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T G Krontiris

Publications and source records attributed to T G Krontiris.

At least 19 recordsLinked to original sources
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↗
PubMed1987

A family of short, interspersed repeats is associated with tandemly repetitive DNA in the human genome.

A family of short, interspersed repeats in the human genome, designated the Mst II family, is described. The canonical structure of the repeat consists of a 220-base-pair (bp) left arm joined to a 160-bp right arm by a 39-bp junction sequence. The right arm is absent in some isolates. Some homology with the "O" and "THE" (transposon-like element) families of repeats was observed, suggesting that the Mst II elements could be a subgroup of a SINE superfamily. The 39-bp junction sequence is tandemly repeated in one of our clones. The association of tandemly repetitive sequences with Mst II elements or the putative superfamily is probably nonrandom; a search of DNA sequence data bases revealed that approximately 80 bp of the Mst II left arm occurs immediately adjacent to the tandem repeat that comprises the human homologue to the BK virus enhancer. The fortuitous occurrence of a gene duplication event involving an Mst II repeat has allowed us to estimate a mutation rate for human DNA.

Base Sequence↗
PubMed1987

Human hypervariable sequences in risk assessment: rare Ha-ras alleles in cancer patients.

A variable tandem repeat (VTR) is responsible for the hyperallelism one kilobase 3' to the human c-Ha-ras-1 (Ha-ras) gene. Thirty-two distinct restriction fragments, comprising 3 allelic classes by frequency of occurrence, have thus far been detected in a sample size of approximately 800 caucasians. Rare Ha-ras alleles, 21 in all, are almost exclusively confined to the genomes of cancer patients (p less than 0.001). From our data we have computed the relative cancer risk associated with possession of a rare Ha-ras allele to be 27. To understand the molecular basis for this phenomenon, we have begun to clone Ha-ras fragments from nontumor DNA of cancer patients. We report here the weak activation, as detected by transfection and transformation of NIH 3T3 mouse cells, of two Ha-ras genes which were obtained from lymphocyte DNA of a melanoma patient. We have mapped the regions that confer this transforming activity to the fragment containing the VTR in one Ha-ras clone and the fragment containing gene coding sequences in the other.

Alleles↗
PubMed1986

A variable tandem repeat locus mapped to chromosome band 10q26 is amplified and rearranged in leukocyte DNAs of two cancer patients.

A highly polymorphic locus associated with the variable tandem repetition of a 35 bp consensus sequence was mapped to chromosome 10, band q26. Examination of leukocyte DNA from a cancer patient revealed the twenty-fold amplification of one allelic fragment of this locus, while the other allelic fragment demonstrated a normal copy number. In another patient, Southern blotting of leukocyte DNA detected the deletion of the 3'-flanking region from one tandem repeat allele. These results indicate that variable tandem repeats may mark highly unstable regions of DNA in the human genome which can be altered by changes more extensive than simple tandem repeat variation.

Base Sequence↗
PubMed1986

Human restriction fragment length polymorphisms and cancer risk assessment.

The polymorphic restriction fragments of the human Ha-ras locus, produced by the variable tandem repetition (VTR) of a short consensus sequence, fall into three classes based on allelic frequencies. Alleles of the "rare" class (individual frequencies less than 0.5%) have been detected only in white blood cell and tumor DNA of cancer patients. This phenomenon is independent of ethnic origin. No significant association of rare alleles with cancer patients has been demonstrated at an independent tandem repeat locus, VTR4.1. The results suggest that the Ha-ras restriction fragment length polymorphism is useful in cancer risk assessment.

Alleles↗
PubMed1986

Oncogenes.

Many of the genes that are likely participants in the pathogenesis of human neoplasia have been identified. The major classes of events that activate these genes in tumors have also been described. We expect that continuing research on the function of oncogenes will greatly inform our understanding of fundamental growth control processes and, eventually, influence our approaches to treating cancer patients.

Animals↗
PubMed1985

Rearrangement of the gene for the beta chain of the T-cell receptor in T-cell chronic lymphocytic leukemia and related disorders.

Although monoclonal B-cell populations can be identified both by surface-marker analysis and by immunoglobulin-gene rearrangements, this has not been possible with T cells. We have employed cDNA probes that are specific for the entire beta chain of the T-cell receptor, and for its constant and variable regions, to investigate gene rearrangements in T-cell chronic lymphocytic leukemia and related disorders. In three malignant proliferations of helper (T4-positive) T cells, rearrangements of the beta-chain constant-region gene were readily demonstrated. A patient from the Caribbean who had adult T-cell lymphoma and antibody to human T-cell lymphotrophic virus Type I (HTLV-I), a patient with virus-negative chronic lymphocytic leukemia, and a patient with cutaneous T-cell lymphoma (Sézary variant) made up the T4-positive group. Three additional patients with chronic T8 (cytotoxic-suppressor) lymphocytosis and neutropenia were studied; in two; rearrangements were found. In all five patients with constant-region rearrangements, deletions of variable-region restriction fragments were observed as well. The presence of rearrangements of a T-cell receptor gene provides presumptive evidence for the clonal nature of T-cell proliferation and for its neoplastic character.

Adult↗