Human cancer and cellular oncogenes

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.

K-Ras gene mutation status as a prognostic and predictive factor in patients with colorectal cancer undergoing irinotecan- or oxaliplatin-based chemotherapy

BACKGROUND

CRC caused more than 600,000 estimated deaths in 2008. Dysregulated signaling through the RAS/RAF/mitogen-activated protein kinase (MEK)/extracellular signal-regulated kinase (ERK) signaling pathway due to mutations in K-Ras and B-Raf are common events in CRC.

METHODS

Incidence of mutations in codons 12 and 13 of K-Ras and exons 11 and 15 of B-Raf were analyzed in amplified PCR products from primary tumors of 273 patients with CRC, and their prognostic and predictive significance was assessed. The prognostic role of clinical and pathological factors was also examined.

RESULTS

K-Ras mutations were present in 89 patients (32.6%), of whom 76 (85.4%) had mutations in codon 12 and 10 (11.2%) had mutations in codon 13. B-Raf gene mutations were present in 17 patients (6.9%), of whom 6 (35.3%) had mutations in exon 15. Multivariate analysis revealed a predictive significance for K-Ras mutations with respect to time to progression in patients treated with irinotecan and oxaliplatin as first-line chemotherapy. There was no predictive significance for B-Raf gene mutation status in these patients. The following risk factors were found to affect overall survival (OS) rates: primary tumor location, lymph node involvement grade, carcinoembryonic antigen (CEA) level before treatment, and performance status according to WHO criteria.

CONCLUSIONS

Based on the results of this study, K-Ras mutation status may be a suitable indicator of patient eligibility and a prognostic indicator for responsiveness to anti-EGFR therapy alone, or in combination with chemotherapy. Also, K-Ras mutation status may predict time to progression in patients treated with irinotecan and oxaliplatin.

Activation of K-RAS by co-mutation of codons 19 and 20 is transforming

The K-RAS oncogene is widely mutated in human cancers. Activating mutations in K-RAS give rise to constitutive signalling through the MAPK/ERK and PI3K/AKT pathways promoting increased cell division, reduced apoptosis and transformation. The majority of activating mutations in K-RAS are located in codons 12 and 13. In a human colorectal cancer we identified a novel K-RAS co-mutation that altered codons 19 and 20 resulting in transitions at both codons (L19F/T20A) in the same allele. Using focus forming transformation assays in vitro , we showed that co-mutation of L19F/T20A in K-RAS demonstrated intermediate transforming ability that was greater than that of individual L19F and T20A mutants, but less than that of G12D and G12V K-RAS mutants. This demonstrated the synergistic effects of co-mutation of codons 19 and 20 and illustrated that co-mutation of these codons is functionally significant.

Metabolic control and future opportunities for growth regulation

The last 10 years have seen a significant expansion in the scope of attempts to manipulate the growth of animals (Buttery, Lindsay and Haynes, 1986). The expansion of interest has been driven by a number of factors, both economic and theoretical. At the economic level the need to develop energetically and economically efficient strategies of animal production has been coupled with a renewed awareness of the implications for human health of excessive intakes of saturated fats. Emphasis then has switched from the maximization of weight gain as an end in itself towards a need to promote protein deposition at any given intake and, at the same time, to reduce the fat content of meat and meat products. These twin objectives might be achieved by one of three strategies: the promotion of protein deposition alone, because at any given rate of weight gain this will tend to minimize the rate of fat deposition (the so-called repartitioning effect); the reduction of fat gain (an approach that has received particularly close attention by those concerned primarily with human obesity); or ideally the simultaneous promotion of protein accretion and depression of that of fat.

DNA–carcinogen interaction: covalent DNA-adducts of benzo(a)pyrene 7, 8-dihydrodiol 9, 10-epoxides studied by biochemical and biophysical techniques

Exposure to various chemicals, either due to occupation or lifestyle, is considered to be a major contributing factor to tumour formation in man (Higginson, 1969; Doll and Peto, 1981). An important and prevalent class of potent carcinogenic compounds present in he environment is polycyclic aromatic hydrocarbons (PAHs), which are found in various petroleum and combustion products derived from heat and power generation and motor vehicle exhausts (Baum, 1978). Furthermore, since PAHs are generally formed by pyrolysis of organic matters such as tobacco smoking and certain procedures of food preparation, the PAH exposure to humans is extensive.

DNA–carcinogen interaction: covalent DNA-adducts of benzo(a)pyrene 7, 8-dihydrodiol 9, 10-epoxides studied by biochemical and biophysical techniques

Exposure to various chemicals, either due to occupation or lifestyle, is considered to be a major contributing factor to tumour formation in man (Higginson, 1969; Doll & Peto, 1981). An important and prevalent class of potent carcinogenic compounds present in the environment is polycyclic aromatic hydrocarbons (PAHs), which are found in various petroleum and combustion products derived from heat and power generation and motor vehicle exhausts (Baum, 1978). Furthermore, since PAHs are generally formed by pyrolysis of organic matters such as tobacco smoking and certain procedures of food preparation, the PAH exposure to humans is extensive

DNA–carcinogen interaction: covalent DNA-adducts of benzo(a)pyrene 7, 8-dihydrodiol 9, 10-epoxides studied by biochemical and biophysical techniques

Exposure to various chemicals, either due to occupation or lifestyle, is considered to be a major contributing factor to tumour formation in man (Higginson, 1969; Doll & Peto, 1981). An important and prevalent class of potent carcinogenic compounds present in the environment is polycyclic aromatic hydrocarbons (PAHs), which are found in various petroleum and combustion products derived from heat and power generation and motor vehicle exhausts (Baum, 1978). Furthermore, since PAHs are generally formed by pyrolysis of organic matters such as tobacco smoking and certain procedures of food preparation, the PAH exposure to humans is extensive.

DNA–carcinogen interaction: covalent DNA-adducts of benzo(a)pyrene 7, 8-dihydrodiol 9, 10-epoxides studied by biochemical and biophysical techniques

Exposure to various chemicals, either due to occupation or lifestyle, is considered to be a major contributing factor to tumour formation in man (Higginson, 1969; Doll and Peto, 1981). An important and prevalent class of potent carcinogeniccompounds present in the environment is polycyclic aromatic hydrocarbons(PAHs), which are found in various petroleum and combustion products derived from heat and power generation and motor vehicle exhausts (Baum, 1978). Furthermore, since PAHs are generally formed by pyrolysis of organic matters such as tobacco smoking and certain procedures of food preparation, the PAH exposure to humans is extensive.

Malolactomycin D, a potent inhibitor of transcription controlled by the Ras responsive element, inhibits Ras-mediated transformation activity with suppression of MMP-1 and MMP-9 in NIH3T3 cells

To search for anti-cancer agents, a screening system for Ras signal inhibitors was developed using a NIH3T3 cell line with an introduced reporter gene which is controlled by the Ras-responsive element (RRE). With this screening system, malolactomycin D was identified as a selective inhibitor of transcription from the RRE. This compound was found to preferentially inhibit the anchorage-independent growth rather than the anchorage-dependent growth of Ras-transformed NIH3T3 cells. The expression of matrix metalloproteinases MMP-1 and MMP-9, which have RRE in their promoters, were reduced by treatment with malolactomycin D at the translational and transcriptional levels. Analysis of the activity of mitogen-activated protein (MAP) kinases, which play important roles in transduction of the Ras signal, showed that malolactomycin D inhibits the activation of p38 MAP kinase and Jun N-terminal-kinase (JNK) but not extracellular signal-regulated kinase 1 or 2 (ERK1 or 2). These findings suggest that by inhibiting the pathway that leads to the activation of p38 MAP kinase and JNK, malolactomycin D suppresses the expression of MMPs. Since MMPs play important roles in metastasis and maintenance of the microenvironment of tumor cells, both of which facilitate tumor growth, the inhibition of MMPs by malolactomycin D is believed to contribute to its ability to inhibit Ras-mediated tumorigenesis.

Cooperation of bcl-2 and myc in the neoplastic transformation of normal rat liver epithelial cells is related to the down-regulation of gap junction-mediated intercellular communication

The objectives of this study were to isolate several rat liver epithelial cell clones containing the human bcl-2 and myc/bcl-2 genes in order to study their potential cooperative effect on neoplastic transformation and gap junction-mediated intercellular communication (GJIC) and to test the hypothesis that the loss of GJIC leads to tumorigenesis. Using anchorage-independent growth as a surrogate marker for neoplastic transformation, we transfected both normal rat liver epithelial cells, WB-F344, and a WB-F344 cell line overexpressing v-myc with human bcl-2 cDNA. Those cell lines that only expressed v-myc or human bcl-2 were unable to form colonies in soft agar. However, those cell lines that overexpressed both v-myc and human bcl-2 showed varying ability to form colonies in soft agar, which did not correlate with their human bcl-2 expression level. In order to test if there was a correlation between cell line growth in soft agar and the ability to communicate through gap junctions, we performed scrape load dye transfer and fluorescence recovery after photobleaching assays. Our results show that v-myc and human bcl-2 can cooperate in the transformation of normal cells, but the degree to which the cells are transformed is dependent on the cells' ability to communicate through gap junctions.

Defective retrovirus insertion activates c-Ha-ras protooncogene in an MNU-induced rat mammary carcinoma

Endogenous retrovirus sequences are present in the genome of a wide variety of animal species. The activation of the proto-oncogenes of the ras family, particularly c-Ha-ras, by either point mutation or overexpression, has been shown to be associated with a vast number, of different cancers. here we report that the insertion of a defective retrovirus in the -1 intron of rat c-Ha-ras is responsible for the activation of the gene by over 10-fold overexpression in an MNU-induced rat mammary cancer. A portion of the 3' end of the retroviral sequence is expressed as a part of the c-Ha-ras transcript in the carcinoma tissue, indicating the direct involvement of this element in the transcription of the c-Ha-ras gene. The c-Ha-ras structural gene transcribed by the promoter of the defective retroviral element can neoplastically transform the NIH 3T3 cell line upon transfection.

Accumulation of genetic alterations and their significance in each primary human cancer and cell line

Analyses of multiple genetic alterations accumulated in each cancer cell is expected to provide useful information to elucidate the molecular mechanisms involved in tumorigenesis. Here, we summarized the results of studies on aberrations of oncogenes and tumor suppressor genes by ourselves and other groups. DNAs analyzed were from particular sets of surgical specimens from human tumors and cancer cell lines derived from non-small cell lung cancers, pancreatic cancers, hepatocellular carcinomas and gliomas. Tumors could be grouped into two types based on the genetic alterations detected. Tumors in group 1 had mutations in genes encoding proteins involved in a limited number of signal transduction cascades such as p16-cyclin D1/CDK4-RB or MDM2-p53-p21, where the aberration of one component seems to be sufficient to cause dysfunction of the cascade. Group 2 contained a subset of tumors in which no alteration was detected in the genes analyzed, even in the advanced stage or established cancer cells, indicating the involvement of completely different oncogenic pathways.

Susceptibility of experimental autoimmune hepatitis in transgenic mice overexpressing the c-H-ras gene

Results from a recent study of ours have demonstrated the significant role of the wild-type ras gene in the development of hepatocellular carcinoma in rasH2 mice having prototype human c-H-ras genes. Chronic cell death and regeneration have been considered to work as co-carcinogens with wild-type ras gene overexpression in this model. To elucidate a role of gene overexpression in the occurrence of chronic inflammation, we tried to induce inflammation in the liver of rasH2 mice by immunizing them with the supernatant of a freshly prepared syngenic liver homogenate. Immunization resulted in a dense inflammatory infiltrate in the portal tract and focal necrosis with spots of fatty or foamy degeneration in the transgenic mouse liver; however, these observations were less frequently observed in non-transgenic mouse liver. Monocytes, granulocytes and plasma cell infiltration were observed in the livers of transgenic mice. An immunohistochemical study showed that CD3-positive lymphocytes also infiltrated the liver. The inflammatory infiltrate was still present in the transgenic liver 24 weeks after the last injection, but little infiltrate was observed at the same time in non-transgenic mice. No hepatic tumours could be produced over the 6 months duration of the study and the results are only preliminary. However, these results do suggest that overexpression of wild-type ras is partially responsible for the occurrence of autoimmune chronic hepatitis.

Stage-specific gene expression during hepatocarcinogenesis in the rat

The alteration of genetic expression ubiquitously seen in both preneoplastic and neoplastic tissues has been investigated for many years in the hope that the critical molecular changes resulting in cancer can be elucidated. The alteration of the expression of specific genes has already been employed in diagnostic and even screening procedures for this disease. In the past many observations of such alterations have led to a variety of theories but not definitive generalizations. Studies of the alteration of genetic expression may now be viewed in the light of our understanding of the multistage nature of neoplastic development. This brief review describes a number of genes the expressions of which are altered during the stages of initiation and promotion, in contrast to the alteration of expression of genes during the stage of progression. The promotion stage is concerned primarily with the chronic interaction of promoting agents in the environment with the genetic apparatus of the cell, played out on the altered genetic background resulting from the stage of initiation. In contrast, the progression stage is characterized primarily by an evolving karyotypic instability resulting in continual genetic changes during this stage. On the basis of these distinctions it is possible to identify genes the altered expression of which is unique to the stage of progression. The identification of these genes and an understanding of mechanisms resulting in their altered expression will allow not only a better molecular characterization of the progression stage but also the quantitative analysis of neoplastic development in several model animal systems as well as eventually in the human.

Synthesis and characterization of 8-methoxy-2'- deoxyadenosine-containing oligonucleotides to probe the syn glycosidic conformation of 2'-deoxyadenosine within DNA

The synthesis of 8-methoxy-2'-deoxyadenosine (moA) protected at N6 as an N,N-dimethylformamidine derivative and incorporation of the modified nucleoside into oligodeoxynucleotides via the phosphoramidite method are described. UV thermal denaturation studies were conducted on duplexes containing moA:G, moA:C and moA:T base pairs to determine the thermodynamic stability of duplexes containing moA relative to their adenosine (A)-containing counterparts. In the case of moA:G base pairs the effect of moA substitution is sequence dependent. In A:G mismatch-containing sequences, which have been shown by structural characterization to have a syn conformational preference at the glycosidic bond of A, moA substitution results in stabilization of the duplex. In contrast, in sequences where the A in the A:G mismatch has been shown to prefer the anti conformation moA substitution is destabilizing to the duplex. Thus moA may be a useful probe for investigating the conformational preferences of the N-glycosidic bond of adenosine within DNA. In addition, moA nucleoside is more resistant to acid-catalyzed depurination than previously described 8-bromo-2'-deoxyadenosine, allowing for facile incorporation into oligonucleotides via automated solid phase DNA synthesis.

Ionizing radiation-induced cell death

Selected aspects of radiation-induced cell death, connected with signal transduction pathways are reviewed. Cell death is defined as insufficiency of the cellular signal transducing system to maintain the cell's physiological functions. The insufficiency may be due to impaired signal reception and/or transduction, lack or erroneous transcription activation, and eventual cellular 'misexpression' of the signal. The molecular basis of this insufficiency would be damage to genomic (but also other cellular) structures and closing of specific signalling pathways or opening of others (like those leading to apoptosis). I describe experimental data that suggest an important role of RAS/NF1 and p53/p105 Rb proteins in cell cycle control-coupled responses to DNA damage.

Site-specific mutation of the human c-Ha-ras transgene induced by dimethylbenzanthracene causes tissue-specific tumors in mice

Forestomach squamous cell carcinomas, lung adenocarcinomas and spleen angiosarcomas were induced by dimethylbenzanthracene (DMBA) in the rasH2 transgenic mouse line carrying human c-Ha-ras genes with their own promoter, encoding the prototype p21 gene product. Fifteen out of 21 mice (71%) developed forestomach squamous cell carcinomas, while 15 out of 21 (71%) had lung adenocarcinomas and 3 out of 21 (14%) showed spleen angiosarcomas within 8 weeks after a single administration of 50 mg/kg DMBA intraperitoneally. Somatic mutation at the 61st codon of the transgenes, from CAG(Gln) to CTG(Leu), was detected in all these newly developed tumors. However, non-transgenic littermates demonstrated no tumors at all. These findings provide strong evidence that the somatic mutational activation of human c-Ha-ras genes is a critical event in tumorigenesis and a close relationship is therefore strongly suggested between the tissue-specific development of tumors and the somatic mutation of human c-Ha-ras genes in these rasH2 transgenic mice.

High incidence of H-ras oncogene mutations in squamous cell carcinoma of lip vermilion

Nine specimens of well-differentiated squamous cell carcinoma of the lip vermilion have been analyzed for the presence of H-ras oncogene mutations, using the technique of hybridization with synthetic oligonucleotide probes on in vitro amplified tumour DNA. Five specimens harbored mutations: four in codon 12 and one in codon 13. This high incidence (55%) of mutated H-ras genes suggests that their activation may play an important role in lip tumour development and may be connected to the exposure to chemical and/or physical carcinogens.

DNA amplifications and elevated expression of proto-oncogene in addition to altered DNA ploidy in metastatic brain tumors

The histopathological characteristics, proto-oncogene amplification, immunohistopathology of the c-erbB-2 product distribution, and the DNA content of nuclei were examined in metastatic brain tumors, which consisted of seven adenocarcinomas, a large cell carcinoma, a squamous cell carcinoma, a renal cell carcinoma and a mucoepidermoid carcinoma. A very high incidence of DNA changes was seen in these tumors. Proto-oncogene amplification and abnormal DNA content in the nuclear portion were found in 64% (7/11) and 67% (6/9) of cases, respectively. We also found double oncogene alteration in three cases metastasizing from lung, esophagus and kidney, and triple oncogene alteration in one case metastasizing from breast. We could not identify the common alterations in the group of metastatic brain tumor cells. These data suggest that the proto-oncogene amplifications and the alteration of DNA ploidy pattern may contribute to the metastatic process.

Site-directed mutagenesis, fluorescence, and two-dimensional NMR studies on microenvironments of effector region aromatic residues of human c-Ha-Ras protein

The Tyr residues in positions 32 and 40 of human c-Ha-Ras protein were replaced by site-directed mutagenesis (Y32F, Y32W, Y40K, and Y40W) to examine their roles in the signal-transducing activity and the sensitivity to the GTPase activating protein (GAP). The signal-transducing activity of the oncogenic Ras protein in PC12 cells was lost upon mutations Y32F and Y40K, but retained upon mutations Y32W and Y40W. These results suggest that residues 32 and 40 are both required to have aromatic groups and residue 32 is further required to have a hydrogen donor. On the other hand, three mutations (Y32F, Y32W, and Y40W) caused no appreciable reduction in either GAP-binding affinity or GAP sensitivity. By the Y40K mutation, GAP-binding affinity was slightly lowered, while GAP sensitivity was drastically impaired. Therefore, for residues 32 and 40 of Ras, interactions with GAP appear to be different from those with the target of signal transduction in the PC12 cell. As for the Y32W-Ras protein bound with an unhydrolyzable GTP analogue (GMPPNP), the Trp32 fluorescence is appreciably red-shifted, weaker, and more susceptible to KI quenching as compared to that of the GDP-bound form. Two-dimensional NMR spectroscopy with selectively deuterated Ras proteins revealed fewer and weaker nuclear Overhauser effects on the aromatic protons of Trp32 in the GMPPNP-bound form than in the GDP-bound form. This indicates that the side chain of Trp32 is more exposed to the solvent in the GMPPNP-bound form than in the GDP-bound form.(ABSTRACT TRUNCATED AT 250 WORDS)

DNA amplifications on chromosomes 7, 9 and 12 in glioblastoma detected by reverse chromosome painting

Biopsies and cell culture, respectively, of four human glioblastoma multiforme (WHO 4) have been evaluated for gene amplification using reverse chromosome painting. Three of the tumours showed amplified domains within chromosome bands 12q13-15. The exact localisation and extension of the amplified domains, however, varies within this region. Southern blot analysis revealed amplification of the GLI oncogene in two of the glioblastomas which were found to contain amplified domains within 12q13-15. Reverse chromosome painting also identified amplified domains within bands 7q21 and 9p23-24. Amplification within region 9p23-24 has previously not been reported in glioblastoma. The amplified domain encompassing 9p23-24 was detected in the same glioblastoma which contained an amplification unit within bands 12q13-14. These data, together with previous reports, indicate that amplifications are predominantly found on chromosomes 7, 9 and 12 in glioblastoma. In addition, this study provides further evidence that coamplification is not a rare event in glioblastoma.

Inherited amplification of an active gene in the cytochrome P450 CYP2D locus as a cause of ultrarapid metabolism of debrisoquine

Deficient hydroxylation of debrisoquine is an autosomal recessive trait that affects approximately 7% of the Caucasian population. These individuals (poor metabolizers) carry deficient CYP2D6 gene variants and have an impaired metabolism of severely commonly used drugs. The opposite phenomenon also exists, and certain individuals metabolize the drugs very rapidly, resulting in subtherapeutic plasma concentrations at normal doses. In the present study, we have investigated the molecular genetic basis for ultrarapid metabolism of debrisoquine. Restriction fragment length polymorphism analysis of the CYP2D locus in two families with very rapid metabolism of debrisoquine [metabolic ratio (MR) for debrisoquine = 0.01-0.1] revealed the variant CYP2D6 gene CYP2D6L. Eco RI RFLP and Xba I pulsed-field gel electrophoresis analyses showed that this gene had been amplified 12-fold in three members (father and his two children) of one of the families, and two copies were present among members of the other family. The CYP2D6L gene had an open reading frame and carried two mutations causing amino acid substitutions: one in exon 6, yielding an Arg-296-->Cys exchange and one in exon 9 causing Ser-486-->Thr. The MR of subjects carrying one copy of the CYP2D6L gene did not significantly differ from that of those with the wild-type gene, indicating that the structural alterations were not of importance of the catalytic properties of the gene product. Examination of the MR among subjects carrying wild-type CYP2D6, CYP2D6L, or deficient alleles revealed a relationship between the number of active genes and MR. The data show the principle of inherited amplification of an active gene. Furthermore, the finding of a specific haplotype with two or more active CYP2D6 genes allows genotyping for ultrarapid drug metabolizers. This genotyping could be of predictive value for individualized and more efficient drug therapy.

Rare mutations of the Gs alpha subunit gene in human endocrine tumors. Mutation detection by polymerase chain reaction-primer-introduced restriction analysis

BACKGROUND

The Gs alpha (Gs alpha) gene can be activated to the putative oncogene gsp by specific point mutations at codons 201 or 227. Such mutations have been reported in growth hormone (GH)-secreting pituitary adenomas and thyroid tumors. To clarify the role of Gs alpha gene in human endocrine tumors, 197 tumors were screened for point mutations at codons 201 or 227 of the Gs alpha gene.

METHODS

Mutations were detected by primer-introduced restriction analysis (PIRA) of the polymerase chain reaction (PCR) product of genomic DNA.

RESULTS

These Gs alpha mutations were present in 4 of 53 pituitary adenomas (4 of 43 GH-secreting adenomas; 1 of these 4 was a GH- and prolactin-secreting adenoma from a patient with familial multiple endocrine neoplasia Type 1), 4 of 66 thyroid tumors (4 of 30 papillary carcinomas), and 1 of 19 adrenocortical adenomas (1 of 6 aldosterone-secreting adenomas). In contrast, none of these Gs alpha mutations were detected in parathyroid tumors, endocrine pancreatic tumors, or pheochromocytomas.

CONCLUSIONS

Gs alpha mutations at these two loci may play a role in the pathogenesis of a small population of GH-secreting pituitary adenomas, papillary thyroid carcinomas, and adrenocortical adenomas, but that they are not involved in the pathogenesis of other types of endocrine tumors.

Cyclobutane thymine dimers in a ras proto-oncogene hot spot activate the gene by point mutation

ras proto-oncogenes with a cyclobutane-type thymine photodimer (cis-syn or trans-syn isomer) were constructed by replacement of a portion of the gene with a chemically synthesized fragment. When the genes were transfected by the calcium phosphate method into mouse NIH3T3 cells, they induced focus-formation, indicating that both photoproducts were mutagenic in mammalian cells. Sequence analysis of the ras gene fragments derived from the transformed cells showed that the genes were activated by a point mutation. The mutations detected most frequently were 3'-T-->A for the cis-syn isomer and 5'-T-->A for the trans-syn isomer. In contrast, a different trend of mutations was observed when a primer on a DNA template with a cis-syn dimer was extended in vitro by either DNA polymerase beta or alpha.

Sequence-specific 1H and 15N resonance assignments and secondary structure of GDP-bound human c-Ha-Ras protein in solution

All the backbone 1H and 15N magnetic resonances (except for Pro residues) of the GDP-bound form of a truncated human c-Ha-ras proto-oncogene product (171 amino acid residues, the Ras protein) were assigned by 15N-edited two-dimensional NMR experiments on selectively 15N-labeled Ras proteins in combination with three-dimensional NMR experiments on the uniformly 15N-labeled protein. The sequence-specific assignments were made on the basis of the nuclear Overhauser effect (NOE) connectivities of amide protons with preceding amide and/or C alpha protons. In addition to sequential NOEs, vicinal spin coupling constants for amide protons and C alpha protons and deuterium exchange rates of amide protons were used to characterize the secondary structure of the GDP-bound Ras protein; six beta stands and five helices were identified and the topology of these elements was determined. The secondary structure of the Ras protein in solution was mainly consistent with that in crystal as determined by X-ray analyses. The deuterium exchange rates of amide protons were examined to elucidate the dynamic properties of the secondary structure elements of the Ras protein in solution. In solution, the beta-sheet structure in the Ras protein is rigid, while the second helix (A66-R73) is much more flexible, and the first and fifth helices (S17-124 and V152-L171) are more rigid than other helices. Secondary structure elements at or near the ends of the effector-region loop were found to be much more flexible in solution than in the crystalline state.

Evidence of gene amplification in the form of double minute chromosomes is frequently observed in lung cancer

Amplification of cellular proto-oncogenes, important in tumor progression, has been correlated with a poor clinical outcome in a variety of human tumor types. Amplified genes are observed in two cytogenetically distinct entities, double minutes (DMs) and homogeneously staining regions (HSR). We examined 54 fresh lung tumor specimens obtained from patients with non-small cell lung cancer for cytogenetic evidence of gene amplification in the form of DMs. The majority of these patients had received no prior treatment. The cells were harvested within 24 hours after receiving the specimens, and the slides were stained with Giemsa to specifically look for DMs. We found DMs in 24 of 31 (77%) specimens that exhibited metaphase spreads. Similar incidences of DMs were found when histologic cell types, primary vs. non-primary tumors, and specimens from patients with prior treatment vs. no prior treatment were compared. Therefore, DMs occur frequently in non cultured lung tumor cells, providing evidence that gene amplification may be an important aspect of tumor behavior in patients with non-small cell lung carcinoma. Further investigation is warranted to identify the specific tumor-related genes located on these abnormal chromosomes. This also suggests that ongoing efforts to eliminate amplified drug-resistant genes or oncogenes contained on DMs in tumor cells may be relevant in patients with non-small cell lung cancer.

Sequencing analysis of Ha-, Ki-, and N-ras genes in rat urinary bladder tumors induced by N-[4-(5-nitro-2-furyl)-2-thiazolyl]formamide (FANFT) and sodium saccharin

Male F344 rats were fed N[4-(5-nitro-2-furyl)-2-thiazolyl]formamide (FANFT) for up to 4 wk, then given the basal diet with or without 5% sodium saccharin for up to 100 wk. In a previous study, we demonstrated point mutations in codons 12 and 61 of Ha-ras gene among eleven transitional cell carcinomas (TCC), one undifferentiated carcinoma, and two sarcomas of the urinary bladder (Mol Carcinogen 3:210-215, 1990). In this study, Ha-ras, Ki-ras, and N-ras sequences were examined by polymerase chain reaction (PCR) and direct DNA sequencing. The results confirm the point mutation in codon 61 (CAA to CGA in 5 TCCs and to CTA in one TCC) of the Ha-ras gene. Mutation at codon 12 was not confirmed. No mutation was found in the Ki-ras gene. Sequences of the N-ras gene exons 1 and 2 were determined, and no mutations was detected. These results suggest the involvement of activated Ha-ras gene, but not Ki-N or N-ras gene, in rat urinary bladder carcinogenesis induced by FANFT. Subsequent sodium saccharin administration did not affect the changes in Ha-ras gene.

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.

c-myc mRNA expression in non-Hodgkin's lymphomas

Steady state c-myc mRNA levels determined by Northern blot analysis were examined in non-Hodgkin's lymphomas (NHL) of both high (n = 29) and low malignancy (n = 18), and in non-specific chronic lymphadenitis (n = 6). High grade NHL, classified according to the updated Kiel classification, revealed significantly larger amounts of c-myc mRNA compared with low grade NHL and lymphadenitis. mRNA levels in non-specific lymphadenitis were lower than in low grade NHL, but the differences were not statistically significant. No correlation between c-myc mRNA levels and the immunologic phenotype was discernible. Growth fractions of the NHL were determined by immunostaining with the monoclonal antibody Ki-67. Significant correlations between the percentages of Ki-67-positive cells, as well as the amounts of c-myc mRNA, and classification into high or low grade NHL were found. However, the percentage of Ki-67 positive cells and c-myc mRNA levels in individual cases and in the various histologic entities of NHL did not correlate. Our results indicate the overexpression of the c-myc gene in NHL, and a highly significant correlation of steady state c-myc mRNA levels with the prognosis-related histomorphologic Kiel classification of NHL into different subgroups of low and high grade malignancy.

Expression of developmentally relevant proteins by rodent embryo CNS cells in vivo and in vitro: proto-oncogene pp60c-src and high molecular weight neurofilament protein

The expression of proteins that play a role in neuronal differentiation was examined in central nervous system (CNS) micromass embryo cell cultures and compared to expression at comparable developmental stages in vivo. The protein product of the src proto-oncogene (pp60c-src) has been postulated to have a specific role in development because, although it is expressed in many tissues, marked increases in amount and activity of pp60c-src occur in neurons at the time of differentiation. Another protein of interest, high molecular weight neurofilament (NF) protein, is found in differentiated neurons. In the present study, changes over time in the expression of these two proteins in vitro and in vivo were examined. In the micromass cell cultures, primary cells from day 12 rat embryo CNS are plated at high density and differentiate into neurons during five days in culture. Tissues from embryos grown in vivo were assessed at 12 and 17 days post-coitum. Proteins were quantified by PAGE separation of equal amounts of total protein followed by transfer to membranes, immunoblotting, and densitometric scanning of blots. Increases in the amount of both proteins with neuronal differentiation was shown. Protein kinase activity of immunoprecipitated pp60c-src also increased in cell cultures and in embryos. Similarity in patterns of expression between in vitro and in vivo tissue samples provides further evidence that the cultures closely simulate in vivo differentiation and are a useful system for examining expression of developmental genes in vitro.

Infrequent mutation of the ras genes in skin tumors of xeroderma pigmentosum patients in Japan

By using PCR amplification and oligonucleotide mismatch hybridization, base-substitution mutations of the ras genes in 26 skin tumors of Japanese xeroderma pigmentosum (XP) patients were studied. Thin sections of tumor tissues which were fixed and embedded in paraffin blocks were used in this study. After analyzing codons 12, 13 and 61 of the H-, K- and N-ras genes by using 66 oligomer probes, we detected only one mutation of the K-ras gene at codon 61 in one tumor sample. All the other tumors were therefore considered not to have a mutation in the ras genes. These results suggest that mutations of the ras genes are not particularly associated with skin tumors of Japanese XP patients.

The biochemistry of ras p21

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Loss of heterozygosity on chromosome 1p in thyroid adenoma and medullary carcinoma, but not in papillary carcinoma

We analyzed 53 loci on 21 chromosomes other than chromosome 4 to detect possible loss of heterozygosity in 31 thyroid tumors using polymorphic DNA markers that detect allelic deletions at specific chromosomal loci. Loss of heterozygosity on chromosomes 1, 7 and 12 was detected in one follicular thyroid adenoma, and on chromosome 1 in two medullary thyroid carcinomas. However, no loss of heterozygosity was detected at any of the loci examined in papillary thyroid carcinomas. These results suggest that chromosomal loss detected in thyroid adenoma is one of the signals for risk of premalignant transformation, and that inactivation of unknown genes on chromosome 1p contributes to tumorigenesis of medullary thyroid carcinoma. Some genetic changes other than chromosomal losses may participate in the tumorigenesis of papillary thyroid carcinoma.

Transforming activity of a synthetic c-Ha-ras gene containing O6-methylguanine in codon 12

A mutagenic DNA-adduct, O6-methylguanine, was introduced into codon 12 of the synthetic c-Ha-ras gene by cassette mutagenesis. Transfection of this modified ras gene into normal NIH3T3 cells by the calcium phosphate procedure resulted in significant induction of focus formation. The ras gene inserted into the transformed cells was found to have a G to A transition at the position of the modified base. These results indicate that an O6-methylguanine residue in DNA may lead to a mutation and be one cause of activation of the ras gene.

The importance of the specific Z-DNA structure and polyamines in carcinogenesis: fact or fiction

In this work some aspects of carcinogenesis are given. The importance of the emergence of Z or H DNA structure in the gene, or in the flanking gene sequences for the gene deletion and unusual gene recombination, is discussed. Some considerations on the role of selective pressure (of polyamines, of Mg2+, of the various levels of topoisomerase II, and of ATP) in the process of oncogene amplification, are given too.

Enhanced immunoreactivity of ras oncogene p21 protein in urinary bladder epithelium of rats treated with N-[4-(5-nitro-2-furyl)-2-thiazolyl]formamide

Normal urothelium and various lesions of the rat urinary bladder induced by the dietary administration of 0.2% N-[4-(5-nitro-2-furyl)-2-thiazolyl]formamide (FANFT) (up to 77 weeks) or by the combination of 0.2% FANFT and the subsequent administration of 5% sodium saccharin or 2% DL-tryptophan (up to 104 weeks) were evaluated for immunoreactivity with monoclonal antibody to ras p21 by avidin-biotin immunohistochemistry. Seventy-one to 100% of transitional cell carcinomas showed strong reactivity to the antibody to ras p21 depending on treatment with long-term administration of FANFT or by 6 weeks administration of FANFT followed by sodium saccharin or DL-tryptophan. Focal reactivity to the ras p21 antibody was frequently observed in the hyperplastic (57-96%) or normal appearing urinary bladder epithelium (50-100%) in rats treated with FANFT (FANFT alone or in combination with sodium saccharin or tryptophan) but not in hyperplasia or normal epithelium in rats given sodium saccharin or tryptophan alone, without pretreatment with FANFT or in untreated controls. The present results show that there is a close association of enhanced immunoreactivity with ras p21 antibody in the urinary bladder epithelium to FANFT treatment, and that ras p21 is expressed in normal, hyperplastic and neoplastic lesions of the bladder of rats treated with FANFT. These results suggest that enhanced immunoreactivity with ras p21 is observed as a consequence of the treatment with FANFT but it alone does not reflect the progression from benign to malignant lesions.

Sequence requirements for the stimulation of gene amplification by a mammalian genomic element

HSAG-1 is a 3.4-kb genomic element from a human chronic lymphocytic leukemia--Chinese hamster ovary (CHO) hybrid cell line shown to stimulate the amplification of expression vectors in cis when transfected into a variety of cell lines [McArthur and Stanners, J. Biol. Chem. 266 (1991) 6000-6005]. Subfragments of HSAG-1 were tested for amplification activity by insertion into the vector, pSV2DHFR. The results suggest that multiple positive- and negative-acting elements were present that influenced amplification activity. The deletion of regions believed to contain positive-acting elements decreased or abolished the amplification stimulatory activity of the most active 1.45-kb fragment, supporting this hypothesis. The construction of composite sequences containing multiple positive elements and lacking negative elements, however, failed to enhance the activity; maximum activity was obtained only with the original intact configuration of elements. Two of two CHO HSAG-1-like elements tested had an activity equivalent to HSAG-1, while one of 24 random CHO genomic fragments tested had an activity as high as HSAG-1. The combination of sequence and structural features needed to affect the frequency of gene amplification may therefore be quite common in the mammalian genome.

Proto-oncogene expression in cultured synovial fibroblasts of patients with rheumatoid arthritis

Total RNA was isolated from cultured synovial fibroblasts of nine patients with rheumatoid arthritis and two controls (cruciate ligament ruptures). RNA was dot-blotted and hybridized with nine different, cloned cellular or viral oncogene probes. None of the proto-oncogenes showed a significant difference of expression in cultured fibroblasts from patients with rheumatoid arthritis when compared to the expression of control fibroblasts.

Diversity in receptor signalling: cellular individuality and the search for selective drugs

Recent developments in the molecular pharmacology of receptor signalling are reviewed. Receptors and other signalling molecules belong to superfamilies characterized by variations on given themes. A remarkable degree of diversity is generated by unique combinations of molecular entities, and there are also interactions between parallel signal transduction pathways. Molecular biology techniques have revealed new targets for drug development, as well as new methods of drug testing. However, it is not yet clear whether molecular and biochemical specificity always correspond to clinical selectivity.

Grading of nuclear pleomorphism in oral carcinomas. Higher prognostic value than stereological assessment of nuclear volume

A more objective and reproducible grading system is needed in order to give better prognostic indicators and thereby offer improved treatment to oral cancer patients. Recently, simple objective stereological techniques for cellular estimates have emerged, of which the estimate of mean nuclear volume has shown a correlation with prognosis for various cancers. We have therefore measured the mean nuclear volume in 44 invasive buccal mucosal squamous cell carcinomas and related it to the survival of patients. The mean nuclear volume did not correlate with prognosis for these patients (p = 0.25). However, the nuclear polymorphism, which is subjective even though it is based on well-described criteria in a histopathological grading system, correlated significantly with prognosis (p = 0.03). These findings indicate that the traditional histopathological evaluation of nuclear polymorphism includes valuable prognostic information.