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Biomedical subjects

A Omar

Publications and source records attributed to A Omar.

At least 55 records · Page 3Linked to original sources
PubMed1989

The use of sulfite to study the mechanism of membrane fusion induced by E1 of Semliki Forest virus.

In this study we have used 35S-labeled sulfite to modify the disulfide bonds of the proteins at the cell surface of Semliki Forest-infected Aedes albopictus cells before and after low pH treatment. This reagent specifically cleaves disulfide bonds and concomitantly reacts with the newly formed cysteines, thereby labeling the respective protein. Treatment of the infected cells with sulfite led to inhibition of the fusion activity only when applied after low pH exposure. These cells exhibited substantial incorporation of the label into the viral E1 glycoprotein as compared to the E2 glycoprotein. These results provide direct evidence for the low pH-induced conformational change of E1 during the generation of its fusogenic potential.

Electrophoresis, Polyacrylamide Gel↗
PubMed1988

Semliki Forest virus particles containing only the E1 envelope glycoprotein are infectious and can induce cell-cell fusion.

Hydrophobic interaction chromatography (phenyl- and octyl-Sepharose) was performed with Semliki Forest virus to investigate the effect of low pH on its hydrophobicity. At neutral pH, the virus could be bound to the column and completely eluted by the detergent NP-40. Low pH treatment of virus prior to application to the column resulted in stronger binding as reflected by the increased amount of detergent necessary to totally elute the virus. If, however, the low pH treatment was done after binding of the virus to the column, only 15% of the input virus could be eluted by the detergent, indicating a drastic increase in hydrophobicity. Thus binding of the virus to a hydrophobic environment potentiates the effect of low pH on viral hydrophobicity. Trypsin digestion of column-bound virus after low pH treatment resulted in complete digestion of E2 and E3; however, E1 was totally resistant. From this result, we conclude that E1 alone is responsible for the hydrophobic interaction. We have made use of these observations to produce viral particles which were devoid of E2 and E3 by trypsin digestion in the presence of octyl glucoside. These E1 viral particles were infectious and could induce membrane fusion. We conclude that only E1 is necessary and sufficient to mediate membrane fusion. Acid pH induces a drastic increase in the hydrophobicity of E1 which probably facilitates its interaction with the lipid bilayers during the fusion event in endosomes.

Hydrogen-Ion Concentration↗
PubMed1986

Fusion of Semliki Forest virus infected Aedes albopictus cells at low pH is a fusion from within.

Herein, it is shown for the first time that the mechanism of fusion followed in Aedes albopictus cells infected with Semliki Forest virus induced by low pH exposure is a "fusion from within". Several parameters were studied disclosing that the development of the fusion capacity of the cells is directly related to the synthesis of viral specific products. These findings were further substantiated by utilizing various chemicals to inhibit viral specific events during infection, protein synthesis and maturation. Removal of exogenous virions produced at 16 hours post infection by proteinase K digestion clearly revealed that the viral proteins located at the cell surface and not the exogenous virions were responsible for the fusogenic activity. The presence of these viral proteins at the cell surface was disclosed by immunofluorescence employing anti-SFV antibodies elicited in rabbits. Additional evidence for the participation of the viral proteins at the cell surface in the fusion reaction was obtained by Bromelaine digestion which inhibited the fusion and tunicamycin treatment which only partially inhibited the fusion but revealed the inevitable presence of the E1 protein.

Aedes↗
PubMed1985

Conformational changes at pH 6 on the cell surface of Semliki Forest virus-infected Aedes albopictus cells.

The mechanism of Semliki Forest virus-induced fusion from within at low pH was studied in Aedes albopictus cells. The fusion was found to occur in at least two steps, namely, a fast initial step which is pH dependent and temperature independent, and a second slower process which is pH independent and temperature dependent. The initiation step induced by low pH exposure constitutes an irreversible conformational change of a protein probably of viral origin located at the cell surface.

Aedes↗
PubMed1985

One-step separation of the components of Semliki Forest virus by cation exchange chromatography.

Although several procedures for isolating viral proteins have been described, the simultaneous separation of all the viral macromolecules in a single step has not yet been reported. We now describe TUA (Triton X-100, urea, acetic acid, pH 4.2)-SP (Sulphopropyl)-Trisacryl cation exchange chromatography, which proved to be ideal for this purpose. Optimal conditions for chromatography were established by screening on TUA-PAGE (polyacrylamide gel electrophoresis) using a horizontal linear 0-8.5 M urea gradient followed by identification of the proteins by SDS-PAGE in the second dimension. Segregation of the constituents of Semliki Forest virus cultivated in two cell lines (chicken embryo fibroblasts and Aedes albopictus cells) was studied, considering that the proteins have identical primary sequences but diverse post-translational modifications, thereby allowing the efficacy of the procedure and its applicability to different viruses to be tested. The results show that the RNA and lipids did not bind to the cation exchange in TUA and were eluted in the flow-through fractions. The proteins were fractionated using 3 linear NaCl gradients in TUA. SDS-PAGE revealed that all the proteins could be purified by this procedure. Furthermore, a direct correlation was obtained between the distance migrated by the proteins in the TUA-PAGE and their order of elution from the TUA-cation exchange column.

Chemical Fractionation↗
PubMed1979

Quantitation of digital clubbing by shadowgram technique.

Finger clubbing was quantified from the magnified silhouette of the right index finger in controls and patients with clubbing, using a simple shadowgram technique. There was good correlation between clinical assessment and measurement of both the profile angle and the hyponychial angle. The hyponychial angle appeared to be a more accurate indicator of clubbing than the profile angle.

Child↗
PubMed1979

Polyploidization and hemiploidization induced by PUVA in vivo.

To obtain additional information on the in vivo injury induced by PUVA treatment, primary cultures were initiated from biopsies of the uninvolved skin of 15 PUVA-treated psoriatic patients, and the cells generated were analysed for morphological and chromosomal modifications. Three biopsies were obtained from each patient, the first one before commencing PUVA therapy (control) and the other two during the course of therapy. It was found that PUVA treatment has diverse effects on the mitotic activity, mitotic mechanisms and chromosomes of the cutaneous cells: (1) an inhibition of cell proliferation during the early stages of therapy followed by a reversion to normal proliferation as the PUVA treatments were continued; the production of (2) cells with more than one nucleus, (3) macrocells, (4) cells with micronuclei, (5) polyploid cells, (6) haploid cells, (7) cells with 13 chromosomes denoting a twofold reduction in the normal number of metaphase chromosomes, (8) end-associations of the chromosomes as in the pachytene phase of meiosis (9) diplotene chromosomes, and (10) chromosomal translocations.

Cell Division↗
PubMed1978

Acute leukemia in Malaysian children.

A review of acute childhood leukemia in the University Hospital, Kuala Lumpur reveals no significant differences in either the epidemiological or clinical features between Malaysian and Caucasian children. BCG does not appear to have conferred any protection against the occurrence of leukemia. With the introduction of total therapy 4 of 10 patients with good prognostic features and 3 of 15 patients with poor prognostic features have survived 3 years. Prognosis appears to correlate with adopted clinical criteria.

Antineoplastic Agents↗
PubMed1977

Induction of multinucleate cells by 8-MOP and UV treatment in vitro and in vivo.

Fibroblast cells were treated with a single dose of 8-methoxypsoralen (8-MOP) and long-wave UV irradiation in vitro and the cytotoxic effects of the treatment followed up for 5 passages. During the first passage, there was an inhibition in cell proliferation, the induction of chromosomal aberrations and the production of macrocells as well as cells with more than one nucleus. In the subsequent passages, the proliferation rate of the cells gradually normalized but there was a concomitant increase in chromosomal aberrations and in the number of macrocells and multinucleate cells. Specimens, which were taken from the uninvolved skin of psoriatic patients who had been treated between 20 and 40 times with an oral dose of 8-MOP and black light irradiation (PUVA) also revealed the presence of binucleate, tetranucleate and multinucleate epidermal cells as well as binucleate and tetranucleate dermal fibroblasts.

Cell Nucleus↗
PubMed1977

Photo-onycholysis induced by 8-methoxypsoralen.

Two patients, who we had under surveillance since 1969, were found to develop photo-onycholysis from orally administered 8-methoxypsoralen and sunlight irradiation. Morphological examination of the nail bed revealed characteristics of a microtrauma. The photosensitizing effect of the drug induced the generation numerous binucleate, tetranucleate and multinucleate epithelial cells as well as numerous binucleate and tetranucleate fibroblasts in the dermis.

Administration, Oral↗