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

Chromosomal Characterization of Methotrexate-resistant Human T-lymphoblast Leukemia Cells (CCRF-CEM) with Impaired Polyglutamylation

Two sublines of the human T-lymphoblast leukemia cell line CCRF-CEM, which were resistant to methotrexate (MTX) due to defective MTX polyglutamate synthesis, were karyologically characterized. No statistically significant differences in the modal number of chromosomes were noted in resistant cells (CCRF-CEM/P) as compared to parent cells (91, range, 86-123; and 93, range; 78-103, respectively). Fifteen marker chromosomes were identified and their origins at least partially established. An isochromosome 7q, (marker 13) was present in all MTX-resistant cells but was not found in any sensitive cell karyotype. This marker chromosome may be involved in the emergence of drug-resistant cells from the parental population of CCRF-CEM cells. In all cell lines, chromosomes 8, 9 and 14 appear to be highly unstable and are involved in the genesis of many marker chromosomes. These chromosomes are also implicated in the in vivo genesis of various leukemias and lymphomas, which suggests that both in vivo tumor progression and in vitro cellular adaptation are marked by chromosome mutations that may activate multiple oncogenes.

Cancer: we should not forget the past

Cancer has been in existence longer than human beings, and man has been facing the illness ever since he made his appearance on Earth. Amazingly, the first human cancer gene was cloned only thirty years ago. This, and other extraordinary scientific goals achieved by molecular cancer research in the last 30 years, seems to suggest that definitive answers and solutions to this severe disease have been finally found. This was not the case, as cancer still remains to be defeated. To do so, cancer must be first understood. This review highlights how cancer onset and progression has been tackled from ancient times to present day. Old theories and achievements have provided the pillars of cancer understanding, in laying the basis of 'modern era' cancer research, are discussed. The review highlights the discovery of oncogenes and suppressor tumor genes, underlining the crucial role of these achievements in cancer diagnosis and therapies. Finally, an overview of how the modern technologies have given impetuous to expedite these goals is also considered.

A small molecule that induces reactive oxygen species via cellular glutathione depletion

A new cytotoxic compound was found in our chemical library. We revealed that the compound induced reactive oxygen species through glutathione depletion. Moreover, the compound was effective against several cancer cell lines including those harbouring KRAS.

A central role for vesicle trafficking in epithelial neoplasia: intracellular highways to carcinogenesis

Epithelial cell carcinogenesis involves the loss of cell polarity, alteration of polarized protein presentation, dynamic cell morphology changes, increased proliferation, and increased cell motility and invasion. Membrane vesicle trafficking underlies all of these processes. Specific membrane trafficking regulators, including RAB small GTPases, through the coordinated dynamics of intracellular trafficking along cytoskeletal pathways, determine the cell surface presentation of proteins and the overall function of both differentiated and neoplastic cells. Although mutations in vesicle trafficking proteins may not be direct drivers of transformation, components of the machinery of vesicle movement have crucial roles in the phenotypes of neoplastic cells. Therefore, the regulators of membrane vesicle trafficking decisions are essential mediators of the full range of cell physiologies that drive cancer cell biology, including initial loss of cell polarity, invasion and metastasis. Targeting of these fundamental intracellular processes may permit the manipulation of cancer cell behaviour.

Identification and characterization of an activating TrkA deletion mutation in acute myeloid leukemia

In this study, we utilized retroviral transfer of cDNA libraries in order to identify oncogenes that are expressed in acute myeloid leukemia (AML). From screens using two different cell types as targets for cellular transformation, a single cDNA encoding a variant of the TrkA protooncogene was isolated. The protein product of this protooncogene, TrkA, is a receptor tyrosine kinase for nerve growth factor. The isolated transforming cDNA encoded a TrkA protein that contains a 75-amino-acid deletion in the extracellular domain of the receptor and was named DeltaTrkA. DeltaTrkA readily transformed fibroblast and epithelial cell lines. The deletion resulted in activation of the tyrosine kinase domain leading to constitutive tyrosine phosphorylation of the protein. Expression of DeltaTrkA in cells led to the constitutive activation of intracellular signaling pathways that include Ras, extracellular signal-regulated kinase/mitogen-activated protein kinase, and Akt. Importantly, DeltaTrkA altered the apoptotic and growth properties of 32D myeloid progenitor cells, suggesting DeltaTrkA may have contributed to the development and/or maintenance of the myeloid leukemia from which it was isolated. Unlike Bcr-Abl, expression of DeltaTrkA did not activate Stat5 in these cells. We have detected expression of DeltaTrkA in the original AML sample by reverse transcriptase PCR and by Western blot analysis. While previous TrkA mutations identified from human tumors involved fusion to other proteins, this report is the initial demonstration that deletions within TrkA may play a role in human cancers. Finally, this report is the first to indicate mutations in TrkA may contribute to leukemogenesis.

The p53 tumor-suppressor gene and ras oncogene mutations in oral squamous-cell carcinoma

The frequencies of mutations in the p53 tumor-suppressor gene and ras proto-oncogenes were investigated systematically in surgically resected oral squamous-cell carcinomas (SCCs) using single-strand conformation polymorphism (SSCP) and/or dot-blot hybridization analysis of DNA fragments which had been amplified by the polymerase chain reaction (PCR). p53 gene mutations, within the region of exons 5 to 8, were detected in 17 out of 27 (63%) tumor specimens. The role of p53 mutations in cell-line establishment was investigated. p53 gene mutations were detected in 5 out of 6 tissue samples from which cell lines were established and in 4 out of 5 specimens from which cell lines could not be established, suggesting that the presence of p53 gene mutations is not by itself sufficient for cell-line establishment. Tumor samples were also analyzed for point mutational activation of the ras proto-oncogenes. One out of 30 (3%) tumors showed an activating point mutation in codon 12 of H-ras, this being consistent with reports from Europe and USA but not with any from India. Compared to frequencies of the other genetic changes so far reported for oral SCC, the p53 mutations have been observed most often to undergo genetic change. p53 gene mutation is thus intimately involved in the genesis of oral SCC and consequently should be useful as a marker for the diagnosis of this neoplasm.

Analysis of N-ras gene mutations in medulloblastomas by polymerase chain reaction and oligonucleotide probes in formalin-fixed, paraffin-embedded tissues

Precise data on the incidence of transforming ras oncogenes in pediatric tumors and the correlations with the histopathological properties of the tumors are very limited. Additionally the presence of ras activation in medulloblastomas has not been investigated so far. Using a combination of techniques including in vitro gene amplification by polymerase chain reaction (PCR) and detection of single base mutations by sequence-specific oligonucleotides we studied N-ras activation (mutations at codon 12, 13, and 61) in 32 medulloblastomas. DNA was isolated from 20 microns sections of formalin-fixed paraffin-embedded tissue. Mutations were found in 3 out of 32 examined medulloblastomas. In all cases only mutations of codon 61 were found: two of three mutations were C to A mutations at position 1 of the codon 61 (leading to a substitution of a glutamine residue for a lysine) and one was A to T mutation at position 3 in the same codon (glutamine-histidine). Our results indicate 10% incidence N-ras mutation in medulloblastoma, higher than in other CNS tumors studied so far. The main advantages of the procedure described are its greatly improved sensitivity, the increased speed with which tumor samples can be analyzed, and the possibility of using paraffin-embedded sections to analyze various rare tumors in retrospect.

Restriction fragment length polymorphisms detected in N-ras-related sequences of rats and their linkage analyses

Novel restriction fragment length polymorphisms (RFLPs) in inbred rats were revealed with the human N-ras gene as probe. Three fragments hybridizing to the probe were detected by Southern blot hybridization under highly stringent conditions, and one of the fragments showed variation in inbred rat strains. Furthermore, on hybridization under low-stringency conditions, an additional fragment hybridizing to the probe was observed, and this fragment also showed interstrain variation. These two variant fragments showed different distributions in 27 inbred rat strains and segregated in backcross progeny as codominant alleles of independent single autosomal loci. Therefore, the loci for these RFLPs were named Nras-1 and Nras-2, respectively. Analyses of linkages between the RFLPs and 11 other loci revealed that the Nras-2 locus was closely linked to the c locus (3.7 +/- 2.6%), which belongs to rat linkage group I.

RAS gene activation in acute myelogenous leukemia: analysis by in vitro amplification and DNA base sequence determination

RAS protooncogene activation has been repeatedly demonstrated in neoplastic cell DNA from patients with AML. Despite the convincing demonstration that activating RAS gene point mutations are critical in model systems, their precise prevalence and importance in human cancers such as AML remain speculative. The technology for identifying RAS mutations has changed considerably in recent years. We examined a prospective cohort of 43 acute myeloid leukemia (AML) patients admitted to the University of Maryland Cancer Center for first and second exon mutations of NRAS and KRAS using PCR and DNA sequence analysis. Six (14%) 1st exon NRAS mutations were identified. No clinical or biologic parameter has yet been observed to segregate with RAS activation, although a larger study may be needed to demonstrate this.

The molecular biology of radiation-induced carcinogenesis: thymic lymphoma, myeloid leukaemia and osteosarcoma

In mice, external X- or gamma-irradiation may induce thymic lymphomas or myeloid leukaemias, while bone-seeking alpha-emitters may induce osteosarcomas and, to a lesser extent, acute myeloid leukaemia. The present paper aims to review briefly some of the experimental data with respect to the molecular mechanisms underlying these radiation-induced carcinogenic processes. Thymic lymphomagenesis proceeds through an indirect mechanism. Recombinant proviruses often occur in the tumour cell DNA, favouring the idea that they might be involved. However, there are indications that they might mediate tumour growth rather than induction. It is plausible that activation of ras oncogenes by somatic point mutations might play a role in the carcinogenic process, although at a yet undetermined stage. Myeloid leukaemogenesis is characterized by a very early, putative initiating event, consisting of non-random rearrangements and/or deletions of chromosome 2. These may be related to deletions in the developmentally important homeobox gene clusters and to rearrangements of the sequences flanking the IL-1 beta gene. Either a gene of the homeobox family or IL-1 beta might be considered as potentially involved in the induction process. Osteosarcomagenesis in mice is often associated with the expression of proviruses, and the tumours often contain somatically acquired proviruses. These viruses may contribute to tumour development by affecting various growth-suppressor genes. Viruses isolated from bone tumours, although non-sarcomagenic, induce osteopetrosis, osteomas and lymphomas upon infection of newborn mice. Osteogenic tumours frequently display amplification of a region on mouse chromosome 15, which encompasses c-myc and Mlvi-1 sequences. Enhanced transcription of various oncogenes is found in individual tumours, but no specificity for osteosarcomas has been identified. In vitro systems of skeletoblast differentiation are being developed to study tumour induction in vitro.

An immunohistochemical analysis of ras oncogene expression in epithelial neoplasms of the colon

Colonic epithelial tumors (101) including villoglandular adenomas, carcinomas in situ, adenocarcinomas, and neuroendocrine (NE) carcinomas were studied immunohistochemically with monoclonal antibodies (MoAb) RAP-5 and RAS-10 recognizing altered and unaltered ras oncogene products. In addition, 20 samples from multiple polyposis including adenomas with and without dysplasia, carcinomas in situ, and invasive carcinomas were studied. Using immunostaining techniques, normal mucosa was weakly stained, whereas the mucosa in the vicinity of tumors or inflammation showed enhanced staining. More tumors stained intensely with MoAb RAP-5 than with MoAb RAS-10. With MoAb RAP-5, most benign and malignant tumors showed enhanced staining. No significant differences in staining were noted in relation to superficial versus deeply invasive carcinomas or clinical staging. Immunostaining was also noted in some metastases. No significant differences in enhanced staining were found in carcinomas. Interestingly, the most extensive and enhanced immunostaining was noted in the villoglandular adenomas, dysplastic adenomas, and carcinomas in situ. The authors conclude that (1) ras protein expression is detectable in most benign, borderline, and malignant epithelial tumors of the colon as determined with MoAb RAP-5 and RAS-10, whereas enhanced expression is more often detected with RAP-5; (2) enhanced ras product expression in colon carcinomas does not seem to correlate with advanced tumor stages or with exocrine, NE, or phenotypically mixed tumors; and (3) the finding of the most intensely enhanced ras products expression in villoglandular polyps and carcinomas in situ suggests a possibly significant role for the oncogene in the early phases of transformation.

Establishment of a human malignant meningioma cell line with amplified c-myc oncogene

A new cell line (KT21-MG1) has been established from a human malignant meningioma transplanted into nude mice. The cultured cells showed epithelial cell-like morphology and were positive immunohistochemically for vimentin as the original tumor. They have been grown continuously in vitro for more than 2 years. The population doubling time was about 24 hours at the 30th passage. The cells are capable of proliferating in soft agar medium and produced tumors in nude mice, the histologies of which were similar to the original patient-derived tumor. Analysis of cellular oncogenes showed that myc and fps were amplified approximately tenfold and threefold, respectively, in this cell line, whereas N-myc, L-myc, N-ras, K-ras, H-ras, abl, erbB2, Blym, src, raf-1, myb, and sis were not changed significantly. The amplification of myc was accompanied by an enhanced expression. Chromosome studies of cultured cells showed the monosomy of chromosome 22 that has been reported to be a specific abnormality in meningiomas.

Origin of rare Ha-ras alleles: relationship of VTR length to a 5' polymorphic Xho I site

Amongst the four common Ha-ras alleles in both controls and cancer patients, we detected the presence of a polymorphic Xho I site associated specifically with the 6.6 and 7.7 kb Bam HI fragments but absent from the 7.1 and 8.2 kb alleles, as recently reported by others. We have extended this study and report here, the consistent appearance of this Xho I site in unusual alleles close in size to the two common alleles of 6.6 and 7.7 kb, in control lymphoblastoid DNA samples in a variety of tumor DNAs. Unusual alleles grouped around the 7.1 and 8.2 kb common alleles on the other hand, did not possess the Xho I site. The consistent presence of the Xho I site polymorphism, in the unusual Ha-ras alleles surrounding the 6.6 and 7.7 kb common alleles and its absence in alleles around the 7.1 and 8.2 kb common alleles, suggests that the unusual ones are derived from the corresponding common alleles to which they are closest in size.

Oncogenicity of human N-ras oncogene and proto-oncogene introduced into retroviral vectors

The N-ras gene is the only member of the ras family which has never been naturally transduced into a retrovirus. In order to study the in vitro and in vivo oncogenicity of N-ras and to compare its pathogenicity to that of H-ras, we have inserted an activated or a normal form of human N-ras cDNA into a slightly modified Harvey murine sarcoma virus-derived vector in which the H-ras p21 coding region had been deleted. The resulting constructions were transfected into NIH 3T3 cells. The activated N-ras-containing construct (HSN) induced 10(4) foci per microgram of DNA and was found to be as transforming as H-ras was. After infection of the transfected cells by either the ecotropic Moloney murine leukemia virus or the amphotropic 4070A helper viruses, rescued transforming viruses were injected into newborn mice. Both pseudotypes of HSN virus containing activated N-ras induced the typical Harvey disease with similar latency. However, we found that the virus which contained normal N-ras p21 (HSn) was also pathogenic and induced splenomegaly, lymphadenopathies, and sarcoma in mice after a latency of 3 to 7 weeks. In addition, Moloney murine leukemia virus pseudotypes of N-ras caused neurological disorders in 30% of the infected animals. These results differed markedly from those of previous experiments in which we had inserted the activated form of N-ras in the pSV(X) vector: the resulting SVN-ras virus was transforming on NIH 3T3 cells but was poorly oncogenic in vivo (M. Souyri, C. F. Koehne, P. V. O'Donnel, T. H. Aldrich, M. E. Furth, and E. Fleissner, Virology 158:69-78). However, similarly poor oncogenicity was also observed when the v-H-ras coding sequence was inserted in pSV(X) vector, which indicated that the vector sequences play a crucial role in the pathogenicity of a given oncogene. Altogether, these data demonstrated unequivocally that N-ras is potentially as oncogenic as H-ras and that such oncogenic effect could depend on the vector environment.

A v-H-ras-dependent hemopoietic tumor model involving progression from a clonal stage of transformation competence to autocrine interleukin 3 production

Autocrine interleukin 3 (IL-3)-secreting tumors were generated from an IL-3-dependent mouse mast cell line (PB-3c) after introduction of the v-H-ras oncogene. Tumor progression was characterized by four distinct phenotypes. The first corresponded to immortalized mast cells unresponsive to the oncogenic effect of v-H-ras. The second was expressed in a clonable subpopulation of PB-3c cells and was marked by the competence to form v-H-ras-dependent tumors (immortalized transformation competence). The third was a direct effect of v-H-ras expression on all PB-3c cells and was characterized in vitro by a reduced IL-3 requirement. Upon injection of v-H-ras-expressing, transformation-competent cells into mice, the final, fully malignant phenotype developed with a long latency period and was marked in vitro by independence of exogenous IL-3 and by autocrine IL-3 stimulation. Northern (RNA) blot analysis and an RNase A-T1 protection assay showed that IL-3 production was strictly associated with the tumor phenotype. Two of six tumors showed an alteration at the 5' region of the IL-3 gene. We conclude that v-H-ras required complementation by IL-3 gene rearrangement or an alternate event to generate autocrine mastocytomas.

The BCR-ABL oncogene transforms Rat-1 cells and cooperates with v-myc

The tyrosine kinase P210 is the gene product of the rearranged BCR-ABL locus on the Philadelphia chromosome (Ph1), which is found in leukemic cells of patients with chronic myelogenous leukemia. It has a weakly oncogenic effect in immature murine hematopoietic cells and does not transform NIH 3T3 cells. We have found that P210 has a strikingly different effect in Rat-1 cells, another line of established rodent fibroblasts. Stable expression of P210 in Rat-1 cells caused a distinct morphological change and conferred both tumorigenicity and capacity for anchorage-independent growth. The introduction of v-myc into Rat-1 cells expressing P210 led to complete morphological transformation and enhanced tumorigenicity. No such interaction took place in NIH 3T3 cells. Thus, Rat-1 cells can be used to detect cooperation between BCR-ABL and other oncogenes and may prove useful for the identification of secondary oncogenic events in chronic myelogenous leukemia.

Transgenic mice carrying the mouse mammary tumor virus ras fusion gene: distinct effects in various tissues

Transgenic mice carrying the v-Ha-ras oncogene under the control of the mouse mammary tumor virus long terminal repeat were produced. These mice exhibit several phenotypes: mammary tumors, bilateral hyperplasia of the harderian lacrimal gland, primary bronchio-alveolar lung adenocarcinoma, and splenomegaly. High levels of the transgene RNA were detected in mammary, harderian, and lung tumors. Accumulation of cells of the myeloid lineages was found in enlarged spleens. This phenotype may represent an indirect effect of v-Ha-ras expression on myeloid progenitors. Our data illustrate the cell-specific effects of v-Ha-ras.

N-RAS mutations in T-cell acute lymphocytic leukaemia: analysis by direct sequencing detects a novel mutation

A novel mutation of the N-RAS gene of T-ALL blast cells was detected by a direct sequencing of in vitro amplified exon-1 of the N-RAS gene. Threonine (ACA) was substituted for alanine (GCA) at codon 11. This mutation would have been overlooked by conventional probe hybridization techniques. A search for other mutations in N-RAS exon-1 in T-ALL revealed a codon 13 mutation substituting aspartic acid (GAT) for glycine (GGT) in one of 18 patients. No mutations at codon 12 were detected.

Evidence of enhancement of the ras oncogene protein product (p21) in a spectrum of human tumors

Using a direct binding liquid competition radioimmunoassay, the amount of the ras oncogene protein product, p21, was quantitated in a variety of human tumors and adjacent apparently normal tissues. In 48 of 50 matched tumor and normal tissue biopsy specimens from 50 patients, more ras p21 was detected in the tumor than in its normal counterpart. Twenty-five of 28 breast tumors demonstrated more ras p21 than the average of the values obtained for fibroadenomas. Furthermore, in 17 of the 19 cases studied, over 20% more ras p21 was observed in breast carcinomas compared with their respective normal counterparts. More ras p21 was also demonstrated in the majority of tumors of the stomach, lung, colon and bladder compared with their respective adjacent normal tissues. Our data therefore indicate that ras p21 expression is quantitatively enhanced in many human tumors originating from several different tissue types.

A v-H-ras-dependent hemopoietic tumor model involving progression from a clonal stage of transformation competence to autocrine interleukin 3 production

Autocrine interleukin 3 (IL-3)-secreting tumors were generated from an IL-3-dependent mouse mast cell line (PB-3c) after introduction of the v-H-ras oncogene. Tumor progression was characterized by four distinct phenotypes. The first corresponded to immortalized mast cells unresponsive to the oncogenic effect of v-H-ras. The second was expressed in a clonable subpopulation of PB-3c cells and was marked by the competence to form v-H-ras-dependent tumors (immortalized transformation competence). The third was a direct effect of v-H-ras expression on all PB-3c cells and was characterized in vitro by a reduced IL-3 requirement. Upon injection of v-H-ras-expressing, transformation-competent cells into mice, the final, fully malignant phenotype developed with a long latency period and was marked in vitro by independence of exogenous IL-3 and by autocrine IL-3 stimulation. Northern (RNA) blot analysis and an RNase A-T1 protection assay showed that IL-3 production was strictly associated with the tumor phenotype. Two of six tumors showed an alteration at the 5' region of the IL-3 gene. We conclude that v-H-ras required complementation by IL-3 gene rearrangement or an alternate event to generate autocrine mastocytomas.

The BCR-ABL oncogene transforms Rat-1 cells and cooperates with v-myc

The tyrosine kinase P210 is the gene product of the rearranged BCR-ABL locus on the Philadelphia chromosome (Ph1), which is found in leukemic cells of patients with chronic myelogenous leukemia. It has a weakly oncogenic effect in immature murine hematopoietic cells and does not transform NIH 3T3 cells. We have found that P210 has a strikingly different effect in Rat-1 cells, another line of established rodent fibroblasts. Stable expression of P210 in Rat-1 cells caused a distinct morphological change and conferred both tumorigenicity and capacity for anchorage-independent growth. The introduction of v-myc into Rat-1 cells expressing P210 led to complete morphological transformation and enhanced tumorigenicity. No such interaction took place in NIH 3T3 cells. Thus, Rat-1 cells can be used to detect cooperation between BCR-ABL and other oncogenes and may prove useful for the identification of secondary oncogenic events in chronic myelogenous leukemia.

Transgenic mice carrying the mouse mammary tumor virus ras fusion gene: distinct effects in various tissues

Transgenic mice carrying the v-Ha-ras oncogene under the control of the mouse mammary tumor virus long terminal repeat were produced. These mice exhibit several phenotypes: mammary tumors, bilateral hyperplasia of the harderian lacrimal gland, primary bronchio-alveolar lung adenocarcinoma, and splenomegaly. High levels of the transgene RNA were detected in mammary, harderian, and lung tumors. Accumulation of cells of the myeloid lineages was found in enlarged spleens. This phenotype may represent an indirect effect of v-Ha-ras expression on myeloid progenitors. Our data illustrate the cell-specific effects of v-Ha-ras.

Detection of the ras p21 gene product in human leukemias by flow cytometry

To date, the detection of oncogene products in human neoplasms has relied primarily upon immunoblot analysis of specimen homogenates. Herein are reported the results of a study using flow cytometry to evaluate the expression of the ras p21 gene product in both fresh and cryopreserved specimens of human acute leukemias. Cell lines known to express ras p21 were used as positive controls and normal peripheral blood was used as a negative control. Intensity of staining for ras p21 (Ip21) was expressed as the ratio of the peak channel numbers of the peak generated by staining with anti-ras p21 to the peak obtained by staining with an isotype control. Using this method, 21 out of 32 clinical specimens of acute leukemia were found to express ras p21 in elevated amounts compared to normal peripheral blood. Flow cytometry appears to be a practical method for routine screening of clinical specimens for the expression of oncogene products on individual cells rather than cell homogenates.

Genetic and cytogenetic changes in acute lymphoblastic leukemia

In recent years, a number of non-random chromosomal alterations have been identified in specific populations of acute lymphoblastic leukemic cells of either B-cell or T-cell lineage. The most frequently involved chromosomal sites are 1q, 4q, 6q, 7q, 8q, 9p, 9q, 10q, 11p, 12p, 14q, 19p and 22q. Genes located near frequent breakpoints include c-myc, c-abl and the genes for the T-cell alpha and beta receptors. In addition, approximately 20 other genes potentially involved in the leukemic process are located near less frequently encountered, but consistent, chromosomal breakpoints.

Analysis of RAS oncogene mutations in human lymphoid malignancies

We investigated the frequency of mutations activating RAS oncogenes in human lymphoid malignancies, including B- and T-cell-derived acute lymphoblastic leukemia, chronic lymphocytic leukemia, and non-Hodgkin lymphoma. By the polymerase chain reaction/oligonucleotide hybridization method, DNA from 178 cases was analyzed for activating mutations involving codons 12 and 61 of the HRAS, KRAS and NRAS genes and codon 13 of the NRAS gene. Mutations involving codons 12 or 13 of the NRAS gene were detected in 6 of 33 cases of acute lymphoblastic leukemia (6/33, 18%), whereas no mutations were found in non-Hodgkin lymphoma or chronic lymphocytic leukemia. Direct nucleotide sequence analysis of polymerase chain reaction products showed that the mutations involved a G----A transition in five of the six cases of acute lymphocytic leukemia. In four cases the mutations seemed to occur in only a fraction of the neoplastic cells, and one case displayed two distinct NRAS mutations, most likely present in two distinct cell populations. These results indicate the following: (i) RAS oncogenes are not found in all types of human malignancies, (ii) significant differences in the frequency of RAS mutations can be found among subtypes of neoplasms derived from the same tissue, (iii) in lymphoid neoplasms the NRAS mutation correlates with the most undifferentiated acute lymphocytic leukemia phenotype, and (iv) NRAS mutations present in only a fraction of malignant cells may result from either the selective loss or the acquisition of mutated alleles during tumor development.

Both N-ras and c-myc are activated in the SHAC human stomach fibrosarcoma cell line

A transforming N-ras gene was isolated from the SHAC human stomach fibrosarcoma cell line. A single-point mutation resulting in the substitution of histidine for glutamine at codon 61 was found in the SHAC transforming allele. The N-ras gene is overexpressed in the tumor cells and transformant cells. The N-ras p21 product was studied by immunoprecipitation and showed no alteration in mobility as compared to the normal p21 protein. The c-myc gene is amplified and overexpressed in these cells. This report gives evidence that an amplified c-myc and a mutated N-ras gene are both present in this tumor cell line and provides support for the idea that co-operation of at least 2 activated cellular oncogenes is required for carcinogenesis.

Analysis of RAS gene mutations in acute myeloid leukemia by polymerase chain reaction and oligonucleotide probes

In vitro DNA amplification followed by oligonucleotide dot blot analysis were used to study RAS gene mutations in acute myeloid leukemia (AML). Fifty-two presentation AML DNAs were screened for mutations in codons 12, 13, and 61 of NRAS and in codons 12 and 61 of KRAS and HRAS. Fourteen (27%) contained mutations--all in NRAS and predominantly in codon 12. The most common amino acid substitution identified was of glycine by aspartic acid at codon 12 (7/18), with a G----A transition being the most common base change (11/18). No particular correlation was observed between disease subtype and the incidence or type of NRAS mutation. In DNA samples from four patients, 2 NRAS mutations were found to coexist. NIH 3T3 focus-formation assays revealed that in each case the mutations were present in different NRAS alleles. We also report the absence of a mutated RAS gene in relapse DNAs of four patients in which a RAS oncogene had been detected at presentation. These observations suggest that RAS mutations arise as part of the evolution of neoplastic transformation.

Mutation analysis of the N-ras proto-oncogene in active and remission phase of human acute leukemias

DNA isolated from blood or bone-marrow samples from 18 patients with acute non-lymphocytic leukemia (ANLL) and 14 patients with acute lymphocytic leukemia (ALL) was analyzed for the presence of mutations in the N-ras gene. Using synthetic oligonucleotide probes we detected mutations in 5 cases of ANLL; 4 GGT----GAT transitions in codon 12 and one CAA----AAA transversion in codon 61. One case exhibited homozygosity for the mutation. No mutations could be detected at these codons in the DNA of the 14 ALL patients. In a follow-up study with 3 of the above 5 patients, the mutation could no longer be detected in 2 cases following successful induction of clinical remission by chemotherapy. However, the mutated N-ras persisted in one patient who did not achieve remission. We show that oligonucleotide hybridization is a sensitive assay for the detection of N-ras point mutations, which in ANLL could be used to follow the fate of the leukemic clone during (and after) therapy.

Oncogenes in human leukemias

Eukaryotic cells contain a family of genes termed cellular oncogenes or proto-oncogenes thought to regulate normal cell growth and development. In some abnormal circumstances, such as following transduction by retroviruses, activation of these genes causes leukemias in animals. Possible mechanisms of activation of cellular oncogenes include: point mutation, deletion, or insertion; amplification; activation by internal rearrangement, chromosomal translocation, or promoter insertion; recombinatorial events resulting in the formation of novel chimeric genes; among others. In this review, we consider data implicating activation of cellular oncogenes in the pathogenesis of leukemia in humans. We discuss possible mechanisms whereby oncogene activation may induce leukemias, as well as potential diagnostic and therapeutic implications.

Oncogenes and human leukemias

Eukaryotic cells contain a family of genes termed "cellular oncogenes" or "proto-oncogenes," thought to regulate normal cell growth and development. In some circumstances, such as following transduction by retroviruses, activation of these genes causes tumors and leukemias in animals. Possible mechanisms of cellular oncogene activation include: 1) DNA point mutation, deletion or insertion, 2) gene amplification, 3) gene activation by internal rearrangement, chromosomal translocation or promoter insertion, 4) recombinative events resulting in the formation of novel chimeric genes, and others. In this review, we consider data which implicates cellular oncogene activation in the pathogenesis of leukemia in humans. We discuss possible mechanisms by which oncogene activation may induce leukemias, as well as potential diagnostic and therapeutic implications.

Absence of the hybrid bcr-abl mRNA in Ph1-positive B lymphoblastoid cell lines established from a patient with chronic myelogenous leukemia

The expression of c-abl, c-sis, c-myc and N-ras oncogenes was examined in 2 lymphoblastoid cell lines, one with Ph1 (PB-1049) and the other without Ph1 (LN-1049), both established from a patient with chronic myelogenous leukemia (CML), and in a Ph1-positive cell line (PB-1049-T) derived from a tumor formed after transplantation of PB-1049 cells in a nude mouse with reference to their tumorigenic potential in nude mice. The normal transcripts of c-abl were detected in all 3 lymphoblastoid cell lines. Although in situ hybridization of v-abl proved, and restriction endonuclease analyses of the bcr region strongly indicated the occurrence of bcr-abl rearrangement in PB-1049 and PB-1049-T, we could not obtain any evidence for the expression of the hybrid bcr-abl mRNA. These results indicate that the Ph1 translocation does not ensure the production of the hybrid bcr-abl mRNA, and that the expression of hybrid bcr-abl gene is not essential for the maintenance of tumorigenicity of these cell lines. Expression of c-sis was not detected in any of the cell lines examined, whereas the expression of c-myc was uniformly higher in the 3 cell lines than in normal control cells. The levels of N-ras expression varied considerably, probably in parallel with the changes in tumorigenicity of the cell lines. N-ras expression in the PB-1049 and PB-1049-T cell lines was higher than that in the LN-1049 line when they retained tumorigenic potential, but it fell to the level of LN-1049 with loss or decline of tumorigenicity.

RAS gene mutations in acute and chronic myelocytic leukemias, chronic myeloproliferative disorders, and myelodysplastic syndromes

We report on investigations aimed at detecting mutated RAS genes in a variety of preleukemic disorders and leukemias of myeloid origin. DNA transfection analyses (tumorigenicity assay) and hybridization to mutation-specific oligonucleotide probes established NRAS mutations in codon 12 or 61 of 4/9 acute myelocytic leukemias (AML) and three AML lines. Leukemic cells of another AML patient showed HRAS gene activation. By using a rapid and sensitive dot-blot screening procedure based on the combination of in vitro amplification of RAS-specific sequences and oligonucleotide hybridization we additionally screened 15 myelodysplastic syndromes, 26 Philadelphia chromosome-positive chronic myelocytic leukemias in chronic or acute phase, and 19 other chronic myeloproliferative disorders. A mutation within NRAS codon 12 could thus be demonstrated in a patient with idiopathic myelofibrosis and in another with chronic myelomonocytic leukemia. Moreover, mutated NRAS sequences were detected in lymphocytes, in granulocytes, as well as in monocytes/macrophages of the latter case.

Analysis of ras genes and linked viral sequences in rat hepatocarcinogenesis

After long-term feeding of a choline-devoid diet to rats, the authors analyzed rasK, rasH, and rasN transcripts and gene structure in livers and liver tumors. They controlled their analysis by studying cell lines derived from chemically induced hepatomas. Transcripts from all three genes were elevated in all tumors, but not in the livers from which they arose. The transcript elevations may represent an effect of active cell proliferation in the tumors. Clone HiHi-3, derived from the Kirsten murine sarcoma virus, detected a large number of hybridization bands, most of which were not part of the rasK-p21 gene. Most tumors had an altered band at 2.6 kb; some had other altered bands. No alterations were seen in liver DNA, and none of the cell lines showed the 2.6 kb band. At low stringency, a rasH probe, which contains a short segment of a similar viral sequence, also detected altered bands in tumors and a single treated liver. These changes in endogenous viral sequences of the rat genome appear to be characteristic of carcinogenesis by a choline-devoid diet.

Alteration of glycolipids in ras-transfected NIH 3T3 cells

Glycosphingolipid alterations upon viral transformation are well documented. Transformation of mouse 3T3 cells with murine sarcoma viruses results in marked decreases in the levels of gangliosides GM1 and GD1a and an increase in gangliotriaosylceramide. The transforming oncogenes of these viruses have been identified as members of the ras gene family. We analyzed NIH 3T3 cells transfected with human H-, K- and N-ras oncogenes for their glycolipid composition and expression of cell surface gangliosides. Using conventional thin-layer chromatographic analysis, we found that the level of GM3 was increased and that of GD1a was slightly decreased or unchanged, and GM1 was present but not in quantifiable levels. Cell surface levels of GM1 were determined by 125I-labeled cholera toxin binding to intact cells. GD1a was determined by cholera toxin binding to cells treated with sialidase prior to toxin binding. All ras-transfected cells had decreased levels of surface GM1 and GD1a as compared to logarithmically growing normal NIH 3T3 cells. Levels of GM1 and, to a lesser extent, GD1a increased as the latter cells became confluent. Using a monoclonal antibody assay, we found that gangliotriaosylceramide was present in all ras-transfected cells studied but not in logarithmically growing untransfected cells. Interestingly, gangliotriaosylceramide appeared when the latter cells became confluent. These results indicated that ras oncogenes derived from human tumors are capable of inducing alterations in glycolipid composition.

Tumor cell heterogeneity: divided-colony assay for measuring drug response

In vitro tests for predicting the response of tumors to chemotherapeutic agents might be improved if they were modified to take into account tumor-cell heterogeneity. We have studied the heterogeneity of cellular growth rate and drug response in mouse fibroblast NIH 3T3 cells and in NIH 3T3 cells transformed with the human HRAS gene (homologue of the Harvey sarcoma virus oncogene v-Ha-ras) from the EJ human bladder carcinoma cell line. Growth-rate heterogeneity was detected as a broad distribution of numbers of cells per colony. In spite of this heterogeneity, secondary colonies have numbers of cells per colony that resemble that of the primary colony from which they were derived. The variance between unrelated secondary colonies is increased by HRASEJ. Colony-size measurements are reliable because primary colonies divided in half formed two groups of secondary colonies (on two separate plates) that had indistinguishable mean colony sizes. Based on these observations, a divided-colony procedure was devised to detect the drug response of heterogeneous cell populations. Primary colonies are divided into two groups of cells, one of which is treated with a drug and the other is left untreated as a control. The size distribution of treated secondary colonies is then compared to that of the untreated control and to that of the primary colony from which it was derived. The divided-colony procedure is proposed as a modification of the human-tumor-cloning system to increase the sensitivity and reliability of in vitro procedures used to determine the drug response of heterogeneous tumor-cell populations.

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.

A point mutation at codon 13 of the N-ras oncogene in myelodysplastic syndrome

Patients with a myelodysplastic syndrome (MDS) which has a risk of leukaemic change exhibit a variable clinical course. It has been suggested that the development of leukaemia in patients with MDS may be related to chromosomal abnormalities or genetic alterations: somatic mutation of the N-ras gene is now considered to be a critical step in the genetic basis of human leukaemogenesis. Here we report that DNAs of bone-marrow cells from three out of eight patients with MDS contained an activated N-ras oncogene, as detected by an in vivo selection assay in nude mice with transfected NIH 3T3 cells. Molecular analysis revealed the same single nucleotide substitution at codon 13 in all three transforming N-ras genes. Each of the three patients showed a progression of the disease and a resulting leukaemic change within the following year. Our observation of the mutation at codon 13 in leukaemic cell DNAs from all three cases suggests that activation of the N-ras gene is important in the development of leukaemia in some MDS cases.

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.

Activation of a cellular proto-oncogene in spontaneous liver tumor tissue of the B6C3F1 mouse

The controversy surrounding the interpretation of observed increases in the high spontaneous liver tumor incidence of the B6C3F1 mouse after administration of certain chemical agents necessitates a mechanistic understanding into the nature of tumor development in this particular strain of mouse. Recently, cancer genes (oncogenes) have been detected in the DNA from a variety of human tumors and tumor cell lines. These genes have been implicated to play a role in the transformation of normal cells into cancerous ones. To investigate the role that cellular oncogenes might play in the development of spontaneous liver tumors in the B6C3F1 mouse, DNA was isolated from spontaneously occurring liver tumors and transfected into NIH 3T3 fibroblasts. DNA from this tumor tissue was capable of transforming NIH 3T3 cells from 82% of the animals examined strongly suggesting the presence of an active cellular oncogene. In contrast, DNA isolated from surrounding non-tumorous liver tissue and liver tissue from non-tumor bearing mice did not cause any transformation in the NIH 3T3 assay. These data demonstrate that the active cellular oncogene is not present in the hepatic tissue via a germ-line transmission but is activated only in those cells of the tumor tissue. Experiments using Southern blot hybridization analysis have identified this active cellular oncogene to be a member of the ras oncogene family. Identification of this cellular oncogene will now allow the evaluation of factors which might modify its expression. These future studies will lead to an increased understanding of potential mechanisms by which hepatic tumors are enhanced and should provide more informed estimates of risk for man based on bioassay data generated in this strain of mouse.