Transcriptional up-regulation of the mouse cytosolic glutathione peroxidase gene in erythroid cells is due to a tissue-specific 3' enhancer containing functionally important CACC/GT motifs and binding sites for GATA and Ets transcription factors

Mechanisms of anthracycline cardiotoxicity and strategies to decrease cardiac damage

Anthracyclines are common chemotherapeutic agents used to treat many different types of cancer. Unfortunately, the use of anthracyclines is limited by their cardiotoxic effects, which may become manifest as late as 20 years from initial exposure. Studies in cells and animals suggest that the mechanism of anthracycline-induced cardiotoxicity (AIC) is multifactorial. Anthracyclines induce multiple forms of cellular injury by free radical production. In addition, anthracyclines alter nucleic acid biology by intercalation into DNA and modulate intracellular signaling, leading to cell death and the disruption of homeostatic processes such as sarcomere maintenance. In an effort to decrease AIC, many strategies have been tested, but no specific therapies are universally acknowledged to prevent or treat anthracycline-induced cardiac dysfunction. Newer imaging modalities and cardiac biomarkers may be useful in improving early detection of cardiac injury and dysfunction. As long as there is no cardiac-specific therapy for AIC, evidence suggests that high-risk patients will benefit from prophylactic treatment with neurohormonal blockade by angiotensin-converting enzyme inhibitors and beta-adrenergic receptor blockers.

MAPK-mediated phosphorylation of GATA-1 promotes Bcl-XL expression and cell survival

In the interleukin 3-dependent hematopoietic cell line Ba/F3, inhibition of mitogen-activated protein kinase, a member of the MAPK/c-Jun N-terminal kinase/stress-activated protein kinase kinase family that plays an important role in cell growth and death control, rapidly leads to severe apoptosis. However, most of the antiapoptotic substrates of MAPK remain to be identified. Here we report that, upon interleukin-3 stimulation of Ba/F3 cells, the transcription factor GATA-1 is strongly phosphorylated at residue serine 26 by a MAPK-dependent pathway. Phosphorylation of GATA-1 increases GATA-1-mediated transcription of the E4bp4 survival gene without significantly changing the DNA-binding affinity of GATA-1. Further characterization of GATA-1 phosphorylation site mutants revealed that the antiapoptotic function of GATA-1 is strongly dependent upon its phosphorylation at the Ser-26 position and is probably mediated through its up-regulation of Bcl-X(L) expression. Taken together, our data demonstrate that MAPK-dependent GATA-1 phosphorylation is important for its transactivation of the E4bp4 gene, Bcl-X(L) expression and cell survival. Therefore, GATA-1 may represent a novel MAPK substrate that plays an essential role in a cytokine-mediated antiapoptotic response.

Endothelin-1 induces phosphorylation of GATA-4 transcription factor in the HL-1 atrial-muscle cell line

The transcription factor GATA-4 plays a central role in the regulation of cardiac-muscle gene transcription. The present study demonstrates that endothelin-1 (ET-1) induces GATA-4 activation and phosphorylation. The treatment of HL-1 adult mouse atrial-muscle cells with ET-1 (30 nM) caused a rapid increase in the DNA binding activity of GATA-4 within 3 min. The activation was associated with an upward mobility shift of the GATA-4 band on native PAGE in an electrophoretic- mobility-shift assay. The upward shift of the GATA-4 band also occurred on SDS/PAGE as monitored by immunoblotting. The in vitro treatment of nuclear extracts with lambda-protein phosphatase abolished the upward shift, indicating that GATA-4 was phosphorylated. ET-1 activated the p44/42 mitogen-activated protein kinase (MAPK) and the MAPK kinase (MEK) within 3 min, and PD98059 (a specific inhibitor of MEK) abolished the ET-1-induced GATA-4 phosphorylation. PMA also caused the rapid activation of MAPK and the phosphorylation of GATA-4. In contrast, the activation of MAPK by phenylephrine or H(2)O(2) was weak and did not lead to GATA-4 phosphorylation. Thus ET-1 induces a GATA-4 phosphorylation by activating a MEK-MAPK pathway.

Ets target genes: past, present and future

Ets is a family of transcription factors present in species ranging from sponges to human. All family members contain an approximately 85 amino acid DNA binding domain, designated the Ets domain. Ets proteins bind to specific purine-rich DNA sequences with a core motif of GGAA/T, and transcriptionally regulate a number of viral and cellular genes. Thus, Ets proteins are an important family of transcription factors that control the expression of genes that are critical for several biological processes, including cellular proliferation, differentiation, development, transformation, and apoptosis. Here, we tabulate genes that are regulated by Ets factors and describe past, present and future strategies for the identification and validation of Ets target genes. Through definition of authentic target genes, we will begin to understand the mechanisms by which Ets factors control normal and abnormal cellular processes.

Structure and activity of mouse S-adenosylmethionine decarboxylase gene promoters and properties of the encoded proteins

The promoter regions of two S-adenosylmethionine decarboxylase genes (AMD genes) were isolated from a mouse genomic library. One promoter was that of the bona fide mouse AMD gene (AMD1) whereas the other was that of the intronless AMD gene (AMD2). There was no sequence identity between the two promoters. The sequence of the AMD1 promoter was highly homologous to the human AMD1 and rat Amd1B promoters. After transient transfection in various cell lines, the AMD1 promoter was one to two orders of magnitude stronger than the AMD2 promoter. Similar results were obtained by using stably transfected mouse FM3A cells. In S-adenosylmethionine decarboxylase (AdoMetDC)-overproducing SAM-1 cells, the AMD1 gene was amplified over 5-fold. AdoMetDC encoded by the intronless AMD2 gene had two amino acid replacements (Met to Ile at codon 70 and Ala to Val at codon 139), compared with the protein encoded by the AMD1 gene, and exhibited decreased catalytic activity (<50%) and decreased processing activity when expressed in AdoMetDC-deficient Escherichia coli cells. When Ile-70 of the protein encoded by AMD2 was converted into Met, both the catalytic and processing activities recovered markedly, indicating that Met-70 adjacent to the proenzyme-processing site is important for both activities. The third AMD locus (AMD3) in FM3A cells contains a pseudogene, in which deletion of two bases generates a premature termination codon at position 57. Since the AMD2 promoter had only 1-10% of the strength of the bona fide AMD1 gene and AMD2 protein possessed lower specific activity, the relative contribution of the AMD2-encoded enzyme to total AdoMetDC activity is small. Thus AdoMetDC activity in murine cells is thought to be due mainly to the product of the AMD1 gene.

Transcription factor GATA-1 permits survival and maturation of erythroid precursors by preventing apoptosis

The transcription factor GATA-1 recognizes a consensus motif present in regulatory regions of numerous erythroid-expressed genes. Mouse embryonic stem cells lacking GATA-1 cannot form mature red blood cells in vivo. In vitro differentiation of GATA-1- embryonic stem cells gives rise to a population of committed erythroid precursors that exhibit developmental arrest and death. We show here that the demise of GATA-1- erythroid cells is accompanied by several features characteristics of apoptosis. This process occurs despite normal expression of all known GATA target genes examined, including the erythropoietin receptor, and independent of detectable accumulation of the tumor suppressor protein p53. Thus, in addition to its established role in regulating genes that define the erythroid phenotype, GATA-1 also supports the viability of red cell precursors by suppressing apoptosis. These results illustrate the multifunctional nature of GATA-1 and suggest a mechanism by which other hematopoietic transcription factors may ensure the development of specific lineages.

Tissue-specific regulation of the rabbit 15-lipoxygenase gene in erythroid cells by a transcriptional silencer

The 15-lipoxygenase (lox) gene is expressed in a tissue-specific manner, predominantly in erythroid cells but also in airway epithelial cells and eosinophils. We demonstrate in this report that the 5' flanking DNA of the 15-lox gene contains sequences which down-regulate its activity in a variety of non-erythroid cell lines but not in two erythroid cell lines. The element has characteristics of a transcriptional 'silencer' since it functions in both orientations. The main activity of the silencer has been mapped to the first 900 bp of 5' flanking DNA, which contains nine binding sites for a nuclear factor present in non-erythroid cells but not in erythroid cells. These binding sites have similar sequences and multiple copies of the binding sites confer tissue-specific down-regulation when attached to a minimal lox promoter fragment. The 5' flanking DNA also contains a cluster of three binding sites for the GATA family of transcription factors.

Identification and characterization of a neuroretina-specific enhancer element in the quail Pax-6 (Pax-QNR) gene

Using nuclear run-on assays, we showed that the tissue-specific expression of quail Pax-6 (Pax-QNR) P0-initiated mRNAs is due in part to regulation of the gene at the transcriptional level. Regulatory sequences governing neuroretina-specific expression of the P0-initiated mRNAs were investigated. By using reporter-based expression assays, we characterized a region within the Pax-QNR gene, located 7.5 kbp downstream from the P0 promoter, that functions as an enhancer in neuroretina cells but not in nonexpressing P0-initiated mRNA cells (quail embryo cells and quail retinal pigment epithelial cells). This enhancer element functioned in a position- and orientation-independent manner both on the Pax-QNR P0 promoter and the heterologous thymidine kinase promoter. Moreover, this enhancer element exhibited a developmental stage-specific activity during embryonic neuroretina development: in contrast to activity at day E7, the enhancer activity was very weak at day E5. This paralleled the level of expression of P0-initiated mRNAs observed at the same stages. Using footprinting, gel retardation, and Southwestern (DNA-protein) analysis, we demonstrated the existence of four neuroretina-specific nuclear protein-binding sites, involving multiple unknown factors. In addition we showed that the quail enhancer element is structurally and functionally conserved in mice. All of these results strongly suggest that this enhancer element may contribute to the neuroretina-specific transcriptional regulation of the Pax-6 gene in vivo.