Three different human tumor cell lines contain different oncogenes

Molecular identification of a human DNA repair gene following DNA-mediated gene transfer

Although it has long been evident that the response of eukaryotes to DNA damaging agents is determined by the effectiveness of a variety of DNA repair systems, there is little detailed knowledge of the nature of these systems or the genes which control them. In humans, a number of hereditary conditions, including xeroderma pigmentosum, ataxia telangiectasia and Fanconi's anaemia, exhibit increased sensitivity to a variety of DNA damaging agents and a predisposition to cancer, suggesting a defect in some aspect of DNA repair. This report describes the identification of a human DNA repair gene following DNA-mediated gene transfer into Chinese hamster ovary (CHO) mutant cells, that like xeroderma pigmentosum cells, are sensitive to a variety of DNA damaging agents and are defective in the initial incision step of DNA repair. The resulting transformants exhibit normal resistance to DNA damaging agents and independent transformants demonstrate a common set of human DNA sequences associated with a human DNA repair gene. These observations provide the basis for the isolation and characterization of the human genes responsible for DNA repair.

Identification by transfection of transforming sequences in DNA of human T-cell leukemias

DNA from human T-cell leukemia cell lines was tested for focus-inducing activity on cultures of NIH 3T3 cells. Three leukemias yielded DNA active in this assay; restriction enzyme sensitivity of this activity indicated that similar, relatively large DNA sequences were involved. Southern blot analysis revealed conserved size classes of restriction fragments containing human repetitive (Alu) sequences in serially transfected foci derived from the active DNAs. Similar blot hybridizations with a probe specific for the human N-ras oncogene detected a 9-kilobase EcoRI fragment in all cases. DNA containing this fragment from one of the leukemias, molecularly cloned in bacteriophage lambda, displayed highly amplified focus-inducing activity in transfection assays. Thus, the N-ras oncogene appears to be active in these three human leukemias of T-cell origin.

The tumor phenotype and the human gene map

The tumor phenotype is associated with the rearrangement of genetic information and the altered expression of many gene products. In this review, genes associated with the tumor phenotype have been arranged on the human gene map and indicate the extent to which the tumor phenotype involves the human genome. Nonrandom chromosomal aberrations that are frequently observed in tumors are presented. Altered metabolic demands of the tumor cell are reflected in altered gene expressions of a wide range of enzymes and other proteins, and these changed enzyme patterns are described. The study of oncogenes increasingly suggests that they may be significant in certain cancers, and the assignment of these genes has been tabulated. The biochemical and metabolic changes observed in tumors are complex; studying the patterns and interactions of these changes will aid our genetic understanding of the origins and development of tumors.

Normal cells of patients with high cancer risk syndromes lack transforming activity in the NIH/3T3 transfection assay

Oncogenes capable of transforming NIH/3T3 cells are often present in human tumors and tumor cell lines. Such oncogenes were not detected in normal fibroblast lines derived from patients with several clinical syndromes associated with greatly increased cancer risk. Thus, germ-line transmission of these oncogenes does not appear to be the predisposing factor responsible for these high cancer risk syndromes.

Transfer of sensitivity to tumor promoters by transfection of DNA from sensitive into insensitive mouse JB6 epidermal cells

Sensitivity to promotion of transformation by tumor promoters in mouse epidermal JB6 cells appears to have a genetic basis since the phenotypes of both promotable and nonpromotable JB6 cells derived from a common parent line are stable. Hybridization of promotable (P(+)) and nonpromotable (P(-)) cells previously indicated that promotability appears to behave as a dominant trait. These results suggest that it should be possible to find DNA sequences which specify sensitivity to promotion of anchorage independence by 12-o-tetradecanoyl-phorbol-13-acetate (TPA). Cellular DNA isolated from one of two P(+) lines, JB6 Cl 41 or JB6 Cl 22, was CaPO(4) precipitated and used to transfect the P(-) cell line JB6 Cl 30. At 7 days posttransfection, the cells were suspended in agar with or without TPA at 1.6 x 10(-8) M and assayed 10 days later for TPA-dependent colony formation. Untreated or Cl 30 DNA-treated P(-) JB6 Cl 30 cells yielded 40 to 50 colonies per 10(5) cells. In contrast, transfection of Cl 30 cells with "P(+) DNA" derived from either Cl 41 or Cl 22 yielded 200 to 500 TPA-induced colonies per 10(5) cells, or a five- to eightfold enhancement of promotability. The enhanced promotability obtained after transfection with P(+) DNA was stable, as judged by the retention of promotability for at least eight passages in cell lines derived from TPA-induced agar colonies. Other transfectants showed irreversible transformation by TPA, as observed in the parental P(+) lines. When NIH 3T3 cells instead of the putative preneoplastic JB6 Cl 30 cells were used as recipients for transfection of P(+) DNA, no evidence for acquisition of promotability was obtained. P(-) JB6 Cl 25, like Cl 30, also permitted expression of transfected P(+) DNA. These results suggest that sensitivity to phorbol ester promotion of transformation in JB6 cells is determined by DNA sequence(s) present in the P(+) DNA and requires recipient cells of the appropriate phenotype for expression.

Pre-crisis mouse cells show strain-specific covariation in the amount of 54-kilodalton phosphoprotein and in susceptibility to transformation by simian virus 40

We have used several inbred mouse strains to examine the role of the 54-kilodalton (kDa) cellular phosphoprotein in transformation by the papovavirus simian virus 40. We have measured the endogenous 54-kDa phosphoprotein in cells obtained from these inbred mouse strains. To study the effect of passage, cell cultures were measured for amount of the 54-kDa phosphoprotein at the 2nd and 12th passages. In the absence of any transforming agent, the amount of endogenous 54-kDa phosphoprotein in early pre-crisis mouse cells varied in a strain-specific way. Transformation frequency varied coordinately with endogenous 54-kDa expression. Mouse strains whose cells produced a high level of endogenous 54-kDa phosphoprotein on passage did not further increase its expression after simian virus 40 transformation.

Oncogenes in retroviruses and cells

Oncogenes are genes that cause cancer. Retroviruses contain oncogenes and cause cancer in animals and, perhaps, in man. The viruses have appropriated their oncogenes from normal cellular DNA by genetic recombination. Correspondingly, uninfected vertebrate cells contain a family of evolutionary conserved cellular oncogenes. Retrovirus infection, introducing additional viral oncogenes into the cells, as well as carcinogen-mediated activation of cellular oncogenes may both lead to increased synthesis of oncogene encoded transforming proteins which convert normal cells to tumor cells. Unique retroviruses of human origin have recently been identified. They may, on occasion, directly cause tumors in man. However, the general significance of retroviruses may better be illustrated by their remarkable genetic composition which allows them to promote tumor growth by a variety of genetic mechanisms.

The emerging genetics of human cancer

A rapid and exciting accumulation of data about cellular oncogenes in human tumors has resulted from convergent research on DNA-mediated gene transfer, retroviruses, and tumor cytogenetics. Such work promises to increase our understanding of the genetic events that predispose to, and result in, malignant disease. This knowledge may quickly find clinical application in tumor classification and prediction of risk. Ultimately, therapeutic benefits may be achieved as we begin to explore the mechanisms by which transforming gene products act to defeat the normal regulatory processes of cells.

Tumorigenic conversion of primary embryo fibroblasts requires at least two cooperating oncogenes

Transfection of embryo fibroblasts by a human ras oncogene does not convert them into tumour cells unless the fibroblasts are established and immortalized before transfection. The embryo fibroblasts become tumorigenic if a second oncogene such as a viral or cellular myc gene or the gene for the polyoma large-T antigen is introduced together with the ras gene.

Structure and organization of the human Ki-ras proto-oncogene and a related processed pseudogene

Analysis of the organization and nucleotide sequence of two human loci related to the transforming gene of Kirsten murine sarcoma virus establishes one as a functional gene and the other as a processed pseudogene. The two final coding exons of the functional gene seem to have arisen by duplication. Differentially spliced mRNAs incorporating one or other of the duplicated exons probably served as the intermediates by which the viral transforming gene and the pseudogene were generated. This suggests that the functional gene may specify either of two related polypeptides depending on the pattern of RNA splicing.

The N-ras oncogene assigned to the short arm of human chromosome 1

The human N-ras oncogene, isolated from the HL-60 promyelocytic leukemia cell line, is distantly related to viral oncogenes of Kirsten and Harvey sarcoma viruses. We have determined its chromosomal location by Southern blot analysis of DNAs from 37 human x rodent hybrid cell lines derived from 8 different human donors, some of whom carried balanced rearrangements of chromosome 1. The results indicate that the N-ras oncogene (RASN) is localized on the proximal part of the short arm of human chromosome 1, in region p3200 leads to cen.

Activation of Ki-ras2 gene in human colon and lung carcinomas by two different point mutations

Kirsten (Ki)-ras cDNA clones were prepared from human lung and colon carcinoma cell lines expressing an activated c-Ki-ras2 gene. DNA sequence analysis and transfection studies indicate that different point mutations at the same codon can activate the gene; that most human c-Ki-ras2 mRNA uses sequences from a fourth coding exon distinct from that of its viral counterpart; and that at least one cell line is functionally homozygous for the activated gene.

Transforming genes of human hematopoietic tumors: frequent detection of ras-related oncogenes whose activation appears to be independent of tumor phenotype

We surveyed 22 human hematopoietic tumors and tumor cell lines for sequences capable of transforming NIH 3T3 cells by DNA transfection. A primary human acute myelogenous leukemia, a chronic myelogenous leukemia cell line, and cell lines derived from three independent acute lymphocytic leukemias demonstrated oncogenes capable of conferring the transformed phenotype to NIH 3T3 cells through serial cycles of transfection. One of three transforming genes associated with acute lymphocytic leukemia cells (classified as thymocyte developmental stage II) was identified as the activated cellular homologue of the Kirsten murine sarcoma virus onc gene, kis, a member of the ras family of onc genes. A transforming gene, which was demonstrated to be common to several human myeloid and lymphoid tumor cells, was shown to be a distantly related member of the ras gene family. Thus, the NIH 3T3 transfection assay commonly detects related oncogenes in human hematopoietic tumor cells. Moreover, the activation of these oncogenes appears to be independent of the specific stage of cell differentiation or tumor phenotype.

Retroviral transforming genes in normal cells?

The hallmark of retroviral transforming genes (onc genes) are specific sequences which are unrelated to essential virion genes but are closely related to sequences in normal cells. Viral onc genes probably originated from rare transductions of these cellular sequences by retroviruses without onc genes. Consequently, it has been suggested that retroviral transforming genes are present in normal cells in a latent form. However, recent structural analyses indicate that viral onc genes and cellular genes, which share specific sequences, are not isogenic. They differ from each other in scattered point mutations and in unique coding regions. The cellular genes containing onc-related sequences are expressed in normal cells compatible with a normal function. There is as yet no functional or consistent circumstantial evidence that these cellular genes cause cancer in animals that are not infected by viruses with onc genes. Therefore, it is still uncertain whether the onc-related cellular genes have oncogenic potential beyond their role as progenitors of retroviral onc genes.

Structure and biological activity of v-raf, a unique oncogene transduced by a retrovirus

We have molecularly cloned a unique acutely transforming replication-defective mouse type C virus (3611-MSV) and characterized its acquired oncogene. The viral genome closely resembles Moloney (M) murine leukemia virus (MuLV), except for a substitution in M-MuLV in the middle of p30 and the middle of the polymerase gene (pol). Heteroduplex analysis revealed that 2.4 kilobases of M-MuLV DNA were replaced by 1.2 kilobases of cellular DNA. The junctions between viral and cellular sequences were determined by DNA sequence analysis to be 517 nucleotides into the p30 sequence and 1,920 nucleotides into the polymerase sequence. Comparison of the transforming gene from 3611-MSV, designated v-raf, with previously isolated retrovirus oncogenes either by direct hybridization or by comparison of restriction fragments of their cellular homologs shows it to be unique. Transfection of NIH 3T3 cells with cloned 3611-MSV proviral DNA leads to highly efficient transformation and the recovered virus elicits tumors in mice typical of the 3611-MSV virus. Transfected NIH 3T3 cells express two 3611-MSV-specific polyproteins (P75 and P90), both of which contain NH2-terminal gag gene-encoded components linked to the acquired sequence (v-raf) translational product. The cellular homolog, c-raf, is present in one or two copies per haploid genome in mouse and human DNA.

Transfer of sensitivity to tumor promoters by transfection of DNA from sensitive into insensitive mouse JB6 epidermal cells

Sensitivity to promotion of transformation by tumor promoters in mouse epidermal JB6 cells appears to have a genetic basis since the phenotypes of both promotable and nonpromotable JB6 cells derived from a common parent line are stable. Hybridization of promotable (P(+)) and nonpromotable (P(-)) cells previously indicated that promotability appears to behave as a dominant trait. These results suggest that it should be possible to find DNA sequences which specify sensitivity to promotion of anchorage independence by 12-o-tetradecanoyl-phorbol-13-acetate (TPA). Cellular DNA isolated from one of two P(+) lines, JB6 Cl 41 or JB6 Cl 22, was CaPO(4) precipitated and used to transfect the P(-) cell line JB6 Cl 30. At 7 days posttransfection, the cells were suspended in agar with or without TPA at 1.6 x 10(-8) M and assayed 10 days later for TPA-dependent colony formation. Untreated or Cl 30 DNA-treated P(-) JB6 Cl 30 cells yielded 40 to 50 colonies per 10(5) cells. In contrast, transfection of Cl 30 cells with "P(+) DNA" derived from either Cl 41 or Cl 22 yielded 200 to 500 TPA-induced colonies per 10(5) cells, or a five- to eightfold enhancement of promotability. The enhanced promotability obtained after transfection with P(+) DNA was stable, as judged by the retention of promotability for at least eight passages in cell lines derived from TPA-induced agar colonies. Other transfectants showed irreversible transformation by TPA, as observed in the parental P(+) lines. When NIH 3T3 cells instead of the putative preneoplastic JB6 Cl 30 cells were used as recipients for transfection of P(+) DNA, no evidence for acquisition of promotability was obtained. P(-) JB6 Cl 25, like Cl 30, also permitted expression of transfected P(+) DNA. These results suggest that sensitivity to phorbol ester promotion of transformation in JB6 cells is determined by DNA sequence(s) present in the P(+) DNA and requires recipient cells of the appropriate phenotype for expression.

Acquisition of transforming properties by alternative point mutations within c-bas/has human proto-oncogene

The transforming gene of a human lung carcinoma-derived cell line, Hs242, has been cloned in biologically active form, and identified as c-bas/has (otherwise known as c-Ha-ras). The genetic lesion responsible for the transforming activity of the Hs242 oncogene has been localized to a point mutation in the second exon which results in the substitution of leucine for glutamine as amino acid 61 of the predicted protein. No changes were observed in the first exon, the region of c-bas/has in which a point mutation is responsible for activation of the T24 and EJ bladder carcinoma oncogenes.

Nucleotide sequence analysis of the T24 human bladder carcinoma oncogene

The nucleotide sequence of the T24 human bladder carcinoma oncogene was determined, and the coding and noncoding sequences of the genome were identified. The amino acid sequence of p21, the translational product of the T24 oncogene, was predicted from the nucleotide sequence of the oncogene. Comparison of this sequence with that of the normal cellular homolog showed that a single point mutation in the coding sequences of the T24 oncogene resulted in the acquisition of transforming properties. Other differences between the T24 oncogene and its normal cellular homolog were found in the 5' noncoding and 3' noncoding sequences, but these differences appear to be due to polymorphism and do not play a significant role in the transformation process.

Identification of transforming gene in two human sarcoma cell lines as a new member of the ras gene family located on chromosome 1

A molecular clone containing part of the transforming gene from two human sarcoma cell lines, HT1080 and RD, has been obtained and shown to represent a new member of the human ras gene family. The transforming gene has undergone no major rearrangements and has not been amplified in either sarcoma cell line. The major transcript from the gene is 2,200 nucleotides long and is present at the same levels in both normal fibroblasts and tumour cells. The same gene is also activated in HL60, a promyelocytic leukaemia line and in SK-N-SH, a neuroblastoma line. The gene, N-ras, is located on chromosome 1.

Identification of a structural gene for a RNA polymerase II polypeptide in Drosophila melanogaster and mammalian species

Using subclones representing 14 kilobase pairs (kb) of DNA from the Drosophila melanogaster RNA polymerase II (EC 2.7.7.6) X-linked genetic locus, RpII, we have identified four poly(A)+ RNA transcripts in adult flies. The DNA encoding only one of these, a 7-kb transcript, cross-hybridized to mammalian DNA. DNA from alpha-amanitin-resistant (AmaR) Chinese hamster ovary (CHO) and human cells was used to transform the temperature-sensitive (TS) RNA polymerase II Syrian hamster mutant TsAF8. The acquisition of the TS+ AmaR RNA polymerase II phenotype was accompanied by the appearance of donor-DNA-specific restriction fragments that cross-hybridize to the D. melanogaster 7-kb transcript DNA. This D. melanogaster DNA and the related DNA detected in mammalian species must therefore be the structural gene for a RNA polymerase II polypeptide.

Mouse skin carcinomas induced in vivo by chemical carcinogens have a transforming Harvey-ras oncogene

Several groups have shown that the malignant phenotype can be transferred to NIH/3T3 fibroblasts by incorporation of DNA isolated from tumour cell lines. These studies have demonstrated that the transforming activity of DNA isolated from human bladder, lung and colon carcinoma cell lines is related to an alteration of the cellular homologues of the ras genes of Harvey or Kirsten murine sarcoma viruses. It is, however, unclear what relevance these observations have to the multi-stage nature of tumorigenesis in vivo, in which several independent events are required in both humans and experimental animals. The activation of a cellular oncogene in a defined experimental system for the progressive induction of solid tumours has not yet been demonstrated. We report here that high molecular weight DNA from transplanted squamous cell carcinomas induced by sequential treatment of mouse skin with initiators and promoters of carcinogenesis causes morphological transformation of NIH/3T3 fibroblasts at high frequency. The transforming properties are due to the transfer of an activated cellular homologue of the Harvey-ras (rasH) oncogene.

Construction and use of a dominant, selectable marker: a Harvey sarcoma virus-dihydrofolate reductase chimera

The transcriptional promoter of the Harvey sarcoma virus long terminal repeat has been used to construct a biologically active dihydrofolate reductase chimera. The construction placed the long terminal repeat at the 5' end of a dihydrofolate reductase cDNA. This chimera mediated methotrexate resistance when introduced into wild-type NIH3T3 mouse cells by transfection. The chimeric sequences were expressed in the form of polyadenylated RNA and dihydrofolate reductase protein and were amplified when the methotrexate-resistant transfectants were selected to grow in increasing methotrexate concentrations. This chimera was dominant acting and able to confer a methotrexate-resistant phenotype on wild-type NIH3T3 cells. It has been used in cotransfection experiments with DNA from human tumor cells to obtain foci of methotrexate-resistant transformed NIH3T3 cells resulting from uptake of exogenous DNA. The transfected methotrexate-resistant cells carried double minute chromosomes that appeared to contain DNA acquired during transfection.

Three human transforming genes are related to the viral ras oncogenes

Three distinct transforming genes present in human tumor cell lines are all related to the viral oncogenes of Harvey and Kirsten murine sarcoma viruses, designated v-H-ras and v-K-ras, respectively. The transforming gene of a bladder carcinoma cell line has been shown to be a human homolog to v-H-ras [Parada, L. F., Tabin, C. J., Shih, C. & Weinberg, R. A. (1982) Nature (London) 297, 474-478; Santos, E., Tronick, S. R., Aaronson, S. A., Pulciani, S. & Barbacid, M. (1982) Nature (London) 298, 343-347]. The transforming gene common to one colon (SK-CO-1) and two lung carcinoma (SK-LU-1 and Calu-1) cell lines is the same human homolog of v-K-ras as is the transforming gene previously identified in a lung carcinoma cell line Lx-1 [Der, C. J., Krontiris, T. G. & Cooper, G. M. (1982) Proc. Natl. Acad. Sci. USA 79, 3637-3640]. The transforming gene of SK-N-SH neuroblastoma cells is weakly homologous to both v-H-ras and v-K-ras. NIH 3T3 cells transformed with the SK-N-SH transforming gene contain increased levels of a protein serologically and structurally related to the protein products of the v-H-ras and v-K-ras genes. Therefore, it represents a third member of the ras gene family, which we have called N-ras. Based on the homology with the v-ras genes, we have established the orientation of transcription and approximate coding regions of the cloned human K-ras and N-ras genes.

Human c-Ki-ras2 proto-oncogene on chromosome 12

A human colonic adenocarcinoma transforming gene, recently identified as a cellular homolog of the Kirsten sarcoma gene (v-ras), was used to assign the human cellular Kirsten ras2 gene to chromosome 12 by the Southern hybridization method. A single 640 base-pair Eco RI--Hind III fragment of the transforming gene, isolated by DNA transfection and molecular cloning, can detect a single Eco RI fragment (2.9 kilobase pairs) of DNA from phenotypically normal cells. The data suggest a constant chromosomal location of c-Ki-ras2.

Characterization of a human colon/lung carcinoma oncogene

DNA sequences capable of inducing oncogenic transformation of NIH3T3 mouse cells are found in a number of human tumour cell lines. When DNAs of these cell lines are applied to monolayer cultures of the mouse fibroblasts, foci of transformed cells are observed 2-3 weeks later. DNA from cells of such primary foci can be used in turn to induce foci in a second cycle of gene transfer. The human DNA sequences responsible for transformation have been called oncogenes, the best characterized of which is closely related to the Harvey murine sarcoma virus oncogene. Here we present a characterization of an oncogene which we found originally to be present in DNA of the SW480 colon carcinoma cell line. We indicate its structural outlines and demonstrate, in extension of reported results, its presence in an activated form in the genome of several types of human tumour cell lines as well as in biopsy tissue from an adenocarcinoma of the large bowel. We identify this tumour oncogene with c-Ki-ras2, one of two known members of the Kirsten ras family of human proto-oncogenes, extending a series of recent reports which have demonstrated homologies between human oncogenes and those of Harvey and Kirsten murine sarcoma viruses. The c-Ki-ras2 oncogene of several tumour cell lines is shown to be amplified.

Complete nucleotide sequences of the T24 human bladder carcinoma oncogene and its normal homologue

DNA sequence analysis of the activated oncogene from the T24 human bladder carcinoma line and two alleles of its normal cellular progenitor (c-Ha-ras-1) indicates that the genes encompass at least four exons, and that only a single point mutation residing within the first exon distinguishes the coding region of both alleles of the normal gene from their activated counterpart. Both versions of the gene encode a protein which is predicted to differ from the corresponding viral gene product at three amino acid residues, one of which was previously shown to represent the major site of phosphorylation of the viral polypeptide.

DNA-mediated alteration of the reversion frequency of transformed NIH/3T3 cells

Cell selection immediately after DNA-mediated transfection of whole-cell DNA into mammalian cells has been used to select for specific DNA sequences that cause a phenotypic effect. Whole-cell mouse or human DNA was cleaved into a distribution of lengths (0.4-25 kilobase pairs) and transfected into anchorage-independent spontaneously transformed NIH/3T3 cells. Immediately after transaction, anchorage-dependent serum concentration-dependent reverents were selected. The Hirt supernatant, containing extrachromosomal DNA resulting from the transfection, was isolated from the revertants and transfected with high molecular weight carrier DNA into a second population of transformed cells; revertants were again selected. After five to seven cycles of transfection of Hirt supernatant DNA (obtained from revertants selected at the previous cycle) into new populations of transformed cells at each cycle, the reversion frequency had become 5-15 times greater than the spontaneous reversion frequency measured for several subclones of nontransfected or mocktransfected transformed NIH/3T3 cells. When nonmammalian genomic DNAs were used in transfecting a first population of cells, there was no effect on the reversion of frequency even after six cycles of selection. The reversion-enhancing activity of sixth-cycle Hirt supernatant DNA resulting after transfection at the first cycle with mouse or human sequences was destroyed by EcoRI but not by BamHI or Sal I. Sequences resembling human Alu I sequences were found in mouse whole-cell DNA isolated from sixth-cycle revertants generated after transfection of human sequences at the first cycle.

The human c-ras1H oncogene: a mutation in normal and neoplastic tissue from the same patient

The c-ras1H oncogene can be distinguished from its normal cellular counterpart by the loss of a restriction endonuclease site. This sequence alteration is the basis of a rapid screening method for the presence of this oncogene. DNA's from 34 individuals were screened by this method, and all were homozygous for the normal allele. In contrast, DNA from a patient's bladder tumor, as well as DNA from his normal bladder and leukocytes, were heterozygous at that restriction endonuclease site. Further restriction enzyme mapping pinpointed the change in the mutant allele as being one of two nucleotides, either of which would change the 12th amino acid (glycine) in the normal c-ras1H gene product. Point mutations in the codon for this amino acid have previously been described in a bladder tumor cell line and in the viral oncogene v-rasH. These results indicate that the patient carried a c-ras1H oncogene in his germ line, raising the possibility that the c-ras1H oncogene confers a predisposition to neoplasia.

Isolation and preliminary characterization of the transforming gene of a human neuroblastoma cell line

DNA from the human neuroblastoma cell line SK-N-SH is capable of inducing foci of transformed NIH 3T3 cells after DNA-mediated gene transfer. Using genetic selection with the Escherichia coli sup F gene, we have isolated human sequences from mouse cells responsible for the oncogenic transformation. These sequences are present in all human DNAs surveyed and no gross rearrangements of these sequences are found in SK-N-SH cells. Although clearly distinct from two other human transforming genes present in bladder, lung, and colon carcinoma cell lines, all three transforming gene sequences may be related members of the ras gene family.

Inhibition of DNA methylation by chemical carcinogens in vitro

A diverse range of ultimate chemical carcinogens inhibited the transfer of methyl groups from S-adenosylmethionine to hemimethylated DNA in a reaction catalyzed by mouse spleen methyltransferase. The formation of alkali-labile sites in DNA lessened its ability to accept methyl groups in vitro, but the methylation reaction was much less sensitive to thymine dimers or double-strand breaks. Carcinogens induced the formation of alkali-labile DNA lesions, but the degree of methyltransferase inhibition observed was greater than that expected for this damage alone. Certain carcinogens were also capable of direct modification and inactivation of the methyltransferase enzyme. Benzo(a)pyrene treatment of living BALB/3T3 A31 clone 1-13 but not C3H/10T1/2 clone 8 cells resulted in a 12% decrease in total 5-methylcytosine content of cellular DNA. Carcinogenic agents may therefore cause heritable changes in 5-methylcytosine patterns in certain cell types by a variety of mechanisms, including adduct formation, induction of apurinic sites and single-strand breaks and direct inactivation of DNA methyltransferase.

Altered gene products are associated with activation of cellular rasK genes in human lung and colon carcinomas

Two lung and two colon carcinoma cell lines of human origin, which contained the same activated rasK transforming gene, expressed abnormal species of p21 that were distinct from the p21 proteins expressed in normal human cells and other human carcinomas. The abnormal species of p21 expressed by three of these cell lines were indistinguishable from each other, but differed from the abnormal p21 expressed by one lung carcinoma cell line. NIH cells transformed by DNAs of these carcinomas expressed the same abnormal p21 species, indicating that these abnormal proteins were encoded by the activated rasK genes detected by transfection. These results indicate that transforming activity of rasK genes in human lung and colon carcinoma cell lines is activated by mutations which alter the structure of their gene products, and that activation of rasK genes can result from different molecular alterations in different individual neoplasms.

Construction and use of a dominant, selectable marker: a Harvey sarcoma virus-dihydrofolate reductase chimera

The transcriptional promoter of the Harvey sarcoma virus long terminal repeat has been used to construct a biologically active dihydrofolate reductase chimera. The construction placed the long terminal repeat at the 5' end of a dihydrofolate reductase cDNA. This chimera mediated methotrexate resistance when introduced into wild-type NIH3T3 mouse cells by transfection. The chimeric sequences were expressed in the form of polyadenylated RNA and dihydrofolate reductase protein and were amplified when the methotrexate-resistant transfectants were selected to grow in increasing methotrexate concentrations. This chimera was dominant acting and able to confer a methotrexate-resistant phenotype on wild-type NIH3T3 cells. It has been used in cotransfection experiments with DNA from human tumor cells to obtain foci of methotrexate-resistant transformed NIH3T3 cells resulting from uptake of exogenous DNA. The transfected methotrexate-resistant cells carried double minute chromosomes that appeared to contain DNA acquired during transfection.

Chromosomal assignment of the endogenous proto-oncogene C-abl

Abelson murine leukemia virus (A-MuLV) is a replication-defective retrovirus that transforms lymphocytes of the B-cell lineage. This virus is a recombinant between the parental Moloney murine leukemia virus and a cellular gene termed C-abl. By analysis of a series of mouse x Chinese hamster hybrid celllines containing various mouse chromosomes, we have mapped the C-abl gene to mouse chromosome 2.

Localization of the normal allele of T24 human bladder carcinoma oncogene to chromosome 11

The development of DNA-mediated gene transfer techniques has made it possible to identify transforming genes present in certain human tumour cells. Such genes have been shown to induce morphological transformation when used to transfect suitable assay cells. Recently a transforming gene has been isolated by molecular cloning techniques from the T24 (ref. 11) and EJ (ref. 12) human bladder carcinoma cell lines. This bladder carcinoma oncogene has been shown to be of human origin, less than six kilobase pairs (kbp) in size, and closely related to the onc genes (v-bas and v-ras) of BALB and Harvey murine sarcoma viruses. These transforming retroviruses arose in nature by transduction of cellular genes from mouse and rat cells, respectively. To understand better the relationship of the T24 oncogene with other human cellular genes, we have determined the chromosomal location of its normal allele within the human genome. We show here that it is carried on chromosome 11 in normal cells.

Activation of the T24 bladder carcinoma transforming gene is linked to a single amino acid change

Several different transforming genes have been observed in the DNA of a variety of tumours and tumour cell lines of human and rodent origin by the ability of these genes to induce morphological transformation in NIH 3T3 cells1-5. The transforming gene found in a human bladder carcinoma cell line, T24, is H-ras-1, the human homologue of the Harvey sarcoma virus oncogene (v-H-ras)6-9. In the present study we have compared the H-ras-1 genes cloned from T24 and normal human DNA. The H-ras-1 gene cloned from T24 DNA induces transformation in NIH 3T3 cells, while the same gene cloned from normal cellular DNA does not. The functionally significant difference between the transforming and normal genes appears to be a single base mutation, which produces an amino acid change in the sequence of the proteins that the genes encode.

Activation of a cellular oncogene by DNA rearrangement: possible involvement of an IS-like element

The cellular oncogene c-mos is rearranged in a mouse myeloma and the tumour mRNA contains transcripts hybridizing with a v-mos probe. The rearranged gene (rc-mos) was cloned in lambda phage and shown to transform mouse fibroblasts in transfection assays, rc-mos differs from its progenitor, c-mos, only at the 5' end of the gene, where c-mos sequences have been substituted by a novel cellular DNA fragment. This fragment contains a 159-base pair (bp) insertion sequence (IS)-like element localized immediately 5' to the junction with c-mos. This is the first demonstration in a non-virally-induced tumour of activation of a cellular oncogene by a mechanism possibly involving DNA transposition.

New method for detecting cellular transforming genes

Tumor induction in athymic nude mice can be used to detect dominant transforming genes in cellular DNA. Mouse NIH 3T3 cells freshly transfected with either cloned Moloney sarcoma proviral DNA or cellular DNA's derived from virally transformed cells induced tumors when injected into athymic nu/nu mice. Tumors were also induced by cells transfected with DNA from two tumor-derived and one chemically transformed human cell lines. The mouse tumors induced by human cell line DNA's contained human DNA sequences, and DNA derived from these tumors was capable of inducing both tumors and foci on subsequent transfection. Tumor induction in nude mice represents a useful new method for the detection and selection of cells transformed by cellular oncogenes.

A point mutation is responsible for the acquisition of transforming properties by the T24 human bladder carcinoma oncogene

The genetic change that leads to the activation of the oncogene in T24 human bladder carcinoma cells is shown to be a single point mutation of guanosine into thymidine. This substitution results in the incorporation of valine instead of glycine as the twelfth amino acid residue of the T24 oncogene-encoded p21 protein. Thus, a single amino acid substitution appears to be sufficient to confer transforming properties on the gene product of the T24 human bladder carcinoma oncogene.

Transforming gene of a human leukaemia cell is unrelated to the expressed tumour virus related gene of the cell

The virally encoded oncogenes (v-onc) of avian and mammalian retroviruses are the recombinant products of normal cellular genes (c-onc) and a retroviral genome. These cellular homologues have been highly conserved during evolution and are found in human DNA. The expression of at least one c-onc under the control of a viral promoter results in transformation of cells in a manner resembling that displayed by the v-onc counterpart; the inappropriate expression of c-onc in the absence of viral influences could likewise result in the malignant state. This proposal would be strongly supported by the presence of c-onc RNAs in a variety of human tumours were they not also demonstrable in normal tissues. The role of these RNAs in the oncogenic process remains unclear. Here we report that RNA homologous to the oncogene (v-abl) of Abelson murine leukaemia virus (A-MLV) is expressed in a unique human leukaemia in a fashion different from that of other human tissues and tumours. In addition, DNA from this tumour transforms NIH-3T3 cells at a high efficiency in a transfection assay. The transfected sequences are not related to the v-abl gene, but the NIH-3T3 transformants manufacture a transforming growth factor which behaves similarly to factors produced by A-MLV-transformed NIH-3T3 fibroblasts.

A transforming gene present in human sarcoma cell lines

Morphological transformation of NIH/3T3 cells by transfection with DNA has been used to identify transforming sequences in human tumours. Transforming activity has been reported for DNAs isolated from bladder, mammary, colon and lung carcinomas, neuroblastoma, lymphoid and myeloid tumours. Each of these tissues seems to contain different transforming sequences except for the colon and lung tumours where the same sequence seems to be involved. We now report that in two different human sarcoma cell lines, a fibrosarcoma and an embryonal rhabdomyosarcoma, the DNAs have transforming activity. The transforming gene is the same in both sarcomas but differs from the activated sequences detected in other tumours. We have also found that the transforming gene has no detectable homology to eight retrovirus oncogenes tested.

Cellular transforming genes

Cellular genes potentially capable of inducing oncogenic transformation have been identified by homology to the transforming genes of retroviruses and by the biological activity of cellular DNA's in transfection assays. DNA's of various tumors induce transformation with high efficiencies, indicating that oncogenesis can involve dominant genetic alterations resulting in activation of cellular transforming genes. The identification and characterization of cellular transforming genes and their possible involvement in naturally occurring cancers, is discussed.

Isolation of a genomic clone partially encoding human hypoxanthine phosphoribosyltransferase

Mouse cells deficient in the enzyme hypoxanthine phosphoribosyltransferase (HPRT; EC 2.4.2.8) have been transfected with total human DNA, and cells producing human enzyme were isolated by growth in selective medium. DNA from several such cell lines has been used to generate secondary transfectants that make human HPRT. Blots of the DNA of these secondary cells have been hybridized with total human DNA probes or with cloned human Alu sequences, and one of several common bands has been cloned in pBR322. Colonies of transformed Escherichia coli containing human sequences were detected by their homology with human DNA, and subclones of resulting recombinant plasmids were prepared. Two subclones free of Alu sequences were found to contain human sequences that hybridized to human X chromosome DNA. One of these, pBR1.5, also hybridized to a single RNA band on gel blots of human and secondary transfectant cytoplasmic poly(A)+RNA but not to RNA from the parent mouse cell line. These results indicate that these clones represent human HPRT gene fragments. This has been confirmed by using pBR1.5 as a probe to isolate an authentic and expressible human HPRT cDNA clone from a library prepared by H. Okayama and P. Berg.