Biomedical subjects

J M Sun

Publications and source records attributed to J M Sun.

At least 37 records · Page 2Linked to original sources

PubMed1996

Developmental changes in transcription factors associated with the nuclear matrix of chicken erythrocytes.

The nuclear matrix has roles in organizing nuclear DNA and in controlling transcription. Transcription factors are associated with the nuclear matrix, with the spectra of transcription factors differing from one cell type to another. In this study we identified the transcription factors and enzymes functioning in the regulation of gene expression that were associated with nuclear matrix and nonmatrix nuclear fractions in erythrocytes isolated from chick embryos at different stages of development, anemic and normal adult birds. We found that the primitive erythroid nuclear matrix had the greatest histone deacetylase activity and highest levels of several transcription factors, including GATA-1, CACCC-binding proteins, and NF1. These transcription factors have key roles in erythroid-specific gene expression. The levels of these transcription factors were lower in the nonmatrix and matrix fractions isolated from definitive erythrocytes. For primitive and definitive erythrocytes, the level of CACCC-binding proteins in the nuclear matrix fraction was greater than that of Sp1. The relative levels of these transcription factors were reversed in the nonmatrix fraction. Casein kinase II was not found in erythroid nuclear matrices. The observed erythroid lineage specific alterations in erythroid nuclear matrix transcription factor composition and abundance may be involved in erythroid-specific gene expression.

Animals↗

PubMed1996

Analysis of human breast cancer nuclear proteins binding to the promoter elements of the c-myc gene.

The expression of the c-myc gene is essential for the proliferation of both hormone-dependent and -independent human breast cancer cells. The regulation of c-myc gene expression in MCF-7 (hormone-dependent, estrogen-receptor (ER)-positive) and MDA MB 231 (hormone-independent, ER-negative) human breast cancer cells differs, with the c-myc gene of MCF-7 but not MDA MB 231 cells being regulated at the transcriptional level by estrogen. We have shown previously that the DNAase I hypersensitive (DH) sites in the c-myc chromatin of hormone-dependent and -independent human breast cancer cells were similar, with the exception of DH site II2. DH site II2, which maps near the P0 promoter, was less sensitive in hormone-dependent than in hormone-independent cells. As DH sites generally indicate the presence of sequence-specific DNA-binding proteins, we undertook a study to identify the nuclear proteins isolated from MCF-7 and MDA MB 231 cells that bound to the P0 and P2 promoter regions of the c-myc gene in vitro. The studies presented here provide evidence that Sp1 and/or Sp1-like proteins bind to the P0 and P2 promoter regions of the c-myc gene of MCF-7 and MDA MB 231 cells. Furthermore, evidence is presented for the presence of several previously unidentified sequence-specific DNA-binding proteins binding to these promoters. The DNA-binding activities of these latter proteins differed in the nuclear extracts of the MCF-7 and MDA MB 231 human breast cancer cells.

Base Sequence↗

PubMed1996

In situ footprinting of chicken histone H5 gene in mature and immature erythrocytes reveals common factor-binding sites.

In vitro DNAase I footprinting and gel mobility shift assays have shown that the activities of several nuclear factors (GATA-1, Sp1) that bind to the promoter and downstream enhancer regions of the chicken histone H5 gene are reduced in mature erythrocytes relative to those in immature erythrocytes. In this study we investigated site occupancy in the promoter and downstream enhancer regions of the H5 gene in mature and immature erythrocytes. The ligation-mediated polymerase chain reaction was used to detect DNAase I footprints generated in situ. Most of the sites that bound to Sp1 and/or Sp1-like proteins and GATA-1 in the promoter and enhancer were occupied in situ in mature and immature erythrocytes. However, the level of protection at Sp1/Sp-1-like binding sites in the H5 enhancer region of mature erythroid cells was generally less than that observed for immature cells, suggesting that for any given mature cell not all of the Sp1/Sp1-like binding sites are occupied. Nevertheless, the results of this study suggest that the enhancer and promoter of the H5 gene in mature erythrocytes should be functional, agreeing with nuclear run-on studies showing transcriptional activity of the H5 gene in mature permeabilized cells.

Animals↗

PubMed1994

Histone acetyltransferase is associated with the nuclear matrix.

Only a small fraction of the adult chicken erythrocyte histones is involved in dynamic acetylation. We have reported previously that the rapidly acetylated and deacetylated H4 histones are primarily associated with the transcriptionally active DNA-enriched chromatin fragments that remain attached to the residual nuclear material following micrococcal nuclease digestion and chromatin solubilization. Furthermore, this nuclear fraction contained most of the histone deacetylase activity. In this study we show that the bulk of the nuclear histone acetyltransferase activity is located with the insoluble residual nuclear material. We demonstrate that in vitro the enzymes associated with the residual nuclear material catalyze reversible acetylation when the endogenous histones of the nuclear skeleton-bound chromatin fragments are used as substrate. Nuclear matrices isolated from adult chicken immature erythrocyte and trout liver nuclei had 60-76% of the nuclear histone acetyltransferase activity. Procedures that solubilized the internal nuclear matrix also resulted in the release of the enzyme from the nuclear matrix. Together, our observations suggest that histone acetyltransferase and deacetylase are associated with the internal nuclear matrix, and one of the functions of these enzymes may be to mediate a dynamic attachment between transcriptionally active chromatin and the nuclear matrix.

Acetates↗

PubMed1994

Nuclear factor 1 is a component of the nuclear matrix.

Chicken histone H5 is an H1-like linker histone that is expressed only in nucleated erythrocytes. The histone H5 promoter has binding sites for Sp1 (a high affinity site) and UPE-binding protein, while the 3' erythroid-specific enhancer has binding sites for Sp1 (one moderate and three weak affinity), GATA-1, and NF1. In this study we investigated whether trans-acting factors that bind to the chicken histone H5 promoter or enhancer are associated with adult chicken immature and mature erythrocyte nuclear matrices. We show that NF1, but not Sp1, GATA-1, or UPE-binding protein, is associated with the internal nuclear matrices of these erythroid cells. Further, we found that a subset of the NF1 family of proteins is bound to the mature erythrocyte nuclear matrix. These results suggest that in chicken erythrocytes NF1 may mediate an interaction between the histone H5 enhancer and the erythroid internal nuclear matrix. NF1 was also present in the internal nuclear matrices of chicken liver and trout liver. The observations of this study provide evidence that NF1 may have a role in a variety of cell types in targeting specific DNA sequences to the nuclear matrix.

Animals↗

PubMed1993

Repression of histone H5 gene expression in chicken mature erythrocytes is correlated with reduced DNA-binding activities of transcription factors Sp1 and GATA-1.

During the final stages of erythroid maturation, the expression of the chicken histone H5 gene ceases. The histone H5 promoter has binding sites for Sp1 and UPE-binding protein. The 3' histone H5 enhancer has binding sites for Sp1, GATA-1 and NF1. Here, we show that the DNA-binding activities of transcription factors Sp1 and GATA-1 is reduced 5- to 10-fold in mature cells, while the activities of UPE-binding protein and NF1 remain the same in mature and immature erythrocytes. The reduced activities of Sp1 and GATA-1 may contribute to the inactivation of the histone H5 gene in mature erythrocytes.

Animals↗

PubMed1992

Analysis of erythroid nuclear proteins binding to the promoter and enhancer elements of the chicken histone H5 gene.

The chicken erythroid proteins binding to the histone H5 5' promoter and 3' erythroid-specific enhancer regions were identified. In DNase I footprinting and gel mobility shift experiments with immature adult erythrocyte nuclear extracts, we have demonstrated the binding of proteins to the GC-box, a high affinity Sp1 binding site, and to the upstream promoter element. We have previously demonstrated that a multisubunit complex containing the transcription factor GATA-1 was associated with the enhancer. Here, we show that the enhancer region also has four Sp1 binding sites (one medium and three weak affinity, one of which may also bind the CACCC factor), a potential NF-E4 binding site, and a binding site for a NF1-like factor. The results of gel mobility-shift and competition experiments provide evidence that the Sp1 binding sites are associated with a high molecular mass (greater than 450 kDa), Sp1 containing protein complex. We propose that Sp1 multimers bound at the promoter and enhancer interact to mediate the juxta-positioning of the enhancer and promoter elements, bringing the GATA-1 multisubunit complex next to the initiation site. The GATA-1 complex may contribute to the protein-protein interactions between the enhancer and promoter.

Animals↗

PubMed1992

Nuclear matrix proteins bind very tightly to specific regions of the chicken histone H5 gene.

The nuclear matrix is operationally defined as the structure remaining after nuclease-digested nuclei are extracted with high concentrations of salt. The nuclear matrix is thought to have a role in organizing higher order chromatin into loop domains. We determined whether specific regions of the histone H5 gene were very tightly bound to protein of erythrocyte and liver nuclear matrices in vitro. We demonstrate that DNA fragments spanning sequences 5' to the promoter and the 3' enhancer region of the histone H5 gene, but not DNA fragments spanning the promoter, were very tightly bound to protein of nuclear matrices of erythrocytes and liver. The nuclear matrix consists of internal nuclear matrix and nuclear pore-lamina complex. Recently, we demonstrated that histone deacetylase could be used as a marker enzyme of the internal nuclear matrix. We demonstrate that nuclear pore-lamina complex preparations that were depleted of histone deacetylase activity, and thus of internal nuclear matrix, retained the protein that bound very tightly to the beta-globin and histone H5 enhancers. These results provide evidence that specific regions of the histone H5 gene are very tightly bound to nuclear pore-lamina complex protein.

Animals↗

PubMed1992

Expression of rainbow trout apolipoprotein A-I genes in liver and hepatocellular carcinoma.

Screening for genes overexpressed in trout aflatoxin B1-induced hepatocellular carcinomas resulted in the isolation of cDNA sequences of two apolipoprotein A-Is, apoA-I-1 and apoA-I-2. The levels of apoA-I-1 and -2 mRNAs of liver and tumor were quite different. ApoA-I-1 mRNA was the major species in liver, while apoA-I-1 and -2 mRNAs were present at similar levels in several tumors. This elevated level of apoA-I-2 mRNA was observed in seven different tumors, suggesting that the overexpression of apoA-I-2 was a general feature of aflatoxin B1-induced liver tumors. Hybridization to genomic DNA demonstrated that trout has two different apoA-I genes which is in contrast to other vertebrates which have one gene coding for apoA-I. Liver apoA-I-1 and -2 cDNA clones specified the same amino acid sequence as the tumor apoA-I-1 and -2 cDNA clones. Analysis of the cDNA-derived amino acid sequences showed that trout apoA-I-1 and -2, like human apoA-I, consist largely of multiple 22 amino acid repeats having the potential to generate an amphipathic alpha-helix. The similarity of the repeat pattern in trout and human apoA-Is suggests that all the internal repeats in these sequences arose before the fish-mammal split, some 400 million years ago.

Aflatoxin B1↗

PubMed1990

Replacement of histone H1 by H5 in vivo does not change the nucleosome repeat length of chromatin but increases its stability.

In vivo competition between histones H1 and H5 for chromatin has been studied in rat sarcoma XC10 cells transfected with a glucocorticoid responsive MMTV-H5 gene. Activation of H5 expression results in accumulation of H5 in the nuclei where it partially replaces H1. H5 displaces H1 from its primary binding sites presumably during chromatin replication and also binds with high affinity to secondary chromatin sites normally not occupied by H1. Replacement of H1 by H5 to levels similar to those of mature chicken erythrocytes does not alter the nucleosome repeat length of chromatin. This indicates that H5 is not solely responsible for the increase in nucleosome spacing of maturing erythroid cells. Exchange of H1 by H5 in vivo or in vitro results in a higher compaction/stability of chromatin.

Animals↗

PubMed1990

Clinical study of late-stage postthrombotic lower extremities.

Through clinical and venographic study of 353 diseased limbs, the authors advocate a new classification for the postthrombotic syndrome of the deep veins of the lower extremity. The postthrombotic lower extremities may be divided into two types: (1) lesions of the whole lower extremity, consisting of the completely obstructed, partially recanalized, and completely recanalized types; (2) local lesions, such as segmental obstruction of the iliac, iliofemoral, superficial femoral, femoropopliteal veins, and the tibioperoneal venous trunk and the venous plexus in calf muscles. Each type has its characteristics related to the duration of symptoms and clinical features, and their management is not the same at all. The authors suggest that clinically this new classification may be of great help in estimating the status of the diseased limb and in selecting proper method of treatment.

Female↗

PubMed1990

[Epidemiologic study on peripheral vascular diseases in Shanghai].

Epidemiologic investigation and study were made on peripheral vascular diseases in Shanghai area during 1988 and 1989. The total number of examined subjects was 30,712, including peasants and workers from heavy and light industries. The number of the subjects suffered from peripheral vascular diseases was 2,679, with an incidence of 8.72%. Among them, varicosity of the superficial veins in the lower extremities was found in 2,577, and other peripheral vascular diseases were found in 102. Risk factors for varicose veins include hard labour, body mass, standing, pregnancy and sitting. New concepts about the varicose veins were advanced by the authors.

Adolescent↗

PubMed1989

Histone H5 in the control of DNA synthesis and cell proliferation.

The linker histones (H1, H5, H1 degrees) are involved in the condensation of chromatin into the 30-nanometer fiber. This supranucleosome organization correlates with the resting state of chromatin, and it is therefore possible that the linker histones play an active role in the control of chromatin activity. The effect of H5 has been directly determined by expression of an inducible transfected H5 gene in rat sarcoma cells, which do not produce H5. Transfection resulted in the reversible inhibition of DNA replication and arrest of cells in G1, at which time H5 concentrations approached that of terminally differentiated avian erythrocytes. The arrest of proliferation was accompanied by specific changes in gene expression probably related to the cell cycle block. The selectivity of these effects suggest that H5 plays an active role in the control of DNA replication and cell proliferation.

Animals↗

PubMed1989

[Percutaneous transpopliteal venography].

The authors advocate percutaneous transpopliteal venography as a new method for evaluating the function of deep venous valves of the lower extremity. At the popliteal fossa, the popliteal vein was punctured and a catheter was inserted cephaladly for venographic study of the valves. By this method, not only the ilio-femoropopliteal vein was clearly visualized, also the competence of the valves in this venous segment may accurately be tested one by one, thus making up the shortcomings of the ascending and descending venography. It was found, through this venography, that even if the highest valve of the superficial femoral vein was competent distal valves in the femoral and popliteal veins may become incompetent resulting in primary valvular incompetence of the deep veins in the lower extremity.

Adult↗

PubMed1988