Annealing helicase HARP closes RPA-stabilized DNA bubbles non-processively.

We investigate the mechanistic nature of the Snf2 family protein HARP, mutations of which are responsible for Schimke immuno-osseous dysplasia. Using a single-molecule magnetic tweezers assay, we construct RPA-stabilized DNA bubbles within torsionally constrained DNA to investigate the annealing action of HARP on a physiologically relevant substrate. We find that HARP closes RPA-stabilized bubbles in a slow reaction, taking on the order of tens of minutes for ∼600 bp of DNA to be re-annealed. The data indicate that DNA re-anneals through the removal of RPA, which is observed as clear steps in the bubble-closing traces. The dependence of the closing rate on both ionic strength and HARP concentration indicates that removal of RPA occurs via an association-dissociation mechanism where HARP does not remain associated with the DNA. The enzyme exhibits classical Michaelis-Menten kinetics and acts cooperatively with a Hill coefficient of 3 ± 1. Our work also allows the determination of some important features of RPA-bubble structures at low supercoiling, including the existence of multiple bubbles and that RPA molecules are mis-registered on the two strands.

The chromatin remodeling factor CHD5 is a transcriptional repressor of WEE1.

Loss of the chromatin remodeling ATPase CHD5 has been linked to the progression of neuroblastoma tumors, yet the underlying mechanisms behind the tumor suppressor role of CHD5 are unknown. In this study, we purified the human CHD5 complex and found that CHD5 is a component of the full NuRD transcriptional repressor complex, which also contains methyl-CpG binding proteins and histone deacetylases. The CHD5/NuRD complex appears mutually exclusive with the related CHD4/NuRD complex as overexpression of CHD5 results in loss of the CHD4 protein in cells. Following a search for genes that are regulated by CHD5 in neuroblastoma cells, we found that CHD5 binds to and represses the G2/M checkpoint gene WEE1. Reintroduction of CHD5 into neuroblastoma cells represses WEE1 expression, demonstrating that CHD5 can function as a repressor in cells. A catalytically inactive mutant version of CHD5 is able to associate with a NuRD cofactor but fails to repress transcription. Our study shows that CHD5 is a NuRD-associated transcriptional repressor and identifies WEE1 as one of the CHD5-regulated genes that may link CHD5 to tumor suppression.

The tumor suppressor chromodomain helicase DNA-binding protein 5 (CHD5) remodels nucleosomes by unwrapping.

Although mutations or deletions of chromodomain helicase DNA-binding protein 5 (CHD5) have been linked to cancer and implicate CHD5 in tumor suppression, the ATP-dependent activity of CHD5 is currently unknown. In this study, we discovered that CHD5 is a chromatin remodeling factor with a unique enzymatic activity. CHD5 can expose nucleosomal DNA at one or two discrete positions in the nucleosome. The exposure of the nucleosomal DNA by CHD5 is dependent on ATP hydrolysis, but continued ATP hydrolysis is not required to maintain the nucleosomes in their remodeled state. The activity of CHD5 is distinct from other related chromatin remodeling ATPases, such as ACF and BRG1, and does not lead to complete disruption or destabilization of the nucleosome. Rather, CHD5 likely initiates remodeling in a manner similar to that of other remodeling factors but does not significantly reposition the nucleosome. While the related factor CHD4 shows strong ATPase activity, it does not unwrap nucleosomes as efficiently as CHD5. Our findings add to the growing evidence that chromatin remodeling ATPases have diverse roles in modulating chromatin structure.

HARP preferentially co-purifies with RPA bound to DNA-PK and blocks RPA phosphorylation.

The HepA-related protein (HARP/SMARCAL1) is an ATP-dependent annealing helicase that is capable of rewinding DNA structures that are stably unwound due to binding of the single-stranded DNA (ssDNA)-binding protein Replication Protein A (RPA). HARP has been implicated in maintaining genome integrity through its role in DNA replication and repair, two processes that generate RPA-coated ssDNA. In addition, mutations in HARP cause a rare disease known as Schimke immuno-osseous dysplasia. In this study, we purified HARP containing complexes with the goal of identifying the predominant factors that stably associate with HARP. We found that HARP preferentially interacts with RPA molecules that are bound to the DNA-dependent protein kinase (DNA-PK). We also found that RPA is phosphorylated by DNA-PK in vitro, while the RPA-HARP complexes are not. Our results suggest that, in addition to its annealing helicase activity, which eliminates the natural binding substrate for RPA, HARP blocks the phosphorylation of RPA by DNA-PK.

Promoter methylation of DAPK1, FHIT, MGMT, and CDKN2A genes in cervical carcinoma.

BACKGROUND AND OBJECTIVES: Aberrant DNA methylation contributes to the malignant phenotype in virtually all types of human cancer. This study explored the relationship between promoter methylation and inactivation of the DAPK1, FHIT, MGMT, and CDKN2A genes in cervical cancer. METHODS: The promoter methylation of DAPK1, FHIT, MGMT, and CDKN2A was investigated by using a methylation-specific polymerase chain reaction in 53 specimens of cervical cancer (42 squamous cell carcinoma, 11 adenocarcinoma), 22 specimens of intraepithelial neoplasia tissues, and 24 control normal cervical tissue specimens. The correlation of promoter methylation with the clinicopathological features of cervical cancer was analyzed. The expressions of DAPK1, FHIT, MGMT, and CDKN2A were detected by measuring relative mRNA levels. RESULTS: The promoter methylation of DAPK1, FHIT, MGMT, and CDKN2A in cervical cancer vs. intraepithelial neoplasia vs. normal cervical tissue was 75.5 vs. 31.8 vs. 4.2 % (p < 0.0001), 66.0 vs. 59.1 vs. 25.0 % (p = 0.0033), 34.0 vs. 27.3 vs. 20.8 % (p = 0.76), and 17.0 vs. 31.8 vs. 8.3 % (p = 0.11), respectively. The methylation of the promoter region significantly decreased the expression of only DAPK1 (p = 0.03). The methylation rate of the DAPK1 gene promoter was significantly higher in cervical cancer tissues than in cervical intraepithelial neoplasia and normal cervical tissues. CONCLUSION: Promoter methylation may therefore lead to the inactivation of the DAPK1 gene, and may be related to the progression of cervical oncogenesis.

Identification of receptor tyrosine kinase, discoidin domain receptor 1 (DDR1), as a potential biomarker for serous ovarian cancer.

Ovarian cancer, one of the most common gynecological malignancies, has an aggressive phenotype. It is necessary to develop novel and more effective treatment strategies against advanced disease. Protein tyrosine kinases (PTKs) play an important role in the signal transduction pathways involved in tumorigenesis, and represent potential targets for anticancer therapies. In this study, we performed cDNA subtraction following polymerase chain reaction (PCR) using degenerate oligonucleotide primers to identify specifically overexpressed PTKs in ovarian cancer. Three PTKs, janus kinase 1, insulin-like growth factor 1 receptor, and discoidin domain receptor 1 (DDR1), were identified and only DDR1 was overexpressed in all ovarian cancer tissues examined for the validation by quantitative real-time PCR. The DDR1 protein was expressed in 63% (42/67) of serous ovarian cancer tissue, whereas it was undetectable in normal ovarian surface epithelium. DDR1 was expressed significantly more frequently in high-grade (79%) and advanced stage (77%) tumors compared to low-grade (50%) and early stage (43%) tumors. The expression of the DDR1 protein significantly correlated with poor disease-free survival. Although its functional role and clinical utility remain to be examined in future studies, our results suggest that the expression of DDR1 may serve as both a potential biomarker and a molecular target for advanced ovarian cancer.

Germline copy number variations in BRCA1-associated ovarian cancer patients.

We investigated characteristics of germline copy number variations (CNV) in BRCA1-associated ovarian cancer patients by comparing them to CNVs present in sporadic ovarian cancer patients. Germline CNVs in 51 BRCA1-associated, 33 sporadic ovarian cancer patients, and 47 healthy women were analyzed by both signal intensity and genotyping data using the Affymetrix Genome-Wide Human SNP Array 6.0. The total number of CNVs per genome was greater in the sporadic group (median 26, range 12-34) than in the BRCA1 group (median 21, range 11-35; post hoc P < 0.05) or normal group (median 20, range 7-32; post hoc P < 0.05). While the number of amplifications per genome was higher in the sporadic group (median 13, range 7-26) than in the BRCA1 group (median 8, range 3-23; post hoc P < 0.001), the number of deletions per genome was higher in the BRCA1 group (median 12, range 6-24) than in the sporadic group (median 9, range 3-17; post hoc P < 0.01). In addition, 31 previously unknown CNV regions were present specifically in the BRCA1 group. When we performed pathway analysis on the 241 overlapping genes mapped to these novel CNV regions, the 'purine metabolism' and '14-3-3-mediated signaling' pathways were over-represented (Fisher's exact test, P < 0.01). Our study shows that there are qualitative differences in genomic CNV profiles between BRCA1-associated and sporadic ovarian cancer patients. Further studies are necessary to clarify the significance of the genomic CNV profile unique to BRCA1-associated ovarian cancer patients.

Meta-analysis of genome-wide association scans for genetic susceptibility to endometriosis in Japanese population.

To identify susceptibility genes for endometriosis in Japanese women, genome-wide association (GWA) analysis was performed using two case-control cohorts genotyped with the Affymetrix Mapping 500K Array or Genome-Wide Human SNP Array 6.0. In each of the two array cohorts, stringent quality control (QC) filters were applied to newly obtained genotype data, together with previously analyzed data from the Japanese Integrated Database Project. After QC-based filtering of samples and single nucleotide polymorphisms (SNPs) in each cohort, 282 838 SNPs in both genotyping platforms were tested for association with endometriosis using a meta-analysis of the two GWA studies with 696 patients with endometriosis and 825 controls. The meta-analysis revealed that a common susceptibility locus conferring a large effect on the disease risk was unlikely. On the other hand, an excess of SNPs with P-values <10(-4) (36 vs 28 SNPs expected by chance) was observed in the meta-analysis. Of note, four of the top five SNPs with P-values <10(-5) were located in and around IL1A (interleukin 1α), which might be a functional candidate gene for endometriosis. Further studies with larger case-control cohorts will be necessary to elucidate the genetic risk factors.

Serum leptin-adiponectin ratio and endometrial cancer risk in postmenopausal female subjects.

OBJECTIVE: Obesity is a well-known risk factor for the development of endometrial cancer. Elevated endogenous estrogen and insulin resistance are recognized to be major factors that link obesity and cancer development. However, there is increasing evidence that the adipokines adiponectin and leptin, which are directly produced in adipose tissue, impact several obesity-related cancers. The purpose of the current study was to investigate the relationships of the concentration of leptin, adiponectin, and the leptin-to-adiponectin ratio (L/A ratio) with the endometrial cancer risk in postmenopausal female subjects. METHODS: A case-control study was performed in 146 postmenopausal female subjects with endometrial cancer and 150 control subjects with no history of cancer. The serum levels of the adipokines leptin and adiponectin were measured, and the associations of these adipokines and the L/A ratios with the endometrial cancer risk were analyzed. RESULTS: The leptin levels and the L/A ratios were significantly higher in the incident cases of endometrial cancer (8.2 ± 0.5, 2.05 ± 1.08 ng/ml) than in the controls subjects (4.5 ± 0.5, 0.98 ± 0.18, P<0.0001), whereas the adiponectin levels were significantly lower in the incident cases (6.2 ± 0.4 µg/ml) than in the control subjects (9.0 ± 0.4 µg/ml, P<0.0001). For the incident cases, the serum levels of the adipokines were significantly correlated with the patient body mass index (BMI) (P<0.001 for leptin, P<0.05 for adiponectin), and the leptin levels and the L/A ratios were significantly correlated with the homeostasis model assessment ratio (HOMA-R) and the fasting insulin levels (P<.001). Higher L/A ratios were found to be significantly associated with an increased risk of endometrial cancer [OR (95% CI) for the top vs. the bottom tertile of the L/A ratio was 6.0 (3.2-11.9), P-value<0.0001]. Moreover, the ORs of the L/A ratios were higher than those of leptin or adiponectin alone. The association of the L/A ratios with endometrial cancer risk remained after adjusting for the obesity indices, hypertension, and presence of diabetes mellitus. CONCLUSION: The present results suggested that the L/A ratio was independently associated with an increased risk for endometrial cancer development. Additional research will elucidate the molecular mechanisms by which these adipokines are associated with the development of endometrial cancer.

Increased apoptosis of germ cells in patients with AZFc deletions.

PURPOSE: AZFc deletions are associated with variable testicular histology ranging from the Sertoli cell only to spermatogenic arrest and hypospermatogenesis. Such variable phenotypes may be explained by progressive germ cell regression over time. Increased apoptosis is likely responsible for progressive regression of spermatogenic potential. This study evaluated germ cell apoptosis as a cause of the progressive decrease in the number of germ cells in patients with AZFc deletions. METHODS: This study evaluated germ cell apoptosis in patients with AZFc deletions. A total of 151 patients who were diagnosed with either severe oligozoospermia or non-obstructive azoospermia were screened for Y chromosome microdeletions. Germ cell apoptosis was examined using terminal deoxy-nucleotidyl transferase-mediated digoxigenin-dUTP nick-end labeling (TUNEL) on formalin-fixed 5-microm sections of testicular specimens. RESULTS: Seven out of 117 (6.0%) patients with azoospermia and 4 of 34 (11.8%) patients with severe oligozoospermia had Y chromosome microdeletions. The percentage of apoptotic germ cells in the testes of patients with AZFc deletions were significantly increased compared to those of patients without AZFc deletions. CONCLUSIONS: These results suggest that increased apoptosis of germ cells is responsible for the progressive decline of spermatogenic potential in patients with AZFc deletions.

Relationship between single nucleotide polymorphisms in CYP1A1 and CYP1B1 genes and the bone mineral density and serum lipid profiles in postmenopausal Japanese women taking hormone therapy.

OBJECTIVE: The genetic variations of the genes encoding cytochrome P-450 enzymes are considered to play an important role in the metabolism of estradiol. The objective of this study was to evaluate the relationships among single nucleotide polymorphisms (SNPs) of cytochrome P-450 genes, lumbar bone mineral density (BMD), and serum lipids and to determine the effects of hormone therapy (HT). DESIGN: The participants were 124 Japanese women who had been diagnosed with osteopenia or osteoporosis and were taking HT for 12 months. Seven single nucleotide polymorphisms in the CYP1A1 and CYP1B1 genes were characterized. Lumbar BMD and the levels of serum lipids were measured before and after HT. RESULTS: A single nucleotide polymorphism in exon 3 of CYP1B1 was found to be significantly associated with the effect of HT on BMD and low-density lipoprotein cholesterol both in univariate and multivariate analyses. In the women with the GG genotype of L432V, the responses to HT of BMD and low-density lipoprotein cholesterol markedly decreased. The serum follicle-stimulating hormone level after HT was significantly higher in the women with the GG genotype of L432V. CONCLUSIONS: These results suggest that the L432V polymorphism in the CYP1B1 gene could therefore be used to predict the effect of HT on lumbar BMD and low-density lipoprotein cholesterol in Japanese women.

Association between single nucleotide polymorphisms of drug resistance-associated genes and response to chemotherapy in advanced ovarian cancer.

BACKGROUND: Single nucleotide polymorphisms (SNPs) may show clinicopathological importance as prognostic markers. This study examined the association of SNPs and the expression of drug resistance-associated markers with response to chemotherapy in advanced ovarian cancer (stages III and IV) patients. MATERIALS AND METHODS: SNPs were analyzed for MDR1, MRP1, MRP2 and LRP in 60 advanced ovarian cancer patients. The protein expression of each factor was analyzed by immunohistochemistry in all patients. RESULTS: As a result of examining the relevance of SNP genotypes to the response to chemotherapy, a significant relevance (p=0.01) was observed regarding MRP1 exon-17 SNP (G2168A) involving amino acid substitution. No significant relationship was observed between protein expression and the response to chemotherapy or disease-free survival time. CONCLUSION: Analysis of drug resistance gene polymorphism appears to be an indicator of the response to chemotherapy in advanced ovarian cancer.

Association of polymorphisms in the beta2 and beta3 adrenoceptor gene with polycystic ovary syndrome.

OBJECTIVE: To investigate polymorphisms of the beta2 and beta3 adrenoceptor (BAR-2 and BAR-3, respectively) genes associated with insulin-resistant polycystic ovary syndrome (PCOS) pathogenesis. STUDY DESIGN: Fifty-nine infertile Japanese women with PCOS and 97 healthy Japanese controls were studied. Blood metabolites and genomic DNA polymorphisms of BAR-2 (Arg16Gly and Gln27Glu) and BAR-3 (Trp64Arg) were analyzed. RESULTS: The PCOS group had significantly higher weight, body mass index, lipidemia and insulin resistance as compared to the control group. Glu 27 allele frequency in BAR-2 was significantly higher in PCOS patients as compared to the controls (0.07 vs 0.02, chi2 = 5.91, p = 0.02, OR 4.63, 95% CI 1.35-5.93), while Gly 16 allele frequency was only slightly higher in the PCOS group as compared to the controls (0.58 vs. 0.47, chi2 = 3.06, p = 0.08, OR 1.51, 95% CI 0.95-2.40). The Arg 64 allele frequency of BAR-3 was not significantly different between the 2 groups. Women with the Gly/Gly genotype for codon 16 or with either the Gln/Glu or Glu/Glu genotype for the codon 27 polymorphism of BAR-2 had significantly higher insulin resistance than those with the Arg/Arg and Gln/Gln genotypes. CONCLUSION: The polymorphism in codon 27 (Gln27Glu) of BAR-2 is linked to the expression of PCOS in Japanese women.