Biomedical subjects

Xin Pan

Publications and source records attributed to Xin Pan.

16 recordsLinked to original sources

PubMed2006

Mammalian cell entry protein of Mycobacterium tuberculosis induces the proinflammatory response in RAW 264.7 murine macrophage-like cells.

Mammalian cell entry (Mce1A) protein of Mycobacterium tuberculosis (Mtb) is involved in bacterial entry and survival in macrophages, which has been shown to induce production of tumor necrosis factor alpha (TNF-alpha). It remains unclear whether and how Mce1A functions upon the type I interleukin-1 receptor-associated protein kinase (IRAK-1) and TNF receptor-associated factor 6 (TRAF-6) of important proinflammatory cytokines. In this study, His-tagged Mce1A was expressed and purified. Also, two pieces of small interfering RNA (siRNA) were designed and synthesized by in vitro transcription, which exhibit specific and efficient silencing effect on mce1a expression. Furthermore, RAW 264.7 murine macrophage-like cells were exposed to His-tagged Mce1A or co-transfected with the Mce1A-expressing plasmid and efficient siRNA, and levels of IRAK-1 and TRAF-6 were then determined by Western blot. We show here that Mce1A induces up-regulations of IRAK-1 and TRAF-6 in macrophages in a dose-dependent manner. The level of Caspase-3 closely related with apoptosis was also determined, whereas no changes were observed. These results indicate that Mtb Mce1A protein induces a proinflammatory response in macrophages.

Animals↗

PubMed2006

PIAS3 induction of PRB sumoylation represses PRB transactivation by destabilizing its retention in the nucleus.

Progesterone receptor (PR) plays a critical role in cell proliferation and differentiation, and its transcriptional activity is known to be modulated by cofactor proteins. In the present study, we demonstrated that in the presence of progesterone, protein inhibitor of activated STAT-3 (PIAS3) significantly inhibited the PR transcriptional activity and the expression of progesterone-responsive genes. Reduction of endogenous PIAS3 by PIAS3 small-interfering RNA enhanced PR transactivation in a ligand-dependent manner. PIAS3 interacted with PR both in vitro and in vivo and the interaction was enhanced by progesterone. Furthermore, our findings suggested that PIAS3 strongly induced PRB sumoylation at three sites, Lys-7, Lys-388 and Lys-531. In addition, novel roles in PRB nuclear retention and transactivation were identified for these sites. Our data also suggested that PIAS3 was recruited in a largely hormone-dependent manner in response to a progesterone-responsive promoter. Finally, we demonstrated that PIAS3 inhibited the DNA-binding activity of PR and influenced its nuclear export as well as PR transactivation. Taken together, these data strongly suggested that PIAS3 played an important physiological role in PR function.

Animals↗

PubMed2006

MDM2 interacts with and downregulates a sarcomeric protein, TCAP.

Recent reports have shown that MDM2 may attenuate hypertrophy of cardiac myocytes. However, mechanism of MDM2 involving in this process is unclear. In this study, we identified a novel specific MDM2-binding protein TCAP by the yeast two-hybrid screen. It was validated by GST pull-down and co-immunoprecipitation assays. Confocal analysis showed that MDM2 and TCAP co-localized in the nucleus, and elevated MDM2 expression could alter the subcellular localization of TCAP. Notably, MDM2 downregulated the protein level of TCAP through the proteasomal pathway, and this downregulation was inhibited by p14(ARF). In addition, our results suggested that the degradation of TCAP by MDM2 was through the ubiquitin-independent pathway. Given that TCAP is a key component involving in the cardiac hypertrophy, the degradation of TCAP by MDM2 might be connected with the roles of MDM2 in cardiac hypertrophy. Further investigation will focus on the biological significance of MDM2-TCAP interaction in cardiac hypertrophy.

Connectin↗

PubMed2006

Ubc9 interacts with SOX4 and represses its transcriptional activity.

SOX4 is a member of SOX transcriptional factor family that is crucial for many cellular processes. In this study, a yeast two-hybrid screening of human mammary cDNA library identified human ubiquitin-conjugating enzyme 9 (hUbc9) that interacted with SOX4. This interaction was confirmed by GST pull-down in vitro and co-immunoprecipitation assays in vivo. Deletion mapping demonstrated that HMG-box domain of SOX4 is required to mediate the interaction with Ubc9 in yeast. Furthermore, confocal microscopy showed that Ubc9 co-localized with SOX4 in the nucleus. Luciferase assays found that Ubc9 specifically repressed SOX4 transcriptional activity in 293T cells. We further demonstrated that Ubc9 could functionally repress the transcriptional activity of endogenous SOX4 induced by progesterone in T47D cells. The C93S mutant of Ubc9, which abrogates SUMO-1 conjugation activity, did not abolish the ability to repress SOX4 activity. It shows that Ubc9 interacts with SOX4 and represses its transcriptional activity independent of its SUMO-1-conjugating activity.

High Mobility Group Proteins↗

PubMed2006

Design and expression of a synthetic phyC gene encoding the neutral phytase in Pichia pastoris.

The 1074-bp phyCs gene (optimized phyC gene) encoding neutral phytase was designed and synthesized according to the methylotrophic yeast Pichia pastoris codon usage bias without altering the protein sequence. The expression vector, pP9K-phyCs, was linearized and transformed in P. pastoris. The yield of total extracellular phytase activity was 17.6 U/ml induced in Buffered Methanol-complex Medium (BMMY) and 18.5 U/ml in Wheat Bran Extract Induction (WBEI) medium at the flask scale, respectively, improving over 90 folds compared with the wild-type isolate. Purified enzyme showed temperature optimum of 70 degrees and pH optimum of 7.5. The enzyme activity retained 97% of the relative activity after incubation at 80 degrees for 5 min. Because of the heavy glycosylation the expressed phytase had a molecular size of approximately 51 kDa. After deglycosylation by endoglycosylase H (EndoH(f)), the enzyme had an apparent molecular size of 42 kDa. Its property and thermostability was affected by the glycosylation.

6-Phytase↗

PubMed2005

Characterization of the degradation of recombinant rat urate oxidase in tetracycline controlled gene expression cells.

Our previous study has shown that uric acid is metabolized by recombinant rat urate oxidase (UOX) and generates hydrogen peroxide leading to DNA damage and cell transformation. However, in transformed cells protein levels of UOX were reduced compared with the control cell. To investigate the characterization and the mechanisms responsible for the degradation of UOX, a controllable gene expression system has been used to switch on/off controlled expression of rat UOX in vitro. Chinese hamster ovary cells were double transfected with regulatory and responsive plasmids, pCMV-tTA and pTRE-rUOX, respectively. The cells expressing rat UOX were subtly controlled by tetracycline (Tc). High levels of UOX mRNA and protein enzymatic activity were observed when the cells were cultured in the absence of Tc. The functional recombinant rat UOX was present in the form of crystalloid cores structures that localized within the peroxisomes of the cells, which was confirmed by transmission and immunoelectron microscopic studies. The addition of Tc into the medium led to the halting of rat UOX gene transcription. As a result, recombinant rat UOX mRNA was lost rapidly followed by loss of crystalloid cores structures and UOX protein degradation. Lysosomes assembled around the UOX specific structures indicating that they were involved in degradation of the protein. The observations suggest that the entire organelle rather than a single protein within the peroxisomes is degraded once the rat UOX gene expression is turned off, and the phagocytic vacuole/lysosome pathway (microautophagic process) may play an important role in degradation of the protein under the present situation.

Animals↗

PubMed2004

A novel eIF5A complex functions as a regulator of p53 and p53-dependent apoptosis.

Although eukaryotic translation initiation factor 5A (eIF5A) was originally designated as an "initiation factor," recent data have shown it to be also involved in apoptosis. However, the actual function of eIF5A in apoptosis is still unknown. In this study, we performed yeast two-hybrid screens to identify eIF5A-interacting proteins to help us understand the mechanisms of eIF5A. Our results demonstrated that eIF5A and syntenin could engage in a specific interaction both in vitro and in vivo and functioned collaboratively to regulate p53 activity. Our findings, for the first time, revealed a new biological activity for eIF5A as the regulator of p53. Overexpression of eIF5A or its EFP domain resulted in up-regulation of p53, and silencing eIF5A by small interfering RNA reduced the p53 protein level. Further analysis by reverse transcription PCR showed eIF5A-activated p53 transcription. The effect of eIF5A on p53 transcriptional activity was further demonstrated by the increasing expressions of p21 and Bax, well known target genes of p53. In contrast, a point mutant of eIF5A, hypusination being abolished, was revealed to be functionally defective in p53 up-regulation. Overexpression of eIF5A led to a p53-dependent apoptosis or sensitized cells to induction of apoptosis by chemotherapeutic agents. However, when eIF5A interacted with its novel partner, syntenin, the eIF5A-induced increase in p53 protein level was significantly inhibited. Therefore, eIF5A seems to be a previously unrecognized regulator of p53 that may define a new pathway for p53-dependent apoptosis, and syntenin might regulate p53 by balancing the regulation of eIF5A signaling to p53 for apoptosis.

Animals↗

PubMed2004

Effects of endostatin-vascular endothelial growth inhibitor chimeric recombinant adenoviruses on antiangiogenesis.

AIM: To investigate the inhibitory effects of endostatin-vascular endothelial growth inhibitor (VEGI151) recombinant adenoviruses on neovascularization. METHODS: We used recombinant adenoviruses to treat human vascular endothelial cell line ECV304, human hepatocellular carcinoma cell line HepG2, and murine fibroblast cell line L929, in order to study the chimeric gene expression in these cell lines. Chick choriallantic membrane (CAM) model, rabbit inflammatory corneal neovascularization (CNV) model, and liver cancer-bearing nude mice model were employed to investigate the negative biological effect of fusion molecules on neovascularization in vivo. RESULTS: Western blot showed that the molecular weight of fusion protein was about 41 kD after infection of ECV304, HepG2 and L929 cells with supernatant of AdhENDO-VEGI151. The fusion protein showed a specific inhibitory effect on the proliferation of ECV304 cells, but no inhibitory effect on the growth of HepG2 and L929 cells (F=13112.13, P=0.0001). In the chick choriallantic membrane (CAM) assay, the expressed fusion protein significantly inhibited neovascularization. Rabbit inflammatory corneal neovascularization (CNV) induced by intrastromal sutures resulted in a uniform neovascular response. In this model, direct subconjunctival injection of AdhENDO-VEGI151 expressed the fusion protein in vivo and suppressed the development of CNV. Topical application of AdhENDO-VEGI151 led to a significant suppression of CNV (F=1413.11, P=0.0001), as compared with the control group of AdLacZ. Immunohistochemical staining showed the fusion protein dominantly expressed in corneal epithelium. Compared with the control group of AdLacZ (4075.9+/-1849.9 mm(3)), the average tumor size of group AdhENDO-VEGI151 reduced in size (487.7+/-241.2 mm(3)) (F=14.80, P=0.0085), with an inhibition rate of 88.03%. Immunohistochemical staining showed the adenoviruses carried the fusion gene expressed on liver cancer cell membrane. MVD decreased more significantly in treated mice (30.75+/-3.31%) than in AdLacZ control (50.25+/-8.65%) (F=17.72, P=0.0056) with an inhibition rate of 39%. CONCLUSION: Fusion protein expressed by recombinant adenoviruses has a significant inhibitory effect on neovascularization.

Adenoviridae↗

PubMed2004

Inhibition of EGFP expression by siRNA in EGFP-stably expressing Huh-7 cells.

The RNA interference (RNAi) is a powerful tool to silence gene expression post-transcriptionally, and causes the degradation of an mRNA containing the same sequence. In this present study, an alternative approach was used to in vitro synthesize enhanced green fluorescent protein (EGFP) specific short interfering RNA (siRNA) using T7 RNA polymerase, and a pEGFP-N1 transfected, human hepatoma cell line Huh-7 derived Huh-7-N cell clone was established. When introduced the siRNA into the EGFP expressing Huh-7-N cells, the EGFP specific siRNA was able to specifically inhibit the expression of EGFP in Huh-7-N. In comparison with that in wild-type Huh-7 or that in Huh-7 co-transfected with pEGFP-N1, the inhibition of EGFP specific siRNA in Huh-7-N cells is more significant and repeatable. It is concluded that a cell clone Huh-7-N, which stably expresses EGFP, has been established, and the in vitro synthesized EGFP siRNA can be used in silencing the EGFP gene expression. This Huh-7-N/EGFP specific siRNA system has been proved reliable and convenient, and can also be applied widely as control in other RNA interference studies.

Cell Line↗

PubMed2004

[Infection of recombinant adenovirus expressing acidic fibroblasts growth factor enhances rabbit corneal endothelium proliferation].

OBJECTIVE: To transfer the gene encoding mammalian aFGF to rabbit corneal endothelial cell and determine transfection efficiency and the effect of Ad-aFGF on proliferation of RCEC. METHODS: Replication-defective adenovirus was used to deliver the LacZ reporter gene to RCEC to determine transfection efficiency by X-gal staining. A cDNA encoding mammalian aFGF was cloned into an adenoviral vector that was used to transfect RCEC. The expression of aFGF gene mRNA and protein were demonstrated by Reverse transcription PCR and Western blot respectively. The effect of Ad-aFGF on proliferation of RCEC was determined by MTT assay. RESULTS: RT-PCR and Western blot from RCEC infected with Ad-aFGF for 48 h detected a specific cDNA amplification and protein expression of aFGF gene, and no positive result in control cells. Consistently, RCEC infected by MOI 20 of Ad-aFGF demonstrated an enhanced RCEC proliferation compared to controls (F = 217.107, P < 0.05). CONCLUSION: Adenoviral-mediated expression of aFGF can stimulate the proliferation of RCEC.

Adenoviridae↗

PubMed2004

[Construction of combined site-directed random mutation libraries of recombinant human lymphotoxin].

To construct the combined site-directed random mutation library of recombinant human Lymphotoxin (rhLT) for in vitro molecular evolution study, and to study the structure and function relationship. The random point mutations at the sites of 46,106 and 130 were individually generated by overlap PCR amplification with the random nucleotide primers. The three point mutations were combined and cloned into pMD-18T vector to construct the combined mutation library. DNA sequencing was used to evaluate the diversity and randomness of the mutation sites. The combined mutation library was re-engineered, inserted in prokaryotic expression vector pBV220, transformed and expressed in Escherichia coli strain DH5alpha. The biological activity of some of the mutants was tested in 1929 mouse fibroblast cells. As much as 1.5 x 10(5) clones were obtained, which represents 4.5 times of the complete mutation libraries at 99% confidence. Sequencing 50 clones revealed no obvious bias in the nucleotide and amino acid mutations at the sites. Among the 30 expressed samples underwent for the bioassay, 70% (21 samples) were inactive, 23.3% (7 samples) had lower activity than rhLT, the remaining 6.7% (2 samples) had higher activity than rhLT. The combined site-directed random mutation library of rhLT has been constructed successfully. In combination with phase display, the library is ready for in vitro molecular evolution study.

Amino Acid Sequence↗

PubMed2003

Protease-activated receptor (PAR)-1 and PAR-2 participate in the cell growth of alveolar capillary endothelium in primary lung adenocarcinomas.

BACKGROUND: Cell growth can be induced via elicitation of protease-activated receptors (PAR) with serine proteases such as thrombin and trypsin. METHODS: To understand whether PAR are involved in tumor vessel formation in the neoplastic cell-bearing alveolar walls, immunohistochemical and reverse transcriptase-polymerase chain reaction analyses were performed using the lung tissues from 16 patients with primary lung adenocarcinomas. RESULTS: In microdissected tumor alveolar walls, the expressions of PAR-1 and PAR-2 mRNA were increased by 10-fold (P < 0.05) and 16-fold (P < 0.01), respectively, as compared with normal alveolar walls. Confocal microscopy revealed that tumor capillary endothelial cells in alveolar walls lost thrombomodulin expression. Instead, the expression of PAR-2 often became obvious at the normal border. Both PAR-1 and PAR-2 were expressed in the microvessel endothelial cells in tumors. Trypsin mRNA was expressed in 7 of the 16 cancer cell-bearing tissue specimens in contrast to 1 of the 14 normal alveolar walls. Immunohistochemically, trypsin was positive in the neoplastic cells from 10 patients and in lung adenocarcinoma cell lines (A549, HLC-1, LC-2, and PC-14). An in vitro assay showed a significant increase in idoxuridine (IdU) or bromodeoxyuridine uptake in human pulmonary artery endothelial cells and human umbilical cord vein endothelial cells after treatments with alpha-thrombin or activating peptides; SFLLRN for PAR-1 and SLIGKV for PAR-2, respectively. CONCLUSIONS: Thus, proliferation of alveolar capillary endothelial cells is initialized in part by PAR activation with serum thrombin and neoplastic cell-released trypsin. These results suggest a synergistic effect of PAR with vascular endothelial growth factor in alveolar angiogenesis.

Adenocarcinoma↗

PubMed2003

[Effect of N-terminal deletion on biological activity of vascular endothelial cell growth inhibitor].

Vascular endothelial cell growth inhibitor (VEGI) is a novel cytokine which belongs to the TNF superfamily. It can inhibit the proliferation of endothelial cells and neovascularization. However, little is known about the structure-function relationship of VEGI. In order to study the effect of the N-terminus of VEGI on biological properties, the sequence alignment among VEGI and TNF superfamily members based on structure knowledge was done, and then two truncated forms of VEGI were constructed, in which 43 and 51 amino acids from N-terminus were deleted and named VEGI(131) and VEGI(123). Recombinant proteins were generated from E. coli. The expression rates were 25.2% (VEGI(131)) and 27.8% (VEGI(123)) of total bacterial proteins. After purification the purity reached 92.5% (VEGI(131)) and 91.6% (VEGI(123)). VEGI(131) showed significant inhibitory effect on growth of human umbilical vein endothelial cells (HUVEC), IC(50) of VEGI(131) being 35 mg/L. Under the same conditions, IC(50) of VEGI(151) (the wild type of VEGI) was 27 mg/L, but VEGI(123) showed no inhibitory effect. On chick choriallantic membrane (CAM) assay, VEGI(151) markedly reduced the number of main vessels, and VEGI131 decreased capillary number, while the effect of VEGI(123) was almost the same as control. These results suggest that the first 43 amino acids from N-terminus of VEGI have no significant effect on biological activity, but the amino acids 44-51 at N-terminus are required for full biological activity.

Allantois↗

PubMed2002

Adenovirus-mediated TGF-beta(1) gene transfer to human degenerative lumbar intervertebral disc cells.

OBJECTIVE: To test the possibility of modification of human degenerative lumbar disc cells by the exogenous growth factor gene, transforming growth factor beta(1) (TGF-beta(1)) cDNA, and the expression of the encoded protein. METHODS: Nucleus pulposus samples were surgically obtained from 8 patients with degenerative lumbar disc disease. The cells were cultured and directly infected by two adenoviral constructs, Ad/CMV-EGFP containing the enhanced green fluorecence protein (EGFP) gene (marker gene) and Ad/CMV-TGF-beta(1) containing the potentially therapeutic TGF-beta(1) gene. Transgene expression was analyzed by fluorescence production and immunohistochemical staining (Ad/CMV-TGF-beta(1)). RESULTS: Culture cells transduced by Ad/CMV-EGFP showed specific green fluorescence under the fluoroscope and expression sustained for at least 4 weeks. When infected by Ad/CMV-TGF-beta(1), approximately 30% of cultured cells were stained brown (+) with TGF-beta(1) staining. CONCLUSION: This study established the strategy of delivering a potentially therapeutic gene, TGF-beta(1), by using an adenoviral vector to human degenerative lumbar intervertebral disc cells.

Adenoviridae↗

PubMed1999

Structure and Function of Vascular Endothelial Growth Factor and Its Related Proteins.

Vascular endothelial growth factor(VEGF) is a highly specific mitogen promoting the formation of blood vessels in embryogenesis and wound healing. It is also a potent inducer of vascular permeability. It is a member of the cystine knot growth factor superfamily. A detailed structural and functional characterization of the interactions between VEGF and its receptors is a prerequisite for the design of molecule antagonists. These structural characterizations and biological properties make VEGF an important research object in the fields of neovascularization of ischemia tissues, prognosis of cancers, tumor metastasis, and the gene therapy.

Journal Article↗

PubMed1998

Gene therapy for human colorectal carcinoma using human CEA promoter contro led bacterial ADP-ribosylating toxin genes human CEA: PEA & DTA gene transfer.

AIM:To establish a tissue-specific gene therapy for colorectal carcinoma using bacterial ADP-ribosylating toxin genes. METHODS:Pseudomonas exotoxin A domain [II+III (PEA) was cloned from genomic DNA of Pseudomonas aeruginosa.PEA and diphtheria toxin A chain gene (DTA) were modified to express eukaryotically. After sequencing, the toxin genes under the control of human carcinoembryonic antigen (CEA)promoter were cloned into retroviral vectors to construct CEAPEA and CEADTA respectively. In vitro cotransfection of the constructs with luciferase vectors and in vivo gene transfer in nude mice were subsequently carried out. RESULTS:Both CEAPEA and CEADTA specifically inhibited the reporter gene expression in the CEA positive human colorectal carcinoma (CRC) cells in vitro. Direct injection of CEAPEA and CEADTA constructs into the established human tumors in BALB/c nude mice led to significant and selective reductions in CRC tumor size as compared with that in control groups.CONCLUSION:The toxin genes, working as therapeutic genes, are suitable for the tissue-specific gene therapy for colorectal carcinoma.

Journal Article↗