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T G Krontiris

Publications and source records attributed to T G Krontiris.

At least 19 recordsLinked to original sources
PubMed1995

The BCL2 major breakpoint region is a sequence- and cell-cycle-specific binding site of the Ku antigen.

The majority of translocations involving BCL2 are very narrowly targeted to three breakpoint clusters evenly spaced over a 100-bp region of the gene's terminal exon. We have recently shown that the immediate upstream boundary of this major breakpoint region (mbr) is a specific recognition site for single-strand DNA (ssDNA) binding proteins on the sense and antisense strands. The downstream flank of the mbr is a helicase binding site. In this report we demonstrate that the helicase and ssDNA binding proteins show reciprocal changes in binding activity over the cell cycle. The helicase is maximally active in G1 and early S phases; the ssDNA binding proteins are maximally active in late S and G2/M phases. An inhibitor of helicase binding appears in late S and G2/M. Finally, at least one component of the helicase binding complex is the Ku antigen. Thus, a protein with helicase activity implicated in repair of double-strand breaks, variable (diversity) joining recombination, and, potentially, cell-cycle regulation is targeted to the BCL2 mbr.

Antigens, Nuclear↗
PubMed1995

Oncogenes.

Explore the source record for details and available documents.

Cell Division↗
PubMed1993

An association between the risk of cancer and mutations in the HRAS1 minisatellite locus.

BACKGROUND: The role of mutations in protooncogenes and their regulatory sequences in the pathogenesis of cancer is under close scrutiny. Minisatellites are unstable repetitive sequences of DNA that are present throughout the human genome. The highly polymorphic HRAS1 minisatellite locus just downstream from the protooncogene H-ras-1 consists of four common progenitor alleles and several dozen rare alleles, which apparently derive from mutations of the progenitors. We previously observed an association of the rare mutant alleles with many forms of cancer, and we undertook the present study to pursue this observation further. METHODS: We conducted a case-control study, typing 736 HRAS1 alleles from patients with cancer and 652 from controls by Southern blotting of leukocyte DNA. We also carried out a meta-analysis of this study and 22 other published studies, estimating the relative risk of cancer (such as bladder, breast, or colorectal cancer) when one of the rare HRAS1 alleles was present. RESULTS: Both the present case-control study (odds ratio, 1.83; 95 percent confidence interval, 1.28 to 2.67; P = 0.002) and the present study combined with our previous study (odds ratio, 2.07; 95 percent confidence interval, 1.47 to 2.92; P < 0.001), as well as the meta-analysis of all 23 studies (odds ratio, 1.93; 95 percent confidence interval, 1.63 to 2.30; chi-square = 57.58; P < 0.001), replicated our original finding and demonstrated a significant association of rare HRAS1 alleles with cancer. We found significant associations for four types of cancer: carcinomas of the breast, colorectum, and urinary bladder and acute leukemia. We also identified suggestive but not statistically significant associations for cancers of the lung and prostate and for non-Hodgkin's lymphoma. CONCLUSIONS: Mutant alleles of the HRAS1 minisatellite locus represent a major risk factor for common types of cancer. Although the relative risk associated with the presence of one rare allele is moderate, the aggregate prevalence of one rare allele is moderate, the aggregate prevalence of this class of mutant alleles implies an extremely important attributable risk: 1 in 11 cancers of the breast, colorectum, and bladder.

Aged↗
PubMed1993

IGH minisatellite suppression of USF-binding-site- and E mu-mediated transcriptional activation of the adenovirus major late promoter.

The 50bp repeat unit of the minisatellite within the DH-JH interval of the human immunoglobulin heavy chain locus binds a nuclear factor present in a wide variety of cell types. The binding site contains the myc/HLH motif, CACGTG, and represents a 15 of 17 base match for the USF/MLTF binding site adjacent to the adenovirus major late promoter (MLP). Unlike the USF/MLTF site, the IGH minisatellite possesses no enhancer activity. However, it can significantly suppress, in cis and in trans, USF-site-mediated transcriptional activation of the MLP. In murine myeloma cells, the IGH minisatellite can suppress, in trans, MLP activation by the murine heavy chain gene enhancer, E mu. These activities potentially represent a DNA-based form of squelching.

Adenoviridae↗
PubMed1993

Allelic variation of reporter gene activation by the HRAS1 minisatellite.

We have recently shown that constitutively expressed members of the rel/NF-kappa B family of transcription factors bind the HRAS1 minisatellite, VTRHRAS1. We now report that, like other NF-kappa B binding sites, VTRHRAS1 displays pleiotropic transcriptional regulatory activity that is promoter- and cell-type-specific. Both enhancement and suppression are restricted to the human bladder carcinoma cell line EJ, in which we have previously defined a unique form of NF-kappa B p50. We also observe allelic variation in functional activity: the rare a2.1 allele, one member of a class of HRAS1 alleles overrepresented in the genomes of cancer patients, possesses twofold greater enhancer activity than the low-risk alleles, a0.1, a1, and a2. Finally, VTRHRAS1 enhancer activity is upregulated by the adenovirus E1A 13S gene product, demonstrating the potential of the minisatellite for influencing gene expression through several distinct interactions with the transcriptional apparatus.

Adenovirus E1A Proteins↗
PubMed1992

BCL2 oncogene translocation is mediated by a chi-like consensus.

Examination of 64 translocations involving the major breakpoint region (mbr) of the BCL2 oncogene and the immunoglobulin heavy chain locus identified three short (14, 16, and 18 bp) segments within the mbr at which translocations occurred with very high frequency. Each of these clusters was associated with a 15-bp region of sequence homology, the principal one containing an octamer related to chi, the procaryotic activator of recombination. The presence of short deletions and N nucleotide additions at the breakpoints, as well as involvement of JH and DH coding regions, suggested that these sequences served as signals capable of interacting with the VDJ recombinase complex, even though no homology with the traditional heptamer/spacer/nonamer (IgRSS) existed. Furthermore, the BCL2 signal sequences were employed in a bidirectional fashion and could mediate recombination of one mbr region with another. Segments homologous to the BCL2 signal sequences flanked individual members of the XP family of diversity gene segments, which were themselves highly overrepresented in the reciprocal products (18q-) of BCL2 translocation. We propose that the chi-like signal sequences of BCL2 represent a distinct class of recognition sites for the recombinase complex, responsible for initiating interactions between regions of DNA separated by great distances, and that BCL2 translocation begins by a recombination event between mbr and DXP chi signals. Since recombinant joints containing chi, not IgRSS, occur in brain cells expressing RAG-1 (Matsuoka, M., F. Nagawa, K. Okazaki, L. Kingsbury, K. Yoshida, U. Muller, D. T. Larue, J. A. Winer, and H. Sakano. 1991. Science [Wash. DC]. 254:81; reference 1), we further suggest that the product of this gene could mediate both BCL2 translocation and the first step of normal DJ assembly through the creation of chi joints, rather than signal or coding joints.

Base Sequence↗
PubMed1992

Members of the rel/NF-kappa B family of transcriptional regulatory proteins bind the HRAS1 minisatellite DNA sequence.

The 28 base pair repeat unit of a minisatellite 1000 bp downstream from the human HRAS1 gene (VTRHRAS1) bound four proteins (p45, p50, p72 and p85) in nuclear extracts from a variety of human cell lines which were indistinguishable from several members of the rel/NF-kappa B family of transcriptional regulatory factors. VTRHRAS1 bound the constitutively expressed, but not the inducible, forms of these proteins. Analysis of partially purified binding factors from different cell lines demonstrated qualitative differences in the p50 subunit; phosphocellulose fractionation also revealed considerable heterogeneity in the p72 and p85 subunits. These results suggest the possibility that the HRAS1 minisatellite, in serving as a tandem array of rel/NF-kappa B binding sites, may function in the transcriptional regulation of HRAS1 and nearby genes.

Base Sequence↗
PubMed1992

The HRAS1 gene cluster: two upstream regions recognizing transcripts and a third encoding a gene with a leucine zipper domain.

We have cloned and characterized a 55-kb region of DNA surrounding HRAS1. It contains a cluster of two, and possibly three, genes associated with CpG islands within the 32 kb immediately upstream of HRAS1. We have sequenced cDNAs representing one of these genes, provisionally designated HRC1. The locus, which is located 29 kb upstream of HRAS1, is divergently transcribed. HRC1 cDNA probe recognizes fragments on Southern blots of DNA from other vertebrate species. In human DNA, multiple homologous fragments are detected in addition to the predicted ones containing HRC1. Therefore, this locus may represent a member of an evolutionarily conserved gene family. HRC1 expression is upregulated with HRAS1 in the EJ bladder carcinoma cell line, suggesting the possibility of coordinate regulation. The deduced translational product of the longest open reading frame (1119 nucleotides, 373 amino acids) predicts a protein with regions rich in glutamine and proline and a region similar to the helix-loop-helix motif adjacent to a carboxy-terminal leucine zipper dimerization motif with four heptad repeats. Alternate splicing of terminal exons occurs, resulting in the truncation of one proline-rich domain and preservation of the leucine zipper. Thus, a biologically important region of chromosome 11p consists of a gene cluster. At least one of these genes, in addition to HRAS1, may be involved in regulation of cell growth or differentiation.

Amino Acid Sequence↗
PubMed1992

Relationship of H-ras-1, L-myc, and p53 polymorphisms with lung cancer risk and prognosis.

Proto-oncogenes (H-ras-1 and L-myc) and tumor-suppressor gene (p53) loci have been implicated in lung carcinogenesis. DNA restriction fragment length polymorphisms at these gene loci are being evaluated in a case-control study as markers predictive of risk for cancer or of prognosis when cancer is present. The cases and controls had a cigarette-smoking history of 40 or more pack years or other abnormalities in pulmonary function tests, their ages were closely matched (64 years for cases and 61 years for controls) and the ratio of Caucasians to African Americans was close to unity (cases, 0.95:1.00, controls, 1.00:0.88). The H-ras-1 gene contains an insertion deletion polymorphism. Inheritance of rare H-ras-1 alleles, defined by MspI digestion, confers a relative risk for lung cancer of 2.0 (95% confidence interval, 0.5-7.3) for Caucasians and 3.2 (0.9-11.6) for African Americans (74 cases, 67 controls). The L-myc gene sequence has a restriction site (EcoR1) polymorphism between the second and third exons. Inheritance of restriction site-present alleles was reported to confer poor prognosis (presence of lymph node metastases) in Japanese lung cancer patients. This hypothesis was tested in both case-control study subjects (56 cases, 55 controls) and additional surgical cases (40), but no evidence was found to support the hypothesis in the U.S. population. The p53 gene is a tumor-suppressor gene that can encode either a proline or an arginine in the 72nd residue. No associations was found between the minor allele (proline) and diagnosis of lung cancer (76 cases, 68 controls).(ABSTRACT TRUNCATED AT 250 WORDS)

Base Sequence↗
PubMed1991

Racial variation in the distribution of Ha-ras-1 alleles.

Restriction fragment length polymorphism analyses of the Ha-ras-1 proto-oncogene were undertaken in white and black populations residing in the Baltimore-Washington metropolitan area to address whether specific rare alleles of the Ha-ras-1 proto-oncogene locus vary in their distribution among different racial groups. High-molecular-weight genomic DNA samples from the lungs of 80 lung cancer patients and 92 accident victims were digested with appropriate restriction enzymes and subjected to Southern analysis using the 6.6-kb BamHI human Ha-ras-1 recombinant fragment from the plasmid pEC. Thirty allelomorphs of different sizes were detected among the 172 study subjects. An association was observed between race and specific alleles. Rare alleles were more frequent in black cancer patients and trauma victims than in whites. Within each racial category, lung cancer patients had an excess of rare alleles. These data indicate the importance of controlling for racial variation when designing studies to determine human cancer risk factors.

Adult↗
PubMed1990

Association of rare alleles of the Harvey ras protooncogene locus with lung cancer.

The hypothesis that rare variable nucleotide tandem repeat alleles of the Ha-ras-1 polymorphism are an inherited predisposing factor in human lung carcinogenesis has been evaluated in an age, race, and smoking matched case-control study. Twenty-three different alleles were identified by their restriction fragment length in DNA isolated from peripheral blood lymphocytes and were categorized into three groups: common; intermediate; and rare. The frequencies of rare alleles in blacks with either squamous cell carcinoma, large cell carcinoma, or small cell carcinoma were found to be significantly higher than those among groups of control subjects that were comprised of chronic obstructive pulmonary disease patients and patients with cancer at sites other than the lung. A similar trend which did not reach statistical significance was observed in whites. These data are consistent with the hypothesis that inheritance of Ha-ras-1 rare restriction fragment length alleles represents a genetic risk factor for some human lung cancers. The biological basis of this observation remains to be clarified, and it is possible that ethnic variations in rare allele frequencies are responsible for the differences noted. However, the data suggest that further evaluation of the Ha-ras-1 polymorphism as a marker of individual lung cancer susceptibility is warranted.

Adenocarcinoma↗
PubMed1990

The human minisatellite consensus at breakpoints of oncogene translocations.

A reexamination of human minisatellite (hypervariable) regions following the cloning and sequencing of the new minisatellite, VTR1.1, revealed that many of these structures possessed a strongly conserved copy of the chi-like octamer, GC[A/T]GG[A/T]GG. In oncogene translocations apparently created by aberrant VDJ recombinase activity, this VTR octamer was often found within a few bases of the breakpoint (p less than 10(-10)). Three bcl2 rearrangements which occurred within 2 bp of one another were located precisely adjacent to this consensus; it defined the 5' border of that oncogene's major breakpoint cluster. Several c-myc translocations also occurred within 2 bp of this sequence. While the appearance of a chi-like element in polymorphic minisatellite sequences is consistent with a role promoting either recombination or replication slippage, the existence of such elements at sites of somatic translocations suggests chi function in site-specific recombination, perhaps as a subsidiary recognition signal in immunoglobulin gene rearrangement. We discuss the implications of these observations for mechanisms by which oncogene translocations and minisatellite sequences are generated.

Base Sequence↗
PubMed1990

Minisatellite allele diversification: the origin of rare alleles at the HRAS1 locus.

Three genetic markers within the promoter-exon 1 region of the HRAS1 locus have been employed to investigate lineage relationships among alleles of the highly polymorphic variable tandem repeat (VTR) immediately downstream of the HRAS1 gene. These markers were in absolute linkage disequilibrium with the HRAS1 VTR, allowing the assignment of unique upstream haplotypes to each of the four common VTR alleles. Analysis of 17 rare alleles revealed a stratification of allele fragment size and upstream haplotype in which each rare VTR allele possessed the markers characteristic of the common allele nearest in size. Therefore, hyperallelism emanated from the four common alleles in a defined fashion, the size of a rare allele specifying its origin. As discussed below, this result implies that unequal crossing-over between homologues is unlikely to be the predominant mechanism for generating new VTR alleles at this minisatellite locus.

Alleles↗
PubMed1989

Allele-specific deletion in exon I of the HRAS1 gene.

We have detected a 6-bp deletion in the untranslated first exon of a unique HRAS1 gene cloned from lymphocyte DNA of a familial melanoma patient. The deletion is without apparent functional consequence. Using an RNase protection assay, we have demonstrated the deletion in leukocyte DNAs of individuals unrelated to the patient. In these cases, the deletion marker is specifically associated with one class of common HRAS1 allele, thereby establishing the origin of the unique allele. We discuss the means by which DNA sequence heterogeneity at other loci may be rapidly analyzed.

Alleles↗
PubMed1988

Clonal analysis of untreated non-Hodgkin's lymphoma utilizing immunoglobulin gene rearrangement and immunophenotype.

We have prospectively examined 66 consecutive initial diagnostic lymph node biopsies from unselected patients suspected of having malignant lymphoma for clonal immunophenotypic and immunogenotypic markers. By morphological and cell surface phenotypic criteria 52 had non-Hodgkin's lymphoma derived from the B-cell lineage and in these we compared surface immunoglobulin criteria for clonality with immunoglobulin gene rearrangement as detected by JH, C kappa, and C lambda gene probes. We found that the addition of BglII and HindIII double digests to the standard BamHI and EcoRI restriction enzymes made it possible to detect rearrangement in the vast majority of lymphomas and that rearrangement of both JH alleles is the rule. A rearranged heavy and/or light chain gene was detected in 47 of 52 (91%) tumors and the JH probe alone detected rearrangements in 87% of tumors when multiple restriction enzymes were used. In contrast, surface immunoglobulin, the standard clonal marker for monoclonal B-cell malignancy, was either undetectable or did not exhibit light chain restriction in 29 of 52 tumors as detected by flow cytometric analysis. Further, in 24 of these 29 tumor DNAs we could detect an Ig gene rearrangement. In follicular (nodular) lymphoma which often gives ambiguous immunophenotypic results by cell suspension techniques, monoclonal gene rearrangements were detected in 16 of 18 tumor DNAs. Monoclonal surface immunoglobulin was detected in only 8 of 18 of this subset of cases. The 52 tumors were also analyzed for potential oligoclonality. We found that the use of BglII, a restriction enzyme that closely spanned the JH region, increased the sensitivity of detecting rearrangements and facilitated the identification of isotype switch variants. In only a single (1 of 52) tumor DNA were more than two rearranged bands seen with JH, C kappa, and C lambda probes, suggesting a multiclonal origin. Additional cases thought to potentially represent oligoclonality by immunophenotypic criteria proved to be isotype switch variants. We conclude that Ig gene rearrangement is an extremely sensitive method for defining monoclonality in lymphoma cell populations, particularly if multiple restriction enzymes are used, and that the vast majority of the clonal diversity seen in initial diagnostic biopsies is the result of isotypic switch within a given clone rather than true oligoclonality.

B-Lymphocytes↗