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J Visvader

Publications and source records attributed to J Visvader.

12 recordsLinked to original sources
PubMed1992

SCL is coexpressed with GATA-1 in hemopoietic cells but is also expressed in developing brain.

The SCL gene encodes a putative transcription factor with a basic helix-loop-helix (B-HLH) motif and is known to be predominantly expressed in erythroid cells. Here we also demonstrate expression of SCL mRNA in normal mast cells, mast cell lines and megakaryocytic cell lines. SCL is therefore expressed in the same three lineages as GATA-1, a well-recognized hemopoietic transcription factor. SCL and GATA-1 mRNA were also co-expressed in interleukin 3-dependent primitive myeloid lines. In murine erythroleukemia (MEL) cells SCL and GATA-1 underwent coordinated biphasic modulation during hexamethylene bisacetamide (HMBA)-induced erythroid differentiation. The kinetics of SCL and GATA-1 mRNA expression was inversely correlated with changes in ID, a negative regulator of B-HLH proteins, and was distinct from changes in MYC, MYB and erythropoietin receptor transcripts. During myeloid differentiation of K562 cells, SCL and GATA-1 mRNA levels also underwent biphasic modulation. Thus SCL and GATA-1 are coordinately expressed in multiple hemopoietic lineages and coordinately regulated during induced erythroid and myeloid differentiation. In nonhemopoietic tissues SCL was only detected in adult and developing brain where GATA-1 is reportedly not expressed. In day 14.5 embryos analysed by in situ hybridization, SCL transcripts were detected in post-mitotic neurons in the metencephalon and roof of the mesencephalon. This suggests a previously unexpected role for SCL in neural differentiation.

Animals↗
PubMed1991

Molecular cloning and chromosomal localization of the murine homolog of the human helix-loop-helix gene SCL.

The human SCL gene is a member of the family of genes that encode the helix-loop-helix (HLH) class of DNA-binding proteins. A murine SCL cDNA was isolated from a normal macrophage cDNA library by using HLH-specific oligonucleotides as hybridization probes. The coding region is 987 base pairs and encodes a predicted protein of 34 kDa. The nucleotide sequence of the coding region shows 88% identity to the human SCL gene, and the amino acid sequence is 94% identical. The HLH motif and upstream hydrophilic region are entirely conserved in the murine and human proteins. The identity between the mouse and human sequences was less marked in the 5' and 3' untranslated regions. Two murine SCL transcripts that differ in the 3' noncoding region have been detected in fetal liver and various cell lines. Variation was also observed in the 5' untranslated region. Interestingly, immediately downstream of the protein-termination codon, both the human SCL sequence and the murine homolog share an E-box element--the suggested target site for DNA binding of HLH proteins. The murine SCL homolog was mapped to the central part of chromosome 4.

Alleles↗
PubMed1991

Helix-loop-helix genes translocated in lymphoid leukemia.

A new class of DNA-binding proteins with a helix-loop-helix (HLH) structure has recently been described. Many of these transcriptional regulators are known to play a central role in cell-specification and differentiation processes. Four members of the HLH family are now implicated in the development of human lymphoid malignancies as a result of aberrant expression following chromosomal translocation events. This review focuses on two of these family members: SCL and LYL-1.

Base Sequence↗
PubMed1991

Differential expression of the LYL, SCL and E2A helix-loop-helix genes within the hemopoietic system.

The helix-loop-helix genes LYL, SCL and E2A are associated with chromosome translocations found in human lymphoid leukemias. To establish their hematopoietic expression patterns, we have isolated murine LYL and SCL cDNA clones and investigated the expression of all three genes by Northern blot analysis of 58 murine hemopoietic cell lines and tissues. The nucleotide sequences of LYL cDNA clones revealed alternative 5' untranslated sequences and differential splicing within the 5' portion of the coding region that may produce a LYL polypeptide lacking an N-terminal segment. The LYL gene was expressed in most myeloid, erythroid and B lymphocyte cell lines and displayed two alternative size classes of transcripts, the smaller size class (1.5-1.8 kb) being typical of the erythroid lineage and the larger class (2.0-2.3 kb) of the B cell lineage. These two size classes were found to differ in the 5' untranslated region. Thus, expression of the LYL gene appears to be differentially regulated in different hemopoietic cell types. In contrast, the E2A gene was expressed throughout the hemopoietic compartment as a single dominant transcript (3.5 kb). SCL expression was restricted to erythroid, mast and early myeloid cell lines, and the level of SCL transcripts (3.0 and 4.7 kb species) increased markedly during DMSO-induced differentiation of erythro-leukemia cells. Hence the SCL gene product may be an important regulatory factor for the erythroid lineage. The low or undetectable expression of both SCL and LYL in most T lymphoid cell sources is consistent with the view that the translocations of these genes in human T cell leukemias alter their normal regulation and may thereby contribute to neoplasia.

Animals↗
PubMed1990

fos-jun conspiracy: implications for the cell.

Two nuclear oncoproteins, fos and jun (AP-1), cooperate in forming a very stable heterodimeric complex that binds to the AP-1 site on DNA with high affinity. The 'leucine zipper' domain of both fos and jun is necessary for the formation of this heterodimer. Mutations of single residues within the leucine zipper domain have no effect on protein complex formation. However, results from mutagenesis of the first leucine of the heptad repeat in either fos or jun basic regions and alteration of the spacing between the basic and leucine zipper domains indicate that the basic region of fos plays a crucial role in determining the DNA binding affinity of the transcriptional complex. Mutations of the basic amino acids in fos protein prevent binding to the tumour promoter response element (TRE) in the presence of wild-type jun protein. Thus fos protein appears to be dominant in jun-fos binding to DNA, even though fos alone cannot bind to TRE. Mutants in the basic region of fos and jun can be exploited as dominant-negative mutants to ablate the normal fos cellular function.

Amino Acid Sequence↗
PubMed1990

Trans-dominant negative mutants of Fos and Jun.

Jun and Fos nuclear oncoproteins form a complex that regulates transcription from promoters containing activator protein AP-1 binding sites. The leucine-zipper and basic-region domains of both Fos and Jun are necessary for formation of the heterodimer that binds to DNA. Reciprocal mutations in the basic region of Fos or Jun can influence the binding of the heterodimer to DNA, implying a symmetrical binding site. DNA-binding mutants of Jun exhibit increased affinity for Fos and are capable of suppressing wild-type Fos-Jun DNA-binding activity. In contrast, mutations in the basic domain of Fos, which prevent binding to DNA in association with Jun, do not significantly diminish the ability of the wild-type heterodimer to bind to DNA. These dominant negative mutants are functional in vivo and can be exploited to study the role of Fos and Jun in normal and transformed cells.

Amino Acid Sequence↗
PubMed1990

Homeobox gene expression plus autocrine growth factor production elicits myeloid leukemia.

In the murine myelomonocytic leukemia WEHI-3B, proviral insertions have induced expression of the Hox-2.4 homeobox gene and the gene for the myeloid growth factor interleukin 3 (IL-3). To assess their potential oncogenic role, normal bone marrow cells were infected with retroviruses bearing the genes for IL-3 or IL-3 plus Hox-2.4. Unlike the IL-3 virus, the IL-3/Hox-2.4 virus was highly leukemogenic. Infected cells expressing both genes exhibited retarded differentiation in vitro, generated myelomonocytic cell lines, and provoked a rapid, transplantable myeloid leukemia in vivo. The oncogenic action of Hox-2.4 appears to derive from its ability to impede the IL-3-driven terminal differentiation of myeloid cells. The results suggest that homeobox genes can regulate key differentiation processes such as self-renewal capacity and that their inappropriate expression can be oncogenic.

Animals↗
PubMed1989

Fos-Jun interaction: mutational analysis of the leucine zipper domain of both proteins.

Jun and Fos oncoproteins form a complex that regulates transcription from promoters containing AP-1 binding sites. The 'leucine zipper' domain of both Fos and Jun is necessary for the formation of the heterodimer, but the role of specific leucine residues is unclear. We have used site-specific mutagenesis to examine the contribution of individual leucine residues to the formation of a stable Fos-Jun protein complex and the binding of this complex to the AP-1 site. Mutation of a single leucine in either Fos or Jun had no effect on protein complex formation. Furthermore, mutations of two consecutive leucines in Jun did not interfere with heterodimer formation; however, in the case of Fos, two consecutive mutations resulted in an inability to form a heterodimer. Although mutagenesis of the first leucine of the heptad repeat had no effect on protein complex formation, this mutation in either Fos or Jun drastically reduced the affinity of the complex for DNA. Thus, both Fos and Jun contribute directly to the DNA-binding potential of the heterodimer.

Amino Acid Sequence↗
PubMed1989

Differential transcription of exon 1 of the human c-fms gene in placental trophoblasts and monocytes.

Structural analysis of the 5' end of the human c-fms gene revealed that a large intron of about 25 kilobases separates an upstream noncoding exon (exon 1) from the signal peptide-containing exon (exon 2). Northern (RNA) blot analysis, S1 nuclease mapping, and primer extensions showed that exon 1 is transcribed in placenta but not in cells of the monocytic lineage. This is due to the differential usage of promoters, separated by approximately 25 kilobases, in a cell-specific manner. One major c-fms transcript was observed in U-937 cells, whereas multiple initiation sites for transcription appeared to be utilized in placental cells. Nucleotide sequence comparisons showed that the 3' end of the human platelet-derived growth factor receptor gene lies approximately 350 base pairs upstream of the major initiation sites for c-fms transcription in placental trophoblasts.

Amino Acid Sequence↗
PubMed1989

fos and jun interaction: the role of the leucine zipper.

Jun and fos oncoproteins form a complex which regulates transcription from promoters containing AP-I binding sites. The "leucine zipper" domain of both fos and jun is necessary for the formation of the heterodimer, but the role of specific leucine residues is unclear. We have used site-specific mutagenesis to examine the contribution of individual leucine residues to the formation of a stable fos/jun protein complex and the binding of this complex to the AP-I site. Mutation of a single leucine in either fos or jun had no effect on protein complex formation. Furthermore, mutations of two consecutive leucines in jun did not interfere with heterodimer formation; however, in the case of fos, two consecutive mutations resulted in an inability to form a heterodimer. Although mutagenesis of the first leucine of the heptad repeat had no effect on protein complex formation, this mutation in either fos or jun drastically reduced the affinity of the complex for DNA. Thus, both fos and jun contribute directly to the DNA binding potential of the heterodimer.

Amino Acid Sequence↗
PubMed1989

fos-jun Conspiracy: implications for the cell.

Two nuclear oncoproteins, fos and jun (AP-1), cooperate in forming a very stable heterodimeric complex that binds to the AP-1 site with increased affinity. The 'leucine zipper' domain of both fos and jun is necessary for the formation of this heterodimer. Mutations of single residues within the leucine zipper domain had no effect on protein complex formation. However, mutagenesis of the first leucine of the heptad repeat in either fos or jun basic regions and alteration of the spacing between the basic and leucine zipper domains indicate that the basic region of fos has a crucial role in determining the DNA binding affinity of the transcriptional complex. Mutations of the basic amino acids in fos protein prevent binding to TPA (phorbol ester)-responsive element (TRE) in the presence of wild-type jun protein. Thus fos protein appears to be dominant in jun-fos binding to DNA, even though fos alone cannot bind to TRE. Mutants in the basic regions of fos and jun can be exploited as dominant-negative mutants to ablate their normal cellular function.

Amino Acid Sequence↗