent with increased DNA breakage. Cell cycle analysis revealed that these effects were due to an S-phase function of p21, but MK1775-induced S-phase CDK activity was not altered as measured by CDK-dependent phosphorylations. In the p21 deficient cancer cells MK1775-induced cell death was also increased. Moreover, p21 deficiency sensitized to combined treatment of MK1775 and the CHK1-inhibitor AZD6772, and to the combination of MK1775 with ionizing radiation. These results show that p21 protects cancer cells against Wee1 inhibition and suggest that S-phase functions of p21 contribute to mediate such protection. As p21 can be epigenetically downregulated in human cancer, we propose that p21 levels may be considered during future applications of Wee1 inhibitors.

High-risk human papillomavirus oncogenes disrupt the Fanconi anemia DNA repair pathway by impairing localization and de-ubiquitination of FancD2

Persistent expression of high-risk HPV oncogenes is necessary for the development of anogenital and oropharyngeal cancers. Here, we show that E6/E7 expressing cells are hypersensitive to DNA crosslinking agent cisplatin and have defects in repairing DNA interstrand crosslinks (ICL). Importantly, we elucidate how E6/E7 attenuate the Fanconi anemia (FA) DNA crosslink repair pathway. Though E6/E7 activated the pathway by increasing FancD2 monoubiquitination and foci formation, they inhibited the completion of the repair by multiple mechanisms. E6/E7 impaired FancD2 colocalization with double-strand breaks (DSB), which subsequently hindered the recruitment of the downstream protein Rad51 to DSB in E6 cells. Further, E6 expression caused delayed FancD2 de-ubiquitination, an important process for effective ICL repair. Delayed FancD2 de-ubiquitination was associated with the increased chromatin retention of FancD2 hindering USP1 de-ubiquitinating activity, and persistently activated ATR/CHK-1/pS565 FancI signaling. E6 mediated p53 degradation did not hamper the cell cycle specific process of FancD2 modifications but abrogated repair by disrupting FancD2 de-ubiquitination. Further, E6 reduced the expression and foci formation of Palb2, which is a repair protein downstream of FancD2. These findings uncover unique mechanisms by which HPV oncogenes contribute to genomic instability and the response to cisplatin therapies.

Fanconi anemia protein FANCI functions in ribosome biogenesis

Fanconi anemia (FA) is a disease of DNA repair characterized by bone marrow failure and a reduced ability to remove DNA interstrand cross-links. Here, we provide evidence that the FA protein FANCI also functions in ribosome biogenesis, the process of making ribosomes that initiates in the nucleolus. We show that FANCI localizes to the nucleolus and is functionally and physically tied to the transcription of pre-ribosomal RNA (pre-rRNA) and to large ribosomal subunit (LSU) pre-rRNA processing independent of FANCD2. While FANCI is known to be monoubiquitinated when activated for DNA repair, we find that it is predominantly in the deubiquitinated state in the nucleolus, requiring the nucleoplasmic deubiquitinase (DUB) USP1 and the nucleolar DUB USP36. Our model suggests a possible dual pathophysiology for FA that includes defects in DNA repair and in ribosome biogenesis.

Multifaceted Fanconi Anemia Signaling

In 1927 Guido Fanconi described a hereditary condition presenting panmyelopathy accompanied by short stature and hyperpigmentation, now better known as Fanconi anemia (FA). With this discovery the genetic and molecular basis underlying FA has emerged as a field of great interest. FA signaling is crucial in the DNA damage response (DDR) to mediate the repair of damaged DNA. This has attracted a diverse range of investigators, especially those interested in aging and cancer. However, recent evidence suggests FA signaling also regulates functions outside the DDR, with implications for many other frontiers of research. We discuss here the characteristics of FA functions and expand upon current perspectives regarding the genetics of FA, indicating that FA plays a role in a myriad of molecular and cellular processes.

Fanconi Anemia Signaling and Cancer

The extremely high cancer incidence associated with patients suffering from a rare human genetic disease, Fanconi anemia (FA), demonstrates the importance of FA genes. Over the course of human tumor development, FA genes perform critical tumor-suppression roles. In doing so, FA provides researchers with a unique genetic model system to study cancer etiology. Here, we review how aberrant function of the 22 FA genes and their signaling network contributes to malignancy. From this perspective, we will also discuss how the knowledge discovered from FA research serves basic and translational cancer research.

Internal Tandem Duplication in FLT3 Attenuates Proliferation and Regulates Resistance to the FLT3 Inhibitor AC220 by Modulating p21Cdkn1a and Pbx1 in Hematopoietic Cells

Internal tandem duplication (ITD) mutations in the Fms-related tyrosine kinase 3 (FLT3) gene (FLT3-ITD) are associated with poor prognosis in patients with acute myeloid leukemia (AML). Due to the development of drug resistance, few FLT3-ITD inhibitors are effective against FLT3-ITD⁺ AML. In this study, we show that FLT3-ITD activates a novel pathway involving p21^Cdkn1a (p21) and pre-B cell leukemia transcription factor 1 (Pbx1) that attenuates FLT3-ITD cell proliferation and is involved in the development of drug resistance. FLT3-ITD up-regulated p21 expression in both mouse bone marrow c-kit⁺-Sca-1⁺-Lin^- (KSL) cells and Ba/F3 cells. The loss of p21 expression enhanced growth factor-independent proliferation and sensitivity to cytarabine as a consequence of concomitantly enriching the S+G₂/M phase population and significantly increasing the expression of Pbx1, but not Evi-1, in FLT3-ITD⁺ cells. This enhanced cell proliferation following the loss of p21 was partially abrogated when Pbx1 expression was silenced in FLT3-ITD⁺ primary bone marrow colony-forming cells and Ba/F3 cells. When FLT3-ITD was antagonized with AC220, a selective inhibitor of FLT3-ITD, p21 expression was decreased coincident with Pbx1 mRNA up-regulation and a rapid decline in the number of viable FLT3-ITD⁺ Ba/F3 cells; however, the cells eventually became refractory to AC220. Overexpressing p21 in FLT3-ITD⁺ Ba/F3 cells delayed the emergence of cells that were refractory to AC220, whereas p21 silencing accelerated their development. These data indicate that FLT3-ITD is capable of inhibiting FLT3-ITD⁺ cell proliferation through the p21/Pbx1 axis and that treatments that antagonize FLT3-ITD contribute to the subsequent development of cells that are refractory to a FLT3-ITD inhibitor by disrupting p21 expression.

The Fanconi anemia ID2 complex: dueling saxes at the crossroads

Fanconi anemia (FA) is a rare recessive genetic disease characterized by congenital abnormalities, bone marrow failure and heightened cancer susceptibility in early adulthood. FA is caused by biallelic germ-line mutation of any one of 16 genes. While several functions for the FA proteins have been ascribed, the prevailing hypothesis is that the FA proteins function cooperatively in the FA-BRCA pathway to repair damaged DNA. A pivotal step in the activation of the FA-BRCA pathway is the monoubiquitination of the FANCD2 and FANCI proteins. Despite their importance for DNA repair, the domain structure, regulation, and function of FANCD2 and FANCI remain poorly understood. In this review, we provide an overview of our current understanding of FANCD2 and FANCI, with an emphasis on their posttranslational modification and common and unique functions.

Hydroxyurea induces chromosomal damage in G2 and enhances the clastogenic effect of mitomycin C in Fanconi anemia cells

Fanconi's anemia (FA) is a recessive disease; 16 genes are currently recognized in FA. FA proteins participate in the FA/BRCA pathway that plays a crucial role in the repair of DNA damage induced by crosslinking compounds. Hydroxyurea (HU) is an agent that induces replicative stress by inhibiting ribonucleotide reductase (RNR), which synthesizes deoxyribonucleotide triphosphates (dNTPs) necessary for DNA replication and repair. HU is known to activate the FA pathway; however, its clastogenic effects are not well characterized. We have investigated the effects of HU treatment alone or in sequential combination with mitomycin-C (MMC) on FA patient-derived lymphoblastoid cell lines from groups FA-A, B, C, D1/BRCA2, and E and on lymphocytes from two unclassified FA patients. All FA cells showed a significant increase (P < 0.05) in chromosomal aberrations following treatment with HU during the last 3 h before mitosis. Furthermore, when FA cells previously exposed to MMC were treated with HU, we observed an increase of MMC-induced DNA damage that was characterized by high occurrence of DNA breaks and a reduction in rejoined chromosomal aberrations. These findings show that exposure to HU during G2 induces chromosomal aberrations by a mechanism that is independent of its well-known role in replication fork stalling during S-phase and that HU interfered mainly with the rejoining process of DNA damage. We suggest that impaired oxidative stress response, lack of an adequate amount of dNTPs for DNA repair due to RNR inhibition, and interference with cell cycle control checkpoints underlie the clastogenic activity of HU in FA cells. Environ. Mol. Mutagen. 56:457-467, 2015. © 2015 Wiley Periodicals, Inc.

Acylglycerol kinase promotes the proliferation and cell cycle progression of oral squamous cell carcinoma

Cell proliferation is a major underlying cause of mortality amongst patients with oral squamous cell carcinoma (OSCC); however, the underlying mechanisms have remained to be elucidated. Acylglycerol kinase (AGK) is a multisubstrate lipid kinase, which is known to be associated with the progression of various types of human cancer. The present study aimed to investigate the role of AGK in cell proliferation and cell cycle progression in OSCC. The expression levels of AGK were detected in cancerous and adjacent normal tissue samples from four patients with OSCC undergoing surgical resection, and in OSCC cell lines, using the polymerase chain reaction (PCR) and western blot analysis. The effects of AGK on the proliferation and cell cycle progression of OSCC cells were assessed using a short hairpin RNA lentivirus or expressed-plasmid transfection. In addition, the expression levels of cyclin D1 and p21, as well as cell proliferation- and cell cycle-associated proteins were detected by PCR and western blotting. The results of the present study demonstrated that the expression levels of AGK were significantly higher in the cancerous tissues and OSCC cell lines, compared with the adjacent normal tissues and control cells, respectively. Furthermore, MTT and colony formation assays, in addition to flow cytometric analysis were conducted, in order to assess the role of AGK in cell proliferation and cell cycle progression. The cell proliferation and cell cycle progression of an established OSCC cell line were demonstrated to be decreased following AGK knockdown, and enhanced by AGK overexpression in vitro. Aberrant AGK expression in OSCC was shown to be associated with cell proliferation and cell cycle progression. The results of the present study provide evidence that AGK may promote cell proliferation and cell cycle progression in OSCC.

CDKN1A and FANCD2 are potential oncotargets in Burkitt lymphoma and multiple myeloma

Background

Comparative genetic and biological studies on malignant tumor counterparts in human beings and laboratory mice may be powerful gene discovery tools for blood cancers, including neoplasms of mature B-lymphocytes and plasma cells such as Burkitt lymphoma (BL) and multiple myeloma (MM).

Methods

We used EMSA to detect constitutive NF-κB/STAT3 activity in BL- and MM-like neoplasms that spontaneously developed in single-transgenic IL6 (interleukin-6) or MYC (c-Myc) mice, or in double-transgenic IL6MYC mice. qPCR measurements and analysis of clinical BL and MM datasets were employed to validate candidate NF-κB/STAT3 target genes.

Results

qPCR demonstrated that IL6- and/or MYC-dependent neoplasms in mice invariably contain elevated mRNA levels of the NF-κB target genes, Cdkn1a and Fancd2. Clinical studies on human CDKN1A, which encodes the cell cycle inhibitor and tumor suppressor p21, revealed that high p21 message predicts poor therapy response and survival in BL patients. Similarly, up-regulation of FANCD2, which encodes a key member of the Fanconi anemia and breast cancer pathway of DNA repair, was associated with poor outcome of patients with MM, particularly those with high-risk disease.

Conclusions

Our findings suggest that CDKN1A and FANCD2 are potential oncotargets in BL and MM, respectively. Additionally, the IL-6- and/or MYC-driven mouse models of human BL and MM used in this study may lend themselves to the biological validation of CDKN1A and FANCD2 as molecular targets for new approaches to cancer therapy and prevention.

Electronic supplementary material

The online version of this article (doi:10.1186/s40164-015-0005-2) contains supplementary material, which is available to authorized users.

Association of human papillomavirus with Fanconi anemia promotes carcinogenesis in Fanconi anemia patients

Fanconi anemia (FA) is a rare recessive disorder associated with chromosomal fragility. FA patients are at very high risk of cancers, especially head and neck squamous cell carcinomas and squamous cell carcinomas caused by infection of human papillomaviruses (HPVs). By integrating into the host genome, HPV oncogenes E6 and E7 drive the genomic instability to promote DNA damage and gene mutations necessary for carcinogenesis in FA patients. Furthermore, E6 and E7 oncoproteins not only inhibit p53 and retinoblastoma but also impair the FANC/BRCA signaling pathway to prevent DNA damage repair and alter multiple signals including cell-cycle checkpoints, telomere function, cell proliferation, and interference of the host immune system leading to cancer development in FA patients. In this review, we summarize recent advances in unraveling the molecular mechanisms of FA susceptibility to HPV-induced cancers, which facilitate rational preventive and therapeutic strategies.

Suppression of C6 gliomas via application of rat hyperplasia gene

BACKGROUND

Among all neurological tumors, tumor incidence of the neuroepithelial tissue is the highest, where 50% are gliomas. Treatment for gliomas has traditionally included surgery and adjuvant therapy. With advancements in medicine, gene therapy has entered the clinical setting, in which control of tumor growth, tumor volume and decrease of supply of blood to the tumor have been observed. Rat hyperplasia suppressor gene (rHSG) has been proven to inhibit the injury-mediated proliferation of vascular smooth muscle cells.

METHODS

A recombinant adenovirus, Adv-rHSG-GFP, was constructed and characterized by in vitro and in vivo studies. The function of rHSG on cell proliferation was determined in vitro by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) exclusion assay and plate clone formation, while a C6/Sprague Dawley rat glioma model was established to observe the effect of rHSG in vivo.

RESULTS

Overexpression of rHSG displayed a strong effect on suppressing C6 cells proliferation in vitro and growth of glioma in vivo, which suggests the use of rHSG as a possible treatment strategy for glioma. p21Cip1, p27Kip1 and proliferating cell nuclear antigen were found to be involved in the tumor suppression mechanism of rHSG.

CONCLUSIONS

rHSG can markedly inhibit of the growth of rat glioma cells. The suppression mechanism of rHSG may be related to cell cycle regulation, which shows that rHSG is a potential therapeutic target of glioma tumor. This preclinical study supports a further in-depth study on the effect of rHSG on cell proliferation, migration and change in the extracellular matrix component of glioma cells.

Coordinate nuclear targeting of the FANCD2 and FANCI proteins via a FANCD2 nuclear localization signal

Fanconi anemia (FA) is a rare recessive disease, characterized by congenital defects, bone marrow failure, and increased cancer susceptibility. FA is caused by biallelic mutation of any one of sixteen genes. The protein products of these genes function cooperatively in the FA-BRCA pathway to repair DNA interstrand crosslinks (ICLs). A central step in the activation of this pathway is the monoubiquitination of the FANCD2 and FANCI proteins. Monoubiquitinated FANCD2 and FANCI localize to discrete chromatin regions where they function in ICL repair. Despite their critical role in ICL repair, very little is known about the structure, function, and regulation of the FANCD2 and FANCI proteins, or how they are targeted to the nucleus and chromatin. In this study, we describe the functional characterization of an amino-terminal FANCD2 nuclear localization signal (NLS). We demonstrate that the amino terminal 58 amino acids of FANCD2 can promote the nuclear expression of GFP and is necessary for the nuclear localization of FANCD2. Importantly, mutation of this FANCD2 NLS reveals that intact FANCD2 is required for the nuclear localization of a subset of FANCI. In addition, the NLS is necessary for the efficient monoubiquitination of FANCD2 and FANCI and, consequently, for their localization to chromatin. As a result, FANCD2 NLS mutants fail to rescue the ICL sensitivity of FA-D2 patient cells. Our studies yield important insight into the domain structure of the poorly characterized FANCD2 protein, and reveal a previously unknown mechanism for the coordinate nuclear import of a subset of FANCD2 and FANCI, a key early step in the cellular ICL response.

USP1 deubiquitinase: cellular functions, regulatory mechanisms and emerging potential as target in cancer therapy

Reversible protein ubiquitination is emerging as a key process for maintaining cell homeostasis, and the enzymes that participate in this process, in particular E3 ubiquitin ligases and deubiquitinases (DUBs), are increasingly being regarded as candidates for drug discovery. Human DUBs are a group of approximately 100 proteins, whose cellular functions and regulatory mechanisms remain, with some exceptions, poorly characterized. One of the best-characterized human DUBs is ubiquitin-specific protease 1 (USP1), which plays an important role in the cellular response to DNA damage. USP1 levels, localization and activity are modulated through several mechanisms, including protein-protein interactions, autocleavage/degradation and phosphorylation, ensuring that USP1 function is carried out in a properly regulated spatio-temporal manner. Importantly, USP1 expression is deregulated in certain types of human cancer, suggesting that USP1 could represent a valid target in cancer therapy. This view has gained recent support with the finding that USP1 inhibition may contribute to revert cisplatin resistance in an in vitro model of non-small cell lung cancer (NSCLC). Here, we describe the current knowledge on the cellular functions and regulatory mechanisms of USP1. We also summarize USP1 alterations found in cancer, combining data from the literature and public databases with our own data. Finally, we discuss the emerging potential of USP1 as a target, integrating published data with our novel findings on the effects of the USP1 inhibitor pimozide in combination with cisplatin in NSCLC cells.

Fancd2 and p21 function independently in maintaining the size of hematopoietic stem and progenitor cell pool in mice

Fanconi anemia patients suffer from progressive bone marrow failure. An overactive p53 response to DNA damage contributes to the progressive elimination of Fanconi anemia hematopoietic stem and progenitor cells (HSPC), and hence presents a potential target for therapeutic intervention. To investigate whether the cell cycle regulatory protein p21 is the primary mediator of the p53-dependent stem cell loss, p21/Fancd2 double-knockout mice were generated. Surprisingly double mutant mice displayed even more severe loss of HSPCs than Fancd2(-/-) single mutants. p21 deletion did not rescue the abnormal cell cycle profile and had no impact on the long-term repopulating potential of Fancd2(-/-) bone marrow cells. Collectively, our data indicate that p21 has an indispensable role in maintaining a normal HSPC pool and suggest that other p53-targeted factors, not p21, mediate the progressive elimination of HSPC in Fanconi anemia.

Cellular functions of the DUBs

Ubiquitylation is a reversible post-translational modification that has emerged as a key regulator of most complex cellular processes. It may rival phosphorylation in scope and exceed it in complexity. The dynamic nature of ubiquitylation events is important for governing protein stability, maintaining ubiquitin homeostasis and controlling ubiquitin-dependent signalling pathways. The human genome encodes ~80 active deubiquitylating enzymes (DUBs, also referred to as deubiquitinases), which exhibit distinct specificity profiles towards the various ubiquitin chain topologies. As a result of their ability to reverse ubiquitylation, these enzymes control a broad range of key cellular processes. In this Commentary we discuss the cellular functions of DUBs, such as their role in governing membrane traffic and protein quality control. We highlight two key signalling pathways--the Wnt and transforming growth factor β (TGF-β) pathways, for which dynamic ubiquitylation has emerged as a key regulator. We also discuss the roles of DUBs in the nucleus, where they govern transcriptional activity and DNA repair pathways.

FAVL impairment of the Fanconi anemia pathway promotes the development of human bladder cancer

Effectiveness of DNA cross-linking drugs in the treatment of bladder cancer suggests that bladder cancer cells may have harbored an insufficient cellular response to DNA cross-link damage, which will sensitize cells to DNA cross-linking agents. Cell sensitivity benefits from deficient DNA damage responses, which, on the other hand, can cause cancer. Many changed cellular signaling pathways are known to be involved in bladder tumorigenesis; however, DNA cross-link damage response pathway [Fanconi anemia (FA) pathway], whose alterations appear to be a plausible cause of the development of bladder cancer, remains an under-investigated area in bladder cancer research. In this study, we found FAVL (variant of FA protein L--FANCL) was elevated substantially in bladder cancer tissues examined. Ectopic expression of FAVL in bladder cancer cells as well as normal human cells confer an impaired FA pathway and hypersensitivity to Mitomycin C, similar to those found in FA cells, indicating that FAVL elevation may possess the same tumor promotion potential as an impaired FA pathway harbored in FA cells. Indeed, a higher level of FAVL expression can promote the growth of bladder cancer cells in vitro and in vivo, which, at least partly, results from FAVL perturbation of FANCL expression, an essential factor for the activation of the FA pathway. Moreover, a higher level of FAVL expression was found to be associated with chromosomal instability and the invasiveness of bladder cancer cells. Collectively, FAVL elevation can increase the tumorigenic potential of bladder cancer cells, including the invasive potential that confers the development of advanced bladder cancer. These results enhance our understanding the pathogenesis of human bladder cancer, holding a promise to develop additional effective tools to fight human bladder cancer.

The Fanconi anemia pathway in replication stress and DNA crosslink repair

Interstand crosslinks (ICLs) are DNA lesions where the bases of opposing DNA strands are covalently linked, inhibiting critical cellular processes such as transcription and replication. Chemical agents that generate ICLs cause chromosomal abnormalities including breaks, deletions and rearrangements, making them highly genotoxic compounds. This toxicity has proven useful for chemotherapeutic treatment against a wide variety of cancer types. The majority of our understanding of ICL repair in humans has been uncovered through analysis of the rare genetic disorder Fanconi anemia, in which patients are extremely sensitive to crosslinking agents. Here, we discuss recent insights into ICL repair gained using new repair assays and highlight the role of the Fanconi anemia repair pathway during replication stress.

p21 promotes error-free replication-coupled DNA double-strand break repair

p21 is a well-established regulator of cell cycle progression. The role of p21 in DNA repair, however, remains poorly characterized. Here, we describe a critical role of p21 in a replication-coupled DNA double-strand break (DSB) repair that is mechanistically distinct from its cell cycle checkpoint function. We demonstrate that p21-deficient cells exhibit elevated chromatid-type aberrations, including gaps and breaks, dicentrics and radial formations, following exposure to several DSB-inducing agents. p21^−/− cells also exhibit an increased DNA damage-inducible DNA-PK_CS S2056 phosphorylation, indicative of elevated non-homologous DNA end joining. Concomitantly, p21^−/− cells are defective in replication-coupled homologous recombination (HR), exhibiting decreased sister chromatid exchanges and HR-dependent repair as determined using a crosslinked GFP reporter assay. Importantly, we establish that the DSB hypersensitivity of p21^−/− cells is associated with increased cyclin-dependent kinase (CDK)-dependent BRCA2 S3291 phosphorylation and MRE11 nuclear foci formation and can be rescued by inhibition of CDK or MRE11 nuclease activity. Collectively, our results uncover a novel mechanism by which p21 regulates the fidelity of replication-coupled DSB repair and the maintenance of chromosome stability distinct from its role in the G1-S phase checkpoint.