bluuebunny/crossref_metadata_2025_split huggingface dataset:
Frequent activation of the Ki‐ras oncogene at codon 12 in N‐methyl‐N‐nitrosourea‐induced rat prostate adenocarcinomas and neurogenic sarcomas
Authors: Sukumar Saraswati , Armstrong Barbara , Bruyntjes Joost P. , Leav Irwin , Bosland Maarten C. 
Published: February 2007

AbstractRat neoplasms induced by methylating carcinogens frequently contain ras genes activated by a single point mutation. Rat prostatic tumors induced by a combination of a single injection of N‐methyl‐N‐nitrosourea (MNU) and long‐term treatment with testosterone were examined for the presence of such activating point mutations in ras genes. These tumors, which arose exclusively in the dorsolateral prostate, included both adenocarcinomas and sarcomas. Activating mutations in codon 12 of the Ki‐ras gene were found in 7 of 10 carcinomas and 4 of 5 sarcomas, using selective oligonucleotide hybridization analysis of DNA amplified by the polymerase chain reaction (PCR). However, no mutated Ha‐ras oncogenes were detected. The presence of PCR‐engineered Hphl restriction sites created by the existence of a G35→A mutation in the rat Ki‐ras oncogene identified the mutation as a GC→A transition at the second position of codon 12. Production of O6‐methylguanine adducts in the Ki‐ras codon 12 followed by base mispairing during replicative DNA synthesis is thus the likely molecular mechanism of initiation of prostatic carcinogenesis by MNU in the rat. Three of the four sarcomas positive for the Ki‐ras G35→A mutation were immunohistochemically defined as of Schwann cell origin, indicating that involvement of the ras gene family is possible in tumorigenesis of this cell lineage. Loss of the wild‐type Ki‐ras allele was also observed in all four of these sarcomas.
Transient expression of the cloned mouse c‐Ha‐ras 5′ upstream region in transfected primary SENCAR mouse keratinocytes demonstrates its power as a promoter element
Authors: Neades Renee , Betz Natalie A. , Sheng Xiaoyang , Pelling Jill C. 
Published: February 2007

AbstractThe mouse Ha‐ras oncogene is activated by point mutation and overexpressed in developing papillomas during two‐stage skin carcinogenesis in SENCAR mice. One of our research aims is to characterize the factors regulating Ha‐ras gene expression at the transcriptional level in SENCAR mouse epidermis. Towards this goal, we sequenced 1400 bp of the 5′ upstream region of the mouse Ha‐ras gene so as to characterize various cis‐regulatory elements present in the gene. We identified seven sites with the proper consensus sequence for binding the SP1 transcription factor and three potential binding sites for the CTF‐1 factor. In addition, we located a 13‐base sequence with 92% homology to the consensus sequence for an estrogen response element and two hexamers with consensus sequences identical to the core sequence of the glucocorticoid response element. A series of transient gene expression vectors was constructed in which various regions of the mouse Ha‐ras 5′ upstream region were fused to the chloramphenicol acetyltransferase (CAT) gene. These expression plasmids were transfected into newborn and adult primary SENCAR epidermal cells, the epidermal cell population that presumably contains the stem cells involved in two‐stage skin tumorigenesis. Transient gene expression assays carried out after 48‐72 h indicated that a 2.3‐kb Ha‐ras 5′ fragment produced CAT activity comparable to that produced by pSV2CAT and pdolCMVCAT, both of which are plasmids with strong viral promoters and enhancers driving CAT gene expression. Maintenance of transfected keratinocytes under both nondifferentiating (0.05 mM calcium) and differentiating (1.2 mM calcium) culture conditions demonstrated that the mouse Ha‐ras upstream region was relatively unresponsive to changes in calcium concentration in transient expression assays carried out in either newborn or adult keratinocytes. Our results demonstrated the power of the cloned mouse Ha‐ras promoter and upstream region in driving transient gene expression after transfection into primary keratinocytes.
Evidence that toxic injury is not always associated with induction of chemical carcinogenesis
Authors: Tennant Raymond W. , Elwell Michael R. , Spalding Judson W. , Griesemer Richard A. 
Published: February 2007

AbstractLong‐term rodent bioassays with chemicals administered at maximum tolerated doses identify noncarcinogens as well as carcinogens. Thirty‐one chemicals recently evaluated for carcinogenic potential by the National Toxicology Program provide unique data on the relationships between mutagenicity, toxicity, and carcinogenicity. Twenty‐two substances were classified as carcinogens, and nine showed no evidence of carcinogenicity. Although cellular proliferation does play an intrinsic role in neoplastic processes, the responses associated with chronic toxicity in these studies were not always sufficient to induce neoplasia. Regardless of their mutagenic potential, 19 carcinogens induced toxic effects at sites that did not show neoplastic changes; similar toxic lesions were also seen among the mutagenic and nonmutagenic noncarcinogens. Although many nonmutagens induced neoplasia at sites that showed toxic effects, some of the same chemicals also exhibited toxicity at other sites that showed no neoplastic effect. These results suggest that for some chemicals, properties other than mutagenicity or toxicity may be responsible for their carcinogenic potential.
Two polychlorinated hydrocarbons cause phospholipid‐dependent protein kinase C activation in vitro in the absence of calcium
Authors: Rotenberg Susan A. , Weinstein I. Bernard 
Published: February 2007

AbstractPolychlorinated hydrocarbons known to be nongenotoxic carcinogens were screened as activators of protein kinase C (PKC)‐β1 either at high concentrations of Ca2+ or in the absence of Ca2+ (i.e., with 1 mM ethylene glycol‐bis(β‐aminoethyl ether) N,N,N′,N′,‐tetraacetic acid). Of those compounds tested, kepone and dicofol significantly stimulated PKC activity in the absence, but not the presence, of Ca2+. PKC activation was most pronounced in the presence of phosphatidylserine. Kepone and dicofol stimulated PKC activity 26% and 13%, respectively, as compared with the PKC activity (100%) stimulated by the tumor‐promoting phorbol ester 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA). Northern blot analysis of expression of TPA‐inducible genes by kepone showed slight expression of phorbin and ornithine decarboxylase in murine embryo fibroblasts. Future studies are required to determine the relevance of PKC activation by kepone and dicofol to the known carcinogenicity of these compounds.
Stable expression of rat cytochrome P450IA2 cDNA and hydroxylation of 17β‐estradiol and 2‐aminofluorene in V79 Chinese hamster cells
Authors: Wölfel Catherine , Platt Karl‐Ludwig , Dogra Satish , Glatt Hansruedi , Wächter Felix , Doehmer Johannes 
Published: February 2007

AbstractIn continuation of our work toward the establishment of a working cell bank for metabolic and toxicological studies, V79 Chinese hamster cells were genetically engineered for stable expression of rat cytochrome P4501A2. Full‐length cDNA encoding rat P4501A2 was obtained by searching a cDNA library made from Aroclor 1254‐induced rat liver mRNA and by joining a small 5′‐end fragment to a fragment containing the rest of the cDNA. The sequence of the cDNA was confirmed by DNA sequencing and comparison to a previously published cDNA sequence. The reconstructed full‐length cDNA was inserted into a simian virus 40 early promoter‐containing eukaryotic expression vector and cotransferred with the neomycin phosphotransferase gene as a selective marker into V79 cells by the calcium/phosphate‐coprecipitation technique. G418‐resistant V79 cell clones were checked for chromosomal integration of the cDNA by Southern blotting, for expression of authentic mRNA and protein by northern and western blotting, and for P4501A2‐specific enzymatic activities such as hydroxylation of 17β‐estradiol and 2‐aminofluorene.
Activating point mutation in Ki‐ras codon 63 in a chemically induced rat renal tumor
Authors: Higinbotham Kathleen G. , Rice Jerry M. , Perantoni Alan O. 
Published: February 2007

AbstractRenal mesenchymal tumors induced in F344 rats with methyl(methoxymethyl)nitrosamine (DMN‐OMe) have previously been shown by our laboratory to contain transforming Ki‐ras sequences, activated most commonly by a variety of codon 12 mutations. Further sequence analysis of one DMN‐OMe‐induced tumor with transforming Ki‐ras sequences detected by NIH 3T3 transfection assay but with no mutation in codon 12 detected by selective oligonucleotide hybridization has now revealed an activating point mutation in codon 63. The observed GAG→AAG transition in codon 63, which replaces glutamic acid with lysine, was the only detectable mutation in exon 1 and 2 hotspot regions of Ki‐ras in this tumor. The same mutation was also detected in Ki‐ras sequences derived from first‐ and second‐cycle transformants in NIH 3T3 transfection assays. Although random mutagene‐sis studies of cloned Ha‐ras sequences by Fasano et al. (Proc Natl Acad Sci USA 81:4008–4012, 1984) had already indicated that GAG→AAG mutations in codon 63 of ras are transforming, this is the first demonstration of the natural occurrence of this particular activating mutation in a tumor. © 1992 wiley‐List, Inc.
Acquisition of responsiveness to chemical carcinogens by rodent embryo fibroblasts expressing high levels of the c‐myc proto‐oncogene
Authors: Hsiao W. L. Wendy , Castro Mark , Giezentanner John , Fan Hung , Hanecak Ronnie 
Published: February 2007

AbstractWe investigated the ability of overexpression of the c‐myc proto‐oncogene to potentiate in vitro transformation by model chemical carcinogens. A mouse c‐myc gene was introduced to C3H 10T1/2 and Rat 6 embryo fibroblast cell lines via a retroviral vector containing the gene for neomycin resistance. Our present work extends previous findings by showing that individual vectored C3H 10T1/2 clones have enhanced (twofold to sevenfold) sensitivity to benzo[a]pyrene (BP) and N‐methyl‐N‐nitro‐N′‐nitrosoguanidine (MNNG). Rat 6 clones acquiring the c‐myc gene display various degrees of altered morphology. They form orderly but densely packed cells, grow to higher saturation density, and yield microcolonies in soft agar. The degree of altered growth properties is directly correlated with the level of c‐myc expression. Transient exposure of c‐myc‐expressing clones to BP and MNNG induced the formation of distinct, large colonies in soft agar, whereas the untreated cells formed microcolonies and the parental Rat 6 cells remained single cells in soft agar. We also demonstrated that the degree of responsiveness to chemical carcinogens of the clones correlates with their ability to form microcolonies in soft agar. These cells overexpressing c‐myc may be used as a model system to study the interaction between oncogenes and chemical carcinogens in the process of multistage carcinogenesis. © 1992 Wiley‐List, Inc.
Multiple molecular alterations in mouse lung tumors
Authors: Re Fabio C. , Manenti Giacomo , Borrello Maria G. , Colombo Mario P. , Fisher James H. , Pierotti Marco A. , Porta Giuseppe Della , Dragani Tommaso A. 
Published: February 2007

AbstractTwenty‐five mouse lung tumors induced by a single urethan treatment in female A/J, BALB/c, and (A/J × C3H/He)F1 (AC3) mice were analyzed for the presence of mutations at codon 61 of the Ki‐ras gene and for the expression of the surfactant protein A (SP‐A). retinoblastoma (Rb), growth arrest‐specific‐3 (gas‐3), p53, c‐myc, and thymidylate synthase (TS) genes. Ki‐ras codon 61 mutations were detected in 22 of 25 tumor samples without differences among strains. In comparison with normal lungs, all the tumors showed increased SP‐A mRNA levels, indicating their derivation from alveolar type II pneumocytes or Clara cells. Rb and gas‐3 transcripts were instead found in all tumors at about tenfold and about 20‐fold reduced levels, respectively. No apparent structural alterations or loss of heterozygosity at the Rb locus was detected in any tumors. The p53 mRNA was observed without variation in quantity or size in lung tumors and normal tissue. A threefold to fivefold c‐myc overexpression was observed, without amplification of the gene. TS expression was only slightly increased, indicating no great differences in cell proliferation between lung tumors and normal tissue. Our data suggest that the pathogenesis of urethan‐induced lung tumors in mice involves specific and recurrent molecular alterations (Ki‐ras mutations, decrease of Rb and gas‐3 expression, and increase of c‐myc expression) that could represent different steps in lung carcinogenesis. © 1992 Wiley‐List, Inc.
Characterization of the syrian hamster c‐Ha‐ras gene and intron‐d‐exon transcript
Authors: Ebert Rolf , Wiseman Roger W. , Barrett. J. Carl , Reiss Eva , Rollich Günther , Schiffmann Deitmar 
Published: February 2007

AbstractThe coding sequences as well as 5′‐ and 3′‐flanking sequences of the Syrian hamster c‐Ha‐ras gene were deduced from cDNA clones derived from embryo fibroblast cell lines. Sequences of introns B, C, and D were obtained from genomic DNA after amplification by the polymerase chain reaction. Sequence comparisons with rat, mouse, and human c‐Ha‐ras genes revealed a high degree of homology. One of 12 cDNA clones contained intron‐D‐exon (IDX) sequences due to alternative splicing that would encode a p19 Ha‐ras gene product. Conservation between species suggests a functional role for the IDX, possibly as a negative control of p21 Ha‐ras expression. © 1992 Wiley‐Liss, Inc.
Efficient protection against oxidative DNA damage in chromatin
Authors: Ljungman Mats , Hanawalt Philip C. 
Published: February 2007

AbstractThe role of histones and higher order chromatin structures in protecting against oxidative DNA damage was investigated using an in vitro system consisting of nuclear and nucleoid monolayers as model chromatin substrates. These substrates, derived from human skin fibroblasts, were challenged with hydroxyl radicals produced via a Fenton reaction involving Fe(ll)‐ethylenediaminetetraacetic acid and ascorbic acid. The resulting DNA strand breaks were measured using the alkaline unwinding technique. The sequential removal of chromosomal proteins from the DNA by pretreating nuclear monolayers with increasing concentrations of salt dramatically increased the frequency of hydroxyl radical‐induced DNA strand breaks. Furthermore, the DNA in decondensed chromatin was found to contain 14‐fold fewer DNA strand breaks than naked, supercoiled DNA, whereas the DNA of “native” chromatin and “condensed” chromatin contained 100‐fold and 300‐fold fewer breaks, respectively. We conclude that the binding of histones to the DNA and its organization into higher order chromatin structures dramatically protects the DNA against hydroxyl radical‐induced DNA strand breaks and thus should be considered part of the cellular defense against the induction of oxidative DNA damage. © 1992 Wiley‐Liss, Inc.
Evidence for coincident mutations in human lymphoblast clones selected for functional loss of a thymidine kinase gene
Authors: Li Chuan‐Yuan , Yandell David W. , Little John B. 
Published: February 2007

AbstractA mitotic “recombination‐competent state” inducible by x‐irradiation is thought to exist in yeast. We sought evidence for such a process in mammalian cells by examining the occurrence of mutations at unlinked loci in clones derived from a human lymphoblast cell line. A total of 169 independent clones that arose spontaneously or after exposure to x‐rays or ethyl methanesulfonate were selected for new somatic mutations at the thymidine kinase gene on chromosome 17q. They were subsequently screened for coincident mutations by use of variable‐number‐of‐tandem‐repeat probes located on different chromosomes. Three coincident mutations were positively identified by Southern analysis on chromosomes 7 and 14; they included one that produced a new allele and two that caused loss of allele heterozygosity. Densitometric analysis of the latter two indicated the presence of two copies of the remaining allele. Several possible coincident genetic events were also observed on chromosome 17. These findings revealed a coincident mutant fraction of about 10−2/cell, whereas the expected mutation fraction at these loci is less than 10−4/cell. These results may thus provide the first molecular evidence that a “global” mutational process capable of inducing genetic instability exists in mammalian cells. © 1992 Wiley‐Liss, Inc.
Malignant transformation of NIH 3T3 fibroblasts by human c‐sis is dependent upon the level of oncogene expression
Authors: Macarthur Linda H. , Clarke Michael F. , Westin Eric H. 
Published: February 2007

AbstractHigh‐level expression of the c‐sis oncogene, which encodes the β chain of platelet‐derived growth factor, transforms immortalized rodent fibroblasts in vitro to a malignant phenotype. c‐sis gene expression has been demonstrated in a variety of human tumors, although generally at levels much lower than those shown to transform cells in vitro. We examined the effect of lower levels of c‐sis expression on the phenotype of NIH 3T3 fibroblasts. Clones with various levels of c‐sis expression were generated by transfecting NIH 3T3 cells with a plasmid that expressed the human c‐sis cDNA and the TN5 neomycin‐resistance gene. G418‐resistant clones, which expressed the c‐sis cDNA, were selected and characterized. Alterations in the phenotype of the clones that expressed c‐sis ranged from increased growth in soft agar to malignant tumor formation in nude and syngeneic mice. Increased levels of c‐sis cDNA expression correlated with the acquisition of features of transformation in a dose‐dependent manner and altered the cellular phenotype in a manner consistent with the progression of cells towards malignancy. These data support a model in which low levels of sis gene expression in tumors contribute to the acquisition of some features of transformation but require complementation by other genes or factors to produce a fully malignant phenotype. © 1992 Wiley‐Liss, Inc.
Expression of the transin, c‐fos, and c‐jun genes in rat transplantable osteosarcomas and malignant fibrous histiocytomas
Authors: Honoki Kanya , Tsutsumi Masahiro , Tsujiuchi Toshifumi , Kondoh Satoshi , Shiraiwa Kazumi , Miyauchi Yoshizumi , Mii Yoshio , Tamai Susumu , Konishi Yoichi , Tim Bowden G. 
Published: February 2007

AbstractThe expression of the transin, c‐fos, and c‐jun genes was assessed in transplantable osteosarcomas and malignant fibrous histiocytomas, as well as in pancreatic duct adenocarcinomas and hepatocellular carcinomas of rats and hamsters. Northern blot analysis revealed that both an undifferentiated osteosarcoma of spontaneous origin (SOS) and 4‐hydroxyaminoquinoline 1‐oxide (4‐HAQO)‐induced malignant fibrous histiocytomas with metastatic potential to the lung showed remarkably increased expression of transin mRNA transcripts. This was not the case for the other tumors. Interestingly, levels of transin mRNA were lower in lung metastatic lesions than in primary subcutaneous SOS tumors. The primary SOS and MFH expressed both c‐fos and c‐jun genes in conjunction with the transin gene, whereas the non‐transin expressers, a 4‐HAQO‐induced osteosarcoma (COS) and the pancreatic duct adenocarcinomas, demonstrated one or the other, but not both. These results suggest a possible involvement of transin expression in the progression of spontaneous osteosarcomas and 4‐HAQO‐induced malignant fibrous histiocytomas in rats. Expression of the c‐fos and c‐jun genes may play a regulatory role in this process. © 1992 wiley‐Liss, Inc.
ras Oncogene activation in mammary carcinomas induced by n‐methyl‐n‐nitrosourea in copenhagen rats
Authors: Lu Shi‐Jiang , Archer Michael C. 
Published: February 2007

AbstractThe occurrence of Ha‐ras and Ki‐ras oncogenes was investigated in mammary tumors produced by treating genetically resistant Copenhagen (Cop) rats with N‐methyl‐N‐nitrosourea. G35A codon 12 mutations in both Ha‐ras and Ki‐ras genes were analyzed by a polymerase chain reaction/liquid hybridization and gel retardation assay. More than half of the adenocarcinomas analyzed contained an activated Ha‐ras gene. This was also the predominant mutation in similar tumors from susceptible Buf/N rats, suggesting a common mechanism of initiation. In contrast, only two of 15 mammary adenosquamous carcinomas from the Cop rats contained an activated Ha‐ras gene, suggesting a different initiation mechanism for most of these tumors. Ki‐ras activation was found in none of five and one of five adenocarcinomas from Buf/N and Cop rats, respectively, and in none of 13 adenosquamous carcinomas from Cop rats. These results suggest that Ki‐ras activation does not play a major role in the initiation of the mammary tumors. © 1992 Wiley‐Liss, Inc.
Transcriptional inhibition by carcinogenic chromate: Relationship to DNA damage
Authors: Manning Francis C. R. , Xu Jian , Patierno Steven R. 
Published: February 2007

AbstractHexavalent chromium compounds are carcinogenic to humans, are potent inducers of tumors in experimental animals, and can neoplastically transform cells in culture. In this study, the effects of sodium chromate on the expression of the 78‐kDa glucose‐regulated protein (GRP78) gene and on general transcription were investigated with respect to the DNA damage induced by this agent. DNA single‐strand breaks, DNA‐protein cross‐links, and chromium‐DNA adducts were present in CHO cells immediately after 2 h of treatment with sodium chromate. Subsequently, these types of damage were repaired at different rates. Single‐strand breaks were essentially repaired after 8 h. By 24 h posttreatment, no cross‐links remained in cells exposed to 30 or 150 μM chromate, although cells treated with the 300‐μM concentration still contained cross‐links at that time. DNA‐chromium adducts remained unrepaired for at least 32 h. The moderate constitutive level of GRP78 mRNA was not affected by chromate. Chromate did, however, suppress induction of this gene by tunicamycin in a concentration‐ and time‐dependent manner. Thirty micromolar sodium chromate (96% survival), which caused the least DNA damage, had no effect on GRP78 induction, general RNA synthesis, or mRNA synthesis. Induction of GRP78 was suppressed immediately and 12 h after treatment with 150 μM chromate (54% survival), although there was a partial recovery of induction at 24 h after treatment, which correlated with the repair of DNA‐protein cross‐links. In contrast, both total cytoplasmic RNA and mRNA synthesis were suppressed by approximately 60–75% for at least 32 h by 150 μM chromate. At the 300‐μM concentration (8% survival), where DNA‐protein cross‐links persisted beyond 24 h, GRP78 induction was totally suppressed for at least 24 h, while total RNA and mRNA synthesis were suppressed by 80–90% for at least 32 h. Overall, the effects of chromate on GRP78 induction correlated most closely with the presence of DNA‐protein cross‐links, but suppression of total RNA and mRNA synthesis correlated with the presence of DNA‐chromium adducts. These results indicate that chromate exerts differential effects on the induction of the GRP78 gene and on general transcription. © 1992 Wiley‐Liss, Inc.