bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ha‐ras p21‐GTP levels remain constant during primary keratinocyte differentiation
Authors: Betz Natalie A. , Pelling Jill C. 
Published: February 2007

AbstractSeveral lines of evidence that indicate that mutation of the Ha‐ras oncogene is the initiating event in mouse skin carcinogenesis. Keratinocytes known to possess a mutated Ha‐ras have been shown to be resistant to differentiation. Thus, overstimulation of the Ha‐ras signaling pathway appears to block normal keratinocyte differentiation, and we hypothesized that for normal keratinocytes to terminally differentiate, the Ha‐ras signaling cascade must be turned off. In the present studies, we measured the level and activity state of Ha‐ras p21 protein in cultured keratinocytes undergoing calcium‐induced differentiation. We have employed Western blot analysis to demonstrate that Ha‐ras p21 protein levels remain constant during primary newborn and adult keratinocyte differentiation. The overall level of Ha‐ras p21 was higher in immortalized, benign, and malignant mouse keratinocyte cell lines than in normal keratinocytes but did not change within each cell type when subjected to differentiating conditions. The percentage of Ha‐ras p21 protein in its active, GTP‐bound form also remained unchanged during primary adult keratinocyte differentiation and in immortalized, benign, and malignant keratinocytes subjected to differentiating conditions. Our results indicate that terminal differentiation of primary adult mouse keratinocytes occurred in the presence of constant levels of Ha‐ras p21‐GTP, suggesting that the Ha‐ras signaling pathway may be blocked at a point distal to a step involving the Ha‐ras p21 protein itself. © 1995 Wiley‐Liss Inc.
Expression of the liver‐enriched transcription factors C/EBPα, C/EBPβ, HNF‐1, and HNF‐4 in preneoplastic nodules and hepatocellular carcinoma in rat liver
Authors: Flodby Per , Liao De‐Zhong , Blanck Agneta , Xanthopoulos Kleanthis G. H. , Hällström Inger Porsch 
Published: February 2007

AbstractThe expression patterns of the liver‐enriched transcription factors CCAAT/enhancer‐binding protein (C/EBP) α and β and hepatocyte nuclear factor (HNF)‐1 and HNF‐4 were studied in liver nodules and hepatocellular carcinomas from male rats treated according to the resistant hepatocyte (RH) model. C/EBPα expression was lower at the transcriptional, mRNA, and protein levels in persistent nodules than in the respective surrounding livers. Expression was further decreased in the tumors. Transcriptional downregulation of C/EBPα gene expression was observed already in very early nodules, isolated 3 wk after partial hepatectomy in the RH model. However, no detectable changes were observed in preneoplastic nodules in the transcription or in steady‐state mRNA levels of C/EBPβ, HNF‐1, and HNF‐4. A slight decrease in C/EBPβ protein and a more pronounced attenuation of HNF‐1 and HNF‐4 levels was observed in nodules, being 67%, 37%, and 46% of the levels in the corresponding surrounding livers, respectively. In conclusion, differential regulation of several transcription factors that are associated with the maintenance of the differentiated state of the hepatocytes was observed in preneoplastic and neoplastic liver lesions. This could have an impact on the regulation of a wide array of genes during liver carcinogenesis. Furthermore, the attenuation of C/EBPα expression, regarded as a negative growth regulator, could contribute to the proliferative advantage of nodules during liver carcinogenesis. © 1995 Wiley‐Liss Inc.
ogt alkyltransferase enhances dibromoalkane mutagenicity in excision repair–deficient escherichia coli K‐12
Authors: Abril Nieves , Luque‐Romero Francisco L. , Prieto‐Alamo María‐josé , Margison Geoffrey P. , Pueyo Carmen 
Published: February 2007

AbstractWe examined the role of the O6‐alkylguanine‐DNA alkyltransferase encoded by ogt gene in the sensitivity of Escherichia coli to the mutagenic effects of the dibromoalkanes, dibromoethane and dibromomethane, by comparing responses in ogt− bacteria to those in their isogenic ogt+ parental counterparts. The effects of the uvrABC excision‐repair system, the adaptive response, mucAB and umuDC mutagenic processing, and glutathione bioactivation on the differential responses of ogt− and ogt+ bacteria were also studied. Mutation induction was monitored by measuring the frequency of forward mutations to L‐arabinose resistance. Induced mutations occurred only in excision repair–defective strains and were totally (with dibromomethane) or substantially (with dibromoethane) dependent on the alkyltransferase (ATase) encoded by the ogt gene. An increased mutagenic response to both dibromoalkanes was also seen in ogt− bacteria that overexpressed the ogt protein from a multicopy plasmid, indicating that the differences in mutability between ogt+ and ogt− bacteria were not dependent on the ogt− null allele carried by the defective strain. The ATase encoded by the constitutive ogt gene was more effective in promoting dibromoalkane mutagenicity than the ada ATase induced by exposure to low doses of a methylating agent. The mutagenicity promoted by the ogt ATase was dependent on both glutathione bioactivation and SOS mutagenic processing. To our knowledge, this paper presents for the first time evidence that DNA ATases, in particular the ATase encoded by the ogt gene, can increase the mutagenic effects of a DNA‐damaging agent. The mechanism of this effect has yet to be established. © 1995 Wiley‐Liss Inc.
p53 status in spontaneous and dimethylnitrosamine—induced renal cell tumors from rats
Authors: Horesovsky Greg , Recio Leslie , Everitt Jeff , Goldsworthy Thomas , Wolf Douglas C. , Walker Cheryl 
Published: February 2007

AbstractRats carrying the Eker tumor–susceptibility mutation (Eker rats) are predisposed to developing renal cell carcinoma. Rats heterozygous for the Eker mutation develop spontaneous multiple bilateral renal cell tumors by the age of 1 yr. In a previous study, Eker‐mutation carrier and noncarrier rats were exposed to the renal carcinogen dimethylnitrosamine (DMN), and male rats carrying the Eker mutation exhibited a 70‐fold increase in the induction of renal adenomas and carcinomas when compared with noncarrier rats. In this study, spontaneous and DMN‐induced rat renal cell tumors (adenomas and carcinomas) were analyzed for mutations of the p53 gene by direct sequencing of cDNA polymerase chain reaction products. There were no mutations in p53 cDNA derived from renal tumors from six untreated rats. Mutations were found in one of 15 of the DMN‐induced tumors: a transition at codon 140, CCT → CTT, in a renal adenoma. Additionally, seven cell lines derived from spontaneous renal cell tumors did not contain mutations in p53. The low frequency of p53 mutations (one of 21 renal cell tumors and none of seven cell lines derived from renal cell tumors) indicates that the development of both spontaneous and carcinogen‐induced renal tumors involved a non–p53‐dependent pathway. As p53 is infrequently mutated in human renal cell carcinomas and in rat renal mesenchymal tumors, it is likely that a tumor suppressor gene or genes other than p53 are involved in the development of renal cancer. © 1995 Wiley‐Liss Inc.
N‐methylnitrosourea—lnduced Ki‐ras codon 12 mutations: Early events in mouse thymic lymphomas
Authors: Newcomb Elizabeth W. , Bayona William , Pisharody Sobha 
Published: February 2007

AbstractN‐Methylnitrosourea (NMU)—induced codon 12 Ki‐ras mutations were analyzed in premalignant thymic lymphomas from C57BL/6J mice by using a selective polymerase chain reaction amplification strategy. The frequency of codon 12 Ki‐ras mutations was 67% (16 of 24) in NMU‐treated animals with premalignant stage I disease. Previously, animals with different stages of disease had been analyzed for cytogenetic changes and for mutations in the p53 tumor suppressor gene. The genetic changes observed were early‐activating codon 12 G35→A transition mutations of the Ki‐ras gene, followed closely by trisomy 15 and infrequent mutation of the p53 gene late in tumor development. The consistent and early detection of Ki‐ras mutations in NMU‐treated animals but not in untreated controls suggests that the mutations result from direct carcinogen exposure. Alternate pathways of NMU‐induced thymic lymphomagenesis were implicated. One pathway involved putative NMU‐induced mutations in other, non‐ras oncogenes that cooperate with trisomy 15 to produce similar T‐cell tumors. The frequency of p53 gene mutations in human and murine T‐cell tumors is similar but low. © 1995 Wiley‐Liss, Inc.
Analysis of loss of heterozygosity in murine hepatocellular tumors
Authors: Manenti Giacomo , De Gregorio Laura , Gariboldi Manuela , Dragani Tommaso A. , Pierotti Marco A. 
Published: February 2007

AbstractBecause allelotype analysis of tumors has been important in the identification of new tumor suppressor genes, here we studied loss of heterozygosity (LOH) in a well‐defined animal experimental system. We analyzed spontaneous liver tumors from C3HHc × C57BL/61 (B6C3F1) mice and urethane‐induced hepatocellular tumors from (C3H/He × Mus spretus) × C57BL/6JBy (HSB) interspecific mice. A total of 95 different genetic markers were tested: 13 in 24 B6C3F1 tumors, 76 in 58 HSB tumors, and six in both groups. Minisatellite fingerprinting analysis detected one case of LOH and less than 1% genomic rearrangements in polymorphic and nonpolymorphic bands, respectively. There were no changes at hepatocellular susceptibility loci or at markers homologous to loci frequently lost in human hepatocellular carcinomas. Therefore, our results suggest that LOH and genomic rearrangements are uncommon in mouse hepatocellular tumors. © 1995 Wiley‐Liss, Inc.
Suppression of the tumorigenic phenotype of a rat liver epithelial tumor cell line by the p11.2–p12 region of human chromosome 11
Authors: Coleman William B. , McCullough Karen D. , Esch Gwyn L. , Civalier Chris J. , Livanos Elizabeth , Weissman Bernard E. , Grisham Joe W. , Smith Gary J. 
Published: February 2007

AbstractComparative chromosomal mapping studies and investigations of tumor‐associated chromosomal abnormalities suggest that the development of hepatic tumors in humans and rats may share a common molecular mechanism that involves inactivation of the same tumor suppressor genes or common genetic loci. We investigated the potential of human chromosomes 2 and 11 to suppress the tumorigenic phenotype of rat liver epithelial tumor cell lines. These tumor cell lines (GN6TF and GP7TB) display elevated saturation densities in culture, efficiently form colonies in soft agar, and produce subcutaneous tumors in 100% of syngeneic rat hosts with short latency periods. Introduction of human chromosome 11 by microcell fusion markedly altered the tumorigenicity and the transformed phenotype of GN6TF cells. In contrast, the tumorigenic potential and phenotype of GP7TB cells was unaffected by the introduction of human chromosome 11, indicating that not all rat liver tumor cell lines can be suppressed by loci carried on this chromosome. Introduction of human chromosome 2 had little or no effect on the tumorigenicity or cellular phenotype of either tumor cell line, suggesting the involvement of chromosome 11–specific loci in the suppression of the GN6TF tumor cell line. The GN6TF‐11neo microcell hybrid cell lines displayed significantly reduced saturation densities in monolayer cultures, and their ability to grow in soft agar was completely inhibited. Although GN6TF‐11neo cells ultimately formed tumors in 80–100% of syngeneic rat hosts, the latency period for tumor formation was much longer. Molecular characterization of GN6TF‐11neo microcell hybrid cell lines indicated that some of the clonal lines had spontaneously lost significant portions of the introduced human chromosome, partially delineating the chromosomal location of the putative tumor suppressor locus to the region between the centromere and 11p12. Molecular examination of microcell hybrid–derived tumor cell lines further defined the minimal portion of human chromosome 11 capable of tumor suppression in this model system to the region 11p11.2‐p12. © 1995 Wiley‐Liss, Inc.
Cellular immortality: A late event in the progression of human squamous cell carcinoma of the head and neck associated with p53 alteration and a high frequency of allele loss
Authors: Edington Kirsten G. , Loughran Oonagh P. , Berry Isabella J. , Parkinson E. Kenneth 
Published: February 2007

AbstractMany human tumors contain variant cells that, unlike their normal counterparts, possess indefinite proliferative potential in vitro. However, little is known of the relevance of these immortal cells to human carcinomas in vivo. To investigate immortality in a human tumor system, we established cultures from different stages of head and neck squamous carcinoma (SCC‐HN). All the neoplastic cultures were transformed because they showed very low cornification in surface or suspension culture and were partially or completely resistant to suspension‐induced death. Immortal variants were not detected in premalignant erythroplakia cultures, but their frequency increased with tumor progression, indicating that immortality is a late event in carcinogenesis. Some late‐stage carcinomas still produced senescent cultures, but, significantly, all recurrent tumors were immortal. Immortal but not senescent carcinoma cultures were associated with p53 dysfunction and a high frequency of allele loss, indicative of tumor suppressor gene inactivation. These results show that there are at least two classes of human SCC‐HN that are phenotypically and genotypically distinct and that the pathological stage of a given tumor is not necessarily indicative of the kind of cells it contains. © 1995 Wiley‐Liss, Inc.
The impact of glutathione s‐transferase M1 and cytochrome P450 1A1 genotypes on white‐blood‐cell polycyclic aromatic hydrocarbon‐dna adduct levels in humans
Authors: Rothman Nathaniel , Shields Peter G. , Poirier Miriam C. , Harrington Anita M. , Ford D. Patrick , Strickland Paul T. 
Published: February 2007

AbstractCarcinogenic polycyclic aromatic hydrocarbons(a) form DNA adducts via a complex metabolic activation pathway that includes cytochrome P450(a) 1A1, whereas intermediate metabolites can be detoxified by conjugation through pathways including glutathione s‐transferase M1 (GSTM1). PAH‐DNA adducts can be measured in peripheral white blood cells (a) and should reflect the net effect of competing activation and detoxification pathways and ONA repair as well as exposure. We have previously shown that WBC PAH‐DNA adducts measured by an enzyme‐linked immunosorbent assay (a) were associated with recent, frequent consumption of charbroiled food among 47 nonsmoking wildland fire‐fighters who provided two blood samples 8 wk apart. In the investigation reported here, which was performed in the same population, we measured the association between the GSTM1 null genotype, which results in loss of enzyme activity, and PAH‐DNA adduct levels, hypothesizing that subjects with this genotype would have higher levels of DNA adducts because of their decreased ability to detoxify PAH metabolites. However, PAH‐DNA adduct levels were nonsignificantly lower in subjects with the GSTM1 null genotype (n = 28) compared with other subjects (n=19) (median 0.04 fmol/μg DNA vs 0.07 fmol/μg DNA, respectively, P = 0.45, Wilcoxon rank‐sum test). Adduct levels were also lower in the nine subjects heterozygous or homozygous for the CYP1A1 exon 7 polymorphism (which codes for a valine rather than isoleucine and is thought to be associated with greater CYP1A1 activity) compared with the 38 wild‐type subjects (P = 0.12). In the entire group, there was a positive association between consuming charbroiled food and PAH‐DNA adduct formation (r = 0.24, P = 0.02, Spearman rank‐order correlation). This association was weaker in the subgroup of subjects with the GSTM1 null genotype (r = 0.03, P = 0.84) and stronger among the remaining subjects (r = 0.57, P = 0.0002). These results suggest that the GSTM1 null genotype and CYPT1A1 exon 7 polymorphism are not associated with increased susceptibility for PAH‐DNA adduct formation in peripheral WBCs measured by ELISA in nonsmoking populations.© 1995 Wiley‐Liss, Inc
Promoter demethylation in MMTV/N‐rasN transgenic mice required for transgene expression and tumorigenesis
Authors: Mangues Ramon , Schwartz Simo , Seidman Irving , Pellicer Angel 
Published: February 2007

AbstractWe studied demethylation within the transgene promoter in transgenic mice carrying the N‐ras proto‐onco‐gene driven by the mouse mammary tumor long terminal repeat (MMTV/N‐rasN) and the relationship of demethy!ation to transgene overexpression and tumorigenesis. Demethylation at Fspl or Clal sites correlated with age of the animal and transgene expression in nontumorous mammary gland. Demethylation preceded expression in this tissue. In lymphomas and mammary tumors, the promoter Fspl and Clal sites were significantly more demethylated than in nontumorous control tissues. The Aval, Cfol, and Hpall sites were also found to be undermethylated in older animals and showed differences between tumor and control tissues. Two additional sites (Eagl and Narl) remained fully methylated in all tissues. In contrast with normal tissue, demethylation at the Fspl and Clal sites and expression were not correlated in tumor tissue. An increase in expression in normal tissue initially occurred and was correlated with the level of promoter demethylation; this increase was followed by a further increment in transgene expression when tumors developed. Thus, promoter demethylation leading to transgene overexpression was associated with long‐latency tumorigenesis in MMTV/N‐rasN transgenic mice. Demethylation of proto‐oncogene promoters may therefore be a mechanism of carcinogenesis that requires further investigation in human tumors.
12‐lipoxygenase isoenzymes in mouse skin tumor development
Authors: Krieg Peter , Kinzig Andreas , Ress‐Löschke Marion , Vogel Sonja , Vanlandingham Ben , Stephan Michael , Lehmann Wolf‐Dieter , Marks Friedrich , Fürstenberger Gerhard 
Published: February 2007

Abstract12‐lipoxygenase‐catalyzed arachidonic acid metabolism in normal and neoplastic mouse epidermis was assessed by cDNA cloning of the epidermal 12‐lipoxygenases and by studying their expression patterns, enzyme activities, and product levels. Papillomas and squamous cell carcinomas induced by the initiation/promotion protocol contained 50‐to 60‐fold more 12‐hydroxy‐5,8,10,14‐eicosatetraenoic acid (a) than normal epidermis. The ratio of S to R enantiomers was 9:1. This indicates that most of this eicosanoid was of enzymatic origin. Accordingly, cell‐free preparations of the tumors exhibited about fivefold elevated 12‐lipoxygenase activities. A papilloma‐derived cDNA library was screened with human platelet‐type 12‐lipoxygenase cDNA probes. Two cDNA clones encoding the platelet‐type and the leukocyte‐type isoforms of murine 12‐lipoxygenase were isolated, demonstrating the coexpression of the isoenzymes in the same tissue and species. When expressed in COS‐7 cells, the recombinant enzymes showed the characteristic substrate selectivity and product profile, with the leukocyte‐type enzyme metabolizing linoleic and arachidonic acid to 13‐hydroxy‐9,11‐octadecadienoic acid and to 12‐ and 15‐HETE, respectively, and the platelet‐type enzyme oxygenating exclusively arachidonic acid to 12‐HETE. In epidermis in vivo and in keratinocytes in culture, only the platelet‐type 12‐lipoxygenase (mRNA and protein) was detectable. In mouse epidermis both isoenzymes were induced transiently by phorbol esters. Most tumors showed constitutive overexpression of platelet‐type mRNA, whereas leukocyte‐type specific transcripts were detectable only in a few tumors. These data suggest that the platelet‐type enzyme is the 12‐lipoxygenase isoform of keratinocytes that is responsible for the generation of most of the 12‐HETE found in neoplastic epidermis. ©1995 Wiley‐Liss, Inc.
Homozygous deletions but no sequence mutations in coding regions of p15 or p16 in human primary bladder tumors
Authors: Packenham Joan P. , Taylor Jack A. , Anna Colleen H. , White Catherine M. , Devereux Theodora R. 
Published: February 2007

AbstractChromosome 9p21 appears to harbor a tumor suppressor gene, as evidenced by deletions in this region in a variety of human primary tumors and cell lines. To map the deletion at 9p21 in bladder tumors, we analyzed DNA from 28 tumor and normal pairs at five microsatellite markers that flank the region occupied by the putative tumor suppressor genes p16 and p15. Loss of heterozygosity (a) at the markers human interferon (a) α and D9S171, which are adjacent to the p15 and p16 loci, was detected in 41% and 33%, respectively, of informative cases of bladder tumors. No sequence mutations were detected in exons 1 or 2 of either p15 or p16 in any of the bladder tumors. Three sequence‐tagged site markers in the region bordered by HIFNα and D9S171 were used to further map the deleted region by multiplex polymerase chain reaction with the HIFNγ marker (on chromosome 12) as a control for amplification. Six of 11 tumors with LOH at surrounding markers had homozygous deletions of the marker c5.1, which is located within the p16 gene; and two tumors appeared to have homozygous deletions within p15(RN1.1) but not p16 (c5.1). A recently identified microsatellite marker, p16‐CA‐1, located 16 kb distal to p16, proved valuable in defining the minimal deletion involved in these bladder tumors. Five tumors exhibited homozygous deletions of this marker but not HIFNα and two tumors showed LOH at this marker and homozygous deletion of p16. Although these data could not be used to identify p16 or p15 as the definitive tumor suppressor gene in this region that is involved in bladder carcinogenesis, they suggest that homozygous deletion is a common mechanism of loss of tumor suppressor gene function in this region. © 1995 Wiley‐ Liss, Inc.
The effect of the JE (MCP‐1) gene, which encodes monocyte chemoattractant protein‐1, on the growth of hela cells and derived somatic‐cell hybrids in nude mice
Authors: Kleine Kerstin , König Gerd , Kreuzer JÖRg , Komitowski Dymitr , Hausen Harald Zur , Rösl Frank 
Published: February 2007

AbstractTo investigate the effect of tumor‐associated macrophages on the in vivo growth properties of cervical carcinoma cells, tumorigenic human papilloma virus (a) 18–positive HeLa cells were transfected with an expression vector harboring the cDNA for the macrophage chemoattractant protein‐1 JE (MCP‐1). Although the endogenous gene is present and not structurally rearranged, its expression seems to be negatively affected by a still unknown mechanism. Inoculation of JE (MCP‐1)‐negative HeLa cells into nude mice led to rapidly growing tumors, where macrophage infiltration into the inner tumor mass was not detectable immunohistochemically. The activity that attracted mononuclear cells under both in vitro and in vivo conditions was reconstituted in HeLa cells after transfection with the JE (MCP‐1) expression vector. Heterotransplantation of those cells into immunocompromised animals resulted in significant growth retardation that was accompanied by a strong infiltration of macrophages. On the other hand, in vivo selection of nonmalignant hybrids made between wild‐type HeLa cells and normal human fibroblasts in nude mice resulted in tumorigenic segregants 4 mo after inoculation into the animals. Monitoring JE (MCP‐1) expression directly within those nodules, we found that transcription was either absent or only weakly detectable. Recultivation of JE (MCP‐1)‐positive tissue grafts under in vitro conditions revealed that the gene was only marginally inducible by tumor necrosis factor‐α, a cytokine that normally induces a very strong activation of transcription in nontumorigenic cells. These findings suggest that functional JE (MCP‐1) expression and in turn activated macrophages may play a pivotal role in controlling the proliferation rate of HPV‐positive cells in vivo. © 1995 Wiley‐ Liss, Inc.