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Paul Meltzer

Publications and source records attributed to Paul Meltzer.

16 recordsLinked to original sources
PubMed2005

Stress-specific signatures: expression profiling of p53 wild-type and -null human cells.

Gene expression responses of human cell lines exposed to a diverse set of stress agents were compared by cDNA microarray hybridization. The B-lymphoblastoid cell line TK6 (p53 wild-type) and its p53-null derivative, NH32, were treated in parallel to facilitate investigation of p53-dependent responses. RNA was extracted 4 h after the beginning of treatment when no notable decrease in cell viability was evident in the cultures. Gene expression signatures were defined that discriminated between four broad general mechanisms of stress agents: Non-DNA-damaging stresses (heat shock, osmotic shock, and 12-O-tetradecanoylphorbol 13-acetate), agents causing mainly oxidative stress (arsenite and hydrogen peroxide), ionizing radiations (neutron and gamma-ray exposures), and other DNA-damaging agents (ultraviolet radiation, methyl methanesulfonate, adriamycin, camptothecin, and cis-Platinum(II)diammine dichloride (cisplatin)). Within this data set, non-DNA-damaging stresses could be discriminated from all DNA-damaging stresses, and profiles for individual agents were also defined. While DNA-damaging stresses showed a strong p53-dependent element in their responses, no discernible p53-dependent responses were triggered by the non-DNA-damaging stresses. A set of 16 genes did exhibit a robust p53-dependent pattern of induction in response to all nine DNA-damaging agents, however.

B-Lymphocytes↗
PubMed2004

Pim-1 is up-regulated by constitutively activated FLT3 and plays a role in FLT3-mediated cell survival.

Constitutively activating internal tandem duplication (ITD) mutations of the receptor tyrosine kinase FLT3 (Fms-like tyrosine kinase 3) play an important role in leukemogenesis, and their presence is associated with poor prognosis in acute myeloid leukemia (AML). To better understand FLT3 signaling in leukemogenesis, we have examined the changes in gene expression induced by FLT3/ITD or constitutively activated wild-type FLT3 expression. Microarrays were used with RNA harvested before and after inhibition of FLT3 signaling. Pim-1 was found to be one of the most significantly down-regulated genes upon FLT3 inhibition. Pim-1 is a proto-oncogene and is known to be up-regulated by signal transducer and activator of transcription 5 (STAT5), which itself is a downstream target of FLT3 signaling. Quantitative polymerase chain reaction (QPCR) confirmed the microarray results and demonstrated approximately 10-fold decreases in Pim-1 expression in response to FLT3 inhibition. Pim-1 protein also decreased rapidly in parallel with decreasing autophosphorylation activity of FLT3. Enforced expression of either the 44-kDa or 33-kDa Pim-1 isotypes resulted in increased resistance to FLT3 inhibition-mediated cytotoxicity and apoptosis. In contrast, expression of a dominant-negative Pim-1 construct accelerated cytotoxicity in response to FLT3 inhibition and inhibited colony growth of FLT3/ITD-transformed BaF3 cells. These findings demonstrate that constitutively activated FLT3 signaling up-regulates Pim-1 expression in leukemia cells. This up-regulation contributes to the proliferative and antiapoptotic pathways induced by FLT3 signaling.

Animals↗
PubMed2004

Microarray expression profiling in melanoma reveals a BRAF mutation signature.

We have used microarray gene expression profiling and machine learning to predict the presence of BRAF mutations in a panel of 61 melanoma cell lines. The BRAF gene was found to be mutated in 42 samples (69%) and intragenic mutations of the NRAS gene were detected in seven samples (11%). No cell line carried mutations of both genes. Using support vector machines, we have built a classifier that differentiates between melanoma cell lines based on BRAF mutation status. As few as 83 genes are able to discriminate between BRAF mutant and BRAF wild-type samples with clear separation observed using hierarchical clustering. Multidimensional scaling was used to visualize the relationship between a BRAF mutation signature and that of a generalized mitogen-activated protein kinase (MAPK) activation (either BRAF or NRAS mutation) in the context of the discriminating gene list. We observed that samples carrying NRAS mutations lie somewhere between those with or without BRAF mutations. These observations suggest that there are gene-specific mutation signals in addition to a common MAPK activation that result from the pleiotropic effects of either BRAF or NRAS on other signaling pathways, leading to measurably different transcriptional changes.

Amino Acid Substitution↗
PubMed2004

Modulation of transcriptional sensitivity of mineralocorticoid and estrogen receptors.

Recent reports describe the ability of factors to modulate the position of the dose-response curve of receptor-agonist complexes, and the amount of partial agonist activity of receptor-antagonist complexes, of androgen, glucocorticoid (GRs), and progesterone receptors (PRs). We now ask whether this modulation extends to the two remaining steroid receptors: mineralocorticoid (MRs) and estrogen receptors (ERs). These studies of MR were facilitated by our discovery that the antiglucocorticoid dexamethasone 21-mesylate (Dex-Mes) is a new antimineralocorticoid with significant amounts of partial agonist activity. Elevated levels of MR, the co-activators TIF2 and SRC-1, and the co-repressor SMRT do modulate the dose-response curve and partial agonist activity of MR complexes. Interestingly, the precise responses are indistinguishable from those seen with GRs in the same cells. Thus, the unequal transactivation of common genes by MRs versus GRs probably cannot be explained by differential responses to changing cellular concentrations of homologous receptor, co-activators, or co-repressors. We also find that the dose-response curve of ER-estradiol complexes is left-shifted to lower steroid concentrations by higher amounts of exogenous ER. Therefore, the modulation of either the dose-response curve of agonists or the partial agonist activity of antisteroid, and in many cases the modulation of both properties, is a common phenomenon for all of the classical steroid receptors.

Affinity Labels↗
PubMed2003

Biology of childhood osteogenic sarcoma and potential targets for therapeutic development: meeting summary.

Childhood osteogenic sarcoma (OS) is a rare bone cancer occurring primarily in adolescents. The North American pediatric cooperative groups have performed a series of clinical treatment trials in this disease over the past several decades, and biology studies of tumor tissue have been an important study component. A meeting was held in Bethesda, Maryland on November 29-30, 2001, sponsored by the NIH Office of Rare Diseases, the Children's Oncology Group, and the National Cancer Institute-Cancer Therapy Evaluation Program with the general objectives: (a) to review the current state of knowledge regarding OS biology; (b) to identify, prioritize, and support the development of biology studies of potential clinical relevance in OS; and (c) to discuss the available tissue resources and the appropriate methods for analysis of OS samples for the conduct of biology studies. This report summarizes the information presented and discussed by the meeting participants.

Angiogenesis Inhibitors↗
PubMed2003

Mutant thyroid hormone receptor beta represses the expression and transcriptional activity of peroxisome proliferator-activated receptor gamma during thyroid carcinogenesis.

The molecular genetics underlying thyroid carcinogenesis is not clear. Recent identification of a PAX8-peroxisome proliferator-activated receptor gamma (PPARgamma) fusion gene in human thyroid follicular carcinoma suggests a tumor suppressor role of PPARgamma in thyroid carcinogenesis. Mice harboring a knockin mutant thyroid hormone beta receptor (TRbetaPV) spontaneously develop thyroid follicular carcinoma through pathological progression of hyperplasia, capsular invasion, vascular invasion, anaplasia, and eventually, distant organ metastasis. This mutant mouse (TRbeta(PV/PV) mouse) provides an unusual opportunity to ascertain the role of PPARgamma in thyroid carcinogenesis. Here, we show that the expression of PPARgamma mRNA was repressed in the thyroid gland of mutant mice during carcinogenesis. In addition, TRbetaPV acted to abolish the ligand (troglitazone)-mediated transcriptional activity of PPARgamma. These results indicate that repression of PPARgamma expression and its transcriptional activity are associated with thyroid carcinogenesis and raise the possibility that PPARgamma could be tested as a therapeutic target in thyroid follicular carcinoma.

Adenocarcinoma, Follicular↗
PubMed2003

Alterations in genomic profiles during tumor progression in a mouse model of follicular thyroid carcinoma.

The molecular genetics underlying thyroid carcinogenesis is not well understood. We have recently created a mutant mouse by targeting a mutation (PV) into the thyroid hormone receptor beta gene (TRbetaPV mouse). TRbetaPV/PV mice spontaneously develop follicular thyroid carcinoma through pathological progression of hyperplasia, capsular and vascular invasion, anaplasia and eventually metastasis to distant organs. TRbetaPV/PV mice provide an unusual opportunity to study the alterations in gene regulation that occur during thyroid carcinogenesis. To this end, we profiled the genomic changes in the thyroids of TRbetaPV/PV mice at 6 months of age, at which time metastasis had begun. From arrays of 20 000 mouse cDNAs, 185 genes were up-regulated (2-17-fold) and 92 were down-regulated (2-20-fold). Functional clustering of named genes with reported functions (100 genes) indicated that approximately 39% of these genes were tumor-, metastasis/invasion- and cell-cycle-related. Among the activated tumor-related genes identified, cyclin D1, pituitary tumor transforming gene-1, cathespin D and transforming growth factor alpha were also found to over-express in human thyroid cancers. Analyses of the gene profiles suggested that the signaling pathways mediated by thyrotropin, peptide growth factors, transforming growth factor-beta, tumor necrosis factor-alpha and nuclear factor-kappaB were activated, whereas pathways mediated by peroxisome proliferation activated receptor gamma were repressed. These results indicate that complex alterations of multiple signaling pathways contribute to thyroid carcinogenesis. The critical genes associated with thyroid follicular carcinogenesis uncovered in the present study could serve as signature genes for diagnostic purposes, as well as for possible therapeutic targets.

Animals↗
PubMed2003

Molecular classification of familial non-BRCA1/BRCA2 breast cancer.

In the decade since their discovery, the two major breast cancer susceptibility genes BRCA1 and BRCA2, have been shown conclusively to be involved in a significant fraction of families segregating breast and ovarian cancer. However, it has become equally clear that a large proportion of families segregating breast cancer alone are not caused by mutations in BRCA1 or BRCA2. Unfortunately, despite intensive effort, the identification of additional breast cancer predisposition genes has so far been unsuccessful, presumably because of genetic heterogeneity, low penetrance, or recessive/polygenic mechanisms. These non-BRCA1/2 breast cancer families (termed BRCAx families) comprise a histopathologically heterogeneous group, further supporting their origin from multiple genetic events. Accordingly, the identification of a method to successfully subdivide BRCAx families into recognizable groups could be of considerable value to further genetic analysis. We have previously shown that global gene expression analysis can identify unique and distinct expression profiles in breast tumors from BRCA1 and BRCA2 mutation carriers. Here we show that gene expression profiling can discover novel classes among BRCAx tumors, and differentiate them from BRCA1 and BRCA2 tumors. Moreover, microarray-based comparative genomic hybridization (CGH) to cDNA arrays revealed specific somatic genetic alterations within the BRCAx subgroups. These findings illustrate that, when gene expression-based classifications are used, BRCAx families can be grouped into homogeneous subsets, thereby potentially increasing the power of conventional genetic analysis.

Adult↗
PubMed2003

Microarray analysis of knockout mice identifies cyclin D2 as a possible mediator for the action of thyroid hormone during the postnatal development of the cerebellum.

Thyroid hormone is a major regulator of postnatal brain development, but the precise molecular mechanisms underlying its action in this organ remain poorly understood. We used microarray analysis to identify new target genes in brain. Thyroid hormone treatment of hypothyroid Pax8(-/-) knockout mice, which lack thyroid follicular cells, had a very limited global effect on brain transcripts. This analysis mainly identified cyclin D2 as a new thyroid hormone target gene in the cerebellum of hypothyroid mice. Thyroid hormone receptor (TRalpha and/or TRbeta) knockout mice studies provided further genetic evidence that cyclin D2 is likely to mediate the antiapoptotic effect exerted by thyroid hormone on the cerebellum external granular layer neuroblasts but that this transcriptional activation is not directly exerted by the thyroid hormone receptors.

Animals↗
PubMed2003

Mechanisms of sarcoma development.

Sarcomas are a rare and diverse group of tumours that are derived from connective tissues, including bone, muscle and cartilage. Although there are instances of hereditary predisposition to sarcomas, the overwhelming majority of such tumours are sporadic. In the past decade, we have gained much insight into the genetic abnormalities that seem to underlie the pathogenesis of these tumours. This information has already led to new classification of many sarcomas, as well as to successful therapies that are targeted at specific genetic abnormalities. It is likely that this approach will lead to continued refinements in classification and treatment of these tumours.

Animals↗
PubMed2003

Differential responses of stress genes to low dose-rate gamma irradiation.

In the past, most mechanistic studies of ionizing radiation response have employed very large doses, then extrapolated the results down to doses relevant to human exposure. It is becoming increasingly apparent, however, that this does not give an accurate or complete picture of the effects of most environmental exposures, which tend to be of low dose and protracted over time. We have initiated direct studies of low dose exposures, and using the relatively responsive ML-1 cell line, have shown that changes in gene expression can be triggered by doses of gamma-rays of 10 cGy and less in human cells. We have now extended these studies to investigate the effects on gene induction of reducing the rate of irradiation. In the ML-1 human myeloid leukemia cell line, we have found that reducing the dose rate over three orders of magnitude results in some protection against the induction of apoptosis, but still causes linear induction of the p53-regulated genes CDKN1A, GADD45A, and MDM2 between 2 and 50 cGy. Reducing the rate of exposure reduces the magnitude of induction of CDKN1A and GADD45A, but not the magnitude or duration of cell cycle delay. In contrast, MDM2 is induced to the same extent regardless of the rate of dose delivery. Microarray analysis has identified additional low dose-rate-inducible genes, and indicates the existence of two general classes of low dose-rate responders in ML-1. One group of genes is induced in a dose rate-dependent fashion, similar to GADD45A and CDKN1A. Functional annotation of this gene cluster indicates a preponderance of genes with known roles in apoptosis regulation. Similarly, a group of genes with dose rate-independent induction, such as seen for MDM2, was also identified. The majority of genes in this group are involved in cell cycle regulation. This apparent differential regulation of stress signaling pathways and outcomes in response to protracted radiation exposure has implications for carcinogenesis and risk assessment, and could not have been predicted from classical high dose studies.

Apoptosis↗
PubMed2003

Soft tissue sarcomas of adults: state of the translational science.

Sarcomas--like leukemias, which are also mesodermal malignancies--carry biological significance disproportionate to their clinical frequency. Identification of mutations and translocations associated with these tumors has illuminated aberrant signaling pathways that cause these diseases, determine their behavior, and are therapeutic targets. Activated receptor-associated tyrosine kinase c-kit, mutated in most gastrointestinal stromal tumors, has proven a clinically effective target for enzyme inhibition. A translocation involving a single gene family, consisting of EWS and related genes, has been identified in five different sarcomas, and its chimeric protein products could prove similarly amenable to inhibitors. Resolution of the histopathological complexity is being aided by data from molecular and chromosomal characterization. Improvements in imaging, definition of prognostic factors, and surgical and radiotherapeutic treatment have resulted in improved local control. Continued progress will depend on further adapting the rapidly evolving technologies of genomics and proteomics. It will also depend upon accurate histopathological diagnosis based on validated reagents and consistent methodologies applied to adequate tissue samples derived from patients with complete clinical data. Finally, multicenter, coordinated trials, such as those that occurred with assessment of imatinib mesylate in metastatic gastrointestinal stromal tumors, will assure the most rapid reductions in morbidity and mortality.

Adult↗
PubMed2003

Gene expression profiles in a panel of childhood leukemia cell lines mirror critical features of the disease.

The development of new drugs against cancer requires established cell lines. They are needed for in vitro studies to identify candidate drugs and in xenograft models to measure drug efficacy in vivo. Specific criteria need to be fulfilled by cell lines used in the evaluation of potential novel therapeutic agents. It is imperative that they display the features of the particular cancer under investigation. Given the documented heterogeneity of cancers, relevant subtypes need to be represented. In this study, we have examined these aspects for pediatric acute lymphoblastic leukemia. A panel of 13 leukemia cell lines recently established in our laboratory was analyzed. We used cDNA microarrays to define the gene expression profiles and compared the data with immunophenotyping and cytogenetic analyses. The expression profiles obtained showed excellent concordance with corresponding protein levels. Importantly, the panel of lines displayed the critical genetic features identified in clinically important acute lymphoblastic leukemia subtypes in childhood leukemia patients.

Child↗
PubMed2002

Stress-gene induction by low-dose gamma irradiation.

Using a human myeloid tumor cell line (ML-1), we detected induction of mRNA expression of several stress-responsive genes by doses of gamma rays as low as 2 cGy. For instance, the dose response for induction of CIP1/WAF1 and GADD45 appears to be linear over the range of 2 to 50 cGy and shows no evidence of a threshold for induction. Although 2 and 5 cGy exposures did not result in any detectable reduction in cloning efficiency nor in increased apoptosis in ML-1 cells, these exposures did produce a brief cell-cycle delay. We also used fluorescent cDNA microarray hybridization to investigate transcriptional stress responses following low doses of gamma rays and to identify additional radiation-responsive genes for inclusion in a stress-specific microarray we are developing. These studies provide insight into the molecular responses to physiologically relevant doses, which cannot necessarily be extrapolated from high-dose studies. The use of high throughput arrays will allow the identification of multiple stress-responsive genes that are radiation inducible in a variety of cell types and tissues. The expectation is that transcriptional stress responses will provide a molecular approach to monitoring for radiation exposure and detecting interindividual differences.

Gamma Rays↗
PubMedDate not supplied

Effects of HIV-1 Nef on cellular gene expression profiles.

The early human immunodeficiency virus (HIV) accessory protein Nef makes an important contribution to virulence, but the mechanisms by which Nef influences pathogenesis remain unclear. Many well-studied effects of Nef, like CD4 and class I MHC downregulation, occur posttranslationally. However, Nef has the potential to affect gene expression by interfering with cell signaling pathways and by virtue of structural features such as the Pro-X-X-Pro motif, which may interact with src homology region-3 domains of src-like kinases. We used a cDNA microarray screening strategy to identify cellular genes whose steady state transcriptional levels may be affected by Nef. We generated HeLa cell lines expressing wild-type or mutant HIV-1 nef protein sequences. Using cDNA microarray technology, we compared the patterns of cellular gene expression in the various cell lines to the pattern in non-Nef-expressing HeLa cells. By matching the patterns of cellular gene expression in HeLa cell lines expressing various Nefs with that of parental HeLa cells, we identified several cellular genes whose expression was modulated differentially by Nef and its mutants. We confirmed the differential expression of selected genes by RNA filter blotting. Genes expressed at higher levels included proteases, transcription factors, protein kinases, nuclear import/export proteins, adaptor molecules and cyclins, some of which have previously been implicated as being important for HIV replication and pathogenesis. The results indicate that Nef expression can alter the expression of cellular genes and suggest that this alteration in cellular gene expression may serve to optimize the cell to support the subsequent stages of viral replication.

Gene Expression↗