Somatic Cell Mutants Resistant to Retrovirus Replication: Intracellular Blocks during the Early Stages of Infection

To identify cellular functions involved in the early phase of the retroviral life cycle, somatic cell mutants were isolated after selection for resistance to infection. Rat2 fibroblasts were treated with chemical mutagens, and individual virus-resistant clones were recovered after selection for resistance to infection. Two clones were characterized in detail. Both mutant lines were resistant to infection by both ecotropic and amphotropic murine viruses, as well as by human immunodeficiency virus type 1 pseudotypes. One clone showed a strong block to reverse transcription of the retroviral RNA, including formation of the earliest DNA products. The second clone showed normal levels of viral DNA synthesis but did not allow formation of the circular DNAs normally found in the nucleus. Cell fractionation showed that the viral preintegration complex was present in a form that could not be extracted under conditions that readily extracted the complex from wild-type cells. The results suggest that the DNA was trapped in a nonproductive state and excluded from the nucleus of the infected cell. The properties of these two mutant lines suggest that host gene products play important roles both before and after reverse transcription

Mutagenesis analysis of the zinc-finger antiviral protein

BACKGROUND: The zinc-finger antiviral protein (ZAP) specifically inhibits the replication of certain viruses, including murine leukemia virus (MLV), by preventing the accumulation of viral mRNA in the cytoplasm. ZAP directly binds to the viral mRNA through the zinc-finger motifs and recruits the RNA exosome to degrade the target RNA. RNA helicase p72 is required for the optimal function of ZAP. In an attempt to understand the structure-function relationship of ZAP, we performed alanine scanning analysis. RESULTS: A series of ZAP mutants was generated, in which three consecutive amino acids were replaced with three alanines. The mutants were analyzed for their antiviral activities against pseudotyped MLV vector. Out of the nineteen mutants analyzed, seven displayed significantly lower antiviral activities. Two mutations were in the very N-terminal domain, and five mutations were within or around the first and second zinc-finger motifs. These mutants were further analyzed for their abilities to bind to the target RNA, the exosome, and the RNA helicase p72. Mutants Nm3 and Nm63 lost the ability to bind to RNA. Mutants Nm 63 and Nm93 displayed compromised interaction with p72, while the binding of Nm133 to p72 was very modest. The interactions of all the mutants with the exosome were comparable to wild type ZAP. CONCLUSIONS: The integrity of the very N-terminal domain and the first and second zinc-finger motifs appear to be required for ZAP's antiviral activity. Analyses of the mutants for their abilities to interact with the target RNA and RNA helicase p72 confirmed our previous results. The mutants that bind normally to the target RNA, the exosome, and the RNA helicase p72 may be useful tools for further understanding the mechanism underlying ZAP's antiviral activity

Isolation of suppressor genes that restore retrovirus susceptibility to a virus-resistant cell line

BACKGROUND: Genetic selections in mammalian cell lines have recently been developed for the isolation of mutant cells that are refractory to infection by retroviruses. These selections have been used to recover lines that block early postentry stages of infection, either before reverse transcription or before nuclear entry. The mechanisms of action of these blocks remain unknown. RESULTS: We have devised a method for the selection of genes from cDNA libraries that suppress the block to virus infection, and so restore virus susceptibility. The protocol involves the transformation of pools of resistant cells by cDNA expression libraries, followed by the selection for rare virus-sensitive cells, using multiple rounds of selection after infection by marked viral vector genomes. The suppressor genes were then recovered from these virus sensitive cells, and their ability to restore virus susceptibility was confirmed by reintroduction of these cDNAs into the resistant line. CONCLUSIONS: The identities of these genes provide insights into the mechanism of virus resistance and will help to define new pathways used during retrovirus infection. The methods for gene isolation developed here will also permit the identification of similar suppressors that modify or override other recently identified virus resistance genes

CMOS optoelectronics: Implementation and application.

An investigation of three different photo sensitive devices (PSD) that can be fabricated by using Northern Telecom\u27s 1.2 and 3.0 micro CMOS technology is described in the thesis. A MOSFET has been optimized to enhance the photocurrent and use a parasitic photodiode formed between the source and substrate as a PSD. A conventional BJT structure with a small emitter area has been optimized to enhance the photocurrent and utilize the parasitic photodiode formed at the base-collector junction as a PSD. In addition, a field effect modified (FEM) vertical BJT with a collector-connected annular ring around a small emitter area has been used to create a more sensitive and faster responding parasitic photodiode at the base-collector junction that can be used as a PSD. Each of the three distinct structures has been fabricated in both 1.2 and 3.0 micro technology in a number of different geometries as part of a parameter optimization study. A number of experiments have been carried out on the test cells to measure photocurrent as a function of light intensity using incandescent and LASER light sources. The most sensitive PSD was formed using a 3.0 micro FEM BJT design. The device is being used to create a photo sensitive array that will act as input nodes for an artificial neural network that is being employed as an intelligent sensor for process control based on non-contact measurement. As the array will be used to image LASER generated patterns formed by object-oriented beam steering, high sensitivity is not necessary, whereas a structure that can be readily integrated into a regular array is most important. Source: Masters Abstracts International, Volume: 33-04, page: 1307. Adviser: W. C. Miller. Thesis (M.Sc.A.)--University of Windsor (Canada), 1994

Hh pathway expression in the blood, synovial cells and chondrocytes of different rheumatoid arthritis models

Purpose: To investigate the effect of the hedgehog (Hh) pathway inhibitor, cyclopamine, and activator purmorphamine on articular cartilage cell proliferation. Methods: Rats were subjected to AA and CIA models. Secondary paw swelling was measured at 12, 15, 18, 21, 24, 27, and 30 days. The rats were sacrificed on day 30. Tissues from the cartilage and knee joints were collected. Cell proliferation was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5- diphenyltetrazolium bromide (MTT) assay while cell apoptosis was determined by annexin V-fluorescein isothiocyanate/propidium iodide assay. Protein expression levels of Shh, Ptch1 and Gli1 were determined by Western blotting. Results: Compared with the control group, arthritis index and secondary foot swelling of the adjuvant arthritis (AA) and collagen-induced arthritis (CIA) groups deteriorated significantly (p < 0.05). MTT data revealed that cyclopamine promoted articular cartilage cell proliferation of the AA and CIA groups. The cell proliferation rates of AA and CIA groups were significantly higher than that of control group (p < 0.05). Flow cytometry showed that the cell apoptosis rates of AA and CIA groups were significantly lower than that of control group (p < 0.05). Compared with control, cyclopamine decreased the protein expression levels of sonic Hh, patched homologue 1 and glioma-associated oncogene homologue, but the effect of purmorphamine was the reverse. Conclusion: Hh pathway inhibitor (cyclopamine) and activator (purmorphamine) affect the expression of Hh pathway. Disruption of the Hh pathway may be of potential therapeutic significance in protecting articular cartilage from rheumatoid arthritis

The nanoscale phase distinguishing of PCL-PB-PCL blended in epoxy resin by tapping mode atomic force microscopy

In this work, we investigated the bulk phase distinguishing of the poly(ε-caprolactone)-polybutadiene-poly(ε-caprolactone) (PCL-PB-PCL) triblock copolymer blended in epoxy resin by tapping mode atomic force microscopy (TM-AFM). We found that at a set-point amplitude ratio (rsp) less than or equal to 0.85, a clear phase contrast could be obtained using a probe with a force constant of 40 N/m. When rsp was decreased to 0.1 or less, the measured size of the PB-rich domain relatively shrank; however, the height images of the PB-rich domain would take reverse (translating from the original light to dark) at rsp = 0.85. Force-probe measurements were carried out on the phase-separated regions by TM-AFM. According to the phase shift angle vs. rsp curve, it could be concluded that the different force exerting on the epoxy matrix or on the PB-rich domain might result in the height and phase image reversion. Furthermore, the indentation depth vs. rsp plot showed that with large tapping force (lower rsp), the indentation depth for the PB-rich domain was nearly identical for the epoxy resin matrix