Biomedical subjects

Xiao-Ming Sun

Publications and source records attributed to Xiao-Ming Sun.

6 recordsLinked to original sources

PubMed2007

Evidence for the involvement of carbon-centered radicals in the induction of apoptotic cell death by artemisinin compounds.

Artemisinin and its derivatives are currently recommended as first-line antimalarials in regions where Plasmodium falciparum is resistant to traditional drugs. The cytotoxic activity of these endoperoxides toward rapidly dividing human carcinoma cells and cell lines has been reported, and it is hypothesized that activation of the endoperoxide bridge by an iron(II) species, to form C-centered radicals, is essential for cytotoxicity. The studies described here have utilized artemisinin derivatives, dihydroartemisinin, 10beta-(p-bromophenoxy)dihydroartemisinin, and 10beta-(p-fluorophenoxy)dihydroartemisinin, to determine the chemistry of endoperoxide bridge activation to reactive intermediates responsible for initiating cell death and to elucidate the molecular mechanism of cell death. These studies have demonstrated the selective cytotoxic activity of the endoperoxides toward leukemia cell lines (HL-60 and Jurkat) over quiescent peripheral blood mononuclear cells. Deoxy-10beta-(p-fluorophenoxy)dihydroartemisinin, which lacks the endoperoxide bridge, was 50- and 130-fold less active in HL-60 and Jurkat cells, respectively, confirming the importance of this functional group for cytotoxicity. We have shown that chemical activation is responsible for cytotoxicity by using liquid chromatography-mass spectrometry analysis to monitor endoperoxide activation by measurement of a stable rearrangement product of endoperoxide-derived radicals, which was formed in sensitive HL-60 cells but not in insensitive peripheral blood mononuclear cells. In HL-60 cells the endoperoxides induce caspase-dependent apoptotic cell death characterized by concentration- and time-dependent mitochondrial membrane depolarization, activation of caspases-3 and -7, sub-G(0)/G(1) DNA formation, and attenuation by benzyloxycarbonyl-VAD-fluoromethyl ketone, a caspase inhibitor. Overall, these results indicate that endoperoxide-induced cell death is a consequence of activation of the endoperoxide bridge to radical species, which triggers caspase-dependent apoptosis.

Antimalarials↗

PubMed2006

Sequencing and analysis of a genomic fragment provide an insight into the Dunaliella viridis genomic sequence.

Dunaliella is a genus of wall-less unicellular eukaryotic green alga. Its exceptional resistances to salt and various other stresses have made it an ideal model for stress tolerance study. However, very little is known about its genome and genomic sequences. In this study, we sequenced and analyzed a 29,268 bp genomic fragment from Dunaliella viridis. The fragment showed low sequence homology to the GenBank database. At the nucleotide level, only a segment with significant sequence homology to 18S rRNA was found. The fragment contained six putative genes, but only one gene showed significant homology at the protein level to GenBank database. The average GC content of this sequence was 51.1%, which was much lower than that of close related green algae Chlamydomonas (65.7%). Significant segmental duplications were found within this fragment. The duplicated sequences accounted for about 35.7% of the entire region. Large amounts of simple sequence repeats (microsatellites) were found, with strong bias towards (AC)(n) type (76%). Analysis of other Dunaliella genomic sequences in the GenBank database (total 25,749 bp) was in agreement with these findings. These sequence features made it difficult to sequence Dunaliella genomic sequences. Further investigation should be made to reveal the biological significance of these unique sequence features.

Animals↗

PubMed2004

Highly sensitive WO3 hollow-sphere gas sensors.

In this paper, we describe how WO(3) hollow spheres have been synthesized in solution phase by the controlled hydrolysis of WCl(6) using novel carbon microspheres as the templates. All of the products were characterized by X-ray powder diffraction (XRD), scanning electronic microscopy (SEM), and transmission electron microscopy (TEM). The as-synthesized spheres had large diameters of about 400 nm and thin shells of about 30 nm composed of numerous small nanocrystals. Prompted by the porous structure and small crystal size of the shell wall, we constructed WO(3) hollow-sphere gas sensors and found that these sensors had good sensitivity to alcohol, acetone, CS(2), and other organic gases.

Journal Article↗

PubMed2004

Caspase activation inhibits proteasome function during apoptosis.

The ubiquitin/proteasome system regulates protein turnover by degrading polyubiquitinated proteins. To date, all studies on the relationship of apoptosis and the proteasome have emphasized the key role of the proteasome in the regulation of apoptosis, by virtue of its ability to degrade regulatory molecules involved in apoptosis. We now demonstrate how induction of apoptosis may regulate the activity of the proteasome. During apoptosis, caspase activation results in the cleavage of three specific subunits of the 19S regulatory complex of the proteasome: S6' (Rpt5) and S5a (Rpn10), whose role is to recognize polyubiquitinated substrates of the proteasome, and S1 (Rpn2), which with S5a and S2 (Rpn1) holds together the lid and base of the 19S regulatory complex. This caspase-mediated cleavage inhibits the proteasomal degradation of ubiquitin-dependent and -independent cellular substrates, including proapoptotic molecules such as Smac, so facilitating the execution of the apoptotic program by providing a feed-forward amplification loop.

Apoptosis↗

PubMed2002

Structure-directing coordination template effect of ethylenediamine in formations of ZnS and ZnSe nanocrystallites via solvothermal route.

ZnS and ZnSe precursors (ZnS x 0.5en and ZnSe x 0.5en, en = ethylenediamine) were prepared via a solvothermal process using ethylenediamine as solvent. Phase-pure hexagonal wurtzite ZnS and ZnSe products were obtained by annealing the precursors in argon stream at temperatures above 350 degrees C. The role of ethylenediamine as a structure-directing coordination molecular template responsible for the morphologies of the annealed products was discussed. This work provided further insights into the solvent coordination molecular template (SCMT) mechanism previously proposed to explain the growth mechanism of CdE (E = S, Se, Te) nanorods in ethylenediamine (Inorg. Chem. 1999, 38, 1382). The as-prepared precursors as well as the annealed products were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), infrared absorbance spectroscopy (IR), thermogravimetric analysis (TGA), X-ray fluorescence (XRF) analysis, and combustion analysis for C, N, H contents.

Journal Article↗

PubMed2002

Bcl-2 and Bcl-xL inhibit CD95-mediated apoptosis by preventing mitochondrial release of Smac/DIABLO and subsequent inactivation of X-linked inhibitor-of-apoptosis protein.

Bcl-2 and Bcl-x(L) are reported to inhibit CD95-mediated apoptosis in "type II" but not in "type I" cells. In the present studies, we found that stimulation of CD95 receptors, with either agonistic antibody or CD95 ligand, resulted in the activation of caspase-8, which in turn processed caspase-3 between its large and small subunits. However, in contrast to control cells, those overexpressing either Bcl-2 or Bcl-x(L) displayed a distinctive pattern of caspase-3 processing. Indeed, the resulting p20/p12 caspase-3 was not active and did not undergo normal autocatalytic processing to form p17/p12 caspase-3, because it was bound to and inhibited by endogenous X-linked inhibitor-of-apoptosis protein (XIAP). Importantly, Bcl-2 and Bcl-x(L) inhibited the release of both cytochrome c and Smac from mitochondria. However, since Smac alone was sufficient to promote caspase-3 activity in vitro by inactivating XIAP, we proposed the existence of a death receptor-induced, Smac-dependent and apoptosome-independent pathway. This type II pathway was subsequently reconstituted in vitro using purified recombinant proteins at endogenous concentrations. Thus, mitochondria and associated Bcl-2 and Bcl-x(L) proteins may play a functional role in death receptor-induced apoptosis by modulating the release of Smac. Our data strongly suggest that the relative ratios of XIAP (and other inhibitor-of-apoptosis proteins) to active caspase-3 and Smac may dictate, in part, whether a cell exhibits a type I or type II phenotype.

Apoptosis↗