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Suppression and re-expression of transformed phenotype in hybrids of HA-ras-1-transformed rat-1 cells and early-passage rat embryonic fibroblasts.

Rat-1 cells which had been transformed with the activated Ha-ras-1 gene from human EJ bladder carcinoma cells were fused with diploid embryonic rat fibroblasts. Four selected cell hybrids expressed the human transforming gene product p21 at levels of 10 to 30% compared to 100% in the transformed parental cells. The hybrid cells, however, exhibited normal morphology, anchorage requirement for proliferation, and largely extended latency periods of tumorigenicity in newborn rats. Tumorigenic hybrid derivatives contained lower numbers of chromosomes than the tetraploid parental hybrids. DNA of the non-tumorigenic cell hybrids transformed Rat-1 cells to anchorage-independent proliferation as expected for the transforming human Ha-ras gene present in the donor DNA. We conclude that the transforming properties of the activated Ha-ras gene in Rat-1 cells can be suppressed at the post-translational level by the presence of the genome from diploid embryonic rat fibroblasts but additional controls of expression of the transforming gene are likely to exist. Normal cells contain suppressor gene(s) which safeguard these cells against transformation by the product of the transforming Ha-ras-1 oncogene.

Animals↗

Genetic transformation of Ascochyta rabiei using Agrobacterium-mediated transformation.

In order to study pathogenic mechanisms of the plant pathogen Ascochyta rabiei, conditions for efficient transformation using Agrobacterium-mediated transformation were investigated. Hygromycin B resistance (hph) was superior to geneticin resistance (nptII) for selecting transformants, and the hph gene was more efficiently expressed by the Aspergillus nidulans trpC promoter than by the Cauliflower mosaic virus 35S promoter CaMV35S. Co-cultivation on solid media for 72 h was optimal for generating transformants, but increasing the ratio of bacterial cells to conidia did not affect transformation efficiency. All hygromycin B-resistant transformants carried transfer-DNA (T-DNA) as determined by polymerase chain reaction (PCR) and the T-DNA integrations appeared to be random and in single copy as detected by Southern hybridization. Transformants remained resistant to hygromycin B in the absence of selection. Variations in colony morphology were observed in the presence of hygromycin B under different culture conditions, and a variety of altered phenotypes including reduced virulence were observed among 550 transformants. Inverse PCR was more efficient than TAIL-PCR in identifying flanking genomic sequences from T-DNA borders, and the possible causes are discussed. This transformation technique and recovery of flanking DNA using inverse PCR will provide a useful tool for genetic studies of A. rabiei.

Ascomycota↗

Isolation of novel cDNA transformation markers from SV40-transformed human keratinocytes.

Differential screening of a cDNA library was used to isolate probes for mRNAs that are induced in simian virus 40 (SV40)-transformed human keratinocytes. Several of these cDNAs hybrid select mRNAs which encode transformation-induced proteins found in the cytoskeletal component of SV40-transformed keratinocytes. One of these cDNAs was used to study the phenotype of normal and transformed cell lines derived from various tissues. We found that mRNA encoding the novel transformation-induced proteins is expressed in two squamous carcinoma cell lines derived from the oral epithelium, four SV40-transformed keratinocyte cell lines, and two SV40-transformed fibroblasts. Normal or transformed lymphoid cells or cell lines derived from carcinoma of the cervix do not express mRNAs which hybridize to these probes. The results from this study suggest that these probes may be used to detect markers of transformation in certain cell types.

Base Sequence↗

Changes in polypeptide pattern in ASV-transformed rat cells are correlated with the degree of morphological transformation.

Normal rat kidney cells (NRK) have been transformed with an avian sarcoma virus (ASV) mutant that induces a temperature-sensitive transformed phenotype. When compared in vitro different ASV-transformed clones showed different degrees of morphological transformation at the permissive temperature, while they all reverted to normal at 39 degrees C. Comparisons of the polypeptide patterns of the different cells showed two things. First, a group of about 30 polypeptides, amounting to 5% of all the polypeptides analyzed in normal cells, were affected in all ASV-transformed clones and also in two papovavirus-transformed clones and also in two papovavirus-transformed NRK clones. Second, the patterns were found to differ between the clones in that varying numbers of polypeptides were found to be affected depending on the clone; the number of polypeptide changes showed a good correlation with the degree of morphological transformation. At the nonpermissive temperature the polypeptide patterns of ts ASV-transformed cells were indistinguishable from that of the untransformed cells, which is in agreement with the morphological data.

Animals↗

Galectin-3 mRNA level depends on transformation phenotype in ras-transformed NIH 3T3 cells.

The increase in galectin-3 lectin content observed in tumours or in in vitro transformed cells suggests that this lectin is important in the transformation process. In the present study, we investigated the mRNA expression level of the galectin-3, galectin-1 and macrophage mannose receptor in normal and ras-transformed NIH 3T3 cells in relation to their transformation state. The galectin-3 mRNA content in ras-transformed cells is increased in fully transformed cells, with a maximum in ras-transformed cells that have lost their growth anchorage-dependence. Under the same conditions, the galectin-1 mRNA level which was high in normal cells, increased slightly in transformed cells. The mRNA for the macrophage mannose receptor was not detected in 3T3 cells or in their ras-transformed counterparts.

3T3 Cells↗

High-copy-number transformants and co-transformation in Dictyostelium.

We have recently established a DNA-mediated transformation system for Dictyostelium. The vector (pB10) contains the promoter from the Dictyostelium actin 6 gene fused to the NmR gene from Tn5 which confers resistance to antibiotic G418. Dictyostelium cells can be stably transformed and express kanamycin phosphotransferase (APHII). There is an average of three to five copies of vector DNA in transformed populations. We have fused an A + T-rich region containing the 3' end of the Dictyostelium actin (Act) 8 gene to the end of the Act6-NmR fusion. Though the fragment is inserted in reverse orientation, this adds a transcription termination and/or 3' processing site and results in the formation of a discretely sized mRNA from the Act6-NmR gene fusion. Using this vector, the number of transformants increases by approx. 5-10-fold. We also describe conditions that allow for the isolation of transformants having a high copy number of vector DNA per cell (approx. 150 copies/cell). In addition, we show that cells can be co-transformed with the transformation vector and other pBR322 derivatives. Both plasmid DNAs are present in transformed Dictyostelium cells in high-Mr DNA. When cells are grown under selective conditions in the presence of the antibiotic G418, both DNAs are present in high copy number and Dictyostelium genes present on both vectors are transcribed and are properly regulated under the conditions examined. These modifications of the original transformation system should facilitate the introduction of modified genes into Dictyostelium to study gene regulation during development and allow one to examine the effects of high gene dosage.

Actins↗

Transformation of human cells by DNAs ineffective in transformation of NIH 3T3 cells.

Neonatal human foreskin fibroblasts can be transformed to anchorage-independent growth by transfection with DNAs inefficient in transforming NIH 3T3 cells. Human cells transfected with DNA from GM 1312, a multiple myeloma cell line, or MOLT-4, a permanent lymphoblast line, grow without anchorage at a much higher frequency than do the parental cells and their DNAs can transform human cell recipients to anchorage-independent growth; they have extended but not indefinite life spans and are nontumorigenic. Human fibroblasts are also transformed by DNAs from two multiple myeloma lines that also transform 3T3 cells; however, restriction analysis suggests that different transforming genes in this DNA are acting in the human and murine systems. These results indicate that the human cell transfection system allows detection of transforming genes not effective in the 3T3 system and points out the possibility of detection of additional transforming sequences even in DNAs that do transform murine cells.

Animals↗

Polyamines are essential for cell transformation by pp60v-src: delineation of molecular events relevant for the transformed phenotype.

Ornithine decarboxylase (ODC), the key enzyme of polyamine biosynthesis, becomes upregulated during cell proliferation and transformation. Here we show that intact ODC activity is needed for the acquisition of a transformed phenotype in rat 2R cells infected with a temperature-sensitive mutant of Rous sarcoma virus. Addition of the ODC inhibitor alpha-difluoromethyl ornithine (DFMO) to the cells (in polyamine-free medium) before shift to permissive temperature prevented the depolymerization of filamentous actin and morphological transformation. Polyamine supplementation restored the transforming potential of pp60v-src. DFMO did not interfere with the expression of pp60v-src or its in vitro tyrosine kinase activity. The tyrosine phosphorylation of most cellular proteins, including ras GAP, did not either display clear temperature- or DFMO-sensitive changes. A marked increase was, however, observed in the tyrosine phosphorylation of phosphatidylinositol 3-kinase and proteins of 33 and 36 kD upon the temperature shift, and these hyperphosphorylations were partially inhibited by DFMO. A DFMO-sensitive increase was also found in the total phosphorylation of calpactins I and II. The well-documented association of GAP with the phosphotyrosine-containing proteins p190 and p62 did not correlate with transformation, but a novel 42-kD tyrosine phosphorylated protein was complexed with GAP in a polyamine- and transformation-dependent manner. Further, tyrosine phosphorylated proteins of 130, 80/85, and 36 kD were found to coimmunoprecipitate with pp60v-src in a transformation-related manner. Altogether, this model offers a tool for sorting out the protein phosphorylations and associations critical for the transformed phenotype triggered by pp60v-src, and implicates a pivotal role for polyamines in cell transformation.

Actin Cytoskeleton↗

Ectopic integration of transforming DNA is rare among neurospora transformants selected for gene replacement.

In a variety of organisms, DNA-mediated transformation experiments commonly produce transformants with multiple copies of the transforming DNA, including both selected and unselected molecules. Such "cotransformants" are much more common than expected from the individual transformation frequencies, suggesting that subpopulations of cells, or nuclei, are particularly competent for transformation. We found that Neurospora crassa transformants selected for gene replacement at the am gene had not efficiently incorporated additional DNA, suggesting that nuclei that undergo transformation by homologous recombination are not highly competent at integration of DNA by illegitimate recombination. Spheroplasts were treated with DNA fragments homologous to am and with an Escherichia coli hph plasmid. Transformants were initially selected for hph (hygromycinR), allowed to conidiate to generate homokaryons and then selected for either Am- (gene replacements) or hph. Surprisingly, most am replacement strains were hygromycinS (124/140) and carried no extraneous DNA (116/140). Most transformants selected for hph also had ectopic copies of am DNA and/or multiple copies of hph sequences (32/35), generally at multiple sites, confirming that efficient cotransformation could occur. To test the implication that cotransformation involving gene replacement and ectopic integration is rare, we compared the yields of am replacement strains with or without prior selection for hph. The initial selection did not appreciably help (or hinder) recovery of strains with replacements.

Blotting, Southern↗

SH2 mutants of c-src that are host dependent for transformation are trans-dominant inhibitors of mouse cell transformation by activated c-src.

The c-src gene encodes a membrane-associated protein-tyrosine kinase, pp60c-src, whose substrates and regulators have not been identified. In an effort to obtain mutants that might assist the search for proteins that interact with pp60c-src, we have generated by site-directed mutagenesis two alleles of chicken c-src that are host dependent for transformation and inhibit transformation of mouse cells by activated c-src in a trans-dominant manner. These alleles, named M6 and M9, encode nonconservative changes within the highly conserved FLVRES sequence in the src homology-2 (SH2) region of pp60c-src, as well as an activating change, Y527F, near the carboxyl terminus. M6 and M9 transform chicken embryo fibroblasts (CEF) more efficiently than the parental allele (Y527F c-src), but fail to transform mouse NIH-3T3 cells. The product of M6-src is less stable than activated pp60c-src in NIH-3T3 cells and shows decreased protein tyrosine kinase activity on all tested substrates; the product of M9-src, however, is stable, has a novel pattern of substrate preference for tyrosine phosphorylation in vitro, and induces a pattern of phosphotyrosine-containing proteins in mouse cells that is similar to that induced by Y527F c-src, even though it fails to transform these cells. Both M6 and M9 inhibit transformation of NIH-3T3 cells by activated c-src in a dose-dependent manner, as assayed by resistance of M6- or M9-expressing cells to transformation by Y527F c-src or by morphological reversion of cells previously transformed by activated c-src following introduction of M6 or M9. When reversion occurs, the concentration of protein encoded by the active allele declines, without change in level of src mRNA or rate of src protein synthesis, implying that the products of M6 and M9, when present at adequate levels, can destabilize transformation-competent src protein. These alleles offer new opportunities for interfering with the actions of src-related genes and for isolating cellular factors required for the functions of those genes.

Animals↗

Effects of nucleoside analogs on Epstein-Barr virus-induced transformation of human umbilical cord leukocytes and Epstein-Barr virus expression in transformed cells.

Two methods of assay, measuring (i) stimulation of host cell DNA synthesis by [(3)H]thymidine incorporation and (ii) morphological transformation in microtiter plates, were employed to determine what effect treatment during infection with adenine arabinoside or 5-iodo-5'-amino-2',5'-dideoxyuridine has on Epstein-Barr virus (EBV) (B95-8)-induced transformation of human umbilical cord leukocytes. It was found that adenine arabinoside inhibited EBV-induced transformation in a dose-dependent manner in both assays, beginning at drug concentrations (<2 mug/ml) which had little effect on either spontaneous or phytohemagglutinin-induced host cell DNA synthesis. Adenine arabinoside was more effective in inhibiting morphological transformation than EBV-induced host DNA synthesis. Adenine arabinoside treatment was also effective in reducing both EB viral capsid antigen expression and production of biologically active extracellular transforming virus in EBV-transformed cells. In contrast, 5-iodo-5'-amino-2',5'-dideoxyuridine, which inhibited herpes simplex virus replication, had little effect on EBV-induced transformation as measured by either method of assay. However, 5-iodo-5'-amino-2',5'-dideoxyuridine was found to be effective in inhibiting viral capsid antigen expression and production of extracellular transforming virus in EBV-transformed cells.

Cell Transformation, Viral↗

Transformation of Bacillus subtilis by DNA bound on montmorillonite and effect of DNase on the transforming ability of bound DNA.

The equilibrium adsorption and binding of DNA from Bacillus subtilis on the clay mineral montmorillonite, the ability of bound DNA to transform competent cells, and the resistance of bound DNA to degradation by DNase I are reported. Maximum adsorption of DNA on the clay occurred after 90 min of contact and was followed by a plateau. Adsorption was pH dependent and was greatest at pH 1.0 (19.9 micrograms of DNA mg of clay-1) and least at pH 9.0 (10.7 micrograms of DNA mg of clay-1). The transformation frequency increased as the pH at which the clay-DNA complexes were prepared increased, and there was no transformation by clay-DNA complexes prepared at pH 1. After extensive washing with deionized distilled water (pH 5.5) or DNA buffer (pH 7.5), 21 and 28%, respectively, of the DNA remained bound. Bound DNA was capable of transforming competent cells (as was the desorbed DNA), indicating that adsorption, desorption, and binding did not alter the transforming ability of the DNA. Maximum transformation by bound DNA occurred at 37 degrees C (the other temperatures evaluated were 0, 25, and 45 degrees C). DNA bound on montmorillonite was protected against degradation by DNase, supporting the concept that "cryptic genes" may persist in the environment when bound on particulates. The concentration of DNase required to inhibit transformation by bound DNA was higher than that required to inhibit transformation by comparable amounts of free DNA, and considerably more bound than free DNase was required to inhibit transformation by the same amount of free DNA. Similarly, when DNA and DNase were bound on the same or separate samples of montmorillonite, the bound DNA was protected from the activity of DNase.

Adsorption↗

TRANSFORMATION OF BACILLUS SUBTILIS TO MOTILITY AND PROTOTROPHY: MICROMANIPULATIVE ISOLATION OF BACTERIA OF TRANSFORMED PHENOTYPE.

Stocker, B. A. D. (Stanford Medical Center, Palo Alto, Calif.). Transformation of Bacillus subtilis to motility and prototrophy: micromanipulative isolation of bacteria of transformed phenotype. J. Bacteriol. 86:797-804. 1963.-A nonmotile (nonflagellated, fla(-)) try(-) strain of Bacillus subtilis was transformed to fla(+) and to try(+) by wild - type deoxyribonucleic acid (DNA) at comparable rates. Bacteria of fla(+) phenotype were recognized by their motility approximately 3 hr after uptake of DNA, and bacteria of try(+) phenotype at about the same time by their elongation into filaments in a medium lacking tryptophan. Of phenotypically transformed bacteria of each sort isolated by micromanipulation, the majority produced only transformed progeny, a mixture of transformed and untransformed, or a mixture of two kinds of transformant. Some produced only untransformed progeny, or progeny transformed only at a locus linked to that concerned in their phenotypic transformation. In a few clones, some partial heterozygotes were present even ten generations after DNA uptake. In nonmotile clones derived from motile isolates, the unilinear transmission of motility to one to four descendants was detected; it is attributed to persistence of a corresponding number of units of some product of an unincorporated fla(+) gene, probably flagella or cell walls each carrying several flagella. No pedigrees indicating unilinear transmission of an unincorporated fla(+) gene were observed.

Bacillus subtilis↗

Revertants of v-fos-transformed rat fibroblasts: suppression of transformation is dominant.

Phenotypic revertants of Finkel-Biskis-Riley (FBR)-murine sarcoma virus-transformed rat fibroblasts were isolated on the basis of their adherence to plastic tissue culture dishes in the absence of divalent cations. Some revertants had sustained deletions or inactivating mutations of the v-fos gene. However, two revertants expressed a functional v-fos gene at levels equal to that in the transformed parental cells, and therefore phenotypic reversion was due to mutations in nonviral genes. These revertants were considered nontransformed according to four criteria: (i) they were flat and had a nontransformed morphology, (ii) they were contact inhibited when grown to confluence, (iii) they did not display anchorage-independent growth in soft agar, and (iv) they did not form tumors in nude mice. Somatic-cell hybrids between the revertants and the transformed parental cells were nontransformed, suggesting that the revertants had sustained an activating mutation of a gene capable of suppressing transformation. The expression of c-jun, junB, and junD was not altered in the revertants, and they could not be transformed by transfection with a c-jun expression vector. The revertants were resistant to transformation by an activated c-Ha-ras gene but were susceptible to transformation by simian virus 40. Our results demonstrate the existence of a class of revertants that harbor genes capable of suppressing transformation by v-fos and some other oncogenes. This contrasts with previously described revertants of transformation by v-fos that contain recessive mutations.

Animals↗

Effects of transformation with the v-src oncogene on inositol phosphate metabolism in rat-1 fibroblasts. D-myo-inositol 1,4,5,6-tetrakisphosphate is increased in v-src-transformed rat-1 fibroblasts and can be synthesized from D-myo-inositol 1,3,4-trisphosphate in cytosolic extracts.

Rat-1 fibroblasts transformed with the v-src oncogene show a 6-fold increase in the apparent amount of an inositol polyphosphate which has a high performance liquid chromatography (HPLC) elution characteristic of the D/L-myo-inositol 1,4,5,6-tetrakisphosphate enantiomeric pair (Johnson, R.M., Wasilenko, W.J., Mattingly, R.R., Weber, M.J., and Garrison, J.C. (1989) Science 246, 121-124). By chemical and enzymatic analysis, the structure of this compound produced in both normal and v-src-transformed rat-1 fibroblasts has been determined to be principally D-myoinositol 1,4,5,6-tetrakisphosphate (D-Ins(1,4,5,6)P4). Chronic stimulation with endothelin-1 in the presence of Li+ significantly increased the amount of D/L-Ins(1,4,5,6)P4 only in the v-src-transformed rat-1 cells, suggesting that production of this compound may be remotely coupled to long term agonist-induced phosphatidylinositol turnover. Further evidence for such a link is provided by the progressive loss of D-Ins(1,4,5,6)P4 from the normal cells deprived of serum stimulation. To define a possible synthetic pathway for D-Ins(1,4,5,6)P4, cytosolic extracts of normal and v-src-transformed cells were incubated with [3H]inositol polyphosphates, and the reaction products were identified by HPLC elution and chemical analysis. Although inositol 1,3,4-trisphosphate 6-kinase activity was prominent in extracts of both normal and transformed cells, only the cytosol from v-src-transformed cells ultimately formed measurable amounts of D-Ins(1,4,5,6)P4 from [3H]inositol 1,3,4-trisphosphate. Approximately 6% of 0.1 microM inositol 1,3,4-trisphosphate was converted to D-Ins(1,4,5,6)P4 during a 2-h incubation at 37 degrees C. Inositol pentakisphosphate was identified as a likely intermediate in this conversion, and extracts of both normal and transformed cells converted [3H]inositol 1,3,4,5,6-pentakisphosphate to D-Ins(1,4,5,6)P4. The synthetic pathway described is consistent with the long term regulation of D/L-Ins(1,4,5,6)P4 levels in rat-1 fibroblasts seen in response to src transformation, serum withdrawal, and chronic endothelin treatment, and identifies several new potential interactions between the pathways of inositol polyphosphate metabolism and those of src transformation.

Animals↗

Transformation of murine myelomonocytic cells by myc: point mutations in v-myc contribute synergistically to transforming potential.

The v-myc oncogenes of chicken retroviruses (including MC29) bear point mutations relative to chicken c-myc. These mutations result in several amino acid differences in the encoded proteins. We have used recombinant murine retroviruses containing various myc alleles to analyse the myelomonocytic transforming potential of the myc oncogene. The myc alleles used were MC29 v-myc, chicken c-myc, chimeric genes combining 5' sections of v- or c-myc with 3' sections of c- or v-myc, and mouse c-myc. The same retroviral vector (based on the genome of Moloney leukemia virus) was used for each allele and the genes were translated from genomic message. By infecting the primary mouse tissues, bone marrow, peritoneal-derived macrophages and mixed embryonic tissue with the recombinant viruses, variation was found in the transforming efficacy of these alleles: v-myc was most effective, followed by the two chimeric genes, whereas c-myc (chicken or mouse) was least effective in eliciting myelomonocytic transformation. Viral gag sequences were not necessary for this transformation. In each case, the transformed monocytes were growth factor-dependent and non-immortal. However, v-myc transformed monocytes (though not monocytes transformed by other myc alleles) were able to progress to an immortal, growth factor-independent phenotype. Our results indicate that v-myc is far more effective than c-myc in eliciting myelomonocytic transformation; that this is due to combinatorial effects of 5' and 3' mutations in the v-myc gene; and that secondary events in addition to these mutations are required for transformation of myelomonocytic cells to an immortal, tumorigenic phenotype.

Animals↗

Characterization of human transforming genes from chemically transformed, teratocarcinoma, and pancreatic carcinoma cell lines.

Dominant transforming genes that were transferred to mouse NIH3T3 cells by cellular DNAs prepared from a chemically transformed human cell line (MNNG-HOS), a human teratocarcinoma cell line (PA1), and a human pancreatic carcinoma cell line (A1165) were characterized (a) analyzing the repetitive human DNA sequences that were associated with the transforming gene and (b) determining their relationship to the oncogenes of the Harvey (rasH) and Kirsten (rasK) sarcoma viruses and to the human neuroblastoma transforming gene (rasN). The results show that the transforming gene activated in the teratocarcinoma cell line is identical to the neuroblastoma transforming gene and that the transforming gene of the pancreatic carcinoma cell line is a human homologue of rasK. In contrast, the transforming gene activated in the chemically transformed human cell line showed no detectable homology to rasK, rasH, and rasN.

9,10-Dimethyl-1,2-benzanthracene↗

Sensitivity of transformed fibroblasts for intercellular induction of apoptosis is determined by their transformed phenotype.

Intercellular induction of apoptosis defines a potential control mechanism of oncogenesis. It is based on induction of apoptosis in transformed fibroblasts by neighboring nontransformed fibroblasts. Transforming growth factor type beta (TGF-beta) represents the initial triggering molecule to induce nontransformed cells to release apoptosis-inducing factors. To test whether sensitivity for intercellular induction of apoptosis is directly dependent on the transformed phenotype, v-src-transformed rat fibroblasts and emerging revertants were tested for their sensitivity. All transformed cell clones were sensitive, whereas all revertant clones had lost their sensitivity in parallel with the loss of the transformed phenotype. In addition, revertants had regained the potential to induce apoptosis in transformed cells. Sensitivity to intercellular induction of apoptosis is therefore directly dependent on the transformed phenotype, whereas the ability to induce apoptosis is a specific feature of nontransformed fibroblasts.

Animals↗