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Biomedical subjects

Y L Sun

Publications and source records attributed to Y L Sun.

At least 55 records · Page 3Linked to original sources
PubMed1992

[The activity of tumor necrosis factor in schistosomiasis japonica].

The activity of tumor necrosis factor (TNF) in both the culture supernatant of peripheral blood mononuclear cells (PBMC) and the serum was examined in 20 patients of advanced schistosomiasis at 8th week after pyquiton treatment, and 6 rabbits infected with S. japonicum cercariae at 8th and 16th weeks post-infection and using L929 cell cytotoxic assay. The results showed that the capacity of PBMC to produce TNF in response to LPS from patients with late schistosomiasis was significantly lower than that from normal subjects (P less than 0.01), whereas the activity of TNF in serum was significantly elevated (P less than 0.01). The capacity of PBMC to produce TNF and the TNF activity in serum of infected rabbits showed sharp rise at 8th week post-infection (P less than 0.01), and remained high at 16th week, then returned to normal level 8 weeks after treatment. The persistent rise of TNF in the circulation indicate that TNF might take part in the formation of hepatic fibrosis.

Adult↗
PubMed1991

Distal cis-acting promoter sequences mediate glucocorticoid stimulation of cardiac atrial natriuretic factor gene transcription.

Although receptors for most steroid hormones are present in the heart, few cardiac-specific target genes have been identified and studied at the molecular level. Transcription of the atrial natriuretic factor (ANF) gene, which encodes the major secretory product of the heart, is induced by glucocorticoids. In both atrial and ventricular cardiac cells in primary cultures, ANF mRNA levels are increased 3-4-fold after dexamethasone treatment in a time- and dose-dependent manner. This response to glucocorticoids is completely abolished by the antagonist RU486. Interestingly, ventricular myocytes appear to be more sensitive to glucocorticoids than atrial myocytes. DNA-mediated gene transfer studies indicate that glucocorticoids affect ANF gene transcription via a glucocorticoid response element located in the distal 5'-flanking sequences of the rat ANF gene between -697 and -1,029 base pairs. In vitro DNase I footprinting experiments reveal the presence of two binding sites for purified glucocorticoid receptor within this region. Mobility shift assays and competition experiments show that binding of the glucocorticoid receptor to both ANF sites results in a DNA-protein complex similar in affinity and specificity to that of the well characterized mammary tumor virus glucocorticoid response element. Since glucocorticoid activation of the ANF promoter appears specific to cardiac cells, the interaction between the glucocorticoid receptor binding sites and cardiac-specific regulatory elements of this promoter could provide a model to study a mechanism of hormone-dependent signal transduction in the heart.

Animals↗
PubMed1990

Transcriptional interference between c-Jun and the glucocorticoid receptor: mutual inhibition of DNA binding due to direct protein-protein interaction.

Glucocorticoids are potent inhibitors of collagenase induction by phorbol esters and inflammatory mediators. The target for this negative effect is the AP-1 site within the collagenase promoter, which also mediates its induction. Negative regulation is due to repression of AP-1 activity by the glucocorticoid receptor (GCR). While the GCR is a potent inhibitor of AP-1 activity (Jun/Fos), both c-Jun and c-Fos are potent repressors of GCR activity. In vitro experiments using purified GCR and c-Jun proteins suggest that mutual repression is due to direct interaction between the two. Direct interaction between GCR and either c-Jun or c-Fos is demonstrated by cross-linking and coimmunoprecipitation. These findings reveal a cross talk between two major signal transduction systems used to control gene transcription in response to extracellular stimuli, and a novel mechanism for transcriptional repression.

Animals↗
PubMed1989

Glucocorticoid repression of pro-opiomelanocortin gene transcription.

Transcription of the pro-opiomelanocortin (POMC) gene is repressed by glucocorticoids in the anterior pituitary gland. We have defined an element within the POMC promoter which is responsible for this regulatory feedback. This element, the "negative glucocorticoid response element" (nGRE), was localized in the proximal region of the POMC promoter and it contains a binding site for the glucocorticoid receptor. Receptor binding to the nGRE was correlated to hormone-dependent repression by using promoter mutagenesis. The nGRE was also shown to contain a binding site for a nuclear protein of the COUP family of transcription factors. Since the binding sites for COUP and the glucocorticoid receptor overlap, glucocorticoid-dependent repression of POMC transcription may result from mutually exclusive binding of these two nuclear transcription factors.

Adrenal Glands↗
PubMed1989

Tissue-specific activity of the pro-opiomelanocortin (POMC) gene and repression by glucocorticoids.

The gene encoding pro-opiomelanocortin (POMC) is specifically expressed in two different cell types of the pituitary gland. We have defined the regulatory DNA sequences of the POMC gene that are responsible for this cell-specific expression. In addition, we have defined a regulatory element, located in the proximal region of the POMC promoter, that confers glucocorticoid repression in the anterior pituitary. Using DNA-mediated gene transfer into transgenic mice and tissue culture cells, the POMC regulatory sequences required for cell-specific expression and glucocorticoid repression were localized within a 543-bp fragment in the 5'-flanking region of the gene. Multiple regulatory elements that bind nuclear proteins are present within this region. In particular, a sequence that binds the glucocorticoid receptor and behaves as a "negative glucocorticoid response element" (nGRE) also binds nuclear proteins of the COUP (chicken ovalbumin upstream promoter) family of transcription factors. Thus, glucocorticoid repression of POMC transcription may result from the mutually exclusive binding of the glucocorticoid receptor and the COUP transcription factor to the POMC nGRE.

Animals↗
PubMed1987

High-resolution mapping of DNase I hypersensitive site in the chicken beta-tubulin gene transfected into monkey cells.

In this report, we describe a method for high-resolution mapping of a nuclease hypersensitive site (HS) at the promoter region of the chicken beta 2-tubulin gene transfected into monkey Cos-7 cells. Using the indirect end-labeling method of Wu, a tissue-specific nuclease HS was located initially approximately 100 base pairs upstream of the transcription start site. For high-resolution mapping of the HS in the transfected DNA, a DNA fragment of about 400 base pairs containing the promoter region of the beta 2 gene was subcloned into M13 phage. A single-stranded DNA probe with a defined restriction enzyme cleavage site at one end was prepared from the M13 phage DNA template. The single-stranded probe and the restriction enzyme-digested DNA, prepared from nuclease-digested nuclei from transfected cells, were sequentially annealed back to the template. After ligation between the probe and the transfected DNA, the HS was determined by DNA sequencing gel electrophoresis. This method permits determination of the 3' boundary of the HS with precision at the single-nucleotide level. We mapped a major HS at -107 nucleotides of the beta 2-tubulin gene, where a CACCC-like sequence is present. The application of this method in determining HS is discussed.

Animals↗
PubMed1986

Digestion of the chicken beta-globin gene chromatin with micrococcal nuclease reveals the presence of an altered nucleosomal array characterized by an atypical ladder of DNA fragments.

The structure of the chicken adult beta-globin gene chromatin in immature and mature erythrocyte nuclei has been analysed using micrococcal nuclease digestion. The resulting DNA fragments were blotted onto DBM-papers and probed with labelled DNA fragments spanning the adult beta-globin gene and its 5'- and 3'-flanking regions. The structure of the nucleosomes within and in the regions flanking the adult beta-globin gene appears to be altered in at least two ways in erythrocyte chromatin, when compared with either bulk or inactive ovalbumin gene chromatin. First, oligomeric DNA fragments containing the beta-globin gene are released faster than those of either bulk or ovalbumin gene chromatin. Second, although the difference in size of the liberated oligomeric DNA fragments is similar to the nucleosomal repeat length of bulk and ovalbumin gene chromatin, the individual oligomers are approximately 100 bp shorter than their bulk or ovalbumin gene counterparts, most noticeably when the nuclease digestion is performed at 37 degrees C. This results in an atypical ladder of approximately 300, 500, 700, 900 bp instead of the canonical chicken erythrocyte ladder which is an integral multiple of 207 bp. The same ladder was obtained from immature erythrocytes, in which the beta-globin gene is actively transcribed, and from mature erythrocytes, in which it is considered to be inactive with RNA polymerase molecules clustered in the 5' moiety of the gene. This indicates that the alteration of the nucleosomal structure is not due to transcription per se.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1982

A simple and efficient method for the separation and detection of small DNA fragments by electrophoresis in formamide containing agarose gels and Southern blotting to DBM-paper.

We show in this report that DNA fragments smaller than 300 bp are separated with high resolution by electrophoresis in concentrated (up to 7%) agarose gels containing 50% formamide. The separated DNA fragments can subsequently be quantitatively transferred to DBM-paper [Alwine, J.C. et al., Proc. Natl. Acad. Sci. USA (1977) 74, 5350-54] using the Southern technique [Southern, E.M., J. Mol. Biol. (1975) 98, 503-517], while preserving the sharpness of the original gel pattern. Since thin (0.2-0.4 mm) and thick (up to 5 mm) agarose slab gels can be easily handled in vertical or horizontal apparatus, this method should prove to be a very useful extention of the Southern technique, applicable to a variety of analytical and preparative purposes.

Base Composition↗
PubMed1982

Characteristics of invasiveness of human nasopharyngeal carcinoma cells in organ culture, as observed by scanning electron microscopy.

Cells of a human nasopharyngeal carcinoma (CNE) were cultured in contact with embryonal mouse heart fragments wrapped in a fibrous kidney capsule as biological permeable membrane. The culture was terminated at different intervals and processed for scanning electron microscopy. Carcinoma cells showed abundant microvilli and filopodia in contact with superficial cells of the heart fragments. Cancer cells appeared firmly attached to the surface of the tissue fragments. Subsequently, malignant cells extended pseudopodia into intercellular spaces of the supporting tissue particle, and beyond the third day of cultivation, cancer cells were also found in deeper parts of the organ. The cancer cells on the surface of the specimen had apparently lost the ability to invade. After a while, microvilli and filopodia decreased in number or adhered to each other. The plasma membrane exhibited signs of degeneration.

Animals↗