bluuebunny/crossref_metadata_2025_split huggingface dataset:
Loss of heterozygosity at chromosome 1q loci in rat mammary tumors
Authors: Gollahon Lauren S. , Chen Aaron , Aldaz C. Marcelo 
Published: February 2007

AbstractTo better characterize abnormalities affecting rat chromosome 1 during mammary carcinogenesis, tumors were induced by nitrosomethylurea in F1 hybrid rats polymorphic at multiple chromosome 1 loci. By means of restriction fragment length polymorphism and microsatellite length polymorphism analyses, we observed loss of heterozygosity or allelic imbalance affecting various loci on the q arm of chromosome 1 in a high percentage of the 49 tumors analyzed. Fifty percent of the tumors showed loss or imbalance affecting the most distal (1q55) INS1 (rat insulin 1 gene) locus. The MT1PA (metallothionein‐1 pseudogene a) locus was observed to be affected in 58% of tumors induced in BUF/NCr × ACI/Vsp rats. Most of the losses appeared to have occurred by mitotic recombination. No parental bias was observed on the affected chromosome 1. Tumors were also screened for mutations in codon 12 of the Ha‐ras‐1 gene, which is located on 1q. We observed an association between the presence of mutation and allelic imbalance. These studies confirm our previous cytogenetic observations of a high level of nonrandom instability affecting rat chromosome 1 during mammary carcinogenesis. The observed loss of heterozygosity may indicate the existence of a putative tumor suppressor gene within the distal half of the 1q arm. These abnormalities, however, could also be related to the early stages of Ha‐ras amplification. © 1995 Wiley‐Liss Inc.
Expression of epidermal ornithine decarboxylase and nuclear proto‐oncogenes in phorbol ester tumor promotion‐sensitive and ‐resistant mice
Authors: Kennard Merle D. , Kang Dong‐Chul , Montgomery Raechelle L. , Butler Andrew P. 
Published: February 2007

AbstractThis study was undertaken to assess the effects of a single or two sequential topical applications of 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA) on the expression of c‐fos, c‐jun, junB, c‐myc, and ornithine decarboxylase (ODC) in promotion‐sensitive SSIN mice and the relatively promotion‐resistant C57BL/6 strain. Northern blot analysis demonstrated that a single promoting dose of TPA induced ODC mRNA expression 10‐to 15‐fold in both strains. Treatment of each strain with a second dose of TPA, 48 h (in C57BL/6 mice) or 72 h (in SSIN mice) after the first, led to hyperinduction of ODC activity. Although this involved transcription of new ODC mRNA, the hyperinduction of ODC enzyme activity was primarily posttranscriptional. Induction of c‐fos mRNA or protein was maximal about 3 h after a single treatment in either strain but was sustained for at least 6 h in C57BL/6 mice. In contrast, two treatments of SSIN mice with TPA caused a rapid, strong c‐fos induction 1–2 h after treatment, whereas C57BL/6 mice responded no more strongly than after a single treatment. c‐jun mRNA and protein were induced only slightly in either strain, but junB was induced about fivefold in SSIN mice and tenfold in C57BL/6 mice. Although c‐myc was induced to comparable levels in both strains, the reponse was more prolonged in C57BL/6 mice. Compared with SSIN mice, C57BL/6 mice responded to TPA treatment, in general, with changes in proto‐oncogene mRNA to a higher level or for longer or both. Thus, although small differences in the expression of these genes were observed, they were not positively correlated with the differential sensitivity of SSIN and C57BL/6 mice toward tumor promotion by phorbol esters, with the possible exception of c‐fos. © 1995 Wiley‐Liss Inc.
Hepatocarcinogenesis in p53‐deficient mice
Authors: Kemp Christopher J. 
Published: February 2007

AbstractTo determine whether a constitutive p53 deficiency would enhance the rate of development of chemically induced hepatocellular carcinoma, we treated groups of wild‐type, p53‐heterozygous (+/‐), and null (‐/‐) male mice with a single dose of diethylnitrosamine at 12 d of age. Although the null mice had to be killed very early, at 15 wk of age because of the development of nonliver tumors, hemangosarcoma of the liver had already developed in two of seven mice. More detailed analysis of the wild‐type and heterozygous mice showed no difference in the number, size, or growth rate of early microscopic lesions or in the number or apparent malignancy of hepatocellular adenomas or carcinomas at later time points. Thus, germline p53 deficiency does not enhance the rate of development of diethylnitrosamine‐induced hepatocellular adenoma or carcinoma but may instead favor development of hepatic hemangiosarcoma. © 1995 Wiley‐Liss Inc.
Expression of phospholipases γ1, β1, and δ1 in primary human colon carcinomas and colon carcinoma cell lines
Authors: Nomoto Koji , Tomita Naohiro , Miyake Masami , Xhu Ding‐Bang , Logerfo Paul R. , Weinstein I. Bernard 
Published: February 2007

AbstractThe levels of expression of phosphoinositide‐specific phospholipase Cs (PLCs) were examined in a series of primary human colon carcinomas and in eight colon carcinoma cell lines by using monoclonal antibodies and cDNA probes for PLCγ1, PLCβ1, and PLCδ1. Western and northern blot analyses of PLCγ1 revealed elevated expression of this isozyme at both the protein and mRNA levels in most tumors when compared with paired adjacent normal mucosa samples (in 11 of 13 pairs in the western blots and 8 of 9 pairs in the northern blots). On the other hand, decreased levels of the PLCδ1 protein were seen in most colon carcinomas (12 of 13 paired samples). The levels of PLCβ1 protein were too low to detect possible differences between the carcinoma and normal mucosa samples. Relatively high expression of PLCγ1 was found in almost all of the eight human colon carcinoma cell lines at both the protein and mRNA levels. Only weak expression of PLCβ1 was detected in these cell lines, by both western and northern blot analyses, and PLCδ1 protein was not detected in any of the carcinoma cell lines. These findings provide evidence that colon carcinomas display altered expression of individual isoforms of PLCs and suggest that increased expression of PLCγ1 may play an important role in colon carcinogenesis. © 1995 Wiley‐Liss Inc.
Inhibition of ras p21 membrane localization and modulation of protein kinase C isozyme expression during regression of chemical carcinogen–induced murine skin tumors by lovastatin
Authors: Khan Sikandar G. , Saxena Ramesh , Bickers David R. , Mukhtar Hasan , Agarwal Rajesh 
Published: February 2007

AbstractWe investigated the ras p21 membrane localization and the expression and activation of protein kinase C (PKC) isozymes in activated ras oncogene–containing tumors and assessed whether these events were related to tumors growth. We used 7,12‐dimethylbenz[a]anthracene–initiated and 12‐O‐tetradecanoylphorbol‐13‐acetate–promoted SENCAR mouse skin tumors, which were shown to contain Ha‐ras oncogene activated by point mutation at codon 61, as an in vivo model for these studies. Compared with levels in epidermis, highly elevated levels of membrane‐bound Ha‐ras p21 were observed in growing tumors, which also showed strong expression and membrane translocation of PKC ζ and βII and weak expression of PCK α. However, when ras p21 membrane localization was blocked in vivo in growing tumors by lovastatin, opposite results were evident. Compared with saline‐treated animals, in which tumor growth continued, lovastatin‐treated animals had significantly inhibited tumor growth, which led to tumor regression with concomitant inhibition of Ha‐ras p21 membrane localization. These regressing tumors from lovastatin‐treated animals also showed a decrease in the expression and membrane translocation of PKC ζ and βII but increased expression of PKC α. Taken together, our results indicate that ras p21 membrane localization and the expression and activation of PKC ζ, βII, and α may be the critical events in the regulation of the growth of tumors that contain activated ras oncogenes. © 1995 Wiley‐Liss Inc.
Novel use of a selectable fusion gene as an “In‐Out” marker for studying genetic loss in mammalian cells
Authors: Trott Deborah A. , Cuthbert Andrew P. , Todd Christopher M. , Themis Michael , Newbold Robert F. 
Published: February 2007

AbstractRecent demonstrations of loss of heterozygosity in a wide variety of human cancers suggest that large multilocus genetic deletions (presumably including tumor suppressor genes) constitute a major class of genetic alteration in human carcinogenesis. Here we show that a bifunctional fusion gene (Hytk), suitable for both positive and negative selection, is an effective marker for studying genetic loss in mammalian cells with minimal interference from point‐mutational changes. Studies with a transgenic V79 cell line in which a single functional copy of Hytk was stably inserted into the genome in a retroviral vector showed that loss of the marker (and presumably flanking cellular genetic material) could be induced efficiently by ionizing radiation (γ‐rays and fast neutrons) but only weakly by the powerful point‐mutagen benzo[a]pyrene diol epoxide. In a first application of the system, we provide evidence that radiation‐induced loss can occur through an indirect mechanism after a high‐frequency event. Collectively, our results suggest that the Hytk marker should be a valuable tool for studying genome position effects on the tolerance of genetic loss in cultured human cells that represent different stages in clonal evolution and tumor progression. © 1995 Wiley‐Liss Inc.
Microsatellite alterations in human and rat esophageal tumors at selective loci
Authors: Mironov Nikolai M. , Aguelon Anne‐Marie , Hollams Elysia , Lozano Jean‐Claude , Yamasaki Hiroshi 
Published: February 2007

Abstract(CA)n simple repeats in DNA were examined at 17 loci in 18 human squamous cell carcinomas of the esophagus and compared with those in normal esophageal tissue from the same patients. Six loci were examined in 32 esophageal papillomas that had been induced by N‐nitrosomethylbenzylamine in BD VI rats. Length‐altered CA repeats were found in two human tumors and four rat papillomas. Loss of heterozygosity was observed in three human tumors; two rat papillomas had lost microsatellite bands that are common in inbred BD VI rats. Both (CA)n microsatellite length alteration and loss of heterozygosity were clustered at certain loci in the human tumor samples and in the chemically induced rat esophageal tumors. Our findings indicate that genomic instability that results in alteration of repeated sequences not only occurs in human tumors but may also be a consequence of chemical carcinogenesis in rodents. © 1995 Wiley‐Liss, Inc.
Induced terminal differentiation and tumorigenic suppression in murine keratinocyte somatic‐cell hybrids
Authors: Schneider Brandt L. , Kulesz‐Martin Molly , Bowden G. Tim 
Published: February 2007

AbstractThe development of malignancy has been associated with both the activation of oncogenes and the inactivation of tumor suppressor genes. Whereas recent data implicate tumor suppressor genes as cell‐cycle checkpoints, the nature and timing of tumor suppressor gene inactivation during multistage carcinogenesis is still largely uncharacterized. To address this issue, we used a syngeneic mouse epidermal model system. By creating somatic‐cell hybrids between nontumorigenic × benign (291 × 291.09RAT), nontumorigenic × malignant (291 × 291.05RAT and 291 × 291.03RAT), benign × malignant (291.09RAT × 291.03RAT) and malignant × malignant (291.03RAT × 291.05RAT) clones, multiple tumor suppressor activities were detected. Most importantly, we demonstrated the first example of the complete suppression of benign papillomas in vivo, thus implicating tumor suppressor gene activity loss as an early event in skin carcinogenesis. In addition, the carcinoma phenotype was suppressed in vivo by nontumorigenic, benign, and heterologous malignant keratinocytes. The somatic‐cell hybrids expressed the differentiation‐specific keratins, K1 and K10, in response to high extracellular calcium concentrations (1.4 mM) in vitro. All of the hybrids had fewer local metastases than did the parental lines, and when tumor formation was not suppressed, the resulting tumors were highly differentiated. Polymerase chain reaction analysis of the neomycin‐resistance gene at nontumorigenic injection sites indicated an absence of injected hybrids, and subsequent analyses failed to detect nontumorigenic 291 cells 1 wk after transplantation. These data demonstrate that distinct tumor suppressor gene activities are lost at discrete stages during multistage carcinogenesis and are consistent with the hypothesis that tumor suppression can occur through induction of terminal differentiation. © 1995 Wiley‐Liss, Inc.
Benzo[a]pyrene‐induced mutagenesis of p53 hot‐spot codons 248 and 249 in human hepatocytes
Authors: Cherpillod Pascal , Amstad Paul A. 
Published: February 2007

AbstractHuman tobacco‐related cancers show a high frequency of G‐to‐T transversions in several mutation hot‐spot regions of the p53 tumor suppressor gene, probably the result of specific mutagens in tobacco smoke, most notably benzo[a]pyrene. To gain insight into the mechanism of formation of these G‐to‐T transversions in tobacco‐associated carcinogenesis, we studied the mutagenesis of p53 codons 247–250 by benzo[a]pyrene in human hepatocellular carcinoma cells by restriction fragment length polymorphism‐polymerase chain reaction genotypic analysis. Benzo[a]pyrene preferentially induced G‐to‐T transversion in the second and third positions of codon 248 and C‐to‐A transversion in the first position of codon 248. However, benzo[a]pyrene did not induce base‐pair changes in codon 249, which is a mutational hot‐spot in aflatoxin‐related hepatocardno‐genesis, in which predominantly G‐to‐T transversion in the third psition of codon 249 is observed. The benzo[a]pyrene‐induced G‐to‐T transversion in the middle position of codon 248, in which arginine is changed into leucine, is frequently observed in tumors of the lung. The other two benzo[a]pyrene‐induced base‐pair changes in codon 248, namely the C‐to‐A transversion in the first position and G‐to‐T transversion in the third position, do not lead to a change in the amino‐acid composition of the p53 protein. These mutations are silent and therefore are not selected in tumors. It follows that benzo[a]pyrene‐induced mutability on the DNA level in p53 codons 247–250 correlates well with the type of mutation found in tumors of the lung. Therefore, our results support the hypothesis that benzo[a]pyrene is the etiological agent in tobacco‐related Cancers. © 1995 Wiley‐Liss, Inc.
Frequent loss of heterozygosity on chromosome 4 in diethylnitrosamine‐induced C3H/MSM mouse hepatocellular carcinomas in culture
Authors: Miyasaka Kazuyoshi , Ohtake Keiko , Nomura Kimie , Kanda Hiroaki , Kominami Ryo , Miyashita Nobumoto , Kitagawa Tomoyuki 
Published: February 2007

AbstractGenetic changes, in particular the loss of heterozygosity (LOH) and the presence of c‐Ha‐ras codon 61 point mutations, were investigated in diethylnitrosamine‐induced hepatocellular carcinomas (HCCs) in C3H/MSM F1 mice. (MSM are wild mice.) LOH analysis of 48 primary tumors with microsatellite probes covering at least one proximal and one distal site of each autosome revealed no obvious positive results for LOH. Analysis of 23 cell lines established from seven of these HCCs, however, showed LOH on chromosome 4 in all (seven of seven), even in early passages (G2‐G3). With regard to other chromosomes, LOH was observed only rarely on chromosomes 16 and 19. These allelotype features were maintained in later passages (G11‐G14), with only a few additional occurrences of LOH appearing on chromosomes 1, 6, and 8. Extensive analyses with multiple micro‐satellite probes from chromosome 4 and with 52 cell lines established from 24 HCCs of 18 mice revealed LOH in 22 of the tumors (92%), with the shortest region about 10 cM distal to the a‐interferon gene. No c‐Ha‐ras oncogene activation in codon 61 was observed. These data indicate that loss of tumor suppressor genes on chromosome 4 may play an important role in mouse hepatocarcinogenesis in progression in vivo or in immortalization in vitro or both. © 1995 Wiley‐Liss, Inc.
Combined effects of ionizing radiation and cycloheximide on gene expression
Authors: Woloschak Gayle E. , Felcher Paolo , Chang‐Liu Chin‐Mei 
Published: February 2007

AbstractWe performed experiments to determine the effects of ionizing radiation exposure on expression of genes such as β‐actin, c‐fos, histone H4, c‐myc, c‐jun, Rb, and p53 after exposure of Syrian hamster embryo (SHE) cells to the protein synthesis inhibitor cycloheximide. The purpose of these experiments was to determine the role of a labile protein in the radiation‐induced response. The results revealed that when ionizing radiation (either fission‐spectrum neutrons or γ rays) was administered 15 min after cycloheximide treatment of SHE cells, the radiation exposure reduced cycloheximide‐mediated gene induction of c‐fos, histone H4, and c‐jun. In addition, dose‐rate differences were found when radiation exposure most significantly inhibited the cycloheximide response. Our results suggest that ionizing radiation does not act as a general protein‐synthesis inhibitor and that the presence of a labile protein is required for the maintenance of specific gene transcription and mRNA accumulation after radiation exposure, especially at high dose‐rates. © 1995 Wiley‐Liss, Inc.
Contribution of O6‐methylguanine‐DNA methyltransferase to resistance to 1,3‐(2‐chloroethyl)‐1‐nitrosourea in human brain tumor‐derived cell lines
Authors: Bobola Michael S. , Berger Mitchel S. , Silber John R. 
Published: February 2007

AbstractTo assess the possible role of the DNA repair protein O6‐methylguanine‐DNA methyltransferase (MGMT) in resistance of brain neoplasms to the clinically important chloroethylating agent 1,3‐bis(2‐chloroethyl)‐1‐nitrosourea (BCNU), we quantitated MGMT activity, BCNU survival, and the effect of ablating MGMT activity on the sensitivity of 14 human medulloblastoma‐ and glioma‐derived cell lines. BCNU resistance, measured as 10% survival dose (LD10), differed eightfold among the lines. Elimination of measurable MGMT activity with the substrate analogue inhibitor O6‐benzylguanine (O6‐BG) revealed a variable but limited contribution of MGMT to survival. In no case did O6‐BG reduce LD10 by more than 3.4‐fold. In contrast, 06‐BG reduced the LD10 for N‐methyl‐N′‐nitro‐N‐nitrosoguanidine up to 31‐fold in the same cell lines (Bobola MS, Blank A, Berger MS, Silber JR, Mol Carcinog 13:70–80, 1995). Variability in BCNU survival, manifested as a sevenfold range of LD10, persists after measurable MGMT was eliminated, indicating that another mechanism or mechanisms is operating to limit cytotoxicity. Cells alkylated while suspended in growth medium are more resistant to BCNU and display less dependence on MGMT than cells treated while proliferating on a plastic substratum. When alkylated in suspension, most of the lines are either unresponsive to O6‐BG or contain a subpopulation that did not respond to O6‐BG. Our results demonstrate that BCNU resistance is multifactorial and that MGMT makes a modest contribution to resistance in our lines. © 1995 Wiley‐Liss, Inc.
Characterization of a murine p53SER246 mutant equivalent to the human p53SER249 associated with hepatocellular carcinoma and aflatoxin exposure
Authors: Ghebranious Nader , Knoll Brian J. , Wu Hongyun , Lozano Guillermina , Sell Stewart 
Published: February 2007

AbstractA mutation in the tumor suppressor p53 gene resulting in an Arg→Ser substitution in position 249 is found frequently in human hepatocellular carcinomas associated with hepatitis B infection and with aflatoxin exposure. To determine the significance of this mutation in an in vivo experimental model using transgenic mice, we introduced a two‐nucleotide change in the mouse p53 gene at amino‐acid position 246, which is equivalent to position 249 in human p53, by the recombinant polymerase chain reaction mismatched primer method. This p53 mutation resulted in the same change, an Arg→Ser substitution, as in the human p53 gene at position 249. We now report that the protein product of this mutant mouse p53ser246 had properties similar to those of the wild‐type protein when tested by binding to (i) monoclonal antibodies PAb246 and PAb240, (ii) simian virus 40 large T antigen, and (iii) heat‐shock protein. However, it had mutant‐type transforming properties when tested for colony formation with an osteosarcoma cell line. It was not active, as is wild‐type p53, in transcription activation of the muscle creatine kinase promoter. These properties are the same as those found in the p53trp248 product of the p53 mutation associated with the Li‐Fraumeni syndrome. Although less is known about the human p53ser249 product associated with hepatocellular carcinoma, the mutant murine p53ser246 protein shares the known properties of the human gene product. © 1995 Wiley‐Liss, Inc.
Mutational specificity of 2‐amino‐3‐methylimidazo‐[4,5‐f]quinoline in the hprt locus of CHO‐K1 cells
Authors: Lee Huei , Shih Ming‐Kuei 
Published: February 2007

Abstract2‐Amino‐3‐methylimidazo[4,5‐f]quinoline (IQ), a food carcinogen formed in cooked meats, can induce gene mutation at the hprt locus of CHO‐K1 cells in the presence of hepatic 59 mix. To elucidate the molecular nature of IQ‐induced mutation, we characterized the entire coding region of the hypoxanthine phosphoribosyl‐transferase gene of 23 independent mutants derived from IQ‐treated CHO cells by direct sequencing of polymerase chain reaction‐amplified cDNA. Ten of the 23 IQ‐induced mutants examined contained single base substitutions; one mutant had three single‐base substitutions. Among the base substitutions, G·C→CG (six of 13) and A·T→CG (three of 13) transversions predominated. Most of the base‐substitution mutations occurred preferentially at a middle G and had a dA in their 3′ ends. Of the 13 other mutations (56.5%), 12 missing one or more complete exons were splice‐site mutations, and one mutant had a partial deletion of an exon. A high frequency of complete exon deletion (11 of 12) in exons 2–5 was observed. Interestingly, 75% of the mutants (nine of 12) with splice‐site mutations were induced by IQ only at higher concentrations (300–500 μM). This was probably due to the occurrence of GC base‐substitution mutations that affected hprt mRNA splicing, especially at the intron‐exon boundaries. © 1995 Wiley‐Liss, Inc.
Effects of 12‐O‐tetradecanoylphorbol‐13‐acetate on human papillomavirus type 16‐positive keratinocytes at different stages of transformation
Authors: Sears Wendy L. , Goto‐Mandeville Ryoko , Mirapuri Mona , Braun Lundy 
Published: February 2007

AbstractNormal human keratinocytes grown under serum‐free conditions can be triggered to differentiate by exposure to serum or to the phorbol ester 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA). We found that TPA treatment of human papillomavirus (HPV) type 16‐immortalized cells in culture induced formation of cornified envelopes indicative of squamous differentiation. Concurrent with differentiation, TPA inhibited the expression of HPV 16 E6 and E7 mRNA transcripts. Adaptation of the immortalized cells to growth in serum‐containing medium led to the selection of a subpopulation of HPV‐transformed cells that was resistant to TPA‐induced differentiation. In this cell line, a transient suppression of HPV transcripts was observed at 5 h, whereas in differentiation‐resistant, carcinoma‐derived lines, TPA had little effect on HPV oncogene expression, c‐myc transcripts were suppressed for the duration of exposure to TPA in only the differentiation‐competent cells; c‐fos and c‐jun were transiently induced in all cell lines. Transforming growth factor‐a mRNAs were also increased approximately eightfold as HPV 16‐immortalized cells were induced to differentiate. These results demonstrate that, in HPV 16‐immortalized keratinocytes, acquisition of resistance to inducers of squamous differentiation is accompanied by altered regulation of cell growth and gene expression. © 1995 Wiley‐Liss, Inc.