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T Quan

Publications and source records attributed to T Quan.

14 recordsLinked to original sources
PubMed2001

Ultraviolet irradiation blocks cellular responses to transforming growth factor-beta by down-regulating its type-II receptor and inducing Smad7.

Transforming growth factor-beta (TGF-beta) is a multi-functional cytokine that regulates cell growth and differentiation. Cellular responses to TGF-beta are mediated through its cell surface receptor complex, which activates transcription factors Smad2 and Smad3. Here we report that UV irradiation of mink lung epithelial cells causes near complete inhibition of TGF-beta-induced Smad2/3-mediated gene expression. UV irradiation inhibited TGF-beta-induced phosphorylation of Smad2 and subsequent nuclear translocation and DNA binding of Smad2/3. Specific cell surface binding of TGF-beta was substantially reduced after UV irradiation. This loss of TGF-beta binding resulted from UV-induced down-regulation of TGF-beta type II receptor (T beta RII) mRNA and protein. UV irradiation significantly inhibited T beta RII promoter reporter constructs, indicating that UV reduction of T beta RII expression involved transcriptional repression. In contrast to its effects on T beta RII, UV irradiation rapidly induced Smad7 mRNA and protein. Smad7 is known to antagonize activation of Smad2/3 and thereby block TGF-beta-dependent gene expression. UV irradiation stimulated Smad7 promoter reporter constructs, indicating that increased Smad7 expression resulted, at least in part, from increased transcription. Overexpression of Smad7 protein to the level induced by UV irradiation inhibited TGF-beta-induced gene expression 30%. Maintaining T beta RII levels by overexpression of T beta RII prevented UV inhibition of TGF-beta responsiveness. Taken together, these data indicate that UV irradiation blocks cellular responsiveness to TGF-beta through two mechanisms that impair TGF-beta receptor function. The primary mechanism is down-regulation of T beta RII, and the secondary mechanism is induction of Smad7.

Animals↗
PubMed2000

c-Jun-dependent inhibition of cutaneous procollagen transcription following ultraviolet irradiation is reversed by all-trans retinoic acid.

The aged appearance of skin following repeated exposure to solar ultraviolet (UV) irradiation stems largely from damage to cutaneous connective tissue, which is composed primarily of type I and type III collagens. We report here that a single exposure to UV irradiation causes significant loss of procollagen synthesis in human skin. Expression of type I and type III procollagens is substantially reduced within 24 hours after a single UV exposure, even at UV doses that cause only minimal skin reddening. Daily UV exposures over 4 days result in sustained reductions of both type I and type III procollagen protein levels for at least 24 hours after the final UV exposure. UV inhibition of type I procollagen synthesis is mediated in part by c-Jun, which is induced by UV irradiation and interferes with procollagen transcription. Pretreatment of human skin in vivo with all-trans retinoic acid inhibits UV induction of c-Jun and protects skin against loss of procollagen synthesis. We have reported previously that UV irradiation induces matrix-degrading metalloproteinases in human skin and that pretreatment of skin with all-trans retinoic acid inhibits this induction. UV irradiation, therefore, damages human skin connective tissue by simultaneously inhibiting procollagen synthesis and stimulating collagen breakdown. All-trans retinoic acid protects against both of these deleterious effects and may thereby retard premature skin aging.

Dose-Response Relationship, Radiation↗
PubMed1999

Cloning and characterization of the human protein kinase C-eta promoter.

Protein kinase C-eta (PKC-eta) is predominantly expressed in epithelial tissue, including lung, intestine, and skin. In skin, PKC-eta expression is limited to keratinocytes in the upper layers of the epidermis. To investigate regulation of cell type-specific expression of PKC-eta, we cloned the 5'-segment of the PKC-eta gene from a P1 genomic library. A 9.4-kilobase pair fragment encompassing the 5'-flanking region, first exon, and first intron, was localized on human chromosome 14 (14q22-23). Two major transcription initiation sites identified by reverse transcriptase polymerase chain reaction, primer extension, and S1 nuclease mapping, were located approximately 650 base pairs upstream from the translation start site. The human PKC-eta proximal promoter region lacks canonical TATA and CAAT boxes and GC-rich regions. A 1.6-kilobase pair 5'-flanking region displayed maximal promoter activity. This promoter was active in human keratinocytes but not human skin fibroblasts, in accord with endogenous PKC-eta gene expression. Stepwise 5' deletion analysis revealed the presence of adjacent regulatory regions containing silencer and enhancer elements located 1821-1702 base pairs and 1259-1189 base pairs upstream of the transcription initiation site. Deletion of the proximal PKC-eta promoter rendered the enhancer element inactive. Both the silencer and enhancer elements regulated heterologous promoters in keratinocytes but not fibroblasts. Electrophoretic mobility shift analysis demonstrated specific protein binding to Ets/heat shock factor and Ets/activator protein-1 consensus sequences in the enhancer and silencer regions, respectively. Mutations of the Ets/heat shock factor binding sites caused loss of functional enhancer activity. These data elucidate transcriptional regulation and tissue-specific expression of the PKC-eta gene.

Base Sequence↗
PubMed1996

Preferential DNA damage in the p53 gene by benzo[a]pyrene metabolites in cytochrome P4501A1-expressing xeroderma pigmentosum group A cells.

Gene-specific DNA damage levels were determined by quantitative polymerase chain reaction (QPCR) after treating cytochrome P450 (CYP) 1A1-expressing xeroderma pigmentosum fibroblasts with [3H]benzo[a]pyrene-trans-7,8-dihydrodiol ([3H]BPD) or [3H]benzo[a]pyrene-trans-7,8-dihydrodiol-9,10-epoxide ([3H]BPDE). DNA damage in the p53 gene (which is transcriptionally active) and the beta-globin gene (which is transcriptionally inactive) was measured in cells treated with [3H](+/-)-anti-BPDE, [3H](+/-)-BPD, and [3H](-)-BPD. DNA adduct formation in the genome overall was determined by measuring the incorporation of 3H into DNA. DNA damage in a p53 gene fragment (exons 8-9, 445 bp) was readily detected by QPCR. DNA damage was either not detected or much reduced in a similarly sized target in the beta-globin gene (exons 1-2, 551 bp). At equivalent levels of genomic DNA adducts, BPD treatment induced more damage in the p53 gene than BPDE treatment did. The lesion frequencies in the p53 and beta-globin genes in purified DNA treated with BPDE in vitro were the same, indicating that there was no sequence-specific basis for preferential lesion formation in the p53 gene in treated cells. DNA damage in both the p53 and beta-globin genes showed a dose response to [3H](-)-BPD. The frequency of BPD-induced lesions in the p53 gene was sixfold to sevenfold greater than in the beta-globin gene and 200- to 300-fold greater than in bulk DNA. The BPD-induced lesion frequency in the beta-globin gene was 30- to 50-fold greater than in bulk DNA. The data indicate that the distribution of BPDE-induced DNA lesions is dramatically nonrandom and suggest that the nonrandomness is governed by DNA sequence composition, chromatin structure, and dose rate.

Base Sequence↗
PubMed1995

Differential mutagenicity and cytotoxicity of (+/-)-benzo[a]pyrene-trans-7,8-dihydrodiol and (+/-)-anti-benzo[a]pyrene-trans-7,8-dihydrodiol-9,10-epoxide in genetically engineered human fibroblasts.

DNA repair-deficient (xeroderma pigmentosum group A (XPA)) and DNA repair-proficient (normal) human skin fibroblasts were genetically engineered by transformation with a controllable human cytochrome P450 (CYP)1A1 expression vector. Induction of CYP1A1 enabled these cells to metabolize (+/-)-benzo[a]pyrene-trans-7,8-dihydrodiol (BPD) into a potent cytotoxicant and mutagen. The XPA cells were more susceptible than the normal cells to the cytotoxic effects of both CYP1A1-metabolized BPD and exogenously supplied (+/-)-anti-benzo[a]pyrene-trans-7,8-dihydrodiol-9,10- epoxide (BPDE). Furthermore, the differential cytotoxicity between XPA and normal cells induced by CYP1A1-metabolized BPD was 8.4-fold greater than that induced by exogenously supplied BPDE. The two cell lines had similar CYP1A1 activities, suggesting that a difference in metabolic potential was not the cause of the differential response to BPD. At comparable cytotoxicity in both XPA and normal cells, BPD treatment induced more mutants and more DNA adducts than BPDE treatment did. At similar levels of DNA adducts in XPA cells, the levels of cytotoxicity induced by CYP1A1-metabolized BPD and exogenously supplied BPDE were similar, but CYP1A1-metabolized BPD induced a threefold higher hypoxanthine phosphoribosyltransferase mutation frequency. In contrast, at similar levels of adducts in CYP1A1-expressing normal cells, BPD induced less cytotoxicity and a lower mutation frequency. DNA adducts were identified and quantified by 32P-postlabeling analyses. The principal adduct formed by both CYP1A1-metabolized BPD and exogenously supplied BPDE was 10-beta-(deoxyguanosin-N2-yl)-7 beta,8 alpha,9 alpha-trihydroxy-7,8,9,10- tetrahydrobenzo[a]pyrene, indicating that the differential effects of BPD- and BPDE-induced adducts were not due to a difference in the types of adducts formed. The results of these studies suggest that CYP1A1-metabolized BPD may form adducts preferentially in transcriptionally active genes or that the intracellular concentration of BPDE may influence the balance between cytotoxicity and mutagenicity (or both).

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗
PubMed1994

Cytotoxicity and genotoxicity of (+/-)-benzo[a]pyrene-trans-7,8-dihydrodiol in CYP1A1-expressing human fibroblasts quantitatively correlate with CYP1A1 expression level.

Cytochrome P450 1A1 (CYP1A1) activity is associated with increased susceptibility to lung cancer induced by polycyclic aromatic hydrocarbons such as benzo[a]pyrene (BP). In non-hepatic human tissues, CYP1A1 is the principal enzyme responsible for the metabolic activation of the proximate BP mutagenic metabolite, (-)-benzo[a]pyrene-trans-7,8-dihydrodiol, to (+)-anti-benzo[a]pyrene-trans-7,8-dihydrodiol-9,10-epoxide, the ultimate BP mutagen. We have genetically engineered both DNA repair-deficient (xeroderma pigmentosum group A) and DNA repair-proficient human skin fibroblasts to express human CYP1A1 under control of the inducible mouse metallothionein-I promoter. CYP1A1 activity was induced by CdSO4 and monitored by following the O-deethylation of ethoxy fluorescein ethyl ester or of 7-ethoxyresorufin. Induced CYP1A1 activities were similar in both cell lines and were dependent on CdSO4 concentration and induction time. Maximal CYP1A1 activities were obtained in 4-6 h with 5-7 microM CdSO4. BPD-induced cytotoxicity and hypoxanthine phosphoribosyl transferase mutagenicity were both quantitatively correlated with the level of CYP1A1 activity and were greater in DNA repair-deficient cells than in DNA repair-proficient cells. The results suggest that modestly induced CYP1A1 activity is a risk factor in polycyclic aromatic hydrocarbon-induced carcinogenesis.

Cadmium↗
PubMed1993

Comparison of the Drosophila melanogaster, human and murine Sm B cDNAs: evolutionary conservation.

To analyze the evolutionary stability of the Sm B polypeptides, the cDNA nucleotide (nt) sequence was derived for the Drosophila melanogaster Sm B polypeptide and compared to the cDNAs encoding human and murine Sm B. The three cDNAs were transcribed and translated in reticulocyte lysates followed by analysis of the synthesized proteins by SDS-PAGE. D. melanogaster B migrated at approximately 25 kDa, in comparison to 28 kDa for the murine and human B proteins, although all three proteins were immunoprecipitated by human anti-Sm autoantibodies and by the Y12 anti-Sm murine monoclonal antibody (Y12 mAb). Immunoblots and immunoprecipitations of [35S]methionine-labeled D. melanogaster S2/M3 cells confirmed the smaller size of the D. melanogaster protein, and revealed that B' was absent in this cell line, as in murine cells. In comparison to the 231 amino acids (aa) of human and murine B, the deduced sequence for the D. melanogaster clone was 199 aa (predicted M(r) of 24,598) with two 5-aa deletions and a 19-aa truncation at the 3' end, compared to the other two clones. D. melanogaster protein B shared 65% aa sequence identity with the human and mouse clones, and 80% similarity when conservative aa substitutions were noted. The C-terminal portion of the D. melanogaster protein was the most evolutionarily variable in comparison to the deduced aa sequences for the other two proteins; however, autoantigenic epitopes bound by human anti-Sm antibodies and the Y12 mAb in this region of the protein were conserved across species lines.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1993

Expression of human cytochrome P450 1A1 in DNA repair deficient and proficient human fibroblasts stably transformed with an inducible expression vector.

Cytochromes P450 catalyze the bioactivation of many carcinogens. In particular, cytochrome P450 1A1 (CYP1A1) catalyzes the conversion of polycyclic aromatic hydrocarbons, such as benzo[a]pyrene, into potent mutagenic agents. Human skin fibroblasts, both DNA repair deficient (xeroderma pigmentosum group A: XPA) and DNA repair normal have been co-transformed with a chimeric gene construct containing human CYP1A1 coding sequences controlled by the cadmium (Cd) ion inducible mouse metallothionein-I promoter and pRSV-NEO, a dominant selectable marker for G418 resistance. Individual G418 resistant colonies were cloned and analyzed for Cd inducible CYP1A1 activity. Six clones of DNA repair deficient cells and five clones of DNA repair proficient cells have been isolated which express Cd inducible CYP1A1. Benzo[a]pyrene-trans-7,8-diol (BPD) is cytotoxic in Cd induced CYP1A1 expressing cells. The cytotoxicity can be inhibited by 10 microM alpha-napthoflavone. Differential cytotoxicity between the DNA repair deficient and proficient CYP1A1 expressing transformants is observed. BPD is cytotoxic to Cd induced CYP1A1 expressing XPA cells at > 10-fold lower doses than it is to Cd induced CYP1A1 expressing DNA repair normal cells. These data indicate that BPD is metabolized to a DNA damaging agent by induced CYP1A1. In contrast, benzo[a]pyrene-trans-7,8-diol-9,10-epoxide added to the media is only slightly more cytotoxic to DNA repair deficient than to proficient cells regardless of CYP1A1 expression. These studies demonstrate the usefulness of the CYP1A1 transformed fibroblasts in examining the cytotoxic effects of benzo[a]pyrene metabolites and suggest the future usefulness in examining the toxic effects of polycyclic aromatic hydrocarbons and other xenobiotics bioactivated by CYP1A1.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗
PubMed1992

A surface protease and the invasive character of plague.

A 9.5-kilobase plasmid of Yersinia pestis, the causative agent of plague, is required for high virulence when mice are inoculated with the bacterium by subcutaneous injection. Inactivation of the plasmid gene pla, which encodes a surface protease, increased the median lethal dose of the bacteria for mice by a millionfold. Moreover, cloned pla was sufficient to restore segregants lacking the entire pla-bearing plasmid to full virulence. Both pla+ strains injected subcutaneously and pla- mutants injected intravenously reached high titers in liver and spleen of infected mice, whereas pla- mutants injected subcutaneously failed to do so even though they establish a sustained local infection at the injection site. More inflammatory cells accumulated in lesions caused by the pla- mutants than in lesions produced by the pla+ parent. The Pla protease was shown to be a plasminogen activator with unusual kinetic properties. It can also cleave complement C3 at a specific site.

Amino Acid Sequence↗
PubMed1985

An outbreak of Yersinia enterocolitica infections caused by contaminated tofu (soybean curd).

The authors investigated 50 Yersinia enterocolitica infections during an outbreak of illness due to contaminated tofu (soybean curd) in Washington State between December 15, 1981 and February 22, 1982. The most common clinical syndrome (36 patients) was gastrointestinal infection for which two patients underwent appendectomies and one a partial colectomy. Of the remaining 14 patients, six had extraintestinal infections, two had fever alone, and six were asymptomatic. The patients with enteric infections were younger (median age three years) than those with extraintestinal infections (median age 28 years). In a case-control study of enteritis patients, illness was associated with ingestion of one brand of tofu (p less than 0.01). Ninety-two per cent of patients with gastrointestinal infections and 33% with extraintestinal infections recalled having eaten the implicated product. Y. enterocolitica serotype O:8, the most common serotype isolated from patients, was also isolated from tofu and the plant's untreated spring water. There was little clinical or laboratory evidence of secondary spread to family members who did not eat tofu. The outbreak demonstrates the transmission of Y. enterocolitica from nature to man and the potential of "natural" foods as vehicles for environmental pathogens.

Adolescent↗
PubMed1976

Bubonic plague from direct exposure to a naturally infected wild coyote.

An 11-year-old boy developed axillary bubonic plague and plague meningitis 3 days after skinning a dead coyote near Albuquerque, New Mexico. The coyoto carcass was recovered 10 days later, and Yersinia pestis was isolated from spleen and marrow of the animal. This is the first report of human plague from exposure to a coyote. A review of experimental and epidemiologic studies suggests that severe plague infection in members of the family Canidae is unusual, and that the risk of acquiring plague from direct contact with coyote tissues is minimal. Nevertheless, certain precautions are outlined for persons working with wild coyotes.

Ampicillin↗