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

Transcriptional enhancer activity in the variable tandem repeat DNA sequence downstream of the human Ha-ras 1 gene

A short term transfection technique using the chloramphenicol acetyltransferase gene as an assay system has been employed to examine the presence of transcriptional regulatory sequences within the variable tandem repeat (VTR) DNA sequence located downstream of the human Ha-ras1 gene. Here we find that the VTR sequences possess an endogenous enhancer activity of both the normal and the T24 mutant Ha-ras1 gene.

Insulin induction of Xenopus laevis oocyte maturation is inhibited by monoclonal antibody against p21 ras proteins

Microinjection of transforming p21 ras protein induces maturation of Xenopus laevis oocytes, and the induction is blocked by coinjection of monoclonal antibody (Y13-259) against p21 ras proteins. Similar to other inducing agents, the effect of p21 ras protein is mediated via the appearance of maturation or meiosis-promoting factor activity. In addition, the neutralizing antibody markedly reduces oocyte maturation after insulin induction, whereas it fails to inhibit progesterone induction. Our results suggest that insulin induces maturation of oocytes via a different pathway than that of steroidal agents. The induction by insulin is ras dependent, and the action of ras may be directed at the steps before meiosis-promoting factor autocatalytic activation. These results suggest a role of p21 ras protein in the events associated with amphibian oocyte maturation.

Microinjection of ras p21 induces a rapid rise in intracellular pH

Quiescent mouse NIH 3T3 cells responded to microinjection of activated ras p21 with a rapid and sustained rise in intracellular pH (approximately 0.17 pH units). The p21-induced pH change was inhibited by amiloride treatment or growth of cells in medium low in sodium, suggesting a role for the Na+/H+ antiporter. Amiloride was found to suppress p21-induced mitosis, also.

Molecular cloning and characterization of an activated human c-raf-1 gene

Results of previous studies have shown that a raf-related transforming DNA sequence is present in NIH 3T3 transformants that are derived from GL-5-JCK human glioblastoma DNA transfection. The transforming DNA was molecularly cloned by using cosmid vector pJB8 to determine its structure and origin. Analyses of selected clones revealed that the transforming DNA consisted of three portions of human DNA sequences, with the 3' half of the c-raf-1 gene as its middle portion. This raf region was about 20 kilobases long and contained exons 8 to 17 and the poly(A) addition site. RNA blot analysis showed that the raf-related transforming DNA was transcribed into 5.3-, 4.8-, and 2.5-kilobase mRNAs; the 2.5-kilobase transcript was thought to be the major transcript. Immunoprecipitation analyses revealed that a 44-kilodalton raf-related protein was specifically expressed in the NIH 3T3 transformants. The raf-related transforming DNA was considered to be activated when its amino-terminal sequence was truncated and the DNA was coupled with a foreign promoter sequence. On hybridization analysis of the original GL-5-JCK glioblastoma DNA, no rearrangement of c-raf-1 was detectable in the tumor DNA. The rearrangement of c-raf-1 may have occurred during transfection or may have been present in a small population of the original tumor cells as a result of tumor progression.

Biochemical and biological properties of the human N-ras p21 protein

We characterized the normal (Gly-12) and two mutant (Asp-12 and Val-12) forms of human N-ras proteins produced by Escherichia coli. No significant differences were found between normal and mutant p21 proteins in their affinities for GTP or GDP. Examination of GTPase activities revealed significant differences between the mutant p21s: the Val-12 mutant retained 12% of wild-type GTPase activity, whereas the Asp-12 mutant retained 43%. Both mutant proteins, however, were equally potent in causing morphological transformation and increased cell motility after their microinjection into quiescent NIH 3T3 cells. This lack of correlation between transforming potency and GTPase activity or guanine nucleotide binding suggests that position 12 mutations affect other aspects of p21 function.

Occurrence in Saccharomyces cerevisiae of a gene homologous to the cDNA coding for the alpha subunit of mammalian G proteins

From cross-hybridization studies with cDNAs that code for the alpha subunits of rat brain guanine nucleotide-binding regulatory (G) proteins, we have isolated a gene from yeast Saccharomyces cerevisiae encoding an amino acid sequence that is highly homologous to the alpha subunit of the G protein that mediates inhibition of adenylate cyclase (Gi alpha) from rat brain. The gene, tentatively designated as GPA1, contains a contiguous, single open reading frame of 1416 nucleotides that codes for a protein of 472 amino acids with a calculated Mr of 54,075. The predicted amino acid sequence of the protein encoded by the GPA1 gene (tentatively designated as G protein 1 alpha or GP1 alpha) is remarkably homologous to the amino acid sequence of rat brain Gi alpha and the alpha subunit of the G protein of unknown function (Go alpha); the primary structure of the sites for GTP hydrolysis as well as GTP interaction are nearly identical. The main difference in the molecular sizes of yeast GP1 alpha (472 amino acids) and rat brain Gi alpha (355 amino acids) is due to the presence of a stretch of 110 extra amino acid residues in yeast GP1 alpha, which are inserted near the NH2-terminal one-third of mammalian Gi alpha. From blot-hybridization analysis, the size of the GP1 alpha mRNA was estimated as 1.7 kilobases.

Insulin induction of Xenopus laevis oocyte maturation is inhibited by monoclonal antibody against p21 ras proteins

Microinjection of transforming p21 ras protein induces maturation of Xenopus laevis oocytes, and the induction is blocked by coinjection of monoclonal antibody (Y13-259) against p21 ras proteins. Similar to other inducing agents, the effect of p21 ras protein is mediated via the appearance of maturation or meiosis-promoting factor activity. In addition, the neutralizing antibody markedly reduces oocyte maturation after insulin induction, whereas it fails to inhibit progesterone induction. Our results suggest that insulin induces maturation of oocytes via a different pathway than that of steroidal agents. The induction by insulin is ras dependent, and the action of ras may be directed at the steps before meiosis-promoting factor autocatalytic activation. These results suggest a role of p21 ras protein in the events associated with amphibian oocyte maturation.

Expression of oncogenes in human tumours with special reference to the head and neck region

A major recent advance in cancer research has been in the field of oncogenes. Oncogenes are genes with a proven cancer association and which appear to be particularly implicated in cellular regulation and proliferation. The oncogenic potential of specific cellular genes has now been recognised and this has influenced current thinking concerning the initiation of carcinogenesis. The specific role of an oncogene is still incompletely understood but research with one particular oncogene (ras) has demonstrated that it can be involved in more than one stage of multi-step carcinogenesis. New techniques are being developed and evaluated to determine the expression of specific oncogenes in normal and neoplastic tissues, with a view to using them in future diagnostic immuno-histopathological methods. This review describes the concept of oncogenes and discusses their role in the development of neoplasia. The results of the expression of various oncogenes in human malignancies with special reference to the head and neck regions are discussed. Finally, the future prospects of this research field are examined their and its possible implications in cancer therapy.

Activation of ras p21 transforming properties associated with an increase in the release rate of bound guanine nucleotide

An Ala-to-Thr substitution at position 59 activates the transforming properties of the p21ras protein without impairment of GTPase activity, a biochemical alteration associated with other activating mutations. To investigate the basis for the transforming properties of the Thr-59 mutant, we characterized guanine nucleotide release. This reaction exhibited a slow rate and stringent temperature requirements. To further dissect the release reaction, we used monoclonal antibodies directed against different epitopes of the p21 molecule. One monoclonal specifically interfered with nucleotide release, while others which recognized different regions of the molecule blocked nucleotide binding. Mutants with the Thr-59 substitution exhibited a three- to ninefold-higher rate of GDP and GTP release than normal p21 or mutants with other activating lesions. This alteration in the Thr-59 mutant would have the effect of increasing its rate of nucleotide exchange. In an intracellular environment with a high GTP/GDP ratio, this would favor the association of GTP with the Thr-59 mutant. Consistent with knowledge of known G-regulatory proteins, these findings support a model in which the p21-GTP complex is the biologically active form of the p21 protein.

Expression of the Kirsten ras viral and human proteins in Escherichia coli

The expression vectors pINIII-A and pINIII (lpp p5) were used to construct plasmids which direct the synthesis in Escherichia coli of the Kirsten ras viral (v-Ki-ras) and human cellular (c-Ki-ras) oncogene products as fusion proteins containing 9 and 10 extra amino acids, respectively, at their N termini. Authenticity of the bacterially produced proteins was determined by immunoprecipitation and immunoblot analyses with ras-specific monoclonal antibodies. After induction with isopropyl-beta-D-thiogalactopyranoside, the viral protein represented approximately 20% of the total cellular protein. The majority of the protein was found in the postsonication low-speed centrifugation pellet. The synthesized viral protein was active in GTP binding, as judged by autophosphorylation and photoaffinity labeling assays.

Characterization of two members of the rho gene family from the yeast Saccharomyces cerevisiae

The rho genes comprise an evolutionarily conserved family with significant homology to the ras oncogene family. Two members of the rho family were isolated from the yeast Saccharomyces cerevisiae and characterized by DNA sequence analysis. The yeast genes RHO1 and RHO2 are 70% and 57% identical, respectively, to the rho gene of the marine snail Aplysia, and they are 53% identical to each other. Inactivation of these genes showed that RHO1 is required for cell viability, while RHO2 is not an essential gene. A mutant allele of RHO1 (RHO1-His68) was constructed with a mutation analogous to one that activates the transforming potential of the human HRAS gene. Diploid strains containing RHO1-His68 in either low or high copy number are unable to sporulate, and the mutant allele is dominant over wild-type RHO1. The requirement for RHO1 cannot be circumvented by introduction of high copy number plasmids containing either the gene encoding the catalytic subunit of cAMP-dependent protein kinase or the mutant allele RAS2-Val19. Despite the conservation between the rho and ras gene families, the finding that RHO1 functions independently of the adenylate cyclase cAMP-dependent protein kinase cascade suggests that rho and ras are involved in distinct biochemical pathways.

Mutational analysis of a ras catalytic domain

We used linker insertion-deletion mutagenesis to study the catalytic domain of the Harvey murine sarcoma virus v-rasH transforming protein, which is closely related to the cellular rasH protein. The mutants displayed a wide range of in vitro biological activity, from those that induced focal transformation of NIH 3T3 cells with approximately the same efficiency as the wild-type v-rasH gene to those that failed to induce any detectable morphologic changes. Correlation of transforming activity with the location of the mutations enabled us to identify three nonoverlapping segments within the catalytic domain that were dispensable for transformation and six other segments that were required for transformation. Segments that were necessary for guanosine nucleotide (GDP) binding corresponded to three of the segments that were essential for transformation; two of the three segments share strong sequence homology with other purine nucleotide-binding proteins. Loss of GDP binding was associated with apparent instability of the protein. Lesions in two of the three other required regions significantly reduced GDP binding, while small lesions in the last required region did not impair GDP binding or membrane localization. We speculate that this latter region interacts with the putative cellular target of ras. The results suggest that transforming ras proteins require membrane localization, guanosine nucleotide binding, and an additional undefined function that may represent interaction with their target.

Monoclonal antibody Y13-259 recognizes an epitope of the p21 ras molecule not directly involved in the GTP-binding activity of the protein

The p21 products of ras proto-oncogenes are GTP-binding proteins with associated GTPase activity. Recent studies have indicated that ras p21 may be required for the initiation of normal cell DNA synthesis, since microinjection of a monoclonal antibody, Y13-259, blocks serum stimulation of DNA synthesis in quiescent cell cultures (L. S. Mulcahy, M.R. Smith, and D. W. Stacey, Nature [London] 313:241-243, 1985). We localized the structural domain within the p21 molecule recognized by the Y13-259 monoclonal antibody. By analysis of a series of bacterially expressed p21 deletion mutants, the monoclonal antibody was found to interact with a region between positions 70 and 89 in the p21 amino acid sequence. By comparison of the coding sequences of different p21 proteins recognized by this monoclonal antibody, a highly conserved amino acid region between positions 70 and 81 was found to be the most likely site for the epitope detected by the Y13-259 antibody. This monoclonal antibody was further shown not to interfere directly with in vitro biochemical functions of the molecule, including GTP binding, GTPase, and autokinase activities.

Cellular events during hepatocarcinogenesis in rats and the question of premalignancy

The cellular, biochemical, and genetic changes that occur in the liver of rats exposed to chemical hepatocarcinogens are reviewed. Multiple new cell types appear in the liver of carcinogen-treated rats including foci, nodules, ducts, oval cells, and atypical hyperplastic areas. The application of phenotypic markers for these cell types suggests that hepatocellular carcinomas may arise from more than one cell type, including a putative liver stem cell that proliferates following carcinogen exposure. Study of DNA, RNA, and proteins produced by hepatocellular carcinomas and putative premalignant cells has so far failed to identify a gene or gene product clearly associated with the malignant or premalignant phenotype. Understanding the cellular lineage from normal cell through putative premalignant cell to cancer is critical to understanding the process of carcinogenesis. Application of new immunological (monoclonal antibody, transplantation) and molecular biological (gene cloning, oncogene identification) approaches to this problem holds promise that the process of hepatocarcinogenesis will be better known in the near future.

Gangliosides as bimodal regulators of cell growth

The B subunit of cholera toxin, which binds specifically to several molecules of ganglioside galactosyl-(beta 1----3)-N-acetylgalactosyminyl(beta 1----4)-[N- acetylneuraminyl(alpha 2----3)]-galactosyl(beta 1----4)glucosyl(beta 1----1) ceramide (GM1) on the cell surface, stimulated DNA synthesis and cell division in quiescent, nontransformed mouse 3T3 cells in a dose-dependent manner. In addition, the B subunit potentiated the response of the 3T3 cells to other mitogens, such as epidermal growth factor, platelet-derived growth factor, and insulin. This synergistic effect indicates that the B subunit does not act identically to any of these growth factors but probably modulates a common effector system crucial for cell proliferation. In distinct contrast, the B subunit inhibited the growth of ras-transformed 3T3 cells as well as rapidly dividing normal 3T3 cells. Thus, the same cells, depending on their state of growth, exhibited a bimodal response to the B subunit. We conclude that endogenous gangliosides may be bimodal regulators of positive and negative signals for cell growth.

Loss of platelet-derived growth factor-stimulated phospholipase activity in NIH-3T3 cells expressing the EJ-ras oncogene

Data indicating that the 21-kDa protein (p21) Harvey-ras gene product shares sequence homology with guanine nucleotide-binding proteins (G proteins) has stimulated research on the influence(s) of p21 on G-protein-regulated systems in vertebrate cells. Our previous work demonstrated that NIH-3T3 mouse cells expressing high levels of the cellular ras oncogene isolated from the EJ human bladder carcinoma (EJ-ras) exhibited reduced hormone-stimulated adenylate cyclase activity. We now report that in these cells another enzyme system thought to be regulated by G proteins is inhibited, namely phospholipases A2 and C. NIH-3T3 cells incubated in plasma-derived serum release significant levels of prostaglandin E2 (PGE2) as determined by radioimmunoassay when exposed to platelet-derived growth factor (PDGF) at 2 units/ml; the levels of PGE2 released from EJ-ras-transfected cells are only 3% those of controls despite a similar basal (unstimulated) release from control and EJ-ras-transfected cells. The lack of PDGF-stimulated PGE2 release from EJ-ras-transfected cells is not due to a defect in the prostaglandin cyclooxygenase enzyme, since incubation of control cells and EJ-ras-transfected cells in 0.33, 3.3, or 33 microM arachidonate resulted in identical levels of PGE2 release. The lack of PDGF-stimulated PGE2 release from EJ-ras-transfected cells also does not result from the loss of functional PDGF receptors. EJ-ras-transformed cells bind 70% as much 125I-labeled PDGF as control cells and are stimulated to incorporate [3H]thymidine and to proliferate after exposure to PDGF. Moreover, this inhibition is not likely the result of a secondary cellular effect related to the transformed phenotype, since NIH-3T3 cells transformed by v-src released PGE2 at wild-type levels after exposure to PDGF. Determination of total water-soluble inositolphospholipids and changes in the specific activities of phosphatidylcholine in control and EJ-ras-transfected cells demonstrated that PDGF-stimulated phospholipase C and A2 activities are inhibited in the EJ-ras-transfected cells.

Biochemical and biological properties of the human N-ras p21 protein

We characterized the normal (Gly-12) and two mutant (Asp-12 and Val-12) forms of human N-ras proteins produced by Escherichia coli. No significant differences were found between normal and mutant p21 proteins in their affinities for GTP or GDP. Examination of GTPase activities revealed significant differences between the mutant p21s: the Val-12 mutant retained 12% of wild-type GTPase activity, whereas the Asp-12 mutant retained 43%. Both mutant proteins, however, were equally potent in causing morphological transformation and increased cell motility after their microinjection into quiescent NIH 3T3 cells. This lack of correlation between transforming potency and GTPase activity or guanine nucleotide binding suggests that position 12 mutations affect other aspects of p21 function.

Tissue localization of Drosophila melanogaster ras transcripts during development

Three ras homologs have been identified in Drosophila melanogaster. Here we describe the tissue distribution of their transcripts as analyzed by in situ hybridization. The RNAs of the three genes show a similar distribution at every developmental stage examined. In embryos, the transcripts are uniformly distributed. In larvae, ras transcripts are restricted to dividing cells (e.g., imaginal disks, gonads, and brain). At the adult stage, several tissues contain ras transcripts. The strongest hybridization signals are localized to the adult ovaries and to the cortex of the brain and ganglia, which at this stage are comprised of differentiated, nondividing cells. The tissue distribution of ras transcripts in D. melanogaster suggests that the ras proteins have multiple roles during development which may be related to both the proliferative and differentiated states of the tissues.

Activation of ras p21 transforming properties associated with an increase in the release rate of bound guanine nucleotide

An Ala-to-Thr substitution at position 59 activates the transforming properties of the p21ras protein without impairment of GTPase activity, a biochemical alteration associated with other activating mutations. To investigate the basis for the transforming properties of the Thr-59 mutant, we characterized guanine nucleotide release. This reaction exhibited a slow rate and stringent temperature requirements. To further dissect the release reaction, we used monoclonal antibodies directed against different epitopes of the p21 molecule. One monoclonal specifically interfered with nucleotide release, while others which recognized different regions of the molecule blocked nucleotide binding. Mutants with the Thr-59 substitution exhibited a three- to ninefold-higher rate of GDP and GTP release than normal p21 or mutants with other activating lesions. This alteration in the Thr-59 mutant would have the effect of increasing its rate of nucleotide exchange. In an intracellular environment with a high GTP/GDP ratio, this would favor the association of GTP with the Thr-59 mutant. Consistent with knowledge of known G-regulatory proteins, these findings support a model in which the p21-GTP complex is the biologically active form of the p21 protein.

A GTP-binding protein of Escherichia coli has homology to yeast RAS proteins

The DNA sequence of a gene (era) located immediately downstream of the gene (rnc) encoding ribonuclease III of Escherichia coli was determined and found to encode a protein of 316 amino acid residues. The amino acid sequence of this protein, Era, has significant similarity to the yeast RAS proteins. Overexpression of the Era protein was achieved and GTP cross-linking experiments demonstrated that the protein was indeed capable of binding GTP, as are the yeast and mammalian ras gene products. These data indicate that ras-related sequences occur not only in eukaryotes but also in prokaryotes.

Identification of the protein encoded by the human diffuse B-cell lymphoma (dbl) oncogene

The dbl oncogene was initially isolated from a human diffuse B-cell lymphoma. Antisera from mice bearing tumors induced by this oncogene specifically detected a protein of about 66 kDa (p66) in dbl transformants. dbl cDNA-selected poly(A)+ RNA isolated from a transfectant clone expressing p66 directed the in vitro synthesis of this protein, establishing that it is encoded by dbl. Subcellular localization studies revealed that p66 is a cytoplasmic protein distributed between cytosol and crude membrane fractions. Moreover, p66 was shown to be a phosphoprotein, with phosphorylation specific to serine residues. Our characterization of the dbl-encoded protein appears to distinguish this transforming gene product from those of other known oncogenes.

DNA analysis in human disease

The analysis of human DNA using recombinant DNA technology is fast becoming an integral part of the diagnosis, assessment, and prevention of inherited and somatic genetic disease. The rationale underlying these methods of analysis is discussed, and the nature and extent of mutational change in heritable disorders and neoplastic development is outlined.

c-K-ras codon 12 GGT-CGT point mutation. An infrequent event in human lung cancer

Hu-c-ras represent a family of oncogenes which are capable of inducing malignant transformation in the NIH/3T3 mouse cell line. Associated with this transformation are specific point mutations observed in the 12th and 61st codon of c-K-ras and N-ras and c-Ha-ras, respectively. These base changes generate, in some instances, a new restriction enzyme cleavage site and a restriction fragment length polymorphism (RFLP). One such RFLP has recently been reported for the mutation GGT-CGT at codon 12 of c-K-ras. Our data suggest that this point mutation is rarely present in human lung cancer and therefore is not likely to play a major role in cancer development.

Development of quantitative liquid competition radioimmunoassays for the ras oncogene and proto-oncogene p21 products

The ras gene family of rodents and humans is highly conserved and consists of several distinct genes, i.e., rodent Harvey and Kirsten, and human Harvey, Kirsten and neuroblastoma. This gene family mediates transformation via (1) a point-mutation resulting in the change of one amino acid in the 21 kDA ras gene product (p21) or (2) increased expression of ras p21. Group-specific, type-selective and interspecies indirect binding liquid competition radioimmunoassays (RIAs), capable of providing truly quantitative analyses of the 21 ras oncogene and proto-oncogene products, have been developed. Using purified recombinant ras p21 from Escherichia coli expressing the full-length T24 mutant human Harvey-ras gene protein product as a standard in these RIAs, we have defined the absolute numbers of pg, fM and molecules of ras p21 in: (1) E. coli expressing the point-mutated or proto-ras p21 and (2) mammalian cell lines of human and murine origin. Two of the RIAs developed can be termed group-specific in that they have the ability to detect the point-mutated and proto forms of all 3 human ras genes (Harvey, Kirsten, and neuroblastoma), while the third RIA is type-selective, since it detects an antigenic determinant located primarily on the Harvey ras p21. All 3 RIAs are interspecies-specific since they are able to detect ras p21 in rodent as well as human cells. The adaptability of the RIAs to various assay conditions and ease of methodology make these immunoassays applicable to the study of several parameters associated with ras p21 expression. These assays, used in conjunction with specific cDNA probes to identify specific ras proto-oncogenes or point-mutated oncogenes being expressed, now provide truly quantitative analysis of ras p21 in mammalian cells to further the study of the association between ras p21 expression and transformation.

Monoclonal antibody specific for an activated RAS protein

Activated RAS transforming genes that encode proteins (p21s) with amino acid substitutions at positions 12, 13, or 61 have been detected in 10-20% of human neoplasms. This report describes a monoclonal antibody (DWP) raised against a synthetic peptide corresponding to amino acids 5-16 of a mutated RAS gene encoding Val instead of Gly at position 12. DWP reacted in competition assays with peptides containing Val or Cys at position 12, but did not react with peptides containing Gly, Arg, Ser, Ala, Asp, or Glu at position 12. Immunoblot analysis of transformed NIH cells and human carcinoma cell lines showed that DWP reacts specifically with activated RAS proteins containing Val at position 12 and not with normal p21s or p21s activated by other amino acid substitutions at positions 12 and 61. Immunohistochemical studies showed that DWP-labeled transformed NIH cells and human carcinoma cells contained p21s with either Val or Cys at position 12 but not normal or other activated p21s. In contrast to the specificity seen with human carcinoma cell lines, analysis of formalin-fixed, primary carcinoma specimens indicated that positive immunoperoxidase staining with DWP did not necessarily correlate with immunoblot and transfection assays for the presence of activated RAS proteins. Immunohistochemical studies did show, however, that DWP preferentially binds human carcinoma cells.

Antibody of predetermined specificity to a carboxy-terminal region of H-ras gene products inhibits their guanine nucleotide-binding function

The high prevalence of ras oncogenes in human tumors has given increasing impetus to efforts aimed at elucidating the structure and function of their p21 products. To identify functionally important domains of the p21 protein, antibodies were generated against synthetic peptides corresponding to various regions of the protein. Antibodies directed against a synthetic peptide fragment corresponding to amino acid residues 161 to 176 in the carboxy-terminal region of the H-ras-encoded p21 molecule specifically recognized H-ras-encoded p21 proteins. This antibody was also shown to strikingly and specifically inhibit the guanine nucleotide-binding function of the p21 protein. The inability of p21 protein to bind guanine nucleotides was associated with a lack of autophosphorylation or GTPase activities. These studies suggest that a region toward its carboxy terminus is directly or indirectly involved in the guanine nucleotide-binding function of the p21 molecule.

Biochemical and biological activities of N-ras proteins

Recombinant N-ras proteins, expressed and produced from synthetic genes cloned into E. coli, have been tested in vitro for GTPase and autophosphorylation activity. The genes corresponding to the assayed proteins were tested for their ability to transform NIH 3T3 cells. Mutations of glutamine to lysine at amino acid position 61 and glycine to valine at position 12 were both found to activate the ability of the N-ras gene to transform NIH 3T3 cells while significantly reducing the GTPase activity of the corresponding protein. N-ras proteins were also found to autophosphorylate in the presence of GTP when a threonine acceptor amino acid is provided at position 59.

p21 ras proteins and guanine nucleotides modulate the phosphorylation of 36- and 17-kilodalton mitochondria-associated proteins

We have found that, when isolated rat liver mitochondria are incubated with [gamma-32P]ATP, there is phosphorylation of 36- and 17-kDa proteins. These proteins together with their protein kinase(s) are released as a complex by incubation of the isolated rat liver mitochondria at 20 degrees C for 30 min with 10 mM glucose 6-phosphate, 0.5 mM inositol phosphate, or 0.01 mM inositol triphosphate. Phosphorylation of the 36- and 17-kDa proteins in this soluble protein fraction is modulated by p21 proteins encoded by ras oncogenes and synthesized in Escherichia coli via recombinant DNA methods. A normal p21 ras protein stimulates phosphorylation of the 36-kDa protein and inhibits phosphorylation of the 17-kDa protein, whereas two transforming p21 ras proteins inhibit phosphorylation of both the 36- and 17-kDa proteins. Although GDP and 5'-guanylyl imidodiphosphate also influence the phosphorylation of these proteins, we present evidence that the effects of p21 ras protein are not simply due to their bound GDP. This novel system may be useful for further studies on the biochemical functions of the p21 ras proteins.

Activating mutations of the c-Ha-ras protooncogene in chemically induced hepatomas of the male B6C3 F1 mouse

Activated c-Ha-ras protooncogenes have recently been identified in the DNA of some spontaneous hepatic tumors found in 2-year-old B6C3 F1 mice. Activation of c-Ha-ras has now been demonstrated in DNA from well-differentiated hepatomas initiated by a single dose of carcinogen given to male B6C3 F1 mice at 12 days of age. DNA from each of 25 hepatomas, induced by N-hydroxy-2-acetylaminofluorene, vinyl carbamate, or 1'-hydroxy-2',3'-dehydroestragole, containing transforming activity in the NIH 3T3 transfection assay. Southern analysis of NIH 3T3 cells transformed by DNA from 24 of these hepatomas revealed amplified and/or rear-ranged restriction fragments homologous to a Ha-ras probe. The other tumor contained an activated Ki-ras gene. Immunoprecipitation and NaDodSO4/PAGE analysis of p21 ras proteins in NIH 3T3 transformants derived from a majority of the hepatomas suggested that the activating mutations were localized in the 61st codon of the c-Ha-ras gene. Creation of a new Xba I restriction site by an AT----TA transversion at the second position of codon 61 was detected in DNA from primary tumors and NIH 3T3 cells transformed by DNA from 6 of 7 vinyl carbamate- and 5 of 10 1'-hydroxy-2',3'-dehydroestragole-induced hepatomas. Selective oligonucleotide hybridization demonstrated a CG----AT transversion at the first position of the 61st codon in NIH 3T3 transformants derived from 7 of 7 N-hydroxy-2-acetylaminofluorene-induced hepatomas. By the same criterion, an AT----GC transition at the second position of codon 61 was the activating mutation in 1 of 7 vinyl carbamate- and 5 of 10 1'-hydroxy-2',3'-dehydroestragole-induced tumors. Thus, c-Ha-ras activation is apparently an early event in B6C3 F1 mouse hepatocarcinogenesis that results directly from reaction of ultimate chemical carcinogens with this gene in vivo.

A unified theory for the development of cancer

It is postulated that cancer is the result of genetic and epigenetic changes that occur mainly in stem (precursor) cells of various cell types. I propose that there are three classes of genes which are involved in the development of cancer. These are: Class I, II and III oncogenes. The classification is based on the way the oncogene acts at the cellular level to further the development of cancer. Genetic changes, that is point mutations, deletions, inversions, amplifications and chromosome translocations, gains or losses in the genes themselves or epigenetic changes in the genes (e.g. DNA hypomethylation) or in the gene products (RNA or protein) are responsible for the development of cancer. Changes of oncogene activity have a genetic or epigenetic origin or both and result in quantitative or qualitative differences in the oncogene products. These are involved in changing normal cells into the cells demonstrating a cancer phenotype (usually a form of dedifferentiated cell) in a multistep process. There are several pathways to cancer and the intermediate steps are not necessarily defined in an orderly fashion. Activation of a particular Class I or II oncogene and inactivation of a Class III oncogene could occur at any step during the development of cancer. Most benign or malignant tumors consist of a heterogeneous mixture of dedifferentiated cells arising from a single cell.

ras p21 deletion mutants and monoclonal antibodies as tools for localization of regions relevant to p21 function

Deletion mutants of the viral Harvey ras oncogene were generated by removing different lengths of the gene from either the amino or the carboxyl terminus. The deletion mutants, ras p21 expressed in Escherichia coli, yielded proteins of approximately 8, 10, 12, 14, 17, 18, 19, and 20 kDa. These proteins were utilized to identify epitopes recognized by a series of recently generated monoclonal antibodies as well as some previously reported monoclonal antibodies. Monoclonal antibodies that inhibited GTP binding, a major biochemical activity of the p21 protein, recognized two major regions of the protein. These regions were localized from amino acids 5 to 69 and 107 to 164, respectively, and were separated by another stretch from residues 70 to 106, whose antigenic determinants were not directly involved in GTP binding. Thus, the mapping of epitopes within the p21 molecule recognized by monoclonal antibodies has made it possible to localize important functional regions within the ras p21 molecule.

Mutagenesis of the Ha-ras oncogene in mouse skin tumors induced by polycyclic aromatic hydrocarbons

The importance of mutational activation of the Ha-ras protooncogene in polycyclic aromatic hydrocarbon-induced mouse skin tumors was investigated in a complete carcinogenesis model using repetitive applications of 7,12-dimethylbenz[a]anthracene (DMBA), or in an initiation-promotion model using a single application of dibenz[c,h]acridine (DB[c,h]ACR) or benzo[a]pyrene (B[a]BP) followed by chronic treatment with phorbol 12-myristate 13-acetate. DNA isolated from carcinomas induced by DMBA or DB[c,h]ACR, but not by B[a]P, efficiently transformed NIH 3T3 cells, and a high percentage of the transformed foci had an amplified Ha-ras gene. Restriction enzyme Southern blot analysis and DNA sequencing revealed that the amplified Ha-ras genes of the transformants had an A----T transversion in the second position of the 61st codon. The same mutation was also detected in primary tumor DNA in a high percentage of the DMBA- or DB[c,h]ACR-induced carcinomas. Identification of the mutation in NIH 3T3 cells transformed with DNA from DB[c,h]ACR-induced benign skin papillomas suggests that it is an early event in skin carcinogenesis. Thus, mutation of the 61st codon of the Ha-ras-1 gene appears to be a critical step in the formation of mouse skin tumors induced in both of the two models tested. Our analyses also delineate two other classes of hydrocarbon-induced carcinomas--namely, tumors whose DNAs efficiently transform 3T3 cells but do not contain mutated ras genes and tumors whose DNAs do not transform 3T3 cells.

Clinical implications of oncogene activation in human neuroblastomas

Amplification of the oncogene N-myc has been identified in almost all human neuroblastoma cell lines tested. Eighty-nine primary neuroblastomas from untreated patients were studied to determine the frequency and clinical significance of N-myc amplification. Tumor DNA was analyzed by hybridization with the radiolabeled probe pNB-1 for N-myc. Amplification (3-300 copies) of the N-myc gene was found in 34 of the 89 tumors (38%). Amplification was not found in 8 Stage I or 5 Stage IV-S tumors, but it was found in 2 of 16 with Stage II, 13 of 20 with Stage III, and 19 of 40 with Stage IV tumors (P less than 0.01). Correlation of N-myc amplification with progression-free survival (PFS) indicated that N-myc amplification was associated with a worse prognosis (P less than 0.0001). The PFS at 18 months was 70%, 30%, and 5% for patients whose tumors had 1, 3-10, and more than 10 copies, respectively. Even within individual stages, the presence of N-myc amplification correlated with rapid progression. For instance, of 16 patients with Stage II disease, the 2 with N-myc amplification developed progressive disease rapidly, whereas only 1 of 14 without amplification progressed (P = 0.03). Similarly, those with Stage III and IV disease whose tumors have multiple copies of N-myc had a substantially worse prognosis. The correlation between N-myc amplification and age at diagnosis was also analyzed. Although N-myc amplification was detected in only 4 of 28 infants less than 1 year of age, compared to 30 of 61 older patients (P less than 0.005), this difference disappeared when corrected for disease stage. The results suggest that N-myc amplification is a powerful prognostic indicator, and that this gene may play an important role in the progression of certain neuroblastomas.

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

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

Mutational analysis of a ras catalytic domain

We used linker insertion-deletion mutagenesis to study the catalytic domain of the Harvey murine sarcoma virus v-rasH transforming protein, which is closely related to the cellular rasH protein. The mutants displayed a wide range of in vitro biological activity, from those that induced focal transformation of NIH 3T3 cells with approximately the same efficiency as the wild-type v-rasH gene to those that failed to induce any detectable morphologic changes. Correlation of transforming activity with the location of the mutations enabled us to identify three nonoverlapping segments within the catalytic domain that were dispensable for transformation and six other segments that were required for transformation. Segments that were necessary for guanosine nucleotide (GDP) binding corresponded to three of the segments that were essential for transformation; two of the three segments share strong sequence homology with other purine nucleotide-binding proteins. Loss of GDP binding was associated with apparent instability of the protein. Lesions in two of the three other required regions significantly reduced GDP binding, while small lesions in the last required region did not impair GDP binding or membrane localization. We speculate that this latter region interacts with the putative cellular target of ras. The results suggest that transforming ras proteins require membrane localization, guanosine nucleotide binding, and an additional undefined function that may represent interaction with their target.

Suppression of tumorigenicity with continued expression of the c-Ha-ras oncogene in EJ bladder carcinoma-human fibroblast hybrid cells

A human tumor cell line (EJ) expressing an activated c-Ha-ras oncogene was fused with a normal human fibroblast cell line. This fusion resulted in hybrids that behaved as transformed cells in culture but failed to form tumors in nude (athymic) mice. After repeated cell passage, two tumorigenic segregants of the hybrids arose in culture. The levels of expression of activated c-Ha-ras mRNA and its protein product, p21, were similar in the EJ cell line, the nontumorigenic hybrids, and the tumorigenic segregants. DNA transfections of the hybrids were performed with activated c-Ha-ras plasmid constructs, and transfectants expressing a 2-fold level of c-Ha-ras relative to the hybrid cells were found to maintain the nontumorigenic phenotype. We suggest that expression of the active c-Ha-ras oncogene is insufficient for the malignant transformation of these human cells.

Tissue localization of Drosophila melanogaster ras transcripts during development

Three ras homologs have been identified in Drosophila melanogaster. Here we describe the tissue distribution of their transcripts as analyzed by in situ hybridization. The RNAs of the three genes show a similar distribution at every developmental stage examined. In embryos, the transcripts are uniformly distributed. In larvae, ras transcripts are restricted to dividing cells (e.g., imaginal disks, gonads, and brain). At the adult stage, several tissues contain ras transcripts. The strongest hybridization signals are localized to the adult ovaries and to the cortex of the brain and ganglia, which at this stage are comprised of differentiated, nondividing cells. The tissue distribution of ras transcripts in D. melanogaster suggests that the ras proteins have multiple roles during development which may be related to both the proliferative and differentiated states of the tissues.

Activation of the transforming potential of p60c-src by a single amino acid change

Previous work showed that overexpression of the cellular src (c-src) gene does not cause transformation of chicken cells in culture. However, viral stocks isolated from cells transfected with Rous sarcoma virus DNA containing the c-src gene in place of the viral src gene did occasionally produce foci. Virus obtained from these foci were highly transforming and appeared to arise via spontaneous mutation in the c-src-containing viral populations. The p60 proteins of the transforming mutant src viruses were found to have higher levels of in vitro tyrosine kinase activity than the levels observed with the parental viruses. In this study, we have molecularly cloned the src DNA sequences of two transforming mutant src viruses. When compared to the DNA sequence of the parental c-src viruses, the mutant viruses contain single point mutations that result in single amino acid changes in the src gene products (p60 proteins). Both amino acid changes reside in the tyrosine kinase domain of the protein. The mutation detected in one virus involves replacement of the normal Glu-378 in p60c-src by Gly, whereas the p60 of the other transforming virus has Phe instead of the normal Ile-441. Our data indicate that when p60c-src is expressed at elevated levels in a retroviral context, a single amino acid change in its primary sequence can activate the kinase activity of this protein and cause cellular transformation.

Reduced hormone-stimulated adenylate cyclase activity in NIH-3T3 cells expressing the EJ human bladder ras oncogene

Recent studies have shown that the 21-kilodalton protein (p21) Ha-ras gene product shares sequence homology with and may exhibit biochemical properties similar to the mammalian guanine nucleotide-binding proteins. These data suggested that one of the biochemical functions of p21 in the vertebrate cell may be to regulate adenylate cyclase [ATP pyrophosphate-lyase (cyclizing), EC 4.6.1.1]. We determined both in intact NIH-3T3 murine cells and in membranes isolated from these cells that the hormone-stimulated adenylate cyclase activity of cells expressing the EJ human bladder carcinoma oncogene (EJ-ras) is significantly reduced compared with control cells. Thus, the levels of cAMP measured in the EJ-ras-transformed cells by radioimmunoassay are reduced 78% and 93% after prostaglandin and isoproterenol stimulation, respectively, compared with the levels in control cells. Treatment of the EJ-ras-transformed cells with pertussis toxin or cholera toxin did not correct the alterations in adenylate cyclase activity. Cells expressing the normal human Ha-ras gene displayed intermediate levels of adenylate cyclase hormone sensitivity; these levels of adenylate cyclase activity were greater than those in the EJ-ras-transformed cells but lower than in control cells. Hormone-stimulated adenylate cyclase activities in cells transfected with Rous sarcoma virus DNA were similar to those in control cells. These data support the hypothesis that both the normal and mutated Ha-ras p21s are related to guanine nucleotide-binding proteins.

Interaction of Trypanosoma cruzi adenylate cyclase with liver regulatory factors

Trypanosoma cruzi adenylate cyclase catalytic subunits may interact with regulatory factors from rat liver membranes, reconstituting heterologous systems which are catalytically active in assay mixtures containing MgATP. The systems show stimulatory responses to glucagon and guanosine 5'-[beta gamma-imido]triphosphate (p[NH]ppG) or fluoride. Reconstitution was obtained by three different methods: fusion of rat liver membranes (pretreated with N-ethylmaleimide) to T. cruzi membranes; interaction of detergent extracts of rat liver membranes with T. cruzi membranes; or interaction of purified preparations of T. cruzi adenylate cyclase and of liver membrane factors in phospholipid vesicles. The liver factors responsible for the guanine nucleotide effect were characterized as the NS protein. Data also indicate that reconstitution requires the presence of a membrane substrate.

Genetic predisposition to human lung cancer

The influence of polymorphic variants of the human c-Ha-ras gene on predisposition to lung cancer has been investigated. The human c-Ha-ras gene has been shown to reside on a polymorphic BamH1 restriction fragment. This restriction fragment length polymorphism (RFLP) results from variation in the size of a region of repetitive DNA 3' to the gene. An attempt has been made to characterise and compare the c-Ha-ras RFLP's in a normal population and in a group of cancer patients. DNA was extracted from the white blood cells of 101 normal donors and four common Ha-ras alleles identified, with occasional rare alleles of various sizes. The allele frequencies were examined in 132 lung cancer patients, comprising 66 individuals with small cell carcinoma of the lung (SCCL) and 66 with non-small cell carcinoma of the lung (non-SCCL). An abnormal allele distribution was found in individuals with non-SCCL compared to both control and SCCL values suggesting a degree of genetic pre-position to non-SCCL. In addition, analysis of the Ha-ras RFLP's in solid samples inferred a deletion of material from the short arm of chromosome 11 in two of 16 informative samples.

Monoclonal antibody Y13-259 recognizes an epitope of the p21 ras molecule not directly involved in the GTP-binding activity of the protein

The p21 products of ras proto-oncogenes are GTP-binding proteins with associated GTPase activity. Recent studies have indicated that ras p21 may be required for the initiation of normal cell DNA synthesis, since microinjection of a monoclonal antibody, Y13-259, blocks serum stimulation of DNA synthesis in quiescent cell cultures (L. S. Mulcahy, M.R. Smith, and D. W. Stacey, Nature [London] 313:241-243, 1985). We localized the structural domain within the p21 molecule recognized by the Y13-259 monoclonal antibody. By analysis of a series of bacterially expressed p21 deletion mutants, the monoclonal antibody was found to interact with a region between positions 70 and 89 in the p21 amino acid sequence. By comparison of the coding sequences of different p21 proteins recognized by this monoclonal antibody, a highly conserved amino acid region between positions 70 and 81 was found to be the most likely site for the epitope detected by the Y13-259 antibody. This monoclonal antibody was further shown not to interfere directly with in vitro biochemical functions of the molecule, including GTP binding, GTPase, and autokinase activities.