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Biomedical subjects

Xin Huang

Publications and source records attributed to Xin Huang.

At least 109 records · Page 6Linked to original sources
PubMed2003

Dihydrogen-bond-promoted catalysis: catalytic hydration of nitriles with the indenylruthenium hydride complex (eta(5)-C(9)H(7))Ru(dppm)H (dppm = bis(diphenylphosphino)methane).

The indenylruthenium hydride complex (eta(5)-C(9)H(7))Ru(dppm)H was found to be active in catalyzing the hydration of nitriles to amides. The chloro analogue (eta(5)-C(9)H(7))Ru(dppm)Cl was, however, found to be inactive. Density functional theory calculations at the B3LYP level provide explanations for the effectiveness of the hydride complex and the ineffectiveness of the chloro complex in the catalysis. It is learned that the presence of a Ru-H.H-OH dihydrogen-bonding interaction in the transition state lowers the reaction barrier in the case of (eta(5)-C(9)H(7))Ru(dppm)H, but in the chloro system, the corresponding transition state does not contain this type of interaction and the reaction barrier is much higher. A similar dihydrogen-bond-promoting effect is believed to be responsible for the catalytic activity of the hydrotris(pyrazolyl)borato (Tp) ruthenium complex TpRu(PPh(3))(CH(3)CN)H in CH(3)CN hydration. The chloro analogue TpRu(PPh(3))(CH(3)CN)Cl shows no catalytic activity.

Journal Article↗
PubMed2003

Lentivirus-mediated gene transfer and expression in established human tumor antigen-specific cytotoxic T cells and primary unstimulated T cells.

In this report, we evaluated the efficiency of stable gene transfer into established CD8(+) human tumor antigen-specific cytotoxic T cell (CTL) lines and peripheral blood lymphocytes (PBL) by oncoretroviral and lentiviral vectors. In the oncoretroviral vector, the green fluorescent protein (GFP) reporter gene was regulated by the murine stem cell virus (MSCV) promoter. In three human immunodeficiency virus type 1 (HIV-1)-based lentiviral vectors, the GFP transgene was regulated by either a chimeric MSCV/HIV-1 promoter, or cellular promoters from human housekeeping genes PGK and EF1 alpha. We found that several lines of proliferating tumor-specific CTL were poorly (=2%) transduced by the oncoretroviral vector that transduced Jurkat T cell line efficiently (=80%). In contrast, three lentiviral vectors transduced 38-63% of these proliferating CTL. More interestingly, all lentiviral vectors packaged without the HIV-1 accessory proteins transduced human bulk PBL and purified CD4(+) and CD8(+) lymphocyte subsets without prior stimulation. Detailed analysis indicated that the lentiviral vectors containing the EF1 alpha or PGK ubiquitous promoter can transduce unstimulated PBL and achieve low-level transgene expression in the absence of any T-cell activation. However, T-cell activation subsequent to the transduction of unstimulated PBL is required for high-level transgene expression. Transduced PBL expressing transgene delivered by the lentiviral vectors still preserved resting and naïve cell phenotypes. Taken together, prior T cell stimulation and HIV-1 accessory proteins are dispensable for lentivirus-mediated gene transfer into resting naïve and memory T lymphocytes. These results will have significant implications for the study of T-cell biology and for the improvement of clinical gene therapies of acquired immune deficiency syndrome (AIDS) and cancer.

Animals↗
PubMed2003

[Human papillomavirus infection and other risk factors for cervical cancer in Chinese and Australian patients].

OBJECTIVE: To investigate the infection rate and genotypes of HPV in cervical cancer and analyse the clinicopathological characteristics and risk factors for cervical cancer with HPV infection in Chinese and Australian patients. METHODS: The human papillomavirus (HPV) DNA in cervical cancer specimens from 115 Chinese women and 79 Australian women was detected by polymerase chain reaction.HPV types were determined by sequencing and reverse hybridization. The relationship a between the HPV types and the clinicopathological characteristics of cervical cancer in Chinese and Australian women were analyzed. RESULTS: HPV DNA positive rate was 76. 5% in the Chinese women (88/115) and 89.9% in the Australian women (71/79, P = 0. 017). There were no significant differences of HPV 16 and HPV 18 prevalence between the two groups (P = 0. 806). HPV 58 and 59 were more prevalent in Chinese women (both 6. 8%) than in Australian women (1. 4% and 0). In China, HPV 58 prevalence rate was significantly higher in the Hunan region than in the Guangdong region (P = 0. 007). The mean ages at diagnosis was 44. 24 +/- 11. 31 years for Chinese and 53.08 +/- 16. 54 years for Australian women (P <0. 001). Combining the two groups, no relationship was found between HPV positivity/negativity and the FIGO stage, macroscopic features, histological type and grade of tumour, as well as pelvic lymphatic metastasis. However, HPV type wa significantly correlated with the histological type (P < 0. 001 ) and grade of cervical tumour (P = 0. 028). In comparison with the Chinese group, the Australian group presented more advanced cancers, a greater proportion of endocervical patterns, and more non-squamous cell carcinoma. There were no significant differences in grade of tumour and lymphatic node status between the two groups. CONCLUSION: The HPV infection rate in cervical cancer patients is significantly higher among Australians than among Chinese, which may be caused by more sexual transmitted diseases and more sex partners among the former group. HPV 58 and HPV 59 tie for third common genotypes in cervical cancers in China, however, these types are uncommon in Australia. There was a significant variation in types of HPV infection among different histological type and grade of cervical tumors. Both HPV 18 and 59 appear to be associated with the malignancy of cervical cancer.

Australia↗
PubMed2003

[Basic research on neck dissection with external jugular vein and cervical plexus preserved].

OBJECTIVE: The aim of this study was to investigate the effects of preserving external jugular vein and cervical plexus in reducing intra-cranial pressure, face swelling as well as in avoiding shoulder arm syndrome in neck dissection. METHODS: 20 patients with oral cancer were divided into two groups. The facial interstitial pressure was examined before and after neck dissection and lymph tubes were stained by immunochemical techniques. RESULTS: The degree and lasting time of the increase of facial interstitial pressure in group with external jugular vein and cervical plexus preserved was lower than that in control group. The density of lymphatic tubes around the internal jugular vein, accessory nerve and sternocleidomastoid muscles was much higher than that around the external jugular vein and cervical plexus. CONCLUSION: Preserving external jugular and cervical plexus during radical treatment is effective not only in reducing the intra-cranial pressure and face swelling, but also in preventing shoulder arm syndrome.

Adult↗
PubMed2003

Interconversion of ATP binding and conformational free energies by tryptophanyl-tRNA synthetase: structures of ATP bound to open and closed, pre-transition-state conformations.

Binding ATP to tryptophanyl-tRNA synthetase (TrpRS) in a catalytically competent configuration for amino acid activation destabilizes the enzyme structure prior to forming the transition state. This conclusion follows from monitoring the titration of TrpRS with ATP by small angle solution X-ray scattering, enzyme activity, and crystal structures. ATP induces a significantly smaller radius of gyration at pH=7 with a transition midpoint at approximately 8mM. A non-reciprocal dependence of Trp and ATP dissociation constants on concentrations of the second substrate show that Trp binding enhances affinity for ATP, while the affinity for Trp falls with the square of the [ATP] over the same concentration range ( approximately 5mM) that induces the more compact conformation. Two distinct TrpRS:ATP structures have been solved, a high-affinity complex grown with 1mM ATP and a low-affinity complex grown at 10mM ATP. The former is isomorphous with unliganded TrpRS and the Trp complex from monoclinic crystals. Reacting groups of the two individually-bound substrates are separated by 6.7A. Although it lacks tryptophan, the low-affinity complex has a closed conformation similar to that observed in the presence of both ATP and Trp analogs such as indolmycin, and resembles a complex previously postulated to form in the closely-related TyrRS upon induced-fit active-site assembly, just prior to catalysis. Titration of TrpRS with ATP therefore successively produces structurally distinct high- and low-affinity ATP-bound states. The higher quality X-ray data for the closed ATP complex (2.2A) provide new structural details likely related to catalysis, including an extension of the KMSKS loop that engages the second lysine and serine residues, K195 and S196, with the alpha and gamma-phosphates; interactions of the K111 side-chain with the gamma-phosphate; and a water molecule bridging the consensus sequence residue T15 to the beta-phosphate. Induced-fit therefore strengthens active-site interactions with ATP, substantially intensifying the interaction of the KMSKS loop with the leaving PP(i) group. Formation of this conformation in the absence of a Trp analog implies that ATP is a key allosteric effector for TrpRS. The paradoxical requirement for high [ATP] implies that Gibbs binding free energy is stored in an unfavorable protein conformation and can then be recovered for useful purposes, including catalysis in the case of TrpRS.

Adenosine Triphosphate↗
PubMed2003

A set of genes selectively expressed in murine dendritic cells: utility of related cis-acting sequences for lentiviral gene transfer.

Professional antigen presenting cells such as dendritic cells (DC) and macrophages (Mphi) share similar characteristics; however, they differ in their ability to initiate an immune response. DCs are much more potent in priming and stimulating nai;ve T-cells. Thus, DCs are good targets for the expression of foreign genes to elicit and specifically modify immune responses. To identify DC markers cDNA subtraction was performed using murine MHC class II(high), B7(high) bone marrow derived DCs as tester and interferon-gamma/E. coli lipopolysaccaride (LPS) treated bone marrow derived macrophages as driver. Analysis of 114 resulting clones revealed a diverse pattern of DC selective (DC(DeltaMphi)) gene expression including known genes whose expression in DCs had not been previously demonstrated as well as multiple novel genes. For several identified DC(DeltaMphi) genes, proximal promoter elements were isolated and incorporated into self-inactivating lentiviral GFP reporter vectors. Promoter activity was measured in bone marrow derived macrophages or dendritic cells. Of the promoters analyzed those for B7-DC and CCL17 drove strong GFP expression in DCs but not in resting or activated macrophages. The CCL17 promoter offered the highest level of expression in DCs and was further activated by culture with LPS or interleukin-4 (IL-4). In contrast, the B7-DC promoter was induced by IL-4 but not by LPS. Endogenous CCL17 and B7-DC mRNAs were increased similarly in IL-4 cultured DCs but only CCL17 was induced by LPS. Additionally, IL-4 increased cell surface expression of B7-DC in both immature and mature DCs.

Animals↗
PubMed2003

Crystal structure of an inactive Akt2 kinase domain.

Akt/PKB represents a subfamily of three isoforms from the AGC serine/threonine kinase family. Amplification of Akt activity has been implicated in diseases that involve inappropriate cell survival, including a number of human malignancies. The structure of an inactive and unliganded Akt2 kinase domain reveals several features that distinguish it from other kinases. Most of the alpha helix C is disordered. The activation loop in this structure adopts a conformation that appears to sterically hinder the binding of both ATP and peptide substrate. In addition, an intramolecular disulfide bond is observed between two cysteines in the activation loop. Residues within the linker region between the N- and C-terminal lobes also contribute to the inactive conformation by partially occupying the ATP binding site.

Adenosine Triphosphate↗
PubMed2003

[Therapeutic effects of octreotide on hepatofibrosis-induced with carbon tetrachloride in rats].

OBJECTIVES: To investigate the therapeutic effects and mechanism of octreotide on experimental hepatic fibrosis in rats. METHODS: Hepatofibrotic rats models were established with carbon tetrachloride. All the experimental rats were divided into four groups: normal control group, pre-and post-treatment model group, and octreotide-treated group in which the rats were injected subcutaneously with octreotide at the dose of 50ng/100g, twice daily, for thirty days. Serum levels of hyaluronic acid (HA), laminin (LN) and pro-collagen type III peptide (PCIII) were detected by radioimmunoassay. Hepatic fibrosis scoring grade was assessed through Van-Gieson staining and observed under light microscope. Protein expression levels of alpha-smooth muscle actin (alpha-SMA) and transforming growth factor beta1 (TGFbeta1) were determined with immunohistochemical staining method. Messenger RNA (mRNA) levels of collagen type I and PCIII were detected by reverse transcription polymerase chain reaction. RESULTS: Serum levels of HA (ng/L), LN (microg/L) and PCIII (ng/L) in pre- and post-treatment model groups were higher than those in normal control group (121.8+/-9.5 and 110.3+/-13.4 vs. 33.1+/-3.7, 85.7+/-12.1 and 78.2+/-7.9 vs. 37.1+/-6.3, 35.9+/-3.5 and 33.7+/-2.6 vs. 15.6+/-2.8, respectively, t > or = 9.41, P<0.05), and there was no significant difference between the two model groups. Concentrations of HA (55.8ng/L+/-7.2ng/L), LN (43.1microg/L+/-3.4microg/L) and PCIII (27.8ng/L+/-3.4ng/L) decreased significantly in octreotide-treated group, compared with those in model groups (t >or=2.76, P<0.05). With histological analysis, fibrotic scoring grade in octreotide-treated group was obviously ameliorated, compared with that in model groups (chi2 > or = 3.97, P<0.05). Imaging analysis revealed that alpha-SMA and TGFbeta1 immunohistological staining areas were markedly shrinked in octreotide-treated group (t > or = 2.47, P < 0.05). In two model groups, PCIII and type I mRNA levels significantly up-regulated as compared with those in normal group (t > or = 9.27, P<0.001), and they were inhibited by octreotide markedly (t > or = 2.47, P<0.05). CONCLUSIONS: Octreotide can inhibit hepatic stellate cells transforming into myofibroblasts, down-regulate TGFbeta1, collagen type I and PCIII transcriptions, so that it has therapeutic effects on experimental hepatic fibrosis.

Actins↗
PubMed2003

[The neck treatment of cN0 patients with squamous cell carcinoma of buccal mucosa].

OBJECTIVE: The purpose of this study was to discuss the principle in neck treatment of cN0 patients with squamous cell carcinoma of buccal mucosa. METHODS: 101 patients of squamous cell carcinoma of buccal mucosa at the stage of cN0, who had hospitalized in West China College of Stomatology, Sichuan University from 1980 to 2000, were investigated retrospectively. All the patients received a comprehensive therapy consisting of surgical procedures combined with chemotherapy and radiotherapy. The combining radical therapy of buccal, mandible and neck was the main surgical method. Lymph nodes were cleared after operation and examined by pathological method. The patients had been followed up for more than 3 years. RESULTS: 17 patients had lymph nodes metastasis, the occult metastasis (OM) rate was 16.83%. It increased in the high stage of original lesion, the OM rate of T3 and T4 was 18.18% and 52.00%, respectively. The metastasized lymph nodes were mainly located in submandible and superior deep cervix lymph nodes, their respective metastasis rate was 41.18% and 29.41%. CONCLUSION: The rate of occult metastasis of squamous cell carcinoma of buccal mucosa is high, and then we should adopt actively selective neck dissection for the cN0 patients of squamous cell carcinoma of buccal mucosa.

Carcinoma, Squamous Cell↗
PubMed2003

[Treatment to cN0 patients with oral squamous cell carcinoma].

OBJECTIVE: To investigate the regularity of cervical lymph-node metastasis in oral squamous cell carcinoma patients and determine the treatment principle to cN0 patients. METHODS: 1,024 oral squamous cell carcinoma cases who underwent neck dissection between 1980-2001 were investigated retrospectively. RESULTS: The total rate of cervical lymph-node metastasis of oral squamous cell carcinoma was 36.62% (375/1,024), the metastasis rate of cancer in tongue, buccal, gingival, and floor of mouth was 42.82%, 31.93%, 32.76%, and 25.00%, respectively; the rate of occult metastasis was 20.94%(71/339), the incidence of occult metastasis was closely related to the location of primary lesion and T stage. CONCLUSION: The results in this study revealed that the therapy regime of the oral squamous cell carcinoma should be based on carefully clinical examination and compositive analysis on primary lesion related to size, location and cervical lymph-node.

Adolescent↗
PubMed2002

Perception of brightness and brightness illusions in the macaque monkey.

Recent physiological studies show that neural responses correlated with the perception of brightness are found in cortical area V1 but not earlier in the visual pathway (Kayama et al., 1979; Reid and Shapley, 1989; Squatrito et al., 1990; Komatsu et al., 1996; Rossi et al., 1996; MacEvoy et al., 1998; Rossi and Paradiso, 1999; Hung et al., 2001; Kinoshita and Komatsu, 2001; MacEvoy and Paradiso, 2001). However, these studies are based on comparisons of neural responses in animals with brightness perception in humans. Very little is known about the perception of brightness in animals typically used in physiological experiments. In this study, we quantify brightness discrimination, brightness induction, and White's effect in macaque monkeys. The results show that, qualitatively and quantitatively, the perception of brightness in macaques and humans is quite similar. This similarity may be an indication of common underlying neural computations in the two species.

Animals↗
PubMed2002

High-resolution mapping of the 11q13 amplicon and identification of a gene, TAOS1, that is amplified and overexpressed in oral cancer cells.

Amplification of chromosomal band 11q13 is a common event in human cancer. It has been reported in about 45% of head and neck carcinomas and in other cancers including esophageal, breast, liver, lung, and bladder cancer. To understand the mechanism of 11q13 amplification and to identify the potential oncogene(s) driving it, we have fine-mapped the structure of the amplicon in oral squamous cell carcinoma cell lines and localized the proximal and distal breakpoints. A 5-Mb physical map of the region has been prepared from which sequence is available. We quantified copy number of sequence-tagged site markers at 42-550 kb intervals along the length of the amplicon and defined the amplicon core and breakpoints by using TaqMan-based quantitative microsatellite analysis. The core of the amplicon maps to a 1.5-Mb region. The proximal breakpoint localizes to two intervals between sequence-tagged site markers, 550 kb and 160 kb in size, and the distal breakpoint maps to a 250 kb interval. The cyclin D1 gene maps to the amplicon core, as do two new expressed sequence tag clusters. We have analyzed one of these expressed sequence tag clusters and now report that it contains a previously uncharacterized gene, TAOS1 (tumor amplified and overexpressed sequence 1), which is both amplified and overexpressed in oral cancer cells. The data suggest that TAOS1 may be an amplification-dependent candidate oncogene with a role in the development and/or progression of human tumors, including oral squamous cell carcinomas. The approach described here should be useful for characterizing amplified genomic regions in a wide variety of tumors.

Amino Acid Sequence↗
PubMed2002

Site-directed mutagenesis and functional analysis of an active site tryptophan of insect chitinase.

Chitinase is an enzyme used by insects to degrade the structural polysaccharide, chitin, during the molting process. Tryptophan 145 (W145) of Manduca sexta (tobacco hornworm) chitinase is a highly conserved residue found within a second conserved region of family 18 chitinases. It is located between aspartate 144 (D144) and glutamate 146 (E146), which are putative catalytic residues. The role of the active site residue, W145, in M. sexta chitinase catalysis was investigated by site-directed mutagenesis. W145 was mutated to phenylalanine (F), tyrosine (Y), isoleucine (I), histidine (H), and glycine (G). Wild-type and mutant forms of M. sexta chitinases were expressed in a baculovirus-insect cell line system. The chitinases secreted into the medium were purified and characterized by analyzing their catalytic activity and substrate or inhibitor binding properties. The wild-type chitinase was most active in the alkaline pH range. Several of the mutations resulted in a narrowing of the range of pH over which the enzyme hydrolyzed the polymeric substrate, CM-Chitin-RBV, predominantly on the alkaline side of the pH optimum curve. The range was reduced by about 1 pH unit for W145I and W145Y and by about 2 units for W145H and W145F. The W145G mutation was inactive. Therefore, the hydrophobicity of W145 appears to be critical for maintaining an abnormal pKa of a catalytic residue, which extends the activity further into the alkaline range. All of the mutant enzymes bound to chitin, suggesting that W145 was not essential for binding to chitin. However, the small difference in Km's of mutated enzymes compared to Km values of the wild-type chitinase towards both the oligomeric and polymeric substrates suggested that W145 is not essential for substrate binding but probably influences the ionization of a catalytically important group(s). The variations in kcat's among the mutated enzymes and the IC50 for the transition state inhibitor analog, allosamidin, indicate that W145 also influences formation of the transition state during catalysis.

Amino Acid Substitution↗
PubMed2002

Mutant tyrosine kinases with unnatural nucleotide specificity retain the structure and phospho-acceptor specificity of the wild-type enzyme.

The direct substrates of one protein kinase in a cell can be identified by mutation of the ATP binding pocket to allow an unnatural ATP analog to be accepted exclusively by the engineered kinase. Here, we present structural and functional assessment of peptide specificity of mutant protein kinases with unnatural ATP analogs. The crystal structure (2.8 A resolution) of c-Src (T338G) with N(6)-(benzyl) ADP bound shows that the creation of a unique nucleotide binding pocket does not alter the phospho-acceptor binding site of the kinase. A panel of optimal peptide substrates of defined sequence, as well as a degenerate peptide library, was utilized to assess the phospho-acceptor specificity of the engineered "traceable" kinases. The specificity profiles for the mutant kinases were found to be identical to those of their wild-type counterparts.

Amino Acid Sequence↗