DNA conformation, topology, and the regulation of c-myc expression.
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Animals↗
Biomedical subjects
T Tomonaga
Publications and source records attributed to T Tomonaga.
Activating transcription from single stranded DNA.
Sequence specific regulators of eukaryotic gene expression, axiomatically, act through double stranded DNA targets. Proteins that recognize DNA cis-elements as single strands but for which compelling evidence has been lacking to indicate in vivo involvement in transcription are orphaned in this scheme. We sought to determine whether sequence specific single strand binding proteins can find their cognate elements and modify transcription in vivo by studying heterogeneous nuclear ribonucleoprotein K (hnRNP K), which binds the single stranded sequence (CCCTCCCCA; CT-element) of the human c-myc gene in vitro. To monitor its DNA binding in vivo, the ability of hnRNP K to activate a reporter gene was amplified by fusion with the VP16 transactivation domain. This chimeric protein was found to transactivate circular but not linear CT-element driven reporters, suggesting that hnRNP K recognizes a single strand region generated by negative supercoiling in circular plasmid. When CT-elements were engineered to overlap with lexA operators, addition of lexA protein, either in vivo or in vitro, abrogated hnRNP K binding most likely by preventing single strand formation. These results not only reveal hnRNP K to be a single strand DNA binding protein in vivo, but demonstrate how a segment of DNA may modify the transcriptional activity of an adjacent gene through the interconversion of duplex and single strands.
Animals↗
A unique transactivation sequence motif is found in the carboxyl-terminal domain of the single-strand-binding protein FBP.
The far-upstream element-binding protein (FBP) is one of several recently described factors which bind to a single strand of DNA in the 5' region of the c-myc gene. Although cotransfection of FBP increases expression from a far-upstream element-bearing c-myc promoter reporter, the mechanism of this stimulation is heretofore unknown. Can a single-strand-binding protein function as a classical transactivator, or are these proteins restricted to stabilizing or altering the conformation of DNA in an architectural role? Using chimeric GAL4-FBP fusion proteins we have shown that the carboxyl-terminal region (residues 448 to 644) is a potent transcriptional activation domain. This region contains three copies of a unique amino acid sequence motif containing tyrosine diads. Analysis of deletion mutants demonstrated that a single tyrosine motif alone (residues 609 to 644) was capable of activating transcription. The activation property of the C-terminal domain is repressed by the N-terminal 107 amino acids of FBP. These results show that FBP contains a transactivation domain which can function alone, suggesting that FBP contributes directly to c-myc transcription while bound to a single-strand site. Furthermore, activation is mediated by a new motif which can be negatively regulated by a repression domain of FBP.
Amino Acid Sequence↗
Cellular nucleic acid binding protein regulates the CT element of the human c-myc protooncogene.
The CT element of the c-myc gene is required for promoter P1 usage and can drive expression of a heterologous promoter. Both double strand (Sp1) and single strand (hnRNP K) CT-binding proteins have been implicated as mediators of CT action. Although significant levels of CT activity persisted following Sp1 immunodepletion, EGTA totally abolished transactivation, thus implicating another metal requiring factor in CT element activity. As hnRNP K binds to one strand of the CT element, but has no metal requirement, the opposite (purine-rich strand) was examined as a target for a metal-dependent protein. A zinc-requiring purine strand binding activity was identified as cellular nucleic acid binding protein (CNBP), a protein previously implicated in the regulation of sterol responsive genes. Two forms of CNBP differed in their relative binding to the CT- or sterol-response elements. CNBP was shown to be a bona fide regulator of the CT element by cotransfection of a CNBP expression vector that stimulated expression of a CT-driven but not an AP1-dependent reporter. These data suggest that hnRNP K and CNBP bind to opposite strands and co-regulate the CT element.
Amino Acid Sequence↗
Heterogeneous nuclear ribonucleoprotein K is a DNA-binding transactivator.
We have previously reported that heterogeneous nuclear ribonucleoprotein K (hnRNP K) binds to the pyrimidine-rich strand of the CT element found in the human c-myc gene and activates CT reporter-driven gene expression in vivo. We now characterize the DNA and protein requirements for the interaction of hnRNP K with the CT element. First, hnRNP K is shown to preferentially bind single-stranded DNA over RNA or native double-stranded DNA. Using specific oligoribonucleotide or deoxyribonucleotide probes with specific or nonspecific RNA or DNA competitors, electrophoretic mobility shift assay revealed hnRNP K to be a DNA-binding protein. Specific binding was not simply a reflection of binding to pyrimidine-rich sequences as the number and arrangement of individual CT elements governed interactions with hnRNP K; at least two CT repeats separated by at least three nucleotides are required for binding, indicating the existence of particular stereochemical constraints regulating CT-hnRNP K complex formation. Deletion analysis showed that hnRNP K possesses several nonoverlapping, DNA binding domains, each capable of specific binding with the CT element and preferring DNA over RNA. Each sequence recognition domain is composed of at least one K homology motif, while a larger portion of hnRNP K may be required for stable RNA binding. Additional experiments indicate that the N-terminal 35 residues of hnRNP K are necessary for transactivating the CT element. These results indicate that hnRNP K is a DNA-binding protein and transcriptional activator.
Animals↗
A sequence-specific, single-strand binding protein activates the far upstream element of c-myc and defines a new DNA-binding motif.
The far upstream element (FUSE) of the human c-myc proto-oncogene stimulates expression in undifferentiated cells. A FUSE-binding protein (FBP) is present in undifferentiated but not differentiated cells. Peptide sequences from the purified protein allowed cloning of cDNAs encoding FBP. Expression of FBP mRNA declined upon differentiation, suggesting transcriptional regulation of FBP. Features in the FBP cDNA suggest that FBP is also regulated by RNA processing, translation, and post-translational mechanisms. Both cellular and recombinant FBP form sequence-specific complexes with a single strand of FUSE. Transfection of FBP into human leukemia cells stimulated c-myc-promoter-driven expression from a reporter plasmid in a FUSE-dependent manner. Deletion and insertion mutagenesis of FBP defined a novel single-strand DNA-binding domain. Analysis of the primary and predicted secondary structure of the amino acid sequence reveals four copies of a reiterated unit comprised of a 30-residue direct repeat and an amphipathic alpha-helix separated by an 18- to 21-residue spacer. The third and fourth copies of this repeat-helix unit constitute the minimum single-stranded DNA-binding domain. To determine whether the FUSE site, in vivo, possesses single-strand conformation, and therefore could be bound by FBP, cells were treated with potassium permanganate (KMnO4) to modify unpaired bases. Modification of genomic DNA in vivo revealed hyperreactivity associated with single-stranded DNA in the FUSE sequence and protection on the strand that binds FBP in vitro. The role of single-stranded DNA and single-strand binding proteins in c-myc regulation is discussed.
Amino Acid Sequence↗
Signaling pathway other than phosphatidylinositol turnover is responsible for constant expression of c-myc gene in primary cultures of rat hepatocytes.
We investigated signal transduction pathways involved in c-myc activation, using rat hepatocytes in primary culture. c-Myc mRNA was constantly expressed in the cultured hepatocytes regardless of the conditions present. When the expression was examined in the presence of various agents modulating intracellular signals, isoflavonoids (genistein, psi-tectorigenin, and orobol) significantly decreased c-myc mRNA levels, in a dose dependent manner. However, genistein did not decrease Li+ induced inositol phosphate accumulation using [3H]inositol-labeled cultured hepatocytes. In addition, we have shown that these isoflavonoids increase cytoplasmic free Ca2+, when measured using aequorin-loaded hepatocytes. In light of these observations, the persistent basal level of c-myc expression seems to be maintained by mechanisms other than phosphatidylinositol turnover.
Animals↗
Specific binding of heterogeneous ribonucleoprotein particle protein K to the human c-myc promoter, in vitro.
A homopurine/homopyrimidine-like sequence is found 100-150 base pairs upstream of the human c-myc promoter P1. This element, termed the CT-element, has been shown to augment expression from P1, and it serves as a positive transcriptional element when coupled to a heterologous promoter in vivo and in vitro. Synthetic oligonucleotides comprising this element were used to form DNA-protein complexes in electrophoretic mobility shift assays. By using conventional and affinity methods, 61- and 34-kDa proteins were shown to be associated with these complexes. Amino acid sequence analysis and immunological methods have identified these proteins as heterogeneous ribonucleoprotein particle (hnRNP) proteins K and A1. Surprisingly, hnRNP protein K binds to the pyrimidine-rich strand of the CT-element in a sequence-specific manner as well as to the double-stranded molecule. Cotransfection of vectors encoding hnRNP protein K in the sense or anti-sense orientations with reporter plasmids driven by wild-type or mutant CT-elements demonstrates that hnRNP protein K augments gene expression in a cis-element-dependent manner. Taken together, these results suggest that hnRNP protein K may play a role in the transcriptional regulation of the human c-myc gene.
Amino Acid Sequence↗
Isoflavonoids, genistein, psi-tectorigenin, and orobol, increase cytoplasmic free calcium in isolated rat hepatocytes.
Isoflavonoid compounds, genistein, psi-tectorigenin and orobol have been implicated as inhibitors of tyrosine-specific protein kinase and phosphatidylinositol turnover. These compounds have been frequently used as a pharmacological tool to assess signal transduction pathways in various cell systems. In the course of analyzing signaling pathways in rat hepatocytes, we obtained an unexpected finding that these compounds transiently increase cytoplasmic free calcium. Since the Ca2+ mobilizing effect was observed in 1 microM calcium containing buffer, the source of the Ca2+ may be intracellular stores. Thus, when interpreting data obtained using these compounds, caution is needed.
Aequorin↗
[A case of chronic idiopathic intestinal pseudoobstruction and a review of literature in Japan].
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Adult↗
Bunina bodies in neurons of the medullary reticular formation in a case of amyotrophic lateral sclerosis.
In an autopsied case of amyotrophic lateral sclerosis (ALS) with dementia (a 65-year-old man with a 4-year course) showing numerous Bunina bodies in the lower motor neurons including those of cranial motor nuclei, eosinophilic inclusions were also observed in several neurons of the reticular formation of the medulla oblongata. Some of them were confirmed to be Bunina bodies by electron microscopy. These findings indicate either that Bunina bodies can appear in neurons other than the so-called motor neurons or that the neurons in the medullary reticular formation that contain such inclusions may be lower motor neurons in the aberrant place.
Aged↗
Effects of the in vivo administration of recombinant human granulocyte colony-stimulating factor following cytotoxic chemotherapy on granulocytic precursors in patients with malignant lymphoma.
We examined the effects of the in vivo administration of recombinant granulocyte colony-stimulating factor (rhG-CSF) on granulocytic precursors in the bone marrow of 4 patients with malignant lymphoma who received chemotherapy. Patients were treated with rhG-CSF at doses of 100-800 micrograms/m2/day intravenously for 14 days only in the first course of chemotherapy (G-CSF course) followed by the second course of chemotherapy without rhG-CSF which was used as a control course. In the G-CSF course, white blood cell counts (WBCs) demonstrated a biphasic response consisting of a first peak observed within a few days after the initiation of rhG-CSF administration, and a second peak observed on the last day of rhG-CSF injection or the day after. In the second peak, the incidence of granulocyte-macrophage colony-forming units (CFU-GM) in mononucleated bone marrow cells did not change significantly after treatment with rhG-CSF as compared with a control. However, since the number of nucleated cells in the bone marrow increased, the absolute number of CFU-GM in the bone marrow increased. The number of mature and immature granulocytes in the bone marrow increased. These findings suggest that G-CSF stimulates the proliferation and differentiation of granulocytic precursors in the bone marrow in granulocytopenic patients who received cytotoxic drugs and causes mature granulocytes to be released from the bone marrow.
Adult↗
[An electromyographic study on elevation of the shoulder joint].
To quantitatively analyze the electromyographic activity of the shoulder girdle muscles during elevation of the arm, the action potentials of nine muscles were integrated over 10-degree intervals of corresponding elevation angle. The trapezius, supraspinatus and deltoideus (anterior and middle fibers) muscles showed high activity and their activity increased in accordance with the magnitude of the elevation angle. The integrated EMG activity in the trapezius, supraspinatus and deltoideus (middle and posterior fibers) muscles increased as the plane of elevation was changed from the sagittal plane to the frontal plane. The correlation between the calculated work and the integrated EMG activity during scapular abduction from 0 to 90 degrees was analyzed. The regression coefficients of the trapezius, supraspinatus and deltoideus (anterior and middle fibers) muscles were higher than those of other muscles. The correlation coefficient of the supraspinatus was significantly lower than those of the trapezius, deltoideus and pectoralis major muscles.
Adolescent↗
[Aortic dissection beginning in the lowermost descending aorta--report of two successfully operated cases].
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Aortic Dissection↗
[Retroperitoneal liposarcoma with various histological figures].
A case of retroperitoneal liposarcoma consisting of three large nodules with three different types of histologic findings is presented. A 69-year-old man was diagnosed as having a malignant tumor in the retroperitoneum and underwent successful tumor extirpation. The resected tumor had three different type of nodules, 18 X 15 X 7.0 cm, 8 X 15 X 4.0 cm, 15 X 10 X 2.5 cm in size, respectively. The histologic examination revealed myxoid, well-differentiated fibrosing and lipoma-like liposarcoma type, respectively. Chemotherapy was undertaken postoperatively, and there is no evidence of recurrence two years after surgery.
Aged↗
[Protective effect of radical scavengers on cerebral infarction--experimental study utilizing the spin trapping method of ESR].
To evaluate the scavenging effect of mannitol, vitamin E and betamethasone in cerebral ischemia, spin trapping technique was applied to the detection of the free radicals generated in ischemic brain homogenate. Thirty Wistar rats were used for this study. In the control group, the brain homogenate prepared immediately after decapitation was preserved at 37 degrees C under N2 gas. Before the preservation and at 30 min, 60 min and 120 min from the start of the preservation, two reaction mixtures containing of spin trapping reagent phenyl-t-butyl nitrone (PBN), NADPH, Fe-EDTA and brain homogenate was prepared from each brain sample--one to be incubated for 20 min at 37 degrees C in air and one to be incubated in nitrogen gas under similar condition. Then the free radical adducts of PBN were measured by electron spin resonance (ESR). In pre-treated group, mannitol, vitamin E and betamethasone were administered intravenously 30 min prior to the decapitation and spin adducts of PBN were detected by same procedures as in control group. The ESR spectra, which hyperfine coupling constants were AN = 16.0-16.6 G and AH beta = 3.0-3.8 G, were obtained from the reaction mixtures in each group. Analyses of their relative intensity in control group revealed that the formation of free radical adducts of PBN was increased dependent on the preservation period under aerobic incubation, and increased gradually for 60 min of preservation time followed by a decrease under anaerobic incubation.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Endoscopic SIS injection into the lower oesophageal sphincter in dogs.
AIM: To determine the usefulness of endoscopically-delivered small intestinal submucosa (SIS) as a scaffold in enhancing the lower oesophageal sphincter (LOS) pressures. METHODS: Six dogs were endoscopically injected--four with the SIS and two with its glycerin carrier. Manometry was performed prior to injection and every four weeks post-op. RESULTS: Adequate and site correct injections were made in four dogs. In one dog, significant augmentation of pressures were obtained at four weeks. None had significant changes in pressure at eight weeks, differences in length at either four or eight weeks or significant differences in the thickness of the examined layers. Four of the six had capillary cushions on pathological examination. The dog injected with the carrier had a loose and disorganise collection, while the others were well organised. CONCLUSION: SIS is a biologically compatible material. Lack of an animal model for gastro-oesophageal reflux disease (GORD) makes determining the ability of injections of SIS to combat reflux problematic.
Animals↗
Surgery for achalasia: 1998.
Technical controversies abound regarding the surgical treatment of achalasia. To determine the value of a concomitant antireflux procedure, the best antireflux procedure, the correct length for gastric myotomy, the optimal surgical approach (thoracic or abdominal), and the equivalency of minimally invasive surgery, a literature review was carried out. The review is based on 23 articles on open transabdominal or transthoracic myotomy, 14 articles on laparoscopic myotomy, and four articles on thoracoscopic myotomy. Postoperative results of traditional open thoracic or transabdominal myotomy as determined by symptomatology were better with fundoplication than without fundoplication. The incidence of postoperative reflux as proved by pH monitoring was high in patients who had an open transabdominal myotomy without fundoplication. The type of antireflux procedure used and the length of gastric myotomy had little effect on results. The results of transthoracic Heller myotomy do not require a concomitant fundoplication. Laparoscopic and thoracoscopic myotomy had excellent results at short-term follow-up. A fundoplication must be added if the myotomy is performed transabdominally. A randomized prospective study is required to determine the best fundoplication and the extent of gastric myotomy. Although minimally invasive surgery for achalasia has excellent initial results, longer follow-up in a larger population of patients is needed.
Digestive System Surgical Procedures↗