Showing papers by "Johns Hopkins University published in 2000"

The Sloan Digital Sky Survey: Technical summary

Abstract: The Sloan Digital Sky Survey (SDSS) will provide the data to support detailed investigations of the distribution of luminous and nonluminous matter in the universe: a photometrically and astrometrically calibrated digital imaging survey of π sr above about Galactic latitude 30° in five broad optical bands to a depth of g' ~ 23 mag, and a spectroscopic survey of the approximately 106 brightest galaxies and 105 brightest quasars found in the photometric object catalog produced by the imaging survey. This paper summarizes the observational parameters and data products of the SDSS and serves as an introduction to extensive technical on-line documentation.

Distinct types of diffuse large B-cell lymphoma identified by gene expression profiling

Abstract: 12 Pathology and Microbiology, and 13 Diffuse large B-cell lymphoma (DLBCL), the most common subtype of non-Hodgkin's lymphoma, is clinically heterogeneous: 40% of patients respond well to current therapy and have prolonged survival, whereas the remainder succumb to the disease. We proposed that this variability in natural history reflects unrecognized molecular heterogeneity in the tumours. Using DNA microarrays, we have conducted a systematic characterization of gene expression in B-cell malignancies. Here we show that there is diversity in gene expression among the tumours of DLBCL patients, apparently reflecting the variation in tumour proliferation rate, host response and differentiation state of the tumour. We identified two molecularly distinct forms of DLBCL which had gene expression patterns indicative of different stages of B-cell differentiation. One type expressed genes characteristic of germinal centre B cells ('germinal centre B-like DLBCL'); the second type expressed genes normally induced during in vitro activation of peripheral blood B cells ('activated B-like DLBCL'). Patients with germinal centre B-like DLBCL had a significantly better overall survival than those with activated B-like DLBCL. The molecular classification of tumours on the basis of gene expression can thus identify previously undetected and clinically significant subtypes of cancer.

Determining Validity in Qualitative Inquiry

Abstract: (2000). Determining Validity in Qualitative Inquiry. Theory Into Practice: Vol. 39, Getting Good Qualitative Data to Improve Eduational Practice, pp. 124-130.

Serial analysis of gene expression

Abstract: PROBLEM TO BE SOLVED: To provide a method for preparing a short nucleotide sequence (tag) which is useful to identify a cDNA oligonucleotide and is derived from a restricted position in a mRNA or a cDNA. SOLUTION: This is the method of preparing a tag for identifying the cDNA oligonucleotide. The above method comprises preparing the cDNA oligonucleotide bearing 5' and 3' terminals, collecting cDNA fragments by cutting the cDNA oligonucleotide with a restriction enzyme at the first restriction endonuclease site, separating a cDNA oligonucleotide bearing 5' or 3' terminal and connecting an oligonucleotide linker to the isolated cDNA fragment bearing the cDNA oligonucleotide 5' or 3' terminal. Here, the oligonucleotide linker contains the recognition site of the second restriction endonuclease enzyme and the isolated cDNA fragment is cut with the second restriction endonuclease enzyme which cuts the cDNA fragment in a section separated from the recognition site to obtain the tag for identifying the cDNA oligonucleotide.

Association of Sleep-Disordered Breathing, Sleep Apnea, and Hypertension in a Large Community-Based Study

Abstract: ContextSleep-disordered breathing (SDB) and sleep apnea have been linked to hypertension in previous studies, but most of these studies used surrogate information to define SDB (eg, snoring) and were based on small clinic populations, or both.ObjectiveTo assess the association between SDB and hypertension in a large cohort of middle-aged and older persons.Design and SettingCross-sectional analyses of participants in the Sleep Heart Health Study, a community-based multicenter study conducted between November 1995 and January 1998.ParticipantsA total of 6132 subjects recruited from ongoing population-based studies (aged ≥40 years; 52.8% female).Main Outcome MeasuresApnea-hypopnea index (AHI, the average number of apneas plus hypopneas per hour of sleep, with apnea defined as a cessation of airflow and hypopnea defined as a ≥30% reduction in airflow or thoracoabdominal excursion both of which are accompanied by a ≥4% drop in oxyhemoglobin saturation), obtained by unattended home polysomnography. Other measures include arousal index; percentage of sleep time below 90% oxygen saturation; history of snoring; and presence of hypertension, defined as resting blood pressure of at least 140/90 mm Hg or use of antihypertensive medication.ResultsMean systolic and diastolic blood pressure and prevalence of hypertension increased significantly with increasing SDB measures, although some of this association was explained by body mass index (BMI). After adjusting for demographics and anthropometric variables (including BMI, neck circumference, and waist-to-hip ratio), as well as for alcohol intake and smoking, the odds ratio for hypertension, comparing the highest category of AHI (≥30 per hour) with the lowest category (<1.5 per hour), was 1.37 (95% confidence interval [CI], 1.03-1.83; P for trend=.005). The corresponding estimate comparing the highest and lowest categories of percentage of sleep time below 90% oxygen saturation (≥12% vs <0.05%) was 1.46 (95% CI, 1.12-1.88; P for trend <.001). In stratified analyses, associations of hypertension with either measure of SDB were seen in both sexes, older and younger ages, all ethnic groups, and among normal-weight and overweight individuals. Weaker and nonsignificant associations were observed for the arousal index or self-reported history of habitual snoring.ConclusionOur findings from the largest cross-sectional study to date indicate that SDB is associated with systemic hypertension in middle-aged and older individuals of different sexes and ethnic backgrounds.

Viral Load and Heterosexual Transmission of Human Immunodeficiency Virus Type 1

Abstract: Background and Methods We examined the influence of viral load in relation to other risk factors for the heterosexual transmission of human immunodeficiency virus type 1 (HIV-1). In a community-based study of 15,127 persons in a rural district of Uganda, we identified 415 couples in which one partner was HIV-1–positive and one was initially HIV-1–negative and followed them prospectively for up to 30 months. The incidence of HIV-1 infection per 100 person-years among the initially seronegative partners was examined in relation to behavioral and biologic variables. Results The male partner was HIV-1–positive in 228 couples, and the female partner was HIV-1–positive in 187 couples. Ninety of the 415 initially HIV-1–negative partners seroconverted (incidence, 11.8 per 100 person-years). The rate of male-to-female transmission was not significantly different from the rate of female-to-male transmission (12.0 per 100 person-years vs. 11.6 per 100 person-years). The incidence of seroconversion was highest among ...

Evidence for a Causal Association Between Human Papillomavirus and a Subset of Head and Neck Cancers

Abstract: Background: High-risk human papillomaviruses (HPVs) are etiologic agents for anogenital tract cancers and have been detected in head and neck squamous cell carcinomas (HNSCCs). We investigated, retrospectively, an etiologic role for HPVs in a large series of patients with HNSCC. Methods: Tumor tissues from 253 patients with newly diagnosed or recurrent HNSCC were tested for the presence of HPV genome by use of polymerase chain reaction (PCR)-based assays, Southern blot hybridization, and in situ hybridization. The viral E6 coding region was sequenced to confirm the presence of tumor-specific viral isolates. Exons 5‐9 of the TP53 gene were sequenced from 166 specimens. The hazard of death from HNSCC in patients with and without HPVpositive tumors was determined by proportional hazards regression analysis. Results: HPV was detected in 62 (25%) of 253 cases (95% confidence interval [CI] = 19%‐30%). Highrisk, tumorigenic type HPV16 was identified in 90% of the HPV-positive tumors. HPV16 was localized specifically by in situ hybridization within the nuclei of cancer cells in preinvasive, invasive, and lymph node disease. Southern blot hybridization patterns were consistent with viral integration. Poor tumor grade (odds ratio [OR] = 2.4; 95% CI = 1.2‐ 4.9) and oropharyngeal site (OR = 6.2; 95% CI = 3.1‐12.1) independently increased the probability of HPV presence. As compared with HPV-negative oropharyngeal cancers, HPVpositive oropharyngeal cancers were less likely to occur among moderate to heavy drinkers (OR = 0.17; 95% CI = 0.05‐0.61) and smokers (OR = 0.16; 95% CI = 0.02‐1.4), had a characteristic basaloid morphology (OR = 18.7; 95% CI = 2.1‐167), were less likely to have TP53 mutations (OR = 0.06; 95% CI = 0.01‐0.36), and had improved disease-specific survival (hazard ratio [HR] = 0.26; 95% CI = 0.07‐0.98). After adjustment for the presence of lymph node disease (HR = 2.3; 95% CI = 1.4‐ 3.8), heavy alcohol consumption (HR = 2.6; 95% CI = 1.4‐4.7), and age greater than 60 years old (HR = 1.4; 95% CI = 0.8‐2.3), all patients with HPV-positive tumors had a 59% reduction in risk of death from cancer when compared with HPV-negative HNSCC patients (HR = 0.41; 95% CI = 0.20‐0.88). Conclusions: These data extend recent molecular and epidemiologic studies and strongly suggest that HPV-positive oropharyngeal cancers comprise a distinct molecular, clinical, and pathologic disease entity that is likely causally associated with HPV infection and that has a markedly improved prognosis. [J Natl Cancer Inst 2000; 92:709‐20]

Final Results from the Hubble Space Telescope Key Project to Measure the Hubble Constant

Abstract: We present here the final results of the Hubble Space Telescope Key Project to measure the Hubble constant. We summarize our method, the results and the uncertainties, tabulate our revised distances, and give the implications of these results for cosmology. The analysis presented here benefits from a number of recent improvements and refinements, including (1) a larger LMC Cepheid sample to define the fiducial period-luminosity (PL) relations, (2) a more recent HST Wide Field and Planetary Camera 2 (WFPC2) photometric calibration, (3) a correction for Cepheid metallicity, and (4) a correction for incompleteness bias in the observed Cepheid PL samples. New, revised distances are given for the 18 spiral galaxies for which Cepheids have been discovered as part of the Key Project, as well as for 13 additional galaxies with published Cepheid data. The new calibration results in a Cepheid distance to NGC 4258 in better agreement with the maser distance to this galaxy. Based on these revised Cepheid distances, we find values (in km/sec/Mpc) of H0 = 71 +/- 2 (random) +/- 6 (systematic) (type Ia supernovae), 71 +/- 2 +/- 7 (Tully-Fisher relation), 70 +/- 5 +/- 6 (surface brightness fluctuations), 72 +/- 9 +/- 7 (type II supernovae), and 82 +/- 6 +/- 9 (fundamental plane). We combine these results for the different methods with 3 different weighting schemes, and find good agreement and consistency with H0 = 72 +/- 8. Finally, we compare these results with other, global methods for measuring the Hubble constant.

Determining the Number of Factors in Approximate Factor Models

Abstract: In this paper we develop some econometric theory for factor models of large dimensions The focus is the determination of the number of factors, which is an unresolved issue in the rapidly growing literature on multifactor models We propose some panel C(p) criteria and show that the number of factors can be consistently estimated using the criteria The theory is developed under the framework of large cross-sections (N) and large time dimensions (T) No restriction is imposed on the relation between N and T Simulations show that the proposed criteria yield almost precise estimates of the number of factors for configurations of the panel data encountered in practice

Current methods in medical image segmentation.

Abstract: ▪ Abstract Image segmentation plays a crucial role in many medical-imaging applications, by automating or facilitating the delineation of anatomical structures and other regions of interest. We present a critical appraisal of the current status of semiautomated and automated methods for the segmentation of anatomical medical images. Terminology and important issues in image segmentation are first presented. Current segmentation approaches are then reviewed with an emphasis on the advantages and disadvantages of these methods for medical imaging applications. We conclude with a discussion on the future of image segmentation methods in biomedical research.

Inactivation of the DNA-Repair Gene MGMT and the Clinical Response of Gliomas to Alkylating Agents

Abstract: Background The DNA-repair enzyme O 6-methylguanine-DNA methyltransferase (MGMT) inhibits the killing of tumor cells by alkylating agents. MGMT activity is controlled by a promoter; methylation of the promoter silences the gene in cancer, and the cells no longer produce MGMT. We examined gliomas to determine whether methylation of the MGMT promoter is related to the responsiveness of the tumor to alkylating agents. Methods We analyzed the MGMT promoter in tumor DNA by a methylation-specific polymerase-chain-reaction assay. The gliomas were obtained from patients who had been treated with carmustine (1,3-bis(2-chloroethyl)-1-nitrosourea, or BCNU). The molecular data were correlated with the clinical outcome. Results The MGMT promoter was methylated in gliomas from 19 of 47 patients (40 percent). This finding was associated with regression of the tumor and prolonged overall and disease-free survival. It was an independent and stronger prognostic factor than age, stage, tumor grade, or performance status. Con...

Fine Particulate Air Pollution and Mortality in 20 U.S. Cities, 1987–1994

Abstract: Background Air pollution in cities has been linked to increased rates of mortality and morbidity in developed and developing countries. Although these findings have helped lead to a tightening of air-quality standards, their validity with respect to public health has been questioned. Methods We assessed the effects of five major outdoor-air pollutants on daily mortality rates in 20 of the largest cities and metropolitan areas in the United States from 1987 to 1994. The pollutants were particulate matter that is less than 10 μm in aerodynamic diameter (PM10), ozone, carbon monoxide, sulfur dioxide, and nitrogen dioxide. We used a two-stage analytic approach that pooled data from multiple locations. Results After taking into account potential confounding by other pollutants, we found consistent evidence that the level of PM10 is associated with the rate of death from all causes and from cardiovascular and respiratory illnesses. The estimated increase in the relative rate of death from all causes was 0.51 pe...

Carbon monoxide has anti-inflammatory effects involving the mitogen-activated protein kinase pathway

Abstract: The stress-inducible protein heme oxygenase-1 provides protection against oxidative stress. The anti-inflammatory properties of heme oxygenase-1 may serve as a basis for this cytoprotection. We demonstrate here that carbon monoxide, a by-product of heme catabolism by heme oxygenase, mediates potent anti-inflammatory effects. Both in vivo and in vitro, carbon monoxide at low concentrations differentially and selectively inhibited the expression of lipopolysaccharide-induced pro-inflammatory cytokines tumor necrosis factor-α, interleukin-1β, and macrophage inflammatory protein-1β and increased the lipopolysaccharide-induced expression of the anti-inflammatory cytokine interleukin-10. Carbon monoxide mediated these anti-inflammatory effects not through a guanylyl cyclase–cGMP or nitric oxide pathway, but instead through a pathway involving the mitogen-activated protein kinases. These data indicate the possibility that carbon monoxide may have an important protective function in inflammatory disease states and thus has potential therapeutic uses.

Genes expressed in human tumor endothelium

Abstract: To gain a molecular understanding of tumor angiogenesis, we compared gene expression patterns of endothelial cells derived from blood vessels of normal and malignant colorectal tissues. Of over 170 transcripts predominantly expressed in the endothelium, 79 were differentially expressed, including 46 that were specifically elevated in tumor-associated endothelium. Several of these genes encode extracellular matrix proteins, but most are of unknown function. Most of these tumor endothelial markers were expressed in a wide range of tumor types, as well as in normal vessels associated with wound healing and corpus luteum formation. These studies demonstrate that tumor and normal endothelium are distinct at the molecular level, a finding that may have significant implications for the development of anti-angiogenic therapies.

A Comparison of Etanercept and Methotrexate in Patients with Early Rheumatoid Arthritis

Abstract: Background Etanercept, which blocks the action of tumor necrosis factor, reduces disease activity in patients with long-standing rheumatoid arthritis. Its efficacy in reducing disease activity and preventing joint damage in patients with active early rheumatoid arthritis is unknown. Methods We treated 632 patients with early rheumatoid arthritis with either twice-weekly subcutaneous etanercept (10 or 25 mg) or weekly oral methotrexate (mean, 19 mg per week) for 12 months. Clinical response was defined as the percent improvement in disease activity according to the criteria of the American College of Rheumatology. Bone erosion and joint-space narrowing were measured radiographically and scored with use of the Sharp scale. On this scale, an increase of 1 point represents one new erosion or minimal narrowing. Results As compared with patients who received methotrexate, patients who received the 25-mg dose of etanercept had a more rapid rate of improvement, with significantly more patients having 20 percent, ...

Recognition of the polyubiquitin proteolytic signal.

Abstract: Polyubiquitin chains linked through Lys48 are the principal signal for targeting substrates to the 26S proteasome. Through studies of structurally defined, polyubiquitylated model substrates, we show that tetraubiquitin is the minimum signal for efficient proteasomal targeting. The mechanism of targeting involves a simple increase in substrate affinity that is brought about by autonomous binding of the polyubiquitin chain. Assigning the proteasomal signaling function to a specific polymeric unit explains how a single ubiquitin can act as a functionally distinct signal, for example in endocytosis. The properties of the substrates studied here implicate substrate unfolding as a kinetically dominant step in the proteolysis of properly folded proteins, and suggest that extraproteasomal chaperones are required for efficient degradation of certain proteasome substrates.

Aggregation-Based Crystal Growth and Microstructure Development in Natural Iron Oxyhydroxide Biomineralization Products

Abstract: Crystals are generally considered to grow by attachment of ions to inorganic surfaces or organic templates. High-resolution transmission electron microscopy of biomineralization products of iron-oxidizing bacteria revealed an alternative coarsening mechanism in which adjacent 2- to 3-nanometer particles aggregate and rotate so their structures adopt parallel orientations in three dimensions. Crystal growth is accomplished by eliminating water molecules at interfaces and forming iron-oxygen bonds. Self-assembly occurs at multiple sites, leading to a coarser, polycrystalline material. Point defects (from surface-adsorbed impurities), dislocations, and slabs of structurally distinct material are created as a consequence of this growth mechanism and can dramatically impact subsequent reactivity.

Underlying causes and long-term survival in patients with initially unexplained cardiomyopathy.

Abstract: Background Previous studies of the prognosis of patients with heart failure due to cardiomyopathy categorized patients according to whether they had ischemic or nonischemic disease. The prognostic value of identifying more specific underlying causes of cardiomyopathy is unknown. Methods We evaluated the outcomes of 1230 patients with cardiomyopathy. The patients were grouped into the following categories according to underlying cause: idiopathic cardiomyopathy (616 patients), peripartum cardiomyopathy (51); and cardiomyopathy due to myocarditis (111), ischemic heart disease (91), infiltrative myocardial disease (59), hypertension (49), human immunodeficiency virus (HIV) infection (45), connective-tissue disease (39), substance abuse (37), therapy with doxorubicin (15), and other causes (117). Cox proportional-hazards analysis was used to assess the association between the underlying cause of cardiomyopathy and survival. Results During a mean follow-up of 4.4 years, 417 patients died and 57 underwent cardiac transplantation. As compared with the patients with idiopathic cardiomyopathy, the patients with peripartum cardiomyopathy had better survival (adjusted hazard ratio for death, 0.31; 95 percent confidence interval, 0.09 to 0.98), and survival was significantly worse among the patients with cardiomyopathy due to infiltrative myocardial disease (adjusted hazard ratio, 4.40; 95 percent confidence interval, 3.04 to 6.39), HIV infection (adjusted hazard ratio, 5.86; 95 percent confidence interval, 3.92 to 8.77), therapy with doxorubicin (adjusted hazard ratio, 3.46; 95 percent confidence interval, 1.67 to 7.18), and ischemic heart disease (adjusted hazard ratio, 1.52; 95 percent confidence interval, 1.07 to 2.17). Conclusions The underlying cause of heart failure has prognostic value in patients with unexplained cardiomyopathy. Patients with peripartum cardiomyopathy appear to have a better prognosis than those with other forms of cardiomyopathy. Patients with cardiomyopathy due to infiltrative myocardial diseases, HIV infection, or doxorubicin therapy have an especially poor prognosis.

Self-reported adherence to antiretroviral medications among participants in HIV clinical trials: The AACTG Adherence Instruments

Abstract: This paper describes the AACTG Adherence Instruments, which are comprised of two self-report questionnaires for use in clinical trials conducted by the Adult AIDS Clinical Trials Group (AACTG). The questionnaires were administered to 75 patients at ten AACTG sites in the USA. All patients were taking combination antiretroviral therapy (ART), including at least one protease inhibitor. Eleven per cent of patients reported missing at least one dose the day before the interview, and 17% reported missing at least one dose during the two days prior. The most common reasons for missing medications included 'simply forgot' (66%) and a number of factors often associated with improved health, including being busy (53%), away from home (57%) and changes in routine (51%). Less adherent patients reported lower adherence self-efficacy (p = 0.006) and were less sure of the link between non-adherence and the development of drug resistance (p = 0.009). They were also more likely to consume alcohol, to be employed outside the home for pay and to have enrolled in clinical trials to gain access to drugs (all p < 0.05). Twenty-two per cent of patients taking drugs requiring special instructions were unaware of these instructions. Each questionnaire took approximately ten minutes to complete. Responses to the questionnaires were favourable. These questionnaires have been included in six AACTG clinical trials to date and have been widely disseminated to investigators both in the USA and abroad.

Incremental and Decremental Support Vector Machine Learning

Abstract: An on-line recursive algorithm for training support vector machines, one vector at a time, is presented. Adiabatic increments retain the Kuhn-Tucker conditions on all previously seen training data, in a number of steps each computed analytically. The incremental procedure is reversible, and decremental "unlearning" offers an efficient method to exactly evaluate leave-one-out generalization performance. Interpretation of decremental unlearning in feature space sheds light on the relationship between generalization and geometry of the data.

Reactive Oxygen Species (Ros-Induced) Ros Release: A New Phenomenon Accompanying Induction of the Mitochondrial Permeability Transition in Cardiac Myocytes

Abstract: We sought to understand the relationship between reactive oxygen species (ROS) and the mitochondrial permeability transition (MPT) in cardiac myocytes based on the observation of increased ROS production at sites of spontaneously deenergized mitochondria We devised a new model enabling incremental ROS accumulation in individual mitochondria in isolated cardiac myocytes via photoactivation of tetramethylrhodamine derivatives, which also served to report the mitochondrial transmembrane potential, ΔΨ This ROS accumulation reproducibly triggered abrupt (and sometimes reversible) mitochondrial depolarization This phenomenon was ascribed to MPT induction because (a) bongkrekic acid prevented it and (b) mitochondria became permeable for calcein (∼620 daltons) concurrently with depolarization These photodynamically produced “triggering” ROS caused the MPT induction, as the ROS scavenger Trolox prevented it The time required for triggering ROS to induce the MPT was dependent on intrinsic cellular ROS-scavenging redox mechanisms, particularly glutathione MPT induction caused by triggering ROS coincided with a burst of mitochondrial ROS generation, as measured by dichlorofluorescein fluorescence, which we have termed mitochondrial “ROS-induced ROS release” (RIRR) This MPT induction/RIRR phenomenon in cardiac myocytes often occurred synchronously and reversibly among long chains of adjacent mitochondria demonstrating apparent cooperativity The observed link between MPT and RIRR could be a fundamental phenomenon in mitochondrial and cell biology

Long-term effects of budesonide or nedocromil in children with asthma.

Abstract: BACKGROUND Antiinflammatory therapies, such as inhaled corticosteroids or nedocromil, are recommended for children with asthma, although there is limited information on their long-term use. METHODS We randomly assigned 1041 children from 5 through 12 years of age with mild-to-moderate asthma to receive 200 microg of budesonide (311 children), 8 mg of nedocromil (312 children), or placebo (418 children) twice daily. We treated the participants for four to six years. All children used albuterol for asthma symptoms. RESULTS There was no significant difference between either treatment and placebo in the primary outcome, the degree of change in the forced expiratory volume in one second (FEV1, expressed as a percentage of the predicted value) after the administration of a bronchodilator. As compared with the children assigned to placebo, the children assigned to receive budesonide had a significantly smaller decline in the ratio of FEV1 to forced vital capacity (FVC, expressed as a percentage) before the administration of a bronchodilator (decline in FEV1:FVC, 0.2 percent vs. 1.8 percent). The children given budesonide also had lower airway responsiveness to methacholine, fewer hospitalizations (2.5 vs. 4.4 per 100 person-years), fewer urgent visits to a caregiver (12 vs. 22 per 100 person-years), greater reduction in the need for albuterol for symptoms, fewer courses of prednisone, and a smaller percentage of days on which additional asthma medications were needed. As compared with placebo, nedocromil significantly reduced urgent care visits (16 vs. 22 per 100 person-years) and courses of prednisone. The mean increase in height in the budesonide group was 1.1 cm less than in the placebo group (22.7 vs. 23.8 cm, P=0.005); this difference was evident mostly within the first year. The height increase was similar in the nedocromil and placebo groups. CONCLUSIONS In children with mild-to-moderate asthma, neither budesonide nor nedocromil is better than placebo in terms of lung function, but inhaled budesonide improves airway responsiveness and provides better control of asthma than placebo or nedocromil. The side effects of budesonide are limited to a small, transient reduction in growth velocity.

Promoter Hypermethylation and BRCA1 Inactivation in Sporadic Breast and Ovarian Tumors

Abstract: Background: Inherited mutations in the BRCA1 gene may be responsible for almost half of inherited breast carcinomas. However, somatic (acquired) mutations in BRCA1 have not been reported, despite frequent loss of heterozygosity (LOH or loss of one copy of the gene) at the BRCA1 locus and loss of BRCA1 protein in tumors. To address whether BRCA1 may be inactivated by pathways other than mutations in sporadic tumors, we analyzed the role of hypermethylation of the gene's promoter region. Methods: Methylation patterns in the BRCA1 promoter were assessed in breast cancer cell lines, xenografts, and 215 primary breast and ovarian carcinomas by methylation-specific polymerase chain reaction (PCR). BRCA1 RNA expression was determined in cell lines and seven xenografts by reverse transcription-PCR. P values are two-sided. Results: The BRCA1 promoter was found to be unmethylated in all normal tissues and cancer cell lines tested. However, BRCA1 promoter hypermethylation was present in two breast cancer xenografts, both of which had loss of the BRCA1 transcript. BRCA1 promoter hypermethylation was present in 11 (13%) of 84 unselected primary breast carcinomas. BRCA1 methylation was strikingly associated with the medullary (67% methylated; P = .0002 versus ductal) and mucinous (55% methylated; P = .0033 versus ductal) subtypes, which are overrepresented in BRCA1 families. In a second series of 66 ductal breast tumors informative for LOH, nine (20%) of 45 tumors with LOH had BRCA1 hypermethylation, while one (5%) of 21 without LOH was methylated (P = .15). In ovarian neoplasms, BRCA1 methylation was found only in tumors with LOH, four (31%) of 13 versus none of 18 without LOH (P = .02). The BRCA1 promoter was unmethylated in other tumor types. Conclusion: Silencing of the BRCA1 gene by promoter hypermethylation occurs in primary breast and ovarian carcinomas, especially in the presence of LOH and in specific histopathologic subgroups. These findings support a role for this tumor suppressor gene in sporadic breast and ovarian tumorigenesis.

Regulation of tumor angiogenesis by p53-induced degradation of hypoxia-inducible factor 1α

Abstract: The switch to an angiogenic phenotype is a fundamental determinant of neoplastic growth and tumor progression. We demonstrate that homozygous deletion of the p53 tumor suppressor gene via homologous recombination in a human cancer cell line promotes the neovascularization and growth of tumor xenografts in nude mice. We find that p53 promotes Mdm2-mediated ubiquitination and proteasomal degradation of the HIF-1α subunit of hypoxia-inducible factor 1 (HIF-1), a heterodimeric transcription factor that regulates cellular energy metabolism and angiogenesis in response to oxygen deprivation. Loss of p53 in tumor cells enhances HIF-1α levels and augments HIF-1-dependent transcriptional activation of the vascular endothelial growth factor (VEGF) gene in response to hypoxia. Forced expression of HIF-1α in p53-expressing tumor cells increases hypoxia-induced VEGF expression and augments neovascularization and growth of tumor xenografts. These results indicate that amplification of normal HIF-1-dependent responses to hypoxia via loss of p53 function contributes to the angiogenic switch during tumorigenesis.