Dual evolutionary origin for the rat genetic sequences of Harvey murine sarcoma virus

Production of chimeric protein coded by the fused viral H-ras and human N-ras genes in Escherichia coli

A new method for the production of a chimeric protein of two related genes has been developed. The nucleotide sequences of the region from the N terminus to the 86th amino acid (aa) residue of human N-ras and of the Harvey sarcoma virus (Ha-MuSV) H-ras are 80% homologous. We isolated the DNA fragment encoding the N-terminal portion up to the 70th aa residue from plasmid pH-1 which encodes the total genome of Ha-MuSV, and the DNA fragment encoding the C-terminal portion from the 40th aa to the C terminus from plasmid p6a1 which includes the human N-ras cDNA but lacks the N-terminal portion. After partial digestion of both fragments with phage lambda exonuclease, which creates 3'-protruding ends, a hybrid was formed between 73% homologous single-stranded DNA portions at the 3' ends of both fragments. The hybrid was recloned on pBR322 after repairing with Escherichia coli DNA polymerase I and DNA ligase. The chimeric v-H/N-ras gene composed of the N-terminal portion of v-H-ras gene and the remaining region of N-ras gene was inserted into an expression vector containing two tandem trp promoters and a terminator, and expressed in E. coli. The chimeric protein was found to accumulate to approx. 10% of total cellular proteins.

Induction of c-Ha-ras transcription in rat cells by simian virus 40 large T antigen

Rat 3Y1 cells expressing simian virus 40 large T antigen under the control of the mouse mammary tumor virus long terminal repeat were established. The amount of c-Ha-ras mRNA in those cells was elevated by about 20 times in parallel with large T antigen after exposure to dexamethasone for 48 h. In chloramphenicol acetyltransferase assays with a plasmid containing the c-Ha-ras-1 promoter the increase in c-Ha-ras mRNA was shown to occur at the transcriptional level.

Biological markers characterizing the development of preneoplastic and neoplastic lesions in rodent liver

The identification of biological "markers" indicating distinctively different functions between preneoplastic and neoplastic as compared with normal cells has been a subject of intensive investigation, especially as additional technology becomes available. Although no distinct single biochemical marker is ubiquitous to the process of neoplasia or even to a single histogenetic type of neoplasm, a variety of histogenetic types of neoplasms in the human and experimental animals exhibit an extreme degree of marker or phenotypic heterogeneity. Particularly well studied are markers which occurred during the process of hepatocarcinogenesis in the rodent as well as in its final product, the hepatoma. Although phenotypic heterogeneity is characteristic of hepatocellular carcinomas in both the rat and mouse, some degree of predominant marker pattern(s) has become apparent. In multistage hepatocarcinogenesis in the rat a frequent but not completely ubiquitous marker is the enzyme gamma-glutamyltranspeptidase. In the mouse, although such markers have not been as extensively studied as in the rat, glucose 6-phosphatase is a predominant but not exclusive histochemical marker. Many preneoplastic lesions occurring during the stage of promotion exhibit reduced levels of enzymes of oxidative xenobiotic metabolism, but this pattern is not ubiquitous. Studies on the transcription of specific genes in mouse liver as well as preneoplastic and neoplastic lesions in this tissue further demonstrate the phenotypic heterogeneity characteristic of differentiated hepatocellular carcinomas. In general, current evidence supports the two theses that no single biologic marker or set of markers is uniquely characteristic of the preneoplastical and/or neoplastic phenotype and marker or phenotypic heterogeneity is by far the rule rather than the exception in hepatocarcinogenesis in the rodent and quite possibly in all histogenetic types of neoplasms in mammals.

Activated Ki-ras oncogene in human prostatic adenocarcinoma

The role of cellular oncogenes in the development of human prostate cancer has not been extensively studied. A search for activated oncogenes was undertaken by testing DNA isolated from prostatic adenocarcinoma tissues for transforming activity in a 3T3 transfection assay. A transforming sequence homologous to Ki-ras was detected in one of the samples. DNA from the other cancers was negative in the transformation assay, suggesting that the activation of oncogenes, at least those detectable by the 3T3 transfection assay, is not a frequent event in prostate cancer. Amplification of genomic oncogene sequences in prostatic tissues was also examined, but amplification of Ki-ras, Ha-ras, c-myc, N-myc, c-sis, or c-fos was not detectable in any of the samples.

Establishment of two rabbit mammary epithelial cell lines with distinct oncogenic potential and differentiated phenotype after microinjection of transforming genes

The goal of this work was to establish an assay for transformation of epithelial cells. Two epithelial cell lines were obtained after microinjecting transforming genes into primary rabbit mammary secretory cells. The cell lines were analyzed for their oncogenic potential and for the maintenance of a differentiated phenotype. A fully transformed cell line, which retained epithelial cell organization, was obtained by coinjecting simian virus 40 DNA and the activated human c-Ha-ras gene. The proliferation rate of these cells was high, with a doubling time of 16 h. Their growth was anchorage independent, and they had lost contact inhibition. The cells were tumorigenic in nude mice, but had no metastatic potential. Both microinjected DNAs were efficiently transcribed and translated, in contrast to the casein genes, which were expressed in primary cells but not in the transformed cell line. An immortalized cell line established after injection with simian virus 40 DNA alone was characterized by a moderate rate of proliferation with a doubling time of approximately 30 h. The growth of these cells was contact inhibited and anchorage dependent. The cells were not tumorigenic in nude mice. The viral DNA was expressed during early passages, as shown by the presence of the large T antigen in cell nuclei, but not at later passages. A high number of lactogenic hormone receptors were found associated with the cell surface. Despite the presence of these receptors, no induction of genes coding for milk proteins was observed after addition of prolactin. These data demonstrate that this assay system can be used to assess the immortalizing and transforming potential of candidate oncogenes in epithelial cells.

Synergism of v-myc and v-Ha-ras in the in vitro neoplastic progression of murine lymphoid cells

Murine bone marrow was either singly or doubly infected with retroviral vectors expressing v-myc (OK10) or v-Ha-ras. The infected bone marrow was cultured in a system that supports the long-term growth of B-lineage lymphoid cells. While the v-myc vector by itself had no apparent effect on lymphoid culture establishment and growth, infection with the v-Ha-ras vector or coinfection with both v-myc and v-Ha-ras vectors led to the appearance of growth-stimulated cell populations. Clonal pre-B-cell lines stably expressing v-Ha-ras alone or both v-myc and v-Ha-ras grew out of these cultures. In comparison with cell lines expressing v-Ha-ras alone, cell lines expressing both v-myc and v-Ha-ras grew to higher densities, had reduced dependence on a feeder layer for growth, and had a marked increase in ability to grow in soft-agar medium. The cell lines expressing both oncogenes were highly tumorigenic in syngeneic animals. These experiments show that the v-myc oncogene in synergy with v-Ha-ras can play a direct role in the in vitro transformation of murine B lymphoid cells.

Identification of an activated c-Ki-ras oncogene in rat liver tumors induced by aflatoxin B1

Weanling male Fischer rats were administered 40 intraperitoneal injections of aflatoxin B1 (25 micrograms per animal per day) over a 2-month period. This chronic dosing regimen resulted in the sequential formation of hyperplastic foci, preneoplastic nodules, and hepatocellular carcinomas in all of the animals treated. The presence of transforming DNA sequences was detected by formation of anchorage-independent foci after transfection of tumor-derived DNA in NIH 3T3 mouse fibroblasts. Transfection of genomic DNA isolated from individual tumors from eight animals resulted in specific transforming activities ranging from 0.05 to 0.2 foci per micrograms of DNA. Primary transfectant DNAs were analyzed by Southern blot hybridization with DNA probes homologous to c-Ha-ras, c-Ki-ras, and N-ras oncogenes. A highly amplified c-Ki-ras oncogene of rat origin was detected in transformants derived from tumors in two of the eight animals tested. There was no evidence to suggest the presence of c-Ha-ras or N-ras sequences in any of the transformants. Analysis of primary liver tumor DNA showed no Ki-ras DNA amplification when compared to control liver DNA samples. Increased levels of c-Ki-ras p21 proteins were detected in 3T3 transformants containing activated rat c-Ki-ras genes. The presence of c-Ki-ras sequences of rat origin capable of inducing transformed foci can be taken as evidence that the c-Ki-ras gene has been activated in the primary liver tumors.

Differential expression of cellular oncogenes in benign and malignant human breast tissue

We have examined 62 specimens of benign fibrocystic breast tissue, fibroadenomas, carcinomas and surrounding non-malignant tissue excised from 50 patients to determine the level of expression of 4 cellular oncogenes, c-myc, c-H-ras, c-K-ras, and c-N-ras. Our results demonstrate that in breast carcinoma the frequency and relative level of expression of these oncogenes are significantly greater than those found for benign breast tissue. However, some fibrocystic specimens having prominent hyperplastic features also exhibited enhanced oncogene expression. In view of the association between the increased frequency of carcinoma of the breast in women with a previous history of benign breast disease, it will be interesting to follow up donors of benign specimens to see if there is any relationship between the expression of oncogenes in such lesions and the development of carcinomas.

Specific activation of the cellular Harvey-ras oncogene in dimethylbenzanthracene-induced mouse mammary tumors

Genomic DNAs from dimethylbenzanthracene-induced BALB/c mouse mammary tumors arising from the transplantable hyperplastic outgrowth (HPO) line designated DI/UCD transformed NIH 3T3 cells upon transfection. Transforming activity was attributed to the presence of activated Harvey ras-1 oncogenes containing an A----T transversion at the middle adenosine nucleotide in codon 61. DNAs from untreated DI/UCD HPO cells and radiation-induced and spontaneous mammary tumors from the DI/UCD HPO line failed to transform NIH 3T3 cells. The results indicated that the mutation activation of Harvey ras-1 oncogenes was specific to dimethylbenzanthracene treatment in the mouse mammary tumor system.

Barium modulates c-fos expression and post-translational modification

The addition of exogenous barium ions to PC12 rat pheochromocytoma cells elicits a transient induction of the c-fos gene. Induction is antagonized by extracellular calcium and the dihydropyridine calcium channel blockers, and it is attenuated in the presence of calmodulin inhibitors. Thus, barium appears to enter the cell through a voltage-dependent calcium channel and, either directly or indirectly, interacts with calmodulin to stimulate c-fos expression. This property of barium is not shared by a range of di- and trivalent cations examined. Agents that induce the c-fos gene in PC12 cells may be divided into two broad categories. The first comprises polypeptide growth factors and phorbol esters, which give rise to a c-fos protein that undergoes extensive post-translational modification. The second, which comprises depolarizing agents and barium ions, acts via calcium channels and yields a c-fos protein that undergoes less extensive post-translational modification. These different forms of c-fos protein can be distinguished on the basis of their apparent molecular weights on sodium dodecyl sulfate/polyacrylamide gels.

Pseudotyped retroviral vectors reveal restrictions to reticuloendotheliosis virus replication in rat cells

Reticuloendotheliosis viruses (Rev) replicate in chicken and dog cells, but not in rat cells. Amphotropic murine leukemia viruses (Am-MLV) replicate in chicken, dog, and rat cells. Transcription from the Rev long terminal repeat, determined by the chloramphenicol acetyltransferase assay, was not significantly different from transcription from the MLV long terminal repeat in rat cells. To determine further the step(s) in the retroviral life cycle that is blocked for Rev replication in rat cells, we took advantage of the wide host range of Am-MLV (S. Rasheed, M. B. Gardner, and E. Chan, J. Virol. 19:13-18, 1976) and the ability to form Rev-Am-MLV pseudotypes. Data from these pseudotypes indicate that the block to Rev replication in rat cells is posttranscriptional.

Dissociated expression of c-myc and a fos-related competence gene during cardiac myogenesis

Cardiac myocytes irreversibly lose their proliferative capacity soon after birth, and cardiac DNA synthesis becomes uncoupled from mitotic division. Therefore, we examined cardiac muscle for developmental down regulation of inducible proto-oncogenes associated with cell proliferation. c-myc mRNA decreased continuously from day 13 of embryonic development and was dissociated from expression of the fos-related gene r-fos, which decreased precipitously between days 3 and 7 after birth.

An activated Harvey ras oncogene produces benign tumours on mouse epidermal tissue

Studies of the mutagenic action required for specific chemicals to produce benign or malignant tumours suggest that in mouse skin at least two genetic events occur before carcinoma formation. The isolation of an activated form of the c-rasH gene from skin papillomas has provided evidence that this gene may be a target for the first mutation, which could constitute the initiating mutation in skin carcinogenesis. In vitro studies indicate that the v-rasH gene of Harvey murine sarcoma virus (Ha-MSV), a replication-defective transforming retrovirus, could impart a conditional initiated phenotype on cultured keratinocytes by blocking their ability to differentiate terminally and arresting them in a late basal cell stage of maturation. We now show that when the Ha-MSV v-rasH gene is introduced into cultured keratinocytes by a defective retroviral vector, skin grafts constructed with cells carrying the mutated ras oncogene produce papillomas on athymic nude mouse recipients. Furthermore, the expression of the exogenous oncogene seems to be regulated at the transcriptional level in the differentiated portions of the benign tumour.

Expression of c-mos proto-oncogene in undifferentiated teratocarcinoma cells

Proto-oncogene c-mos, the cellular homologue of the transforming gene of Moloney murine sarcoma virus, has been characterized by the lack of expression in a variety of differentiated tissues, possibly because of the existence of an inhibitory upstream sequence. We detected mos-related transcripts in undifferentiated embryonal carcinoma cells of pluripotential cell line 311. The sizes of three major transcripts detected were estimated to be 1.8, 4.6 and 6.1-kilobases (kb) by northern analysis. Furthermore, these transcriptions were suppressed when the cell differentiation was induced by retinoic acid. Taken together, the results suggest that mos product plays a role in early stages of development.

In vitro expression of human p53 cDNA clones and characterization of the cloned human p53 gene

The human p53 gene was cloned and characterized by using a battery of p53 DNA clones. A series of human cDNA clones of various sizes and relative localizations to the mRNA molecule were isolated by using the human p53-H14 (2.35-kilobase) cDNA probe which we previously cloned. One such isolate, clone p53-H7 (2.65 kilobases), spans the entire human mature p53 mRNA molecule. Construction of the human cDNA clones in the pSP65 RNA transcription vector facilitated the generation of p53 transcripts by the SP6 bacteriophage RNA polymerase. The p53-specific RNA transcripts obtained without further processing were translated into p53 proteins in a cell-free system. By using this rapid in vitro transcription-translation assay, we found that whereas clone p53-H7 (2.65 kilobases) coded for a mature-sized p53 protein, a shorter cDNA clone, p53-H13 (1.8 kilobases), dictated the synthesis of a smaller-sized p53 protein (45 kilodaltons). The p53 proteins synthesized in vitro immunoprecipitated efficiently with human-specific anti-p53 antibodies. Genomic analysis of human DNA revealed the presence of a single p53 gene residing within two EcoRI fragments. Heteroduplex analysis between the full-length cDNA clone p53-H7 and the cloned p53 gene indicated the presence of seven major exons.

Augmented expression of normal c-myc is sufficient for cotransformation of rat embryo cells with a mutant ras gene

We studied the effect of altered c-myc structure and expression upon the ability of c-myc to promote the transformation of normal rat embryo cells when it was supplemented by EJras (the mutant c-H-ras1 gene from EJ/T24 bladder carcinoma cells). We tested several c-myc alleles cloned from normal and tumor tissues of chicken and human origin and found that only LL4myc (derived from a bursal lymphoma in which an avian leukosis virus long terminal repeat resides within the first c-myc intron in the same transcriptional orientation) had cotransforming activity. No activity was observed with normal chicken and human c-myc alleles, two other bursal lymphoma c-myc alleles (LL3myc and LL6myc), and two human c-myc genes (HSRmyc and DMmyc) from human neuroectodermal tumor cell line COLO320, in which c-myc is amplified. Some of these inactive alleles had the following alterations that are frequently found in tumor-derived c-myc: point mutations affecting the encoded protein (LL3myc); a truncated structure with loss of the first, noncoding exon (LL3myc and DMmyc); and proviral integration within or near the myc locus (LL3myc and LL6myc). The following two experimental approaches indicated that cotransforming activity was directly related to the transcriptional activity of the alleles in cultured rat cells: when cotransfected into Rat-2 cells, LL4myc was more highly expressed than the other (inactive) alleles; and augmented expression of HSRmyc, DMmyc, or normal human or normal chicken c-myc placed under the transcriptional control of retroviral long terminal repeats or increased expression of normal human c-myc under the influence of a retroviral enhancer element was accompanied by cotransformation activity. We concluded that augmented expression of even a normal c-myc gene is sufficient for cotransforming activity and that additional structural alterations frequently found in tumor-derived alleles are neither necessary nor sufficient for the gene to acquire rat embryo cell cotransforming properties.

Synergism of v-myc and v-Ha-ras in the in vitro neoplastic progression of murine lymphoid cells

Murine bone marrow was either singly or doubly infected with retroviral vectors expressing v-myc (OK10) or v-Ha-ras. The infected bone marrow was cultured in a system that supports the long-term growth of B-lineage lymphoid cells. While the v-myc vector by itself had no apparent effect on lymphoid culture establishment and growth, infection with the v-Ha-ras vector or coinfection with both v-myc and v-Ha-ras vectors led to the appearance of growth-stimulated cell populations. Clonal pre-B-cell lines stably expressing v-Ha-ras alone or both v-myc and v-Ha-ras grew out of these cultures. In comparison with cell lines expressing v-Ha-ras alone, cell lines expressing both v-myc and v-Ha-ras grew to higher densities, had reduced dependence on a feeder layer for growth, and had a marked increase in ability to grow in soft-agar medium. The cell lines expressing both oncogenes were highly tumorigenic in syngeneic animals. These experiments show that the v-myc oncogene in synergy with v-Ha-ras can play a direct role in the in vitro transformation of murine B lymphoid cells.

v-ras genes from Harvey and BALB murine sarcoma viruses can act as initiators of two-stage mouse skin carcinogenesis

Activated Harvey murine sarcoma virus ras genes were introduced into epidermal cells in vivo by direct application of retroviruses to mouse skin. Subsequent treatment with the tumor promoter 12-O-tetradecanoyl-phorbol-13-acetate (TPA) induced benign papillomas, some of which progressed to invasive carcinomas. Initiation with virus was irreversible for at least 4 months, since TPA treatment after this latency period produced papillomas within 4 weeks. Analysis of viral integration sites showed that carcinomas are clonal in origin. Both papillomas and carcinomas express virus-specific ras mRNA and the viral form of ras P21 protein. The results show that activated ras genes can replace chemical carcinogens in initiation of mouse skin carcinogenesis. This system presents a novel approach to in vivo analysis of the biological role of oncogenes in epithelial tumorigenesis.

Decreased c-myc expression is an early event in retinoic acid-induced differentiation of F9 teratocarcinoma cells

Retinoic acid-induced differentiation of mouse F9 teratocarcinoma cells is known to be accompanied by changes in gene expression. We examined the expression of the c-myc gene during retinoic acid-induced differentiation of F9 cells. Retinoic acid caused a 50% reduction in the level of c-myc mRNA after 3 hr of treatment and a 90% reduction after 12 hr. We have also examined several features of c-myc genomic structure in F9 cells, PYS2 (differentiated parietal yolk sac) cells, and liver--namely, methylation, amplification, and gross organization. Comparison of Hpa II and Msp I digests of DNAs from F9, PYS2, and liver showed that the c-myc gene in F9 cells is hypomethylated relative to that in PYS2 cells and in liver. The Hpa II sites that undergo methylation during differentiation were found to be in the second intron. Gross structural changes of the c-myc gene have not occurred in F9 or PYS2, and the c-myc gene is not amplified.

Expression of the c-Ha-ras and c-myc genes in aflatoxin B1-induced hepatocellular carcinomas

Expression and activation of several c-oncogenes in seven hepatocellular carcinomas from seven separate rats treated with aflatoxin B1 (AFB1) were examined by Northern and Southern blot analyses. Both c-Ha-ras and c-myc transcripts were elevated at high levels in all hepatomas. Moreover, in one of them, T2-1 hepatoma, the c-myc gene was amplified only in a tumor part of liver without significant rearrangement. N-ras specific transcripts were not elevated in these hepatomas. The present data suggest that the consistently increased expression or deregulation of the c-myc and c-Ha-ras genes may play an important role in the development of hepatomas induced by AFB1.

Carcinogen-specific mutation and amplification of Ha-ras during mouse skin carcinogenesis

Cellular proto-oncogenes can be activated by both point mutations and chromosomal translocations, suggesting that there may be a direct link between exposure to agents which damage DNA and genetic change leading to malignancy. Several groups have therefore analysed mutations found in cellular oncogenes of tumours induced by particular physical or chemical carcinogens. Here, we have analysed the molecular changes at different stages of carcinogenesis in mouse skin tumours induced by initiating and promoting agents. Over 90% of tumours, including premalignant papillomas, initiated with dimethylbenzanthracene (DMBA) have a specific A----T transversion at the second nucleotide of codon 61 of the Harvey-ras (Ha-ras) gene. The frequency of this mutation was dependent on the initiating agent used, but not on the promoter, suggesting that the mutation occurs at the time of initiation. The mutation was heterozygous in most papillomas tested, but was homozygous or amplified in some carcinomas. The development of further chromosomal changes at the c-Ha-ras gene locus is therefore a common feature of tumour progression.

Efficient constitutive production of human IFN-gamma in Chinese hamster ovary cells

A human genomic DNA segment of 5.6 kb containing the entire gene for immune interferon-gamma was fused through its 5'-untranslated region to the corresponding region of the simian virus 40 (SV40) T-antigen gene. The SV40 early promoter used contained a modified transcriptional enhancer element with a 93-bp repeat. Supercoiled plasmid DNA was used to transfect Chinese hamster ovary (CHO) cells, the selectable marker being a SV40-dihydrofolate gene construct. Constitutive expression of the IFN-gamma gene in primary transformants was high, especially if a Harvey murine sarcoma virus long terminal repeat (LTR) was present in addition to the SV40 promoter. After gene amplification by methotrexate selection, CHO-gamma cell lines were obtained that produce 1.5-2 million units of IFN-gamma per million cells and per day (200,000 molecules per cell per minute). Metabolic labeling showed that over 90% of the protein secreted by such cells is human IFN-gamma. A one-step immuno-affinity chromatography on monoclonal antibodies yielded pure IFN-gamma with 1-2 X 10(8) units/mg protein. Like IFN-gamma from human white blood cells, the IFN-gamma from CHO-gamma cells is a mixture of two glycoproteins of 26,000 and 20,000 daltons with traces of the unglycosylated 17,000-dalton polypeptide. Large-scale cultures in 1% serum routinely yield over 600,000 units of human IFN-gamma/ml culture per day.

Expression of the human fes cellular oncogene in renal cell tumors

Renal cell tumors were screened for expression of the cellular oncogenes c-abl, c-fes, c-fms, c-myc, c-ras, and c-sis in dot blot hybridization analysis. Expression of c-ras and c-myc was clearly detectable in most of the 15 tumors that were studied. The c-fes oncogene appeared to be expressed in only two of them. Comparative Southern blot analysis of molecularly cloned human c-fes DNA and genomic DNA of the 15 renal tumors revealed no major genetic differences. Northern blot analysis of poly(A)-selected RNA from the fes-positive tumors with the complete viral v-fes oncogene of the Gardner-Arnstein strain of feline sarcoma virus as a molecular probe revealed hybridization of RNA species of 3.0 and 4.5 kb, respectively. The 3.0 kb c-fes transcript has also been reported in RNA from patients suffering from acute myelogenous leukemia. The 4.5 kb transcript, however, has not been described before and represents either a c-fes-related splicing intermediate or, more likely, a completely processed transcript. The results of this study could imply that human c-fes coding sequences are more extensive than was previously assumed.

Expression of p21 proteins in Escherichia coli and stereochemistry of the nucleotide-binding site

v-Ha-ras encoded p21 protein (p21V), the cellular c-Ha-ras encoded protein (p21C) and its T24 mutant form p21T were produced in Escherichia coli under the control of the tac promoter. Large amounts of the authentic proteins in a soluble form can be extracted and purified without the use of denaturants or detergents. All three proteins are highly active in GDP binding, GTPase and, for p21V, autokinase activity. Inhibition of [3H]GDP binding to p21C by regio- and stereospecific phosphorothioate analogs of GDP and GTP was investigated to obtain a measure of the relative affinities of the three diphosphate and five triphosphate analogs of guanosine. p21 has a preference for the Sp isomers of GDP alpha S and GTP alpha S. It has low specificity for the Sp isomer of GTP beta S. Together with the data for GDP beta S and GTP gamma S these results are compared with those obtained for elongation factor (EF)Tu and transducin. This has enabled us to probe the structural relatedness of these proteins. We conclude that p21 seems to be more closely related to EF-Tu than to transducin.

Establishment of two rabbit mammary epithelial cell lines with distinct oncogenic potential and differentiated phenotype after microinjection of transforming genes

The goal of this work was to establish an assay for transformation of epithelial cells. Two epithelial cell lines were obtained after microinjecting transforming genes into primary rabbit mammary secretory cells. The cell lines were analyzed for their oncogenic potential and for the maintenance of a differentiated phenotype. A fully transformed cell line, which retained epithelial cell organization, was obtained by coinjecting simian virus 40 DNA and the activated human c-Ha-ras gene. The proliferation rate of these cells was high, with a doubling time of 16 h. Their growth was anchorage independent, and they had lost contact inhibition. The cells were tumorigenic in nude mice, but had no metastatic potential. Both microinjected DNAs were efficiently transcribed and translated, in contrast to the casein genes, which were expressed in primary cells but not in the transformed cell line. An immortalized cell line established after injection with simian virus 40 DNA alone was characterized by a moderate rate of proliferation with a doubling time of approximately 30 h. The growth of these cells was contact inhibited and anchorage dependent. The cells were not tumorigenic in nude mice. The viral DNA was expressed during early passages, as shown by the presence of the large T antigen in cell nuclei, but not at later passages. A high number of lactogenic hormone receptors were found associated with the cell surface. Despite the presence of these receptors, no induction of genes coding for milk proteins was observed after addition of prolactin. These data demonstrate that this assay system can be used to assess the immortalizing and transforming potential of candidate oncogenes in epithelial cells.

Harvey ras genes transform without mutant codons, apparently activated by truncation of a 5' exon (exon -1)

The hypothesis is tested that the ras gene of Harvey sarcoma virus (Ha-SV) and the proto-ras DNAs from certain tumor cells derive transforming function from specific codons in which they differ from normal proto-ras genes. Molecularly cloned Harvey proviral vectors carrying viral ras, normal rat proto-ras, and recombinant ras genes in which the virus-specific ras codons 12 and 59 were replaced by proto-ras equivalents each transformed aneuploid mouse 3T3 cells after latent periods that ranged from 4 to 10 days. Viruses with or without virus-specific ras codons all transformed diploid rat cells in 3-5 days equally well. However, in the absence of virus replication, mutant codons were beneficial for transforming function. Deletion of non-ras regions of Ha-SV did not affect transforming function. We conclude that specific ras codons are not necessary for transforming function. Comparisons of the ras sequences of Ha-SV, BALB SV, and Rasheed SV with sequences of proto-ras genes from rat and man revealed an upstream proto-ras exon, termed exon -1. The 3' end of this exon is present in all three viruses and in a ras pseudogene of the rat. Since ras genes transform without mutation and since exon -1 is truncated in viral ras genes and all transforming proto-ras DNAs of the Harvey and the Kirsten ras family, we propose that ras genes are activated by truncation of exon -1 either via viral transduction or artificially via cloning and transfection. The proposal implies that untruncated proto-ras genes with point mutations may not be cellular cancer genes.

Diverse long terminal repeats are associated with murine retroviruslike (VL30) elements

The VL30 family is a retroviruslike gene family with no apparent nucleic acid homology to any known retrovirus. Over 100 copies of VL30 DNA elements are dispersed throughout the mouse genome. Sequence analysis of the VL30 long terminal repeat (LTR) units showed that, whereas the LTR units of a given VL30 DNA element were almost identical, the LTR units associated with distinct members of the family were very different from one another. Comparison of the LTR sequences possessed by two particular VL30 DNA elements revealed a pattern of extensively homologous DNA segments adjacent to only distantly related DNA sequences. With the aid of sub-LTR probes, it was shown that a certain LTR is composed of both U5 sequences that are abundantly present in all species of the genus Mus and a U3 region detected only in Mus musculus. In addition, we isolated a VL30 DNA element in which the LTR units were replaced by the LTR units of an apparently novel retroviruslike family. These findings suggest that recombinations have played a role in generating the diverse population of VL30-associated LTRs.

Multistep process of neoplastic transformation of normal human fibroblasts by 60Co gamma rays and Harvey sarcoma viruses

As reported previously (Namba et al., 1985), normal human fibroblasts were transformed by 60Co gamma-ray irradiation into immortal cells with abnormal karyotypes. These transformed cells (KMST-6), however, showed a low cloning efficiency in soft agar and no transplantability. However, upon treatment with Harvey murine sarcoma virus (Ha-MSV), the cells acquired elevated clonability in soft agar and transplantability in nude mice. Ha-MSV alone, however, did not convert normal human fibroblasts into either immortal or tumorigenic cells. The Ha-MSV-transformed KMST-6 cells showed an enhanced expression of the ras oncogene, but normal and 60Co gamma-ray-transformed cells did not. Our current data suggest that gamma rays worked against normal human cells as an initiator, giving rise to chromosome aberrations and immortality, and that Ha-MSV, probably through its ras oncogene, played a role in the progression of the malignant cell population to a more malignant one showing enhanced colony formation in soft agar and tumorigenicity in nude mice.

Adenylate cyclase activity of NIH 3T3 cells morphologically transformed by ras genes

The observed homology between G-proteins which regulate adenylate cyclase and ras proteins and the suggested role of ras in the regulation of adenylate cyclase in yeast prompted us to examine the regulation of adenylate cyclase in three cell lines: (i) NIH 3T3 cells, (ii) NIH 3T3 cells transformed by high levels of the normal rasH gene product and (iii) NIH 3T3 cells transformed by a mutated rasH gene product. We found that the regulation of adenylate cyclase by G-proteins is identical in the three cell lines, although the response of the transformed NIH 3T3 cells to agonists is strongly attenuated. Our data suggest that mammalian ras products do not interact directly with adenylate cyclase, although their increased expression may indirectly inhibit the interaction of adenylate cyclase stimulatory receptors with G-proteins.

Unique sequence, ski, in Sloan-Kettering avian retroviruses with properties of a new cell-derived oncogene

The Sloan-Kettering viruses (SKVs) are a group of transforming retroviruses that were isolated from chicken embryo cells which had been infected with the avian leukosis virus transformation-defective Bratislava 77 (tdB77). Each of the SKV isolates was shown to contain multiple genomes of different sizes indicating the presence of several viruses in addition to tdB77. To identify and characterize the putative transforming gene(s) of the SKVs, we used hybridization selection to isolate the fraction of a representative cDNA which was SKV specific. Both solution and blot hybridization studies with viral RNAs showed that the specific probe contained a sequence, ski, that was at least partially held in common by the multiple SKV genomes. This conclusion was confirmed by the observation that a molecularly cloned ski probe also hybridized to each of the multiple SKV genomes. Southern blots of chicken DNA revealed homologs of ski (c-ski) which were not associated with endogenous viral loci. Results showing that c-ski was expressed in polyadenylated cytoplasmic RNA of uninfected chicken cells indicated that it is a functional gene. Other data showed that c-ski was conserved in avian and mammalian evolution, suggesting a functional role for the gene in species other than chickens. Using ski cDNA in solution hybridizations with viral RNAs and in Southern blot hybridization with cloned retroviral oncogenes, we did not detect any relationship between ski and any of 15 previously identified oncogenes.

Kinetics of cellular oncogene expression in mouse lymphocytes. I. Expression of c-myc and c-ras-Ha in T lymphocytes induced by various mitogens

Murine splenic T lymphocytes display maximal cellular myc gene (c-myc) expression already 3 h after concanavalin A stimulation and subsequent down-regulation before the onset of DNA synthesis. Stimulation by leucoagglutinin in the presence or absence of interleukin 2 leads to only low initial levels of c-myc-specific RNA which, however, increase later on. A similar pattern of c-myc expression is shown by the Lyt-2+ T cell subpopulation stimulated with either concanavalin A or leucoagglutinin in the presence of interleukin 2. Although [3H]thymidine incorporation was identical, the leucoagglutinin-stimulated Lyt-2+ T cells were void of any demonstrable c-myc-specific RNA at 3 h post-stimulation. Thus, the kinetics of c-myc expression in mouse T lymphocytes are not at all uniform, but depend on the mitogen and the subpopulation. In contrast, levels of c-ras-Ha-specific RNA were always low at early times, always increased towards the onset of DNA synthesis and down-regulation was not observed.

c-rasH and ornithine decarboxylase are induced by oestradiol-17 beta in the mouse uterine luminal epithelium independently of the proliferative status of the cell

Oestradiol-17 beta (E2) treatment of the ovariectomized mouse results in a synchronised wave of cell proliferation in the uterine luminal epithelium. At the peak of DNA synthesis the mRNA level of the c-rasH proto-oncogene and ornithine decarboxylase were significantly increased. Progesterone treatment completely inhibits the E2 induced wave of DNA synthesis but does not greatly influence the level of these 2 mRNAs. Thus in the uterine luminal epithelium E2 regulates the level of ornithine decarboxylase and c-rasH independently of cell proliferation.

The relation of ras family oncogene expression to conventional staging criteria and clinical outcome in colorectal carcinoma

The elevated levels of ras-related cellular RNA in a series of colorectal carcinomata (n = 12) was correlated with conventional staging criteria (tumour morphology and Dukes' staging) and with clinical outcome with particular reference to the development of metastatic disease. No direct relationship was evident between these parameters suggesting that although abnormal expression of ras oncogenes may be critical in the development of malignancy, variations in the level of their expression do not appear to be directly related to clinically evident phenotypic differences.

Cyclic AMP suppresses expression of v-rasH oncogene linked to the mouse mammary tumor virus promoter

Clone 433.3 of NIH 3T3 cells is a stable carrier of the MMTV LTR:v-rasH chimeric DNA. Only in the presence of dexamethasone (a synthetic glucocorticoid), 433.3 cells exhibit an induced level of p21 transforming protein and phenotypic transformation. N6,O2'-dibutyryl cAMP (DBcAMP) antagonized the effect of dexamethasone in a time - and concentration - dependent manner. DBcAMP (5 X 10(-4)M) added 18 hr prior to the addition of dexamethasone (10(-7)M) almost completely blocked the hormone effect: cells contained levels of p21 20% of that in the cells treated with dexamethasone alone, and formed flat, contact inhibited monolayers. On the basis of these results together with our previous data on mammary carcinomas in vivo, we postulate that cAMP may be an intracellular suppressor acting at a regulatory locus of both cellular and viral ras genes.

The pathophysiology of murine retrovirus-induced leukemias

Murine leukemia viruses (MuLVs) are retroviruses which induce a broad spectrum of hematopoietic malignancies. In contrast to the acutely transforming retroviruses, MuLVs do not contain transduced cellular genes, or oncogenes. Nonetheless, MuLVs can cause leukemias quickly (4 to 6 weeks) and efficiently (up to 100% incidence) in susceptible strains of mice. The molecular basis of MuLV-induced leukemia is not clear. However, the contribution of individual viral genes to leukemogenesis can be assayed by creating novel viruses in vitro using recombinant DNA techniques. These genetically engineered viruses are tested in vivo for their ability to cause leukemia. Leukemogenic MuLVs possess genetic sequences which are not found in nonleukemogenic viruses. These sequences control the histologic type, incidence, and latency of disease induced by individual MuL Vs.

Augmented expression of normal c-myc is sufficient for cotransformation of rat embryo cells with a mutant ras gene

We studied the effect of altered c-myc structure and expression upon the ability of c-myc to promote the transformation of normal rat embryo cells when it was supplemented by EJras (the mutant c-H-ras1 gene from EJ/T24 bladder carcinoma cells). We tested several c-myc alleles cloned from normal and tumor tissues of chicken and human origin and found that only LL4myc (derived from a bursal lymphoma in which an avian leukosis virus long terminal repeat resides within the first c-myc intron in the same transcriptional orientation) had cotransforming activity. No activity was observed with normal chicken and human c-myc alleles, two other bursal lymphoma c-myc alleles (LL3myc and LL6myc), and two human c-myc genes (HSRmyc and DMmyc) from human neuroectodermal tumor cell line COLO320, in which c-myc is amplified. Some of these inactive alleles had the following alterations that are frequently found in tumor-derived c-myc: point mutations affecting the encoded protein (LL3myc); a truncated structure with loss of the first, noncoding exon (LL3myc and DMmyc); and proviral integration within or near the myc locus (LL3myc and LL6myc). The following two experimental approaches indicated that cotransforming activity was directly related to the transcriptional activity of the alleles in cultured rat cells: when cotransfected into Rat-2 cells, LL4myc was more highly expressed than the other (inactive) alleles; and augmented expression of HSRmyc, DMmyc, or normal human or normal chicken c-myc placed under the transcriptional control of retroviral long terminal repeats or increased expression of normal human c-myc under the influence of a retroviral enhancer element was accompanied by cotransformation activity. We concluded that augmented expression of even a normal c-myc gene is sufficient for cotransforming activity and that additional structural alterations frequently found in tumor-derived alleles are neither necessary nor sufficient for the gene to acquire rat embryo cell cotransforming properties.

Absence of gross change in primary DNA sequence during aging process of mice

The possibility of age-associated changes in DNA sequence in terms of amplification and rearrangement was examined in mouse spleen, liver and brain using the method of Southern transfer and filter hybridization. The DNA regions studied were at and around nine cloned sequences, most of which are known to move or amplify in certain situations. No detectable age-associated change, however, was observed in all DNA regions studied. These results suggest that widespread DNA sequence rearrangements or amplifications do not occur during the ageing process in mice.

Activation of K-ras and oncogenes other than ras family in rat fibrosarcomas induced by 1,8-dinitropyrene

Oncogenes of fibrosarcomas of rats, induced by subcutaneous injection of 1,8-dinitropyrene (1,8-DNP), were examined by NIH 3T3 cell transfection assay and Southern blot analysis. Transformants containing rat specific repetitive sequences were obtained with DNAs of 4 fibrosarcomas, 1,8-DNP1, 1,8-DNP2, 1,8-DNP3 and 1,8-DNP7. A transformant, 1,8-DNP2-2, induced by DNA of a fibrosarcoma, 1,8-DNP2, and 7 secondary transformants derived from it contained rat K-ras sequences. Another transformant, 1,8-DNP2-1, induced by the same sarcoma did not have a ras family oncogene. This indicates that the sarcoma, 1,8-DNP2, has at least 2 transforming genes. The transforming genes of 6 other transformants derived from 3 sarcomas did not contain ras family or neu transforming genes.

Expression of proto-oncogenes in normal and papovavirus-transformed or -infected rat fibroblasts

Dot blot hybridization was used to determine the transcript levels of 10 cellular oncogenes in Fischer rat fibroblasts transformed or infected in tissue culture by polyoma virus or SV40. The level of these messages was compared to that determined for nontransformed, noninfected control cells. The analysis includes the oncogenes myc, sis, mos, erbB, erbA, Ha-ras, Ki-ras, src, fps, and abl. For all the oncogenes tested, except for mos, detectable expression was observed in all cell lines studied including the normal control cells; when normal and transformed or infected cells were compared, no significant difference in transcript level was found for any of the oncogenes except one. A slight elevation of sis message was observed for some transformants. The results of this study apply to six polyoma and seven SV40 transformants which were chosen with the purpose of analyzing transformants displaying a variety of properties. Thus, the polyoma-transformed cell lines varied in their expression of the transformed phenotype as judged by anchorage-independent growth and cell morphology, in their coding capacity for and expression of early gene products, and included two classes of rat fibroblasts transformed by ts-a mutants: those with a temperature-insensitive transformed phenotype, and those with a temperature-sensitive phenotype, A-type and N-type, respectively. Concerning the latter two types, no differences in oncogene expression were observed between cells grown at low and those grown at high temperatures, or between the two groups of cells at either temperature.

Activated c-raf gene in a rat hepatocellular carcinoma induced by 2-amino-3-methylimidazo[4,5-f]quinoline

A rat hepatocellular carcinoma, IQ7, induced by 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) gave two transformants of NIH 3T3 cells on DNA mediated gene transfer. One of these transformants was examined further and secondary and tertiary transformants were obtained. The secondary transformant was tumorigenic in nude mice. The activated oncogene in this primary transformant was identified as rat c-raf by Southern blot analysis.

Harvey ras induction of metastatic potential depends upon oncogene activation and the type of recipient cell

NIH-3T3 cells and early passage fibroblasts transformed by various members of the rasH gene family were found to express metastatic potential in nude (Nu/Nu) mice. NIH-3T3 cells transformed by either the cloned DNA of the Harvey sarcoma virus or by the T24 human rasH oncogene were both tumorigenic after subcutaneous injection and metastatic after intravenous injection. In contrast, NIH-3T3 cells transformed by elevated levels of the proto-oncogene were tumorigenic but not metastatic. Tumor growth potential by itself, therefore, was not sufficient to induce metastatic behavior. Diploid fibroblasts transformed with the T24 rasH oncogene were tumorigenic and metastatic after intravenous injection and also produced extensive spontaneous metastases. Thus, induction of the complete metastatic phenotype by the T24 rasH oncogene does not require the use of aneuploid recipient cells such as NIH-3T3 cells. An alternative murine recipient cell type C127, when transformed by the cloned DNA of the Harvey sarcoma virus, was tumorigenic but not metastatic. The transformed C127 cells made less of the viral gene product P21 than the NIH-3T3 rasH transformants. To ensure that the decreased levels of P21 were not responsible for the lack of metastatic potential, C127 cells were transformed with altered constructs of the plasmid containing the Harvey sarcoma virus which elicited enhanced levels of P21. The augmented P21 levels, although equivalent to or greater than that seen in the NIH-3T3 transformants, did not confer metastatic potential on the C127 transformants. These results indicate that at least two complementation groups may be required for induction of metastatic capacity in this system, one involving the "activated" oncogenic form of the rasH gene and the second another as yet undefined factor in the cellular background present in NIH-3T3 cells but absent in C127 cells.

Unstable expression and amplification of a transfected oncogene in confluent and subconfluent cells

NIH 3T3 cells were transfected with a plasmid containing the transforming gene, v-src, from Rous sarcoma virus. One of the transformed cell lines isolated reverted to a flat, nontransformed morphology after cloning through soft agar. This cell line did not express the src gene and could no longer grow in soft agar. When these cells were held at confluence, spontaneous foci appeared which eventually covered the dish. The appearance of foci correlated with an increase in v-src gene expression, ability to grow in soft agar, and tumorigenicity in mice. When these transformed cells were trypsinized and held at subconfluence, both v-src expression and the transformed phenotype were progressively lost. Whereas rearrangement of the transfected gene was not detected, the gene copy number in the transformed cells was markedly increased (greater than 50-fold). Confluence-dependent gene amplification and deamplification have been retained after several cycles of growth alternately at high and low density, in cells recloned through soft agar, and after cells had been maintained continuously at high or low density. The results suggest that, in this cell line, reversible gene amplification plays a central role in expression of the transfected gene.

Superinduction of c-fos by nerve growth factor in the presence of peripherally active benzodiazepines

Alterations in proto-oncogene expression after stimulation of rat pheochromocytoma (PC12) cells by nerve growth factor (NGF) have been investigated. A specific stimulation of c-fos messenger RNA and protein was detected 30 minutes after treatment. This induction was enhanced more than 100-fold in the presence of peripherally active benzodiazepines. The effect was specific as very little change was observed in the levels of c-rasHa, c-rasKi, c-myc, and N-myc messenger RNA's. Under the conditions used here, NGF treatment ultimately results in neurite outgrowth, with a reduction or cessation of cell division. Thus, stimulation of the c-fos gene in this system appeared to be associated with differentiation and not with cellular proliferation. The effect of benzodiazepines was stereospecific and represents a novel action of these compounds at the level of gene expression.

Detection of a raf-related and two other transforming DNA sequences in human tumors maintained in nude mice

High molecular weight DNAs prepared from a variety of human tumors maintained in nude mice were assayed for their ability to transform NIH 3T3 cells. DNAs from 4 of 21 tumors tested induced transformed foci in cultures of NIH 3T3 cells. They were from a Ewing sarcoma line, a glioblastoma line, a leiomyosarcoma line, and a lung carcinoma line. Hybridization analyses of the NIH 3T3 transformant DNAs with a human repetitive sequence as probe revealed that four distinct transforming DNA sequences were transferred to NIH 3T3 cells from the four tumor lines. The transforming DNA in a lung carcinoma line was a human homologue of the oncogene of Kirsten murine sarcoma virus (Ki-ras). On the other hand, the three other transforming DNAs showed no similarity to any known human transforming gene detected by the NIH 3T3 transformation assay. Further analyses with a series of cloned oncogenes as probes revealed that the transforming DNA in a glioblastoma line was a human homologue of the oncogene of 3611-murine sarcoma virus (raf). However, the two transforming DNAs in a Ewing sarcoma line and a leiomyosarcoma line had no sequence homology to any of the cloned oncogenes.