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N Chen

Publications and source records attributed to N Chen.

At least 37 records · Page 2Linked to original sources
PubMed2002

[Difficult diagnosis for a lingual ulceration. Wegener granulamotosis].

Making the correct diagnosis for a lingual ulceration can be difficult. We present the case of a 55-year-old man, alcoholic and smoker who presented with a single lingual ulceration. The initial diagnosis suggested a cell-squamed carcinoma but histological examination revealed a Wegener Granulomatosis. Wegener Granulomatosis in the oral cavity is found in 6-13% of cases but rarely primary sign of the disease. The authors review differential diagnosis that should be taken into consideration when presented with similar lesion.

Alcoholism↗
PubMed2001

Cannabinoid-receptor-independent cell signalling by N-acylethanolamines.

Anandamide and other polyunsaturated N-acylethanolamines (NAEs) exert biological activity by binding to cannabinoid receptors. These receptors are linked to G(i/o) proteins and their activation leads to extracellular-signal-regulated protein kinase (ERK) and c-Jun N-terminal kinase (JNK) mitogen-activated protein kinase (MAP kinase) activation, inhibition of cAMP-dependent signalling and complex changes in the expression of various genes. Saturated and monounsaturated NAEs cannot bind to cannabinoid receptors and may thus mediate cell signalling through other targets. Here we report that both saturated/monounsaturated NAEs and anandamide (20:4(n-6) NAE) stimulate cannabinoid-receptor-independent ERK phosphorylation and activator protein-1 (AP-1)-dependent transcriptional activity in mouse epidermal JB6 cells. Using a clone of JB6 P(+) cells with an AP-1 collagen-luciferase reporter construct, we found that 16:0, 18:1(n-9), 18:1(n-7), 18:2(n-6) and 20:4(n-6) NAEs stimulated AP-1-dependent transcriptional activity up to 2-fold, with maximal stimulation at approx. 10-15 microM. Higher NAE concentrations had toxic effects mediated by alterations in mitochondrial energy metabolism. The AP-1 stimulation appeared to be mediated by ERK but not JNK or p38 signalling pathways, because all NAEs stimulated ERK1/ERK2 phosphorylation without having any effect on JNK or p38 kinases. Also, overexpression of dominant negative ERK1/ERK2 kinases completely abolished NAE-induced AP-1 activation. In contrast with 18:1(n-9) NAE and anandamide, the cannabinoid receptor agonist WIN 55,212-2 did not stimulate AP-1 activity and inhibited ERK phosphorylation. The NAE-mediated effects were not attenuated by pertussis toxin and appeared to be NAE-specific, as a close structural analogue, oleyl alcohol, failed to induce ERK phosphorylation. The data support our hypothesis that the major saturated and monounsaturated NAEs are signalling molecules acting through intracellular targets without participation of cannabinoid receptors.

Analgesics↗
PubMed2001

Intrachromosomal genomic instability in human sporadic colorectal cancer measured by genome-wide allelotyping and inter-(simple sequence repeat) PCR.

We have used genome-wide allelotyping with 348 polymorphic autosomal markers spaced, on average, 10 cM apart to quantitate the extent of intrachromosomal instability in 59 human sporadic colorectal carcinomas. We have compared instability measured by this method with that measured by inter-(simple sequence repeat) PCR and microsatellite instability assays. Instability quantitated by fractional allelic loss rates was found to be independent of that detected by microsatellite instability analyses but was weakly associated with that measured by inter-(simple sequence repeat) PCR. A set of seven loci were identified that were most strongly associated with elevated rates of fractional allelic loss and/or inter-(simple sequence repeat) PCR instability; these seven loci were on chromosomes 3, 8, 11, 13, 14, 18, and 20. A lesser association was seen with two loci flanking p53 on chromosome 17. Coordinate loss patterns for these loci suggest that at least two separate sets of cooperating loci exist for intrachromosomal genomic instability in human colorectal cancer.

Alleles↗
PubMed2001

[The presence and significance of hepatitis B virus DNA and RNA in kidney].

OBJECTIVE: To study the presence and pathogenesis of hepatitis B virus (HBV) DNA and RNA in renal tissues. METHODS: The presence and distribution of HBV DNA and RNA were investigated in renal biopsy tissues of 27 patients with HBV associated glomerulonephritis by in situ hybridization assay to explore the pathogenesis of HBV in renal tissue. RESULTS: HBV DNA and RNA, the same as HBV antigens, were present in renal tissues and located in the nuclei and cytoplasm of renal tubular epithelial cells, glomerular mesangium and capillary loops. HBV DNA and RNA were detected in tubular epithelia with the positive rates of 81.5%, 63.0% respectively, which were significantly higher than those in glomeruli (48.1%, 25.9% respectively) (P < 0.05). CONCLUSION: That HBV exists and replicates too in renal tissues, predominantly in tubular epithelia. The HBV antigens expressed in situ, as well as the antigens from circulation, and lead to renal lesions through immune complex formation or cell immune involvement. Besides glomerular lesions, tubulointerstitial lesions might also determine the progression and prognosis of HBV associated glomerulonephritis.

Adolescent↗
PubMed2001

Leukotrienes play protective roles early during experimental VSV encephalitis.

Leukotrienes (LT) are potent lipid mediators of inflammation. 5-Lipoxygenase (5-LO) is the key enzyme in the conversion of arachidonic acid to LT. There are four LT: LTB(4), LTC(4), LTD(4) and LTE(4). LT have been extensively studied in airway inflammation but little is known about their roles in viral infection in the CNS. LTB(4) is a chemoattractant for neutrophils. In this work, we studied the roles of LT in acute vesicular stomatitis virus (VSV) encephalitis. Two methods were used to disrupt 5-LO activity: mice were treated with Zileuton, an enzyme antagonist, or 5-LO genetic knockout mice were used. We found that inhibition or deletion of 5-LO resulted in: (a) impaired process of neutrophil infiltration into the CNS early during viral infection; (b) fewer neurons expressed nitric oxide synthase-1 (NOS-1); (c) higher viral titers 1 day after viral infection; and (d) increased disruption of blood brain barrier (BBB). Our studies suggest that LT are important innate immune players during VSV pathogenesis and are beneficial to the host in early control of viral replication in the CNS.

Animals↗
PubMed2001

Pattern changes of mucin gene expression with pneumococcal otitis media.

OBJECTIVE: mucins, known to be important components of the mucociliary transport system in the middle ear and Eustachian tube, are subject to changes under inflammatory conditions. Which mucin genes are up-regulated or activated during an inflammatory reaction of the middle ear and Eustachian tube, however, is poorly understood. The purpose of this study was to characterize mucin gene expression in middle ears and Eustachian tubes with pneumococcal ear infection. METHODS: sixteen rats received intrabullar inoculation of Streptococcus pneumoniae type 6A at 2.5x10(6) colony forming units (CFU). Four animals were sacrificed on days 1, 3, 7, and 14, respectively. The profile of mucin gene expression in the middle ear and Eustachian tube was examined by reverse transcription polymerase chain reaction (RT-PCR) at the above time points. Sixteen rats that received intrabullar inoculation of phosphate-buffered saline (PBS) served as controls. RESULTS: the Muc2 mucin gene was expressed in middle ear mucosa of the control rats. Following pneumococcal inoculation, Muc1-Muc5 mucin genes were expressed in the middle ear mucosa in a time-dependent manner. In the Eustachian tube, the Muc2, Muc4 and Muc5 mucin genes were expressed in both control and pneumococcal inoculation groups. CONCLUSION: Muc1, Muc3, Muc4, and Muc5 mucin genes were activated in the middle ear mucosa by pneumococci, which may contribute to hyper-production of mucin in acute pneumococcal otitis media.

Animals↗
PubMed2001

Chemopreventive property of a soybean peptide (lunasin) that binds to deacetylated histones and inhibits acetylation.

Lunasin is a unique 43-amino acid soybean peptide that contains at its carboxyl end: (a) nine Asp (D) residues; (b) an Arg-Gly-Asp (RGD) cell adhesion motif; and (c) a predicted helix with structural homology to a conserved region of chromatin-binding proteins. We demonstrated previously that transfection of mammalian cells with the lunasin gene arrests mitosis, leading to cell death. Here we show that exogenous application of the lunasin peptide inhibits chemical carcinogen-induced transformation of murine fibroblast cells to cancerous foci. To elucidate its mechanism of action we show that lunasin: (a) internalizes in the cell through the RGD cell adhesion motif; (b) colocalizes with hypoacetylated chromatin; (c) binds preferentially to deacetylated histone H4 in vitro; and (d) inhibits histone H3 and H4 acetylation in vivo in the presence of a histone deacetylase inhibitor. These results suggest a mechanism whereby lunasin selectively induces apoptosis, mostly in cells undergoing transformation, by preventing histone acetylation. In support of this, lunasin selectively induces apoptosis in E1A-transfected cells but not in nontransformed cells. Finally, in the SENCAR mouse skin cancer model, dermal application of lunasin (250 microg/week) reduces skin tumor incidence by approximately 70%, decreases tumor yield/mouse, and delays the appearance of tumors by 2 weeks relative to the positive control. These results point to the role of lunasin as a new chemopreventive agent that functions possibly via a chromatin modification mechanism.

Acetylation↗
PubMed2001

Transactivation of the epidermal growth factor receptor is involved in 12-O-tetradecanoylphorbol-13-acetate-induced signal transduction.

The mechanism of 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced tumor promotion is still not well understood even though it is thought to be related to the protein kinase C/mitogen-activated protein kinase/AP-1 pathway. Recently, TPA was also found to induce epidermal growth factor receptor (EGFR) activity. Here, we investigated whether the EGFR is a necessary component for TPA-induced signal transduction associated with tumor promotion. We demonstrated that potent inhibitors of the EGFR, PD153035 and AG1478, blocked TPA-induced phosphorylation of extracellular signal-regulated kinases (ERKs), AP-1 activity, and cell transformation. Egfr gene deficiency blocked TPA-induced ERK activity and AP-1 binding activity. The blocking of the ectodomain of the EGFR by a monoclonal antibody depressed TPA-induced ERK activity and AP-1 DNA binding activity. The use of a neutralizing antibody for heparin-binding EGF, one of the ligands of EGFR, blocked TPA-induced phosphorylation of ERKs. BB-94, a potent inhibitor of matrix metalloproteinases, which are activators of ectodomain shedding of EGFR ligands, also blocked TPA-induced ERK activity, AP-1 DNA binding, and cell transformation but had no effect on EGF-induced signal transduction. Anti-EGFR, anti-heparin-binding EGF, and BB-94 each blocked TPA-induced EGFR phosphorylation, but only anti-EGFR could block EGF-induced EGFR phosphorylation. Based on these results, we conclude that the EGFR is required for mediating TPA-induced signal transduction. EGFR transactivation induced by TPA is a mechanism by which the EGFR mediates TPA-induced tumor promotion-related signal transduction.

Animals↗
PubMed2001

Synthesis and structure-activity relationships of trisubstituted phenyl urea derivatives as neuropeptide Y5 receptor antagonists.

1-((1R,2R)-2-Hydroxy-1-methyl-2-phenylethyl)-1-methyl-3-(4-phenoxyphenyl)urea (1) was identified as a hit from the screening of the neuropeptide Y5 (NPY5) receptor. This lead was optimized for in vitro potency by changing the stereochemistry, the phenylethyl segment, the urea portion, and the 4-phenoxyphenyl group on the molecule. Over 40 analogues of 1 were prepared to study the structure-activity relationship for this series. The most potent compounds in this class have IC(50)s less than 0.1 nM at the NPY5 receptor (e.g., 40f, 44a, and 47). To determine the functional activity for this series of compounds, selected analogues were tested in a cellular assay measuring forskolin-induced cyclic AMP accumulation in 293 cells transfected with the human NPY5 receptor. All urea analogues tested in the functional assay acted as antagonists (e.g., 1, 32, 40a, and 44e).

Cell Line↗
PubMed2001

Suppression of skin tumorigenesis in c-Jun NH(2)-terminal kinase-2-deficient mice.

Previous studies have shown that c-Jun NH(2)-terminal kinase (JNK) belongs to the mitogen-activated protein kinase (MAPK) family of signal transduction components that are rapidly initiated and activated by many extracellular stimuli. However, the potential role of JNK in mediating tumor promotion and carcinogenesis is unclear. We show here that in JNK2-deficient (Jnk2(-/-)) mice, the multiplicity of papillomas induced by 12-O-tetradecanoylphorbol-13-acetate (TPA) was lower than that in wild-type mice. Papillomas on wild-type mice grew rapidly and were well vascularized compared with Jnk2(-/-) mice. After the 12th week of TPA treatment, the mean number of tumors per mouse was 4.13-4.86 in wild-type mice but only 1.13-2.5 in Jnk2(-/-) mice. TPA induced phosphorylation of extracellular signal-regulated kinases and activator protein-1 DNA binding activity in wild-type mice, but the phosphorylation of extracellular signal-regulated kinases and activator protein-1 DNA binding were inhibited in Jnk2(-/-) mice. These data suggest that JNK2 is critical in the tumor promotion process.

Animals↗
PubMed2001

Proteinase inhibitors I and II from potatoes block UVB-induced AP-1 activity by regulating the AP-1 protein compositional patterns in JB6 cells.

Proteinase inhibitor I (Inh I) and proteinase inhibitor II (Inh II) from potato tubers are effective proteinase inhibitors of chymotrypsin and trypsin. Inh I and Inh II were shown to suppress irradiation-induced transformation in mouse embryo fibroblasts suggesting that they possess anticarcinogenic characteristics. We have previously demonstrated that Inh I and Inh II could effectively block UV irradiation-induced activation of transcription activator protein 1 (AP-1) in mouse JB6 epidermal cells, which mechanistically may explain their anticarcinogenic actions. In the present study, we investigated the effects of Inh I and Inh II on the expression and composition pattern of the AP-1 complex following stimulation by UV B (UVB) irradiation in the JB6 model. We found that Inh I and Inh II specifically inhibited UVB-induced AP-1, but not NFkappaB, activity in JB6 cells. Both Inh I and Inh II up-regulated AP-1 constituent proteins, JunD and Fra-2, and suppressed c-Jun and c-Fos expression and composition in bound AP-1 in response to UVB stimulation. This regulation of the AP-1 protein compositional pattern in response to Inh I or Inh II may be critical for the inhibition of UVB-induced AP-1 activity by these agents found in potatoes.

Base Sequence↗
PubMed2001

CYR61 stimulates human skin fibroblast migration through Integrin alpha vbeta 5 and enhances mitogenesis through integrin alpha vbeta 3, independent of its carboxyl-terminal domain.

CYR61, an angiogenic factor and a member of the CCN protein family, is an extracellular matrix-associated, heparin-binding protein that mediates cell adhesion, promotes cell migration, and enhances growth factor-stimulated cell proliferation. CYR61 induces angiogenesis and promotes tumor growth in vivo and is expressed in dermal fibroblasts during cutaneous wound healing. It has been demonstrated recently that adhesion of primary skin fibroblasts to CYR61 is mediated through integrin alpha(6)beta(1) and cell surface heparan sulfate proteoglycans, resulting in adhesive signaling and up-regulation of matrix metalloproteinases 1 and 3. CYR61 is composed of four discrete structural domains that bear sequence similarities to the insulin-like growth factor-binding proteins, von Willebrand factor type C repeat, thrombospondin type 1 repeat, and a carboxyl-terminal (CT) domain that resembles cysteine knots found in some growth factors. In this study, we show that a CYR61 mutant (CYR61DeltaCT) that has the CT domain deleted is unable to support adhesion of primary human skin fibroblasts but is still able to stimulate chemotaxis and enhance basic fibroblast growth factor-induced mitogenesis similar to wild type. In addition, fibroblast migration to CYR61 is mediated through integrin alpha(v)beta(5) but not integrins alpha(6)beta(1) or alpha(v)beta(3). Furthermore, we show that CYR61 binds directly to purified integrin alpha(v)beta(5) in vitro. By contrast, CYR61 enhancement of basic fibroblast growth factor-induced DNA synthesis is mediated through integrin alpha(v)beta(3), a known receptor for CYR61 that mediates CYR61-dependent cell adhesion and chemotaxis in vascular endothelial cells. Thus, CYR61 promotes primary human fibroblast adhesion, migration, and mitogenesis through integrins alpha(6)beta(1), alpha(v)beta(5), and alpha(v)beta(3), respectively. Together, these findings establish CYR61 as a novel ligand for integrin alpha(v)beta(5) and show that CYR61 interacts with distinct integrins to mediate disparate activities in a cell type-specific manner.

Animals↗
PubMed2001

Signal transduction pathways involved in phosphorylation and activation of p70S6K following exposure to UVA irradiation.

Ultraviolet light A (UVA) plays an important role in the etiology of human skin cancer, and UVA-induced signal transduction has a critical role in UVA-induced skin carcinogenesis. The upstream signaling pathways leading to p70(S6K) phosphorylation and activation are not well understood. Here, we observed that UVA induces phosphorylation and activation of p70(S6K). Further, UVA-stimulated p70(S6K) activity and phosphorylation at Thr(389) were blocked by wortmannin, rapamycin, PD98059, SB202190, and dominant negative mutants of phosphatidylinositol (PI) 3-kinase p85 subunit (DNM-Deltap85), ERK2 (DNM-ERK2), p38 kinase (DNM-p38), and JNK1 (DNM-JNK1) and were absent in Jnk1-/- or Jnk2-/- knockout cells. The p70(S6K) phosphorylation at Ser(411) and Thr(421)/Ser(424) was inhibited by rapamycin, PD98059, or DNM-ERK2 but not by wortmannin, SB202190, DNM-Deltap85, or DNM-p38. However, Ser(411), but not Thr(421)/Ser(424) phosphorylation, was suppressed in DNM-JNK1 and abrogated in Jnk1-/- or Jnk2-/- cells. In vitro assays indicated that Ser(411) on immunoprecipitated p70(S6K) proteins is phosphorylated by active JNKs and ERKs, but not p38 kinase, and Thr(421)/Ser(424) is phosphorylated by ERK1, but not ERK2, JNKs, or p38 kinase. Moreover, p70(S6K) co-immunoprecipitated with PI 3-kinase and possibly PDK1. The complex possibly possessed a partial basal level of phosphorylation, but not at MAPK sites, which was available for its activation by MAPKs in vitro. Thus, these results suggest that activation of MAPKs, like PI 3-kinase/mTOR, may be involved in UVA-induced phosphorylation and activation of p70(S6K).

Androstadienes↗
PubMed2001

Mutations in the transcriptional activator EYA4 cause late-onset deafness at the DFNA10 locus.

We identified Eyes absent 4 (EYA4), a member of the vertebrate Eya family of transcriptional activators, as the causative gene of postlingual, progressive, autosomal dominant hearing loss at the DFNA10 locus. In two unrelated families from Belgium and the USA segregating for deafness at this locus, we found different mutations in EYA4, both of which create premature stop codons. Although EYA proteins interact with members of the SIX and DACH protein families in a conserved network that regulates early embryonic development, this finding shows that EYA4 is also important post-developmentally for continued function of the mature organ of Corti.

Age of Onset↗
PubMed2001

UVA induces Ser381 phosphorylation of p90RSK/MAPKAP-K1 via ERK and JNK pathways.

UVA exposure plays an important role in the etiology of skin cancer. The family of p90-kDa ribosomal S6 kinases (p90(RSK)/MAPKAP-K1) are activated via phosphorylation. In this study, results show that UVA-induced phosphorylation of p90(RSK) at Ser(381) through ERKs and JNKs, but not p38 kinase pathways. We provide evidence that UVA-induced p90(RSK) phosphorylation and kinase activity were time- and dose-dependent. Both PD98059 and a dominant negative mutant of ERK2 blocked ERKs and p90(RSK) Ser(381) phosphorylation, as well as p90(RSK) activity. A dominant negative mutant of p38 kinase blocked UVA-induced phosphorylation of p38 kinase, but had no effect on UVA-induced Ser(381) phosphorylation of p90(RSK) or kinase activity. UVA-induced p90(RSK) phosphorylation and kinase activity were markedly attenuated in JnK1(-/-) and JnK2(-/-) cells. A dominant negative mutant of JNK1 inhibited UVA-induced JNKs and p90(RSK) phosphorylation and kinase activity, but had no effect on ERKs phosphorylation. PD169316, a novel inhibitor of JNKs and p38 kinase, inhibited phosphorylation of p90(RSK), JNKs, and p38 kinase, but not ERKs. However, SB202190, a selective inhibitor of p38 kinase, had no effect on p90(RSK) or JNKs phosphorylation. Significantly, ERKs and JNKs, but not p38 kinase, immunoprecipitated with p90(RSK) when stimulated by UVA and p90(RSK) was a substrate for ERK2 and JNK2, but not p38 kinase. These data indicate clearly that p90(RSK) Ser(381) may be phosphorylated by activation of JNKs or ERKs, but not p38 kinase.

Enzyme Activation↗
PubMed2001

DNA synthesis and mitotic clonal expansion is not a required step for 3T3-L1 preadipocyte differentiation into adipocytes.

Upon differentiation induction of 3T3-L1 preadipocytes by a hormone mixture containing 1-isobutyl-3-methylxanthine, dexamethasone, and insulin, the preadipocytes undergo approximately 2 rounds of mitotic clonal expansion, which just precedes the adipogenic gene expression program and has been thought to be an essential early step for differentiation initiation. By inducing 3T3-L1 preadipocytes with each individual hormone, it was determined that the mitotic clonal expansion was induced only by insulin and not by 1-isobutyl-3-methylxanthine or dexamethasone. Cell number counting and fluorescence-activated cell-sorting analysis indicated that a significant fraction of 3T3-L1 preadipocytes differentiated into adipocytes without mitotic clonal expansion when induced with the combination of 1-isobutyl-3-methylxanthine and dexamethasone. Furthermore, when normally induced 3T3-L1 preadipocytes were treated with PD98059 (an inhibitor of mitogen-activated protein kinase/extracellular signal-regulated kinase kinase 1) to block the activation of extracellular signal-regulated kinase (Erk) 1 and Erk2, the mitotic clonal expansion was blocked, but adipocyte differentiation was not affected. These observations were confirmed by bromodeoxyuridine labeling. The differentiated adipocytes induced with 1-isobutyl-3-methylxanthine and dexamethasone or standard hormone mixture plus PD98059 were not labeled by bromodeoxyuridine. Thus, it is evident that 3T3-L1 preadipocytes could differentiate into adipocytes without DNA synthesis and mitotic clonal expansion. Our results also suggested that activation of Erk1 and Erk2 is essential to but not sufficient for induction of mitotic clonal expansion.

1-Methyl-3-isobutylxanthine↗
PubMed2001

A photobiological and photophysical-based study of phototoxicity of two chlorins.

To understand the fundamental determinants of phototoxic efficacy and absorbed photodynamic dose, the triplet state and photobleaching quantum yields in living cells, cellular uptake, intracellular localization, and correlation with cell viability were studied for the two purpurins tin ethyl etiopurpurin 1 (SnET2) and tin octaethylbenzochlorin (SnOEBC) in ovarian cancer cells (OVCAR5). Although the triplet yields of these two photosensitizers were not significantly affected by cellular incorporation, the photobleaching yields were shown to be 3 orders of magnitude higher for cellular-bound sensitizer than for free or albumin-bound photosensitizer and higher for SnET2 than for SnOEBC for all of the cases. The intracellular concentration of SnOEBC was half that of SnET2 after 3 h- and 24 h-incubation times for both 0.1 microM and 1.0 microM incubation concentrations. Despite the lower concentrations of SnOEBC, the phototoxicity of the two photosensitizers was comparable at 1-microM incubation concentration and was up to 10-fold higher for SnOEBC at the lower concentration. The subcellular localization established using confocal microscopy and molecular probes showed that both photosensitizers were primarily lysosomally localized. SnOEBC, however, had an extra-lysosomal, mitochondrial localization component. The photophysical measurements allowed calculation of the intracellular singlet oxygen production, which indicated that the photosensitizer-light dose reciprocity was limited by photobleaching for SnET2 but only minimally for SnOEBC, and this was confirmed through cell-survival studies. Taken together, these data indicate that the critical determinant of differences in phototoxicity between the two molecules was their relative rates of photobleaching and their subcellular localization. The study points to the importance of combining photosensitizer uptake and localization with photophysical measurements in the relevant biological milieu to reasonably interpret and/or predict photosensitization efficacies.

Cell Survival↗