Characterization of AKR murine leukemia virus sequences in AKR mouse substrains and structure of integrated recombinant genomes in tumor tissues

A specific cDNA probe of AKR murine leukemia virus (AKR-MLV) was prepared to detect AKR-MLV sequences in normal and tumor tissues in a variety of AKR mouse substrains. AKR strains contained up to six endogenous AKR-MLV genomes. All substrains tested had one AKR-MLV locus in common, and closely related substrains had several proviruses integrated in an identical site. Virus-induced tumors in the AKR/FuRdA and AKR/JS strains showed a reintegration pattern of AKR-MLV sequences unique for the individual animal, suggesting a monoclonal origin for the outgrown tumors. An analysis of tumor DNAs from the AKR/FuRdA and AKR/JS substrains with restriction enzymes cleaving within the proviral genome revealed a new EcoRI restriction site and BamHI restriction site not present in normal tissues. The positions of these sites corresponded both with cleavage sites of EcoRI and BamHI in integrated Moloney recombinants and with the structure of isolated AKR mink cell focus-forming viruses. All tumors analyzed to data contain nearly identical integrated recombinant genomes, suggesting a causal relationship between the formation of recombinants and the leukemogenic process.

Viral RNA content of bovine leukemia virus-infected cells

A bovine leukemia virus (BLV)-producing cell line, fetal lamb kidney cells infected with BLV (FLK) contains one or a few copies of BLV proviral DNA in its genome. These cells contain 0.002% of viral RNA which sediments, in a sucrose gradient, at about 35S and between 18S and 28S. In cattle affected by enzootic bovine leukosis, tumor cells and circulating lymphocytes also contain one or a few copies of BLV proviral DNA integrated in their genome. However, in all cases tested (except one), no viral RNA was detected in these cells in conditions where one or two copies of viral genomic RNA per cell would have been easily detected.

The metabolic behaviour of nuclear and cytoplasmic non-polyadenylated RNAs with an affinity for poly(adenylic acid) from Friend murine leukaemia cells

Using poly(A)-Sepharose and poly(U)-Sepharose affinity chromatography, various classes of nuclear RNA can be distinguished in Friend leukaemia cells. One of these contains a poly(A) tract (poly(A)+-RNA) and another lacks a poly(A) tract but has an affinity for poly(A)-Sepharose (poly(A)-u+-RNA). The stability of these two particular nuclear RNA classes was examined by using a 'pulse-chase' technique involving D-glucosamine treatment. Nuclear poly(A)-u+-RNA was found to decay as a single component with a half-life of about 12 min. In contrast, nuclear poly(A)+-RNA appears to consist of at least two distinct metabolic components with half-lives of about 22 min and 120 min. Furthermore, poly(A)-u+-RNA is transported from the nuclei much more rapidly than the poly(A)+-RNA. The 'pulse-chase' approach also allowed a quantitative estimate to be made of the conversion of nuclear poly(A)+-RNA and poly(A)-u+-RNA to cytoplasmic poly(A)-RNA and poly(A)-u+-RNA.

Isolation and characterisation of a non-polyadenylated mRNA species with an affinity for poly(adenylic acid) from Friend leukaemia cells

Utilizing the technique of poly(A)-Sepharose affinity chromatography, it is possible to isolate a novel class of RNA molecules from polysomes of Friend leukaemia cells. These RNA species display messenger RNA-like behaviour. They are released from polysomes on treatment with EDTA and are able to direct polypeptide synthesis in a cell-free protein synthesising system. They appear to be distinct from the polyadenylated mRNAs, as judged by their lack of a 3'-terminal poly(A) tract, by their different size distribution, by their unusual base composition, by the presence of a possible 'uridylate rich' region towards their 3'-end, by their low sequence homology to polyadenylated mRNAs and by the difference in at least some of their translation products.

Relationship between adenosine deaminase and a human thymus leukemia antigen isolated from MOLT 4 cells

The relationship between adenosine deaminase (ADA) and a human membrane thymus leukemia (HTL) antigen-detected by an antithymocyte serum was explored. A freeze-thaw extract of the T-cell-derived cell line, MOLT 4, was applied to an immunoabsorbant column of a rabbit antiserum to calf ADA. The bound MOLT 4 ADA was eluted with 6 M urea. The recovered ADA had a specific activity of 490 mumol of adenosine deaminated per min per mg protein, and the yield was 32%. No HTL antigenic activity was detected in the purified ADA. In addition, no ADA activity was detected in the unbound fraction containing the HTL antigenic activity, supporting the conclusion that ADA and HTL antigen are independent molecules. Affinity-purified anti-calf ADA was not cytotoxic for several HTL antigen-positive cells, including thymocytes, MOLT 4, and thymus-derived acute leukemia lymphoblasts.

Measurement of a stimulatory protein of RNA polymerase II in various mouse organs by the complement fixation test

The amount of S-II, a protein specifically stimulating RNA polymerase II, was measured in various mouse organs by a micro complement fixation assay. The amount was almost the same in brain, liver, kidney, spleen, and Ehrlich ascites tumor cells on the basis of DNA, being about 3.8 micrograms/mg DNA, which corresponds to 3.6 X 10(5) molecules/cell. However, the amount of S-II decreased greatly during erythro-differentiation of Friend leukemia cells and no S-II was detected matured erythrocytes.

Characterization of slow reacting substances (SRSs) of rat basophilic leukemia (RBL-1) cells: effect of cysteine on SRS profile

When RBL-1 cells were incubated with L-cysteine (7.5 mM) and the ionophore A23187, the slow reacting substances SRS-GSH and SRS-Cys-Gly were formed. When L-cysteine was omitted in the incubation, SRS-GSH and SRS-Cys were isolated but only a trace amount of SRS-Cys-Gly was detectable. Each of the characterized SRSs was accompanied by an as yet uncharacterized structural isomer showing UV absorption at 278 nm. L-Cysteine and other thiols inhibited an aminopeptidase that transforms the highly bioactive SRS of anaphylaxis (SRS-Cys-Gly) into the less bioactive SRS-Cys. SRS-GSH, SRS-Cys-Gly, and SRS-Cys may be readily distinguished from each other by means of their bioactivities, antagonism by FPL 55712, and relative susceptibilities to the actions of soybean lipoxygenase, microsome-bound leucine aminopeptidase, and gamma-glutamyl transpeptidase.

[Metal content of nucleic acids in experimental leukosis]

An instrumental neutron-activated analysis was carried out to study metal content in nucleic acids preparations of the rat liver and tumour subjected to Shvets erythromyelosis. It was determined that the DNA and RNA preparations contain iron, zinc, silver, cobalt and scandium. According to the level of concentration of revealed metals are arranged in the row in the following order: iron less than zinc less than silver less than cobalt less than scandium. The iron and zinc contents in RNA is almost twice as high as those in DNA. The content shifts in some of the revealed metals (the iron and scandium contents in DNA preparation of the liver, zinc and iron contents in the DNA preparation of the tumour and zinc content in the RNA preparations of the liver) in the process of the development of leukosis are characterized by a tendency to their increase.

[Intragenomic specificity of DNA methylation in animals. Qualitative differences in tissues and changes in methylation of repeating sequences during aging, carcinogenesis and hormonal induction]

5-methylcytosine (m5C) is nonrandomly distributed in mammalian genome. The unique sequences in DNA of all species studied (mouse, rat, cow) methylated to a similar extent and are characterized by a minimal m5C content (0.8--0.9 mole%). The very renaturating sequences (including satellite DNA) possess a maximal m5C amount. The rarely repeated (10 to 1000 folds) sequences which are known to contain genes for rRNA and tRNA as well as for histones are characterized by an elevated level of methylation. It is established that tissue differences in m5C content in DNA as well as decrease in the DNA methylation level with age and on spontaneous lympholeukosis in cattle and, on the contrary, increase in DNA methylation degree in rat liver as a result of induction with hydrocortisone, are due to tissue specific changes in the methylation level of repeated but not unique sequences. The methylation level of sequences differing in the reiteration degree seems to be mainly due to CG-dublet frequencies. In the unique sequences this particular dinucleotide is almost completely methylated. Nevertheless, the multiplicity of DNA methylases in the animal nucleus is not ruled out. Methylation of the CG sequence is supposed to protect animal DNA's, especially structural genes, against restriction endonucleases. The decrease in DNA methylation in animals with age and on lympholeukosis detected by us is considered to be one of the possible reasons for chromosome lesions and for distortions in DNA replication and transcription.

Studies on the distribution of ribosomal proteins in mammalian ribosomal subunits

Murine L5178Y cell ribosomes were dissociated into subunits either with potassium chloride in the presence of puromycin or with the chelating agent EDTA. The proteins of ribosomal subunits obtained by these different methods were compared by means of bidimensional polyacrylamide gel electrophoresis. KCl-derived 60S and 40S subunits were shown to contain 38 and 31 proteins respectively, 3 of them having identical electrophoretic mobilities. Preparations of EDTA-dissociated ribosomal subparticles contained different proportions of these proteins, and 11 major spots were shared between the EDTA-derived large and small ribosomal subunits. Furthermore, 10 proteins absent from subunits treated by high concentrations of KCl were reproducibly found in EDTA-treated ribosomal subparticles.

The interaction of chromatin with alkylating agents. The monofunctional action of bis(2-chloroethyl)methylamine

The reaction of L5178Y lymphoblast cell chromatin with the alkylating agent bis(2-chloroethyl)methylamine has been studied as a function of time, pH and reagent concentration. The reaction with DNA of chromatin from which the proteins were dissociated, as well as with purified calf thymus DNA, was studied in parallel. The extent of alkylation of DNA in intact chromatin was 4--5 times as much as in parallel free DNA samples; up to 4% of nucleotide base pairs were substituted. The extent of monofunctional substitution of the proteins was similar, on a weight basis, to that of DNA. Chromatographic analysis of the depurinated products showed that in chromatin, as in DNA, position N-7 of guanine is the major site of reaction. Up to 25% of the reaction products were guanines cross-linked as bis(2-guanin-7-yl-ethyl)methylamine, indicating a considerable degree of DNA-DNA cross linking. Column analysis shows that up to 40% of the nuclear proteins are cross-linked to DNA at 10 mM bis(2-chloroethyl)methylamine. The increased reactivity of intact chromatin is interpreted in terms of a conformational change in the position of the DNA bases when in the organized nucleohistone complex.

Heterogeneity of DNA methylation in murine L5178Y lymphoblasts

Comparison of the extent of methylation in mouse DNA fragments rendered MgCl2 soluble after mild DNase II digestion of nuclei, with different reassociation rate and nucleoli-bound, revealed the existence of 3 regions of the genome particularly 5-methylcytosine-rich: the sequences considered to be related to the transcriptionally active chromatin with the highest content of this base and fast reassociating, as well as nucleolar DNA with somewhat lower proportion of the methylated cytosines.

Isolation and characterization of actin and myosin from B-lymphocytic guinea pig leukemia cells

Actin and myosin have been isolated from a guinea pig B cell leukemia line, L2C. The m.w. and amino acid compositions of these proteins are similar to actin and myosin from other nonmuscle cell types. L2C actin polymerizes to form filaments and activates the ATPase activity of skeletal muscle myosin. Actin in crude lymphocyte extracts does not polymerize as well as predicted from the critical concentration of purified lymphocyte actin suggesting that other factors in lymphocyte extracts regulate actin polymerization. Lymphocyte myosin polymerizes to form synthetic filaments at low ionic strength. Lymphocyte myosin binds to actin, but its ATPase activity is not activated by actin. Possible mechanisms for regulation of the lymphocyte contractile apparatus and its importance in a number of lymphocyte functions are discussed.

[Quantitative cytochemical study of the RNA in tumor cells. II. The characteristics of the cell populatoins]

The quantity of DNA and RNA in tymocytes of AKR mice has been determined by Methylen blue staining. Cell populations of normal and tumor animals were divided into two groups with equal content of DNA to measure RNA content in either of them. The tumor cells had up to 380% RNA, if the normal content be taken for 100%. Dynamics of RNA modifications in cells of normal tymocytes corresponded to the increasing DNA quantity. The RNA quantity in tumor cells increased in the beginning of S-phase.

Intracytoplasmic type A particles from mammary tumours and leukaemias of strain ICRC mice

The ovarian-hormone-induced leukaemias of strain ICRC mice, with an abundance of intracytoplasmic type A particles in primary as well as transplanted lesions, were used to study morphological, biophysical, immunological and structural characteristics of type A particles. Mammary tumours of strains ICRC and C3H(Jax) were also used as sources for type A particles. The purified virions banded at the density of 1.20 g/ml in 12--60% linear sucrose-density gradient when subjected to spinning at 113,000 g for 4 h. The SDS-polyacrylamide-gel electrophoresis of type A particles from mammary tumours and leukaemias reproducibly resolved at least 8 polypeptides, 2 of these 54,000 and 24,000 dalton proteins, showing variable expression. Type A particles and B particles, despite the fact that each had a distinct polypeptide pattern, showed common antigens with different electrophoretic mobilities. Proteins of 24,000, 18,000 and 12,000 daltons from B particles were found to be antigenically related to those from type A particles. The bioassay studies carried out with purified A particles showed that 2/7 males of strain ICRC and 1/6 females of strain DBA-MTI developed leukaemias, as against none in the controls, when inoculated between the ages of 1-7 days. Spleen tumour and cervical tumour were seen in one female each of strain DBA-MTI.

Rigid plasma-membrane-derived vesicles, enriched in tumour-associated surface antigens (MLr), occurring in the ascites fluid of a murine leukaemia (GRSL)

Extracellular membraneous vesicles of GRSL leukaemia cells were isolated from the ascites fluid bathing the cells in vivo, and from cell washes. Mammary tumour virus-induced antigens (MLr) expressed on the surface of the cells are enriched on these vesicles as compared to plasma membranes isolated from the cell homogenate. The lipid fluidity of the vesicles is much smaller than that of the plasma membranes, and the content of the pertinent lipid parameters, cholesterol and sphingomyelin, are accordingly greatly increased. The extracellular vesicles which are also enriched in sialic acid and 5'-nucleotidase are apparently derived from the plasma membrane, probably at least partly by exfoliation of selected parts or domains of the surface of living cells. An analogy between this shedding of vesicles, the formation of endocytotic vesicles and the budding of viruses is noted; all these processes select or assemble rigid lipid domains of the cell membrane. The possible participation of surface microvilli and sub-lethal autolysis in the process of shedding is discussed.

Two-dimensional polyacrylamide gel analysis on nuclear proteins from human tumor cell lines

Two-dimensional polyacrylamide gel electrophoretic analysis was carried out on HeLa, KB, ALL and GW-39 cell "Chromatin Fraction II" proteins. Of the many proteins found, most were visualized in earlier studies on rodent tumors and normal tissues. Of these the greater density of protein CP and the presence of protein CG' differentiates tumors from the nontumor tissues. In samples of normal and mitogen stimulated human lymphocytes, protein CG' was absent and protein CP was present in small amounts. Two-dimensional patterns of 0.4N H2SO4 soluble nuclear proteins showed elevated amounts of proteins C16-18 in the GS-39 cell patterns. Proteins Hu1, G1, G2, G3 and G5 were detected only in human cell nuclei. The increased density of staining for protein CP and the presence of CG' are potential biological markers for neoplastic cells.