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Biomedical subjects

M Guo

Publications and source records attributed to M Guo.

At least 109 records · Page 6Linked to original sources
PubMed1997

[Detection of P-glycoprotein in squamous cell carcinoma of larynx].

The multidrug resistance (MDR) of malignant tumor is a troublesome problem in the chemotherapy. One established mechanism of multidrug resistance is elevated expression of the P-glycoprotein (PGP). JSB1 (which is a special monoclonal antibody of human MDR, PGP) was used to examine the expression of PGP by immunohistochemistry in 23 specimens of squamous cell carcinoma of larynx. The expression of JSB1 in 10 normal laryngeal tissue specimens was also studied, no positive result was found. Of the 23 laryngeal cancer specimens, positive reaction to JSB1 was showed in 15, and there was no relationship between the positive expression, and the tumor differentiation, T staging and lymph-node metastasis. However, by using another newly developed monoclonal antibody C219, a different result was obtained from specimens of the same patients.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1997

Characterization of radiation-induced apoptosis in rodent cell lines.

For REC:myc(ch1), Rat1 and Rat1:myc(b) cells, we determined the events in the development of radiation-induced apoptosis to be in the following order: cell division followed by chromatin condensation, membrane blebbing, loss of adhesion and the uptake of vital dye. Experimental data which were obtained using 4He ions of well-defined energies and which compared the dependence of apoptosis and clonogenic survival on 4He range strongly suggested that in our cells both apoptosis and loss of clonogenic survival resulted from radiation damage to the cell nucleus. Corroboratory evidence was that BrdU incorporation sensitized these cells to radiation-induced apoptosis. Comparing the dose response for apoptosis and the clonogenic survival curves for Rat1 and Rat1:myc(b) cells, we concluded that radiation-induced apoptosis contributed to the overall radiation-induced cell inactivation as assayed by clonogenic survival, and that a modified linear-quadratic model, proposed previously, modeled such a contribution effectively. In the same context, the selective increase in radiation-induced apoptosis during late S and G2 phases reduced the relative radioresistance observed for clonogenic survival during late S and G2 phases.

Animals↗
PubMed1996

Diorganotin(IV) antitumor agent. (C2H5)2SnCl2 (phen)/nucleotides aqueous and solid-state coordination chemistry and its DNA binding studies.

This contribution reports a solution and solid-state study of the aqueous nucleotide coordination chemistry of the diethyltin(IV) antitumor agent, (C2H5)2SnCl2(phen). [trans-en2Os(eta-H2)] (CF3SO3)2, a versatile 1H NMR probe for biomolecules, is first used to investigate the interaction of (C2H5)2SnCl2(phen) with DGMP in neutral aqueous solution, and then the synthesis of mixed-ligands complexes formulated as (C2H5)2SnCl(phen)(Nu) (Nu is nucleotide) by reactions of (C2H5)2SnCl2(phen) with equimolar nucleotides under biologically relevant conditions is described. The new complexes were characterized by 500 MHz 1H, 31P NMR spectra; these spectroscopic data suggest that one of cis-chloro atoms in (C2H5)2SnCl2(phen) is substituted by nucleotide, and that Sn(IV) is directly coordinated to the phosphate group of the nucleotide. No evidence was found for the coordination via donor atoms of the base. On the basis of the above model studies, absorbance, fluorescence and cyclic voltammetric methods, viscosity determination, as well as agrose gel electrophoresis of superhelical pBR322 plasmid DNA were used to study the interaction of (C2H5)2SnCl2(phen) with DNA. The results indicate that (C2H5)2SnCl2(phen) binds to DNA by double modes. The drug first reacts electrostatically with the sugar-phosphate backbone of DNA; this results in changes of DNA conformation, and then phen ligand can intercalate into double-helix DNA and cause unwinding of the DNA.

Antineoplastic Agents↗
PubMed1996

Down-regulation of gadd153 by c-myc in rat fibroblasts and its effect on cell growth and radiation-induced apoptosis.

Using differential display reverse transcription PCR (DDRT - PCR), we found that a 360 bp cDNA fragment was absent in several c-myc transfected rat fibroblasts: REC:myc, REC:myc + ras and rat1-myc. These cells also showed enhanced sensitivity to gamma ray-induced apoptosis. This cDNA fragment was present in the parental REC (Rat Embryo Cells) and rat1 cells, and in c-Ha-ras transfected REC (REC:ras), all of which were relatively resistant to gamma ray-induced apoptosis. The cDNA fragment was subsequently cloned and used as a probe to screen a rat1 cDNA library, and identified as one of the growth arrest and DNA damaging-inducible genes, gadd153. In addition to the down-regulation of rat gadd153 in all the c-myc transfectants, methyl methanesulfonate (MMS)-induced transcription of the gadd153 was attenuated. The rat1-myc cells, when successfully transfected with and stably expressing the rat gadd153, showed a significantly longer doubling time compared to the parental cells. However, overexpression of gadd153 in rat1-myc cells did not affect gamma ray-induced apoptosis. Thus, the suppression of gadd153 appears to be inversely correlated with that of myc, but not involved in the myc-dependent apoptotic pathway.

Animals↗
PubMed1996

Mutational studies of conserved residues in the dimer interface of nerve growth factor.

An understanding of the structure-function relationship of nerve growth factor (NGF) requires precise knowledge of all the residues and regions that participate in NGF receptor binding, receptor activation, and biological activity. Seven recombinant human NGF mutants having alanine substituted for residues located either in the NGF dimer interface or beta-strand region were studied to determine the role of each amino acid residue in NGF biological activity. F86A, T91A, R100A, and R103A remained nearly full active with 61, 120, 91, and 73% of wild-type activity, respectively, in the PC12 cell bioassay. Hydrophobic core and dimer interface residues Y52, F53, and F54 were studied in more detail. Y52A and F54A were expressed in very low levels, suggesting that these two residues may be important for protein stability. Y52A retained full biological activity (91%). F53A had a 20- and 70-fold reduction in biological activity and TrkA phosphorylation, respectively, with only a 5- to 10-fold effect on TrkA binding and no effect on low-affinity receptor binding. F54A had significantly decreased TrkA phosphorylation and biological activity (40-fold). The results suggest that F53 and F54 may play a structural role in TrkA receptor activation subsequent to binding.

Animals↗
PubMed1996

Control of daughter cell fates during asymmetric division: interaction of Numb and Notch.

During development of the Drosophila peripheral nervous system, a sensory organ precursor (SOP) cell undergoes rounds of asymmetric divisions to generate four distinct cells of a sensory organ. Numb, a membrane-associated protein, is asymmetrically segregated into one daughter cell during SOP division and acts as an inherited determinant of cell fate. Here, we show that Notch, a transmembrane receptor mediated cell-cell communication, functions as a binary switch in cell fate specification during asymmetric divisions of the SOP and its daughter cells in embryogenesis. Moreover, numb negatively regulates Notch, probably through direct protein-protein interaction that requires the phosphotyrosine-binding (PTB) domain of Numb and either the RAM23 region or the very C-terminal end of Notch. Notch then positively regulates a transcription factor encoded by tramtrack (ttk). This leads to Ttk expression in the daughter cell that does not inherit Numb. Thus, the inherited determinant Numb bestows a bias in the machinery for cell-cell communication to allow the specification of distinct daughter cell fates.

Animals↗
PubMed1996

Dosage effects on gene expression in a maize ploidy series.

Previous studies on gene expression in aneuploids revealed numerous trans-acting dosage effects. Segmental aneuploidy of each varied chromosomal region exhibited predominantly inverse effects on several target genes. Here, dosage regulation was examined in a maize (Zea mays L.) ploidy series where the complete genomic complement is varied. Total RNA from leaf tissue of monoploid, diploid, triploid, and tetraploid plants (1x, 2x, 3x, and 4x, respectively) was analyzed for the expression of 18 genes. For most tested genes, the transcript level per cell is directly proportional to structural gene dosage; that is, on a per genome basis, there is approximately equal expression among the four ploidies. Exceptional cases show a negative correlation of expression with ploidy or a positive correlation greater than expected from the structural gene dosage. These studies suggest that, in general, as structural gene dosage increases in multiples of the monoploid complement, the absolute level of gene expression per cell increases. In contrast, addition or subtraction of only a single chromosome arm tends to alter gene expression patterns extensively. The combined results of the euploid and aneuploid studies suggest that aneuploid effects result from an altered stoichiometry of the factors contributing to the mechanisms of gene expression.

Blotting, Northern↗
PubMed1996

[The experimental treatment of laryngeal cancer using local draining lymph node lymphocytes].

In order to know whether laryngeal cancer draining lymph node lymphocytes (INL) have antitumor effects in vivo, we transfered IL-2 activated LNL to nude mice with human laryngeal squamous cell carcinoma line PHC3 xenografts, and observed a suppressive effect on tumor growth. It was also found in the epitype changes of LNL by indirect immunofluorencence method the major composition of freshly isolated LNL was CD3+ T cells in which there were more Th/i cells than Ts/c cells, CD4+/CD8+ ratio was 3.30 +/- 0.653. No evidence of lymphocytes multiplication or CD3+, CD4+, CD8+ epitype changes was found after short term IL-2 culture, but we found more HLA-DR+, CD25+ cells which means there was an increase in activated lymphocytes after culture. The experiment suggests that laryngeal cancer draining lymph node lymphocytes have antitumor effects in vivo after IL-2 short term culture, and can be used in clinical immunotherapy.

Aged↗
PubMed1996

[Wound infection and recurrence after total laryngectomy].

95 patients who received total laryngectomy for laryngeal carcinoma were reviewed. They were divided into two groups, those with postoperative wound infection and those without. The relations between postoperative wound infection and local recurrence were discussed. The results showed that the recurrence rate of postoperative infection group was higher than that of no postoperative infection (P < 0.001), and the patients with gram-negative bacilli infection also had much higher recurrence rates (P < 0.05). For the laryngeal cancer, the development of a wound infection after total laryngectomy may be related to the local tumour recurrence within one year.

Adult↗
PubMed1996

[Study on expression of nm23-H1 gene in laryngeal cancer tissues].

The nm23 gene is a metastasis suppressor gene. There are now two known isotypes of human nm23, namely nm23-H1 and nm23-H2. Several investigators have reported that reduced expression of nm23-H1 is associated with metastasis or disease progression in some of the tumor cases. In this study, the expression of nm23-H1 mRNA in the human laryngeal squamous cell carcinoma was investigated by Northern blot analysis. The levels of nm23-H1 mRNA were higher in cancers (n = 31) than in the adjacent normal tissues (n = 7), but the difference was not significant (P > 0.05). There was a significant decrease of nm23-H1 mRNA levels in tumors with lymph node metastasis (n = 11) as compared with those without (n = 20) (P < 0.01). Cancer tissues in clinical stages III-IV. (n = 23) also exhibited lower levels of nm23-H1 mRNA expression than those in stages I-II (n = 8) (P < 0.05). These results suggest that the nm23-H1 gene may play a role in the suppression of lymph node metastasis or disease progression in laryngeal cancer.

Adult↗
PubMed1995

Radiation-induced apoptosis: effects of cell age and dose fractionation.

The cell cycle dependence of radiation-induced apoptosis was measured using mitotically synchronized REC:myc(ch1) and Rat1:mycb cells. Cells in S and G2 phases were more susceptible; the apoptotic fraction was about 0.7-0.8 as compared to about 0.4 for G1 cells at a dose of 10 Gy. Two-dimensional cytofluorimetric analysis of cells, pulsed-labeled with bromodeoxyuridine and then irradiated with 10 Gy, showed both G1 and G2 blocks (6-8 h) for REC:myc(ch1) cells but only G2 block for Rat1:mycb cells. Consistent with these results, wild-type p53 and WAF1 (or p21), known to play a role in G1 delay, was induced by radiation in REC:myc(ch1) but not in Rat1:mycb cells. The cell cycle dependence of radiation-induced apoptosis and the absence of a G1 block for Rat1:mycb cells led to the prediction and observation of the novel "inverse split-dose effect," i.e., a radiation dose given in two equal halves separated by a few hours yielded a higher level of apoptosis relative to that resulting from the same total dose given all at once. This effect is due to cell cycle progression from G1 to the more sensitive S-G2 phase during the interval between the split doses. In contrast, the inverse split-dose effect for apoptosis is absent for REC:myc(ch1), due presumably to the radiation-induced G1 delay. Parallel split-dose experiments, but using clonogenic survival as end points, show recovery for REC:myc(ch1) cells but not for Rat1:mycb cells, reflecting the influence of split-dose, radiation-induced apoptosis.

Animals↗
PubMed1995

Localization of sequences required for size-specific splicing of a small Drosophila intron in vitro.

Many introns in Drosophila and other invertebrates are less than 80 nucleotides in length, too small to be recognized by the vertebrate splicing machinery. Comparison of nuclear splicing extracts from human HeLa and Drosophila Kc cells has revealed species-specificity, consistent with the observed size differences. Here we present additional results with the 68 nucleotide fifth intron of the Drosophila myosin heavy chain gene. As observed with the 74 nucleotide second intron of the Drosophila white gene, the wild-type myosin intron is accurately spliced in a homologous extract, and increasing the size by 16 nucleotides both eliminates splicing in the Drosophila extract and allows accurate splicing in the human extract. In contrast to previous results, however, an upstream cryptic 5' splice site is activated when the wild-type myosin intron is tested in a human HeLa cell nuclear extract, resulting in the removal of a 98 nucleotide intron. The size dependence of splicing in Drosophila extracts is also intron-specific; we noted that a naturally larger (150 nucleotide) intron from the ftz gene is efficiently spliced in Kc cell extracts that do not splice enlarged introns (of 84, 90, 150 or 350 nucleotides) derived from the 74 nucleotide white intron. Here, we have exploited that observation, using a series of hybrid introns to show that a region of 46 nucleotides at the 3' end of the white intron is sufficient to confer the species-specific size effect. At least two sequence elements within this region, yet distinct from previously described branchpoint and pyrimidine tract signals, are required for efficient splicing of small hybrid introns in vitro.

Animals↗
PubMed1995

Structural analysis of the N- and C-termini in a peptide with consensus sequence.

We present a structural analysis of a peptide, the sequence of which includes amino acids that show preferences for specific positions near the N- and C-termini in protein helices. This peptide has the sequence ac-YMSEDELKAAEAAFKRHGVP-amide, which includes a strong version of an N-terminal Harper-Rose capping box structure as well as a Gly located close to the C-terminus designed to elucidate its role in C-terminal capping. The sequence of five residues at the middle is inserted to separate effects at the two ends via a helix-stabilizing linker. Application of a simulated annealing procedure using interproton distance constraints derived from 1H NOESY experiments in water reveals the presence of a C-terminal structure in this model. The C-terminus forms a folded back structure in a significant fraction of structures generated by the annealing, in most of which Gly assumes an alpha L conformation. This structure occurs within a highly flexible region of the molecule and hence is occupied only a fraction of the time.

Amino Acid Sequence↗
PubMed1995

tramtrack acts downstream of numb to specify distinct daughter cell fates during asymmetric cell divisions in the Drosophila PNS.

Asymmetric cell divisions allow a sensory organ precursor (SOP) cell to generate a neuron and its support cells in the Drosophila PNS. We demonstrate a role of tramtrack (ttk), previously identified as a zinc finger-containing putative transcription factor, in the determination of different daughter cell fates. Both loss of function and overexpression of ttk affect the fates of the SOP progeny. Whereas loss of ttk function transforms support cells to neurons, ttk overexpression results in the reverse transformation. ttk is expressed in support cells but not in neurons. It has been shown that numb, a membrane-associated protein asymmetrically distributed during the SOP division, confers different daughter cell fates. Loss of ttk or numb function results in reciprocal cell fate transformation. Epistatic studies suggest that ttk acts downstream of numb. We propose that ttk executes the command dictated by asymmetrically localized numb to specify distinct daughter cell fates during multiple asymmetric divisions.

Animals↗