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Biomedical subjects

J Ma

Publications and source records attributed to J Ma.

At least 613 records · Page 34Linked to original sources
PubMed1988

Converting a eukaryotic transcriptional inhibitor into an activator.

GAL80, an inhibitor of the yeast transcriptional activator GAL4, is converted into an activator by inserting an acidic activating sequence into it. This hybrid activator does not bind to DNA directly, but is brought to DNA by interacting with a derivative of GAL4 that interacts with both DNA and GAL80.

DNA, Fungal↗
PubMed1988

Ryanodine receptor of skeletal muscle is a gap junction-type channel.

In the sarcoplasmic reticulum membrane of skeletal muscle, the ryanodine receptor forms an aqueous pore identified as the calcium-release pathway that operates during excitation-contraction coupling. The purified ryanodine receptor channel has now been shown to have four properties usually associated with gap junction channels: (i) a large nonspecific voltage-dependent conductance consisting of several open states; (ii) an inhibition of open probability by low pH; (iii) an inhibition of open probability by calcium; and (iv) a sensitivity to blockade by heptanol and octanol but not other alcohols. This functional homology may provide an insight into the mechanism of how muscle cells transduce depolarization into an intracellular release of calcium.

Alcohols↗
PubMed1988

GAL4-VP16 is an unusually potent transcriptional activator.

Recent work has defined a class of transcriptional activators, members of which activate transcription in yeast, plant, insect and mammalian cells. These proteins contain two parts: one directs DNA binding and the other, called the activating region, presumably interacts with some component of the transcriptional machinery. Activating regions are typically acidic and require some poorly-understood aspect of structure, probably at least in part an alpha-helix. Here we describe a new member of this class, formed by fusing a DNA-binding fragment of the yeast activator GAL4 to a highly acidic portion of the herpes simplex virus protein VP16 (ref. 11; also called Vmw65). VP16 activates transcription of immediate early viral genes by using its amino-terminal sequences to attach to one or more host-encoded proteins that recognise DNA sequences in their promoters. We show that the hybrid protein (GAL4-VP16) activates transcription unusually efficiently in mammalian cells when bound close to, or at large distances from the gene. We suggest that the activating region of VP16 may be near-maximally potent and that it is not coincidental that such a strong activator is encoded by a virus.

Animals↗
PubMed1988

Yeast activators stimulate plant gene expression.

GAL4 is a transcriptional activator found in yeast. Two distinct functions of the protein are required for its activity: one directs sequence-specific DNA binding, and another interacts with some other component of the transcriptional machinery, for example, RNA polymerase II or a TATA-binding protein. Two short regions of GAL4 function as 'activating sequences' when attached to the DNA-binding portion of GAL4 and these regions can be replaced by a large number of peptides encoded by Escherichia coli genomic DNA fragments or by a synthetic peptide designed to form an amphiphilic alpha-helix. All of these activating sequences, like that found in another yeast activator, GCN4 bear an excess negative charge. GAL4 and its derivatives that are active in yeast stimulate transcription in mammalian cells when GAL4 binding sites are introduced upstream of a mammalian gene; similarly, GAL4 activates transcription in Drosophila cells. Here we show that GAL4 derivatives stimulate gene expression in plant cells.

Acetyltransferases↗
PubMed1988

Mechanisms for cisplatin-FUra synergism and cisplatin resistance in human ovarian carcinoma cells both in vitro and in vivo.

Cisplatin and FUra act synergisticly in human carcinomas. An increase in the availability of reduced folates necessary for tight binding of FdUMP to thymidylate synthase (TS) contributes to the enhanced cytotoxicity of this drug combination. The human ovarian A2780 cell line made three-fold resistant to cisplatin has been shown to have a three-fold elevation of m-RNA for dihydrofolate reductase (DHFR) and TS. However, this increase did not result from an amplification of the genes for these two enzymes. In contrast, ovarian carcinoma cells from patients who failed treatment with cisplatin and FUra have been shown to have both enhanced gene expression and increased gene copy number for DHFR and TS.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1988

Giardia lamblia in patients undergoing endoscopy: lack of evidence for a role in nonulcer dyspepsia.

Previous studies have suggested that Giardia lamblia may cause nonulcer dyspepsia as the sole manifestation of infection. To explore this premise, duodenal aspirates from patients undergoing upper endoscopy were examined for Giardia and results were correlated with endoscopic findings and symptoms. Of 155 patients, 15.5% had Giardia. Patients with dyspepsia, with or without obvious lesions at endoscopy, had a similar prevalence. Patients with vomiting and diarrhea had an increased prevalence (38.5%) (p less than 0.05). The prevalence of Giardia lamblia in this patient population is surprisingly high. This study suggests that Giardia lamblia infection is not a major cause of nonulcer dyspepsia.

Adolescent↗
PubMed1988

Heterogeneity of conductance states in calcium channels of skeletal muscle.

The single channel conductance of the dihydropyridine (DHP)-sensitive calcium channel from rabbit skeletal muscle transverse tubules was analyzed in detail using the planar bilayer recording technique. With 0.1 M BaCl2 on both sides of the channel (symmetrical solutions), the most frequent conductance is 12 pS, which is independent of holding potential in the range of -80 to +80 mV. This conductance accounts for approximately 80% of all openings analyzed close to 0 mV. Two additional channels of conductance 9 and 3 pS are also present at all positive potentials, but their relative occurrence close to 0 mV is low. All channels depend on the presence of agonist Bay K 8644 and are inhibited by the antagonist nitrendipine. The relative occurrence of 9 and 3 pS can be increased, and that of 12 pS decreased, by several interventions such as external addition of cholesterol, lectin (wheat germ agglutinin), or calmodulin inhibitor R24571 (calmidazolium). The 9- and 3-pS channels are also conspicuous at positive potentials larger than +40 mV. We suggest that 9- and 3-pS channels are two elementary conductances of the same DHP-sensitive Ca channel. Under most circumstances, these two conductances are gated in a coupled way to generate a channel with a unitary conductance of 12 pS. Interventions tested, including large depolarizations, probably decompose or uncouple the 12-pS channel into 9 and 3 pS.

Animals↗
PubMed1988

Intestinal mucin antigens in ulcerative colitis and their relationship with malignancy.

The expression of two intestinal mucin-associated antigens large intestine mucin antigen (LIMA) and small intestine mucin antigen (SIMA) were investigated by indirect immunoperoxidase staining of rectal mucosa from patients suffering from ulcerative colitis with (n = 6) and without (n = 31) associated carcinoma and in noncolitic controls (n = 40). The aim was to assess the relationship between antigen patterns and malignant change. SIMA, which is localised predominantly in the small intestine, is virtually undetectable in the normal adult colonic mucosa. However, this antigen is present in the foetal colon and colonic carcinoma. LIMA is expressed in normal colonic mucosa, but absent from the small intestine. LIMA staining patterns were not significantly different among the three groups. In contrast, expression of SIMA was significantly higher in the patients who had developed carcinoma (6/6) than in the noncancer group (7/71) (P less than 0.001). The presence of SIMA was also significantly related to areas of dysplasia compared to normal (P = .03) or inflammation (P less than .05), but it did not differ from mucosa showing "indefinite" atypia. The finding of 31% SIMA-positive biopsies associated with severe inflammation in colitis with active disease, but no evidence of malignancy, is difficult to explain at the present stage. A followup study would be necessary to determine its significance. Perhaps the most important finding is the increased frequency of SIMA-positive foci in histologically normal mucosa in carcinoma patients compared with the noncancer group (P less than .001), suggesting a field change. These observations may be prove useful for the identification of patients who may be at risk of developing carcinoma.

Adult↗
PubMed1988

Expression of intestinal mucin antigens in the gastric epithelium and its relationship with malignancy.

The expression of large and small intestinal mucin antigens (LIMA and SIMA) was investigated in 30 gastrectomy specimens of carcinoma and in 11 controls resected for various pathologic conditions. One hundred eighty-five samples of normal mucosa, hyperplasia, intestinal metaplasia (types I, II, and III), dysplasia, and tumor were studied to identify phenotypes indicative of premalignant change. Our results showed LIMA and SIMA were not detected in normal gastric epithelium from either control or carcinoma specimens. SIMA characterized goblet cell mucin in all types of intestinal metaplasia and was not discriminatory between controls and carcinoma groups. On the other hand, LIMA was extensively expressed in columnar and goblet cells in carcinoma-bearing stomachs (97 per cent) but was absent in controls. There was a crescendo intensity and frequency of LIMA staining in an inverse relation to the degree of cell maturation and differentiation from type I intestinal metaplasia (60 per cent) to type II (85 per cent), type III (100 per cent), and dysplasia (100 per cent). In contrast, intestinal metaplasia of any type in controls did not show LIMA. The distribution of LIMA seemed to be intimately related to cell differentiation in the proliferative zone at the base of metaplastic glands. Carcinomas revealed antigenic phenotype heterogenicity. Our data indicate that LIMA sharpens the diagnosis of dysplasia, discriminates between reactive and preneoplastic epithelium (particularly within intestinal metaplasia), and detects abnormal phenotypes that may represent early stages in carcinogenesis.

Antigens, Neoplasm↗
PubMed1988

No strict alignment is required between a transcriptional activator binding site and the "TATA box" of a yeast gene.

GAL4 is a transcriptional activator of the galactose metabolism genes in the yeast Saccharomyces cerevisiae. We show that GAL4 expressed in yeast activated transcription equally well when a single GAL4 binding site was placed at any of nine positions upstream of the GAL1 (galactokinase gene) "TATA box." We chose a sufficient number of positions for the binding site to ensure that, in several of these positions, GAL4 was on the opposite side of the DNA helix with respect to the TATA box. Smaller GAL4 derivatives were similar to wild-type GAL4 in that they also activated transcription in a manner independent of the side of the DNA helix they bound with respect to the TATA box. Unlike wild-type GAL4, however, these smaller GAL4 derivatives activated transcription better when we placed a binding site progressively closer to the TATA box over a distance of 34 base pairs.

Bacterial Proteins↗
PubMed1988

Purified ryanodine receptor from rabbit skeletal muscle is the calcium-release channel of sarcoplasmic reticulum.

The ryanodine receptor of rabbit skeletal muscle sarcoplasmic reticulum was purified as a single 450,000-dalton polypeptide from CHAPS-solubilized triads using immunoaffinity chromatography. The purified receptor had a [3H]ryanodine-binding capacity (Bmax) of 490 pmol/mg and a binding affinity (Kd) of 7.0 nM. Using planar bilayer recording techniques, we show that the purified receptor forms cationic channels selective for divalent ions. Ryanodine receptor channels were identical to the Ca-release channels described in native sarcoplasmic reticulum using the same techniques. In the present work, four criteria were used to establish this identity: (a) activation of channels by micromolar Ca and millimolar ATP and inhibition by micromolar ruthenium red, (b) a main channel conductance of 110 +/- 10 pS in 54 mM trans Ca, (c) a long-term open state of lower unitary conductance induced by ryanodine concentrations as low as 20 nM, and (d) a permeability ratio PCa/PTris approximately equal to 14. In addition, we show that the purified ryanodine receptor channel displays a saturable conductance in both monovalent and divalent cation solutions (gamma max for K and Ca = 1 nS and 172 pS, respectively). In the absence of Ca, channels had a broad selectivity for monovalent cations, but in the presence of Ca, they were selectively permeable to Ca against K by a permeability ratio PCa/PK approximately equal to 6. Receptor channels displayed several equivalent conductance levels, which suggest an oligomeric pore structure. We conclude that the 450,000-dalton polypeptide ryanodine receptor is the Ca-release channel of the sarcoplasmic reticulum and is the target site of ruthenium red and ryanodine.

Adenosine Triphosphate↗
PubMed1988

Virulence properties and protective efficacy of the capsular polymer of Haemophilus (Actinobacillus) pleuropneumoniae serotype 5.

The role of the capsule of Haemophilus (Actinobacillus) pleuropneumoniae serotype 5 in bacterial virulence, and the protective efficacy of antibody to serotype 5 capsule was investigated. Encapsulated H. pleuropneumoniae serotype 5 were resistant to killing by complement and antibody to capsule or somatic antigens, whereas a noncapsulated mutant was sensitive to killing by the alternative complement pathway alone. Antiserum to whole H. pleuropneumoniae serotype 5 bacteria or monospecific antiserum to capsule was capable of opsonizing bacteria of the homologous serotype for phagocytosis by swine polymorphonuclear leukocytes but was not opsonic for a heterologous serotype. An immunoglobulin M monoclonal antibody to the serotype 5 capsule was not opsonic for any serotype. Mice were protected against lethal, intranasal challenge with the homologous or heterologous serotype after immunization with live encapsulated or noncapsulated bacteria, but not after immunization with killed bacteria, lipopolysaccharide, or a capsule-protein conjugate vaccine. The protection induced by immunization with live bacteria was transferred to nonimmune, syngeneic mice by serum but not by spleen cells. Nonimmune pigs passively immunized with monospecific swine serum to capsule were protected from lethal infection but not from development of hemorrhagic lung lesions, whereas pigs passively immunized with swine antiserum to live bacteria did not develop severe respiratory lesions. Thus, the capsule of H. pleuropneumoniae serotype 5 was inhibitory to the bactericidal activity of serum and was antiphagocytic. Antibody to the capsule was opsonic but was not fully protective.

Animals↗
PubMed1988

Temporal lobe and hypothalamic-pituitary dysfunctions after radiotherapy for nasopharyngeal carcinoma: a distinct clinical syndrome.

Eleven patients with combined neurological and endocrine complications after external radiotherapy for nasopharyngeal carcinoma are described. Neurologically, memory disturbance, complex partial seizures and hypodense areas in one or both temporal lobes on CT were typical features. Endocrinologically, hypopituitarism was the prominent manifestation. This constellation of clinical features in a patient with previous radiotherapy to the nasopharynx characterises radiation injury to the inferomedial aspects of the temporal lobes and the hypothalamic-pituitary axis. While the parenchymal brain lesions may mimic metastases or glioma on CT, the associated endocrine disturbance would betray the correct diagnosis. The importance of recognising the hypopituitarism which may be clinically asymptomatic and which is amenable to therapy is emphasised, as is the need for a proper fractionation of the radiation dose to minimise the incidence of these disabling complications.

Adult↗
PubMed1988

Glomerulonephropathy of Laurence-Moon-Biedl syndrome.

A patient with Laurence-Moon-Biedl syndrome and nephrotic range proteinuria is presented. Radiological investigation of the urinary tract revealed clubbed calyces but no evidence of obstruction or vesicoureteric reflux. Renal biopsy revealed occasional sclerotic glomeruli, extensive foot-process fusion and segmental glomerular basement membrane abnormalities with negative immunofluorescence for immunoglobulins and complement. Nephrotic proteinuria responded to steroid therapy but mild proteinuria persisted. The findings were consistent with minimal change nephropathy superimposed on the glomerular lesions of Lawrence-Moon-Biedl syndrome.

Adult↗