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

Chromosomal localization of three human ras genes by in situ molecular hybridization

Three human ras family protooncogenes, c-Ki-ras-1, and c-Ki-ras-2, and N-ras, have been mapped to chromosome bands 6p11-12, 12p11.1-12.1, and 1p11-13, respectively by in situ molecular hybridization. Certain human cancers display consistent and specific alterations involving chromosomes 1, 6, and 12. The precise chromosomal localization of ras genes will permit evaluation of the possible effect of these chromosome changes on the structure and activities of ras protooncogenes in human neoplasia.

Expression of p21ras in fresh primary and metastatic human colorectal tumors

Activation of the cellular oncogene ras has been implicated in many types of human malignancies. In this study, the relative levels of p21 protein product of ras (p21ras) in primary and metastatic colon tumors were compared to those in adjacent normal tissues. Nine of the 17 primary tumors had substantially elevated levels of p21ras with respect to adjacent normal tissues. Eight of these tumors were from Dukes' B and C stages. Four of the five tumors classified as "D" stage (in which distant metastases are present) did not show elevated levels of p21ras. In metastases from primary colon tumors, nine of nine were considerably reduced in p21ras expression regardless of the site of metastasis. These data suggest that elevation of p21ras may be a common event in early stages of colon tumors, and tumor progression may lead to a more autonomous population of cells in which other growth factors supplant the role of this protein.

Activation of N-ras in a human melanoma cell line

DNA isolated from cell line Mel Swift, a human melanoma cell line, transforms NIH3T3 cells. Southern blot analysis of DNA from secondary foci revealed conserved 8.8- and 7.8-kilobase EcoRI fragments which hybridized with a human repetitive sequence clone, blur 8. The activated transforming gene was identified as N-ras, and the 8.8-kilobase EcoRI fragment from a secondary transformant was cloned. Synthetic 17-mer oligonucleotides which spanned either the normal codon 61 (CAA) or a mutant codon 61 (AAA) were used for hybridization. Cloned N-ras from melanoma cell line Mel Swift hybridized to the mutant (AAA) oligonucleotide. From this we predicted a glutamine-to-lysine substitution in amino acid 61, a change confirmed by conventional sequencing of the first and second exons of N-ras from cell line Mel Swift. Transfection experiments showed that only those recombinant clones with the mutation in position 61 were biologically active.

Chemical carcinogens and proto-oncogens activation

The induction of proto-oncogens H-ras-1 by nitrosomethylurea (Sukumar et al. (1983), 306, 658-661) is discussed in term of lack of DNA-repair of lesions induced in DNA by this alkylating agent, particularly O6-methylguanine residues and apurinic/apyrimidinic sites.

Nucleotide sequence analysis of the BALB/c murine sarcoma virus transforming gene

We determined the nucleotide sequence of the v-H-ras-related oncogene of BALB/c murine sarcoma virus. This oncogene contains an open reading frame of 189 amino acids that initiates and terminates entirely within the mouse cell-derived ras sequence. The protein encoded by this open reading frame matches the sequence predicted for the T24 human bladder carcinoma oncogene product, p21, in all but two positions. The presence of a lysine residue in position 12 of BALB/c murine sarcoma virus p21 likely accounts for its oncogenic properties.

Activation of the c-K-ras oncogene in a human pancreas carcinoma

The human pancreas carcinoma cell line T3M-4 contains activated c-Kirsten (K)-ras oncogene detectable by the DNA-mediated gene transfer technique using NIH/3T3 cells. DNA fragments containing coding lesions have been cloned, and nucleotide sequence analysis suggests that the T3M-4 oncogene has been activated by a single nucleotide transition from A to C in the second exon, which results in the substitution of histidine for glutamine in coden 61 of the predicted amino acid sequence. The quantity analysis of c-K-ras oncogene in the DNA and RNA of T3M-4 cells revealed that the c-K-ras gene was amplified and overexpressed in T3M-4 cells. These findings indicate that the T3M-4 c-K-ras oncogene is activated by different mutational events.

Modulation of adenylate cyclase by guanine nucleotides and Kirsten sarcoma virus mediated transformation

Certain tumour cells contain activated ras genes that code for 21 000 dalton proteins (p21). These proteins associate with the inner face of the plasma membrane and bind guanine nucleotides specifically. In order to determine whether p21s have functions similar to other GTP binding proteins, we investigated the regulation, by guanine nucleotides, of adenylate cyclase (AC) activity in membrane preparations isolated from fibroblasts (C127) transformed by a temperature sensitive mutant of Kirsten sarcoma virus (Ts 371). The degree of AC stimulation by GMP P(NH)P increased when these cells were shifted from the permissive temperature (33 degrees C) to the non-permissive temperature (39 degrees C). This effect was more pronounced at low Mg++ and low GMP P(NH)P concentrations. AC stimulation remained unchanged in rat fibroblasts infected with a temperature sensitive mutant of Rous Sarcoma virus. AC activity was depressed in C127 cells infected with wild type KiMSV. Our data illustrate the feasibility of correlating alterations in the AC system with ras gene expression and using such experimental approaches to elucidate the physiological functions of the p21 proteins.

Yeast and mammalian ras proteins have conserved biochemical properties

Mammalian ras oncogenes encode polypeptides of relative molecular mass (Mr) 21,000 (p21) which bind GTP and GDP. Oncogenic ras-encoded proteins differ from their normal homologues by an amino acid substitution for Gly 12, Ala 59 or Gln 61. Recently, we and others have observed that normal p21, encoded by the Ha-ras gene, has a GTP hydrolytic activity that is reduced by the oncogenic substitutions Val 12 or Thr 59. The yeast Saccharomyces cerevisiae contains two ras-related genes, RASsc1 and RASsc2, the expression of either of which is sufficient for viability. RASsc1 and RASsc2 encode proteins of 309 (SC1) and 322 (SC2) residues which are 62% homologous to mammalian p21 in their 172-amino acid N-terminal sequences. We report here that the N-terminal domain of SC1 binds GTP and GDP and has a GTP hydrolytic activity that is reduced in the variants SC1[Thr 66] and SC1[Leu 68] which are analogous to oncogenic Ha[Thr 59] and Ha[Leu 61], respectively. These results suggest that yeast and mammalian ras proteins have similar biochemical and possibly biological functions.

Amplification and expression of a cellular oncogene (c-myc) in human gastric adenocarcinoma cells

Three of 16 human gastric adenocarcinoma samples, maintained as solid tumors in nude mice, were found to carry amplified c-myc genes. In two samples with a high degree of c-myc DNA amplification (15- to 30-fold), double minute chromosomes were observed in karyotype analysis. The level of c-myc RNA was markedly elevated in a rapidly growing and poorly differentiated tumor, whereas it was only slightly elevated in a slowly growing and more differentiated tumor.

Activation of an N-ras gene in acute myeloblastic leukemia through somatic mutation in the first exon

A transforming N-ras gene has been cloned from acute myeloblastic leukemia bone marrow cells, in parallel with the N-ras gene derived from fibroblasts of the same patient. N-ras derived from fibroblasts lacked focus-forming activity in NIH/3T3 cells, indicating that gene activation in the leukemia cells must have occurred by a somatic event. Construction of chimeric molecules between the transforming and the normal N-ras genes and subsequent biological and sequence analysis of these constructs revealed that the transforming gene was altered by a point mutation changing amino acid 12 of the N-ras protein from glycine to aspartic acid.

Characterization of functional domains of p21 ras by use of chimeric genes

Comparison of the predicted amino acid sequences of different members of the ras family in vertebrates has shown that the N-terminal 120 residues are highly conserved while the C terminus is variable. To test the possible role of the variable residues in cell transformation, chimeras were constructed containing the N-terminal 111 amino acids of the human Ha-ras EJ oncogene and the C terminus of two Drosophila ras genes. We show that one of these constructs which has only 20 conserved residues between positions 121 and 189, can transform rat-1 cells, and the transformed cells are capable of inducing lethal tumors in rats. The second construct containing the C terminus of another Drosophila ras gene exhibits a transforming capacity as well, but only after linkage to a viral transcriptional promoter. These results show that the majority of residues within the C terminus can be replaced without abolishing the transforming potential of p21 ras.

"Retroposon" insertion into the cellular oncogene c-myc in canine transmissible venereal tumor

We examined by Southern blotting the state of the cellular oncogene c-myc in the dog transmissible venereal tumor. The tumor DNA contains a 16.8-kilobase pair (kbp) rearranged c-myc fragment in addition to the normal 15-kbp and 7.5-kbp fragments. We compared the structure of the cloned rearranged c-myc (re-myc) with that of a cloned normal c-myc and found that the rearrangement was due to the insertion of a 1.8-kbp DNA upstream to the first exon of c-myc. The inserted DNA is flanked by 10-base-pair direct repeats and contains a dA-rich tail, suggesting its origin from mRNA. Partial sequence of the inserted element showed 62% homology with the primate interdispersed Kpn I repetitive element. These results provide an example for the behavior of repetitive DNA sequences like the Kpn I family, as movable elements that can transpose nearby to oncogenes or other structural genes and perhaps affect their activity.

Expression and characterization of ras mRNAs from Saccharomyces cerevisiae

The cellular homologs of the Harvey and Kirsten murine sarcoma virus oncogenes comprise a multigene family, ras, that displays striking evolutionary conservation. We recently reported [DeFeo-Jones et al., Nature (London) 306:707-709, 1983] the cloning of two ras homologs from the yeast Saccharomyces cerevisiae. The nucleotide sequences of these genes predict polypeptides that show remarkable homology to p21, the mammalian ras gene product. We have also found proteins in yeast lysates with serological cross-reactivity to p21 (Papageorge et al., Mol. Cell. Biol. 4:23-29, 1984). In this work, we explored the relationship between the immunoprecipitated proteins and the yeast ras genes. We show that both ras genes are expressed in the wild-type cell. Furthermore, we demonstrate by in vitro translation of hybrid-selected RASsc1 mRNA and immunoprecipitation of the translation products that the cloned RASsc1 gene encodes the proteins immunoprecipitated from yeast lysates by anti-p21 monoclonal antibody. Finally, we used anti-p21 monoclonal antibodies to detect a guanine nucleotide binding activity in yeast lysates. The structural and biochemical homologies between ras gene products of S. cerevisiae and mammalian cells suggest that information obtained by genetic analysis of ras function in a lower eucaryote should be applicable to higher organisms as well.

Methylation of the serum albumin gene as compared to the Kirsten-ras oncogene in hepatocytes and non-parenchymal cells of rat liver

The extent of methylation of a gene, i.e. percent of cytosine present as 5-methylcytosine, is correlated with its activity. Hypermethylation is associated with non-expression, whereas hypomethylation is a necessary but not sufficient condition for expression. In this study, the methylation state of the serum albumin gene as compared to the Kirsten-ras (Ki-ras) oncogene was assessed in hepatocytes and non-parenchymal cells (NPC) isolated from rat liver. The results of this investigation indicate that the serum albumin gene is hypomethylated in hepatocytes and hypermethylated in NPC. This is consistent with expression of the gene in the former cell type, and non-expression in the latter. In contrast, the Ki-ras oncogene is hypermethylated in both hepatocytes and NPC, suggesting that it is, at most, minimally expressed in normal rat liver.

Analysis of gene expression during hematopoiesis: present and future applications

Recombinant DNA technology now provides the strategies required to identify genes whose expression controls the development of normal and pathologic blood cells. Characterization of the gene families responsible for synthesis of hemoglobins, immunoglobulins, histocompatibility antigens, and cellular enzymes have already, or are about to, provide major insights into the mechanisms producing normal erythroid cells, immunocytes, and immune surface features. Hemoglobinopathies, leukemias, and autoimmune diseases of the bone marrow can now be examined to a degree of detail previously inaccessible to investigators. Oncogene translocation analysis is shedding new light on the pathogenesis of leukemias and lymphomas. Recent basic advances now permit direct cloning and identification of genes in host organisms which express their protein products, thus allowing isolation of genes coding for the hematopoietic surface markers and growth factors which characterize and regulate blood cell progenitors. This review summarizes the molecular genetic approach to analysis of normal and pathologic hematopoiesis, surveys major findings which have resulted, and examines the potential use of refined gene cloning strategies for improved understanding of blood cell development.

Effects of two major activating lesions on the structure and conformation of human ras oncogene products

ras oncogenes are frequently activated in human tumors by mutations at codon 12 or 61 in their coding sequences. To investigate how these subtle alterations exert such profound effects on the biologic activities of these genes, we studied structural and conformational properties of human ras-oncogene-encoded 21-kDa proteins (p21s). We observed striking differences in the electrophoretic mobilities of the proteins under reducing and nonreducing conditions. These findings imply that intramolecular disulfide bonds affect native p21 conformation. The two activating lesions were shown to induce distinctly different alterations in p21 electrophoretic mobility that were unmasked only under reducing conditions. These results suggest that regions of the molecule containing such alterations are either not exposed or under conformational constraints in the native p21 molecule. We confirmed the opposing effects on protein mobility induced by the two activating lesions by using a recombinant gene containing both lesions. The recombinant gene's high-titer transforming activity further established that the two lesions do not negatively complement one another with respect to transforming-gene function. Our findings of distinct alterations in electrophoretic mobilities of position-12- and position-61-altered p21 molecules should be applicable to the rapid immunologic diagnosis of ras oncogenes in human malignancies.

A system to determine basepair substitutions at the molecular level, based on restriction enzyme analysis; influence of the muc genes of pKM101 on the specificity of mutation induction in E. coli

A system has been developed for the analysis of basepair substitutions that are involved in the reversion of a specific missense mutation. The method is based on the ability of restriction enzymes to recognize and cut specific DNA sequences. Wild-type revertants arising from AT----GC transitions, pseudo wild-type revertants arising from AT-transversions and second site revertants can be distinguished. 4 mutagenic agents have been used, 2,6-diaminopurine, MMS, EMS and ENU, which differ in the types of damage they cause in DNA and in the susceptibility of the damage to repair. All 4 mutagens effectively enhanced the reversion of the mutation studied, trpA223, particularly by increasing the fraction of AT----GC transitions. In this system the influence of the muc genes of plasmid pKM101 was investigated. The presence of these genes reduced the fraction of AT----GC transitions and enhanced the fraction of AT-transversions as well as the fraction of second-site mutations. This change in mutation specificity is found irrespective whether mutation induction occurs mainly via SOS repair (MMS, ENU) or via mainly misreplication (2,6-diAP, EMS). These data suggest that the muc genes are involved in the induction of mutations not only during SOS repair, but also during misreplication. The change in mutation specificity may be caused by a change in the selection and insertion of nucleotides by the DNA-polymerising complex, or by interference with the repair of mismatched bases.

Functional homology of mammalian and yeast RAS genes

Yeast spores lacking endogenous RAS genes will not germinate. If such spores contain chimeric mammalian/yeast RAS genes or even the mammalian H-ras gene under the control of the galactose-inducible GAL10 promoter, they will germinate in the presence of galactose and produce viable haploid progeny dependent on galactose for continued growth and viability. These results indicate that the biochemical function of RAS proteins is essential for vegetative haploid yeast and that this function has been conserved in evolution since the progenitors of yeast and mammals diverged.

Ha-ras proteins exhibit GTPase activity: point mutations that activate Ha-ras gene products result in decreased GTPase activity

Several ras genes have been expressed at high levels in Escherichia coli and the resultant ras proteins were shown to be functional with respect to their well-known specific, high-affinity, GDP/GTP binding. We were able to detect a weak GTPase activity associated with the purified proteins. The normal cellular ras protein (p21N) exhibits approximately equal to 10 times higher GTPase activity than the "activated" proteins. Even though the turnover rate of the reaction is very low (0.02 mol of GTP hydrolyzed per mol of p21N protein per minute), the reaction appears to be catalytic; one molecule of p21N hydrolyzes more than one molecule of GTP. The GTPase and the GDP binding activities both have been recovered from a Mr 23,000 protein eluted following NaDodSO4/polyacrylamide gel electrophoresis, suggesting that these two activities are associated with the same protein. Mg2+ ions and dithiothreitol are required for GTPase activity and the optimal pH is between 7 and 8. Guanidine X HCl, which is required for solubilizing bacterially expressed ras protein, is strongly inhibitory to GTPase activity at concentrations higher than 0.5 M.

In yeast, RAS proteins are controlling elements of adenylate cyclase

S. cerevisiae strains containing RAS2val19, a RAS2 gene with a missense mutation analogous to one that activates the transforming potential of mammalian ras genes, have growth and biochemical properties strikingly similar to yeast strains carrying IAC or bcy1. Yeast strains carrying the IAC mutation have elevated levels of adenylate cyclase activity. bcy1 is a mutation that suppresses the lethality in adenylate cyclase deficient yeast. Yeast strains deficient in RAS function exhibit properties similar to adenylate cyclase deficient yeast. bcy1 suppresses lethality in ras1- ras2- yeast. Compared to wild-type yeast strains, intracellular cyclic AMP levels are significantly elevated in RAS2val19 strains, significantly depressed in ras2- strains, and virtually undetectable in ras1- ras2- bcy1 strains. Membranes from ras1- ras2- bcy1 yeast lack the GTP-stimulated adenylate cyclase activity present in membranes from wild-type cells, and membranes from RAS2val19 yeast strains have elevated levels of an apparently GTP-independent adenylate cyclase activity. Mixing membranes from ras1- ras2- yeast with membranes from adenylate cyclase deficient yeast reconstitutes a GTP-dependent adenylate cyclase.

New human transforming genes detected by a tumorigenicity assay

We have developed a sensitive bioassay for transforming genes based on the tumorigenicity of cotransfected NIH3T3 cells in nude mice. The assay differs substantially from the NIH3T3 focus assay. Using it, we have detected the transfer of three transforming genes from the DNA of MCF-7, a human mammary carcinoma cell line. One of these is N-ras, which is amplified in MCF-7 DNA. The other two, which we have called mcf2 and mcf3, do not appear to be related to known oncogenes. We cannot detect their transfer by using the NIH3T3 focus assay. We do not yet know whether either mcf2 or mcf3 is associated with genetic abnormalities in MCF-7 cells.

Activation of a human c-K-ras oncogene

The human lung carcinomas PR310 and PR371 contain activated c-K-ras oncogenes. The oncogene of PR371 was found to present a mutation at codon 12 of the first coding exon which substitutes cysteine for glycine in the encoded p21 protein. We report here that the transforming gene of PR310 tumor contains a mutation in the second coding exon. An A----T transversion at codon 61 results in the incorporation of histidine instead of glutamine in the c-K-ras gene product. By constructing c-K-ras/c-H-ras chimeric genes we show that this point mutation is sufficient to confer transforming potential to ras genes, and that a hybrid ras gene coding for a protein mutant at both codons 12 and 61 is also capable of transforming NIH3T3 cells. The relative transforming potency of p21 proteins encoded by ras genes mutant at codons 12, 61 or both has been analyzed. Our studies also show that the coding exons of ras genes, including the fourth, can be interchanged and the chimeric p21 ras proteins retain their oncogenic ability in normal rodent established cell lines.

Three different mutations in codon 61 of the human N-ras gene detected by synthetic oligonucleotide hybridization

The activation of ras genes in naturally occurring tumors has, thus far, been found to be due to mutations in codon 12 or 61 resulting in single amino acid substitutions. We have used highly labeled synthetic oligonucleotides to detect mutations in these codons and to determine the exact position of the mutation. Using this approach we have found three different mutations in codon 61 of the N-ras gene of various human tumor cell lines. In the fibrosarcoma line HT1080 the first nucleotide of the codon is mutated; in the promyelocytic line HL60 the second and in the rhabdomyosarcoma line RD301 the third nucleotide. For RD301 this implies that the normal glutamine residue at position 61 is replaced by histidine. In addition to the mutated N-ras gene the three cell lines have a normal N-ras gene which is indicative of the dominant character of the mutations.

Metabolic turnover of human c-rasH p21 protein of EJ bladder carcinoma and its normal cellular and viral homologs

The EJ bladder carcinoma oncogene is activated by a point mutation in the c-rasH proto-oncogene at the 12th amino acid codon. In an attempt to understand the mechanism of oncogenic activation, a comparative study was undertaken to examine the metabolic turnover and subcellular localization of the p21 protein encoded by the EJ oncogene, the viral oncogene, and its normal cellular homolog. Pulse-labeling experiments indicated that both c-ras p21 proteins were synthesized by a very similar pathway, as was observed for the viral p21 protein of Harvey murine sarcoma virus. The pro-p21 proteins were detected in free cytosol, and the processed products were associated with plasma membrane. The intracellular half-life of p21 proteins was determined by pulse-labeling and chasing in the presence of excess unlabeled methionine. Although both p21 proteins of EJ and the normal c-ras genes which are not phosphorylated have a half-life of 20 h, the viral p21 protein of Harvey murine sarcoma virus which includes a phosphorylated form is much more stable in cells, having a half-life of 42 h, apparently due to phosphorylation.

Human colon carcinoma Ki-ras2 oncogene and its corresponding proto-oncogene

We isolated cDNA clones corresponding to the normal human Ki-ras2 gene and to the transforming allele of the Ki-ras2 gene present in the human colon carcinoma cell line SW480. These two cDNAs encode p21 proteins which differ only at the amino acid at position 12. The normal cDNA encodes a glycine at this position, and the transforming allele encodes a valine. Expression of these cDNAs indicates that this amino acid 12 alteration confers oncogenic activity on the mutated gene. Analysis of the relationship of the cDNAs and Kirsten sarcoma virus ras gene to a genomic clone allowed us to identify two alternative 3' coding exons for the Ki-ras2 gene, suggesting that the Ki-ras2 gene encodes two p21 proteins which differ at their carboxy termini. Our data also show that only one of the p21s is necessary to convert cells to a tumorigenic phenotype.

Expression and characterization of ras mRNAs from Saccharomyces cerevisiae

The cellular homologs of the Harvey and Kirsten murine sarcoma virus oncogenes comprise a multigene family, ras, that displays striking evolutionary conservation. We recently reported [DeFeo-Jones et al., Nature (London) 306:707-709, 1983] the cloning of two ras homologs from the yeast Saccharomyces cerevisiae. The nucleotide sequences of these genes predict polypeptides that show remarkable homology to p21, the mammalian ras gene product. We have also found proteins in yeast lysates with serological cross-reactivity to p21 (Papageorge et al., Mol. Cell. Biol. 4:23-29, 1984). In this work, we explored the relationship between the immunoprecipitated proteins and the yeast ras genes. We show that both ras genes are expressed in the wild-type cell. Furthermore, we demonstrate by in vitro translation of hybrid-selected RASsc1 mRNA and immunoprecipitation of the translation products that the cloned RASsc1 gene encodes the proteins immunoprecipitated from yeast lysates by anti-p21 monoclonal antibody. Finally, we used anti-p21 monoclonal antibodies to detect a guanine nucleotide binding activity in yeast lysates. The structural and biochemical homologies between ras gene products of S. cerevisiae and mammalian cells suggest that information obtained by genetic analysis of ras function in a lower eucaryote should be applicable to higher organisms as well.

Guanosine nucleotide binding by highly purified Ha-ras-encoded p21 protein produced in Escherichia coli

High-level expression of the p21 protein product of the BALB murine sarcoma virus v-ras gene (similar to the product of the Harvey murine sarcoma virus v-Ha-ras gene) has been reported recently, and highly purified preparations of this protein have been obtained. We used a nitrocellulose filter assay for measuring the binding of GDP and GTP to the purified protein. Previously p21 antibodies had been used to precipitate p21-guanosine nucleotide complexes from crude extracts containing the protein. Using the filter assay, we find that the v-Ha-ras gene product binds [3H]GDP stoichiometrically. The binding is time-dependent and is faster at 30 degrees C than at 0 degrees C. Optimum binding is obtained in the presence of dithiothreitol and magnesium ions and at pH 7.4. In terms of its GDP binding activity, p21 is heat stable and pronase sensitive. The dissociation constants (Kd) of p21 for [3H]GDP and [3H]GTP, determined by Scatchard analysis, are 6 X 10(-8) M and 2.5 X 10(-8) M, respectively.

An artefact explains the apparent association of the transferrin receptor with a ras gene product

There is substantial evidence implicating ras genes in a number of human neoplasms. The ras genes of several human tumours display mutational changes which are likely to be responsible for their transforming activity. Normal cells also express ras genes, over-expression of which can induce cellular transformation. ras genes encode proteins of approximately 21,000 molecular weight (MW) (p21) that are localized to the inner surface of the plasma membrane. Much effort is being focused on the elucidation of the physiological function of ras-encoded proteins in normal and transformed cells, concentrating on interactions between p21 and other cellular elements. Recently, Finkel and Cooper reported that p21 in extracts of human bladder carcinoma cells is involved in a molecular complex with the transferrin receptor of these cells. This report aroused considerable interest, particularly as expression of the transferrin receptor has been linked to cell proliferation. I present here evidence that the apparent association of p21 and the transferrin receptor is an artefact of the immunoprecipitation technique.

The product of ras is a GTPase and the T24 oncogenic mutant is deficient in this activity

Ha-ras is a member of a multigene family in man which encode highly related proteins of 189 amino acids (p21). In vitro, ras proteins bind GTP, and p21 mutants with treonine at position 59 autophosphorylate at that residue. Mutation (at amino acids 12 or 61) and elevated expression of ras genes result in cell transformation in culture, and are also observed in many types of human tumours. Normal and mutant transforming ras proteins show no differences in localization, lipidation or GTP binding. However, mutations at position 12 in recombinant (Thr 59) p21 molecules were observed to affect autophosphorylation. We have expressed the full-length normal and T24 transforming (Gly----Val at position 12) Ha-ras proteins in Escherichia coli and have purified them to homogeneity (ref. 19 and M.G. et al., in preparation); these proteins bound GTP with approximately molar stoichiometry and with an affinity comparable to partially purified mammalian proteins. Microinjection of the T24 protein into quiescent rodent fibroblasts resulted in a rapid alteration in cell morphology, stimulation of DNA synthesis and cell division; in contrast, little response was observed with the normal protein. We now report that the normal ras protein has an intrinsic GTPase activity, yielding GDP and Pi. In contrast, the T24 transforming protein is reduced 10-fold in this activity. We suggest that this deficiency in GTPase is the probable cause for the transforming phenotype of the T24 protein.

Activation of a c-K-ras oncogene by somatic mutation in mouse lymphomas induced by gamma radiation

Mouse tumors induced by gamma radiation are a useful model system for oncogenesis. DNA from such tumors contains an activated K-ras oncogene that can transform NIH 3T3 cells. This report describes the cloning of a fragment of the mouse K-ras oncogene containing the first exon from both a transformant in rat-2 cells and the brain of the same mouse that developed the tumor. Hybrid constructs containing one of the two pieces were made and only the plasmid including the first exon from the transformant gave rise to foci in NIH 3T3 cells. There was only a single base difference (G----A) in the exonic sequence, which changed glycine to aspartic acid in the transformant. By use of a synthetic oligonucleotide the presence of the mutation was demonstrated in the original tumor, ruling out modifications during DNA-mediated gene transfer and indicating that the alteration was present in the thymic lymphoma but absent from other nonmalignant tissue. The results are compatible with gamma radiation being a source of point mutations.

Isolation, characterization, and chromosome assignment of mouse N-ras gene from carcinogen-induced thymic lymphoma

Treatment of mice with the carcinogen N-methylnitrosourea results in the development of thymic lymphomas with frequent involvement of the N-ras oncogene. The activated mouse N-ras gene was isolated from one of these lymphomas and, by transformation in concert with restriction digestion, a map of the gene was prepared and its approximate boundaries were determined. By means of somatic cell hybrids the normal N-ras gene was found to be unlinked to other members of the ras gene family.

A position 12-activated H-ras oncogene in all HS578T mammary carcinosarcoma cells but not normal mammary cells of the same patient

Among 21 human mammary tumors analyzed for transforming genes by transfection of NIH/3T3 cells, only DNA of a carcinosarcoma cell line, HS578T, registered as positive. A Harvey (H)-ras oncogene identified in this line was cloned in biologically active form and the activating lesion was identified as a single nucleotide substitution of adenine for guanine in the 12th codon. This results in substitution of aspartic acid for glycine at this position of the p21 coding sequence. Knowledge that this alteration creates a restriction site polymorphism for Msp I/Hpa II in the H-ras protooncogene made it possible to survey for the presence of the activated H-ras allele in normal cells as well as in clonally derived tumor cell lines of the same patient. We demonstrated the presence of unaltered H-ras alleles in normal HS578 cells. In contrast, every clonally derived HS578T tumor cell line analyzed contained the H-ras oncogene possessing the genetic alteration at position 12. These findings establish that activation of this oncogene was the result of a somatic event selected within all HS578T tumor cells.

Intrinsic GTPase activity distinguishes normal and oncogenic ras p21 molecules

The 21-kilodalton protein (p21) encoded by normal cellular Harvey-ras has been expressed in Escherichia coli as a fusion protein by using the pUC8 vector and has been purified to greater than 95% homogeneity by ion-exchange chromatography and gel filtration. The purified protein molecules possess intrinsic GTPase activity on the basis of the following criteria: (i) elution of the GTPase activity with p21 GDP-binding activity in two different chromatography systems, (ii) parallel thermal inactivation of GTPase activity and p21 GTP-binding activity, and (iii) immunoprecipitation of the GTPase activity with monoclonal antibodies to p21. At 37 degrees C, the rate of GTP hydrolysis by the purified normal p21 assayed in solution was 5.3-6.6 mmol/min per mol of p21. The rate of GTP hydrolysis by a form of p21 [Val12] encoded by a human oncogene was significantly lower (1.4-1.9 mmol/min per mol of p21). The presence of a threonine phosphate acceptor site at residue 59 also decreased p21 GTPase activity. For regulatory proteins that use GTP as part of their biochemical mechanism, the hydrolysis of GTP to GDP reverses the biological activity of the respective proteins. The observation that oncogenic forms of p21 lose GTPase activity suggests that GTP hydrolysis may be a biochemical event that inactivates the growth-promoting effects of a p21 X GTP complex.

Expression of normal and transforming H-ras genes in Escherichia coli and purification of their encoded p21 proteins

The H-ras gene of the BALB murine sarcoma virus (BALB-MSV) was placed under the transcriptional control of the tightly regulated PL promoter of bacteriophage lambda in the expression vectors pEV-vrf-1 and pRC23. Upon derepression of the PL promoter, large amounts (10-20% of total cellular protein) of the H-ras gene product p21 are synthesized in Escherichia coli. We constructed three H-ras gene expression vectors, designated pJCL-H5, pJCL-E30, and pJCL-33. pJCL-H5 directs the synthesis of p21, a fusion protein whose four amino-terminal residues are replaced by eight amino acids coded for by plasmid sequences. The 13 5' coding nucleotides of the BALB-MSV H-ras gene missing in pJCL-H5 were regenerated in pJCL-E30 by inserting a pair of complementary synthetic oligodeoxynucleotides. As a result, pJCL-E30 encodes a p21 protein, p21T, of sequence identical to that of the transforming p21 protein of BALB-MSV. pJCL-33 is a derivative of pJCL-E30 in which the 12th codon, AAA, a lysine codon, was replaced by GGA, a glycine codon. Thus, pJCL-33 directs the synthesis of a p21 protein, p21N, whose sequence corresponds to that of a normal cellular p21 protein. We report the purification of H-ras p21 proteins to apparent homogeneity by a method involving solubilization with chaotropic agents followed by reverse-phase high-performance liquid chromatography.

New human transforming genes detected by a tumorigenicity assay

We have developed a sensitive bioassay for transforming genes based on the tumorigenicity of cotransfected NIH3T3 cells in nude mice. The assay differs substantially from the NIH3T3 focus assay. Using it, we have detected the transfer of three transforming genes from the DNA of MCF-7, a human mammary carcinoma cell line. One of these is N-ras, which is amplified in MCF-7 DNA. The other two, which we have called mcf2 and mcf3, do not appear to be related to known oncogenes. We cannot detect their transfer by using the NIH3T3 focus assay. We do not yet know whether either mcf2 or mcf3 is associated with genetic abnormalities in MCF-7 cells.

Comparative biochemical properties of normal and activated human ras p21 protein

Human Ha-ras1 cDNAs encoding normal and activated p21 polypeptides have been efficiently expressed in Escherichia coli and the biochemical activities associated with each polypeptide compared. In addition to the guanine nucleotide binding activity, normal p21 displays a GTPase activity which is selectively impaired by a mutation which activates its oncogenic potential.

Activation of c-Ha-ras-1 proto-oncogene by in vitro modification with a chemical carcinogen, benzo(a)pyrene diol-epoxide

Chemical carcinogenesis generally proceeds via the formation of strongly electrophilic reactants, termed ultimate carcinogens. The observation that many ultimate carcinogens are potent mutagens and the results of studies on the covalent binding of carcinogens to cellular macromolecules suggest that tumour initiation results from mutations arising from the binding of ultimate carcinogens to DNA. Recently, gene transfer experiments have shown that some tumours contain activated oncogenes which are members of the ras gene family (reviewed in refs 6. 7) and which differ by single base pair substitutions from their non-transforming counterparts, the proto-oncogenes (see, for example, refs 8-11). Here we have used clones of the c-Ha-ras-1 proto-oncogene to show that reaction in vitro with an ultimate carcinogen generates a transforming oncogene when the modified DNA is introduced into NIH 3T3 cells. As DNA is the only cellular macromolecule present in the reactions, our experiments also show that reaction of an ultimate carcinogen with DNA alone can lead to the induction of mutations in mammalian cells.

Molecular cloning and chromosome assignment of murine N-ras

The murine N-ras gene was cloned by screening an EMBL-3 recombinant phage library with a human N-ras specific probe. Hybridization of two separate unique sequence N-ras probes, isolated from the 5' and 3' flanking sequences of the murine gene, to a mouse-Chinese hamster hybrid mapping panel assigns the N-ras locus to mouse chromosome three.

An activated rasN gene: detected in late but not early passage human PA1 teratocarcinoma cells

Early passages of the human teratocarcinoma cell line PA1 are not tumorigenic in nude mice, while late passages are. A transforming gene present in late passages of PA1 cells was isolated as a biologically active molecular clone and is a new isolate of the human rasN locus. Its transforming activity is due to a single G---A (G, guanine; A, adenine) point mutation at the codon for amino acid 12 which changes the codon for glycine so that an aspartic acid residue is expressed. In contrast to late passage PA1 cells (passages 106, 330, and 338), DNA from the PA1 cell line at early passages (passage 36) does not yield rasN foci in DNA transfection assays. Thus, the presence of an activated rasN in PA1 cells correlates with enhanced tumorigenicity of the cell line and, more importantly, may have arisen during cell culture in vitro.

Transformation of NIH 3T3 cells by microinjection of Ha-ras p21 protein

Alteration in gene structure has been shown to occur in some human tumours. These altered genes, termed oncogenes, were originally identified by their ability to induce foci of transformed cells on transfected mouse 3T3 cultures. The oncogene identified in the EJ/T24 human bladder carcinoma is similar to the transforming gene of BALB and Harvey murine sarcoma virus (MSV) and differs from its counterpart in normal cells by a single amino acid. All three of these Ha-ras genes direct the production of similar proteins (p21). While the ras gene appears to be involved in tumour formation in some situations, its role is unclear. The ras protein product (p21) binds guanine nucleotides and has a unique autophosphorylating activity, but no other enzymatic activity has been found. We report here the injection of purified Ha-ras p21 protein, made in Escherichia coli from the gene of BALB-MSV, into NIH 3T3 cells and show that the purified protein itself is sufficient to induce a transformed morphology. In addition, the injected protein stimulates quiescent cells to enter the S-phase of the cell cycle. This result clearly demonstrates that the ras gene functions directly through the protein product. It also establishes an assay for the protein which depends on its activity within a living cell. The transforming activity of a p21 ras protein equivalent to the product of the normal cellular ras gene, is also demonstrated.

Metabolic turnover of human c-rasH p21 protein of EJ bladder carcinoma and its normal cellular and viral homologs

The EJ bladder carcinoma oncogene is activated by a point mutation in the c-rasH proto-oncogene at the 12th amino acid codon. In an attempt to understand the mechanism of oncogenic activation, a comparative study was undertaken to examine the metabolic turnover and subcellular localization of the p21 protein encoded by the EJ oncogene, the viral oncogene, and its normal cellular homolog. Pulse-labeling experiments indicated that both c-ras p21 proteins were synthesized by a very similar pathway, as was observed for the viral p21 protein of Harvey murine sarcoma virus. The pro-p21 proteins were detected in free cytosol, and the processed products were associated with plasma membrane. The intracellular half-life of p21 proteins was determined by pulse-labeling and chasing in the presence of excess unlabeled methionine. Although both p21 proteins of EJ and the normal c-ras genes which are not phosphorylated have a half-life of 20 h, the viral p21 protein of Harvey murine sarcoma virus which includes a phosphorylated form is much more stable in cells, having a half-life of 42 h, apparently due to phosphorylation.