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PubMed1992

Characterization of the chicken alpha 1(VI) collagen promoter.

The promoter of the chicken alpha 1(VI) collagen gene resembles the 5'-flanking regions of many housekeeping genes. It lacks a canonical TATAA box but contains potential binding sites for transcription factors AP1 and SP1. The promoter region has a relatively high GC content and forms a typical CpG island. In accordance with the absence of a TATAA element, the gene contains multiple transcription-initiation sites distributed over 80 bp genomic DNA. A 621-bp fragment derived from the 5' end of the alpha 1(VI) collagen gene is able to direct transcription of a heterologous reporter gene in transient-expression assays. Other DNA fragments that are either shorter or longer than the 621-bp fragment show markedly reduced promoter activity. Thus, the basic promoter element of the alpha 1(VI) collagen gene must reside within this 621-bp fragment.

Animals↗
PubMed1998

Salmonella typhimurium encodes an SdiA homolog, a putative quorum sensor of the LuxR family, that regulates genes on the virulence plasmid.

Quorum sensing is a phenomenon in which bacteria sense and respond to their own population density by releasing and sensing pheromones. In gram-negative bacteria, quorum sensing is often performed by the LuxR family of transcriptional regulators, which affect phenotypes as diverse as conjugation, bioluminescence, and virulence gene expression. The gene encoding one LuxR family member, named sdiA (suppressor of cell division inhibition), is present in the Escherichia coli genome. In this report, we have cloned the Salmonella typhimurium homolog of SdiA and performed a systematic screen for sdiA-regulated genes. A 4.4-kb fragment encoding the S. typhimurium sdiA gene was sequenced and found to encode the 3' end of YecC (homologous to amino acid transporters of the ABC family), all of SdiA and SirA (Salmonella invasion regulator), and the 5' end of UvrC. This gene organization is conserved between E. coli and S. typhimurium. We determined that the S. typhimurium sdiA gene was able to weakly complement the E. coli sdiA gene for activation of ftsQAZ at promoter 2 and for suppression of filamentation caused by an ftsZ(Ts) allele. To better understand the function of sdiA in S. typhimurium, we screened 10,000 random lacZY transcriptional fusions (MudJ transposon mutations) for regulation by sdiA. Ten positively regulated fusions were isolated. Seven of the fusions were within an apparent operon containing ORF8, ORF9, rck (resistance to complement killing), and ORF11 of the S. typhimurium virulence plasmid. The three ORFs have now been named srgA, srgB, and srgC (for sdiA-regulated gene), respectively. The DNA sequence adjacent to the remaining three fusions shared no similarity with previously described genes.

Amino Acid Sequence↗
PubMed2003

Erwinia chrysanthemi tolC is involved in resistance to antimicrobial plant chemicals and is essential for phytopathogenesis.

TolC is the outer-membrane component of several multidrug resistance (MDR) efflux pumps and plays an important role in the survival and virulence of many gram-negative bacterial animal pathogens. We have identified and characterized the outer-membrane protein-encoding gene tolC in the bacterial plant pathogen Erwinia chrysanthemi EC16. The gene was found to encode a 51-kDa protein with 70% identity to its Escherichia coli homologue. The E. chrysanthemi gene was able to functionally complement the E. coli tolC gene with respect to its role in MDR efflux pumps. A tolC mutant of E. chrysanthemi was found to be extremely sensitive to antimicrobial agents, including several plant-derived chemicals. This mutant was unable to grow in planta and its ability to cause plant tissue maceration was severely compromised. The tolC mutant was shown to be defective in the efflux of berberine, a model antimicrobial plant chemical. These results suggest that by conferring resistance to the antimicrobial compounds produced by plants, the E. chrysanthemi tolC plays an important role in the survival and colonization of the pathogen in plant tissue.

Anti-Bacterial Agents↗
PubMed2005

Complete functional rescue of the ABCA1-/- mouse by human BAC transgenesis.

Humanized mouse models are useful tools to explore the functional and regulatory differences between human and murine orthologous genes. We have combined a bioinformatics approach and an in vivo approach to assess the functional and regulatory differences between the human and mouse ABCA1 genes. Computational analysis identified significant differences in potential regulatory sites between the human and mouse genes. The effect of these differences was assessed in vivo, using a bacterial artificial chromosome transgenic humanized ABCA1 mouse model that expresses the human gene in the absence of mouse ABCA1. Humanized mice expressed human ABCA1 protein at levels similar to wild-type mice and fully compensated for cholesterol efflux activity and lipid levels seen in ABCA1-deficient mice. Liver X receptor agonist administration resulted in significant increases in HDL values associated with parallel increases in the hepatic ABCA1 protein and mRNA levels in the humanized ABCA1 mice, as seen in the wild-type animals. Our studies indicate that despite differences in potential regulatory regions, the human ABCA1 gene is able to functionally fully compensate for the mouse gene. Our humanized ABCA1 mice can serve as a useful model system for functional analysis of the human ABCA1 gene in vivo and can be used for the generation of potential new therapeutics that target HDL metabolism.

ATP Binding Cassette Transporter 1↗
PubMed1995

Leukemic transformation of primary myelofibrosis: immunophenotype, genotype and growth characteristics of blast cells.

Blast cells from six patients with leukemic transformation of primary myelofibrosis (PMF) were studied by morphology, immunophenotype and genotype as well as response to hematopoietic growth factors. The majority of the patients showed granulocytic or granulo-monocytic blasts, and only one had T lymphoid-monocytic blasts. None of the patients showed rearrangement of Ig or TCR genes, or the existence of the bcr-abl fused gene. A prominent growth response to GM-CSF and IL-3 was evident in all of the patients examined in liquid as well as semisolid cultures. The response to G-CSF was observed in four of the six patients in suspension culture, and in two of three patients in the clonogenic assay. Stem cell factor (SCF) was a weak growth stimulant, however the combination of this factor with GM-CSF or IL-3 was synergistically stimulatory. These results suggest that leukemic transformation of PMF occurs mainly at the level of myeloid stem cell, and that GM-CSF, IL-3, G-CSF and SCF are major growth factors for the blast cells in these cases.

Aged↗
PubMed2006

The decreased susceptibility of Bcr/Abl targets to NK cell-mediated lysis in response to imatinib mesylate involves modulation of NKG2D ligands, GM1 expression, and synapse formation.

Chronic myeloid leukemia is a clonal multilineage myeloproliferative disease of stem cell origin characterized by the presence of the Bcr/Abl oncoprotein, a constitutively active tyrosine kinase. In previous studies, we have provided evidence that Bcr/Abl overexpression in leukemic cells increased their susceptibility to NK-mediated lysis by different mechanisms. In the present study, using UT-7/9 cells, a high level Bcr/Abl transfectant of UT-7 cells, we show that the treatment of Bcr/Abl target by imatinib mesylate (IM), a specific Abl tyrosine kinase inhibitor, hampers the formation of the NK/target immunological synapse. The main effect of IM involves an induction of surface GM1 ganglioside on Bcr/Abl transfectants that prevents the redistribution of MHC-related Ag molecules in lipid rafts upon interaction with NK cells. IM also affects cell surface glycosylation of targets, as assessed by binding of specific lectins resulting in the subsequent modulation of their binding to lectin type NK receptor, particularly NKG2D. In addition, we demonstrate that the tyrosine kinase activity repression results in a decrease of MHC-related Ags-A/B and UL-16-binding protein expression on Bcr/Abl transfectants UT-7/9. We show that NKG2D controls the NK-mediated lysis of UT-7/9 cells, and IM treatment inhibits this activating pathway. Taken together, our results show that the high expression of Bcr/Abl in leukemic cells controls the expression of NKG2D receptor ligands and membrane GM1 via a tyrosine kinase-dependent mechanism and that the modulation of these molecules by IM interferes with NK cell recognition and cytolysis of the transfectants.

Antineoplastic Agents↗
PubMed1990

The Philadelphia translocation in CML and ALL: recent investigations, new detection methods.

As a consequence of the Ph translocation, a bcr-abl fusion gene is formed that encodes chimeric bcr-abl proteins. The latter are probably causally involved in leukemogenesis, although the mechanism is not yet known. Meanwhile, the heterogeneous aspects of the Ph translocation have been explored in an effort to disclose their eventual clinical significance. Innovative and useful methods have been devised for the detection of the Ph translocation products e.g. the PCR technique or the production of specific antibodies that undoubtedly will prove to be of great help to patients and clinicians in future.

Chromosome Mapping↗
PubMed1993

BCR-ABL-induced oncogenesis is mediated by direct interaction with the SH2 domain of the GRB-2 adaptor protein.

BCR-ABL is a chimeric oncoprotein that exhibits deregulated tyrosine kinase activity and is implicated in the pathogenesis of Philadelphia chromosome (Ph1)-positive human leukemias. Sequences within the first exon of BCR are required to activate the transforming potential of BCR-ABL. The SH2/SH3 domain-containing GRB-2 protein links tyrosine kinases to Ras signaling. We demonstrate that BCR-ABL exists in a complex with GRB-2 in vivo. Binding of GRB-2 to BCR-ABL is mediated by the direct interaction of the GRB-2 SH2 domain with a phosphorylated tyrosine, Y177, within the BCR first exon. The BCR-ABL-GRB-2 interaction is required for activation of the Ras signaling pathway. Mutation of Y177 to phenylalanine (Y177F) abolishes GRB-2 binding and abrogates BCR-ABL-induced Ras activation. The BCR-ABL (Y177F) mutant is unable to transform primary bone marrow cultures and is impaired in its ability to transform Rat1 fibroblasts. These findings implicate activation of Ras function as an important component in BCR-ABL-mediated transformation and demonstrate that GRB-2 not only functions in normal development and mitogenesis but also plays a role in oncogenesis.

Adaptor Proteins, Signal Transducing↗
PubMed1988

The bcr gene is joined to c-abl in Ph1 chromosome negative chronic myelogenous leukemia.

The relationship between chronic myelogenous leukemia (CML) with and without the Ph1 chromosome is controversial. Although some suggest that these disorders are identical, other reports suggest that Ph1 chromosome negative CML is a distinct entity. To resolve this issue, we studied 11 patients with Ph1 chromosome negative CML for the translocation of the Abelson proto-oncogene (c-abl) to the breakpoint cluster region gene (bcr), internal genomic rearrangement of bcr, and transcription of a chimeric bcr/abl mRNA. Our data indicate that c-abl is translocated to chromosome 22 where it is inserted after exon "2" or "3" of the bcr gene. This results in transcription of a chimeric bcr/abl mRNA in which the splice is between bcr exon "2" or "3" and c-abl exon 2. These data suggest that CML with and without the Ph1 chromosome are molecularly identical disorders with regard to bcr and abl.

Adult↗
PubMed1987

cDNA sequence for human bcr, the gene that translocates to the abl oncogene in chronic myeloid leukaemia.

The hallmark of human chronic myeloid leukaemia is a 9;22 chromosome translocation that fuses most of the c-abl oncogene to the 5' portion of the breakpoint cluster region (bcr) gene, such that a hybrid bcr-abl mRNA and polypeptide are generated. To clarify further the nature of this translocation, we have analysed the structure of normal human bcr mRNA by isolating large cDNA clones that collectively span the entire coding region and extend 2.6 kb upstream of those previously described. The 3150-bp nucleotide sequence reported here includes 534 bp of a GC-rich 5' non-coding segment and indicates, in conjunction with published sequences, that the bcr polypeptide comprises 1271 amino acid residues. The predicted polypeptide is unrelated to serine or tyrosine kinases, or indeed to any previously published sequence; its structure provides no evidence of a transmembrane region. Since probes from throughout the 4.8-kb cloned region hybridized to both the 4.5 and 6.7 kb normal bcr transcripts, both RNAs contain most or all of that region.

Amino Acid Sequence↗
PubMed1994

Detection of Philadelphia chromosome using PCR and europium-labeled DNA probes.

More than 95% of the patients with chronic myelogenous leukemia (CML) carry translocations between protooncogene abl of chromosome 9 and bcr gene of chromosome 22, resulting in the Philadelphia chromosome (Ph1). After allogeneic bone marrow transplantation (BMT) it is important to detect possible residual malignant cells in CML patients. A new sensitive hybridization method combined with polymerase chain reaction (PCR), based on the detection of the europium (Eu3+) label by time-resolved fluorescence, was applied for the detection of Ph1 chromosome. Total RNA from 10(6) peripheral blood leukocytes was isolated by the acid guanidinium thiocyanate-phenol-chloroform extraction. After cDNA synthesis by reverse transcriptase, the PCR amplification (30 cycles) was carried out. In the detection phase two oligonucleotide probes were used in the hybridization reaction, one biotinylated (bcr gene, exon 2) and one (abl gene) labeled with Eu3+. The hybrids were collected in a streptavidin-coated microtitration well and the bound Eu3+ was measured in a time-resolved fluorometer. To assess the sensitivity of the method, different numbers of CML cell line K562 cells were mixed with 10(5) apparently normal human leukocytes. Five K562 cells/10(5) leukocytes could be detected. Six patients with CML confirmed by clinical and cytogenetic criteria were studied. Three of the patients underwent an allogeneic BTM 6-18 months before the investigation and all of them were Ph1-negative. The other three patients who were nontransplanted were positive as expected.

Base Sequence↗
PubMed2001

BCR gene expression blocks Bcr-Abl induced pathogenicity in a mouse model.

It is well accepted that the Bcr-Abl oncoprotein encoded by the Philadelphia chromosome is responsible for causing chronic myelogenous leukemia (CML). We have previously demonstrated that expression of Bcr interferes with the oncogenic effects of Bcr-Abl. To examine the effects of increased Bcr expression on Bcr-Abl oncogenic effects in a more physiological system, we tested the leukemogenic potential of a clone of K562 cells (K6 K562) containing an inducible BCR gene in NOD/scid mice. In this clone, the BCR gene was placed under the control of a tetracycline (Tet) repression system with a cytomegalovirus (CMV) promoter. Induction of exogenous Bcr protein by removal of Tet from the culture medium caused a dramatic increase in Bcr serine kinase activity, yielding predominantly phosphoserine Bcr, despite the presence of Bcr-Abl in the kinase reaction mixture. Prior to induction, the endogenous Bcr was predominantly in the phosphotyrosine form because of phosphorylation by Bcr-Abl, which we previously have shown suppresses Bcr serine/threonine kinase activity. Injection of K6 K562 cells into NOD/scid mice under conditions where BCR expression was suppressed resulted in death or terminal illness in 100% of the mice within 35 days after injection. These mice had a severe wasting syndrome characterized by atrophy of bone marrow hematopoiesis, and/or neoplasia of liver, bone marrow and spleen. Neoplastic spleens from these mice usually contained b3a2 Bcr-Abl transcripts. In contrast, induction of BCR expression at the time of injection allowed 80% survival; these healthy mice had no detectable microscopic lesions in blood forming organs. This difference in survival was significant with P<0.0001. Of interest, mice that were fed Tet for 19 days to initiate the disease syndrome and then released from the BCR transcriptional block had a significantly better survival pattern than mice exposed to Tet throughout the entire period. Moreover, 30% of these mice (three mice) survived through day 50. We conclude from these findings that BCR gene expression strongly inhibits the oncogenic effects of Bcr-Abl in NOD/scid mice, yielding healthy mice in most cases.

Animals↗
PubMed1995

A structurally abnormal breakpoint cluster region gene in a transcription factor, hLH-2-negative human leukemia cell line.

hLH-2, a transcription factor that contains double cysteine rich regions (LIM motifs) and a homeobox (Hox) DNA-binding domain shows aberrant high expression in all cases of chronic myelogenous leukemia (CML). This gene has been mapped to the chromosome 9q33-34.1, the same region as the reciprocal translocation that creates the breakpoint cluster region (BCR)-ABL chimera of the Philadelphia chromosome (Ph'). To investigate the possible involvement between the BCR-ABL fusion gene and hLH-2 in the pathogenesis of CML, an hLH-2-negative CML cell line, JK-1 that carries double Ph' chromosomes, was examined. Like other CML cells, high BCR-ABL fusion mRNA levels are expressed, but no transcript of hLH-2 was detected in JK-1 cells as determined by reverse transcriptase-polymerase chain reaction (RT-PCR). Compared with the CML cell line, K-562, an additional rearrangement of the BCR gene was observed in JK-1 as determined by Southern blot hybridization; however, the hLH-2 gene was normal. These findings raise interesting questions about the possible roles of either the abnormal BCR gene or other genetic events such as the complex chromosomal abnormalities that result in hLH-2 being turned off in JK-1 cells.

Base Sequence↗
PubMed1999

Extremely high and specific activity of DNA enzymes in cells with a Philadelphia chromosome.

BACKGROUND: Chronic myelogenous leukemia (CML) results from chromosome 22 translocations (the Philadelphia chromosome) that creates BCR-ABL fusion genes, which encode two abnormal mRNAs (b3a2 and b2a2). Various attempts to design antisense oligonucleotides that specifically cleave abnormal L6 BCR-ABL fusion mRNA have not been successful. Because b2a2 mRNA cannot be effectively cleaved by hammerhead ribozymes near the BCR-ABL junction, it has proved very difficult to engineer specific cleavage of this chimeric mRNA. Nonspecific effects associated with using antisense molecules make the use of such antisense molecules questionable. RESULTS: The usefulness of DNA enzymes in specifically suppressing expression of L6 BCR-ABL mRNA in mammalian cells is demonstrated. Although the efficacy of DNA enzymes with natural linkages decreased 12 hours after transfection, partially modified DNA enzymes, with either phosphorothioate or 2'-O-methyl groups at both their 5' and 3' ends, remained active for much longer times in mammalian cells. Moreover, the DNA enzyme with only 2'-O-methyl modifications was also highly specific for abnormal mRNA. CONCLUSIONS: DNA enzymes with 2'-O-methyl modifications are potentially useful as gene-inactivating agents in the treatment of diseases such as CML. In contrast to conventional antisense DNAs, some of the DNA enzymes used in this study were highly specific and cleaved only abnormal BCR-ABL mRNA.

Cells, Cultured↗
PubMed1998

The kinase activity of c-Abl but not v-Abl is potentiated by direct interaction with RFXI, a protein that binds the enhancers of several viruses and cell-cycle regulated genes.

c-Abl, the non-receptor tyrosine kinase is associated with EP, a DNA element found in promoters/enhancers of different viruses and cell-cycle regulated genes. EP-DNA binds RFXI, a member of a novel family of DNA-binding proteins that is conserved through evolution and in yeast, it controls differentiation and exit from the mitotic cycle to G0. EP-associated proteins are preferentially tyrosine phosphorylated and the associated c-Abl has strong tyrosine kinase activity. Here we investigated the molecular mechanism underlying this c-Abl kinase activity. We show that RFXI and c-Abl are in direct interaction, in vitro and in cell extracts, through the RFXI proline rich (PxxP) motif and the c-Abl SH3 domain. Remarkably, this interaction significantly potentiates c-Abl but not v-Abl auto-kinase activity. Collectively, we describe a novel mechanism of c-Abl recruitment to a defined DNA-cis element with its concomitant kinase activation. We propose that this mechanism may act to regulate cell-cycle control genes.

Cell Nucleus↗
PubMed2002

Nuclear structure and gene activity in human differentiated cells.

The nuclear arrangement of the ABL, c-MYC, and RB1 genes was quantitatively investigated in human undifferentiated HL-60 cells and in a terminally differentiated population of human granulocytes. The ABL gene was expressed in both cell types, the c-MYC gene was active in HL-60 cells and down-regulated in granulocytes, and expression of the RB1 gene was undetectable in HL-60 cells but up-regulated in granulocytes. The distances of these genes to the nuclear center (membrane), to the center of the corresponding chromosome territory, and to the nearest centromere were determined. During granulopoesis, the majority of selected genetic structures were repositioned closer to the nuclear periphery. The nuclear reposition of the genes studied did not correlate with the changes of their expression. In both cell types, the c-MYC and RB1 genes were located at the periphery of the chromosome territories regardless of their activity. The centromeres of chromosomes 8 and 13 were always positioned more centrally within the chromosome territory than the studied genes. Close spatial proximity of the c-MYC and RB1 genes with centromeric heterochromatin, forming the chromocenters, correlated with gene activity, although the nearest chromocenter of the silenced RB1 gene did not involve centromeric heterochromatin of chromosome 13 where the given gene is localized. In addition, the role of heterochromatin in gene silencing was studied in retinoblastoma cells. In these differentiated tumor cells, one copy of the RB1 gene was positioned near the heterochromatic chromosome X, and reduced RB1 gene activity was observed. In the experiments presented here, we provide evidence that the regulation of gene activity during important cellular processes such as differentiation or carcinogenesis may be realized through heterochromatin-mediated gene silencing.

Cell Differentiation↗
PubMed1993

Characterization of the DNase I hypersensitive site 3' of the human beta globin gene domain.

The members of the human beta globin gene family are flanked by strong DNase I hypersensitive sites. The collection of sites 5' to the epsilon globin gene is able to confer high levels of expression of linked globin genes, but a function has not been assigned to the site 3' to the beta globin gene (3'HS1). Our analysis of this DNase I super hypersensitive site shows that the region is composed of multiple DNase I sites. By examination of the DNA sequence, we have determined that the region is very A/T-rich and contains topoisomerase II recognition sequences, as well as several consensus binding motifs for GATA-1 and AP-1/NF-E2. Gel mobility shift assays indicate that the region can interact in vitro with GATA-1 and AP-1/NF-E2, and functional studies show that the region serves as a scaffold attachment region in both erythroid and nonerythroid cell lines. Whereas many of the physical features of 3'HS1 are shared by 5'HS2 (a component of the 5' locus control region), transient expression studies show that 3' HS1 does not share the erythroid-specific enhancer activity exhibited by 5'HS2.

Base Sequence↗
PubMed1986

The c-abl, bcr and C lambda genes are amplified in a cell line but not in the uncultured cells from a patient with chronic myelogenous leukemia.

Structural alterations of the oncogenes in human tumors are reported to result from a variety of mechanisms: point mutations, chromosomal translocations and gene amplifications. In over 90% of the cases of chronic myelogenous leukemia (CML), the c-abl oncogene is translocated from chromosome 9 to chromosome 22, and forms in part the Philadelphia (Ph1) chromosome. We have molecularly analysed a double Ph1-positive (Ph1+) cell line, KBM-5 that was established from a patient with CML in the blast-transformed phase (CML-BP). We report that the c-abl, bcr, and C lambda genes are amplified approximately eight-fold in the cell line but not in the fresh uncultured cells from which KBM-5 was derived.

Cell Line↗