Changes in biophysical parameters and in phospholipid composition associated with resistance to doxorubicin

Friend leukemia cells (FLC) resistant to different concentrations of doxorubicin were used to investigate the biochemical and biophysical changes associated with resistance. We have found that fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene analyzed on single cell level increased in resistant as compared to sensitive FLC. Furthermore, phospholipid analysis of sensitive and doxorubicin-resistant cells revealed changes in ratios of phosphatidyl-choline to phosphatidyl-ethanolamine and phosphatidyl-choline to sphingomyelin. These results correlate with decreased electrophoretic mobility in resistant cells. Our results indicate that changes in cell structure occur with the level of resistance to doxorubicin. These changes are probably the consequence rather than the cause of resistance.

Structural relationship between tRNALys2 and tRNALys4 from mouse lymphoma cells

Mouse lymphoma cells have three major isoaccepting lysine tRNAs. Two of these isoacceptors, tRNALys2 and tRNALys4, were sequenced by rapid gel or chromatogram readout methods. They have the same primary sequence but differ in two modified nucleotides. tRNALys4 has an unmodified uridine replacing one dihydrouridine and an unidentified nucleotide, t6A*, replacing t6A. This unidentified nucleotide is not a hypomodified form of t6A. Thus, tRNALys4 is not a simple precursor of tRNALys2. Both tRNAs have an unidentified nucleotide, U**, in the third position of the anticodon. Also, partial sequences of minor homologs of tRNALys2 and tRNALys4 were obtained. The distinctions between tRNALys2 and tRNALys4 may be part of significant cellular roles as illustrated by the differential effects of these isoacceptors on the synthesis by lysyl-tRNA synthetase of diadenosine-5',5'''-P1,P4-tetraphosphate, a putative signal in DNA replication.

Functional and biochemical characterization of a secreted I-J(+) suppressor factor that binds to immunoglobulin

A secreted product of a T cell leukemic cell line, LH-8, was examined for its biochemical and biological properties. The factor that we have termed Immunoglobulin-Binding T cell Suppressor Factor (IgB-TsF) was shown to be suppressive for the in vitro and in vivo humoral response to a variety (but not all) antigens tested. The cell surface phenotype of the LH-8.1 subclone was M.Ig(-), Thy-1(+), L3T4(-), Lyt-2(+), FcR(-), MAC-1(-), and H-2b(+). In addition, both the cell surface and secreted factor, IgB-TsF, of LH-8.1 expressed determinants that were recognized by anti-I-Jb mAbs but not by an anti-I-Jd monoclonal. The same factor also retained an affinity for the Fc portion of approximately 30% of randomly selected, purified mAbs. This binding could be abolished if the Fab or F(ab')2 fragments of these mAb were used, but was found to be unrelated to isotype of the respective mAbs. Using subclones that expressed quantitative differences in their ability to exert suppression as sources of biosynthetically labeled IgB-TsF, we have shown the suppressor activity correlated with a single, 28 kD protein. Furthermore, comparisons of these same subclones that differ in their suppressor activity, do not show any direct correlation of this biological activity with the expression of the previously described T cell receptor genes. It also suggests that at least some suppressor cell subsets may use the same or related family of T cell receptor genes for their recognitive stage of activation as helper and cytotoxic T cell subsets, but not for their effector stage of immunologic suppression.

Membrane-associated proteins of adriamycin sensitive and resistant murine leukemic P388 cells

We have isolated an 84-fold adriamycin resistant subline, P388/R84, from mouse leukemia P388 cells by serial cultivation in methylcellulose in the presence of increasing drug concentrations. Electrophoresis of detergent soluble fractions of radiolabeled sensitive and resistant cells suggested marked alterations in the protein fractions of 160, 100, 60, 45, and 30 kd. In resistant clones labeled with 125I an increase in 160 and 100 kd proteins was accompanied by concomitant reduction in the 60, 45, and 30 kd proteins. In 35S methionine-labeled resistant cells, similar increases in the 160 and 100 kd components were observed but in contrast to 125I-labeled cells the 30 kd component was also higher. Alterations in surface proteins were confirmed in experiments where the cell extracts were adsorbed to concanavalin A polymers and extracted with 0.26 M methyl-alpha-D-mannopyranoside. Our data confirm earlier reported observations on cell-surface protein changes in cells resistant to anthracyclines and alkaloids.

Minor serine tRNA containing anticodon NCA (C4 RNA) from human and mouse cells

The nucleotide sequence of C4 RNA, one of the "4.5S RNAs" of HeLa cells, was determined. This RNA consists of 90 nucleotides containing C-C-A at its 3'-terminus. The sequence can be drawn to form a clover-leaf structure with several unusual features and with anticodon NCA. The short term labeled molecule contains triphosphates at its 5'-terminus, whereas the mature molecule contains only monophosphate. Therefore, there must be no precursor nucleotide at the 5'-end in the primary transcript of this tRNA. Mouse cells also contain C4 RNA. Only one base exchange was observed in the extra arm in human and mouse C4 RNAs. The molecule purified from mouse liver showed serine acceptor ability.

Vincristine-resistant P388 leukemia cells contain a large amount of calcium

P388 leukemia cells resistant to vincristine contained more calcium in the cells than the parent sensitive line, especially in the form of EGTA-removable (surface-bound) calcium. Although the relationship, if any, between the high cellular calcium of resistant cells and drug-resistant phenotype is not clear, the possible implications of this result for the elucidation of the mechanisms of drug resistance are interesting.

Factors affecting expression of glycolipid tumor antigens: influence of ceramide composition and coexisting glycolipid on the antigenicity of gangliotriaosylceramide in murine lymphoma cells

Gangliotriaosylceramide (Gg3Cer) was previously described as a tumor-associated antigen in murine L5178Y lymphoma [Young, W. W., Jr., and Hakomori, S., Science (Wash. D.C.), 211: 487-489, 1981]. This paper describes the major factors affecting the expression of Gg3Cer at the surface of various clones of L5178Y lymphoma. Of 26 sublines that were recloned, six cell lines showing different degrees of Gg3Cer expression at the cell surface were used for analysis of the glycolipid composition as related to its cell surface antigenicity. Three remarkable correlations between glycolipid composition and the antigenicity of Gg3Cer have been found: (a) high-expressor sublines were characterized by a large proportion of a unique molecular species of Gg3Cer having alpha-hydroxypalmitic acid in its ceramide moiety in striking contrast to low expressors which did not contain this molecular species; (b) low expressors contained a large quantity of ganglio-N-tetraosylceramide (Gg4Cer) and NeuAc alpha 2 leads to 3Gal beta 1 leads to 3GalNAc beta 1 leads to 4Gal beta 1 leads to 4Glc beta 1 leads to 1 Cer (GM1b) gangliosides, whereas these glycolipids were almost absent in high-expressor clones; and (c) nonexpressors, which were converted from the high expressors in vivo through immunotherapy with the monoclonal antibodies to Gg3Cer, contained a large quantity of ganglio-N-tetraosylceramide and NeuAc alpha 2 leads to 3Gal beta 1 leads to 3GalNAc beta 1 leads to 4Gal beta 1 leads to 4Glc beta 1 leads to 1Cer. The nonexpressors should have an induced enzyme system to metabolize Gg3Cer to ganglio-N-tetraosylceramide and NeuAc alpha 2 leads to 3Gal beta 1 leads to 3GalNAc beta 1 leads to 4Gal beta 1 leads to 4Glc beta 1 leads to 1Cer. Three factors, i.e., ceramide composition, coexisting glycolipids, and an antibody-dependent glycolipid change, are therefore important in determination of glycolipid antigenicity and antigen modulation by antibodies. The ceramide composition may affect glycolipid organization in membranes, and the coexisting glycolipid having a longer carbohydrate chain may mask the accessibility of antibody to the antigenic glycolipid. The antigenic modulation by the action of the antibody in vivo may be based on activation of a new glycosyltransferase.

Presence of a novel spleen focus-forming virus-specific glycoprotein (gp51) in a Friend leukemia cell line and its decrease during erythrodifferentiation

All Friend leukemia cell lines induced by polycythemic strains of Friend leukemia virus complex express an appreciable amount of spleen focus-forming virus (SFFV)-coding envelope gene (env)-related glycoprotein with a molecular weight of 55 kilodaltons (gp55). A clonal, highly differentiation-inducible Friend leukemia cell line, T3-C1-2-O(2-O), possesses not only gp55 but also gp51 as SFFV-specific gene products. The peptide map of gp51 is quite similar to that of gp55 and the difference in their molecular weights is primarily dependent on their oligosaccharide content. In the differentiation-induced state, gp51 becomes far less detectable than gp55 in 2-O cells. The biological significance of this novel SFFV-coding glycoprotein is discussed.

[Composition of gangliosides in experimental rat tumors]

Spectrum of gangliosides was studied in some tumors. It was the same in a hepatocellular carcinoma induced by N-nitrosomorpholine in Wistar rats as in control liver In addition, several tumors contained an unidentified fraction between GD1b and GT1b. There were total ganglioside differences both in tumours and controls. Lymphatic leukemia samples had lower contents of GD1a and higher contents of GM1 ganglioside. Spontaneous breast sarcoma of Lewis rats (SAM) failed to differ from a sarcoma of low grade malignancy induced by ferridextran (FL) with the exception of slight increase in GD1a and GD2. All the tumours contained higher gangliosides in concentration at least the same as controls.

Characterization of tumor-associated ganglio-N-triaosylceramide in mouse lymphoma and the dependency of its exposure and antigenicity on the sialosyl residues of a second glycoconjugate

Ganglio-N-triaosylceramide (GalNAc beta 1 leads to 4Gal beta 1 leads to 4Glc beta 1 leads to 1Cer), a tumor-associated marker for L5178 cells, was previously reported to separate on thin layer chromatography into three distinct bands (bands a, b, and c). The present paper describes the characterization of these bands and the factor that determines the degree of glycolipid exposure at the cell surface and its antigenicity. 1) The resolution of ganglio-N-triaosylceramide into three bands was found to be due to molecules having different fatty acid compositions. Band a contained nervonic (C24:1) and lignoceric (C24:0) acids, band b contained palmitic acid (C16:0), and band c contained alpha-hydroxypalmitic acid. 2) Surface labeling of L5178c127 cells with galactose oxidase/sodium borotritide, followed by fluorography of the isolated glycolipids, revealed that all three bands were exposed on the surface of the cell. However, treatment of cells with sialidase before treatment with galactose oxidase resulted in a 10-fold increase of label incorporated into ganglio-N-triaosylceramide. Since no sialylated form of ganglio-N-triaosylceramide was detected on these cells, and no change in the chemical amount of this glycolipid could be detected, the increase of label into this molecule was due to the exposure by sialidase of a normally cryptic glycolipid. The exposure of ganglio-N-triaosylceramide after sialidase treatment was also reflected by the increased sensitivity of these cells to monoclonal antibodies to the glycolipid and complement after enzyme treatment. Thus, the results provide clear evidence that crypticity, as well as antigenicity, of a membrane glycolipid is determined by the degree of sialylation in a second membrane glycoconjugate.

Appearance of altered cell-surface fucosyl glycopeptides in concomitance with chromosomal alterations in the gross virus-infected pre-leukemic thymus of the rat

The appearance of a class of fast-eluting cell-surface glycopeptides that are encountered almost exclusively in malignant and certain pre-malignant cells was monitored in the course of leukemogenesis in the thymus of rats injected at birth with Gross leukemia virus. The altered glycopeptides appeared as early as 15 days after virus injection, when the animals were still clinically healthy and no histological signs of the disease were present in the thymus. Their amount was further increased at 30 days, and reached a maximum in the fully developed lymphoma. The development of this early phenotypic marker of malignancy appeared to be concomitant with that of chromosomal anomalies in the thymus. Since these anomalies are non-random, the existence of a causal relationship between the glycopeptide change and the loss of specific chromosomes might be hypothesized.

Sequential association of nucleolar 7-2 RNA with two different autoantigens

Anti-Th serum from a patient with systemic lupus erythematosus immunoprecipitates from both human and mouse cell extracts small ribonucleoproteins containing 7-2 RNA, 8-2 RNA, and the Ro RNAs. Human 7-2 RNA, which must be complexed with protein to be antigenic, is about 300 nucleotides long and has mostly pG at its 5' end. A related 7-2 RNA, precipitated by anti-La antibody, gives identical Tl and pancreatic RNase fingerprints, but has more pppG at its 5' end. La 7-2 RNA is, therefore, likely to be a precursor of Th 7-2 RNA. The synthesis of 7-2 RNA in isolated nuclei exhibits a pattern of sensitivity to alpha-amanitin that is characteristic for RNA polymerase III transcription. Thus, 7-2 RNA can be added to the list of mammalian RNA polymerase III transcripts that initially bind the La protein and then become incorporated into other types of antigenic RNP particles.

Phospholipids stabilize the interaction between the alpha and beta subunits of the solubilized receptor for immunoglobulin E

The cell-surface component (alpha) which binds monomeric immunoglobulin E with high affinity is associated with a second polypeptide (beta) in the plasma membrane. The latter component tends to dissociate during purification of the alpha chain from detergent extracts of cells, even at neutral pHs and physiological ionic strengths. We now report that the interaction of alpha and beta can be stabilized by maintaining an appropriate phospholipid to detergent ratio. Under such conditions, other discrete components reproducibly copurify with the alpha and beta chains. These results suggest that the subunits of this membrane protein--or the interaction of it with other constituents in the cell--may be stabilized in ways not observed with ordinary soluble proteins.

Insulin receptors on cultured murine lymphoid tumor cell lines

Eight murine lymphoid tumor cell lines have been examined for the presence of high-affinity insulin receptors. The eight cell lines included two Abelson murine leukemia virus-transformed pre-B cell lines, three plasmacytoma cell lines, and three spontaneous T-cell lymphomas from AKR mice. All of the cell lines in the B-cell series had high-affinity insulin binding sites. The apparent equilibrium association constant (Ka) for the high-affinity binding sites on these cells was 1.3-3.3 X 10(9) M-1. Two of the T-cell lymphomas had high-affinity receptor levels so low as to be undetectable in the whole cell binding assay under the conditions used for assaying the other cell lines, although in binding assays performed at very high cell densities, these two cell lines did appear to have a small number of high-affinity insulin binding sites. These results indicate that the growth stimulus provided by the tumor virus in neoplastic transformation of the AKR thymic lymphocytes differs from that provided by lectins in blast transformation of lymphocytes in that the neoplastic transforming event does not always result in the emergence of large numbers of high-affinity insulin receptors. In addition, the existence of cell lines such as the T-cell lymphomas that have nearly exclusively low-affinity binding sites suggests that the low-affinity sites may represent a distinct receptor that is not freely interconvertible with the high-affinity receptor.

Acquisition of proviral DNA of mouse mammary tumor virus in thymic leukemia cells from GR mice

Male mice of strain GR develop T-cell leukemia at a low frequency late in life. These leukemia cells contain large amounts of mouse mammary tumor virus (MMTV) RNA and MMTV proteins in a precursor form (Nusse et al., J. Virol. 32:251-258, 1979). We used restriction enzyme analysis and molecular hybridization to identify MMTV proviruses in the DNA of these leukemia cells. GR leukemia cells contained additional integrated MMTV proviruses at various sites in the genome. This amplification of MMTV proviruses in GR leukemia cells is not restricted to one particular endogenous MMTV provirus of strain GR. The number and location of the extra MMTV proviruses present in transplants of GR leukemia cells did not change upon serial transplantation of the leukemia cells. Acquisition of MMTV proviruses was also found in a similar leukemia, L1210 of the DBA/2 mouse strain, but not in three other leukemias, SL2 of DBA/2, BW5147 of AKR, and a spontaneous thymoma of BALB/c. The two main classes of MMTV RNA, 35S and 24S, were present in the cytoplasmic RNA of GR leukemia cells, indicating that the aberrant processing of MMTV precursor proteins is not due to anomolously sized RNAs. We could not detect extra RNAs in GR leukemia cells which would represent read-through transcripts of cellular genes adjacent to the extra MMTV proviruses, initiated by a promoter signal in the right MMTV long terminal repeat sequence. These data suggest that acquisition of MMTV proviruses may coincide with the onset of leukemogenesis in GR male mice.

Nuclear precursor molecules of the two beta-globin mRNAs in Friend erythroleukemia cells

Processing of the beta major and beta minor globin pre-mRNAs has been compared in murine erythroleukemia cells induced to synthesize hemoglobin by dimethyl sulfoxide or hemin treatment, using both the Northern blot technique and S1 nuclease mapping with 3' and 5' end-labeled probes. The small intervening sequence of both beta-globin pre-mRNAs was removed in one step, although minor amounts of incompletely spliced RNA were detected. During the processing of the large intervening sequence of beta major globin pre-mRNA two internal splice sites were clearly detected. On the contrary, the beta minor globin pre-mRNA did not show any internal splice sites. A model of processing of the mouse adult beta major globin pre-mRNA is proposed.

Comparative lipid analysis of purified plasma membranes and shed extracellular membrane vesicles from normal murine thymocytes and leukemic GRSL cells

The lipid fluidity in purified plasma membranes (PM) of murine leukemic GRSL cells, as measured by fluorescence polarization, is much higher than in PM of normal thymocytes. This was found to be due to relatively low contents of cholesterol and sphingomyelin and a high amount of unsaturated fatty acyl chains, especially linoleic acid, in the phospholipids. PM from GRSL cells contain markedly more phosphatidylethanolamine than those from thymocytes. For both GRSL cells and thymocytes the detailed lipid composition of isolated PM was compared with that of the corresponding shed extracellular membranes (ECM), which were isolated from the ascites fluid and from thymus cell suspensions, respectively. The somewhat decreased lipid fluidity of thymocyte ECM as compared to their PM, can be ascribed to the increased cholesterol/phospholipid molar ratio (0.88 vs. 0.74). No other major differences were found between the lipid composition of these membranes. In contrast, significant differences were found between PM and ECM from GRSL cells. In this system a much lower lipid fluidity of the shed ECM was found, due to the much increased cholesterol/phospholipid molar ratio (3.5-fold) and sphingomyelin (9-fold) content, as compared to the PM. Further, the ECM contain relatively more lysophosphatidylethanolamine and less phosphatidylcholine and -inositol. ECM contain a higher amount of polyunsaturated fatty acids, especially in the phosphatidylethanolamine and lysophosphatidylethanolamine classes. On the other hand, the fatty acids of phosphatidylcholine and lysophosphatidylcholine are more saturated than in PM. In particular, ECM of GRSL cells contain less oleic and linoleic acid residues and more arachidonic acid and 22:polyunsaturated fatty acid residues than PM. The possible relevance of these differences with respect to the mechanism of shedding of vesicles from the cell surface, is discussed.

Improved preparation of poly(A) Sepharose and the isolation of oligo(U) containing heterogeneous nuclear RNA from Friend erythroleukemic cells

When poly(A) sepharose (prepared according to previously published procedures) was stored in aqueous buffer at 4 degrees C for 5 days or longer, it bound nonspecifically a high percentage of the input RNA which could not be eluted with formamide. We have found that treatment with ethanolamine, followed by dehydration with ethanol yielded poly(A) sepharose which was stable for many months and possessed a low degree of nonspecific binding. Chromatography on poly(A) sepharose permitted the specific isolation of that fraction of Friend erythroleukemic cell heterogeneous nuclear RNA (hnRNA) which contained oligo(U) sequences. Approximately 10% of the hnRNA which contained a poly(A) sequence [poly(A+)] also contained an oligo(U) sequence. Interestingly, prior HCHO denaturation of the hnRNA enhanced binding of the poly(A+) oligo(U+) hnRNA to poly(A) sepharose by tenfold. This suggested that the oligo(U) sequence may be in a region with secondary structure, possibly an intramolecular duplex with the 3' poly(A). Friend cell oligo(U) sequences ranged from 20 to 50 nucleotides in length and, thus, were similar to the oligo(U) sequences which heretofore had only been shown to be present in HeLa cell hnRNA. These results established that rodent cell hnRNA contain oligo(U) sequences and demonstrate, for the first time, that hnRNA containing both a poly(A) and an oligo(U) sequence can be separated from other classes of hnRNA. In addition, conditions are presented for the removal of HCHO from nucleic acid.

Sequence divergence of nucleus-confined polyadenylated ribonucleic acids in Friend erythroleukemic cells

For determination of whether any potential protein-coding RNA sequences are confined to the nucleus in Friend cells, a comparison has been made of the sequence divergence of polyadenylated RNA molecules which are either nucleus confined or transported to the cytoplasm. Both unique DNA and cDNA probes enriched in such sequences were reacted with a large excess of mouse or rat DNA. The extent of hybridization and the thermal stability of hybrids formed under various stringency conditions were used as a measure of the amount of sequence divergence which had taken place. The results confirmed that messenger sequences are relatively conserved during evolution. Furthermore, experiments involving both unique DNA probes representative of the full length of nucleus-confined RNA molecules and cDNA probes complementary to their poly(A)-adjacent fragments indicated that the polyadenylated nucleus-confined sequences have, on average, diverged during evolution much more than mRNA sequences. The vast majority of these sequences therefore probably do not represent potential mRNAs which are confined to the nucleus and subject to posttranscriptional control in a manner similar to those which have been demonstrated in sea urchins [Wold, B., Klein, W. H., Hough-Evans, B. R., Britten, R. J., & Davidson, E. H. (1978) Cell (Cambridge, Mass.) 14, 941-950].

Lack of AKR ecotropic provirus amplification in AKR leukemic thymuses

A DNA fragment from the 3' region of a molecularly cloned AKR ecotropic provirus was identified to be specific for the AKR ecotropic murine leukemia virus (MuLV). This selected DNA fragment was used to analyze the integrated MuLV proviruses in normal and leukemic tissue DNAs of AKR mice. In comparison with a DNA fragment from the 5' region of the cloned AKR genome or one representing the entire genome, this selected probe hybridized to only a few MuLV proviruses. By comparing transformed and nontransformed tissue DNAs, it appeared that no amplification of proviral sequences related to the AKR ecotropic MuLV had occurred in thymomas of AKR mice during the development of leukemia in these animals. Analysis of the AKR ecotropic MuLV proviruses revealed a significant degree of polymorphism for these sequences among individuals in the AKR/J strain of mouse.

Lipophilic proteins of Friend erythroleukemia cells

Lipophilic proteins can be extracted from Friend mouse erythroleukemia cells (MELC) with acidic chloroform-methanol. The acidic extract contains at least 4 polypeptides of apparent M.W. 5, 9, 5, 14 and 17 kdaltons as determined by SDS-polyacrylamide gel electrophoresis (PAGE). Delipidation of the extract with ether causes the formation of polymers of an apparent molecular weight ranging from 25 to 85 kdaltons, and strong binding of aminoacids, sugars and phospholipids, in particular phosphatidylinositol and phosphatidylethanolamine, to the polypeptides. Through the majority of the lipophilic proteins are of cellular origin, part of the polypeptides of M.W. 14 and 17 kdaltons may be viral components.

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.