Biomedical subjects

Xiaoling Yuan

Publications and source records attributed to Xiaoling Yuan.

15 recordsLinked to original sources

PubMed2006

Induction of heme oxygenase-1 (HO-1) and NAD[P]H: quinone oxidoreductase 1 (NQO1) by a phenolic antioxidant, butylated hydroxyanisole (BHA) and its metabolite, tert-butylhydroquinone (tBHQ) in primary-cultured human and rat hepatocytes.

PURPOSE: This study was aimed to investigate the effects of a phenolic antioxidant, butylated hydroxyanisole (BHA) and its metabolite, tert-butylhydroquinone (tBHQ) on the induction of HO-1, NQO1 and Nrf2 proteins and their regulatory mechanisms in primary-cultured hepatocytes. METHODS: After exposure of BHA and tBHQ to primary-cultured rat and human hepatocytes and mouse neonatal fibroblasts (MFs), Western blot, semi-quantitative RT-PCR and microarray analysis were conducted. RESULTS: Induction of HO-1, NQO1 and Nrf2 proteins and activation of ERK1/2 and JNK1/2 were observed after BHA and tBHQ treatments in primary-cultured rat and human hepatocytes. Semi-quantitative RT-PCR study and microarray analysis revealed that HO-1 and NQO1 were transcriptionally activated in primary-cultured rat hepatocytes and a substantial transcriptional activation, including HO-1 occurred in primary-cultured human hepatocytes after BHA treatment. Whereas BHA failed to induce HO-1 in wild-type and Nrf2 knock-out MFs, tBHQ strongly induced HO-1 in wild-type, but not in Nrf2 knock-out MFs. CONCLUSIONS: Our data demonstrate that both BHA and tBHQ are strong chemical inducers of HO-1, NQO1 and Nrf2 proteins in primary-cultured human and rat hepatocytes with the activation of MAPK ERK1/2 and JNK1/2. However, in MFs, BHA failed to induce HO-1, whereas tBHQ strongly induced HO-1 in Nrf2 wild-type but not in Nrf2 knock-out, suggesting that Nrf2 is indispensable for tBHQ-induced HO-1 in MF.

Animals↗

PubMed2006

Mechanism of action of sulforaphane: inhibition of p38 mitogen-activated protein kinase isoforms contributing to the induction of antioxidant response element-mediated heme oxygenase-1 in human hepatoma HepG2 cells.

Exposure of sulforaphane to HepG2 cells increased heme oxygenase-1 (HO-1) expression by activating antioxidant response element (ARE) through induction of Nrf2 and suppression of Kelch-like ECH-associated protein 1 (Keap1). Using human HO-1 promoter reporter plasmids and ChIP assay, we have identified that sulforaphane transcriptionally activated the upstream ARE-rich enhancer region, located at -9.0 kb upstream human HO-1 promoter. Induction of HO-1 by sulforaphane was attenuated by overexpression of mutant Nrf2 plasmid in HepG2 cells and totally abolished in Nrf2 knockout mouse embryonic keratinocytes and fibroblasts. Overexpression of individual p38 mitogen-activated protein (MAP) kinase (MAPK) isoforms also suppressed constitutive as well as sulforaphane- or Nrf2-induced ARE-dependent gene expression. Among the upstream kinases, although MKK3 was not involved in suppression of ARE by any of p38 MAPK isoforms, MKK6 selectively suppressed ARE by p38 gamma or p38 delta, but not by p38 alpha or p38 beta. Importantly, sulforaphane not only activated MAP/extracellular signal-regulated kinase (ERK) kinases 1/2 and ERK1/2, but also strongly suppressed anisomycin-induced activation of p38 MAPK isoforms by blocking phosphorylation of upstream kinases, MKK3/6. Finally, we found that stimulation of p38 MAPK isoforms phosphorylated purified Nrf2 protein and caused an increase in the interaction between Nrf2 and Keap1 in vitro and the suppression of Nrf2 translocation into the nucleus. Collectively, our results indicate that transcriptional activation of Nrf2/ARE is critical in sulforaphane-mediated induction of HO-1, which can be modulated in part by the blockade of p38 MAPK signaling pathway. In addition, our study shows that p38 MAPK can phosphorylate Nrf2 and promotes the association between Nrf2 and Keap1 proteins, thereby potentially inhibiting nuclear translocation of Nrf2.

Animals↗

PubMed2006

Inhibition of 7,12-dimethylbenz(a)anthracene-induced skin tumorigenesis in C57BL/6 mice by sulforaphane is mediated by nuclear factor E2-related factor 2.

Sulforaphane, a dietary isothiocyanate, possesses potent chemopreventive effects through the induction of cellular detoxifying/antioxidant enzymes via the transcription factor nuclear factor E2-related factor 2 (Nrf2). To investigate carcinogenesis mechanisms related to the regulation of Nrf2, we examined the tumor incidence and tumor numbers per mouse in Nrf2 wild-type (+/+) and Nrf2 knockout (-/-) mice. 7,12-Dimethylbenz(a)anthracene/12-O-tetradecanoylphorbol-13-acetate treatments resulted in an increase in the incidence of skin tumors and tumor numbers per mouse in both genotypes; however, both indices were markedly higher in Nrf2(-/-) mice as compared with Nrf2(+/+) mice. Western blot analysis revealed that Nrf2 as well as heme oxygenase-1, a protein regulated by Nrf2 were not expressed in skin tumors from mice of either genotype, whereas expression of heme oxygenase-1 in Nrf2(+/+) mice was much higher than that in Nrf2(-/-) mice in nontumor skin samples. Next, we examined the chemopreventive efficacy of sulforaphane in mice with both genotypes. Topical application of 100 nmol of sulforaphane once a day for 14 days prior to 7,12-dimethylbenz(a)anthracene/12-O-tetradecanoylphorbol-13-acetate applications decreased the incidence of skin tumor in the Nrf2(+/+) mice when compared with the vehicle-treated group. Importantly, there was no chemoprotective effect elicited by sulforaphane pretreatment in the Nrf2(-/-) mice group. Taken together, our results show for the first time that Nrf2(-/-) mice are more susceptible to skin tumorigenesis and that the chemopreventive effects of sulforaphane are mediated, at least in part, through Nrf2.

9,10-Dimethyl-1,2-benzanthracene↗

PubMed2006

Regulation of Nrf2 transactivation domain activity by p160 RAC3/SRC3 and other nuclear co-regulators.

Transcription factor NF-E2-related factor 2 (Nrf2) regulates the induction of Phase II detoxifying enzymes and antioxidant enzymes in response to many cancer chemopreventive compounds. In this study, we investigated the role of receptor associated coactivator (RAC3) or steroid receptor coactivator-3 (SRC3) and other nuclear co-regulators including CBP/p300 (CREB-binding protein), CARM1(Coactivator-associated arginine methyltransferase), PRMT1(Protein arginine methyl-transferase 1), and p/CAF (p300/CBP-associated factor) in the transcriptional activation of a chimeric Gal4-Nrf2-Luciferase system containing the transactivation domain (TAD) of Nrf2 in HepG2 cells. The results indicated that RAC3 up-regulated the transactivation activity of Gal4-Nrf2-(1-370) in a dose-dependent manner. The enhancement of transactivation domain activity of Gal4-Nrf2-(1-370) by RAC3 was dampened in the presence of dominant negative mutants of RAC3. Next we studied the effects of other nuclear co-regulators including CBP/ p300, CARM1, PRMT1 and p/CAF, and the results showed that they had different level of positive effects on this transactivation domain activity of Gal4-Nrf2-(1-370). But importantly, synergistic effects of these co-regulators in the presence of RAC3/SRC3 on the transactivation activity of Gal4-Nrf2-(1-370) were observed. In summary, our present study showed for the first time that the 160 RAC3/SRC3 is involved in the functional transactivation of TAD of Nrf2 and that the other nuclear co-regulators such as CBP/p300, CARM1, PRMT1 and p/CAF can also transcriptionally activate this TAD of Nrf2 and that they could further enhance the transactivation activity mediated by RAC3/SRC3.

Acetyltransferases↗

PubMed2006

Mitochondrial location of severe acute respiratory syndrome coronavirus 3b protein.

Severe acute respiratory syndrome-associated coronavirus (SARS-CoV), a distant member of the Group 2 coronaviruses, has recently been identified as the etiological agent of severe acute respiratory syndrome (SARS). The genome of SARS-CoV contains four structural genes that are homologous to genes found in other coronaviruses, as well as six subgroup-specific open reading frames (ORFs). ORF3 encodes a predicted 154-amino-acid protein that lacks similarity to any known protein, and is designated 3b in this article. We reported previously that SARS-CoV 3b is predominantly localized in the nucleolus, and induces G0/G1 arrest and apoptosis in transfected cells. In this study, we show that SARS-CoV 3b fused with EGFP at its N- or C- terminus co-localized with a mitochondria-specific marker in some transfected cells. Mutation analysis of SARS-CoV 3b revealed that the domain spanning amino acids 80 to 138 was essential for its mitochondria localization. These results provide new directions for studies of the role of SARS-CoV 3b protein in SARS pathogenesis.

Animals↗

PubMed2006

Interaction between Snapin and G-CSF receptor.

Granulocyte colony-stimulating factor (G-CSF) is the major cytokine involved in the control of neutrophil development. G-CSF activates the special receptor, the G-CSF receptor (GCSF-R), which subsequently triggers multiple signaling events. To obtain more interactive molecules with GCSF-R and to further understand the cellular signaling mechanism of GCSF-R, yeast two-hybrid system was used to screen a mouse liver library. Here, the interaction of GCSF-R and Snapin was found by yeast two-hybrid experiment, and the interaction of the two proteins was further confirmed by GST pull-down experiment, mammalian two-hybrid experiment and co-immunoprecipitation study. Moreover, the immuno-fluorescence assay was shown that the two proteins of GCSF-R with Snapin were co-localized in the cytoplasm and plasma membrane. The region of C-terminal GCSF-R between box2 and box3, including the residue Tyr703, was responsible for the interaction with Snapin. These data suggested that Snapin is a new interactive protein of GCSF-R.

Animals↗

PubMed2006

Butylated hydroxyanisole regulates ARE-mediated gene expression via Nrf2 coupled with ERK and JNK signaling pathway in HepG2 cells.

Many natural and synthetic cancer chemopreventive compounds are potent inducers of phase II detoxifying and antioxidant stress responsive genes. The phase II/antioxidant gene expression plays critical role in chemoprevention of carcinogenesis. The antioxidant responsive element (ARE), located on many phase II/antioxidant genes, binds with the transcription factor Nrf2, and is required for the activation of these phase II/antioxidant gene expression induced by many natural and synthetic cancer chemopreventive compounds. In this study, we investigated the potential roles of extracellular signal-regulated kinase (ERK) and c-jun N-terminal kinase (JNK) in the regulation of butylated hydroxyanisole (BHA)-induced and Nrf2-dependent ARE transcriptional activity and ARE-mediated endogenous heme oxygenase-1 (HO-1) protein expression in HepG2 cells. ARE transcriptional activity and HO-1 protein expression were increased dose dependently after treatment with BHA in HepG2 cells. Dose-response and time-course experiments showed that BHA increased the accumulation of Nrf2, and concomitantly decreased the protein level of Keap1. We next examined the phosphorylation of the MAPKs, and found that BHA significantly increased the phosphorylation levels of ERK1/2 and JNK1/2. Importantly BHA-induced ARE transcriptional activity was attenuated by the inhibition of ERK and JNK signaling using biochemical inhibitors and their dominant-negative mutants. Using confocal microscopy technique, treatment with BHA showed the release of Nrf2 sequestered by Keap1 in the cytosol, and that Nrf2 translocated into the nucleus. Importantly, cDNA transfections of ERK and JNK signaling pathways similarly released Nrf2 from Keap1 cytosolic sequestration and translocating Nrf2 into the nucleus. Taken together, these results strongly suggested that ERK and JNK signaling pathways played important and positive roles in BHA-induced and Nrf2-dependent regulation of ARE-mediated gene expression, as well as the nuclear translocation of Nrf2 in HepG2 cells.

Blotting, Western↗

PubMed2006

Expression and characterization of earthworm Eisenia foetida lumbrokinase-3 in Pichia pastoris.

Lumbrokinase-3 (LK-3, AY438622), first cloned from the earthworm Eisenia foetida in our laboratory, is a component of earthworm fibrinolytic enzymes. In this study, cDNA encoding the LK-3 gene was sub-cloned into yeast pPIC9K expression vector and transformed into the Pichia pastoris GS115 cells by electroporation. High level expression of LK-3 in yeast cells was confirmed with a different induction time. The activity of expressed LK-3 was observed in fibrin plates. In addition, the expressed LK-3 protein could dissolve fibrinogen and bovine serum albumin. The use of this system for the high level production of biological protein is implicated from this study.

Animals↗

PubMed2006

Mechanism of action of isothiocyanates: the induction of ARE-regulated genes is associated with activation of ERK and JNK and the phosphorylation and nuclear translocation of Nrf2.

The up-regulation of phase II detoxifying and stress-responsive genes is believed to play an important role in cancer prevention, and many natural compounds have been shown to be potent inducers of these genes. Previous studies showed that the antioxidant responsive element (ARE), found in these genes, can be bound by the transcription factor Nrf2, and is responsive to the activation by chemopreventive compounds and by oxidative stress. In the present study, we investigated the roles of extracellular signal-regulated kinase (ERK) and c-Jun-NH(2)-kinase (JNK) in the regulation of phenethyl isothiocyanate (PEITC)-induced and Nrf2-dependent ARE activity and ARE-driven heme oxygenase-1 (HO-1) gene expression in PC-3 cells. ARE activity and HO-1 expression were strongly increased after treatment with PEITC. PEITC also increased the phosphorylation of ERK1/2 and JNK1/2 and caused release of Nrf2 from sequestration by Keap1, and its subsequent translocation into the nucleus. Importantly, Nrf2 was also translocated into the nucleus after transfection with ERK or JNK and that these activated ERK and JNK colocalized with Nrf2 in the nucleus. Activation of ERK and JNK signaling also resulted in the elevation of ARE activity and HO-1 expression. Importantly, PEITC-induced ARE activity was attenuated by inhibition of ERK and JNK signaling. In vitro kinase assays showed that both ERK2 and JNK1 could directly phosphorylate glutathione S-transferase-Nrf2 protein. Taken together, these results strongly suggest a model in which PEITC treatment of PC-3 cells activates ERK and JNK, which, in turn, phosphorylate Nrf2 and induce its translocation to the nucleus. Nuclear Nrf2 activates ARE elements and induces expression of stress-responsive genes, including HO-1.

Active Transport, Cell Nucleus↗

PubMed2005

SARS coronavirus 7a protein blocks cell cycle progression at G0/G1 phase via the cyclin D3/pRb pathway.

The genome of severe acute respiratory syndrome-associated coronavirus (SARS-CoV) contains four structural genes that are homologous to genes found in other coronaviruses, and also contains six subgroup-specific open reading frames (ORFs). Expression of one of these subgroup-specific genes, ORF7a, resulted in apoptosis via a caspase-dependent pathway. Here, we observed that transient expression of ORF7a protein fused with myc or GFP tags at its N or C terminus inhibited cell growth and prevented BrdU incorporation in different cultural cells, suggesting that ORF7a expression may regulate cell cycle progression. Analysis by flow cytometry demonstrated that ORF7a expression was associated with blockage of cell cycle progression at G0/G1 phase in HEK 293 cells after 24 to 60 h post-transfection. Similar results were observed in COS-7 and Vero cells. Mutation analysis of ORF7a revealed that the domain spanning aa 44-82 of 7a protein was essential for its cytoplasmic localization and for induction of the cell cycle arrest. After analyzing the cellular proteins involving in regulation of cell cycle progression, we demonstrated that ORF7a expression was correlated with a significant reduction of cyclin D3 level of mRNA transcription and expression, and phosphorylation of retinoblastoma (Rb) protein at ser795 and ser809/811, not with the expression of cyclin D1, D2, cdk4 and cdk6 in HEK 293 cells. These results suggest that the insufficient expression of cyclin D3 may cause a decreased activity of cyclin D/cdk4/6, resulting in the inhibition of Rb phosphorylation. Accumulation of hypo- or non-phosphorylated pRb thus prevents cell cycle progression at G0/G1 phase.

Animals↗

PubMed2005

ERK and JNK signaling pathways are involved in the regulation of activator protein 1 and cell death elicited by three isothiocyanates in human prostate cancer PC-3 cells.

Many isothiocyanates (ITCs) such as sulforaphane (SFN), phenethyl isothiocyanate (PEITC) and allyl isothiocyanate (AITC) are highly effectively in chemoprevention or reduction of the risk of cancer and possess antitumor activities in vitro and in vivo. The activator protein 1 (AP-1) and MAPK signaling pathways are believed to play an important role in cancer chemoprevention and chemotherapy due to their involvement in tumor cell growth, proliferation, apoptosis and survival. In the present study, we determined the effects of SFN, PEITC and AITC on AP-1 activation, and investigated the roles of extracellular signal-regulated protein kinase (ERK) and c-Jun N-terminal kinase (JNK) signaling pathways in the regulation of AP-1 activation and cell death elicited by these ITCs in human prostate cancer PC-3 cells. SFN, PEITC and AITC each induced AP-1 activity potently and caused a significant elevation in the phosphorylation of ERK1/2, JNK1/2, Elk-1 and c-Jun. Transfection with ERK2 and upstream kinase DNEE-MEK1 activated AP-1 activity, and transfection with dominant-negative mutant ERK2 (dnERK2) potently decreased AP-1 activation induced by SFN, PEITC and AITC. Transfection with JNK1 and upstream kinase MKK7 activated AP-1 activity, and transfection with dominant-negative mutant JNK1-APF significantly attenuated AP-1 activation induced by SFN, PEITC and AITC. Pretreatment with MEK1-ERK inhibitor U0126 and JNK inhibitor SP600125 substantially attenuated the decrease in cell viability induced by SFN, PEITC and AITC. Transfection with dnERK2 and JNK1-APF significantly reversed the decrease of Bcl-2 expression elicited by these ITCs. Furthermore, transfection with dnERK2 and JNK1-APF blocked the apoptosis induced by these ITCs in PC-3 cells. Taken together, our results indicate that the activation of the ERK and JNK signaling pathways is important for transcriptional activity of AP-1 and is involved in the regulation of cell death elicited by ITCs in PC-3 cells.

Anticarcinogenic Agents↗

PubMed2005

G0/G1 arrest and apoptosis induced by SARS-CoV 3b protein in transfected cells.

Severe Acute Respiratory Syndrome coronavirus (SARS-CoV), cause of the life-threatening atypical pneumonia, infects many organs, such as lung, liver and immune organ, and induces parenchyma cells apoptosis and necrosis. The genome of SARS-CoV, not closely related to any of the previously characterized coronavirus, encodes replicase and four major structural proteins and a number of non-structural proteins. Published studies suggest that some non-structural proteins may play important roles in the replication, virulence and pathogenesis of viruses. Among the potential SARS-CoV non-structural proteins, 3b protein (ORF4) is predicted encoding 154 amino acids, lacking significant similarities to any known proteins. Till now, there is no report about the function of 3b protein. In this study, 3b gene was linked with the EGFP tag at the C- terminus. Through cell cycle analysis, it was found that over-expression of 3b-EGFP protein in Vero, 293 and COS-7 cells could induce cell cycle arrest at G0/G1 phase, and that especially in COS-7 cells, expression of 3b-EGFP was able to induce the increase of sub-G1 phase from 24 h after transfection, which was most obvious at 48 h. The apoptosis induction of 3b fusion protein in COS-7 cells was further confirmed by double cell labeling with 7-AAD and Annexin V, the function of 3b protein inducing cell G0/G1 arrest and apoptosis may provide a new insight for further study on the mechanism of SARS pathogenesis.

Animals↗

PubMed2005

Nucleolar localization of non-structural protein 3b, a protein specifically encoded by the severe acute respiratory syndrome coronavirus.

The open reading frame 3 (ORF3) of the severe acute respiratory syndrome coronavirus (SARS-CoV) genome encodes a predicted 154-amino acid protein, which lacks similarities to any known protein, and is named 3b. In this study, it was shown that 3b protein was predominately localized to nucleus with EGFP tag at its N- or C-terminus. The localization patterns were similar in different transfected cells. Immuno-fluorescence assay revealed that 3b protein was co-localized well with C23 in nucleolus. C23, B23 and fibrillarin all are important nucleolar proteins, which localize in the region of the nucleolus. Co-transfection of p3b-EGFP with pC23-DsRed, pB23-DsRed and pfibrillarin-DsRed further confirmed 3b's nucleolus localization. With construction of serial truncated mutants of 3b, a region (residues 134-154 aa) responsible for nucleolar localization was determinated in 3b protein. These results provide a new insight for further functional studies of SARS-CoV 3b protein.

Amino Acid Sequence↗

PubMed2005

Subcellular localization and membrane association of SARS-CoV 3a protein.

SARS-CoV 3a protein was a unique protein of SARS coronavirus (SARS-CoV), which was identified in SARS-CoV infected cells and SARS patients' specimen. Recent studies revealed that 3a could interact specifically with many SARS-CoV structural proteins, such as M, E and S protein. Expressed 3a protein was reported to localize to Golgi complex in SARS-CoV infected cells. In this study, it was shown that 3a protein was mainly located in Golgi apparatus with different tags at N- or C-terminus. The localization pattern was similar in different transfected cells. With the assay of truncated 3a protein, it was shown that 3a might contain three transmembrane regions, and the second or third region was properly responsible for Golgi localization. By ultra-centrifugation experiment with different extraction buffers, it was confirmed that 3a was an integral membrane protein and embedded in the phospholipid bilayer. Immunofluorescence assay indicated that 3a was co-localized with M protein in Golgi complex in co-transfected cells. These results provide a new insight for further study of the 3a protein on the pathogenesis of SARS-CoV.

Animals↗

PubMed2004

Regulation of LIP level and ROS formation through interaction of H-ferritin with G-CSF receptor.

A variety of hematopoietic factors including granulocyte macrophage colony-stimulating factor (GM-CSF), granulocyte colony-stimulating factor (G-CSF), interleukin 3 (IL-3) and thrombopoietin (TPO) induce a rapid increase of intracellular reactive oxygen species (ROS). ROS induces the activation of many signaling molecules, including Shc, Lck, syk, PKC, MAPK, STAT3, through inhibition of protein phosphatase. Each growth factor has a specific cell-surface receptor, which activates both unique and shared signal transduction pathways. The processes of signal transduction linking cell-surface receptor to the formation of intracellular ROS have not been elucidated fully. Ferritins are composed of two subunit types, H and L, and made of 24 subunits that sequester up to 4500 atoms of iron. When the stored iron atoms are released from H-ferritin, through iron-catalyzed reaction, they have the capacity to promote the formation of ROS. Here, the interaction of G-CSFR and H-ferritin was confirmed by yeast two-hybrid screen, mammalian two-hybrid assays, glutathione-S-transferase (GST) pull-down experiments and immunoprecipitation studies in vitro and in vivo. Additional immunofluorescence assay showed that the two proteins colocalized along the plasma membrane and partly in the cytoplasm. The binding site for H-ferritin was demonstrated to locate to the box3 motif on the C-terminal region of granulocyte colony-stimulating factor receptor (G-CSFR). Furthermore, we found the interaction of full-length G-CSFR with H-ferritin was dissociated at 30 minutes after G-CSF induction and then began to assemble at 45 minutes. The labile iron pool (LIP) is a pool of redox-active iron complexes, which is regulated tightly by the expression of H-ferritin. Experiments showed that the level of LIP increased significantly at 30 minutes after G-CSF stimulation and intracellular ROS formation changed in a pattern similar to LIP response to G-CSF in bone-marrow hematopoietic cells. G-CSF-induced changes in the level of LIP and ROS formation could be blocked by pretreatment with iron chelators that repressed the expression of H-ferritin. In addition, the phosphorylation of STAT3 induced by G-CSF was decreased in iron chelator-treated hematopoietic cells. These data suggested that LIP may be released from the dissociated H-ferritin, and then induce intracellular ROS formation in the bone-marrow hematopoietic cells. ROS, acting as a second messenger, might take part in G-CSF receptor signal transduction. So, here, a new G-CSFR-H-ferritin-LIP-ROS pathway is proposed for regulation of intracellular ROS formation in bone-marrow hematopoietic cells.

Animals↗