[Fatty-acid composition of lipids and physicochemical characteristics of membrane fractions and the membrane of endoplasmic reticulum of thymus and Pliss' lymphosarcoma]

The paper is concerned with composition of neutral lipids and phospholipids, the regularity of lipid bilayer and structural reorganization of plasma membranes, and membranes of smooth and rough cell reticulum of thymus and Pliss lymphosarcoma are studied at linear and stationary growth phase. No qualitative differences are found in the fatty-acid composition of lipid membranes in normal and tumour cells. In plasma membranes of phospholipids and in membranes of smooth reticulum of tumour cells the unsaturated lipid component increases in the process of growth, the cholesterin/phospholipids ratio decreases, fluidity of the lipid bilayer diminishes and structural heterogeneity of these membranes rises while in membranes of rough reticulum the saturation of lipids increases, but the cholesterin/phospholipids ratio does not change. The temperatures of structural reorganization also does not change, which evidences for a less structural lability of membranes of rough reticulum as compared with other membranes.

Mechanisms for dissociating proteoglycan aggregates

Preformed Cs2SO4 zonal gradients were used to purify aggregates from proteoglycan preparations derived from associative extracts of the Swarm rat chondrosarcoma. Zonal gradients were used in solvents with different concentrations of guanidine HCl and different solvent pH values to study the mechanisms for dissociating the aggregates. Aggregates are stable in concentrations of guanidine HCl up to 1.5 M at pH 6.6. At 2 M guanidine HCl, partial dissociation occurs over 20 h in which a link protein is completely dissociated for every monomer proteoglycan dissociated from the aggregate structure. This suggests that in this solvent disaggregation occurs concurrent with complete separation of link protein from monomer. At solvent pH 2.7 to 3.3 in ionic conditions which normally promote aggregation, dissociation occurs by a mechanism in which the link protein remains associated with monomer. Thus, link protein-monomer complexes dissociate as bimolecular units from hyaluronic acid; such complexes then exhibit physical properties indistinguishable from pure monomers. The link protein-monomer complexes reassociate with hyaluronic acid to form link-stabilized aggregates when the solvent pH is raised to pH 7, i.e. to associative conditions. The study provides additional evidence for the role that link protein-monomer interactions have in proteoglycan aggregate structures.

Detection of Raji binding activity in hyperimmune allogeneic tumor bearing sera associated with anti-BSA activity

Brown Norway (BN) rats were implanted twice with allogeneic (Lewis strain) Moloney sarcoma tumors (LM-2) and serum samples were assessed for Raji binding activity during primary and secondary tumor growth and rejection. Maximum Raji binding was observed 25 days after a primary tumor implant; thereafter, the binding activity decreased. Accelerated tumor rejection was observed after a second tumor implant and was associated with a 3-fold increase in serum Raji binding activity which remained elevated up to 40 days post-tumor implant. Raji binding activity in hyperimmune rats co-migrated with IgG in G-200 fractionated serum. Polyacrylamide gel electrophoresis (PAGE) revealed the presence of bovine serum albumin (BSA) on Raji cell membranes which reacted immunochemically with rabbit anti-BSA antiserum. Immunodiffusion studies revealed that sera from hyperimmune rats produced a precipitin band when reacted with Noniodet P-40 (NP-40) lysates of Raji cells and formed a line of identity with BSA.

Isolation of a mouse DNA fraction which encodes more informational than non informational RNA sequences

A small fraction of single-stranded DNA (ssDNA), amounting to 1.5--2% of the total DNA, was isolated from native nuclear DNA of mouse Ascites tumour cells. In RNA-driven annealing reactions, 40--42% of the ssDNA, (labelled with [3H]-thymidine or 125I) could be hybridized to cytoplasmic RNA was compared with 4--4.5% for the non repetitious component of bulk DNA and 60--63% of the ssDNA could be hybridized to nuclear RNA as compared with 20--22% for bulk DNA. It was also found that most of the ssDNA sequences which are hybridizable to homologous RNA, consisted of non self-reassociating DNA regions (which can be reassociated with non repetitious bulk DNA). These findings complete earlier data obtained in other cell systems and demonstrate that ssDNA mainly originates from active DNA transcription sites which encode informational RNA sequences. It is proposed that ssDNA is formed via selective endogenous nuclease attacks presumably at an early stage of the DNA purification procedure.

Extremely underwound chromosomal DNA in nucleoids of mouse sarcoma cells

The superhelical properties of chromosomal DNA from cells of a mouse sarcoma were investigated in neutral sucrose gradients containing ethidium bromide. Removal of negative supercoiling from the DNA of the sarcoma cells required a substantially higher dye concentration than was necessary in the case of DNA from cultured mouse fibroblasts. The calculated value of the mean superhelical density in malignant cells (sigma = -0.14) appears abnormally high compared with the value (sigma = -0.09) obtained for DNA of mouse fibroblasts. Chromosomal DNA from mouse sarcoma cells is therefore concluded to be highly deficient in helical turns.

Immunological and biochemical characteristics of acid citrate eluates from tumour cells: a major non-immunoglobulin component

Using competitive double-antibody radioimmunoassays we have shown that immunoglobulin (especially IgA) can be recovered in pH 3.5, 0.12M acid citrate eluates of freshly excised CCH1 tumour-cell suspensions. Studies with 125I-labelled eluates indicate that such preparations exhibit a variable, but appreciable, degree of non-specific binding to unrelated syngeneic tumour and normal tissues. PAGE/SDS gel electrophoresis of the labelled eluates revealed the presence of a major non-immunoglobulin component of 33-36K dalton which could account in part for the non-specific binding observed. This component was also detected in similar eluates from cultured CCH1 tumour and in all other tumour-cell eluates examined to date. In contrast, preliminary data suggest that it is less prevalent in acid citrate eluates from normal tissue, with the exception of peritoneal-exudate cells. The possible origins, nature and significance of this non-immunoglobulin component are discussed.

Structural and functional domains of the Rous sarcoma virus transforming protein (pp60src)

The transforming protein (pp60src) of the Rous sarcoma virus (RSV) is a phosphoprotein with the enzymatic ability to phosphorylate tyrosine in protein substrates. Previous work has indicated that the bulk of pp60src may be attached to the plasma membrane of infected cells. In an effort to better understand the mechanism by which pp60src induces the neoplastic phenotype, we have characterized further the attachment of pp60src to the plasma membrane, and we have identified separate molecular domains that are responsible for the attachment to membranes and for the protein kinase activity. Our results indicate that pp60src may be an integral membrane protein that is nevertheless synthesized on soluble polyribosomes. Subsequent to its synthesis, the protein attaches to plasma membrane without concomitant cleavage of a signal polypeptide. The amino-terminal quarter (or some portion thereof) of pp60src anchors the protein to the plasma membrane by forces that can be disrupted only with detergents. By contrast, protein kinase activity is located in the carboxyl-terminal half of the molecule. It appears that pp60src is designed on the one hand for tethering to the plasma membrane and on the other hand for enzymatic activity beyond the confines of the membrane. The fact that pp60src is but one of at least four different viral transforming proteins located on the plasma membrane implies that neoplastic transformation may commonly originate in events that occur at the periphery of the cell.

[Phospholipid composition of mitochondria and microsomes from some transplantable rat tumors]

The phospholipid compositions of mitochondria and microsomes from rat liver, kidney, nephroma RA and sarcoma 45 were investigated. The "lipid dedifferentiation" of hepatoma membranes found earlier was shown to extend also to other tumours. However, this phenomenon may concern some, but not all phospholipids.

Purification and characterization of a lipolytic factor (toxohormone-L) from cell-free fluid of ascites sarcoma 180

A lipolytic substance in the ascites fluid of mice with Sarcoma 180, called toxohormone-L, was purified and characterized. The lipolytic activity of toxohormone-L was measured in vitro using rat adipose tissue slices. Toxohormone-L, purified approximately 90-fold from the ammonium sulfate fraction, gave a single band on polyacrylamide gel electrophoresis. Its molecular weight was about 75,000, and its isoelectric point was 4.7. Toxohormone-L is heat labile and nondialyzable, but, on its digestion with trypsin, an active fragment that was heat stable and dialyzable was produced. Toxohormone-L is a protein and is also present in the ascites fluid of patients with hepatoma and Grawitz's tumor.

The cytospectrophotometrical determination of proteins by the tetrazonium coupling reaction. II. Calibration of the staining method

The protein content of identical samples from 5 different cell types (lymphocytes of the thymus and of the bursa of FABRICIUS of the chicken, EHRLICH ascites tumor cells, YOSHIDA ascites tumor cells, and rat liver cells) have been determined both macroscopically, by the method of LOWRY (1951), and microspectrometrically, by the tetrazonium coupling method of NOHAMMER (1978). In all the different cell types, a strong correlation is shown between the protein values determined by the 2 methods. By comparing the values thus measured, a conversion factor has been obtained such that an extinction of 0.4235, determined microspectrometrically, corresponds to a protein mass of 1 pgm. To test the accuracy of the microspectrometric method of protein determination at the lowest extreme point, the protein content of rat liver mitochondria has been measured and a mean value of 0.239 pgm protein per mitochondrion obtained. This corresponds well with the value of 0.233 pgm per mitochondrion as determined macroscopically by GEAR (1972).

Malignant properties and DNA content of daughter clones from a mouse fibrosarcoma: differentiation between malignant properties

Freshly isolated cones of high cloning efficiency from a mouse fibrosarcoma were examined for DNA content, cell size, protein content, and malignant characteristics such as artificial lung-colony-forming ability, s.c. tumour take, host survival, and spontaneous metastatic ability. These malignant characteristics and other cell properties were heterogeneous among these clones; the malignant characteristics could vary and were not "all or none" in their nature. The higher the DNA content or the larger the cell volume, the higher the malignancy in terms of artificial lung-colony forming, efficiency, s.c. tumour take, and host survival. Despite variability of each parameter, the ratio of DNA content to cell size or protein content remained constant through these variations: the increased DNA paralleled increased protein and increased cell volume. The increased DNA was correlated with the more malignant characteristics of local growth and lung-colony-forming efficiency. Spontaneous metastasis to the lung was totally different from the local growth abilities; the small-cell clone produced more metastases. The graded nature of malignant properties and the differentiation between local growth and metastatic potential among the daughter clones indicate that malignancy reflects a complex moiety of cell properties.

Characterization of pepsin fragments of laminin in a tumor basement membrane. Evidence for the existence of related proteins

Laminin was extracted with neutral buffer from a tumor basement membrane and subjected to extensive degradation by pepsin. The treatment released two homogenous fragments P1 (Mr = 290,000) and P2 (Mr = 45,000) in addition to a mixture of smaller peptides. Fragments P1 and P2 together contained more than 90% of the disulfide bonds and accounted for about one third of the mass of laminin. Both peptides differed in amino acid composition, immunological properties and a complex chain structure demonstrating the existence of two disulfide-bonded domains in the molecule. Part of the laminin in the tumor matrix could only be solubilized by pepsin treatment and several fragments were purified. The major fragment P1i closely resembled P1 of soluble laminin in its chemical and immunological properties. Minor fragments Pa, Pb, Pc and Pd (Mr = 44,000-74,000) were only related to P1 or P2 in amino acid composition, chain pattern and antigenicity. The data were interpreted as indicating that proteins similar but not identical to laminin exist in the basement membrane and account for the minor peptide variants.

Solubilization and purification of bone morphogenetic protein (BMP) from Dunn osteosarcoma

The 4 M GuHCl soluble proteins of Dunn osteosarcoma were fractionated in two steps by means of CsCl density gradient centrifugation. Further purification of bone morphogenetic protein (BMP) was accomplished by molecular sieve techniques utilizing thin-channel diafiltration (Amicon), Sepharose CL-6B and Sephacryl S-200 gel filtration. Partially purified BMP fractions were analyzed by electrophoresis on 7.5% SDS polyacrylamide gel. The molecular weight of BMP active fractions ranges from 30,000 to a few thousand daltons. BMP may be one of the two proteins of MW of 12,500 and 16,000 daltons.

The 3'-terminal primary structure of five eukaryotic 18S rRNAs determined by the direct chemical method of sequencing. The highly conserved sequences include an invariant region complementary to eukaryotic 5S rRNA

The 3'-terminal sequences of 18S rRNA from chicken reticulocyte, mouse sarcoma, rat liver, rabbit reticulocyte and barley embryo were determined by the direct chemical sequencing method. The regions sequenced show complete homology for the first 73 nucleotides. A sequence 5'-proximal to the m6(2)Am6(2)A residues that is complementary to eukaryotic 5S RNAs is totally conserved. This supports the hypothesis that base-paired interaction between 5S and 18S rRNA, which are present in the large and small ribosomal subunits respectively, may be involved in the reversible association of ribosomal subunits during protein synthesis.

Transforming growth factors: isolation of polypeptides from virally and chemically transformed cells by acid/ethanol extraction

Polypeptides characterized by their ability to confer a transformed phenotype on an untransformed indicator cell have been isolated directly from tumor cells growing both in culture and in the animal, by using an acid/ethanol extraction procedure. Assay of these polypeptides is based on their ability to induce normal rat kidney fibroblasts to form colonies in soft agar. Peptides from murine sarcoma virus-transformed mouse 3T3 cells grown in culture had the highest specific activity in this assay; peptides from sarcomas produced from these cells or from chemically induced transplantable bladder carcinomas of mice were one-third as active; and peptides from a chemically induced rat tracheal carcinoma had only one-tenth the activity. Treatment with either trypsin or dithiothreitol destroyed the activity of all of these materials. The properties of these intracellular polypeptides from both virally and chemically transformed cells are similar to those described for the sarcoma growth factors (SGFs) previously isolated from the conditioned medium of sarcoma virus-transformed mouse 3T3 cells, suggesting the definition of a class of transforming growth factors common to tumor cells of different origins. The transforming peptides from the cultured sarcoma virus-infected cells were separately by gel filtration into two fractions of apparent molecular weight 7000 and 10,000. The major fraction at molecular weight 7000 represented approximately 0.1% of the original cell protein and had a specific activity 50 times that of the original acid/ethanol extract.