Biomedical subjects

H Xin

Publications and source records attributed to H Xin.

At least 19 recordsLinked to original sources

PubMed2002

Drinking water temperature effects on laying hens subjected to warm cyclic environments.

Two experiments were conducted to evaluate the effects of drinking water temperature (Tw) on laying hens subjected to warm cyclic air temperature (Ta) conditions. Each experiment consisted of a 1-wk acclimation under thermoneutrality (TN) (Ta = Tw = 21 C), a 4-wk heat exposure or treatment period, and a 2-wk recovery under TN. Each experiment involved 24 individually caged hens at the initial age of 29 wk (Experiment 1) or 30 wk (Experiment 2). In Experiment 1, Tw of 18 or 27 C was provided to 12 birds per Tw regimen under a diurnal Ta of 27 to 35 C (daily mean of 31 C). In Experiment 2, Tw of 15, 19, 23, or 27 C was provided to six birds per Tw regimen under a diurnal Ta of 27 to 38 C (daily mean of 32.5 C). Experiment 1 showed that Tw of 18 C enhanced hourly and daily feed and water intake during the first 2 wk of heat exposure, as compared with Tw of 27 C. Experiment 2 showed that daily feed and water intake were greatest for hens in the 23 C Tw regimen and least for hens in the coolest or warmest Tw regimens. Reduction in daily feed intake with increase in daily mean Ta ranged from 2.0 to approximately 3.2 g/C-day (first week of heat exposure) to 1.1 to approximately 1.9 g/C-day (fourth week of heat exposure). Water to feed intake ratio was 1.8 to approximately 2.0 during acclimation and recovery, but increased to 3.0 to approximately 3.4 during heat exposure. Internal egg quality parameters were in general unaffected by Tw. The two warmer Tw regimens in Experiment 2 had less reduction in egg size than did the two cooler Tw. In both experiments, hens displayed anticipatory increase in feed and water intake 2 to 3 h prior to lights-off. However, the stimulus of lights-on did not elicit a strong return to feed and water consumption as typically seen in broilers. The results revealed the potential existence of an optimal Tw range (near 23 C) for heat-chal lenged laying hens. Larger-scale tests are warranted to further verify the findings.

Acclimatization↗

PubMed2001

Effects of noise on the off rate of Ca(2+) binding proteins in a coupled biochemical cell system.

We investigated numerically the kinetic properties of calcium binding proteins by using a three-calcium store model and discussed the response of a two-way coupled biochemical cell system, whose subsystems were coupled via diffusion-like cytosolic calcium transfer through gap junctions, to the external stimulation. When we used noise to modulate the off rate of the Ca(2+) binding proteins in simulation, an SR-like phenomenon of synchronous oscillations is observed. In addition, the interaction involving noise, coupling and the dynamics of Ca(2+) binding proteins is discussed.

Animals↗

PubMed2001

Dynamics of spiral waves under the modulation of noise pulses.

This work aims at investigating the dynamics of spiral waves under the modulation of noise pulses. Both rigid rotating and meandering spirals are considered. The numerical simulations show that for meandering spirals there exists a minimal external radius of the tip trajectory at an optimal intensity when keeping the duration constant, or for an optimal duration when keeping the intensity constant. For rigid rotating spirals an interesting phenomenon is that the clockwise-counterclockwise transition of the trajectory occurs when we raise the duration of the noise pulse for a fixed intensity.

Journal Article↗

PubMed2001

p202, an interferon-inducible negative regulator of cell growth, is a target of the adenovirus E1A protein.

Studies have revealed that human adenovirus-encoded E1A protein promotes cell proliferation through the targeted interaction with cellular proteins that act as key negative regulators of cell growth. The targets of E1A protein include the retinoblastoma tumor suppressor protein (pRb). Because p202, an interferon (IFN)-inducible murine protein (52-kDa), negatively regulates cell growth in part through the pRb/E2F pathway, we tested whether the p202 is a target of the adenovirus-encoded E1A protein for functional inactivation. Here we report that the expression of E1A protein overcame p202-mediated inhibition of cell growth and this correlated with an alleviation of p202-mediated inhibition of the transcriptional activity of E2F. Furthermore, E1A protein relieved p202-mediated inhibition of the specific DNA-binding activity of E2F complexes, including those containing the pocket proteins. Additionally, the E1A protein bound to p202 both in vitro and in vivo and a deletion of four amino acids in the conserved region 2 (CR2) of E1A protein significantly reduced the binding of E1A to p202. Interestingly, ectopic expression of p202 under reduced serum conditions significantly reduced E1A-mediated apoptosis. Taken together, our observations provide support to the idea that the p202 and adenovirus E1A protein functionally counteract each other and E1A protein targets p202 to promote cell proliferation.

Adenovirus E1A Proteins↗

PubMed2001

Stochastic resonance induced by fluctuation in liquid membrane oscillator without input signals.

We investigated numerically the dynamic behavior of the oil/water liquid membrane, which is a promising model for excitable bio-membrane. When we use noise to modulate the parameters in simulation, noise-induced coherent oscillation is observed. With the increment of the noise intensity, the coherence of noise-induced oscillation can go through a maximum, which indicating the occurrence of stochastic resonance (SR) without input signals. We compared the SR effects under the condition that noise is added to different control parameters. When noise was added to both of the parameters, a complicated SR-like phenomemon was observed. The interaction of coherent SRs induced by two independent noises is discussed. The possibly constructive role of noise in some sensory cells is discussed also.

Computer Simulation↗

PubMed2001

The gene encoding p202, an interferon-inducible negative regulator of the p53 tumor suppressor, is a target of p53-mediated transcriptional repression.

The p53 tumor suppressor protein regulates the transcription of regulatory genes involved in cell cycle arrest and apoptosis. We reported previously that overexpression of p202, an interferon-inducible negative regulator of cell growth, negatively regulates the transcriptional activity of p53. Now we identify the gene encoding p202 as one whose mRNA and protein expression decrease in cells following the expression of wild-type, but not mutant, p53. Furthermore, the levels of p202 also decrease after exposure of cells to ultra violet light, which correlate with increase in the levels of p53. We report that the sequence-specific DNA binding of p53 to the 5'-regulatory region of the 202 gene contributes to the transcriptional repression of the 202 gene. Interestingly, overexpression of p202 in cells induced to undergo p53-dependent apoptosis significantly delays this process, indicating that the negative regulation of the 202 gene by wild-type p53 is important to potentiate apoptosis.

Animals↗

PubMed2001

Interactions between HMG boxes.

Many proteins consist of subdomains that can fold and function independently. We investigate here the interaction between the two high mobility group (HMG) box subdomains of the nuclear protein rHMG1. An HMG box is a conserved amino acid sequence of approximately 80 amino acids rich in basic, aromatic and proline side chains that is active in binding DNA in a sequence or structure-specific manner. In the case of HMG1, each box can bind structural DNA substrates including four-way junctions (4WJs) and branched or kinked DNA duplexes. Since proteins containing up to six HMG boxes are known, the question arises whether linking subdomains together influences the folding or function of individual boxes. In an effort to understand interactions between individual DNA-binding domains in HMG1, we created new fusion proteins: one is an inversion of the order of the AB di-domain in HMG1 (BA); in the second, we added a third A domain C-terminal to the AB di-domain (ABA). Pairs of boxes, AB or BA, behave similarly and are functionally active. By contrast, the ABA triple subdomain construct is partially unfolded and is less active than individual boxes or di-domains. Thus, long-range inter-domain effects can influence the activity of HMG boxes.

Amino Acid Sequence↗

PubMed2001

Syringocystadenoma papilliferum: a study of potential tumor suppressor genes.

Syringocystadenoma papilliferum (SP) is a benign tumor most commonly located on the scalp or face, which frequently arises from a nevus sebaceus (NS). Transition of SP to basal cell carcinoma (BCC) and, albeit rarely, to metastatic adenocarcinoma may occur. Allelic deletions of the human homologue of the drosophila patched gene (PTCH) occur in both NS and BCC. To search for genetic changes in SP, a microdissection-based genetic analysis using polymorphic markers at 9q22 (PTCH; D9S15, D9S303, D9S287, D9S252) as well as markers at 9p21 flanking the tumor suppressor gene p16 (IFNA, D9S171) was performed. Glandular epithelium consisting of two rows of cells as well as adjacent normal tissue or inflammatory infiltrates in the stroma, when present, was dissected and subjected to single-step DNA extraction and loss of heterozygosity (LOH) analysis. Two of 10 informative SP cases showed LOH at 9q22 (PTCH). Three of 7 informative SP cases showed allelic deletions at 9p21 (p16). Allelic loss at 9q22 is consistent with the clinical observation of transition of SP to BCC. The finding of frequent allelic loss at 9p21 is unlikely to be related to the rare transition of SP to metastatic adenocarcinoma. Our study supports the hypothesis of a gatekeeper role of the tumor suppressor gene p16 in a variety of benign and malignant tumors, including SP.

Adenocarcinoma, Papillary↗

PubMed2001

Heterogeneity of allelic deletions within melanoma metastases.

During the initiation and progression of malignant melanoma, a series of different genetic events accumulate on several different chromosomes. The biological heterogeneity of tumour cells presents a major problem, preventing effective treatment of melanoma. To examine the degree of genetic heterogeneity, we searched for allelic losses (loss of heterozygosity; LOH) on chromosomes 9p, 9q, 1p and 17p, examining different areas within human melanoma metastases. All of the examined metastases were informative within at least one dissected area for at least one marker. Out of 29 areas in 11 melanoma metastases, 58% showed LOH with at least one marker. On chromosome 9p21-22, eight out of 26 informative loci (31%) showed LOH at D9S171 (three not informative), two out of 18 (11%) at IFNA (11 not informative) and seven out of 24 (29%) at D9S169 (five not informative). LOH on chromosome 9q22.3 was examined by the microsatellite marker D9S12; three out of 24 areas (12.5%) showed LOH, and five were not informative. Deletions on chromosome 1p were assessed using D1S450. Four out of 25 (16%) showed LOH; four were not informative. Deletions on chromosome 17p13 were examined with TP53; two out of 21 cases (9%) showed LOH, and eight were not informative. Our data demonstrate an impressive heterogeneity of allelic losses in the investigated chromosomal areas within the same metastatic lesion. This suggests that there is not one specific genetic alteration that accounts for melanoma progression to metastases. Rather there seem to be multiple genetic alterations accumulating even on the same chromosome, and progression from melanoma to metastases is paralleled by the accumulation of clones harbouring multiple genetic abnormalities.

Adult↗

PubMed2001

Natronobacterium nitratireducens sp. nov., a aloalkaliphilic archaeon isolated from a soda lake in China.

Two novel haloalkaliphilic archaea, strains C231T and C42, were isolated from a soda lake in China. Cells of the two strains were rod-shaped and gram-negative and colonies were bright red. They required at least 2.5 M NaCl for growth, with an optimum at 3.5 M NaCl, and grew over a pH range from 8.0 to 10.5, with an optimum at pH 8.5. Hypotonic treatment with less than 1.5 M NaCl caused cell lysis. They had similar polar lipid compositions, possessing the diphytanyl (C20:C20) and phytanyl-sesterterpanyl (C20:C25) diether derivatives of phosphatidylglycerol and phosphatidylglycerophosphate methyl ester and a minor phospholipid, PL1. No glycolipids were detected. Comparison of 16S rDNA sequences and morphological features placed them in the genus Natronobacterium. Detailed phenotypic characterization and DNA-DNA hybridization studies revealed that the two strains belong to a new species in the genus Natronobacterium, for which the name Natronobacterium nitratireducens sp. nov. is proposed. The type strain is C231T (= AS 1.1980T = JCM 10879T).

China↗

PubMed2001

The MCP silencer of the Drosophila Abd-B gene requires both Pleiohomeotic and GAGA factor for the maintenance of repression.

Silencing of homeotic gene expression requires the function of cis-regulatory elements known as Polycomb Response Elements (PREs). The MCP silencer element of the Drosophila homeotic gene Abdominal-B has been shown to behave as a PRE and to be required for silencing throughout development. Using deletion analysis and reporter gene assays, we defined a 138 bp sequence within the MCP silencer that is sufficient for silencing of a reporter gene in the imaginal discs. Within the MCP138 fragment, there are four binding sites for the Pleiohomeotic protein (PHO) and two binding sites for the GAGA factor (GAF), encoded by the Trithorax-like gene. PHO and the GAF proteins bind to these sites in vitro. Mutational analysis of PHO and GAF binding sequences indicate that these sites are necessary for silencing in vivo. Moreover, silencing by MCP138 depends on the function of the Trithorax-like gene, and on the function of the PcG genes, including pleiohomeotic. Deletion and mutational analyses show that, individually, either PHO or GAF binding sites retain only weak silencing activity. However, when both PHO and GAF binding sites are present, they achieve strong silencing. We present a model in which robust silencing is achieved by sequential and facilitated binding of PHO and GAF.

Animals↗

PubMed2000

Human DNA polymerase kappa synthesizes DNA with extraordinarily low fidelity.

Escherichia coli DNA polymerase IV encoded by the dinB gene is involved in untargeted mutagenesis. Its human homologue is DNA polymerase kappa (Polkappa) encoded by the DINB1 gene. Our recent studies have indicated that human Polkappa is capable of both error-free and error-prone translesion DNA synthesis in vitro. However, it is not known whether human Polkappa also plays a role in untargeted mutagenesis. To examine this possibility, we have measured the fidelity of human Polkappa during DNA synthesis from undamaged templates. Using kinetic measurements of nucleotide incorporations and a fidelity assay with gapped M13mp2 DNA, we show that human Polkappa synthesizes DNA with extraordinarily low fidelity. At the lacZalpha target gene, human Polkappa made on average one error for every 200 nucleotides synthesized, with a predominant T-->G transversion mutation at a rate of 1/147. The overall error rate of human Polkappa is 1.7-fold lower than human Poleta, but 33-fold higher than human Polbeta, a DNA polymerase with very low fidelity. Thus, human Polkappa is one of the most inaccurate DNA polymerases known. These results support a role for human Polkappa in untargeted mutagenesis surrounding a DNA lesion and in DNA regions without damage.

Base Pair Mismatch↗

PubMed2000

DNA binding by single HMG box model proteins.

The HMG1/2 family is a large group of proteins that share a conserved sequence of approximately 80 amino acids rich in basic, aromatic and proline side chains, referred to as an HMG box. Previous studies show that HMG boxes can bind to DNA in a structure-specific manner. To define the basis for DNA recognition by HMG boxes, we characterize the interaction of two model HMG boxes, one a structure-specific box, rHMGb from the rat HMG1 protein, the other a sequence-specific box, Rox1 from yeast, with oligodeoxynucleotide substrates. Both proteins interact with single-stranded oligonucleotides in this study to form 1:1 complexes. The stoichiometry of binding of rHMGb to duplex or branched DNAs differs: for a 16mer duplex we find a weak 2:1 complex, while a 4:1 protein:DNA complex is detected with a four-way DNA junction of 16mers in the presence of Mg(2+). In the case of the sequence-specific Rox1 protein we find tight 1:1 and 2:1 complexes with its cognate duplex sequence and again a 4:1 complex with four-way branched DNA. If the DNA branching is reduced to three arms, both proteins form 3:1 complexes. We believe that these multimeric complexes are relevant for HMG1/2 proteins in vivo, since Mg(2+) is present in the nucleus and these proteins are expressed at a very high level.

Animals↗

PubMed2000

The human RAD18 gene product interacts with HHR6A and HHR6B.

During DNA replication, lesion bypass is an important cellular response to unrepaired damage in the genome. In the yeast Saccharomyces cerevisiae, Rad6 and Rad18 are required for both the error-free and error-prone lesion bypass mechanisms. Furthermore, Rad6-Rad18 interaction is thought to be critical at an early step during lesion bypass in yeast. Two closely related human homologs of yeast Rad6 have been identified as HHR6A and HHR6B. Here, we report a full-length cDNA coding for the human homolog of yeast Rad18. The human RAD18 gene codes for a protein of 484 amino acid residues with a calculated molecular weight of 54 804 Da, and the gene is localized to chromosome 3 between reference intervals D3S3591 and D3S1283. Human RAD18 protein (hRAD18) was found to interact with HHR6A and HHR6B. When co-expressed in yeast cells, stable hRAD18-HHR6A and hRAD18-HHR6B protein complexes were identified and purified to near homogeneity. Thus, through interaction and complex formation with HHR6A and HHR6B, RAD18 protein may play an important role in lesion bypass mechanisms in humans. Consistent with its role as a fundamental lesion bypass protein, the RAD18 gene is ubiquitously expressed in various human tissues.

Amino Acid Sequence↗

PubMed2000

Identification of a novel aspartic-like protease differentially expressed in human breast cancer cell lines.

Four different human breast cancer cell lines were examined to search for genes associated with tumor growth and metastasis. Each of these cell lines, MDA-MB-453, MCF-7, MDA-MB-231 and MDA-MB-435, displays different phenotypic characteristics ranging from poorly to highly tumorigenic and metastatic. The differences in gene expression profiles of these cell lines generated by differential display technique should allow one to identify candidates as putative oncogenes or tumor/metastasis suppressor genes. A novel cDNA expressed in the highly tumorigenic and metastatic cell line, MDA-MB-435, was identified and isolated by this approach. The function for this gene, designated ALP56 (aspartic-like protease 56 kDa), in tumor progression is suggested by the homology of the encoded protein to aspartic proteases, such as cathepsin D. The amino acid residues in two catalytic domains of this family are highly conserved in those domains of ALP56. Northern hybridization indicated that the expression of ALP56 is associated with growth and metastasis of MDA-MB-435 tumors in immunodeficient mice. In situ hybridization of biopsies from breast cancer and colon cancer patients indicated that ALP56 is upregulated in human primary tumors and liver metastasis. These results suggest that this novel gene correlates with human tumor progression.

Amino Acid Sequence↗

PubMed2000

Cytoplasmic localization of the interferon-inducible protein that is encoded by the AIM2 (absent in melanoma) gene from the 200-gene family.

While interferons (IFNs) (alpha, beta and gamma), a family of cytokines, have the ability to exert the growth-inhibitory effect on target cells, the molecular mechanism(s) by which IFNs inhibit cell growth remains to be identified. Because IFN-inducible 'effector' proteins mediate the biological activities of IFNs, characterization of IFN-inducible proteins is critical to identify their functional role in IFN action. One family (the 200-family) of IFN-inducible proteins is encoded by structurally related murine (Ifi202a, Ifi202b, Ifi203, Ifi204 and D3) and human (IFI16, MNDA and AIM2) genes. The proteins encoded by genes in the family share a unique repeat of 200-amino acids and are primarily nuclear. The AIM2 gene is a newly identified gene that is not expressed in a human melanoma cell line. Here we report that AIM2 is estimated to be a 39 kDa protein and, unlike other proteins in the family, is localized primarily in the cytoplasm. Interestingly, overexpression of AIM2 in transfected cells retards proliferation and, under reduced serum conditions, increases the susceptibility to cell death. Moreover, AIM2 can heterodimerize with p202 in vitro. Together, these observations provide support to the idea that AIM2 may be an important mediator of IFN action.

Amino Acid Sequence↗

PubMed2000

Alanine mutagenesis of high-mobility-group-protein-1 box B (HMG1-B).

We have generated a set of alanine-scanning substitutions in high-mobility-group protein 1 box B (HMG1-B; the second domain of the HMG1 nuclear protein from the rat) in order to explore the influence of specific surface side chains on its function and folding. Guanidine hydrochloride and thermal unfolding studies have been carried out to investigate the effect of substituted residues on the folding pathway. Binding to four-way junction and linear-duplex DNA has been assayed to determine which residues play an important role in DNA binding. We have identified several mutants that are more stable or bind more tightly to the junction than the wild-type, including the particular phenylalanine side chain that is thought to intercalate into the DNA. Thus the interaction between HMG1-B and branched DNA substrates should exhibit differences from present models based on the structure of the complexes that have been solved to date.

Alanine↗

PubMed2000

Sporadic trichoepithelioma demonstrates deletions at 9q22.3.

BACKGROUND: Trichoepithelioma (TE) is a benign cutaneous tumor that originates from hair follicles and occurs either in multiple or solitary lesions. Multiple TE is transmitted as an autosomal dominant trait, and a region at 9p21 is thought to be involved in the tumorigenesis. Solitary TE occurs more commonly than multiple TE and is not inherited. Histologically, TE tumors contain horn cysts and abortive hair papillae. A basal cell carcinoma appearance in some or all regions of a TE tumor can happen. In sporadic basal cell carcinoma, frequent deletions at 9q22.3 (Drosophila patched gene) have occurred. The objective of this study is to test whether loss of heterozygosity (LOH) on either 9p21 or on chromosome 9q22.3 could be detected in archival sporadic TE. OBSERVATIONS: We studied 29 randomly selected cases of sporadic TE by microdissection and polymerase chain reaction using paraffin-embedded, formalin-fixed tissue specimens on glass slides. Analysis was performed with the polymorphic markers IFNA and D9S171 (9p21) as well as D9S15, D9S303, D9S287, and D9S252 (9q22.3). RESULTS: The LOH at 9q22.3 was identified in 14 (48%) of 29 cases with at least 1 marker, while LOH could not be demonstrated using the markers IFNA and D9S171 (9p21). CONCLUSIONS: The results show that the Drosophila patched gene LOH can be frequently identified in paraffin-embedded sporadic TE after routine processing and indicates a common gatekeeper mechanism for both TE and basal cell carcinoma.

Chromosomes, Human, Pair 9↗