Decreased transcription-coupled nucleotide excision repair capacity is associated with increased p53- and MLH1-independent apoptosis in response to cisplatin

The ubiquitin ligase UBR4 and the deubiquitylase USP5 modulate the stability of DNA mismatch repair protein MLH1

MLH1 plays a critical role in DNA mismatch repair and genome maintenance. MLH1 deficiency promotes cancer development and progression, but the mechanism underlying MLH1 regulation remains enigmatic. In this study, we demonstrate that MLH1 protein is degraded by the ubiquitin-proteasome system and have identified vital cis-elements and trans-factors involved in MLH1 turnover. We found that the region encompassing the amino acids 516-650 is crucial for MLH1 degradation. The mismatch repair protein PMS2 may shield MLH1 from degradation as it bind to the MLH1 segment key to its turnover. Furthermore, we have identified the E3 ubiquitin ligase UBR4 and the deubiquitylase USP5, which oppositely modulate MLH1 stability. In consistence, UBR4 or USP5 deficiency affects the cellular response to nucleotide analog 6-TG, supporting their roles in regulating mismatch repair. Our study has revealed important insights into the regulatory mechanisms underlying MLH1 proteolysis, critical to DNA mismatch repair related diseases.

CUL4A silencing attenuates cervical carcinogenesis and improves Cisplatin sensitivity

CUL4A is an ubiquitin ligase deregulated in numerous pathologies including cancer and even hijacked by viruses for facilitating their survival and propagation. However, its role in Human papilloma virus (HPV)-mediated cervical carcinogenesis remains elusive. The UALCAN and GEPIA datasets were analyzed to ascertain the transcript levels of CUL4A in cervical squamous cell carcinoma and endocervical adenocarcinoma (CESC) patients. Subsequently, various biochemical assays were employed to explore the functional contribution of CUL4A in cervical carcinogenesis and to shed some light on its involvement in Cisplatin resistance in cervical cancer. Our UALCAN and GEPIA datasets analyses reveal elevated CUL4A transcript levels in cervical squamous cell carcinoma and endocervical adenocarcinoma (CESC) patients that correlate with adverse clinicopathological parameters such as tumor stage and lymph node metastasis. Kaplan-Meier plot and GEPIA assessment depict poor prognosis of CESC patients having high CUL4A expression. Varied biochemical assays illustrate that CUL4A inhibition severely curtails hallmark malignant properties such as cellular proliferation, migration, and invasion of cervical cancer cells. We also show that CUL4A knockdown in HeLa cells causes increased susceptibility and better apoptotic induction toward Cisplatin, a mainstay drug used in cervical cancer treatment. More interestingly, we find reversion of Cisplatin-resistant phenotype of HeLa cells and an augmented cytotoxicity towards the platinum compound upon CUL4A downregulation. Taken together, our study underscores CUL4A as a cervical cancer oncogene and illustrates its potential as a prognosis indicator. Our investigation provides a novel avenue in improving current anti-cervical cancer therapy and overcoming the bottle-neck of Cisplatin resistance.

The Role of Extracellular Vesicles in Mediating Resistance to Anticancer Therapies

Although advances in targeted therapies have driven great progress in cancer treatment and outcomes, drug resistance remains a major obstacle to improving patient survival. Several mechanisms are involved in developing resistance to both conventional chemotherapy and molecularly targeted therapies, including drug efflux, secondary mutations, compensatory genetic alterations occurring upstream or downstream of a drug target, oncogenic bypass, drug activation and inactivation, and DNA damage repair. Extracellular vesicles (EVs) are membrane-bound lipid bilayer vesicles that are involved in cell-cell communication and regulating biological processes. EVs derived from cancer cells play critical roles in tumor progression, metastasis, and drug resistance by delivering protein and genetic material to cells of the tumor microenvironment. Understanding the biochemical and genetic mechanisms underlying drug resistance will aid in the development of new therapeutic strategies. Herein, we review the role of EVs as mediators of drug resistance in the context of cancer.

Cockayne Syndrome Group B (CSB): The Regulatory Framework Governing the Multifunctional Protein and Its Plausible Role in Cancer

Cockayne syndrome (CS) is a DNA repair syndrome characterized by a broad spectrum of clinical manifestations such as neurodegeneration, premature aging, developmental impairment, photosensitivity and other symptoms. Mutations in Cockayne syndrome protein B (CSB) are present in the vast majority of CS patients and in other DNA repair-related pathologies. In the literature, the role of CSB in different DNA repair pathways has been highlighted, however, new CSB functions have been identified in DNA transcription, mitochondrial biology, telomere maintenance and p53 regulation. Herein, we present an overview of identified structural elements and processes that impact on CSB activity and its post-translational modifications, known to balance the different roles of the protein not only during normal conditions but most importantly in stress situations. Moreover, since CSB has been found to be overexpressed in a number of different tumors, its role in cancer is presented and possible therapeutic targeting is discussed.

Adipose most abundant 2 protein is a predictive marker for cisplatin sensitivity in cancers

Cisplatin (CDDP) is one of the chemotherapeutic drugs being used to treat various cancers. Although effective in many cases, as high doses of CDDP cause cytotoxic effects that may worsen patients' condition, therefore, a marker of sensitivity to CDDP is necessary to enhance the safety and efficiency of CDDP administration. This study focused on adipose most abundant 2 (APM2) to examine its potential as a marker of CDDP sensitivity. The relationship of APM2 expression with the mechanisms of CDDP resistance was examined in vitro and in vivo using hepatocellular carcinoma (HCC) cells, tissues and serum of HCC patients (n = 71) treated initially with intrahepatic arterial infusion of CDDP followed by surgical resection. The predictability of serum APM2 for CDDP sensitivity was assessed in additional 54 HCC patients and 14 gastric cancer (GC) patients. APM2 expression in CDDP-resistant HCC was significantly higher both in serum and the tissue. Bioinformatic analyses and histological analyses demonstrated upregulation of ERCC6L (DNA excision repair protein ERCC6-like) by APM2, which accounts for the degree of APM2 expression. The serum APM2 level and chemosensitivity for CDDP were assessed and cut-off value of serum APM2 for predicting the sensitivity to CDDP was determined to be 18.7 µg/mL. The value was assessed in HCC (n = 54) and GC (n = 14) patients for its predictability of CDDP sensitivity, resulted in predictive value of 77.3% and 100%, respectively. Our study demonstrated that APM2 expression is related to CDDP sensitivity and serum APM2 can be an effective biomarker of HCC and GC for determining the sensitivity to CDDP.Trial registration: This study was registered with the University Hospital Medical Information Network Clinical Trials Registry (UMIN000028487).

A Nobel-Winning Scientist: Aziz Sancar and the Impact of his Work on the Molecular Pathology of Neoplastic Diseases

Aziz Sancar, Nobel Prize winning Turkish scientist, made several discoveries which had a major impact on molecular sciences, particularly disciplines that focus on carcinogenesis and cancer treatment, including molecular pathology. Cloning the photolyase gene, which was the initial step of his work on DNA repair mechanisms, discovery of the "Maxicell" method, explanation of the mechanism of nucleotide excision repair and transcription-coupled repair, discovery of "molecular matchmakers", and mapping human excision repair genes at single nucleotide resolution constitute his major research topics. Moreover, Sancar discovered the cryptochromes, the clock genes in humans, in 1998, and this discovery led to substantial progress in the understanding of the circadian clock and the introduction of the concept of "chrono-chemoterapy" for more effective therapy in cancer patients. This review focuses on Aziz Sancar's scientific studies and their reflections on molecular pathology of neoplastic diseases. While providing a new perspective for researchers working in the field of pathology and molecular pathology, this review is also an evidence of how basic sciences and clinical sciences complete each other.

Role of Nucleotide Excision Repair in Cisplatin Resistance

Cisplatin is a chemotherapeutic drug used for the treatment of a number of cancers. The efficacy of cisplatin relies on its binding to DNA and the induction of cytotoxic DNA damage to kill cancer cells. Cisplatin-based therapy is best known for curing testicular cancer; however, treatment of other solid tumors with cisplatin has not been as successful. Pre-clinical and clinical studies have revealed nucleotide excision repair (NER) as a major resistance mechanism against cisplatin in tumor cells. NER is a versatile DNA repair system targeting a wide range of helix-distorting DNA damage. The NER pathway consists of multiple steps, including damage recognition, pre-incision complex assembly, dual incision, and repair synthesis. NER proteins can recognize cisplatin-induced DNA damage and remove the damage from the genome, thereby neutralizing the cytotoxicity of cisplatin and causing drug resistance. Here, we review the molecular mechanism by which NER repairs cisplatin damage, focusing on the recent development of genome-wide cisplatin damage mapping methods. We also discuss how the expression and somatic mutations of key NER genes affect the response of cancer cells to cisplatin. Finally, small molecules targeting NER factors provide important tools to manipulate NER capacity in cancer cells. The status of research on these inhibitors and their implications in cancer treatment will be discussed.

CSB affected on the sensitivity of lung cancer cells to platinum-based drugs through the global decrease of let-7 and miR-29

Background

Transcription-coupled nucleotide excision repair (TC-NER) plays a prominent role in the removal of DNA adducts induced by platinum-based chemotherapy reagents. Cockayne syndrome protein B (CSB), the master sensor of TCR, is also involved in the platinum resistant. Let-7 and miR-29 binding sites are highly conserved in the proximal 3′UTR of CSB.

Methods

We conducted immunohistochemisty to examine the expression of CSB in NSCLC. To determine whether let-7 family and miR-29 family directly interact with the putative target sites in the 3′UTR of CSB, we used luciferase reporter gene analysis. To detect the sensitivity of non-small cell lung cancer (NSCLC) cells to platinum-based drugs, CCK analysis and apoptosis analysis were performed.

Results

We found that let-7 and miR-29 negatively regulate the expression of CSB by directly targeting to the 3′UTR of CSB. The endogenous CSB expression could be suppressed by let-7 and miR-29 in lung cancer cells. The suppression of CSB activity by endogenous let-7 and miR-29 can be robustly reversed by their sponges. Down-regulation of CSB induced apoptosis and increased the sensitivity of NSCLC cells to cisplatin and carboplatin drugs. Let-7 and miR-29 directly effect on cisplatin and carboplatin sensitivity in NSCLC.

Conclusions

In conclusion, the platinum-based drug resistant of lung cancer cells may involve in the regulation of let-7 and miR-29 to CSB.

Comparative study of cytotoxic effects induced by environmental genotoxins using XPC- and CSB-deficient human lymphoblastoid TK6 cells

Background

The human genome is constantly exposed to numerous environmental genotoxicants. To prevent the detrimental consequences induced by the expansion of damaged cells, cellular protective systems such as nucleotide excision repair (NER) exist and serve as a primary pathway for repairing the various helix-distorting DNA adducts induced by genotoxic agents. NER is further divided into two sub-pathways, namely, global genomic NER (GG-NER) and transcription-coupled NER (TC-NER). Both NER sub-pathways are reportedly involved in the damage response elicited by exposure to genotoxins. However, how disruption of these sub-pathways impacts the toxicity of different types of environmental mutagens in human cells is not well understood.

Results

To evaluate the role of NER sub-pathways on the cytotoxic effects of mutagens, we disrupted XPC and CSB to selectively inactivate GG-NER and TC-NER, respectively, in human lymphoblastoid TK6 cells, a standard cell line used in genotoxicity studies. Using these cells, we then comparatively assessed their respective sensitivities to representative genotoxic agents, including ultraviolet C (UVC) light, benzo [a] pyrene (B(a)P), 2-amino-3,8-dimethylimidazo [4,5-f] quinoxaline (MeIQx), 2-amino-1-methyl-6-phenylimidazo [4,5-b] pyridine (PhIP), γ-ray, and 2-acetylaminofluorene (2-AAF). CSB^−/− cells exhibited a hyper-sensitivity to UVC, B(a)P, and MeIQx. On the other hand, XPC^−/− cells were highly sensitive to UVC, but not to B(a)P and MeIQx, compared with wild-type cells. In contrast with other genotoxins, the sensitivity of XPC^−/− cells against PhIP was significantly higher than CSB^−/− cells. The toxicity of γ-ray and 2-AAF was not enhanced by disruption of either XPC or CSB in the cells.

Conclusions

Based on our findings, genetically modified TK6 cells appear to be a useful tool for elucidating the detailed roles of the various repair factors that exist to combat genotoxic agents, and should contribute to the improved risk assessment of environmental chemical contaminants.

Portrait of a cancer: mutational signature analyses for cancer diagnostics

BACKGROUND

In the past decade, systematic and comprehensive analyses of cancer genomes have identified cancer driver genes and revealed unprecedented insight into the molecular mechanisms underlying the initiation and progression of cancer. These studies illustrate that although every cancer has a unique genetic make-up, there are only a limited number of mechanisms that shape the mutational landscapes of cancer genomes, as reflected by characteristic computationally-derived mutational signatures. Importantly, the molecular mechanisms underlying specific signatures can now be dissected and coupled to treatment strategies. Systematic characterization of mutational signatures in a cancer patient's genome may thus be a promising new tool for molecular tumor diagnosis and classification.

RESULTS

In this review, we describe the status of mutational signature analysis in cancer genomes and discuss the opportunities and relevance, as well as future challenges, for further implementation of mutational signatures in clinical tumor diagnostics and therapy guidance.

CONCLUSIONS

Scientific studies have illustrated the potential of mutational signature analysis in cancer research. As such, we believe that the implementation of mutational signature analysis within the diagnostic workflow will improve cancer diagnosis in the future.

Cisplatin resistance in cell models: evaluation of metallomic and biological predictive biomarkers to address early therapy failure

Cisplatin, one of the most extensively used metallodrugs in cancer treatment, presents the important drawback of patient resistance. This resistance is the consequence of different processes including those preventing the formation of DNA adducts and/or their quick removal. Thus, a tool for the accurate detection and quantitation of cisplatin-induced adducts might be valuable for predicting patient resistance. To prove the validity of such an assumption, highly sensitive plasma mass spectrometry (ICP-MS) strategies were applied to determine DNA adduct levels and intracellular Pt concentrations. These two metal-relative parameters were combined with an evaluation of biological responses in terms of genomic stability (with the Comet assay) and cell cycle progression (by flow cytometry) in four human cell lines of different origins and cisplatin sensitivities (A549, GM04312, A2780 and A2780cis), treated with low cisplatin doses (5, 10 and 20 μM for 3 hours). Cell viability and apoptosis were determined as resistance indicators. Univariate linear regression analyses indicated that quantitation of cisplatin-induced G-G intra-strand adducts, measured 1 h after treatment, was the best predictor for viability and apoptosis in all of the cell lines. Multivariate linear regression analyses revealed that the prediction improved when the intracellular Pt content or the Comet data were included in the analysis, for all sensitive cell lines and for the A2780 and A2780cis cell lines, respectively. Thus, a reliable cisplatin resistance predictive model, which combines the quantitation of adducts by HPLC-ICP-MS, and their repair, with the intracellular Pt content and induced genomic instability, might be essential to identify early therapy failure.

CSB: An Emerging Actionable Target for Cancer Therapy

The DNA repair protein Cockayne syndrome group B (CSB) is frequently found overexpressed in cancer cells. High CSB levels favor tumor cell proliferation whilst inhibiting apoptosis. Conversely, the suppression of CSB has significant anticancer effects. In this manuscript we describe CSB downregulation as a potential new therapeutic approach in cancer.

Modulation of Cytotoxicity by Transcription-Coupled Nucleotide Excision Repair Is Independent of the Requirement for Bioactivation of Acylfulvene

Bioactivation as well as DNA repair affects the susceptibility of cancer cells to the action of DNA-alkylating chemotherapeutic drugs. However, information is limited with regard to the relative contributions of these processes to the biological outcome of metabolically activated DNA alkylating agents. We evaluated the influence of cellular bioactivation capacity and DNA repair on cytotoxicity of the DNA alkylating agent acylfulvene (AF). We compared the cytotoxicity and RNA synthesis inhibition by AF and its synthetic activated analogue iso-M0 in a panel of fibroblast cell lines with deficiencies in transcription-coupled (TC-NER) or global genome nucleotide excision repair (GG-NER). We related these data to the inherent bioactivation capacity of each cell type on the basis of mRNA levels. We demonstrated that specific inactivation of TC-NER by siRNA had the largest positive impact on AF activity in a cancer cell line. These findings establish that transcription-coupled DNA repair reduces cellular sensitivity to AF, independent of the requirement for bioactivation.

Loss of CUL4A expression is underlying cisplatin hypersensitivity in colorectal carcinoma cells with acquired trabectedin resistance

Background:

Colorectal carcinoma (CRC) is the third most common cancer worldwide. Platinum-based anticancer compounds still constitute one mainstay of systemic CRC treatment despite limitations due to adverse effects and resistance development. Trabectedin has shown promising antitumor effects in CRC, however, again resistance development may occur. In this study, we aimed to develop strategies to circumvent or even exploit acquired trabectedin resistance in novel CRC treatment regimens.

Methods:

Human HCT116 CRC cells were selected for acquired trabectedin resistance in vitro and characterised by cell biological as well as bioinformatic approaches. In vivo xenograft experiments were conducted.

Results:

Selection of HCT116 cells for trabectedin resistance resulted in p53-independent hypersensitivity of the selected subline against cisplatin. Bioinformatic analyses of mRNA microarray data suggested deregulation of nucleotide excision repair and particularly loss of the ubiquitin ligase CUL4A in trabectedin-selected cells. Indeed, transient knockdown of CUL4A sensitised parental HCT116 cells towards cisplatin. Trabectedin selected but not parental HCT116 xenografts were significantly responsive towards cisplatin treatment.

Conclusions:

Trabectedin selection-mediated CUL4A loss generates an Achilles heel in CRC cancer cells enabling effective cisplatin treatment. Hence, inclusion of trabectedin in cisplatin-containing cancer treatment regimens might cause profound synergism based on reciprocal resistance prevention.

Nucleotide excision repair deficiency increases levels of acrolein-derived cyclic DNA adduct and sensitizes cells to apoptosis induced by docosahexaenoic acid and acrolein

The acrolein derived cyclic 1,N(2)-propanodeoxyguanosine adduct (Acr-dG), formed primarily from ω-3 polyunsaturated fatty acids such as docosahexaenoic acid (DHA) under oxidative conditions, while proven to be mutagenic, is potentially involved in DHA-induced apoptosis. The latter may contribute to the chemopreventive effects of DHA. Previous studies have shown that the levels of Acr-dG are correlated with apoptosis induction in HT29 cells treated with DHA. Because Acr-dG is shown to be repaired by the nucleotide excision repair (NER) pathway, to further investigate the role of Acr-dG in apoptosis, in this study, NER-deficient XPA and its isogenic NER-proficient XAN1 cells were treated with DHA. The Acr-dG levels and apoptosis were sharply increased in XPA cells, but not in XAN1 cells when treated with 125μM of DHA. Because DHA can induce formation of various DNA damage, to specifically investigate the role of Acr-dG in apoptosis induction, we treated XPA knockdown HCT116+ch3 cells with acrolein. The levels of both Acr-dG and apoptosis induction increased significantly in the XPA knockdown cells. These results clearly demonstrate that NER deficiency induces higher levels of Acr-dG in cells treated with DHA or acrolein and sensitizes cells to undergo apoptosis in a correlative manner. Collectively, these results support that Acr-dG, a ubiquitously formed mutagenic oxidative DNA adduct, plays a role in DHA-induced apoptosis and suggest that it could serve as a biomarker for the cancer preventive effects of DHA.

Weighted gene co-expression network analysis of pneumocytes under exposure to a carcinogenic dose of chloroprene

AIMS

Occupational exposure to chloroprene via inhalation may lead to acute toxicity and chronic pulmonary diseases, including lung cancer. Currently, most research is focused on epidemiological studies of chloroprene production workers. The specific molecular mechanism of carcinogenesis by chloroprene in lung tissues still remains obscure, and specific candidate therapeutic targets for lung cancer are lacking. The present study identifies specific gene modules and valuable hubs associated with lung cancer.

MAIN METHODS

We downloaded the dataset GSE40795 from the Gene Expression Omnibus (GEO) and divided the dataset into the non-carcinogenic dose chloroprene exposed mice group and the carcinogenic dose chloroprene exposed mice group. With a systemic biological view, we discovered significantly altered gene modules between the two groups and identified hub genes in the carcinogenic dose exposed group using weighted co-expression network analysis (WGCNA).

KEY FINDINGS

A total of 2434 differentially expressed genes were identified. Twelve gene modules with multiple biological activities were related to the carcinogenesis of chloroprene in lung tissue. Seven hub genes that were critical for the carcinogenesis of chloroprene in lung tissue were ultimately identified, including Cftr, Hip1, Tbl1x, Ephx1, Cbr3, Antxr2 and Ccnd2. They were implicated in inflammatory response, cell transformation, gene transcription regulation, phase II detoxification, angiogenesis, cell adhesion, motility and the cell cycle.

SIGNIFICANCE

The seven hub genes may become valuable candidates for risk assessment biomarkers and therapeutic targets in lung cancer.

The effect of adenovirus-conjugated NDRG2 on p53-mediated apoptosis of hepatocarcinoma cells through attenuation of nucleotide excision repair capacity

NDRG2 mRNA and protein levels can be upregulated in a p53-dependent manner. NDRG2 enhances p53-mediated apoptosis, whereas overexpression of NDRG2 suppresses tumor cell growth, regardless of whether p53 is mutated. However, the complicated mechanism by which NDRG2 suppresses tumor cell growth and enhances apoptosis mediated by p53 is not fully understood. Here, we demonstrated that Ad-NDRG2 enhanced the apoptosis of HepG2 cells (wild-type p53). Additionally, Ad-NDRG2 combined with rAd-p53 enhanced the apoptosis of Huh7 cells (mutant p53) after chemotherapy, and the expression of the ERCC6 gene (Cockayne syndrome group B protein gene) was suppressed in this process. Ad-NDRG2 combined with rAd-p53 induced the apoptosis of tumor cells (HepG2 and Huh7 cells); however, apoptosis was attenuated after transfection with ERCC6. Our results indicate that Ad-NDRG2 enhances the p53-mediated apoptosis of hepatocarcinoma cells (HepG2 and Huh7) by attenuating the nucleotide excision repair capacity (i.e., by downregulating ERCC6), and ERCC6 is a NDRG2-inducible target gene that is involved in the p53-mediated apoptosis pathway.

Expression of the mismatch repair gene hMLH1 is enhanced in non-small cell lung cancer with EGFR mutations

Mismatch repair (MMR) plays a pivotal role in keeping the genome stable. MMR dysfunction can lead to carcinogenesis by gene mutation accumulation. HMSH2 and hMLH1 are two key components of MMR. High or low expression of them often mark the status of MMR function. Mutations (EGFR, KRAS, etc) are common in non-small cell lung cancer (NSCLC). However, it is not clear what role MMR plays in NSCLC gene mutations. The expression of MMR proteins hMSH2 and hMLH1, and the proliferation markers PCNA and Ki67 were measured by immunohistochemistry in 181 NSCLCs. EGFR and KRAS mutations were identified by high resolution melting analysis. Stronger hMLH1 expression correlated to a higher frequency of EGFR mutations in exon 19 and 21 (p<0.0005). Overexpression of hMLH1 and the adenocarcinoma subtype were both independent factors that related to EGFR mutations in NSCLCs (p=0.013 and p<0.0005). The expression of hMLH1, hMSH2 and PCNA increased, while Ki67 expression significantly decreased (p=0.030) in NSCLCs with EGFR mutations. Overexpression of hMLH1 could be a new molecular marker to predict the response to EGFR-TKIs in NSCLCs. Furthermore, EGFR mutations might be an early event of NSCLC that occur before MMR dysfunction.

Arresting transcription and sentencing the cell: the consequences of blocked transcription

Bulky DNA adducts induced by agents like ultraviolet light, cisplatin and oxidative metabolism pose a block to elongation by RNA polymerase II (RNAPII). The arrested RNAPII can initiate the repair of transcription-blocking DNA lesions by transcription-coupled nucleotide excision repair (TC-NER) to permit efficient recovery of mRNA synthesis while widespread sustained transcription blocks lead to apoptosis. Therefore, RNAPII serves as a processive DNA damage sensor that identifies transcription-blocking DNA lesions. Cockayne syndrome (CS) is an autosomal recessive disorder characterized by a complex phenotype that includes clinical photosensitivity, progressive neurological degeneration and premature-aging. CS is associated with defects in TC-NER and the recovery of mRNA synthesis, making CS cells exquisitely sensitive to a variety of DNA damaging agents. These defects in the coupling of repair and transcription appear to underlie some of the complex clinical features of CS. Recent insight into the consequences of blocked transcription and their relationship to CS will be discussed.

Characteristics of myeloid differentiation and maturation pathway derived from human hematopoietic stem cells exposed to different linear energy transfer radiation types

Exposure of hematopoietic stem/progenitor cells (HSPCs) to ionizing radiation causes a marked suppression of mature functional blood cell production in a linear energy transfer (LET)- and/or dose-dependent manner. However, little information about LET effects on the proliferation and differentiation of HSPCs has been reported. With the aim of characterizing the effects of different types of LET radiations on human myeloid hematopoiesis, in vitro hematopoiesis in Human CD34⁺ cells exposed to carbon-ion beams or X-rays was compared. Highly purified CD34⁺ cells exposed to each form of radiation were plated onto semi-solid culture for a myeloid progenitor assay. The surviving fractions of total myeloid progenitors, colony-forming cells (CFC), exposed to carbon-ion beams were significantly lower than of those exposed to X-rays, indicating that CFCs are more sensitive to carbon-ion beams (D₀ = 0.65) than to X-rays (D₀ = 1.07). Similar sensitivities were observed in granulocyte-macrophage and erythroid progenitors, respectively. However, the sensitivities of mixed-type progenitors to both radiation types were similar.

In liquid culture for 14 days, no significant difference in total numbers of mononuclear cells was observed between non-irradiated control culture and cells exposed to 0.5 Gy X-rays, whereas 0.5 Gy carbon-ion beams suppressed cell proliferation to 4.9% of the control, a level similar to that for cells exposed to 1.5 Gy X-rays. Cell surface antigens associated with terminal maturation, such as CD13, CD14, and CD15, on harvest from the culture of X-ray-exposed cells were almost the same as those from the non-irradiated control culture. X-rays increased the CD235a⁺ erythroid-related fraction, whereas carbon-ion beams increased the CD34⁺CD38⁻ primitive cell fraction and the CD13⁺CD14^+/−CD15⁻ fraction. These results suggest that carbon-ion beams inflict severe damage on the clonal growth of myeloid HSPCs, although the intensity of cell surface antigen expression by mature myeloid cells derived from HSPCs exposed to each type of radiation was similar to that by controls.

The CSB repair factor is overexpressed in cancer cells, increases apoptotic resistance, and promotes tumor growth

In the present study we show that a number of cancer cell lines from different tissues display dramatically increased expression of the Cockayne Syndrome group B (CSB) protein, a DNA repair factor, that has recently been shown to be involved in cell robustness. Furthermore, we demonstrated that ablation of this protein by antisense technology causes devastating effects on tumor cells through a drastic reduction of cell proliferation and massive induction of apoptosis, while non-transformed cells remain unaffected. Finally, suppression of CSB in cancer cells makes these cells hypersensitive to a variety of commonly used cancer chemotherapeutic agents. Based on these results, we conclude that cancer cells overexpress CSB protein in order to enhance their anti-apoptotic capacity. The fact that CSB suppression specifically affects only cancerous cells, without harming healthy cells, suggests that CSB may be a very attractive target for the development of new anticancer therapies.

Alterations in nuclear pore architecture allow cancer cell entry into or exit from drug-resistant dormancy

Phenotypic diversity arises in tumors just as it does in developing organisms, and tumor recurrence frequently manifests from the selective survival of divergent drug-resistant cells. Although the expanding tumor cell population may be successfully targeted, drug-resistant cells may persist and sustain the tumor or enter dormancy before igniting a future relapse. Herein, we show that partial knockdown of nucleoporin p62 (NUP62) by small-interfering RNA confers cisplatin resistance to cultured high-grade ovarian carcinoma cells. Treatment with NUP62 small-interfering RNA and cisplatin leaves resistant cells in a state of dormancy; some dormant cells can be induced to proliferate by transient induction of NUP62 expression from an ectopic expression construct. In addition to suggesting functional links between nuclear pore complex architecture and cancer cell survival, the culture system provides a novel experimental window into the dynamics of tumor cell drug resistance and dormancy.