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Articles by S Chen
Total Records ( 11 ) for S Chen
  S Chen , M. L. Y Bangaru , L Sneade , J. A Dunckley , N Ben Jonathan and S. Kansra

Both estrogen (E2) and EGF regulate lactotrophs, and we recently demonstrated that EGF phosphorylates S118 on estrogen receptor- (ER) and requires ER to stimulate prolactin (PRL) release. However, the interactions between ligand-occupied ER and activated ErbB1 and its impact on lactotroph function are unknown. Using rat GH3 lactotrophs, we found that both E2 and EGF independently stimulated proliferation and PRL gene expression. Furthermore, their combination resulted in an enhanced stimulatory effect on both cell proliferation and PRL gene expression. Inhibitors of ER as well as ErbB1 blocked the combined effects of E2 and EGF. Pretreatment with UO126 abolished the combined effects, demonstrating Erk1/2 requirement. Although bidirectionality in ER-ErbB1 cross-talk is a well-accepted paradigm, interestingly in lactotrophs, ErbB1 kinase inhibitor failed to block the effect of E2 on proliferation and stimulation of PRL gene expression, suggesting that ER does not require ErbB1 to mediate its effects. Furthermore, E2 did not affect the ability of EGF to induce c-Fos expression or modulate AP-1 activity. However, both E2 and EGF combine to enhance S118 phosphorylation of ER, leading to enhanced E2-mediated estrogen response element transactivation. Taken together, our results suggest that, in lactotrophs, activated ErbB1 phosphorylates ER to enhance the stimulatory effect of E2, thereby providing the molecular basis by which EGF amplifies the response of E2.

  C Pehmoller , J. T Treebak , J. B Birk , S Chen , C MacKintosh , D. G Hardie , E. A Richter and J. F. P. Wojtaszewski

TBC1D1 is a Rab-GTPase-activating protein (GAP) known to be phosphorylated in response to insulin, growth factors, pharmacological agonists that activate 5'-AMP-activated protein kinase (AMPK), and muscle contraction. Silencing TBC1D1 in L6 muscle cells by siRNA increases insulin-stimulated GLUT4 translocation, and overexpression of TBC1D1 in 3T3-L1 adipocytes with low endogenous TBC1D1 expression inhibits insulin-stimulated GLUT4 translocation, suggesting a role of TBC1D1 in regulating GLUT4 translocation. Aiming to unravel the regulation of TBC1D1 during contraction and the potential role of AMPK in intact skeletal muscle, we used EDL muscles from wild-type (WT) and AMPK kinase dead (KD) mice. We explored the site-specific phosphorylation of TBC1D1 Ser237 and Thr596 and their relation to 14-3-3 binding, a proposed mechanism for regulation of GAP function of TBC1D1. We show that muscle contraction increases 14-3-3 binding to TBC1D1 as well as phosphorylation of Ser237 and Thr596 in an AMPK-dependent manner. AMPK activation by AICAR induced similar Ser237 and Thr596 phosphorylation of, and 14-3-3 binding to, TBC1D1 as muscle contraction. Insulin did not increase Ser237 phosphorylation or 14-3-3 binding to TBC1D1. However, insulin increased Thr596 phosphorylation, and intriguingly this response was fully abolished in the AMPK KD mice. Thus, TBC1D1 is differentially regulated in response to insulin and contraction. This study provides genetic evidence to support an important role for AMPK in regulating TBC1D1 in response to both of these physiological stimuli.

  S Chen , B Feng , B George , R Chakrabarti , M Chen and S. Chakrabarti

Sustained hyperglycemia in diabetes causes alteration of a large number of transcription factors and mRNA transcripts, leading to tissue damage. We investigated whether p300, a transcriptional coactivator with histone acetyl transferase activity, regulates glucose-induced activation of transcription factors and subsequent upregulation of vasoactive factors and extracellular matrix (ECM) proteins in human umbilical vein endothelial cells (HUVECs). HUVECs were incubated in varied glucose concentrations and were studied after p300 small interfering RNA (siRNA) transfection, p300 overexpression, or incubation with the p300 inhibitor curcumin. Histone H2AX phosphorylation and lysine acetylation were examined for oxidative DNA damage and p300 activation. Screening for transcription factors was performed with the Luminex system. Alterations of selected transcription factors were validated. mRNA expression of p300, endothelin-1 (ET-1), vascular endothelial growth factor (VEGF), and fibronectin (FN) and its splice variant EDB+FN and FN protein production were analyzed. HUVECs in 25 mmol/l glucose showed increased p300 production accompanied by increased binding of p300 to ET-1 and FN promoters, augmented histone acetylation, H2AX phosphorylation, activation of multiple transcription factors, and increased mRNA expression of vasoactive factors and ECM proteins. p300 overexpression showed a glucose-like effect on the mRNA expression of ET-1, VEGF, and FN. Furthermore, siRNA-mediated p300 blockade or chemical inhibitor of p300 prevented such glucose-induced changes. Similar mRNA upregulation was also seen in the organ culture of vascular tissues, which was prevented by p300 siRNA transfection. Data from these studies suggest that glucose-induced p300 upregulation is an important upstream epigenetic mechanism regulating gene expression of vasoactive factors and ECM proteins in endothelial cells and is a potential therapeutic target for diabetic complications.

  M Cuendet , J Guo , Y Luo , S Chen , C. P Oteham , R. C Moon , R. B van Breemen , L. E Marler and J. M. Pezzuto

Isoliquiritigenin (2',4',4-trihydroxychalcone; ILG), a chalcone found in licorice root and many other plants, has shown potential chemopreventive activity through induction of phase II enzymes such as quinone reductase-1 in murine hepatoma cells. In this study, the in vivo metabolism of ILG was investigated in rats. In addition, ILG glucuronides and ILG-glutathione adducts were observed in human hepatocytes and in livers from rats treated with ILG. ILG glucuronides were detected in both plasma and rat liver tissues. In addition, in a full-term cancer chemoprevention study conducted with 7,12-dimethylbenz(a)anthracene–treated female Sprague-Dawley rats, dietary administration of ILG slightly increased tumor latency but had a negative effect on the incidence of mammary tumors starting at ~65 days after 7,12-dimethylbenz(a)anthracene administration. Further, no significant induction of phase II enzymes was found in mammary glands, which is consistent with the low level of ILG observed in these tissues. However, ILG significantly induced quinone reductase-1 activity in the colon, and glutathione as well as glutathione S-transferase in the liver. Analysis of mRNA expression in tissues of rats treated with ILG supported these findings. These results suggest that ILG should be tested for chemopreventive efficacy in nonmammary models of cancer. Cancer Prev Res; 3(2); 221–32

  C Cai , D. C Portnoy , H Wang , X Jiang , S Chen and S. P. Balk

Prostate cancers (PCa) that relapse after androgen deprivation therapies [castration-resistant PCa (CRPC)] express high levels of androgen receptor (AR) and androgen-regulated genes, and evidence from several groups indicates that ErbB family receptor tyrosine kinases [epidermal growth factor (EGF) receptor (EGFR) and ErbB2] may contribute to enhancing this AR activity. We found that activation of these kinases with EGF and heregulin-β1 rapidly (within 8 hours) decreased expression of endogenous AR and androgen-regulated PSA in LNCaP PCa cells. AR expression was similarly decreased in LAPC4 and C4-2 cells, but not in the CWR22Rv1 PCa cell line. The rapid decrease in AR was not due to increased AR protein degradation and was not blocked by phosphatidylinositol 3-kinase (LY294002) or MEK (UO126) inhibitors. Significantly, AR mRNA levels in LNCaP cells were markedly decreased by EGF and heregulin-β1, and experiments with actinomycin D to block new mRNA synthesis showed that AR mRNA degradation was increased. AR mRNA levels were still markedly decreased by EGF and heregulin-β1 in LNCaP cells adapted to growth in androgen-depleted medium, although AR protein levels did not decline due to increased AR protein stability. These findings show that EGFR and ErbB2 can negatively regulate AR mRNA and may provide an approach to suppress AR expression in CRPC. [Cancer Res 2009;69(12):5202–9]

  W Han , L Wu , S Chen and K.N. Yu

In the present work, the inhibitory effect of carbon monoxide (CO), generated by tricarbonyldichlororuthenium (II) dimer [CO-releasing molecule (CORM-2)], on the toxicity of radiation-induced bystander effect (RIBE) after -particle irradiation was studied in a mixed coculture system. CO (CORM-2) treatment showed a significant inhibitory effect to the formation of p53 binding protein 1 (BP1) and micronuclei (MN) induced by RIBE in a concentration-dependent manner, but in the directly irradiated cell population no distinct decreases of BP1 and MN formation were observed. In this mixed coculture system, nitric oxide (NO) or superoxide anion $${(\hbox{ O }}_{2}^{\cdot -})$$ was also proved to mediate the transduction of RIBE by using a NO synthase inhibitor or NADPH-oxidase-specific inhibitor treatment. The elevated $${\hbox{ O }}_{2}^{\cdot -}$$ was attenuated by CO (CORM-2) treatment in the bystander cells as measured by hydroethidine staining and fluorescence assessment. The exogenous NO (sper) or $${\hbox{ O }}_{2}^{\cdot -}$$ (H2O2) was used to mimic NO/O2-mediated RIBE, and CO (CORM-2) treatment also showed a protective effect to cells against the toxicity of these exogenous factors. Considering the inhibitory effect of CO on RIBE and the wide use of CO in therapy of diseases, it is hoped that a low concentration of CO can protect normal tissues against RIBE during radiotherapy.

  N Dong , S Chen , J Yang , L He , P Liu , D Zheng , L Li , Y Zhou , C Ruan , E Plow and Q. Wu

Background— Corin is a transmembrane protease that processes natriuretic peptides in the heart. Like many membrane proteins, corin is shed from the cell surface.

Methods and Results— In this study, we obtained plasma samples from healthy controls and patients with heart failure (HF) and acute myocardial infarction. Soluble corin levels in plasma were measured by an ELISA method. In healthy adults (n=198), plasma corin levels were 690 pg/mL (SD, 260 pg/mL). The corin levels did not differ significantly among different age groups. In patients with HF (n=291), plasma corin levels were significantly lower compared with that of healthy controls (365 pg/mL [SD, 259]; P<0.001). The reduction in plasma corin levels seemed to correlate with the severity of HF. In patients of New York Heart Association classes II, III, and IV, plasma corin levels were 450 pg/mL (SD, 281 pg/mL; n=69), 377 pg/mL (SD, 270 pg/mL; n=132), and 282 pg/mL (SD, 194 pg/mL; n=90), respectively (P<0.001 class II vs class IV; P<0.05 class III vs class IV). In contrast, plasma corin levels in patients with acute myocardial infarction (n=73) were similar to that of healthy controls (678 pg/mL [SD, 285 pg/mL]; P>0.05).

Conclusions— Soluble corin was detected in human plasma. Plasma corin levels were reduced significantly in patients with HF but not in those with acute myocardial infarction. Our results indicate that corin deficiency may contribute to the pathogenesis of HF and that plasma corin may be used as a biomarker in the diagnosis of HF.

  D Yip , M. N Le , J. L. K Chan , J. H Lee , J. A Mehnert , A Yudd , J Kempf , W. J Shih , S Chen and J. S. Goydos

Purpose: Ectopic expression of GRM1 in murine melanocytes results in transformation into a form of melanoma, and more than 60% of human melanoma samples tested ectopically express GRM1. Stimulation of this receptor in vitro results in up-regulation of activated extracellular signal–regulated kinase (ERK). Furthermore, a xenograft model of melanoma treated with riluzole, an oral GRM1 blocking agent, showed decreased tumor growth compared with the untreated controls. We have now completed a phase 0 trial of riluzole in patients with melanoma.

Experimental Design: Patients enrolled on this trial underwent a pretreatment biopsy, took 200 mg of oral riluzole per day for 14 days, and then underwent resection of their remaining tumor. We compared the levels of pERK and pAKT in the pretreatment and post-treatment samples and assessed the metabolic activity of pretreatment and post-treatment tumors using fluorodeoxyglucose positron emission tomography (FDG-PET) scanning.

Results: We accrued 12 patients and all expressed GRM1. We found a significant decrease in pAKT and/or pERK in post-treatment tumor samples as compared with pretreatment samples in 4 (34%) patients. These four patients had a significant decrease in FDG-PET intensity post-treatment as well. Two other patients had a clinical response with no corresponding metabolic response; five patients had similar pretreatment and post-treatment FDG-PET scan findings; and one patient had progressive disease.

Conclusions: Our data show that glutamate blockade with riluzole can inhibit signaling through the mitogen-activated protein kinase and phosphatidylinositol 3-kinase/AKT pathways and suppress the metabolic activity of melanoma. The ectopic expression of metabotropic glutamate receptors may be important in the pathogenesis of human melanoma, and targeting this pathway may be an effective therapy.

  R Li , A Maminishkis , T Banzon , Q Wan , S Jalickee , S Chen and S. S. Miller

The present experiments show that IFN receptors are mainly localized to the basolateral membrane of human retinal pigment epithelium (RPE). Activation of these receptors in primary cultures of human fetal RPE inhibited cell proliferation and migration, decreased RPE mitochondrial membrane potential, altered transepithelial potential and resistance, and significantly increased transepithelial fluid absorption. These effects are mediated through JAK-STAT and p38 MAPK signaling pathways. Second messenger signaling through cAMP-PKA pathway- and interferon regulatory factor-1-dependent production of nitric oxide/cGMP stimulated the CFTR at the basolateral membrane and increased transepithelial fluid absorption. In vivo experiments using a rat model of retinal reattachment showed that IFN applied to the anterior surface of the eye can remove extra fluid deposited in the extracellular or subretinal space between the retinal photoreceptors and RPE. Removal of this extra fluid was blocked by a combination of PKA and JAK-STAT pathway inhibitors injected into the subretinal space. These results demonstrate a protective role for IFN in regulating retinal hydration across the outer blood-retinal barrier in inflammatory disease processes and provide the basis for possible therapeutic interventions.

  Y Wang , D Liang , S Wang , Z Qiu , X Chu , S Chen , L Li , X Nie , R Zhang , Z Wang and D. Zhu

It has been previously reported by us that hypoxia activates lung 15-lipoxygenase (15-LO), which catalyzes arachidonic acid to 15-hydroxyeicosatetraenoic acid (15-HETE), leading to the constriction of pulmonary artery (PA). Rho-associated serine/threonine kinase (ROK), a downstream effector of small GTPase RhoA that may be modulated by G-protein and tyrosine kinase, plays an important role in smooth muscle contraction. However, whether the 15-HETE induced PA vasoconstriction involves the Rho/ROK pathway remains to be demonstrated. Therefore, we studied the contribution of ROK as well as G-protein and tyrosine kinase to the 15-HETE induced pulmonary vasoconstriction using PA ring technique, RNA interference technology, RP-HPLC, western blot and RT-PCR combined with the blockers. The hypoxia-induced expression of ROK is regulated by 15-HETE in rat PA smooth muscle cells (PASMCs), leading to vasoconstriction. The up-regulation of ROK expression caused by 15-HETE appears to be mediated by the G-protein and tyrosine kinase pathways. The translocation of ROK2 from the nucleus to the cytoplasm during hypoxia exposure relies on the mechanism for 15-HETE production. These results suggest that 15-HETE may mediate the up-regulation of ROK expression through G-protein and tyrosine kinase pathways under hypoxic condition, leading to PA vasoconstriction.

  W Yuan , J Xie , C Long , H Erdjument Bromage , X Ding , Y Zheng , P Tempst , S Chen , B Zhu and D. Reinberg

The presence of histone H3 lysine 36 methylation (H3K36me) correlates with actively transcribed genes. In yeast, histone H3K36me mediated by KMT3 (also known as Set2) recruits a histone deacetylase complex, Rpd3s, to ensure the fidelity of transcription initiation. We report the purification of human KMT3a (also known as HYPB or hSet2) complex and the identification of a novel, higher eukaryotic specific subunit, heterogeneous nuclear ribonucleoprotein L (HnRNP-L). Interestingly, although KMT3a has intrinsic activity in vitro, HnRNP-L is essential in vivo. Moreover, KMT3a generates mono-, di-, and trimethylated products in vitro, but RNA interference against KMT3a or HnRNP-L down-regulates exclusively the H3K36me3 mark in vivo.

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