Properties of a sarcoma-growth-factor-like peptide from cells transformed by a temperature-sensitive sarcoma virus

Serum-free conditioned media was collected from three sarcoma virus-transformed cell lines and an untransformed cell line. All three virally transformed lines produced and released growth factors into their serum-free media. The major activity in all cases, whether the cells were transformed by Moloney sarcoma virus (MSV) or Kirsten sarcoma virus (KiSV), or whether they were mouse or rat, was a sarcoma-growth-factor (SGF)-like activity with an apparent molecular weight of 10,000. The SGF-like pools from a Moloney sarcoma virus-transformed mouse 3T3 cell and a Kirsten sarcoma virus-transformed NRK cell were further purified by carboxymethyl cellulose chromatography. The elution profiles of these peptides were very similar. The serum-free conditioned media from the untransformed cells showed no detectable growth stimulating activity. The temperature sensitivity of an SGF-like growth factor from the supernate of a NRK cell transformed by a wild-type Kirsten sarcoma virus (KiSV) was compared with that of the SGF-like activity from the supernates of a NRK cell transformed by a ts-mutant of KiSV that is temperature sensitive with respect to transformation (ts-371 Cl 5). Neither the cells transformed by the wild-type sarcoma virus nor those transformed by the temperature sensitive virus released a SGF-like activity that was temperature sensitive under the conditions of the assays.     

Loss of epidermal growth factor receptors and release of transforming growth factors do not correlate with sarcoma virus-transformation in clonally-related NIH/3T3-derived cell lines.

Transformation of NIH/3T3 cells by Kirsten murine sarcoma virus (MSV) caused a dramatic reduction in the number of cell-surface receptors for epidermal growth factor (EGF). However, the number of EGF receptors remained at a very low level in a non-tumourigenic revertant cell line isolated from the virus-transformed cells, indicating that an increase in EGF receptors is not a requirement for the phenotypic reversion of Kirsten MSV-transformed 3T3 cells. Serum-free conditioned medium from normal and virus-transformed cell lines contained similar amounts of cell growth-promoting activity as assayed by the ability to stimulate DNA synthesis in quiescent Swiss 3T3 cell cultures. However, the concentrated conditioned medium from these cell lines showed no evidence of beta-transforming growth factor (TGF) activity as assayed by promotion of anchorage-independent growth of untransformed normal rat kidney (NRK) fibroblasts in agarose. The cellular release of alpha-TGF activity was assayed by measuring the ability of concentrated conditioned medium to inhibit the binding of 125I-EGF to Swiss 3T3 cells. Conditioned medium protein from the virus-transformed cell line inhibited 125I-EGF binding but only to the same extent as conditioned medium protein prepared from the untransformed cell line. The alpha-TGF secretion by these cell lines was estimated to be 30-45-fold lower than the level of alpha-TGF released by a well-characterized alpha-TGF-producing cell line (3B11). These results suggest that the induction of TGF release is not a necessary event in the transformation of NIH/3T3 cells by Kirsten MSV.     

Dimethyl-10,12-benz(a)acridine; evidence for differential effects on the synthesis of RNA of mammalian or avian fibroblasts and some RNA viruses.

We have studied the differential effect of dimethyl-10,12-benz(a)acridine (DBMAcr) on the synthesis of RNA of chicken or mouse fibroblasts in culture and that of some RNA-containing viruses such as Rous sarcoma virus and Mengovirus. DMBAcr at low concentrations blocks the cell multiplication of both normal and Rous sarcoma virus-transformed chicken fibroblasts in culture; it affects transformed cells more than normal ones. The cell growth inhibiting effect of DMBAcr is reversible after short periods of incubation. DMBAcr depresses the synthesis of cellular DNA and RNA in parallel. Concurrently the synthesis of protein proceedes at a relatively high rate in DMBAcr-treated cultures. Its inhibitory effect on cellular RNA synthesis is mostly due to a block in the formation of 28 S and 18 S ribosomal RNA species; in contrast, the synthesis of 45 S ribosomal RNA precursor is proceeding at almost control rate. Also, the synthesis of heterogeneous nuclear RNA is not blocked by DMBAcr. The production of Rous sarcoma virus in transformed fibroblasts is not affected by DMBAcr. Since this is correlated with persisting high rates of protein and heterogenous nuclear RNA synthesis, the effects of DMBAcr suggest that the synthesis of Rous sarcoma virus-RNA shares the specificity of messenger and heterogeneous nuclear RNA. DMBAcr inhibits the synthesis of viral RNA of Mengovirus under conditions where the synthesis of total cellular RNA is not appreciably depressed, suggesting its differential effect on the DNA-directed and the RNA-directed RNA synthesis.     

Infectivity and RNA Patterns as Functions of High- and Low-Dilution Passage of Murine Sarcoma-Leukemia Virus: Evidence for Autointerference Within an Oncornavirus Population

Heterogeneity of buoyant density and RNA content of virions of Moloney murine leukemia-sarcoma complex [MSV (MLV)] was the result of passage at low dilution. Heterogeneous stocks revealed two major RNA components in the population, with the smaller component, apparent mol wt 4 x 10(6) to 5 x 10(6), becoming predominant upon serial passage at low dilution. Concomitantly, infectivity titers of both MLV and MSV decreased upon serial passage at low dilution. MSV (MLV) passaged at high dilution retained high titers and a rather homogeneous high-molecular-weight RNA population characteristic of high-buoyant-density virions. Interference of both MLV and MSV replication was demonstrated by employing mixed inocula containing both low- and high-dilution passage stocks of MSV (MLV). In contrast to results with MSV (MLV), MLV freed of MSV by limit dilution did not show heterogeneity of buoyant density or of RNA when propagated at low dilution.     

Spontaneous Release of Endogenous Ecotropic Type C Virus from Rat Embryo Cultures

Type C viruses were isolated from embryo cultures of two different rat strains, Sprague-Dawley and Fischer. Both viruses (termed rat leukemia virus, RaLV) were released spontaneously from rat embryo cells, have a density of 1.14 to 1.15 g/cm(3) based on equilibrium sedimentation in sucrose gradients, contain 60-70S RNA, RNA-directed DNA polymerase, and rat type C virus-specific 30,000 molecular-weight-protein determinants. Molecular hybridization studies using the Sprague-Dawley RaLV 60-70S RNA show that the virus-specific nucleotide sequences are present in the DNA of rat embryos. Both Sprague-Dawley and Fischer RaLV can rescue the murine sarcoma virus genome from Kirsten murine sarcoma virus-transformed nonproducer cells and are neutralized by antisera to the RPL strain of RaLV. In contrast to previous RaLV's, these viruses propagate in their own cells of origin as well as in cells of heterologous rat strains.     

In vitro tumoricidal activity of macrophages against virus-transformed lines with temperature-dependent transformed phenotypic characteristics.

The susceptibility of targets to destruction by tumoricidal rat and mouse macrophages was studied with virus-transformed cell lines in which various elements of the transformed phenotype are only expressed at specific temperatures. BHK cells transformed by the ts3 mutant of polyoma virus, rat embryo 3Y1 cells transformed by a temperature-sensitive A cistron mutant of simian virus 40 (SV40) and the ts-H6-15 temperature-sensitive line of SV40-transformed mouse 3T3 cells were killed in vitro by macrophages at both the permissive (33 °C) or nonpermissive (39 °C) temperatures for expression of the transformed phenotype. 3T3, 3Y1 and BHK cells transformed by wild-type SV40 or polyoma virus were also destroyed by tumoricidal macrophages at both 33 and 39 °C, but untransformed 3T3, 3Y1, and BHK cells were not. Thus, transformed cells are killed by macrophages regardless of whether or not they express cell surface LETS protein or Forssman antigen, display surface changes which permit agglutination by low doses of plant lectins, express SV40 T antigen, have a low saturation density, or exhibit density-dependent inhibition of DNA synthesis.     

Phosphorylation of chromatin- and ribosome-associated proteins in cells transformed by adenovirus, murine sarcoma virus, and methylcholanthrene.

Endogenous protein phosphorylation in chromatin and ribosomes of monkey, mouse, and rat cells transformed by DNA, RNA tumor viruses, and a chemical carcinogen revealed the association of a protein of approximately 90,000 daltons (90K), which is highly phosphorylated in vitro. Peptide map analysis showed that the 90K proteins associated with these organelles of various transformed cells are similar irrespective of the species of cells and transforming agents. This species of protein could not be detected, or was scarcely detected, by phosphorylation in chromatin and ribosomes of untransformed cells and in revertants of transformed cells. These results suggest that the alteration in the pattern of endogenous protein phosphorylation in these organelles is closely related to the transformed state of cells.     

Deoxyribinucleic acid-binding proteins in virus-transformed cell lines.

The synthesis of proteins with affinity for DNA has been studied in clones of a Syrian hamster cell line (NIL) and subclones of this line transformed by polyoma virus (NIL-Py) or hamster sarcoma virus (NIL-HSV). The results show that the synthesis of DNA-binding proteins in NIL and in its virus-transformed derivatives NIL-Py and NIL-HSV is very similar in exponentially growing cells, but in dense culture there is a very significant difference in the level of a protein (P8), which is much higher in the transformed lines than in untransformed NIL. The high levels of P8 in dense transformed cells have been observed in all the clones of transformed cells examined, indicating that this behavior of P8 is related to transformation and not simply due to a fortuitous clonal selection from the NIL. Experiments with synchronized cells indicate that the time of maximal P8 synthesis relative to cellular DNA synthesis in NIL-HSV precedes that observed in NIL cells. P8 has a molecular weight of 30,000 as determined by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate and is present in large amounts in the transformed cells in dense culture, where it makes up 0.5 to 1% of the total soluble protein.     

Transformation by Murine Sarcoma Virus: Fixation (Deoxyribonucleic Acid Synthesis) and Development

Transformation of rat embryo cells by murine sarcoma virus (MSV) was contingent upon synthesis of deoxyribonucleic acid (DNA) during the first 12 hr of infection. Inhibition of DNA synthesis by thymidine (20 mm) or cytosine arabinoside (0.1 mm) resulted in the protection of cells from transformation by MSV. Transient suppression of DNA synthesis prior to infection or after a 12-hr delay had little effect on subsequent transformation, emphasizing the critical time period in in which DNA synthesis was necessary for intracellular fixation of the viral genome. These results are similar to those previously described for Rous sarcoma virus. Development of transformed cells after viral fixation was shown to be influenced by cellular density. Under conditions which allowed fixation of virus in confluent cellular monolayers, less than 20% of these cells developed into transformed foci.     

Mechanism for selective secretion of a lysosomal protease by transformed mouse fibroblasts

Studies in recent years have indicated that secretion of certain lysosomal hydrolases can be enhanced under various conditions. One such protein, the major excreted protein (MEP) of Kirsten virus-transformed NIH 3T3 (KNIH) fibroblasts, is a lysosomal cysteine protease whose synthesis and secretion are affected by viral transformation and growth factors. We have been studying the synthesis and transport of MEP in order to understand better the mechanisms responsible for regulation of lysosomal enzyme secretion. Synthesis of MEP in KNIH cells was found to be 25-fold greater than that in untransformed NIH cells, and 94% of the MEP made was secreted. This was in contrast to NIH cells which secreted only 11% of the newly synthesized MEP. The high level of secretion by the transformed cells was relatively specific in that most other lysosomal enzymes were retained. MEP isolated from both NIH and KNIH cells exhibited a low intrinsic affinity for the mannose-6-phosphate receptor which was at least 10-fold lower than that of other lysosomal enzymes. On the basis of these results, we suggest that both the high level of MEP synthesis and the intrinsic low affinity of MEP for the receptor are responsible for the specific increase in MEP secretion by transformed cells.     

Coordinate regulation of the levels of type III and type I collagen mRNA in most but not all mouse fibroblasts

A mouse genomic clone was isolated by cross-hybridization with a DNA fragment which codes for the NH2-propeptide of chick alpha1(III) collagen. The region of cross-hybridization within the mouse clone was localized, its sequence determined, and an exon coding for the NH2-propeptide of mouse alpha1(III) collagen was identified. This DNA fragment hybridizes to an RNA species of approximately 5300 nucleotides, slightly larger than the major alpha2(I) collagen RNA species. The mouse type III collagen probe was used to examine the effect of transformation on alpha1(III) collagen RNA levels in mouse fibroblasts. The levels of type III and type I collagen mRNA levels were compared in control and sarcoma virus-transformed murine cell lines, as well as in NIH 3T3 cells transformed by members of the human ras oncogenes. The levels of type III RNA decreased about 10-15-fold in Moloney sarcoma virus-transformed cells and in a cell line transformed with a v-mos-containing plasmid, but showed only a 50% decrease in a Kirsten murine sarcoma virus-transformed BALB 3T3 cell line, and increased 4-fold in a Rous sarcoma virus (RSV)-transformed BALB 3T3 cell line. In contrast, the levels of alpha2(I) collagen mRNA are 8- to 10-fold lower in all these cell lines when compared to untransformed cells. NIH 3T3 cells transformed with two human ras oncogenes showed decreased levels of alpha2(I) and alpha1(III) mRNAs. In contrast to the RSV-transformed mouse cell line, RSV-transformed chick embryo fibroblasts contained much smaller amounts of type III RNA than control chick embryo fibroblasts. We conclude that the levels of alpha1(III) and alpha2(I) collagen mRNA are often but not necessarily coordinately regulated by transformation in mouse cells.     

DNA ligase activity in human cell lines from normal donors and Bloom''s syndrome patients.

DNA ligase activity was studied in several untransformed or virus-transformed human cell lines from normal donors and from Bloom's syndrome (BS) patients. This proneness genetic disease is characterized by several cytological abnormalities and cancer proneness and, recently, some transformed cell lines from these patients were described to present a reduced activity of DNA ligase I. Results presented in this work indicate that: (i) the total DNA ligase activity in crude extract from untransformed or transformed cell lines from several BS patients was significantly higher than in control cells; (ii) the partial purification of the enzyme after gel filtration on fast protein liquid chromatography of crude extracts from lymphoblastoid BS cells showed that the enzyme activity was eluted in a major 180 kDa form in which activity was higher than in control cells; (iii) the activity gel analysis of these enzyme fractions revealed that DNA ligase of human cells was correlated to a major 130 kDa polypeptide and, in BS cells, the extent of the activity of this band was equal or higher than that in control untransformed or transformed cells.     

Regulation of DNA replication by serum and the transforming function in cultured rat fibroblasts transformed by Rous sarcoma virus.

The onset and rate of semiconservative DNA replication were measured in stimulated cultured rat fibroblasts and their Rous sarcoma virus-transformed derivatives after a period of serum deprivation. Rat-1 (tsLA24/RSV) cells initiated DNA synthesis following a shift to the permissive temperature or addition of serum at the non-permissive temperature. Their rate of DNA replication was unaffected by the presence of serum at the permissive temperature, however, there was a serum requirement at the non-permissive temperature. The transition probability was less at the permissive temperature, independent of serum, than at the non-permissive temperature in the presence of serum. The amount of DNA induced to replicate by addition of serum at the non-permissive temperature or by a shift to the permissive temperature was similar. Using the untransformed Rat-1 cells and these cells transformed by wild-type RSV (Rat-1 (wt/RSV)), it was confirmed that the rate of entry into S phase (transition probability) was always lower in the transformed cell line at both 39° and 35°. In both cell lines the rate of DNA replication was independent of temperature, but the onset was delayed at the lower temperature. These results indicate that in the cell lines examined, (1) serum was able to commit the cells to replicate DNA (alter the transition probability) in both transformed and untransformed cells, but the transforming function was able to supplant a serum-dependent process during G₁ necessary for the initiation of DNA replication, and (2) the effects of the transforming function and serum factor(s) on the alteration of the transition probability are not additive, suggesting that the transforming function initiates a process which acts at the level of the commitment to DNA replication which may render the normal serum-related control mechanisms ineffective in the regulation of growth.     

Intracellular Viral RNA Species in Mouse Cells Nonproductively Transformed by the Murine Sarcoma Virus

The size and quantity of virus-specific RNA in five non-virus-producing mouse cells transformed by the Moloney isolate of murine sarcoma virus (MSV) was determined. Hybridization of RNA from transformed cells with the [(3)H]DNA product of the RNA-directed DNA polymerase of the murine sarcoma-leukemia virus was used to detect and quantitate virus-specific RNA. The amount of virus-specific RNA in non-virus-producing cells was less than one-sixth of that found in virus-producing cells. A striking correlation was found between the amount of intracellular virus-specific RNA and the degree of agglutination by conconavalin A previously reported for the four non-virus-producing NIH/3T3 cell lines (Salzberg and Green, 1974). A major RNA subunit sedimenting at 26 to 28S was detected in all five MSV-transformed non-virus-producing cells. This could represent the RNA genome of defective MSV.     

Role of simian virus 40 gene A function in maintenance of transformation.

Mouse, hamster, and human cells were transformed at the permissive temperature by mutants from simian virus 40 (SV40) complementation group A in order to ascertain the role of the gene A function in transformation. The following parameters of transformation were monitored with the transformed cells under permissive and nonpermissive conditions: morphology; saturation density; colony formation on plastic, on cell monolayers, and in soft agar; uptake of hexose; and the expression of SV40 tumor (T) and surface (S) antigens. Cells transformed by the temperature-sensitive (ts) mutants exhibited the phenotype of transformed cells at the nonrestrictive temperature for all of the parameters studied. However, when grown at the restrictive temperature, they were phenotypically similar to normal, untransformed cells. Growth curves showed that the (ts) A mutant-transformed cells exhibited the growth characteristics of wild-type virus-transformed cells at the permissive temperature and resembled normal cells when placed under restrictive conditions. There were 3-to 51-fold reductions in the levels of saturation density, colony formation, and uptake of hexose when the mutant-transformed cells were the elevated temperature as compared to when they were grown at the permissive temperature. Mutant-transformed cells from the nonpermissive temperature were able to produce transformed foci when shifted down to permissive conditions, indicating that the phenotypically reverted cells were still viable and that the reversion was a reversible event. SV40 T antigen was present in the cells at both temperatures, but S antigen was not detected in cells maintained at the nonpremissive temperature. All of the wild-type virus-transformed cells exhbited a transformed cells exhibited a transformed phenotype when grown under either restrictive or nonrestrictive conditions. Thers results indicate that the SV40 group A mutant-transformed cells are temperature sensitive for the maintenance of growth properties characteristics of transformation. Virus rescued from the mutant-transformed cells by the transfection method was ts, suggesting that the SV40 gene A function, rather than a cellular one, is responsible for the ts behavior of the cells.     

Specific changes in the synthesis of mitochondrial DNA in chick embryo fibroblasts transformed by Rous sarcoma viruses

In chick-embryo fibroblasts infected with the Schmidt-Ruppin strain of Rous sarcoma virus, subgroup A (wild type), or with a thermosensitive mutant of this virus, T5, the rates of mitochondrial DNA synthesis differ in cells that exhibit normal and malignant phenotypes. In wild type virus-infected cells grown at 36 or 41 degrees C, morphological transformation is expressed, the rate of 2-deoxy-D-[3H]glucose uptake is stimulated, and mitochondrial DNA synthesis in vivo is stimulated three- to fivefold over that in uninfected cells. In T5-infected cells these changes occur only at the permissive temperature (36 degrees C); a shift to the nonpermissive temperature (41 degrees C) causes the reversal of these effects, and the specific activity of purified mitochondrial DNA is characteristic of that from uninfected cells. In contrast, the specific activities of nuclear DNA purified from cells maximally transformed under the permissive conditions do not differ between wild type-infected and uninfected with the T5 virus. In parallel experiments with isolated mitochondria, the rate of mtDNA synthesis in vitro is again greater in mitochondria isolated from transformed cells. In addition, mitochondrial DNA synthesis in vitro in mitochondria from nontransformed and virus-transformed cells exhibits differential sensitivity to inhibition by mercaptoethanol. Furthermore, the ntDNAP polymerase activity in mitochondrial extracts prepared from cells with transformed phenotypes is about sevenfold higher than in extracts from cells with nontransformed phenotypes.     

Four different classes of retroviruses induce phosphorylation of tyrosines present in similar cellular proteins.

Chicken embryo cells transformed by the related avian sarcoma viruses PRC II and Fujinami sarcoma virus, or by the unrelated virus Y73, contain three phosphoproteins not observed in untransformed cells and increased levels of up to four other phosphoproteins. These same phosphoproteins are present in increased levels in cells transformed by Rous sarcoma virus, a virus which is apparently unrelated to the three aforementioned viruses. In all cases, the phosphoproteins contain phosphotyrosine and thus may be substrates for the tyrosine-specific protein kinases encoded by these viruses. In one case, the site(s) of tyrosine phosphorylation within the protein is the same for all four viruses. A homologous protein is also phosphorylated, at the same major site, in mouse 3T3 cells transformed by Rous sarcoma virus or by the further unrelated virus Abelson murine leukemia virus. A second phosphotyrosine-containing protein has been detected in both Rous sarcoma virus and Abelson murine leukemia virus-transformed 3T3 cells, but was absent from normal 3T3 cells and 3T3 cells transformed by various other viruses. We conclude that representatives of four apparently unrelated classes of transforming retroviruses all induce the phosphorylation of tyrosines present in the same set of cellular proteins.