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Biomedical subjects

L J Sun

Publications and source records attributed to L J Sun.

8 recordsLinked to original sources
PubMed2006

Overexpression of PrPC and its antiapoptosis function in gastric cancer.

Cellular prion protein (PrP(C)), a glycosylphosphatidylinositol-anchored membrane protein, was found in our lab to be widely expressed in gastric cancer cell lines. In order to evaluate its biological significance in human gastric cancer, we investigated its expression in a large series of gastric tissue samples (n = 124) by immuno histochemical staining with the monoclonal antibody 3F4. Compared with normal tissues, gastric adenocarcinoma showed increased PrP(C) expression, correlated with the histopathological differentiation (according to the WHO and Lauren classifications) and tumor progression (as documented by pTNM staging). To better understand the underlying mechanism, we introduced the PrP(C) and two pairs of RNAi into the poorly differentiated gastric cancer cell line AGS and found that PrP(C) suppressed ROS and slowed down apoptosis in transfected cells. Further study proved that the apoptosis-related protein Bcl-2 was upregulated whereas p53 and Bax were downregulated in the PrP(C)-transfected cells. A reverse effect was observed in PrP(C) siRNA-transfected cells. These results strongly suggested that PrP(C) might play a role as an effective antiapoptotic protein through Bcl-2-dependent apoptotic pathways in gastric cancer cells. Further study into the mechanism of these relationships might enrich the knowledge of PrP, better our understanding of the nature of gastric carcinoma, and further develop possible strategies to block or reverse the development of gastric carcinoma.

Adult↗
PubMed2001

Chemical communication across the zinc tetrathiolate cluster in Escherichia coli Ada, a metalloactivated DNA repair protein.

The Escherichia coli Ada protein repairs methylphosphotriesters in DNA through direct, irreversible transfer to a cysteine residue on the protein, Cys 69. Methylation of Cys 69 increases the sequence-specific DNA-binding activity of Ada by 10(3)-fold, enabling the methylated protein to activate transcription of a methylation-resistance regulon. The thiolate sulfur atom of Cys 69 is coordinated to a tightly bound zinc ion in the Ada N-terminal domain, and this metal-ligand interaction plays a direct role in promoting the DNA repair chemistry. Ada is thus the founding member of a mechanistic class of proteins that employ metalloactivated thiolates as nucleophiles, other examples of which include protein prenyltransferases and cobalamin-independent methionine synthase. Here we have probed the role of the three other Cys residues in Ada that together with Cys 69 coordinate the zinc through mutation to the alternative ligand residues Asp and His. All of the mutant proteins folded properly and bound zinc, but none of them exhibited measurable levels of DNA repair activity. Significantly, the Cys-to-His mutant proteins retained nearly wild-type sequence-specific DNA-binding activity in the unmethylated state. These findings demonstrate that the three "spectator" Cys ligands communicate chemically with Cys 69 through the bound metal ion.

Bacterial Proteins↗
PubMed1998

Solution structure of the core NFATC1/DNA complex.

The nuclear factor of the activated T cell (NFAT) family of transcription factors regulates cytokine gene expression by binding to the promoter/enhancer regions of antigen-responsive genes, usually in cooperation with heterologous DNA-binding partners. Here we report the solution structure of the binary complex formed between the core DNA-binding domain of human NFATC1 and the ARRE2 DNA site from the interleukin-2 promoter. The structure reveals that DNA binding induces the folding of key structural elements that are required for both sequence-specific recognition and the establishment of cooperative protein-protein contacts. The orientation of the NFAT DNA-binding domain observed in the binary NFATC1-DBD*/ DNA complex is distinct from that seen in the ternary NFATC2/AP-1/DNA complex, suggesting that the domain reorients upon formation of a cooperative transcriptional complex.

Amino Acid Sequence↗
PubMed1997

Dual role of the nuclear factor of activated T cells insert region in DNA recognition and cooperative contacts to activator protein 1.

The transcription factors nuclear factor of activated T cells (NFAT) and activator protein 1 (AP-1) coordinately regulate cytokine gene expression in activated T-cells by binding to closely juxtaposed sites in cytokine promoters. The structural basis for cooperative binding of NFAT and AP-1 to these sites, and indeed for the cooperative binding of transcription factors to composite regulatory elements in general, is not well understood. Mutagenesis studies have identified a segment of AP-1, which lies at the junction of its DNA-binding and dimerization domains (basic region and leucine zipper, respectively), as being essential for protein-protein interactions with NFAT in the ternary NFAT/AP-1/DNA complex. In a model of the ternary complex, the segment of NFAT nearest AP-1 is the Rel insert region (RIR), a feature that is notable for its hypervariability in size and in sequence amongst members of the Rel transcription factor family. Here we have used mutational analysis to study the role of the NFAT RIR in binding to DNA and AP-1. Parallel yeast one-hybrid screening assays in combination with alanine-scanning mutagenesis led to the identification of four amino acid residues in the RIR of NFAT2 (also known as NFATC1 or NFATc) that are essential for cooperativity with AP-1 (Ile-544, Glu-545, Thr-551, and Ile-553), and three residues that are involved in interactions with DNA (Lys-538, Arg-540, and Asn-541). These results were confirmed and extended through in vitro binding assays. We thus conclude that the NFAT RIR plays an essential dual role in DNA recognition and cooperative binding to AP-1 family transcription factors.

Amino Acid Sequence↗
PubMed1996

A critical arginine residue mediates cooperativity in the contact interface between transcription factors NFAT and AP-1.

The heterologous transcription factors NFAT and AP-1 coordinately regulate cytokine gene expression through cooperative binding to precisely juxtaposed DNA recognition elements. The molecular origins of cooperativity in the binding of NFAT and AP-1 to DNA are poorly understood. Herein we have used yeast one-hybrid screening and alanine-scanning mutagenesis to identify residues in AP-1 that affect cooperative interactions with NFAT on DNA. Mutation of a single conserved Arg residue to Ala in the cJun spacer region (R285A) led to a virtually complete abolition of cooperative interactions with NFAT. The DNA-binding activity of AP-1 alone was unaffected by the cJun R285A mutation, thus indicating that this residue influences cooperative binding only. Ala-scanning mutations elsewhere in AP-1, including the cFos subunit, revealed no other strongly interacting single positions. We thus conclude that NFAT contacts AP-1 in the spacer region of the cJun subunit, making an especially important contact to R285, and that these interactions drive formation of the cooperative NFAT/AP-1/DNA complex. These results provide a general strategy for selectively ablating cooperativity between transcription factors without affecting their ability to act alone and yield insights into the structural basis for coordinate regulation of gene expression.

Alanine↗
PubMed1991

Intrapartum amnioinfusion for replacement of meconium-stained-amniotic-fluid to prevent meconium aspiration syndrome.

The presence of meconium-stained amniotic-fluid (MSAF) during labor in cephalic presentation is a potentially ominous sign of fetal distress and, a direct cause of meconium aspiration syndrome (MAS). The authors designed a new method of intrapartum amnioinfusion for replacement (IAR) of the MSAF with normal saline solution. A total of 177 parturients with MSAF were studied from July 1986 to January 1987. Seventy-three cases receiving IAR treatment were analysed and 104 cases treated routinely served as controls. The newborn infants receiving IAR treatment had a significantly lower incidence of neonatal asphyxia (P less than 0.001) and MAS (P less than 0.05). No neonatal death occurred in the treated group; whereas, three infants died in the controls. There was no significant difference in puerperal morbidity between these two groups. The results of this study suggest that IAR might be a hopeful and effective treatment for parturients with MSAF in reducing the incidence of MAS.

Amnion↗
PubMed1990

[A rapid FIA-spectrophotometric method with online extraction for the content uniformity test of atropine sulfate tablets].

A rapid spectrophotometric method based on FIA for the content uniformity test of atropine sulfate tablets has been developed. By means of the self-designed FIA system with an on-line extraction device, many difficulties resulting from extraction, such as slow analytical rate, environmental pollution, poor reproducibility, etc, were overcome, and the routine procedure of the official content uniformity test was tremendously simplified. Results obtained with the proposed method agree well with those obtained with the official test. Furthermore, the proposed method attained a sampling rate of 60 samples per hour, a recovery of 100.0%, a relative standard deviation of 0.7%, and a detection limit of 0.24 micrograms/ml. Uniform design proves effective to optimize complex FIA conditions, and FIA promises a new approach to test the content uniformity of pharmaceutical tablets.

Atropine↗