bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mutations at codon 61 of the Ha‐ras proto‐oncogene in precancerous liver lesions of the B6C3F1 mouse
Authors: Buchmann Albrecht , Mahr Johanna , Bauer‐Hofmann Richard , Schwarz Michael 
Published: February 2007

AbstractLiver tumors of the B6C3F1 mouse frequently contain mutations at specific sites of codon 61 of the Ha‐ras proto‐oncogene. To address whether these mutations occur early or late during carcinogenesis, we analyzed mutations in the Ha‐ras gene in small precancerous liver lesions of the B6C3F1 mouse. For this purpose, 10‐μm frozen liver sections were prepared and stained for glucose‐6‐phosphatase activity. Using punching cannuli, we then took small tissue samples of approximately 5–30 μg from enzyme‐deficient liver lesions and from normal parts of the liver. These tissue samples were analyzed for mutations in the Ha‐ras gene by in vitro amplification of DNA via the polymerase chain reaction combined with selective oligonucleotide hybridization. By this approach we were able to analyze mutations in the Ha‐ras gene within lesions with diameters of less than 0.5 mm. Our results demonstrate that approximately 15% of the glucose‐6‐phosphatase‐negative lesions that occurred 24–28 wk after a single injection of diethylnitrosamine contain either C → A transversions at the first base or A → G transitions and A → T transversions at the second base of codon 61 of the Ha‐ras gene. The same types of mutations, although with a somewhat higher frequency (33%), were found in liver tumors taken 68 wk after diethylnitrosamine treatment. These findings demonstrate that Ha‐ras mutations can be detected even in very small precancerous liver lesions, suggesting that these mutations may be an early, perhaps even the first, critical event during murine hepatocarcinogenesis.
Glutathione and glutathione S‐transferases in clones of cultured rat liver epithelial cells that express varying activity of γ‐glutamyl transpeptidase
Authors: Tsao Ming‐Sound , Duong Minh , Batist Gerald 
Published: February 2007

AbstractIn rat chemical hepatocarcinogenesis models, the hepatocytes in the preneoplastic/neoplastic nodules characteristically demonstrate common biochemical changes including significant and often marked elevation in the cellular glutathione (GSH) content and in the activities of the enzymes γ‐ glutamyl transpeptidase (GGT) and glutathione S‐transferase (GST). Such consistent and concomitant biochemical changes may signify a common regulatory mechanism in the expression of these enzymes. We have utilized a panel of clonally derived rat liver epithelial cell lines that express varying activities of GGT to study the quantitative correlation between these three cellular components of the phase II drug metabolizing enzyme system. The results indicate that in confluent cultures, cells with high GGT activities have significantly higher cellular GSH content, and a linear correlation exists between the glutathione content and the logarithm of the GGT activity. In contrast, the basal activities of GST and GGT were not coordinately regulated. However, most of the chemical carcinogen‐treated cell lines, regardless of their GGT activity, expressed higher GST activity than the normal parental rat liver epithelial cells. The basal expressions of both the Yb and Yp subunits of GST were also not correlated with the relative expression of GGT. Since GGT may play an important role in supplying the cells with the basic constituents for the synthesis of GSH and since GSH is an important cellular molecule in the protection of cells from toxic electrophiles, enhancement of GGT activity in preneoplastic/neoplastic nodules of chemical carcinogen‐treated rats may represent a necessary biochemical adaptation for the induction of the “resistant” phenotype of these hepatocytes.
Activation of ras oncogenes in chemically transformed BALB/MK‐2 mouse keratinocytes
Authors: Weissman Bernard E. , Arboleda Marie J. , Kimoto Kathleen A. , Macdonald Marsha J. , Ochiai Ruth , Der Channing J. 
Published: February 2007

AbstractBALB/MK‐2 cells are an epidermal growth factor (EGF)‐dependent cell line derived from BALB/c mouse epidermis that can undergo terminal differentiation under appropriate conditions. Previous studies have shown that transformation of these cells by retroviral oncogenes relieves the EGF requirement while blocking the terminal differentiation program. In this report we show that BALB/MK‐2 cells are sensitive to transformation by the chemical carcinogens dimethylbenz[a]anthracene (DMBA), 3‐methylcholanthrene (MCA), and N‐methyl‐N‐nitro‐N‐nitrosoguanidine (MNNG). BALB/MK‐2 cells transformed by these carcinogens proliferate in the absence of EGF and do not undergo terminal differentiation in response to calcium. However, the cells retain their anchorage growth dependence and are nontumorigenic in nude mice. NIH 3T3 transfection analysis showed that the endogenous Ha‐ras gene had been activated in both DMBA‐ and MNNG‐transformed cells and the Ki‐ras gene had been activated in the MCA‐transformed cells. Additionally, non‐ras transforming activity was detected in some MNNG‐transformed BALB/MK‐2 cells. Thus, the BALB/MK‐2 cell line provides a reproducible in vitro assay system for chemical transformation of epithelial cells and for identification of oncogene activations associated with changes in growth control and differentiation.
A Human Endonuclease Incises Ultraviolet‐Irradiated DNA at Cytosines and Oxidized DNA at Thymines
Authors: Gallagher Patricia E. , Weiss Randi B. , Brent Thomas P. , Duker Nahum J. 
Published: February 2007

AbstractBoth ultraviolet irradiation and oxidation of DNA produce a variety of pyrimidine base damages. A human endonuclease recognizes such altered bases on these DNA substrates. This human endonuclease incises ultraviolet‐irradiated DNA exclusively at sites of photochemically modified cytosines. The precise sites of incision by the human enzyme were determined by DNA sequencing. Chemically oxidized DNA was incised exclusively at thymine loci. The degree of enzymic cleavage at cytosine photoproducts was identical at each site. However, the extent of incision at selected oxidized thymine residues varied within the DNA sequence. These results indicate that the distribution of thymine oxidative modifications is influenced by the neighboring DNA bases.
Oncogene Expression in Cell Lines Derived From Rat Tracheal Implants Exposed In Vivo to 7,12‐Dimethylbenz[a]anthracene
Authors: Cosma Greg N. , Marchok Ann C. , Garte Seymour J. 
Published: February 2007

AbstractExpression of four oncogenes and two keratin genes was determined in rat tracheal epithelial cell lines derived from tracheal implants exposed in vivo to 7,12‐dimethylbenz[a]anthracene. Cell lines were grouped into four stages of neoplastic progression based on phenotypic markers in order to correlate oncogene expression with stage of malignancy. Northern analysis of RNA revealed a significantly enhanced expression of the c‐myc oncogene in the most tumorigenic or tumor‐derived cell lines, whereas preneoplastic cells expressed approximately fivefold less transcript. Southern analysis of tracheal cell DNA did not demonstrate amplification of the c‐myc gene in any of the positive cell lines. In contrast to c‐myc, other oncogenes such as ras and fos were expressed in all cell lines, as well as in control cell cultures, to a similar extent. Patterns of differentiation were examined in these epithelial cell lines by determining the expression of two distinct keratin genes, KA‐1 and KB‐2. Both malignant and preneoplastic cells expressed the KB‐2 gene at variably high levels, whereas the expression of the KA‐1 keratin was barely detectable in any of the cell lines. The stage‐specific expression of the c‐myc oncogene in these tracheal cell lines suggests a correlation between the regulation of certain oncogenes and neoplastic progression in this model of respiratory carcinogenesis.
Role of TGF‐Beta in Normal Differentiation and Oncogenesis in Rat Liver
Authors: Nagy Peter , Evarts Ritva P. , McMahon James B. , Thorgeirsson Snorri S. 
Published: February 2007

AbstractTransforming growth factor‐β1 (TGF‐β1) is capable of eliciting a myriad of biological responses associated with cellular proliferation, as well as effects unrelated to the control of cell growth. We examined the possible role of TGF‐β1 in the differentiation of rat liver epithelial (RLE) cells in vitro and studied the cellular distribution of TGF‐β1 transcripts and protein during in vivo differentiation of oval cells. Furthermore, we followed the cellular distribution of TGF‐β1 transcripts and protein during chemical hepatocarcinogenesis. By using in situ hybridization and immunohistochemical techniques, we showed that both TGF‐β1 transcripts and protein are localized in nonparenchymal cells in normal liver, are expressed in oval cells during very early stages of hepatocytic differentiation in vivo, and are exclusively expressed in the nontumorous mesenchymal cell compartment during hepatocarcinogenesis. Furthermore, we showed that TGF‐β1 is capable of inducing differentiation of RLE cells in vitro consistent with early stages of hepatocytic lineage differentiation. Our data indicate that the RLE cells similar to the oval cells in vivo may be an epithelial progenitor cell for hepatocytic cell lineage in adult mammalian liver.
Increased levels of phorbin, c‐myc, and ornithine decarboxylase RNAs in human colon cancer
Authors: Guillem Jose G. , Levy Miriam F. , Hsieh Ling Ling , Johnson Mark D. , Logerfo Paul , Forde Kenneth A. , Weinstein I. Bernard 
Published: February 2007

AbstractOur previous work on protein kinase C (PKC) and colon cancer has shown altered levels of PKC activity in human colon tumors, as well as activation of PKC by colon tumor promoters such as bile acids. To understand further the role of PKC in colon carcinogenesis, we analyzed the expression of phorbin, a gene induced by PKC activation, in a series of different stages of human colon tumors. As shown by northern blot analyses of poly (A)+ RNA, higher levels of phorbin RNA were seen in 26 colon tumor samples than in their adjacent normal colonic mucosa. There also appeared to be a correlation between the abundance of phorbin RNA in the tumors and the extent of invasion (tumor‐to‐normal tissue phorbin RNA ratio = 4.2, 8.0, and 11.9 for Dukes' A, B, and C, respectively). Phorbin RNA was also abundant in a human colon cancer line (HT29). We also examined the expression of other mitogen‐responsive genes (c‐myc, ODC, and β‐actin) in a set of 19 colon tumor samples. All tumors displayed significant (mean 3.8‐fold) increases in the level of c‐myc RNA compared with their adjacent normal colonic mucosa. About 47% and 16% of these tumor samples also showed increased levels of ODC (mean 3.1‐fold) and β‐actin (mean 1.6‐fold) RNA, respectively. The increased levels of c‐myc, ODC, and β‐actin RNA did not correlate with the extent of tumor invasion. Taken together, these results demonstrate that human colon tumors usually display increased levels of both phorbin and c‐myc RNAs. The marked increases in phorbin RNA suggest that this could serve as a useful biomarker in studies on human colon cancer.
Novel phenotype of C3H 10T1/2 fibroblasts cotransfected with the c‐Ha‐ras and adenovirus 5 E1A oncogenes
Authors: Davenport Elizabeth A. , Taparowsky Elizabeth J. 
Published: February 2007

AbstractC3H 10T1/2 fibroblasts are converted to fully transformed phenotype following coexpression of an activated c‐Ha‐ras gene and either a constitutively expressed viral or cellular myc gene. In this report, we examined whether the early region 1A (E1A) of adenovirus 5, which synergizes with ras to convert primary embryonic cells to a transformed phenotype, can synergize with ras to transform the established mouse embryonic cell line, C3H 10T1/2. We demonstrate that coexpression of ras and E1A generated a transformed phenotype that could be scored by colony assays and by soft agarose assays but not by standard focus assays. The ras‐E1A‐transformed phenotype relies on sequences present in conserved regions 1 and 2 of the E1A proteins and, in part, on information encoded by the extreme carboxy terminus of E1A. The contrast between the transformed phenotypes generated following the transfection of C3H 10T1/2 cells with either ras and myc or ras and E1A suggests that myc and E1A cooperate with ras to transform C3H 10T1/2 cells by mechanisms that can be distinguished using this established cell line as a model system.
Mutational specificities of environmental carcinogens in the lacl gene of Escherichia coli. III: The cyclic nitrosamine N‐nitrosopyrrolidine is a complex mutagen
Authors: Zielenska Maria , Ahmed Alia , Glickman Barry W. 
Published: February 2007

AbstractThe mutational specificity of the cyclic nitrosamine N‐nitrosopyrrolidine (NPYR) was determined through the DNA sequence characterization of 33 lacl−d mutations of Escherichia coli. Base substitution was the predominant class of mutation induced (91%). The majority of these (64%) occurred at GC base pairs, in accordance with the predicted significance of NPYR‐derived guanine adducts. In addition, this nitrosamine efficiently produced other kinds of base substitution events as 11 of the 33 mutations occurred at AT base pairs. Deletion, frameshift, and duplication events were also recovered. The complexity of the NPYR mutational spectrum appears to be consistent with the suggestion that this compound acts through both direct and indirect mutational pathways.
Chemical induction of thymomas in AKR mice: Interaction of chemical carcinogens and endogenous murine leukemia viruses. Comparison of N‐methyl‐N‐nitrosourea and methyl methanesulphonate
Authors: Warren William , Clark Jeremy P. , Gardner Emily , Harris Gilmour , Cooper Colin S. , Lawley Philip D. 
Published: February 2007

AbstractThe time course of development of thymic lymphoma, which occurs spontaneously in mice of the AKR strain, is accelerated by the methylating agents N‐methyl‐N‐nitrosourea (MNU) and methyl methanesulphonate (MMS). Since MNU is a potent mutagen inducing G → A transition mutations and MMS a relatively weak mutagen, it was of interest to examine the genetic alterations associated with each class of the chemically induced tumors and to compare these alterations with those found in the spontaneous tumors. The same spectrum of genetic alterations was found for MMS‐induced and spontaneous thymomas. Both showed rearrangements of c‐myc and Pim‐1 genes that appeared to result from integration of recombinant mink cytopathic focus‐forming (MCF) proviruses but failed to reveal evidence for activation of ras oncogenes, either by DNA transfection experiments or by hybridization of DNA to specific oligonucleotide probes. Some alterations in c‐myc and Pim‐1 genes were also found in MNU‐induced tumors, but, mainly, these involved integration of ecotropic‐like rather than recombinant MCF viruses. Furthermore, MNU‐induced tumors frequently (in 24% of thymomas) contained G → A transition mutations, activating the Ki‐ras oncogene at codon 12 position 2. Another feature that distinguishes the MNU‐induced tumors from those occurring in untreated and MMS‐treated mice was the consistently high level of c‐myc mRNA that occurred in the absence of c‐myc gene rearrangement. Taken together, the data indicate that the mechanisms of development of tumors following treatment with MNU and MMS are distinct, and that the effect of MMS is probably to speed up the process of viral leukemogenesis.
Enhancement of adenovirus transformation of cloned rat embryo fibroblast cells by gamma irradiation
Authors: Su Zao‐Zhong , Zhang Peiquan , Geard Charles , Fisher Paul B. 
Published: February 2007

AbstractWe have analyzed the effect of γ irradiation on the induction of morphological transformation of cloned rat embryo fibroblast (CREF) cells by the host‐range cold‐sensitive type 5 adenovirus mutant, H5hr1. Treatment of CREF cells with 1–6 Gy of γ irradiation immediately prior to viral infection resulted in dose‐dependent decrease in cell survival and concomitant increase in viral transformation frequency. Exposure of CREF cells to 1–6 Gy of γ radiation alone resulted in a similar dose‐dependent inhibition in cell survival but without any subsequent morphological transformation. The effect of γ irradiation on viral transformation was greatest when cells were irradiated directly before viral infection. The reduction in the enhancement of transformation was both dose and time dependent. The ability of γ irradiation to enhance viral transformation was substantially reduced if CREF cells were treated with inhibitors of RNA (actinomycin D) and protein (cycloheximide) synthesis. Employing a single‐cell colony transfer assay and in situ hybridization with a 32P‐labeled Ad5 DNA probe, we found that γ irradiation of CREF cells prior to infection with H5hr1 resulted, 10 and 17 d after infection and replating, in an increase in the percentage of surviving CREF colonies that contain Ad5 DNA. Analysis of viral DNA integration by DNA‐filter hybridization (Southern blot analysis) in H5hr1‐transformed CREF clones isolated from untreated and γ‐irradiated cultures indicates that γ irradiation caused increases in both the number of copies of Ad5 E1A DNA sequences integrated into cellular DNA and the number of unique Ad5 E1A DNA integration sites in transformed cells. These results indicate that γ irradiation enhancement of adenovirus transformation was a consequence of radiation‐induced cellular factors with finite life spans that are mediators of enhanced viral transformation. Potentially important components of the radiation enhancement process appear to involve an alteration in both the retention of free Ad5 DNA in surviving cells and an alteration in the profile of viral‐DNA integration in γ‐irradiated cells.
Plasma membrane—mediated nuclear uptake and chromatin binding of insulin in tumor cell lines
Authors: Rakowicz‐Szulczynska Ewa M. , Otwiaska Danuta , Koprowski Hilary 
Published: February 2007

AbstractAnalysis of different cellular fractions after incubation of SW 948 and SW 707 colorectal carcinoma cells or WM 266‐4 melanoma cells with 125I‐insulin revealed the nondegraded hormone in the chromatin of these cells. Nuclear 1251‐insulin was bound to specific fragments of EcoRI‐, Haelll‐, and Hincll‐digested chromatin. A 45‐kDa chromatin protein species that binds 125I‐insulin was identified. Actinomycin D and cycloheximide inhibited the insulin‐stimulated expression of chromatin receptors. Uptake of 125I‐insulin by isolated nuclei occurred only in the presence of plasma membranes. Thus, at least some effects of insulin on target cells can be explained by direct gene regulation instead of “second messenger” action.
Ha‐ras oncogene mutations in cell lines derived from rat tracheal implants exposed in vivo to 7,12‐dimethylbenz[a]anthracene
Authors: Cosma Greg N. , Wirgin Isaac I. , Marchok Ann C. , Garte Seymour J. 
Published: February 2007

AbstractThe frequency of Ha‐ras mutations was determined as a function of neoplastic progression in cell lines derived from rat tracheal implants exposed in vivo to 7,12‐dimethylbenz[a]anthracene. Restriction fragment‐length polymorphism (RFLP) analysis revealed an A → T transversion in the second base of codon 61 in 2 of 11 cell lines. One of the positive cell lines was tumorigenic, but the other was neither tumorigenic nor anchorage independent, thus indicating a lack of correlation between neoplastic stage and ras mutation. Densitometry analysis of the RFLP bands indicated that approximately 50% of the cells within these two heterogeneous populations contained the mutation. Direct sequence analysis of polymerase chain reaction—amplified DNA confirmed these results and did not reveal any other mutations in this region of the Ha‐ras gene.
Changes in rasT24 expression do not induce changes in c‐jun, jun‐B, or jun‐D RNA levels in rat liver epithelial cells
Authors: Krizman David B. , Lebovitz Russell M. , Lieberman Michael W. 
Published: February 2007

AbstractWe used a series of rat liver epithelial (RLE) cell lines that carry a zinc‐regulatable metallothionein/rasT24 fusion gene (MTrasT24) to investigate the relation of ras oncogene expression to steady‐state RNA levels of the jun family of genes. In these cells, steady‐state RNA levels of c‐jun, jun‐B, and jun‐D were unrelated to rasT24 RNA levels or the phenotypic changes induced by the ras oncogene. Steady‐state levels of the three jun mRNAs varied among different rasT24 transformed clones, and, although some clones exhibited concomitant induction of rasT24 and jun mRNAs, other clones exhibited no such correlation. We conclude that the effects of rasT24 in transformed RLE cells do not appear to be mediated by c‐jun, jun‐B, or jun‐D and that studies examining only a single transformed clone may give misleading results with respect to the role of various oncogenes in the transformation process.
Polyoma DNA replication dependent upon growth condition of SEWA sarcoma cells
Authors: Robinson Richard , Ronai Zeev 
Published: February 2007

AbstractExtrachromosomal replication of viral DNA sequences has been observed in transformed as well as in normal cells following “stress”‐inducing treatments. To explore the effect of growth conditions on the ability to support such replication, we analyzed SEWA sarcoma cells that grew subcutaneously or as ascites tumors in vivo as well as cell lines that were established from each of these tumors. The replicative form of polyoma DNA sequences was observed in SEWA tumors grown in ascites fluids but not in cells maintained as solid tumors. Polyoma DNA replication was found in ascites‐derived cells that were adapted to grow in culture, only when the cultured cells are stimulated with UV irradiation. Immunoprecipitation of T antigens enabled detection of large T antigen only in the ascites‐derived cells. The mechanisms that may regulate this phenomenon and the possible role large T may play in different growth conditions of SEWA cells are discussed.
Loss of a tumor suppressor gene function is correlated with downregulation of chondrocyte‐specific collagen expression in syrian hamster embryo cells
Authors: Cizdziel Paul E. , Hosoi Junichi , Montgomery Jeffry C. , Wiseman Roger W. , Barrett J. Carl 
Published: February 2007

AbstractWe previously described the isolation of closely related, preneoplastic Syrian hamster cell lines that have retained (supB+) or lost (supB−) the ability to suppress the anchorage‐independent growth and tumorigenicity of a sarcoma cell line (BP6T) in cell hybrids. In this report, we have used differential cDNA screening to clone several genes that are expressed in supB+ cells and downregulated in supB− cells. The nontumorigenic supB+ and supB− variants are advantageous for differential cDNA cloning because multiple independent cell lines differing in their tumor suppressor activity have been isolated. Differentially expressed cDNAs were isolated and placed into one of four groups based on DNA cross‐hybridization. Representative cDNAs from Groups I and II, which were expressed at relatively high levels in two independently derived supB+ cell lines (DES4 and 10W) and downregulated in the supB− and tumor cell lines, were sequenced. The DNA and predicted amino acid sequences of these genes were found to be highly homologous to the chondrocyte‐specific collagens type II and type IX. In contrast to the chondrocyte‐specific collagens, another collagen isoform, collagen type I, was expressed at similar levels in both supB+ and supB− cells. These results suggest that carcinogen‐induced immortalization selected for chondrocyte‐like cell lines from the mixed embryo cell population. As these cells progressed toward tumorigenicity, the ability to express the chondrocyte differentiation markers was lost concomitantly with the ability to suppress the tumorigenicity of the BP6T sarcoma cell line. These results are consistent with the hypothesis that the supB+ tumor suppressor gene is involved in the regulation of differentiation. The identification of genes regulated by this suppressor gene may aid in its isolation.