Biomedical subjects

Min Zhuang

Publications and source records attributed to Min Zhuang.

15 recordsLinked to original sources

PubMed2006

The mismatch repair protein Msh6 influences the in vivo AID targeting to the Ig locus.

Somatic hypermutation (SHM) and class switch recombination (CSR) are initiated by activation-induced cytidine deaminase (AID), which preferentially deaminates deoxycytidines at WRC (W = A/T, R = A/G) motifs in vitro. The mechanisms responsible for targeting AID and for organizing the queue of enzymes involved in vivo have been elusive. Here, we examined point mutant knockin Msh6 mice (Msh6(TD/TD)), which lack the second phase of SHM but retain all the proteins involved, and found that AID was frequently targeted to non-WRC motifs. Unexpectedly, by comparing SHM and CSR in wild-type, Msh6(TD/TD), and age-matched Msh6(-/-) mice, we discovered that the presence of Msh6 protein influenced the AID targeting in phase one of SHM and mediated the proper targeting of recombination sites in CSR in vivo. Our data suggest that Msh6 plays a scaffolding role in the first phase of SHM, in addition to its enzymatic role in the second phase of SHM.

Animals↗

PubMed2006

YMDD mutations and genotypes of hepatitis B virus in northern China.

The objective of this research was to determine the relationship between YMDD mutations and the genotypes of hepatitis B virus (HBV) during lamivudine treatment. HBV genotypes were determined by nested PCR with 6 pairs of HBV genotype-specific primers (A to F) in serum specimens from 142 hepatitis B patients receiving lamivudine antiviral therapy. YMDD mutations were detected by fluorescent hybridization bioprobe PCR and melting curve assay (FH-PCR-MC). Among 142 serum specimens, 13 samples were genotype B (9.2%), 125 samples were genotype C (88%), 4 samples were genotype D (2.8%), and 80 YMDD mutations were found. The YMDD mutation rates were 69.2 and 54.4% in genotype B and genotype C, respectively. There was no significant difference in the YMDD mutation rate between genotypes B and C. Nine genotype B sera with YMDD mutations were found, including 2 YIDD mutations and 7 YVDD (M + V) mutations. Sixty-eight genotype C sera with YMDD mutations were found, including 34 mutations I (M + I) and 17 mutations V (M + V). There was a significant difference in the YMDD mutation types between genotypes B and C. Our results suggested that the YMDD mutation rate was 56.3% in patients treated with lamivudine for 2-4 years. YIDD was the main mutation type. The YMDD mutation rate showed no significant difference between HBV types B and C (P > 0.05), while the YMDD mutation types showed a significant difference between HBV types B and C in Northern China (chi2 test = 4.6, P < 0.05).

Antiviral Agents↗

PubMed2005

p27kip1 in intestinal tumorigenesis and chemoprevention in the mouse.

Targeted inactivation of p27(kip1) was sufficient for intestinal tumor formation in mice, but this was strictly a function of diet: tumors formed in p27(+/-) or p27(-/-) mice fed control AIN-76A diet and were increased by a western-style diet but did not develop in mice fed standard chow diet. When crossed with the Apc1638N(+/-) mouse, Apc(+/-),p27(+/-) or Apc(+/-),p27(-/-) mice not only formed twice as many tumors than the sum of the tumors from mutation at either locus alone, but on AIN76A diet also developed intestinal intussusception, a tumor-associated pathology in patients leading to intestinal blockage that has not been reported for intestinal cancer in mouse models. Moreover, the frequency of intussusception was increased when the compound mutant mice were maintained on the western diet, leading to early death. Despite this more aggressive tumor phenotype generated by inactivation of p27 than by inactivation of another cyclin-dependent kinase inhibitor, p21(WAF1/cip1), the nonsteroidal anti-inflammatory drug sulindac was still effective in inhibiting intestinal tumor formation in Apc(+/-),p27(+/-) or Apc(+/-),p27(-/-) mice, which contrasts with the abrogation of the effects of sulindac in Apc(+/-),p21(+/-) or Apc(+/-),p21(-/-) mice, indicating that p27 is not necessary for tumor inhibition by sulindac. Furthermore, tumor inhibition by sulindac was linked to the induction of p21 expression by the drug, regardless of p27 status, leading to suppression of cell proliferation and promotion of cell differentiation and apoptosis in the intestinal mucosa.

Alleles↗

PubMed2005

Side-chain effects in molecular electronic devices.

We discuss the effect of an abundant structural element of molecules on the transmission probabilities of molecular electronic devices. We show that an attachment of side chains to a molecular conductor may lead to zero transmission probabilities. The gaps in the transmission-probability appear approximately at the eigenvalues of the isolated side chains, provided that the corresponding eigenstates are not localized away from the molecular conductor. Simple Hückel-type calculations serve to illustrate the described effect. Furthermore, we show that complex transmission-probability curves, obtained with Kohn-Sham density-functional theory, also exhibit the described side-chain effect.

Journal Article↗

PubMed2005

Approximate density functionals applied to molecular quantum dots.

Recently, molecular quantum dots (MQDs) have been investigated experimentally and found to exhibit the Kondo effect. The Kondo effect leads to an enhancement of the zero-voltage conductance. Here, we study a finite cluster model of a MQD by means of Kohn-Sham density functional theory. Furthermore, employing an implementation of Landauer's formula, we calculate the conductance of the dot. We find that the electronic structure and the molecular conductance depend strongly on the exchange-correlation functional employed. While the local spin density approximation and the Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation qualitatively reproduce certain features of the Kondo effect, PBE hybrid does not. Based on the MQD, we discuss the limitations of using density functional theory to model molecular electronic devices.

Journal Article↗

PubMed2005

Structural basis for recruitment of Ubc12 by an E2 binding domain in NEDD8's E1.

E2 conjugating enzymes play a central role in ubiquitin and ubiquitin-like protein (ublp) transfer cascades: the E2 accepts the ublp from the E1 enzyme and then the E2 often interacts with an E3 enzyme to promote ublp transfer to the target. We report here the crystal structure of a complex between the C-terminal domain from NEDD8's heterodimeric E1 (APPBP1-UBA3) and the catalytic core domain of NEDD8's E2 (Ubc12). The structure and associated mutational analyses reveal molecular details of Ubc12 recruitment by NEDD8's E1. Interestingly, the E1's Ubc12 binding domain resembles ubiquitin and recruits Ubc12 in a manner mimicking ubiquitin's interactions with ubiquitin binding domains. Structural comparison with E2-E3 complexes indicates that the E1 and E3 binding sites on Ubc12 may overlap and raises the possibility that crosstalk between E1 and E3 interacting with an E2 could influence the specificity and processivity of ublp transfer.

Amino Acid Sequence↗

PubMed2005

Inactivation of p21WAF1/cip1 enhances intestinal tumor formation in Muc2-/- mice.

In the Apc1638(+/-) mouse model of intestinal tumorigenesis, targeted inactivation of the cyclin-dependent kinase inhibitor p21(WAF1/cip1) is highly effective in enhancing Apc-initiated tumor formation in the intestine. Because p21(WAF1/cip1) plays a critical role in regulating intestinal cell proliferation, maturation, and tumorigenesis, we examined whether its inactivation would enhance tumor formation in a different mouse model of colon cancer. Therefore, we mated p21(-/-) mice with mice carrying a genetic deficiency of the Muc2 gene, which encodes the major gastrointestinal mucin. Muc2(-/-) mice develop tumors in the small and large intestine and the rectum, but in contrast to tumors in Apc1638(+/-) mice, this does not involve increased expression or nuclear localization of beta-catenin. We found that inactivation of p21(WAF1/cip1) significantly increased the frequency and size of intestinal tumors in Muc2 knockout mice and also led to development of more invasive adenocarcinomas. This enhanced tumorigenesis significantly decreased mouse life span. Further, inactivation of p21(WAF1/cip1) increased cell proliferation, decreased apoptosis, and decreased intestinal trefoil factor expression in the mucosa of both the small and large intestine. Surprisingly, reduced expression of p27(kip1) was also observed in the Muc2(-/-), p21(+/-), and p21(-/-) mice. In contrast, the expression of c-myc was significantly elevated. Thus, p21 modulates the formation of tumors whose initiation does (Apc) or does not (Muc2) involve altered beta-catenin-Tcf4 signaling, but which may converge on common elements downstream of this signaling pathway.

Adenocarcinoma↗

PubMed2005

Gene expression profiling of intestinal epithelial cell maturation along the crypt-villus axis.

BACKGROUND & AIMS: To define the genetic reprogramming that drives intestinal epithelial cell maturation along the crypt-villus axis, enterocytes were sequentially isolated from the villus tip to the crypts of mouse small intestine. METHODS: Changes in gene expression were assessed using 27,405-element complementary DNA microarrays (14,685 unique genes) and specific changes validated by Western blotting. RESULTS: A total of 1113 genes differentially expressed between the crypt and villus were identified. Among these, established markers of absorptive and goblet cell differentiation were up-regulated in villus cells, whereas Paneth cell markers were maximally expressed in crypt cells. The 1113 differentially expressed genes were significantly enriched for genes involved in cell cycle progression, RNA processing, and translation (all predominantly down-regulated during maturation) and genes involved in cytoskeleton assembly and lipid uptake (predominantly up-regulated during maturation). No enrichment for apoptosis-regulating genes was observed. We confirmed that Wnt signaling was maximal in the proliferative compartment and observed a decrease in MYC and an increase in MAD and MAX expression during the maturation program. Consistent with these changes, the 1113 genes were enriched for MYC targets, establishing the importance of this network in intestinal cell maturation. CONCLUSIONS: This database serves as a resource for understanding the molecular mechanisms of intestinal cell maturation and for dissection of how perturbations in the maturation process can lead to changes in gastrointestinal physiology and pathology, particularly intestinal tumorigenesis.

Animals↗

PubMed2005

[Distribution and species of mercury in water and sediments from Huangpu River].

Levels of total mercury, soluble mercury and particle mercury in water of Huangpu River change greatly, their average values are (0.4 +/- 0.44) ng/mL, (0.27 +/- 0.42)ng/mL, (0.13 +/- 0.10) ng/mL respectively. Mercury in water is mainly in the form of soluble mercury. Average mercury content in sediment of Huangpu River is relative high and up to (204.03 +/- 97.41) ng/g, with a range of 70.52 ng/g - 387.30 ng/g. Mercury content is high in the middle reach of Huangpu River, especially in section of Xidu-Nanpu Bridge, and low in upstream and downstream. Distribution of mercury is hightly related with distribution of industry plants and farming. Locations with high mercury content in sediment are in the downstream of locations with high mercury content in water. Mercury (in sediments) is mainly in the form of residue, exchangeable ions, and humics-bound, seldom is in the form of carbonate-bound. Contrary to residue-bound mercury, exchangeable mercury is low in the middle reach, and high in upstream and downstream. There mainly are residue-bound mercury and little humics-bound mercury, exchangeable mercury, and carbonate-bound mercury in sediment in profile, and the residue-bound mercury increases irregularly with depth. Nearing the Mouth of Yangtze River, mercury in sediment becomes more active.

China↗

PubMed2004

Quantitative rather than qualitative differences in gene expression predominate in intestinal cell maturation along distinct cell lineages.

Several cell types are present in the intestinal epithelium that likely arise from a common precursor, the stem cell, and each mature cell type expresses a unique set of genes that characterizes its functional phenotype. Although the process of differentiation is intimately linked to the cessation of proliferation, the mechanisms that dictate intestinal cell fate determination are not well characterized. To investigate the reprogramming of gene expression during the cell lineage allocation/differentiation process, we took advantage of a unique system of two clonal derivatives of HT29 cells, Cl16E and Cl19A cells, which spontaneously differentiate as mucus producing goblet and chloride-secreting cells, respectively, as a function of time. By profiling gene expression, we found that these two cell lines show remarkably similar kinetics of change in gene expression and common clusters of coordinately regulated genes. This demonstrates that lineage-specific differentiation of intestinal epithelial cells is characterized overall by the sequential recruitment of functionally similar gene sets independent of the final phenotype of the mature cells.

Animals↗

PubMed2004

Examination of Msh6- and Msh3-deficient mice in class switching reveals overlapping and distinct roles of MutS homologues in antibody diversification.

Somatic hypermutation and class switch recombination (CSR) contribute to the somatic diversification of antibodies. It has been shown that MutS homologue (Msh)6 (in conjunction with Msh2) but not Msh3 is involved in generating A/T base substitutions in somatic hypermutation. However, their roles in CSR have not yet been reported. Here we show that Msh6(-)(/)(-) mice have a decrease in CSR, whereas Msh3(-)(/)(-) mice do not. When switch regions were analyzed for mutations, deficiency in Msh6 was associated with an increase in transition mutations at G/C basepairs, mutations at RGYW/WRCY hotspots, and a small increase in the targeting of G/C bases. In addition, Msh6(-)(/)(-) mice exhibited an increase in the targeting of recombination sites to GAGCT/GGGGT consensus repeats and hotspots in Sgamma3 but not in Smicro. In contrast to Msh2(-)(/)(-) mice, deficiency in Msh6 surprisingly did not change the characteristics of Smicro-Sgamma3 switch junctions. However, Msh6(-)(/)(-) mice exhibited a change in the positioning of Smicro and Sgamma3 junctions. Although none of these changes were seen in Msh3(-)(/)(-) mice, they had a higher percentage of large inserts in their switch junctions. Together, our data suggest that MutS homologues Msh2, Msh3, and Msh6 play overlapping and distinct roles during antibody diversification processes.

Animals↗

PubMed2004

Zero-voltage conductance of short gold nanowires.

Using the Landauer formula, the conductance of short gold wires is studied. The required electronic structure calculations are performed with a self-consistent tight-binding method. We consider gold wires of single-atom diameter with a variable number (N=1, em leader,5) of atoms. Depending on N, we find considerable conductance variations with one conductance quantum being the upper limit. The results are confirmed by means of Friedel's sum rule. Tip-shaped clusters are used to provide the contact-wire interfaces and the relation between various tip structures and the conductance is discussed. Our predictions about the conductance variations agree qualitatively with new experimental results.

Journal Article↗

PubMed2004

[Effect of IL-6/sIL-6R on ex vivo expansion of human cord blood derived CD34+ cells].

BACKGROUND & OBJECTIVE: Hematopoietic stem cells (HSC) have the ability of regeneration, differentiation, and reconstructing hematopoietic function, and it is widely used in many fields such as hematopoietic stem cell transplantation, immune therapy, gene therapy and so on. Human cord blood (CB) is abundant of HSC. But a single collection of CB has only a limited amount of HCS and cannot fit the clinical and research use. Thus ex vivo expansion of human CB derived HSC is important. We know that there are some cytokines, which can synergize for enhancing the expansion of CB derived CD34(+) cells in vitro. Currently, some experiments have discovered that IL-6/sIL-6R or its chimera can enhance the ex vivo expansion of CD34(+)gp130+IL-6R- subpopulation. This study was designed to observe the effect of IL-6/sIL-6R on the ex vivo expansion of human CB derived CD34(+) cells, and explore the optimal cytokine combinations. METHODS: Human CB derived CD34(+) cells were isolated by Mini MACS and cultured in ex vivo liquid media in the presence of different cytokine cocktails for 7 or 14 days. After cultured on the seventh or the fourteenth day, the total number of the cultured cells were counted, the ratio of the CD34(+) cell were assayed by flow cytometry (FCM) and the number of it were calculated, and CFU-GM were cultured, then the effects of different cytokine combinations on the ex vivo expansion of CD34(+) cells were compared. In line with the different cytokine cocktails, our experiment divided into five groups: (A) control,(B) SCF,(C) IL-6/sIL-6R+SCF,(D) IL-6/sIL-6R+SCF+FL,and (E) SCF+FL. RESULTS: After cultured in vitro for 7 or 14 days, (1) the number of CD34(+) cells descended apparently in groups A and B; (2) the number of nucleated cells and CD34(+) cells after cultural on the seventh or the fourteenth day increased 7.1+/-2.4 folds, 39.0+/-14.0 folds; 1.8+/-0.7 folds, 4.8+/-2.4 folds, respectively in group C; 16.5+/-5.7 folds, 110.0+/-28.0 folds; 3.5+/-1.5 folds, 10.2+/-4.2 folds in Group D; 17.3+/-3.8 folds, 104.0+/-21.0 folds; 3.6+/-2.1folds, 8.4+/-3.5 folds in Group E. The expansion effects of group C, D, and E were all superior to the group A or B (P< 0.01). The expansion effects of group D and E were superior to group C (P< 0.01). But there was no difference between group D and E (P >0.05); (3) Adding the concentration of sIL-6R to 400 ng/ml, the number of nucleated and CD34(+) cells increased 24.0+/-4.8 folds and 5.6+/-1.2 folds in group D after cultured for seven days superior to group E (P< 0.05). CONCLUSION: IL-6/sIL-6R, SCF, FL can synergize for enhancing the ex vivo expansion of human CB derived CD34(+) cells. But this synergetic effect depends on the concentration of sIL-6R.

Antigens, CD34↗

PubMed2002

Synthesis of Ser-His-Gly.DNA conjugates.

There are strong interactions between the bases of oligonucleotides. Based on Watson-Crick principle, they can form stable secondary and tertiary structure such as hairpin, duplex, triplex, G-quartet, pseudoknot, which can serve as the scaffold of molecules. Peptides contain active groups such as amino, carboxyl, imidazole, hydroxyl. A protected Ser-His-Gly-Threoninol phosphoramidite was synthesized in this work and was incorporated into a triplex-forming oligonucleotide. The results indicate that the oligonucleotide containing Ser-His-Gly-Threoninol in the middle could still form triplex with the target duplex and the dissociation constant was 0.5 micromol/L.

DNA↗

PubMed2002

[Expression and purification of human papillomavirus type16 L1 protein in a prokaryotic expression system].

This study was intended to establish a method of purification of HPV16 L1 protein expressed in a prokaryotic system and to obtain the purified protein. The prokaryotic expression vector pGEX-4T-1-HPV16 L1 was constructed and transformed into E. coli BL21 cell, and induced by 1 mM IPTG to express HPV16L1 protein. The inclusion bodies were isolated and solubilized with 8 M urea. After the urea was removed by gradual dialysis, the denatured L1 protein were renatured and then were purified by affinity chromatography. The results showed that HPV16L1 protein formed inclusion bodies in bacterial expression system, suggesting that this assay can be used to purify HPV16L1 protein and hence provide a basis for studying the applications of HPV16 L1 protein.

Capsid Proteins↗