Search PubMed⌕ Search

Biomedical subjects

Z Suo

Publications and source records attributed to Z Suo.

53 records · Page 3Linked to original sources
PubMed1998

Role of peroxynitrite in the vasoactive and cytotoxic effects of Alzheimer's beta-amyloid1-40 peptide.

Increasing evidence implicates oxidative stress as partially responsible for the neurodegenerative process of Alzheimer's disease (AD). Recent reports show an increased production of nitrotyrosine in AD brains, suggesting that peroxynitrite is produced in excess in this disease. Furthermore, incidence of cerebral amyloid angiopathy in AD cases is very frequent (83%), strongly suggesting a vascular component of AD pathogenesis. We have evaluated the hypothesis that peroxynitrite could be responsible for mediating the cytotoxicity and vasoactivity induced by the amyloid-beta1-40 (Abeta) peptide. Rat brain endothelial cells (RBE-4) appear to be sensitive to Abeta-induced toxicity but not to the cytotoxicity induced by peroxynitrite. Addition of Cu/Zn superoxide dismutase to cell culture media, which is only able to clear extracellular superoxide, was not effective in blocking Abeta-induced toxicity. However, we were able to partially block Abeta-induced cytotoxicity by using Mn(III)tetrakis(4-benzoic acid) porphyrin (MnTBAP) which dismutes superoxide intracellularily. Yet, MnTBAP was not able to prevent the vasoactivity triggered by Abeta. Moreover, addition of peroxynitrite to rat aortae did not modulate the vasotension induced by Abeta. We conclude that intracellular superoxide radicals may contribute to Abeta-induced cytotoxicity. Our results also indicate that peroxynitrite does not significantly contribute to Abeta-induced cytotoxicity in rat brain endothelial cells (RBE-4) or vasoactivity in rat aortae. These results suggest that therapeutic efforts aimed at removal of reactive oxygen species with SOD is unlikely to be beneficial for treatment of Abeta-induced endothelial dysfunction. However, compounds that clear free radicals intracellularly may well be beneficial.

Alzheimer Disease↗
PubMed1998

Type 1 protein tyrosine kinases in benign and malignant breast lesions.

AIMS: To determine their significance, we examined the expression pattern of the four epidermal growth factor receptor (EGFR) family members as well as the phosphotyrosine kinase activity in breast tumour tissues. METHODS AND RESULTS: Fifty-three malignant breast tumours, four breast cancer cell lines, and 10 benign breast tumours were investigated. Fifty-three per cent (28/53) of the malignant tumours expressed EGFR protein, and the majority of these positive tumours were strongly positive. Eighty per cent (8/10) of the benign tumours also expressed EGFR protein, but all in a lower or moderate level. An association between EGFR expression and increasing malignancy grade was found in the group of infiltrating ductal carcinomas. Of the malignant tumours, 35.8% (19/53) expressed c-erbB-2 protein and 17% (9/53) c-erbB-3 protein, while no expression of c-erbB-2 and c-erbB-3 proteins was found in the benign tumours. Contrary to previous reports, we observed c-erbB-4 receptor protein to be less expressed in the malignant breast tumours. The 'normal' breast epithelial cells adjacent to the malignant tumours and the benign tumours demonstrated intensified membrane staining for c-erbB-4, while a number of the malignant tumours demonstrated a weak cytoplasmic staining or were negative. However, several malignant tumours with strong membrane staining for the c-erbB-4 protein were also found. No simple association between the expression of the four receptors and phosphotyrosine kinase activity was found. CONCLUSION: Our study has revealed a complex expression pattern of the EGFR family members in breast tumour cells. While the data about EGFR, c-erbB-2, c-erbB-3 and phosphotyrosine are largely in line with what has been reported, we found the c-erbB-4 protein expression to be decreased in the malignant tumours.

Adult↗
PubMed1997

RNA secondary structure switching during DNA synthesis catalyzed by HIV-1 reverse transcriptase.

Changes in RNA secondary structure have been found to play important roles in translational regulation, protein synthesis, and mRNA splicing. In studies utilizing a 66 nucleotide RNA template with a stable hairpin structure, we have examined the effects of RNA secondary structure on HIV-1 reverse transcriptase activity. We identify several pause sites in the stem of the hairpin and show that these pause sites are correlated with the free energy of melting the next base pair in the stem. We also identify a pause site appearing in the loop of the hairpin and show that this is due to the rapid formation of a new hairpin structure occurring during the progress of DNA polymerization through the hairpin. The rapid change in RNA secondary structure to form the new hairpin selectively destabilizes the major hairpin and thereby accelerates the rate at which reverse transcriptase reads through RNA secondary structure.

Base Sequence↗
PubMed1997

Effect of RNA secondary structure on the kinetics of DNA synthesis catalyzed by HIV-1 reverse transcriptase.

The effect of RNA secondary structure on the kinetics of DNA synthesis catalyzed by HIV-1 RT was determined using a 66 nucleotide RNA template containing a stable 12 base pair hairpin structure. Prior to reaching the hairpin structure, the primer elongation by RT was fast and the kinetics of polymerization was not affected by the presence of the secondary structure. Once within the regions of template secondary structure, polymerization was much slower and RT paused at five distinct sites [Suo, Z., & Johnson, K. A. (1997) Biochemistry (manuscript submitted for publication)]. Kinetic analysis of single nucleotide incorporation at the pause sites showed polymerization occurred by both a fast phase (54-76 s-1) and a slow phase (0.07-0.4 s-1) during a single binding event. The biphasic kinetics suggests that the DNA substrates are initially bound in both productive and nonproductive states at the polymerase site of RT. The nonproductively bound DNA is slowly converted into a productive state without dissociation from the enzyme. At the pause sites, the enzyme amplitudes of the fast phase are small (4.0-15%) while the amplitudes of the slow phase are large (11-40%). In contrast, only the reaction at the fast phase was observed at the nonpause sites and the enzyme amplitudes were large (63-66%) although the nucleotide incorporation rates (62-78 s-1) are similar to the fast phase rates at the pause sites. These indicate that DNA substrates were bound predominantly nonproductively at pause sites and productively at nonpause sites. However, the overall binding affinity of DNA substrates was measured by the nitrocellulose-DEAE double filter binding assay, binding affinity at both pause sites and nonpause sites was similar (9-38 nM). This indicates that substrates are bound tightly at the large binding cleft of HIV-1, although they may not be productively bound at the polymerase active site. These results and those reported elsewhere [Suo, Z., & Johnson, K. A. (1997) Biochemistry (manuscript submitted for publication)] are consistent with a model in which, at pause sites, HIV-1 RT remains bound to DNA substrates waiting for the melting of the next stem base pair of template secondary structure. Upon melting of the stem base pair, polymerization to fill the open template site is fast and largely irreversible, allowing RT to read through the stable hairpin structures.

Base Sequence↗
PubMed1997

Effect of RNA secondary structure on RNA cleavage catalyzed by HIV-1 reverse transcriptase.

Using a synthetic 66 nucleotide RNA template containing a stable hairpin structure derived from the HIV-1 genome, six predominant RNA cleavage products are found during DNA synthesis catalyzed by HIV-1 RT. These major RNA cleavage sites correlate well with the pause sites seen during primer elongation [Suo, Z., & Johnson, K. A. (1997) Biochemistry (manuscript submitted for publication)]. Thus, the RNase H and polymerase activities of RT are coupled as RT reads through the RNA secondary structure. The distance between the two active sites of HIV-1 RT is 19-20 base pairs of DNA/RNA heteroduplex when the next template base is not paired. The heteroduplex region was enlarged by 2-3 base pairs once RT encounters the template hairpin. A model for this change is presented. At the pause sites, the burst amplitudes of RNA cleavage are larger than the corresponding reaction amplitudes of next nucleotide incorporation at the polymerase site. Measurement of the steady state rates of RNA cleavage confirms that all substrates dissociate slowly from RT. These results suggest that while substrates are bound nonproductively at the polymerase site, they are still bound productively at the RNase H active site of RT. Characterization of an RNase H-deficient RT mutant (D443N) shows that RNase H activity is not critical for RT to read through the RNA secondary structure. HIV-1 nucleocapsid does not increase the processivity of HIV-1 RT but inhibits DNA elongation by blocking the binding of RT to DNA substrates.

Base Sequence↗
PubMed1997

The vasoactivity of A beta peptides.

We have demonstrated that freshly solubilized A beta peptides can enhance vasoconstriction by phenylephrine or endothelin of isolated rat aorta. Concentrations of peptide producing these effects (100 nM-1 microM) are much lower than those requiring toxicity to endothelial cells in culture, and effects are immediate, not requiring the prolonged time periods for aggregation necessary in A beta cell culture toxicity experiments. Pre-treatment with SOD diminishes the enhancement of vasoconstriction by A beta peptides, suggesting that the effects are partly mediated via a decrease in the nitric oxide/superoxide ratio. Enhancement of endothelin vasoconstriction is observed with A beta 1-40 and A beta 1-42, but not with A beta 25-35 even at 5 microM, again suggesting the mechanism of A beta vasoactivity is distinct from that of A beta cytotoxicity. These observations raise the possibility that A beta peptides in contact with the cerebrovasculature could result in vasoconstriction, hypoperfusion and oxygen free radical imbalance contributing to the neurodegeneration of AD.

Amyloid beta-Peptides↗
PubMed1997

Superoxide free radical and intracellular calcium mediate A beta(1-42) induced endothelial toxicity.

The 39-42 amino acid residue amyloid beta peptide (A beta), the major protein component in senile plaques and cerebrovascular amyloidosis in the brain in Alzheimer's disease (AD), has been shown to be neurotoxic in vitro. Accumulating data from several areas suggest that cerebrovascular dysfunction and damage may also play a significant role in the AD process. For instance, we have recently demonstrated enhanced vasoconstriction and resistance to relaxation in intact rat aorta treated with A beta [Thomas et al., beta-Amyloid-mediated vasoactivity and vascular endothelial damage, Nature, 380 (1996) 168-171]. Significant vessel damage occurred after thirty minutes of exposure, but could be prevented with superoxide dismutase. To further investigate the role of A beta toxicity on endothelial cells, we have applied A beta peptides to cultures of human aortic endothelial cells (HAEC). Our results show that both A beta(1-42) and A beta(25-35) are toxic to HAEC in a time- and dose-dependent manner, and that this toxicity can be partially prevented by the calcium channel blocker, verapamil, and the antioxidant, superoxide dismutase. The common form of A beta, A beta(1-40), which has been shown to be neurotoxic, is much less toxic to HAEC. A beta toxicity to HAEC occurs within 30 min of treatment with relatively lower doses than those usually observed in primary cultured neurons and vascular smooth muscle cells. It was recently reported that a variety of mutations in the beta-amyloid protein precursor gene and the Presenilin-1 and -2 genes linked to early-onset familial AD cause an increase in the plasma concentration of A beta(1-42) in mutation carriers [Scheuner et al., Secreted amyloid beta-protein similar to that in the senile plaques of Alzheimer's disease is increased in vitro by the presenilin 1 and 2 and APP mutations linked to familial Alzheimer's disease, Nature Med., 2 (1996) 864-870]. Human aortic endothelial cells are more sensitive to A beta(1-42) than A beta(1-40), via a pathway involving an excess of superoxide free radicals and influx of extracellular calcium. Finally, we have evidence that both apoptotic and necrotic processes are activated by the A beta peptides in these endothelial cells.

Amyloid beta-Peptides↗
PubMed1997

A novel grid polymerase chain reaction (G-PCR) approach at ultrastructural level to detect target DNA in cell cultures and tissues.

A novel grid polymerase chain reaction (G-PCR) method has been developed to be used at the ultrastructural level and with a high degree of resolution. Samples applied to test the method were fresh cell lines (CaSki, SiHa) and HPV-16 DNA-containing tissues rescued from routine paraffin blocks. The specimens were embedded in Epon-Araldite and/or hydrophilic-resin LRWhite. Ultrathin sections mounted on grids were subjected to G-PCR using an HPV-16-specific primer set. The amplified products were identified by auro-immunohistochemical labelling of the biotinylated nucleotide. The results indicated successful amplification of target DNA in both cell and tissue samples, being confined to the intranuclear region. The negative controls [HeLa cells, isolated mammary carcinoma cell cultures (MCF 7, and T47-D) (ATCC) (U.S.A.), normal thyroid tissue and steroid-producing tumour tissue] failed to exhibit any amplification of the target DNA sequences. The sensitivity of the G-PCR system was evaluated by performing a parallel in situ hybridization (ISH) of serial sections. The signals obtained from G-PCR were more intense than those of ISH and more informative as to the precise subcellular localization of amplicons.

Cell Line↗
PubMed1997

Diagnostic implications of p53 protein reactivity in nasal mucosa of nickel workers.

OBJECTIVE: To investigate whether the quantitation of p53 protein reactivity in nasal biopsies could be related to nickel exposure by comparing nickel workers with various control groups. STUDY DESIGN: Nasal biopsies taken from nickel workers (n = 93) were compared immunohistochemically to various controls, including office staff members (n = 34) and hospital attendants (n = 6). The material was studied immunohistochemically with p53 antibody DO-1. p53 Protein-positive cells were counted at 400x magnification. RESULTS: p53 Protein reactivity was found in 54% (49/93) of nickel workers, 50% (17/34) of office staff members, 67% (4/6) of hospital attendants. No differences were seen between roasting/smelting, electrolysis and other workers in the refinery. The positive cells were present predominantly in the basal layer of the epithelium. The number of positive nasal cells per field in the hospital attendants on the average was half of that in the workers and the office staff in the refinery. In no case in the control group were more than 10 cells per field seen. No significant differences in p53 protein positivity were observed between the three nickel worker groups and between production workers and office staff members. CONCLUSION: Accumulation of p53 protein in nickel workers seems not to be attributable to nickel exposure. The lack of p53 protein positivity in fetal tissues shows that the accumulation of p53 protein is an event taking place after birth. Stimuli in the natural environment during life may explain p53 protein positivity.

Adolescent↗
PubMed1993

Squamous cell carcinomas. An immunohistochemical study of cytokeratins and involucrin in primary and metastatic tumours.

The expression of cytokeratins (CK) 1, 4, 5/6, 8, 13, 18, 19 and 20 and involucrin in 42 cases of squamous cell carcinomas from various locations was examined. The tumours expressed CK5/6 in 55%, CK8 in 76%, CK13 in 43% and CK19 in 95% of cases. The CK5/6-positive primary tumours were from uterine cervix, head and neck, lung, skin, oesophagus and urinary bladder, and the CK13-positive primary tumours were from uterine cervix, lung and vulva. Metastatic squamous cell carcinomas from head and neck more frequently expressed CK5/6 and 13, 7/7 (100%) and 6/7 (86%) compared with 3/5 (60%) and 0/5 (0%) in the primary squamous cell carcinomas. Few cases were CK1, CK4 and CK18 immunoreactive. CK20 immunoreactivity was not observed. Involucrin was expressed in 71% of tumours, and most of the involucrin-positive cells were located at the central parts of tumour cell clusters except for one case in which the peripheral cells around tumour cell clusters were positive. Thus, expression of the so-called simple epithelial markers CK8 and CK19 occurs in the majority of squamous cell carcinomas. The absence of CK20 immunoreactivity may be helpful in differential diagnosis.

Carcinoma, Squamous Cell↗
PubMedDate not supplied

Phyllodes tumor of the breast: EGFR family expression and relation to clinicopathological features.

The expression of EGFR family members was examined by immunohistochemistry in 22 phyllodes tumors, and the results were evaluated together with immunohistochemical findings for proliferation markers Ki67 and BM28, and the tumor suppressor gene product p53. Light and electron microscopy were performed in all cases. Clinical information was obtained from the medial records. We did find that expression of EG FR, c-erbB-3 and c-erbB-4 proteins could be detected in the neoplastic mesenchymal cells, and that the expression increased with increasing malignancy. Increased expressions of Ki67, BM28, p53 and EGFR family members in neoplastic cells were associated with malignancy and unfavorable clinical course. Furthermore, the expression of ER-alpha and PR in the epithelial cells of phyllodes tumors was increased compared to that in normal breast epithelium. Finally, the application of electron microscopy helped to identify a group of malignant tumors, revealing neoplastic cells with characteristic nuclear indentations, as well as an increasing number of myofibroblasts.

Adolescent↗
PubMedDate not supplied

Expression of EGFR family and steroid hormone receptors in ductal carcinoma in situ of the breast.

The expression of EGFR family and steroid hormone receptors was examined in a series of 40 cases of pure ductal carcinoma in situ (DCIS) of the breast by immunohistochemical staining of paraffin-embedded sections. Hematoxylin and eosin-stained sections were used to classify the tumors according to the published criteria by Holland et al. (Holland R, Peterse JL, Millis RR, et al. Semin Diagn Pathol. 1994;1 1:167-180). Of the tumors 48% were immunoreactive for EGFR, 63% for c-erbB-2, 78% for c-erbB-3, 95% for c-erbB-4, 88% for estrogen receptor (ER) and 80% for progesterone receptor (PR). Statistically significant association between histological grade (differentiation) and c-erbB-2 protein expression was seen (p <.001). In addition, expression of c-erbB-4 protein was associated with c-erbB-2 (p=.004), c-erbB-3 (p=.058), ER (p=.002) and PR (p=.004). It is concluded that c-erbB-2 expression in DCIS is associated with high-grade pathological features, and a higher c-erbB-2 expression is seen in DCIS than in invasive breast carcinomas. A possible association between extensive expression of c-erbB-4 and steroid hormone receptors in proliferative and premalignant breast epithelial cells and the c-erbB-2 expression in DCIS and invasive breast carcinomas is discussed.

Adult↗
PubMedDate not supplied

Squamous cell carcinomas, an immunohistochemical and ultrastructural study.

Fourty-seven squamous cell carcinomas (SCCs) were studied by light microscopy, immunohistochemistry and electronmicroscopy. Nineteen percent (9 cases) of SCCs in different locations were immunoreactive for CAM5.2 and three poorly differentiated SCCs did not express cytokeratins 6 and 18. No cases were positive for c-erbB2 protein. p53 protein overexpression was found in malignant cells in 40% of the primary tumours and in 60% of the lymph node metastases. Four poorly differentiated SCCs expressed vimentin and in these cases the tumour cells had accumulations of less dense intermediate filaments in cytoplasm.

Biomarkers, Tumor↗
PubMedDate not supplied

Growth factor receptors in hematopoietic stem cells: EPH family expression in CD34+ and CD133+ cell populations from mobilized peripheral blood.

Cell-surface antigen expression of hematopoietic stem cells has a crucial role in characterizing cell subpopulation with distinct functional properties. The Eph receptors are the largest receptor tyrosine kinase family being involved in processes like vascular remodelling during development and physiological and pathological angiogenesis. Some Eph/Ephrin members are expressed in hematopoietic cells. The ability to isolate purified cell populations co-expressing CD34 and CD133 antigens as most commonly used markers for identification of hematopoietic progenitors has provided the opportunity to identify their surface-receptor profile. As positively expressed CD34 and CD133 cells take place not only in hematopoietic but also in endothelial differentiation, we aimed to define the Eph/Ephrin characteristic of these cells and relate these findings to new therapy strategies. Positive selections of CD34 and CD133 cells from PBPC in lymphoma patients were performed using magnetic beads and AutoMACS (Miltenyi Biotec) device. The purity of isolated cells was tested by flow cytometry. Immunocytochemistry was used to assess the Eph/Ephrin expression profile of positively selected samples. Our study revealed that all samples (10 from CD34+ and 8 from CD133+ cells) expressed one or more of Eph/Ephrin antigens in different proportions. All CD34+ cell samples, and 6 of 8 in the CD133+ cell fraction were strongly immunoreactive for EphA2. EphB2 was strongly expressed in all CD133+ cases, but 50% of the CD34 positive group lacked or weakly expressed this receptor. EphB4 was negative in 9 of 10 CD34+ cases and in all CD133+ cells. Thus, we have shown the surface marker profile of positively selected CD34 and CD133 cells in leukapheresis samples from lymphoma patients with regard to Eph/Ephrin receptors and discussed their biological clinical potential.

AC133 Antigen↗
PubMedDate not supplied

Undifferentiated carcinoma: an immunohistochemical and ultrastructural study.

Twenty-eight undifferentiated carcinomas (UCs) were immunohistochemically investigated with antibodies against cytokeratins (CKs), vimentin, p53 protein, c-erbB-2 protein and CEA. The diagnoses were based on the findings of conventional histopathology, immunohistochemistry and electron microscopy. CKs8, 18 and 19 were the CKs most frequently present in these tumors, in 61%, 61% and 82% of the cases, respectively. Nine of the 28 (32%) UCs were CKs5/6 positive. Expression of CK20 was found in three (11%) cases. Four UCs were sub-type Cks negative, but one of them was confirmed AE1/AE3 positive. P53 protein overexpression was found in nine (32%) cases. One of the patients with p53 protein positive tumors has been alive for 174 months. Nine (32%) UCs expressed vimentin, which included all of the three thyroid UCs. Comparing with our previous study of squamous cell carcinomas, we found that vimentin and CK18 are more frequently expressed in UCs. The overexpression of p53 protein is similar in the two groups of carcinomas and thus, p53 protein is not a differentiation marker in these tumors. Finally, we recommend the use of a CK "cocktail of antibodies" in the diagnosis of UCs.

Adolescent↗
PubMedDate not supplied

Lack of expression of c-erbB-2 oncoprotein in human esophageal squamous cell carcinomas.

Fifty-one cases of esophageal squamous cell carcinoma were immunohistochemically investigated with monoclonal c-erbB 2 oncoprotein antibody. No tumor showed plasma membrane immunostaining for c-erbB-2 protein. Occasionally, unspecific cytoplasmic staining was found in minor tumor cell populations. The present results show that c-erbB-2 oncoprotein is not overexpressed in esophageal squamous cell carcinomas and does not play a central role in the tumorigenesis.

Animals↗