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Biomedical subjects

G Luo

Publications and source records attributed to G Luo.

At least 73 records · Page 4Linked to original sources
PubMed1999

Disruption of mRad50 causes embryonic stem cell lethality, abnormal embryonic development, and sensitivity to ionizing radiation.

The Mre11/Rad50 protein complex functions in diverse aspects of the cellular response to double-strand breaks (DSBs), including the detection of DNA damage, the activation of cell cycle checkpoints, and DSB repair. Whereas genetic analyses in Saccharomyces cerevisiae have provided insight regarding DSB repair functions of this highly conserved complex, the implication of the human complex in Nijmegen breakage syndrome reveals its role in cell cycle checkpoint functions. We established mRad50 mutant mice to examine the role of the mammalian Mre11/Rad50 protein complex in the DNA damage response. Early embryonic cells deficient in mRad50 are hypersensitive to ionizing radiation, consistent with a role for this complex in the repair of ionizing radiation-induced DSBs. However, the null mrad50 mutation is lethal in cultured embryonic stem cells and in early developing embryos, indicating that the mammalian Mre11/Rad50 protein complex mediates functions in normally growing cells that are essential for viability.

Animals↗
PubMed1999

Molecular interactions of N-RAP, a nebulin-related protein of striated muscle myotendon junctions and intercalated disks.

N-RAP is a recently discovered muscle-specific protein that is concentrated at the myotendon junctions in skeletal muscle and at the intercalated disks in cardiac muscle. The C-terminal half of N-RAP contains a region with sequence homology to nebulin, while a LIM domain is found at its N-terminus. N-RAP is hypothesized to perform an anchoring function, linking the terminal actin filaments of myofibrils to protein complexes located beneath the sarcolemma. We used a solid-phase assay to screen myofibrillar and junctional proteins for binding to several recombinant fragments of N-RAP, including the nebulin-like super repeat region (N-RAP-SR), the N-terminal half including the LIM domain (N-RAP-NH), and the region of N-RAP between the super repeat region and the LIM domain (N-RAP-IB). Actin is the only myofibrillar protein tested that exhibits specific binding to N-RAP, with high-affinity binding to N-RAP super repeats, and 10-fold weaker binding to N-RAP-IB. In contrast, myosin, isolated myosin heads, tropomyosin, and troponin exhibited no specific interaction with N-RAP domains. A recombinant fragment corresponding to the C-terminal one-fourth of vinculin also binds specifically to N-RAP super repeats, while no specific N-RAP binding activity was observed for other regions of the vinculin molecule. Finally, talin binds with high affinity to the LIM domain of N-RAP. These results support our hypothesis that N-RAP is part of a complex of proteins that anchors the terminal actin filaments of the myofibril to the membrane, and functions in transmitting tension from the myofibrils to the extracellular matrix.

Actins↗
PubMed1999

Cellular proteins bind to the poly(U) tract of the 3' untranslated region of hepatitis C virus RNA genome.

UV cross-linking analyses were performed in an attempt to determine cellular protein-viral RNA interactions with the 3' untranslated region (3' UTR) of the hepatitis C virus RNA genome. Two cellular proteins, with estimated molecular masses of 58 kDa (p58) and 35 kDa (p35), respectively, were found to specifically bind to the 3' UTR. The p58 protein was determined to be the polypyrimidine tract-binding protein. In addition to binding to the conserved 98 nucleotides (nt) of the 3' UTR, p58 also binds to the poly(U) tract of the 3' UTR. The p35 protein was found to interact only with the poly(U) tract of the 3' UTR. These conclusions are supported by the following findings: (1) p58, and not p35, binds to the 3' end conserved 98 nt, (2) both p58 and p35 bind to a 3' UTR RNA with a deletion of the conserved 98 nt, (3) the 98-nt deletion mutant 3' UTR competed out both p58 and p35 binding, (4) a poly(U) homopolymer competed out both p58 and p35 binding, (5) a 3' UTR RNA with deletion of the poly(U) tract competed out only p58 binding but not p35 binding, and (6) an RNA containing the variable region of the 3' UTR with a deletion of both poly(U) tract and 98 nt failed to compete for binding of either p58 or p35. Interaction of these cellular proteins with the HCV 3' UTR is probably involved in regulation of translation and/or replication of the HCV RNA genome.

3' Untranslated Regions↗
PubMed1999

A functional DNA binding domain is required for growth hormone-induced nuclear accumulation of Stat5B.

The mechanisms regulating the cellular distribution of STAT family transcription factors remain poorly understood. To identify regions of Stat5B required for ligand-induced nuclear accumulation, we constructed a cDNA encoding green fluorescent protein (GFP) fused to the N terminus of Stat5B and performed site-directed mutagenesis. When co-expressed with growth hormone (GH) receptor in COS-7 cells, GFP-Stat5B is tyrosyl-phosphorylated, forms dimers, and binds DNA in response to GH in a manner indistinguishable from untagged Stat5B. In multiple cell types, laser scanning confocal imaging of GFP-Stat5B co-expressed with GH receptor shows that GFP-Stat5B undergoes a rapid, dramatic accumulation in the nucleus upon GH stimulation. We introduced alanine substitutions in several regions of Stat5B and assayed for GH-dependent nuclear localization. Only the mutation that prevented binding to DNA (466VVVI469) abrogated GH-stimulated nuclear localization. This mutant fusion protein is tyrosyl-phosphorylated and dimerizes in response to GH. These results suggest that either high affinity binding to DNA contributes to nuclear accumulation of Stat5B or that this region is crucial for two functions, namely accumulation of Stat5B in the nucleus and DNA binding. Thus, we have identified a mutant Stat5 defective in nuclear localization despite its ability to be tyrosyl-phosphorylated and to dimerize.

Animals↗
PubMed1999

Relationship between plain radiographic patterns and three- dimensional trabecular architecture in the human calcaneus.

The purpose of this study was to determine the relationship between three-dimensional (3D) trabecular structure and two-dimensional plain radiographic patterns. An in vitro cylinder of human calcaneal trabecular bone was three-dimensionally imaged by micro-CT using synchrotron radiation, at 33.4 micrometer resolution. The original 3D image was processed using 14 distinct sequences of morphologic operations, i.e., of dilations and erosions, to obtain a total of 15 3D models or images of calcaneal trabecular bone. These 15 models had distinct densities (volume fractions) and architectures. The 3D structure of each calcaneal model was assessed using mean intercept length (fabric), by averaging individual fabric measurements associated with each medial-lateral image slice, and determining the relative anisotropy, R(3D), of the structure. A summated pattern or plain radiograph was also computed from the 3D image data for each calcaneal model. Each summated pattern was then locally thresholded, and the resulting two-dimensional (2D) binary image analyzed using the same fabric analysis as used for the 3D data. The anisotropy of the 2D summated pattern was denoted by R(x-ray). The volume fractions of the 15 models ranged from 0.08 to 0.19 with a mean of 0. 14. The medial-lateral anisotropies, R(3D), ranged from 1.38 to 2.54 with a mean of 1.88. The anisotropy of the 2D summated patterns, R(x-ray), ranged from 1.35 to 2.18 with a mean of 1.71. The linear correlation of the 3D trabecular architecture, R(3D), with the radiographic trabecular architecture, R(x-ray), was 0.99 (p<0.0001). This study shows that the plain radiograph contains architectural information directly related to the underlying 3D structure. A well-controlled sequential reproducible plain radiograph may prove useful for monitoring changes in trabecular architecture in vivo and in identifying those individuals at increased risk of osteoporotic fracture.

Anisotropy↗
PubMed1999

The effect of surface roughness on the stress adaptation of trabecular architecture around a cylindrical implant.

The effect of implant-bone bonding and the effect of implant surface roughness on bone remodeling near the bone-implant interface were studied by using a surface remodeling theory and the boundary element method. The study has shown that implant attachment plays an important role in bone remodeling near the implant. It has been observed in animal experiments and in clinical situations that the remodeled trabecular bone architecture around a cylindrical implant could vary, on one hand, from a hub surrounding the implant with a set of external spokes to, on the other hand, a hubless situation in which a set of spokes attach directly to the implant. It is shown here that the difference in these structures may be attributed to differences in implant attachment. The results show that the bone with perfect bonding or roller boundary condition without a gap remodeled to a hubless spoke trabecular bone architecture. On the other hand, the roller boundary condition with a specified gap yielded a spoke trabecular architecture with a hub or ring surrounding the implant. These quantitative results mirror the experimental and clinical observations. It is concluded that the hub is a consequence of the gap and not a consequence of the lack of friction between the implant and the bone.

Humans↗
PubMed1999

Computational methods for ultrasonic bone assessment.

Ultrasound has been proposed as a means to noninvasively assess bone and, particularly, bone strength and fracture risk. Although there has been some success in this application, there is still much that is unknown regarding the propagation of ultrasound through bone. Because strength and fracture risk are a function of both bone mineral density and architectural structure, this study was carried out to examine how architecture and density interact in ultrasound propagation. Due to the difficulties inherent in obtaining fresh bone specimens and associated architectural and density features, simulation methods were used to explore the interactions of ultrasound with bone. A sample of calcaneal trabecular bone was scanned with micro-CT and subjected to morphological image processing (erosions and dilations) operations to obtain a total of 15 three-dimensional (3-D) data sets. Fifteen two-dimensional (2-D) slices obtained from the 3-D data sets were then analyzed to evaluate their respective architectures and densities. The architecture was characterized through the fabric feature, and the density was represented in terms of the bone volume fraction. Computer simulations of ultrasonic propagation through each of the 15 2-D bone slices were carried out, and the ultrasonic velocity and mean frequency of the received waveforms were evaluated. Results demonstrate that ultrasound propagation is affected by both density and architecture, although there was not a simple linear correlation between the relative degree of structural anisotropy with the ultrasound measurements. This study elucidates further aspects of propagation of ultrasound through bone, and demonstrates as well as the power of computational methods for ultrasound research in general and tissue and bone characterization in particular.

Biophysical Phenomena↗
PubMed1999

Up-regulation of Fas ligand and down-regulation of Fas expression in oral carcinogenesis.

An important molecule involved in delivering the death signal that initiates apoptosis is called Fas, or Apo-1, which sits on the cell surface. When another molecule called the Fas ligand (FasL) binds to it, Fas triggers a series of events inside the cell that leads to apoptosis. In order to investigate the mechanism of immune escape and the expression of Fas and FasL in oral premalignant lesions (OPLs) and oral squamous cell carcinomas (OSCCs), a total of 64 samples were evaluated by an immunohistochemical method using a labelled streptavidin-biotin assay. These samples comprised nine hyperkeratotic and 24 oral premalignant lesions (nine of mild, moderate, and six of severe dysplastic lesions), and 24 OSCCs, together with seven healthy controls. The results demonstrated that the majority of invasive OSCCs showed down-regulation of Fas expression but up-regulation of FasL expression. These phenomena were also detected in OPLs. The results indicate that the expression of Fas and FasL is involved in oral carcinogenesis and this may be a mechanism by which the cancer cells evade the host immune assault. Perhaps, in future, Fas/FasL system may be used as a prognostic biomarker in predicting the behavior of oral premalignant lesions.

Apoptosis↗
PubMed1999

Sepsis stimulates release of myofilaments in skeletal muscle by a calcium-dependent mechanism.

Sepsis is associated with a pronounced catabolic response in skeletal muscle, mainly reflecting degradation of the myofibrillar proteins actin and myosin. Recent studies suggest that sepsis-induced muscle proteolysis may reflect ubiquitin-proteasome-dependent protein breakdown. An apparently conflicting observation is that the ubiquitin-proteasome pathway does not degrade intact myofibrils. Thus, it is possible that actin and myosin need to be released from the myofibrils before they can be ubiquitinated and degraded by the proteasome. We tested the hypothesis that sepsis results in disruption of Z-bands, increased expression of calpains, and calcium-dependent release of myofilaments in skeletal muscle. Sepsis induced in rats by cecal ligation and puncture resulted in increased gene expression of micro-calpain, m-calpain, and p94 and in Z-band disintegration in the extensor digitorum longus muscle. The release of myofilaments from myofibrillar proteins was increased in septic muscle. This response to sepsis was blocked by treating the rats with dantrolene, a substance that inhibits the release of calcium from intracellular stores to the cytoplasm. The present results provide evidence that sepsis is associated with Z-band disintegration and a calcium-dependent release of myofilaments in skeletal muscle. Release of myofilaments may be an initial and perhaps rate-limiting component of sepsis-induced muscle breakdown.

Actin Cytoskeleton↗
PubMed1999

Expression of p16 and CDK4 in oral premalignant lesions and oral squamous cell carcinomas: a semi-quantitative immunohistochemical study.

The protein, p16, the product of cyclin-dependent kinase number 2 (CDKN2) gene, is one of the negative regulators of the cell cycle. CDK4, encoded by CDK4 gene, is the substrate of p16. We investigated the expression of p16 and CDK4 and their role in the progression of oral premalignant lesions (OPLs) and oral squamous cell carcinomas (OSCCs) in a Chinese cohort. A total of 74 samples were obtained from patients with hyperkeratosis (10), OPLs [30; mild (10), moderate (10) and severe (10) dysplastic lesions], OSCCs (15; 8 non-metastatic, 7 metastatic), and normal oral tissues (10), together with local lymph nodes (9) of patients with metastatic OSCCs. A labelled streptavidin biotin (LSAB) immunohistochemistry assay was performed and a semi-quantitative method was used to evaluate the staining intensity. The staining patterns of p16 and CDK4 were similar in all tissues and were located in both the nuclei and the cytoplasm. However, the antigen distribution characteristics and the degree of expression of both p16 and CDK4 varied at different developmental stages of the lesions. Hyperkeratotic and dysplastic lesions tended to display a progressively increasing degree of p16- and CDK4-positive nuclei as compared with normal tissues. Also, positive staining cytoplasm was highly evident in OSCCs with a very low nuclear staining (P<0.05). Forty-six of 56-, p16-positive cases were CDK4-positive, while only 6 were CDK4-positive but p16-negative, implying a high correlation between these parameters (r=0.813, P<0.001). This study indicates that the expression of p16 and CDK4 is intimately involved in the development of OPLs and OSCCs and the likely existence of a positive feedback loop between p16 and CDK4.

Adult↗
PubMed1999

pH-dependent changes in photoaffinity labeling patterns of the H1 influenza virus hemagglutinin by using an inhibitor of viral fusion.

The hemagglutinin (HA) protein undergoes a low-pH-induced conformational change in the acidic milieu of the endosome, resulting in fusion of viral and cellular membranes. A class of compounds that specifically interact with the HA protein of H1 and H2 subtype viruses and inhibit this conformational change was recently described (G. X. Luo et al., Virology 226:66-76, 1996, and J. Virol. 71:4062-4070, 1997). In this study, purified HA trimers (bromelain-cleaved HA [BHA]) are used to examine the properties and binding characteristics of these inhibitors. Compounds were able to inhibit the low-pH-induced change of isolated trimers, as detected by resistance to digestion with trypsin. Protection from digestion was extremely stable, as BHA-inhibitor complexes could be incubated for 24 h in low pH with almost no change in BHA structure. One inhibitor was prepared as a radiolabeled photoaffinity analog and used to probe for specific drug interactions with the HA protein. Analysis of BHA after photoaffinity analog binding and UV cross-linking revealed that the HA2 subunit of the HA was specifically radiolabeled. Cross-linking of the photoaffinity analog to BHA under neutral (native) pH conditions identified a stretch of amino acids within the alpha-helix of HA2 that interact with the inhibitor. Interestingly, cross-linking of the analog under acidic conditions identified a different region within the HA2 N terminus which interacts with the photoaffinity compound. These attachment sites help to delineate a potential binding pocket and suggest a model whereby the BHA is able to undergo a partial, reversible structural change in the presence of inhibitor compound.

Amino Acid Sequence↗
PubMed1999

[Changes of simple epithelial cytokeratin during oral carcinogenesis].

OBJECTIVE: To investigate whether the simple epithelial cytokeratin CK18 and CK19 can be used as a marker of oral precancerous lesions. METHODS: Formalin-fixed, paraffin-embedded tissue sections of normal oral mucosa, epithelial hyperplasia, mild epithelial dysplasia, moderate epithelial dysplasia, severe epithelial dysplasia and oral squamous cell carcinomas were stained with a CK18-specific antibody and CK19-specific antibody respectively by LSAB immunohistochemical method. The stained sections were observed under light microscopy. The results were described and analyzed with Rank Sum Test. RESULTS: CK18 was not detected in normal and abnormal oral tissue sections. But in normal nonkeratinized mucosa, CK19 was detected in the basal cell layer dispersively. In epithelial dysplasia, CK19 was detected in the suprabasal cell layer and the number of CK19-positive cell layers was correlated with the dysplasia degree of epithelia. Furthermore, CK19 was detected in oral squamous cell carcinoma, especially in the poor-differentiated cancer cells. CONCLUSION: CK19 expression in suprabasal cell layer of oral mucosa can be used as a candidate marker for diagnosis of oral precancerous lesions and determination of the differentiation level of oral squamous cell carcinoma.

Biomarkers, Tumor↗
PubMed1999

[Expression of CDK4 protein in oral carcinogenesis].

OBJECTIVE: To study the expression of cyclin dependent kinase 4(CDK4) protein in oral carcinogenesis. METHODS: An LSAB immunohistochemistry method was applied to 80 cases of paraffine-fixed tissues to study the expression and distribution of CDK4 in normal oral mucosa, oral premalignant lesion (OPL) and oral squamous cell carcinoma. RESULTS: The overexpression of CDK4 protein was observed in the progression of OPL. Meanwhile, a correlation analysis was applied to investigate the relationship between P16 and CDK4 expression, and the result showed that the coefficient of correlation was 0.813, which was statistically significant. CONCLUSION: The overexpression of CDK4 is involved in the progression of OPL, and there is a positive feedback loop between CDK4 and P16.

Cyclin-Dependent Kinase 4↗
PubMed1999

[Analysis of rice leaf proteins induced by Magnaporthe grisae with capillary zone electrophoresis].

Intercellular and intracellular proteins which were extracted from rice seedling leaves induced by Magnaporthe grisae, as well as those of control, were analysed by capillary zone electrophoresis. Intercellular proteins were extracted with sterilized water, while intracellular proteins were extracted with acidic protein extraction buffer. Protein adsorption to capillary wall was suppressed by using linear polyacrylamide coated capillary (75 microns x 57 cm) instead of uncoated capillary. Separations were performed at 25 degrees C with a positive voltage of 20 kV. Samples were injected into the capillary by applying pressure (3.0 kPa) for 5 s. The running buffer consisted of 50 mmol/L phosphoric acid (pH 2.0), and detection was achieved at 200 nm with a diode array detector. Being compared with a control, a new kind of protein induced by Magnaporthe grisae was identified in rice leaf intracellular proteins with Grubbs method which is used to test outliers in mathematical statistics.

English Abstract↗
PubMed1999

[Analysis of blue ballpoint ink components by FT-IR microspectrometry].

Systematical analysis on the 108 kinds of blue ballpoint writing inks with FT-IR microspectrometry is presented in this paper. The results show that the differences of the ink compounds keep some regular. These blue ballpoint writing inks can be classified by the transmittance spectra. The method is rapid, accurate, highly sensitive and nondestructive.

English Abstract↗
PubMed1999

Conquering influenza: recent advances in anti-influenza drug discovery.

Morbidity and mortality associated with influenza virus infection have cut a wide swathe through medical history. Even with the development of killed virus vaccines, illness due to influenza virus infection continues to be a major health problem throughout the world. This may change over the next few years with the development of a new class of antiviral agents targeting the catalytic site of the viral neuraminidase enzyme. These agents have been demonstrated to be both efficacious and clinically beneficial. In addition, investigation into alternative anti-influenza targets continues. These include inhibitors of hemagglutinin-mediated functions, the viral polymerase and new inhibitors of M2 ion channel activity.

Journal Article↗
PubMed1998

A selenium-containing abzyme, the activity of which surpassed the level of native glutathione peroxidase.

Using two different glutathione derivatives as hapten, we have prepared two abzymes, which display glutathione peroxidase (GPX) activity. Their GPX activities are 0.2 and 1.6 times that of natural GPX from rabbit liver, respectively. Selenium content analysis indicates that the activity difference between the two abzymes is possibly attributed to the conformation difference of the abzymes.

Animals↗