Mechanism of activation of a human oncogene

Nucleotide sequence of Abelson murine leukemia virus genome: structural similarity of its transforming gene product to other onc gene products with tyrosine-specific kinase activity

The nucleotide sequence of the proviral genome of Abelson murine leukemia virus (A-MuLV), an acute transforming virus of murine origin, has been determined. Like other transforming viruses, A-MuLV contains sequences derived from its helper virus, Moloney murine leukemia virus (M-MuLV), and a cell-derived protooncogene (abl) insertion sequence. By comparison of the A-MuLV sequence with that of M-MuLV, it was possible to precisely localize and define sequences contributed by the host cellular DNA. From the nucleotide sequence, we have predicted the amino acid sequence of p120gag-abl, the product of the A-MuLV gag-abl hybrid gene. The amino acid sequence of the putative abl gene, when compared with the sequences of other tyrosine-specific protein kinases (src, fes, fps, and yes), revealed significant homologies, indicating that all these functionally related transforming genes are derived from divergent members of the same protooncogene family. In addition to the gag-abl sequence, the proviral genome was found to contain an additional open reading frame that could code for an 18,000-dalton protein, whose role is at present undetermined.

Tumorigenesis by mouse mammary tumor virus: evidence for a common region for provirus integration in mammary tumors

We have prepared specific probes for unique-sequence cellular DNA adjacent to each of the newly integrated proviruses in tumors induced by mouse mammary tumor virus (MMTV). The use of such probes to screen a large number of independent mammary tumors in the BR6 strain of mouse has indicated that in at least 17 out of the 40 tumors examined so far, an MMTV provirus has integrated into a common chromosomal domain. A 10 kb Eco RI fragment of single copy DNA from this region has been isolated and partially characterized by restriction enzyme mapping. Of the proviruses located within this fragment in different tumors, all but one are complete, in the same orientation, and clustered within about 3 kb of cellular DNA. These findings are consistent with an insertional mutagenesis model for tumorigenesis by MMTV, in which the integration of a provirus in a particular region of cellular DNA may activate a neighboring oncogene. The region we describe here appears to be different from that reported for mammary tumors in the C3H strain of mouse.

Complete nucleotide sequence of a human c-onc gene: deduced amino acid sequence of the human c-fos protein

The complete nucleotide sequence of the c-fos(human) gene, the human cellular homolog of the oncogene (v-fos) of Finkel-Biskis-Jinkins murine osteosarcoma virus, has been determined. The c-fos(human) gene contains four discontinuous regions when compared with the v-fos gene. Three of the discontinuities are flanked by sequences characteristic of introns, while the fourth discontinuity is due to a deletion of 104 base pairs in the v-fos gene. As a consequence of the deletion, the predicted c-fos(human) and v-fos gene products differ at their carboxyl termini. Transcripts of 2.2 kilobases from the c-fos(human) gene have been identified in human cells. The sizes of these transcripts are in close agreement with the size expected from the nucleotide sequence after removal of introns.

Structure of mouse rRNA precursors. Complete sequence and potential folding of the spacer regions between 18S and 28S rRNA

We have determined the complete nucleotide sequence of the regions of mouse ribosomal RNA transcription unit which separate mature rRNA genes. These internal transcribed spacers (ITS) are excised from rRNA precursor during ribosome biosynthesis. ITS 1, between 18S and 5.8S rRNA genes, is 999 nucleotides long. ITS 2, between 5.8S and 28S rRNA genes, is 1089 nucleotides long. Both spacers are very rich in G + C, 70 and 74% respectively. Mouse sequences have been compared with the other available eukaryotes: while no homology is apparent with yeast or xenopus, mouse and rat ITS sequences have been largely conserved, with homologous segments interspersed with highly divergent tracts. Homology with rat is much more extensive for ITS 1 than for ITS 2. Tentative secondary structure models are proposed for the folding of these regions within rRNA precursor; they are closely related in mouse and rat.

Specifically alkylated DNA fragments. Synthesis and physical characterization of d[CGC(O6Me)GCG] and d[CGT(O6Me)GCG]

Two hexamer DNA fragments containing a carcinogenic modified base, O6-methyl guanine, have been synthesized by a solid-phase phosphotriester method, in which the unmodified guanine residues present were O6 protected with the 4-nitrophenylethyl group. These two alkylated oligonucleotides were found to have similar Tm's about 40 degrees lower than the unmodified parent compound, d(CG)3. Moreover, the presence of the (O6Me)G appears to inhibit the B leads to Z transition, as determined by CD spectroscopy.

AAF linked to the guanine amino group: a B-Z junction

Minimized conformational potential energy calculations have been performed for AAF linked to dCpdG at the guanine amino group. This is a model for the minor AAF adduct observed in DNA, whose conformational influence has been difficult to ascertain. A global minimum energy conformation was computed with torsion angles like those of the dCpdG residue of Z-DNA. This conformation was incorporated into a larger polymer model at a B-Z junction, with the carcinogen residing in the groove in the Z direction. Local minimum energy conformations of the B type were also computed. In addition, two minima were found with fluorenecytidine stacking. These results suggest that existing B-Z junctions may be vulnerable to modification by AAF at the guanine amino group, or that such junctions may be induced by the carcinogen if the base sequence is appropriate. Otherwise the carcinogen can be located in the minor groove of the B helix (5, 10, 11) or covalently intercalated (13-15).

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.

Human and mouse cellular myc protooncogenes reside on chromosomes involved in numerical and structural aberrations in cancer

A molecular clone of viral myc (v-myc), the oncogene of avian myelocytomatosis virus, MC29, detected homologous human, mouse, and Chinese hamster cellular myc (c-myc) sequences by Southern filter hybridization. A v-myc probe, containing sequences from the 3' domain of the gene, hybridized to single human HindIII and mouse EcoRI genomic DNA fragments of the cellular myc genes whose segregation could be followed in interspecies somatic cell hybrids. Human c-myc segregated concordantly with the enzyme marker glutathione reductase and with a karyotypically normal chromosome 8. A rearrangement of human c-myc was observed in Burkitt's lymphoma cells possessing the t(8;14) translocation. These results suggest that human c-myc is located close to the breakpoint on chromosome 8 (q24) involved in the t(8;14) translocation. The mouse c-myc gene segregated concordantly with chromosome 15 in mouse-Chinese hamster cell hybrids. These gene assignments are noteworthy, as structural and numerical abnormalities of human chromosome 8 and mouse chromosome 15 are associated frequently with B-cell neoplasms.

Base substitution mutations induced by metabolically activated aflatoxin B1

We have determined the base substitutions generated by metabolically activated aflatoxin B1 in the lacI gene of a uvrB- strain of Escherichia coli. By monitoring over 70 different nonsense mutation sites, we show that activated aflatoxin B1 specifically induced GxC leads to TxA transversions. One possible pathway leading to this base change involves depurination at guanine residues. We consider this mechanism of mutagenesis in the light of our other findings that the carcinogens benzo[a]pyrene diol epoxide and N-acetoxyacetylaminofluorene also specifically induce GxC leads to TxA transversions.

Predicted nucleotide-binding properties of p21 protein and its cancer-associated variant

Recently, it has been demonstrated that a single point mutation is responsible for the acquisition of transforming properties by the EJ and T24 human bladder carcinoma gene. The point mutation consists of the conversion of guanine into thymine, which results in the replacement of a glycine by a valine at position 12 of the p21 protein encoded by the EJ and T24 genes. Sequence data of retroviral analogues of the p21 protein also indicate the importance for a glycine residue at position 12 in normal p21. Comparison of the sequence of the 37 N-terminal residues of the normal human p21 protein with the sequence of the dinucleotide-binding beta alpha beta unit in a group of structurally related enzymes, suggests that these residues of p21 fold into a very similar unit which is also involved in binding a nucleotide. We present here a three-dimensional model of the p21 beta alpha beta unit which explains directly why glycine at position 12 cannot be replaced by another residue without altering the nucleotide-binding properties of p21.

Analysis of FBJ-MuSV provirus and c-fos (mouse) gene reveals that viral and cellular fos gene products have different carboxy termini

The complete nucleotide sequence of the FBJ-MuSV proviral DNA and the cellular homolog (c-fos) of its oncogene (v-fos) have been determined. The 4026 nucleotide long FBJ-MuSV proviral DNA contains two long terminal repeats, a substitution of 1639 nucleotides of mouse cellular DNA (v-fos) and the 3' end of the env gene derived from FBJ-MuLV. The sequences of the parental FBJ-MuLV and the cellular c-fos (mouse) gene share five of five nucleotides at the 5' end and ten of 11 nucleotides at the 3' end of the v-fos substitution. When compared with the v-fos sequences, the c-fos gene contains four discontinuous regions, three of which are flanked by sequences characteristic of introns. Direct sequence analysis of c-fos (mouse) RNA by primer extension demonstrates that the fourth discontinuity is due to a 104 bp deletion in the v-fos gene. As a consequence of the deletion, the predicted v-fos and c-fos gene products differ at their C termini.

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.

Homogeneously staining chromosomal regions contain amplified copies of an abundantly expressed cellular oncogene (c-myc) in malignant neuroendocrine cells from a human colon carcinoma

Two human neuroendocrine tumor cell lines derived from a colon carcinoma contain either numerous double minute chromosomes (COLO 320 DM) or a homogeneously staining marker chromosome (COLO 320 HSR). We found amplification and enhanced expression of the cellular oncogene c-myc in both COLO 320 DM and HSR cells, and we were able to show that the homogeneously staining regions of the COLO 320 HSR marker chromosome contain amplified c-myc. From previous and present karyotypes, it appears that the homogeneously staining regions reside on a distorted X chromosome. Therefore, amplification of c-myc has been accompanied by translocation of the gene from its normal position on chromosome 8 (8q24). Because double minute chromosomes were features of primary cultures from the original tumor, it seems reasonable to suspect that amplification of c-myc may have contributed to tumorigenesis.

Hypomethylation of ras oncogenes in primary human cancers

We have examined the methylation status of two cellular oncogenes, c-Ha-ras and c-Ki-ras, in primary human carcinomas and the adjacent analogous normal tissues from which the tumors derived. The c-Ha-ras gene was hypomethylated in six of eight carcinomas, including five colonic adenocarcinomas and one small cell lung carcinoma, when compared to adjacent normal tissues. The c-Ki-ras gene was hypomethylated to a lesser extent in two colonic adenocarcinomas. This is the first demonstration of alterations in methylation of cellular oncogenes in human cancer.

Identification and nucleotide sequence of a human locus homologous to the v-myc oncogene of avian myelocytomatosis virus MC29

Avian myelocytomatosis virus MC29 is a replication-defective acute leukaemia virus which induces a variety of tumours in chickens including sarcomas, renal and hepatic carcinomas, and myelocytomatosis. The oncogenic potential of the virus is mediated by the gene v-myc, acquired from sequences (c-myc) present in normal uninfected chicken DNA. Sequences closely related to chicken c-myc have been highly conserved throughout evolution, from Drosophila to vertebrates. The hypothesis that c-myc may be involved in neoplastic transformation has been strengthened by the finding that B-cell lymphomas induced in chickens by avian leukosis virus (ALV) are often associated with increased expression of c-myc resulting from integration of the ALV provirus adjacent to the c-myc gene. More recently, it has been demonstrated that the malignant human cell line HL-60, derived from the peripheral blood leukocytes of a patient with acute promyelocytic leukaemia, expresses elevated levels of myc-related mRNA associated with an amplification of the c-myc gene. To explore the relationship of the human cellular myc gene with the corresponding viral oncogene from MC29, and to provide a framework for the analysis of the mechanism and significance of c-myc amplification in human tumours, we have isolated and determined the nucleotide sequence of a genomic clone prepared from a normal human library which contains all domains sharing homology with v-myc.

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.

Oncogene from human EJ bladder carcinoma is located on the short arm of chromosome 11

The human cellular homolog of the transforming DNA sequence isolated from the bladder carcinoma cell line EJ was localized on the short arm of human chromosome 11 by Southern blot analysis of human-rodent hybrid cell DNA. This locus contains human sequences homologous to the Harvey murine sarcoma virus v-Ha-ras oncogene.

Identity of some human bladder cancer cell lines

Recent reports on transfection of mouse cells with DNA from the established human urinary bladder cancer cell lines T24, J82 and EJ (MGH-U1), and the presence of an identical genetic modification in T24 and EJ cells have led us to examine the identity of these and other cultures of urothelial origin. By the criteria of HLA-A-B-C typing 7 and isozyme analysis, we conclude that EJ (MGH-U1) and some cultures of J82 are in fact T24 cells. However, five other bladder cancer cell lines, J82 (CO'T), RT4, RT112, TCCSuP and SCaBER, are clearly distinct from T24 by HLA typing (ref. 7) and/or isozyme patterns.

Homology between human bladder carcinoma oncogene product and mitochondrial ATP-synthase

More than 10 different dominant transforming genes (oncogenes) have been identified in human tumours. A human bladder carcinoma oncogene, closely related in sequence to retroviral transforming genes, is split into four exons; the first encodes the N-terminal 37 residues of p21, a protein of unknown function. The oncogene is activated by a single point mutation (guanine to thymine) resulting in the change glycine to valine at position 12 of p21 (refs 3, 4). We report here that the amino acid sequence surrounding this residue is highly homologous to the beta-subunit of mitochondrial and bacterial ATP-synthase in the region of the polypeptide that is believed to contribute to nucleotide binding. Thus, p21 may form part of an enzyme that uses purine nucleotides in catalysis. This is consistent with the finding that an equivalent murine oncogene product binds GTP.

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.