bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modulation of pp60v‐src and pp60c‐src expression in rous sarcoma virus—transformed hamster fibroblasts transfected with activated N‐ras
Authors: Topol Lilia Z. , Gutierrez Maria L. , Blair Donald G. , Kisseljova Natalya P. , Musatkina Elena A. , Shtutman Michael S. , Zakamaldina Tatyana Z. , Tatosyan Alexander G. , Deichman Galina I. 
Published: February 2007

AbstractThree phenotypically different hamster cell lines transformed with Rous sarcoma virus (RSV) were transfected with plasmid DNA containing an activated N‐ras oncogene, and nine clones expressing various levels of p21N‐ras were characterized. We examined the effects of p21N‐ras on expression and kinase activity of resident src proteins by using a variety of assays that allowed us to discriminate between viral and cellular src proteins. In eight clones with a 10‐ to 20‐fold increase in p21N‐ras levels relative to the endogenous protein, we observed a marked reduction in the synthesis and kinase activity of p60v‐src. This decrease correlated with transcriptional downregulation of RSV genomic and v‐src subgenomic mRNAs. In the same cells, we found a concomitant accumulation of p60c‐src and, accordingly, an increase in its protein kinase activity without an apparent increase in c‐src mRNA levels. Therefore, modulation of viral and cellular src proteins in cells overexpressing p21N‐ras appeared to result from two distinct effects: a downregulation of long terminal repeat—driven transcription and a more complex interaction with cellular effectors that control the stability of p60c‐src. Such modulation also seemed to depend on the levels of p21N‐ras and, possibly, on host‐cell factors, since it was not observed in the third cell line, in which the relative increase in p21N‐ras was only 2.5‐fold to fivefold.
Comparison of pulmonary O6‐methylguanine dna adduct levels and Ki‐ras activation in lung tumors from resistant and susceptible mouse strains
Authors: Devereux Theodora R. , White Catherine M. , Hegi Monika E. , Patel Arti C. , Anderson Marshall W. , Maronpot Robert R. , Foley Julie F. , Greenwell Arnold , Belinsky Steven A. 
Published: February 2007

AbstractThe role of O6‐methylguanine (O6MG) DNA adduct formation and persistence in the formation of 4‐(methylnitrosamino)‐1‐(3‐pyridyl)‐1‐butanone (NNK)—induced lung tumors from resistant C57BL/6 and susceptible A/J mice was investigated. In addition, the frequencies of pulmonary tumor formation and Ki‐ras activation were defined in C57BL/6 mice treated with NNK or vinyl carbamate (VC), and the role of the p53 gene in pulmonary carcinogenesis in these resistant mice was examined. One day after treatment with 100 mg/kg NNK, O6MG adduct concentrations were twofold to eightfold higher in Clara cells and type II cells than in small cells or whole lungs from both mouse strains. The concentrations of O6MG in isolated cells decreased at a similar rate in the two strains of mice. Lung tumors were detected by 27 mo of age in 18% of the C57BL/6 mice after a single 100 mg/kg dose of NNK and in 46% of these mice after a single 60 mg/kg dose of VC. In contrast, the tumor incidence in untreated C57BL/6 mice was 4%. Only one of 22 lung tumors from C57BL/6 mice treated with NNK contained an activated Ki‐ras gene that was associated with an O6MG DNA adduct, whereas previous studies detected activated Ki‐ras oncogenes in most of the NNK‐induced lung tumors analyzed from susceptible A/J and resistant C3H mice. The small differences in formation and persistence of the O6MG adduct in whole lung or isolated lung cells from A/J and C57BL/6 strains do not account for the differences in either susceptibility for tumor formation or activation of the Ki‐ras gene between these strains. In contrast to the low number of NNK‐induced tumors with Ki‐ras mutations in the resistant mice, 11 of 20 lung tumors from VC‐treated mice contained activated Ki‐ras genes. Neither p53 tumor suppressor gene mutations nor overexpression of the p53 protein were detected in spontaneous or chemically induced lung tumors in C57BL/6 mice. Thus, although Ki‐ras activation was detected in some tumors, pathways independent of ras activation and p53 inactivation also appear to be involved in lung tumorigenesis in this resistant mouse strain.
Low frequency of retinoblastoma gene alterations in rat hepatocellular carcinomas
Authors: Smith Martin L. , Lombardi Benito , Chandar Nalini 
Published: February 2007

AbstractAbnormalities of the retinoblastoma (Rb) gene have been reported in some human cancers, including hepatocellular carcinomas (HCCs). We examined by Southern blotting the status of the Rb gene in HCCs induced in rats in four experimental models. A low frequency of Rb gene alterations, detected as novel hybridizing bands unique to each tumor, was observed. Expression of the Rb protein product was examined in the HCCs and in seven established rat hepatoma cell lines studied. It appears, therefore, that alterations in the structure or expression of the Rb gene do occur but probably do not contribute in a major way to hepatocarcinogenesis in the rat. © 1993 Wiley‐Liss, Inc.
Restoration of gap‐junctional intercellular communication in a communication‐deficient rat liver cell mutant by transfection with connexin 43 cDNA
Authors: Jou Yuh‐Shan , Matesic Diane , Dupont Emmanuel , Lu Shu‐Chen , Rupp Heather L. , Madhukar Burra V. , Oh Saw Yin , Trosko James E. , Chang Chia‐Cheng 
Published: February 2007

AbstractTo study the biochemical basis of gap‐junctional intercellular communication (GJIC) and its role in tumorigenesis, a mammalian cell expression vector carrying both a rat connexin 43 (Cx43) cDNA and an amplifiable dihydrofolate reductase (DHFR) gene was transfected into the GJIC‐deficient rat liver mutant cell line aB1. Two stable transfectants were selected for further amplification of the transfected Cx43 gene by increasing stepwise the concentration of methotrexate (MTX) in the culture medium. The results indicate that GJIC was restored in these two Cx43 cDNA transfectants after they became highly resistant to MTX but not in the control‐vector transfectants, in which the DHFR gene was similarly amplified. The amount of Cx43 DNA revealed by Southern blot analysis and the expression of Cx43 gene revealed by northern and western blot analyses were concomitantly increased in the Cx43 cDNA transfectants resistant to high concentrations of MTX. Western blot analysis, using an antipeptide antibody that specifically recognizes Cx43 protein, further revealed that an approximately 46‐kDa phosphorylated Cx43 protein that was prominent in the parental GJIC‐competent cells was absent in the aB1 cells. This Cx43 protein, however, reappeared in the two Cx43 cDNA transfectants after amplification. After treatment of the membrane proteins with alkaline phosphatase in vitro, the approximately 46‐ and 44‐kDa proteins disappeared, whereas the approximately 42‐kDa proteins remained with increasing intensity, indicating that the higher molecular‐weight proteins were the phosphorylated Cx43. These results indicate that a defect in posttranslational phosphorylation of Cx43 protein associated with low expression of the Cx43 gene might be responsible for the GJIC deficiency in aB1 cells and that increased expression of Cx43 by gene amplification might restore this phosphorylated Cx43 protein and so reestablish GJIC. © 1993 Wiley‐Liss, Inc.
Carbon tetrachloride induction of rapid changes in liver nuclear protein factors capable of sequence‐specific binding to regulatory elements in the long terminal repeat of polytropic‐class endogenous murine leukemia virus—related proviruses
Authors: Wang Tzu‐Hao , Henley Donald C. , Yang Den Mei , Ch'Ang Lan‐Yang , Yang Wen K. , Hoyt Peter R. 
Published: February 2007

AbstractTreatment of mice with hepatic carcinogens, including CCl4, has been shown to rapidly enhance the transcription of endogenous murine leukemia virus—related proviral sequences in the liver. To understand the mechanism for this transcriptional stimulation, we used nuclear protein preparations from mouse livers to perform DNase I protection analyses and identified nuclear protein binding on approximately 20 individual sequences within the regulatory regions of the long terminal repeat (LTR) of a polytropic‐class endogenous provirus clone. From 3 to 144 h after treatment with CCl4, the livers of FVB/N mice were analyzed for specific nuclear protein binding to the LTR DNA. Three to nine hours after CCI4 treatment, decreased protection was seen at potential regulatory cis‐elements throughout the LTR, including specific sites within the putative negative regulatory element (located 5′ of the consensus enhancer sequences) and the 3′ terminal portion of the polytropic class‐specific enhancer‐like inserted sequence element and around the CCAA(C/T) box in the promoter region. In addition, by 3–6 h after treatment, a transient increase in protection activity for the transcription initiation site occurred. The loss of cis‐element protection expanded to other binding sites and became most marked by 48 h after treatment. As the regenerating liver recovered, the nuclear protein binding activities for these LTR sequences also recovered, but protection at the TATAA and transcription initiation sites remained deprotected at 144 h after treatment. Nuclear protein protection of other sites, particularly in the conserved LTR enhancer sequences, was minimally affected by CCl4 treatment. Three nuclear protein binding sites that showed rapid CCI4‐induced kinetic changes were homologous to the consensus sequence for the binding of the transcription factor families MEF‐2, HNF‐1, and C/EBP. The complex kinetic changes in factors that may contribute to the rapid and transient induction of endogenous retroviral gene expression in the liver after CCI4 exposure are discussed.
Constitutive ap‐1 dna binding and transactivating ability of malignant but not benign mouse epidermal cells
Authors: Domann Frederick E. , Levy John P. , Finch Joanne S. , Tim Bowden G. 
Published: February 2007

AbstractThe mouse epidermal cell line 308 contains an activated Ha‐ras gene and forms benign papillomas when transplanted to the skin of athymic nude mice. A radiation‐associated malignant variant of this cell line, 308‐10Gy5, has been isolated and shown to form squamous cell carcinomas in nude mice. To further examine the molecular events involved in malignant conversion of 308‐10Gy5, we assessed the activator protein‐1 (AP‐1) binding and transactivating ability of 308 and 308‐10Gy5. In nuclear protein extracts of 308, AP‐1 sequence‐specific binding to an oligonucleotide containing a single high‐affinity AP‐1 binding site was induced by the tumor promoter 12‐O‐tetradecanoylphorbol‐13‐acetate, as determined by gel shift analysis. Nuclear extracts of 308‐10Gy5 bound to the AP‐1 oligonucleotide without treatment with tumor promoters. Not only was sequence‐specific AP‐1 DNA binding constitutively active in malignant versus benign tumor cells, but so was transactivation of a unique AP‐1‐responsive chloramphenicol acetyltransferase reporter construct, pTiCTaK. Constitutive transactivation of this AP‐1–responsive reporter construct was observed in the malignant but not the benign tumor cells. Furthermore, steady‐state transcript levels of the tumor‐associated AP‐1–responsive genes stromelysin, urokinase‐type plasminogen activator, c‐jun, and c‐fos were higher in malignant 308‐10Gy5 cells than in benign 308 cells. These results suggest that acquisition of constitutive AP‐1 DNA binding and transactivation can result in sustained deregulation of gene expression. While malignant progression in keratinocytes is probably not due solely to the acquisition of constitutive cellular AP‐1 activity, the effect of deregulated expression of AP‐1–regulated genes, especially basement membrane–degrading enzymes, may be functionally related to malignant conversion. © 1994 Wiley‐Liss, Inc.
2‐hydroxyamino‐1‐methyl‐6‐phenylimidazo [4,5‐b] pyridine induction of recombinational mutations in mammalian cell lines as detected by dna fingerprinting
Authors: Kitazawa Tomoji , Kominami Ryo , Tanaka Ryuichi , Wakabayashi Keiji , Nagao Minako 
Published: February 2007

Abstract2‐Amino‐1‐methyl‐6‐phenylimidazo[4,5‐b]pyridine (PhIP) is the most abundant mutagenic heterocyclic amine in cooked foods. Two mouse tumor cell lines, BMT11 and FM3A, were exposed to its proximate form, 2‐hydroxyamino‐1‐methyl‐6‐phenylimidazo[4,5‐b]pyridine (N‐OH‐PhIP). Fifty‐six subclones of BMT11 and 39 subclones of FM3A were isolated and analyzed by DNA fingerprinting. Treatment with 10–20 μM N‐OH‐PhIP gave rise to extra bands or shifted bands, but treatment without N‐OH‐PhIP did not. This suggests that mutations resulting from recombination were induced. The mutation frequencies were 21–53% and 22–35% for BMT11 and FM3A, respectively. These findings suggest that PhIP induces recombinational mutations. © 1994 Wiley‐Liss, Inc.
Combined effects of human papillomavirus‐18 and n‐methyl‐n‐nitro‐n‐nitrosoguanidine on the transformation of normal human oral keratinocytes
Authors: Shin Ki‐Hyuk , Min Byung‐Moo , Cherrick Henry M. , Park No‐Hee 
Published: February 2007

AbstractWe immortalized oral keratinocytes by transfecting them with recombinant human papillomavirus (HPV) type 18 DNA and established three cell lines. These lines were morphologically different from their normal counterpart, contained integrated entire HPV‐18 DNA, and expressed the viral E6/E7 genes. The cells contained less p53 protein and more c‐myc mRNA than normal cells. However, they proliferated only in keratinocyte growth medium (KGM) containing low calcium and were not tumorigenic in nude mice. To test the hypothesis that tumors result from the combined effect of a “high‐risk” HPV and chemical carcinogens in the human oral cavity, we exposed the immortalized cells to the chemical carcinogen N‐methyl‐N′‐nitro‐N‐nitrosoguanidine. Three chemically transformed cell colonies were isolated. These cells (a) proliferated well in both KGM and Dulbecco′s modified minimum essential medium containing physiological levels of calcium; (b) were capable of proliferating in nude mice; (c) contained intact, integrated HPV‐18 sequences; (d) transcribed substantially more HPV‐18 E6/E7, transforming growth factor‐α, and c‐myc than the immortalized counterpart; and (e) contained, like the immortalized counterpart, less wild‐type p53 protein and DCC message. These data indicate that human oral keratinocytes can be transformed by sequential exposure of normal keratinocytes to a “high‐risk” HPV and chemical carcinogens. © 1994 Wiley‐Liss, Inc.
p53 mutations in primary human lung tumors and their metastases
Authors: Reichel Martin B. , Ohgaki Hiroko , Petersen Iver , Kleihues Paul 
Published: February 2007

AbstractIn a total of 26 primary human lung tumors and 60 metastases derived from them, exons 5–8 of the p53 tumor suppressor gene were analyzed by single‐strand conformation polymorphism and subsequent direct DNA sequencing of amplified DNA. Mutational inactivation of the p53 gene was identified in four of five squamous cell carcinomas, three of nine adenocarcinomas, and two of nine small‐cell carcinomas, the overall incidence being 35%. Point mutations occurred at a similar incidence in exons 5–8, with a preference for G←T transversions. In seven of nine cases (78%), mutations were identical in the primary tumor and all of its metastases, indicating that in lung tumors, p53 mutations usually precede metastasis and that hematogenic and lymphogenic dissemination of tumor cells to other tissues is not associated with a selection against p53 inactivation. In one case, a kidney metastasis had the same mutation as the primary squamous cell carcinoma, whereas a liver metastasis had no mutation, indicating heterogeneity of the primary lung neoplasm and selective metastasis of mutated and nonmutated tumor cells to kidney and liver, respectively. Only in one liver metastasis was a mutation identified that was neither present in the primary lung tumor nor in a kidney metastasis, suggesting that occasionally p53 mutations occur after metastatic spread. © 1994 Wiley‐Liss, Inc.
Assignment of two human epidermal squamous cell carcinoma cell lines to more than one complementation group for the immortal phenotype
Authors: Berry Isabella J. , Burns Julie E. , Parkinson E. Kenneth 
Published: February 2007

AbstractTwo human cell lines derived from squamous cell carcinomas (SCCs) of the epidermis, SCC‐12 clone F and SCC‐13 clone Y, were made to be independent of the Swiss 3T3 feeder layer to perform somatic‐cell genetic experiments. We fused these SCC lines with normal human fibroblasts, and all resulting hybrids senesced after completing 12–17 population doublings, suggesting that in part, immortalization of the keratinocyte during SCC development results from the loss of gene function. We also tested whether these two SCC lines mapped to known complementation groups for immortality by fusing them with representatives of groups A (GM847), B (HeLa), and C (143B), but most of these hybrids were indistinguishable from those derived from homotypic crosses set up as immortal hybrid controls. As reported by others, fusions of cell lines from different complementation groups–143B (group C) × HeLa (group B) or GM847 (group A) × HeLa (group B)–resulted in predominantly senescent hybrids. Our results confirmed and extended previous observations by others that the phenomenon of senescence is dominant to that of immortality, but they did not allow us to assign either of the SCC lines we studied to a complementation group for immortality. © 1994 Wiley‐Liss, Inc.
Recovery from ultraviolet‐induced growth arrest of primary rat hepatocytes by p53 antisense oligonucleotide treatment
Authors: Tsuji Kunihiko , Ogawa Katsuhiro 
Published: February 2007

AbstractRecent evidence suggests that wild‐type p53 prevents cell‐cycle progression after DNA damage, which may provide a sufficient period for the cells to repair the genetic lesions that may otherwise lead to cell death or cellular transformation. We tested whether this hypothesis is generally applicable to parenchymal cells of internal organs. When primary neonatal rat hepatocytes were exposed to a nonlethal dose of ultraviolet light, actinomycin D, or mitomycin C, most cells expressed abundant p53 with an abnormally extended half life in their nuclei, and their growth was arrested despite treatment with growth factors (epidermal growth factor and insulin). When DNA‐damaged cells were treated with p53‐antisense oligonucleotides, p53 expression was significantly suppressed, and an appreciable fraction of the cells entered S phase. However, when damaged cells were administered p53‐sense or retinoblastoma susceptibility gene‐antisense oligonucleotides, there was no recovery from growth arrest. The data strongly suggest that p53 is a component of at least one signal transduction pathway leading to growth arrest in DNA‐damaged cells. © 1994 Wiley‐Liss, Inc.
In vitro and in vivo accelertration of the neoplastic phenotype of a low‐tumorigenicity rat bladder carcinoma cell line by transfected transforming growth factor‐α
Authors: Kawamata Hitoshi , Kameyama Shuji , Oyasu Ryoichi 
Published: February 2007

AbstractWe conducted an experiment to determine whether expression of transforming growth factor‐α (TGF‐α) enhances tumorigenicity in a low‐tumorigenicity rat bladder carcinoma cell line and whether it is sufficient to induce a tumorigenic phenotype in a nontumorigenic rat bladder cell line. D44c cells (which are nontumorigenic) were derived from a minute nodule from a bladder treated with N‐methyl‐N‐nitrosourea (MNU); G1‐200 cl‐17 cells (which have low tumorigenicity) were isolated from D44c cells exposed to MNU in vitro. Neither cell line expressed TGF‐α mRNA. The cells were contransfected with pSV2neo and pSRα‐rTGF‐α. The latter plasmid contains the rat TGF‐αcDNA under the transcriptional control of the SRα promoter. In the low‐tumorigenicity G1‐200 cl‐17 cells, the expression of TGF‐α mRNA and the subsequent synthesis of TGF‐α protein activated epidermal growth factor receptors (EGFRs) and markedly enhanced tumorigenicity in nude mice (i.e., shortened the latency period before tumor appearance, accelerated the rate of growth, and increased the size of the tumors) as well as anchorage‐independent growth in vitro. In nontumorigenic D44c cells, however, transfected TGF‐α did not induce either anchorage‐independent growth or tumorigenicity in nude mice, in spite of overexpression of EGFR mRNA and the constitutive expression of c‐jun and junB mRNA. These results suggest that the increased signal transduction mediated by TGF‐α enhanced tumorigenicity in a cell that was already tumorigenic but was not sufficient to induce tumorigenicity in a nontumorigenic cell. © 1994 Wiley‐Liss, Inc.
Mutations in a shuttle vector exposed to activated mitomycin C
Authors: Srikanth Nadadur S. , Mudipalli Anuradha , Maccubbin Alexander E. , Gurtoo Hira L 
Published: February 2007

AbstractThe cytotoxicity of the potent antibiotic and antitumor agent mitomycin C (MMC) is due to its irreversible binding to DNA. Alkylating species generated by bioreductive activation of MMC are known to cause monoadducts and cross‐links in DNA by specifically binding to guanine residues. To gain insight into how these lesions lead to base‐ and sequence‐specific mutations, shuttle vector pSP189 was treated with MMC chemically reduced by treatment with sodium borohydride, replicated in human Ad293 cells, rescued in bacteria, and analyzed for mutations in the supF tRNA gene sequence. The MMC‐induced mutations were predominantly base substitutions. Eighty‐four percent of the base substitutions were transversions, with G:C←T:A the major transversion. Single base deletions were the other major mutational event, and 77% of these were G:C deletions. Base positions 115, 123, and 163 were mutational hot spots based on the frequency of independent mutations. Identification of a single MMC adduct (presumed to be a modified G on the basis of its Rf value) and clustering of MMC‐induced mutations at three GC‐rich areas (nt 100–123, 152–163, and 168–176) suggested that the mutational spectrum we found was due to binding of MMC to guanine on either strand of the plasmid DNA. © 1994 Wiley‐Liss, Inc.