Cross-infection enhancement among African flaviviruses by immune mouse ascitic fluids

Cross-infection enhancement of seven African flaviviruses by subneutralising concentrations of antibody in immune ascitic fluids was investigated in P388D1 cell culture. Infection by all the seven flaviviruses tested was enhanced by homologous and at least one of six heterologous immune mouse ascitic fluids (IMAF) tested. Enhancement ratios and enhancing antibody titres were higher in homologous than in heterologous enhancement. Zika, Wesselsbron, Uganda S and West Nile viruses were enhanced in culture by all the IMAF tested. Enhancement of Dakar bat and Yellow fever viruses was produced by five heterologous IMAF, but Potiskum virus was enhanced by one heterologous flavivirus antibody. The antibody to Potiskum virus was the most potent mediator of heterologous infection enhancement; all six heterologous flaviviruses were markedly enhanced by this antibody.     

Effect of mouse interferons on the development of Ehrlich ascitic carcinoma

Intraperitoneal injection of various preparations of mouse interferons (L cell tissue culture interferons, concentrated or partly purified, and also serum interferon) significantly inhibited the development of Ehrlich's ascites carcinoma in randombred mice. In view of comparatively low activity of serum interferon, the effect of normal mouse serum on the tumour development and its action on L cell tissue culture interferon was investigated. It was shown that normal mouse serum inhibits the action of L cell tissue culture interferon and promotes the development of Ehrlich's ascites carcinoma.     

Native structure of rat liver immune proteasomes

Native structure of active forms of rat liver immune proteasomes has been studied by two-dimensional electrophoresis method modified for analysis of unpurified protein fractions. The developed method allowed revealing the proteasome immune subunits LMP7 and LMP2 in 20S subparticles and in the structures bound to one or two PA28αβ activators, but not to the PA700 activator, which is involved in the hydrolysis of ubiquitinated proteins. The results obtained indicate the participation of the immune proteasomes in delicate regulatory mechanisms based on the production of biologically active peptides and exclude their participation in processes of crude degradation of “rotated” ubiquitinated proteins.     

Selective shedding of gangliosides by cells of mouse ascitic sarcoma-37

The profile and content of gangliosides associated with tumour cells of mouse sarcoma-37 and exfoliated from the cell surface were determined. It was shown that 20% of tumour gangliosides shed from the cell surface and only about 7% of all the shed gangliosides were contained in plasma membrane fragments. When incubated in vitro at 37 degrees C for 1 hour, the tumour cells were found to release less than 2% of cellular gangliosides. The main components of cellular gangliosides corresponded in their chromatographic behaviour to GM2 (31-32% of the total ganglioside content), GD3 (17-18%), GD1a (9-11%), GD2 (16-17%) and hematosides (19-21%). The profiles of in vivo and in vitro shed gangliosides were similar but strongly differed from those of cellular gangliosides: the relative content of GM2 was 70-75% and the other gangliosides were found in negligible amounts. The data show that GM2 accumulation in extracellular spaces is rather the result of its selective shedding than the shedding of products of "incomplete" cellular ganglioside synthesis.     

Phosphorylation of proteasomes and alpha-RNP from rat liver cells

In eukaryotic cells the population of proteasomes is heterogeneous. Here we have shown that proteasomes from nuclei and cytoplasm of rat liver cells differ in their subunit patterns. The subunit pattern of alpha-RNP differs from that of proteasomes, however, alpha-RNP particles contain the number of 26S proteasome subunits. Moreover, the proteasomes contain subunits of alpha-RNP. We have shown for the first time that nuclear proteasomes and alpha-RNP are hyperphosphorylated on threonine residues. Differences in phosphorylation state of subunits of nuclear and cytoplasmic proteasomes and alpha-RNP on threonine and tyrosine residues have been revealed. A suggestion is put forward that hyperphosphorylation of subunits may determine nuclear localization of these complexes in rat liver cells. The results obtained suggest that a highly specialized system of protein kinases and phosphatases may be involved in the regulation of phosphorylation state of different populations of proteasomes and alpha-RNP in rat liver cells.     

4,5-S-RNAI in virus-specific polyribosomes from ascitic Krebs 2 carcinoma cells infected with encephalomyocarditis virus

Polyribosomes of Krebs 2 ascite carcinoma cells non-infected and infected with encephalomyocarditis (EMC) virus contain a heterogeneous population of low molecular weight small RNAs. Analysis of the RNAs by polyacrylamide gel electrophoresis did not reveal any qualitative differences in the small RNA sets within the composition of polyribosomes from virus-infected and non-infected cells. However, the content of one of the small RNAs was markedly elevated in polyribosomes from virus-infected cells. As can be followed from partial determination of its primary structure, this small mRNA is identical to 4,5S-RNAI previously detected in the nuclei of Novikov hepatoma cells of the rat. The data obtained suggest that 4,5S-RNAI can be involved in the regulation of protein synthesis in virus-infected cells.     

Formation of immune proteasomes and development of the immune system in mammalian ontogenesis

Current concepts of the structure of immune proteasomes and their role in immune response have been considered. The main attention has been paid to the formation of immune proteasomes in secondary lymphoid and nonlymphoid organs during ontogenesis of mammals. The causes of ineffective formation of immune system in early postnatal development have been discussed.     

Formation of immune proteasomes and development of immune system in ontogenesis of mammals

Current concepts of the structure of immune proteasomes and their role in immune response have been considered. The main attention has been paid to the formation of immune proteasomes in secondary lymphoid and nonlymphoid organs during ontogenesis of mammals. The causes of ineffective formation of immune system in early postnatal development have been discussed.     

Localization of proteasomes in plant cells

Summary Proteasomes, also known as multicatalytic proteinase complexes, were localized in suspension cells of potato (Solanum tuberosum) by direct immunofluorescence using polyclonal antibodies labelled with fluorescein isothiocyanate. The method used allows an estimate of relative amounts of proteasomal antigens in different cell components. Proteasomes are present in the nuclei and the cytoplasm. The nucleoplasm contains small areas of weak fluorescence. The peripheral cytoplasm and possibly elements of the cytoskeleton show higher fluorescence than other parts of the cytoplasm. This indicates a localization of proteasomes similar to that known from animal cells.Abbreviations DMSO dimethylsulfoxide - EGTA ethyleneglycol-bis-(-aminoethylether)-N,N,N,N-tetra acetic acid - FITC fluorescein isothiocyanate - PBS phosphate buffered saline - PIPES piperazine-1,4-bis-(2-ethanesulfonic acid)     

Isolation of metabolic cooperation-defective variants from mouse embryonal carcinoma cells

We describe the isolation from the HGPRT^? embryonal carcinoma cell line PC13TG8 of a variant, R5/3, defective in metabolic cooperation. This was achieved in two stages via an intermediate, R2/1, using a selective system in which the HGPRT^? embryonal carcinoma cells were co-cultured with HGPRT⁺ cells in 6-thioguanine. R5/3 cells show increased survival compared with PC13TG8 when retested under selection conditions, and a reduction in grain count index when tested by autoradiography as recipients of [³H]hypoxanthine-labelled nucleotides from wild-type donors and as donors of [³H]thymidine- and [³H]adenine-labelled nucleotides to suitably marked recipients. However, a low residual fraction of heavily labelled recipients is found in all autoradiographic experiments with R5/3 cells. This is not due to heterogeneity of either donor or recipient populations. We also describe the development of a colony-formation assay for metabolic cooperation based on the “kiss of life” phenomenon, in which R5/3 shows very poor survival compared with PC13TG8. R2/1 shows behaviour intermediate between PC13TG8 and R5/3 in all the tests described above. We conclude that two steps can be identified in the change of phenotype by which R5/3 is derived from PC13TG8, and that both steps modify the ability of the cells to form permeable junctions.     

Choroid plexus carcinoma. Cytologic identification of malignant cells in ascitic fluid

Abdominal deposits of a choroid plexus carcinoma in a patient with a ventriculoperitoneal shunt were cytologically diagnosed by examination of ascitic fluid after regression of the primary tumor. The morphology of the malignant cells in ascitic fluid was more similar to that of mesothelial cells than to the appearance of cells from this lesion in cerebrospinal fluid.     

An RNA-dependent nucleoside triphosphate hydrolase from Krebs-II ascites tumor cells. Detection and preliminary characterization

A novel enzymatic activity, RNA-dependent, NTPase, was isolated from Krebs-II ascites tumor cells. This activity is associated with ribosomes and can be detached from them by washing in KCl solutions of a higher than 0.3 M concentration. The enzyme hydrolyzes all the four nucleoside triphosphates to the corresponding nucleoside diphosphates and orthophosphate. The rate of NTP hydrolysis increases about 10-fold in the presence of natural RNAs and synthetic polyribonucleotides [except poly(G)]. Natural DNAs, both double and single-stranded, are poor cofactors, although pol(dA) and poly(dT) stimulate, to a certain extent, the rate of ATP hydrolysis. Possible involvement of RNA-dependent NTPase in protein biosynthesis is discussed.