bluuebunny/crossref_metadata_2025_split huggingface dataset:
Inhibition of plasmid reporter gene expression in cho cells by DNA adducts of 2‐amino‐3‐methylimidazo[4,5‐f]quinoline and 2‐amino‐1‐methyl‐6‐phenylimidazo[4,5–b]pyridine
Authors: Fan Liju , Snyderwine Elizabeth G. 
Published: February 2007

Abstract2‐Amino‐3‐methylimidazo[4,5‐f]quinoline (IQ) and 2‐amino‐1‐methyl‐6‐phenylimidazo[4,5‐b)]pyridine (PhIP) are two members of a family of carcinogenic heterocyclic amines (HAs) found in cooked meats that form DNA adducts after activation to N‐acetoxy derivatives. The ability of IQ‐ and PhlP‐DNA adducts to inhibit gene expression was investigated using a human growth hormone (hGH) reporter gene in a pUC12‐based mammalian expression vector under the control of either the herpes simplex virus‐1 thymidine kinase promoter or the human immunodeficiency virus‐1 long terminal repeat. The plasmids were treated in vitro with 0, 5, 10, or 40 μM N‐hydroxy‐IQ or N‐hydroxy‐PhIP in the presence of a 10‐fold molar excess of acetic anhydride to generate the N‐acetoxy derivatives in situ. The adduct levels in the plasmids were quantitated by the 32P‐postlabeling method. The adducted (and control) plasmids were each transfected into repair‐deficient or ‐proficient Chinese hamster ovary cells, and expression of hGH was measured by immunoassay of growth hormone secreted into the cell medium. The results showed that IQ‐ and PhlP‐DNA adducts inhibited gene expression in both plasmids and that the degree of inhibition of hGH production was proportional to the levels of IQ‐ and PhlP‐DNA adducts. The degree of inhibition, however, was independent of the promoter, despite the differences in the strengths of the two promoters to drive hGH production. Repair capacity influenced the extent of inhibition of gene expression by HA adducts since, in general, fewer adducts were needed to inhibit reporter gene expression in repair‐deficient cells than in repair‐proficient cells. In both cell lines, DNA adducts of PhIP appeared to be more potent in inhibiting hGH expression than adducts of IQ. Whether alteration of gene expression by HA adducts plays a role in the carcinogenicity of these compounds deserves further study. © 1994 Wiley‐Liss, Inc.
Absence of p53 mutations and various frequencies of ki‐ras exon 1 mutations in rat hepatic tumors induced by different carcinogens
Authors: Tokusashi Yoshihiko , Fukuda Ikue , Ogawa Katsuhiro 
Published: February 2007

AbstractMutations of p53 and Ki‐ras exon 1 were investigated in rat hepatic lesions induced by four kinds of hepatocarcinogenic protocols: continuous feeding of 3′‐methyl‐4‐dimethylaminoazobenzene (3′‐Me‐DAB), daily intraperitoneal injection of aflatoxin B, (AFB,), and the Soft and Farber regimen (Nature 236:701–703, 1976), in which diethylnitrosamine (DEN) or nitrosomethylurea (NMU) was used as initiating agents. DNA from microdissected tissue sections was amplified by the polymerase chain reaction (PCR) directly using primers for p53 exons 5–8 and Ki‐ras exon 1 and analyzed for mutations by denaturing gradient gel electrophoresis (DGGE) or constant denaturant gel electrophoresis (CDGE). One or both of the p53 PCR primers were located within introns to prevent amplifying the p53 processed pseudogenes. In a total of 59 hepatocellular carcinomas (HCCs), no p53 aberrations were detected, indicating that p53 mutations are not very important in rat hepatic carcinogenesis. On the other hand, Ki‐ras codon 12 mutations were found at low frequency in HCCs, hyperplastic foci, and cholangiof ibroses induced by 3′‐Me‐DAB and by AFB! but not in the lesions induced by the Solt and Farber regimen. Although Ki‐ras codon 12 mutations are generally infrequent in rat hepatic tumors, their incidence thus appears to vary depending on the carcinogen used for their induction. © 1994 Wiley‐Liss, Inc.
Mediation of suppression of c‐fos transcription in rasT24‐transformed rat cells by a cis‐acting represser element
Authors: Osei‐Frimpong Joseph , Sepulveda Jorge , Rangdaeng Samreung , Lebovitz Russell M. 
Published: February 2007

AbstractProlonged expression of activated ras mutants resulted in both neoplastic transformation and suppression of serum‐induced c‐fos expression in Rat1 fibroblasts. Expression of other serum‐inducible genes, including c‐jun and β‐actin, was not suppressed in ras‐transformed Rat1 cells, indicating that these effects are specific for c‐fos and that growth‐factor signal transduction pathways remain essentially intact. Run‐on transcription studies indicated that c‐fos transcription was blocked at the level of initiation in these cells. Transient transfection studies using 360 bp from the wild‐type c‐fos promoter as well as a series of mutated c‐fos promoter fragments linked to the chloramphenicol acetyltransferase gene indicated that repression of c‐fos was mediated by approximately 49 bp immediately upstream of the dyad symmetry element (DSE). Deletion of this region, referred to as the upstream represser region (URR), restored serum inducibility to the c‐fos promoter in ras‐transformed cells. In contrast, suppression of c‐fos transcription was not affected by either deletion of 240 bp between the DSE and the TATA element or by base‐substitution mutations that inactivate the ternary complex factor and fos‐AP‐1‐like binding sites. In addition, in vitro competition studies indicated that ras‐transformed cells express one or more represser factors that interact with as‐yet‐unidentified elements within the c‐fos promoter (possibly the URR) and block serum induction of c‐fos. These findings suggest that prolonged expression of activated ras results in the activation of one or more as‐yet‐unidentified proteins that suppress transcription of the c‐fos gene by interacting with the URR. © 1994 Wiley‐Liss, Inc.
Increased actin cable organization after single chromosome introduction: Association with suppression of in vitro cell growth rather than tumorigenic suppression
Authors: Miyamoto Shingo , Nishida Makoto , Miwa Katsuhiro , Kato Hidenori , Imamura Toshiro , Barrett J. Carl , Shimizu Motoyuki , Oshimura Mitsuo , Wake Norio 
Published: February 2007

AbstractWe previously showed that introduction of a single human chromosome 1, 6, or 9 derived from normal fibroblasts into HHUA endometrial carcinoma cells resulted in suppression of tumorigenicity. The tumorigenic suppression was accompanied by remarkable morphological changes in the microcell hybrids containing an extra copy of chromosome 1. The study presented here was undertaken to search for target cytoskeletal components affected by chromosome 1 transfer into endometrial carcinoma cells. We found that the microcell hybrids containing an extra copy of chromosome 1 were characterized by intracellular actin bundle formation and an excessive accumulation of actin and vinculin. The latter was a result of increased stabilization of the proteins. Additionally, chromosome 3 introduction into RCC23 human renal carcinoma cells resulted in prolongation of cell division and in senescence of a significant proportion of the microcell hybrids. In these microcell hybrids, the intracellular actin network was also reorganized, but the amounts of actin and vinculin protein were not increased. These findings suggest that the increased actin organization, which appeared not to cause tumorigenic suppression in the microcell hybrids, is associated with complementation of tumor suppressor genes and senescence by multiple mechanisms. © 1994 Wiley‐Liss, Inc.
Only wild‐type c‐ki‐ras codons 12, 13, and 61 in human pancreatic acinar cell carcinomas
Authors: Terhune Pamela Guay , Heffess Clara S. , Longnecker Daniel S. 
Published: February 2007

AbstractActivation of the c‐Ki‐ras proto‐oncogene is more common in carcinomas of the pancreas than in other human carcinomas. Most such carcinomas are of the ductal cell phenotype. Ductal adenocarcinomas of the hamster pancreas have similar mutations, but acinar cell carcinomas of the mouse and rat pancreas lack the common c‐Ki‐ras mutations. Therefore, we examined 11 acinar cell carcinomas of the human pancreas for evidence of mutations at codons 12, 13, and 61. DNA was isolated from tumor cells in paraffin‐embedded sections. The polymerase chain reaction was used to amplify the appropriate DNA sequence, and then allele‐specific oligonucleotide hybridization and DNA sequence analysis were used to evaluate c‐Ki‐ras structure. Only wild‐type sequences were found in codons 12, 13, and 61. Thus, in both the human and rodent species, mutations of c‐Ki‐ras appear to be more important in the genesis of ductal carcinomas than in the genesis of acinar cell carcinomas of the pancreas. © 1994 Wiley‐Liss, Inc.
Altered expression of the epidermal growth factor receptor and transforming growth factor‐α during multistage skin carcinogenesis in SENCAR mice
Authors: Rho Okkyung , Beltrán Linda M. , Gimenez‐Conti Irma B. , Digiovanni John 
Published: February 2007

AbstractIn the study presented here, we examined the possible role of the transforming growth factor‐α (TGFα)/epidermal growth factor receptor (EGFR) system during multistage carcinogenesis in mouse skin. In this regard, the expression (mRNA and protein) of both TGFα and EGFR was examined in primary papillomas and squamous cell carcinomas (SCCs) obtained from SENCAR mice treated with standard initiation‐promotion regimens and compared with the levels of expression in normal epidermis. The level of a 4.8‐kb TGFα transcript was elevated in 100% of the skin tumors examined (both papillomas and SCCs), including papillomas obtained 13 wk after the start of promotion, compared with normal epidermis. Immunohistochemical analyses detected elevated levels of TGFα protein in these skin tumors and in papillomas as early as 10 wk after the start of promotion. The levels of EGFR transcripts were also significantly elevated in most (90%) of the skin tumors examined, including again those harvested after 13 wk of promotion. Interestingly, multiple EGFR transcripts (10.5, 5.8, 2.8, and 1.8 kb) were detected in both papillomas and SCCs. The two smaller transcripts appeared to encode truncated versions of the EGFR, and the 1.8‐kb transcript appeared to be unique to RNA samples isolated from skin tumors, based on comparative analyses of several normal tissues. As with TGFα, immunohistochemical analyses detected elevated levels of EGFR protein in these skin tumors (both papillomas and SCCs), including papillomas harvested as early as 10 wk after the start of promotion. Southern analyses of genomic DNAs for TGFα and EGFR failed to detect any cases of gene rearrangements or amplification as a possible explanation for the elevated levels of the transcripts of these two genes. These results support the hypothesis that a key step in the development of autonomous growth in mouse skin papillomas generated in SENCAR mice by an initiation‐promotion regimen may involve alterations in the synthesis of TGFα and its cognate receptor. ©1994 Wiley‐Liss, Inc.
bcl‐2 delay of alkylating agent‐induced apoptotic death in a murine hemopoietic stem cell line
Authors: Fairbairn Leslie J. , Cowling Graham J. , Dexter T. Michael , Rafferty Joseph A. , Margison Geoffrey P. , Reipert Birgit 
Published: February 2007

AbstractMany cytotoxic agents kill cells by invoking a specific death pathway termed physiological cell death, or apoptosis. Treatment of a murine hemopoietic stem cell line, FDCP‐mix, with methylmethanesulfonate (MMS) orN′‐methyl‐N′‐nitrosourea (MNU) leads to death by apoptosis. Retroviral gene transfer was used to overexpress thebcl‐2 oncogene in FDCP‐mix cells, and this was associated with a delay in apoptosis in these cells after treatment with MNU and MMS and decreased sensitivity of colony formation to the cytotoxic effects of MMS. These data suggest an explanation for the refractory nature ofbcl‐2—expressing follicular lymphoma to cytotoxic chemotherapy and furthermore suggest that DNA‐damaging antitumor therapy may contribute to the progression of disease. ©1994 Wiley‐Liss, Inc.
Induction of specific cytochrome P450s involved in aflatoxin B1 metabolism in hepatitis B virus transgenic mice
Authors: Kirby Gordon M. , Chemin Isabelle , Montesano Ruggero , Chisari Francis V. , Lang Matti A. , Wild Christopher P. 
Published: February 2007

AbstractThe relative roles of hepatitis B virus (HBV) and aflatoxn and their possible mechanism of interaction in the etiopathogenesis of hepatocellular carcinoma (HCC) are not understood. One hypothesis is that viral infection and associated liver injury alter expression of carcinogen‐metabolizing enzymes. We tested this hypothesis in an HBV‐transgenic mouse model in which a synergistic interaction occurs between aflatoxin B1 (AFB1) and HBV in the induction of HCC (Sell et al., Cancer Res 51:1278–1285, 1991). In this transgenic mouse lineage, overproduction of the HBV large envelope protein results in progressive liver cell injury, inflammation, and regenerative hyperplasia. Initially, two cytochrome P450s of importance in AFB1 metabolism in the mice were identified, namely Cyp2a‐5 and Cyp3a, using specific antibodies and chemical inhibitors. The expression of these P450 isoenzymes and an α‐class glutathione S‐transferase (GST) isoenzyme, YaYa, were examined. Increased expression and altered distribution of Cyp2a‐5 were demonstrated, by immunohistochemical analysis, to be associated with the development of liver injury in mice and to increase with age between 1 and 12 months. Cyp3a expression was also increased in HBV‐transgenic mice, but the increase was not as clearly related to age. GST YaYa levels were the same in HBV‐transgenic mice and their nontransgenic littermates of all ages. These results show that expression of specific cytochrome P450s is altered in association with overexpression of HBV large envelope protein and liver injury in this model. This may have general relevance to human HCC, the etiology of which is associated with a diverse range of liver‐damaging agents. ©1994 Wiley‐Liss, Inc.
Association of liver fluke (Opisthorchis viverrini) infestation with increased expression of cytochrome p450 and carcinogen metabolism in male hamster liver1,2
Authors: Kirby Gordon M. , Pelkonen Päivi , Vatanasapt Vanchai , Camus Anne‐Marie , Wild Christopher P. , Lang Matti A. 
Published: February 2007

AbstractSynergy between exposure to chemical carcinogens (nitrosamines) and infestation with the liver fluke Opisthorchis viverrini has been demonstrated in a hamster model of hepatocarcinogenesis (Flavell et al., Carcinogenesis 4:927–930, 1983; Thamavit et al., Carcinogenesis 8:1351–1353, 1987). to elucidate the mechanisms of this interaction we tested the hypothesis that liver parasitism might influence the expression and activity of carcinogen metabolizing enzymes. We found that one, and perhaps more, hamster liver cytochrome P450 (CYP) isozymes immunorelated to mouse CYP2A5 contributed up to 50 or 60% of the hepatic aflatoxin B1(AFB) and N‐nitrosodiethylamine (NDEA) metabolism, respectively. As inferred from average enzyme activities and from western blot, immunoinhibition, and substrate (coumarin) inhibition analyses, O. viverrini infestation increased the expression of enzymes detectable by anti‐CYP2A5 antibody as well as NDEA metabolism in male but not in female hamsters. Immunohistochemical analysis of CYP2A expression by anti‐mouse CYP2A5 antibody demonstrated that the O. viverrini‐associated increase was not uniformly distributed throughout the lever but occurred in hepatocytes immediately adjacent to areas of inflammation. Immunohistochemical analysis of AFB‐DNA adducts in the livers of O. viverrini‐infested hamsters treated with AFB showed that the highest levels of adducts were found in the regions of liver where hepatocellular expression of enzymes detectable by anti‐CYP2A5 antibody is induced. These results suggest that a high local expression of CYP isozymes in O. viverrini‐infested livers could be a contributing risk factor in the development of liver cancers associated with paraitic hepatitis. ©1994 Wiley‐Liss, Inc.
Induction of different genetic changes by different classes of chemical carcinogens during progression of mouse skin tumors
Authors: Bremner Rod , Kemp Christopher J. , Balmain Allan 
Published: February 2007

AbstractBy analysis of skin tumors from F1 hybrid mice we demonstrated that the genetic events that occur during tumor progression depend on the type of chemical carcinogenesis protocol used to induce tumor growth. More than 95% of tumors induced by initiation with 7, 12‐dimethylbenz[a]anthracene (DMBA) and promotion with 12‐O‐tetradecanoyl‐phorbol‐13‐acetate (TPA) exhibited mutations in Ha‐ras and trisomy of chromosome 7. Carcinomas induced with multiple DMBA treatments had a lower frequency of alterations on chromosome 7 (50%), but only in tumors with Ha‐ras mutations, and had a much wider spectrum of alterations, including trisomy, mitotic recombination, deletion, and gene duplication. Carcinomas induced with multiple N‐methyl‐N‐nitro‐N‐nitrosoguanidine treatments only rarely exhibited alterations on chromosome 7 (8%), even if they contained mutant Ha‐ras. More frequent numerical alterations of chromosome 11 were also seen in TPA‐promoted tumors (23%) than in tumors induced by multiple carcinogen treatments (8%). These results show that postinitiation events are nonrandom and fit a model in which promoting agents induce numerical chromosomal alterations but in which mutagens cause more directed mutational events. ©1994 Wiley‐Liss, Inc.
A connexin 43 antisense vector reduces the ability of normal cells to inhibit the foci formation of transformed cells
Authors: Goldberg Gary S. , Martyn Kendra Dean , Lau Alan F. 
Published: February 2007

AbstractAntisense gene constructs have been very useful in the functional analysis of genes and their products. In this report we used a connexin 43 (Cx43) antisense gene construct to study the role that heterologous gap‐junctional intracellular communication (GJIC) plays in the ability of untransformed fibroblasts to suppress the foci‐forming ability of src oncogene‐transformed cells. Untransformed Rat‐1 fibroblasts transfected with the Cx43 antisenese DNA construct showed marked decreases in Cx43 RNA and protein, which were accompanied by a corresponding decrease in GJIC. These Cx43 antisense‐transfected cells maintained normal cell morphology, growth rates, and saturation densities and did not grow in soft‐agar suspension. However, in coculture experiments, the Cx43 antisense cells were less effective than vector‐alone‐transfected, sense‐trans‐fected, and untransfected cells at in hibiting foci formation of pp60v‐src‐transformed cells. These effects of junctionally competent, normal cells were associated with the existence of heterologous GJIC with the transformed cells and did not appear to result from the elaboration of a stable, diffusible inhibitory factor. Thus, gap‐junction‐mediated transfer of putative regulatory molecules may play a role in the ability of untransformed cells to suppress the expression of certain properties of transformed cells. ©1994 Wiley‐Liss, Inc.
Analysis of transcriptional activation of a cyclic AMP response element by 2,6,10,14‐tetramethylpentadecane (pristane) in JB6 mouse epidermal cells
Authors: Banbura Marcin , Ackland‐Berglund Cathleen , Lee Soong‐Ho , Hamernik Deborah , Jones Clinton 
Published: February 2007

AbstractPristane is a naturally occurring isoprenoid that is believed to be derived from the phytyl moity of chlorophyll. Thus, it is not surprising that pristane is present in many common fruits and vegetables. Furthermore, pristane can be detected in the tissues of fish and mammals. In animal models using rodents, pristane canfunction as a potent tumour promoter. At the molecular level, pristane can induce changes in the plasma membrane, alter the conformation of chromatin, and selectively activate gene expression. Addition of pristane to a mouse epidermal cell line (JB6 P+) allows these cells to grow in an anchorage‐independent manner. In contrast, JB6 P‐cells are not transformed by pristane. Our study was undertaken to correlate transformation of P+ cells with changes induced by pristane. Transcriptional activation of a cyclic AMP response element (CRE) was in duced by pristane in P+ and P‐cells. Point mutations in the CRE abolished activation by pristane, thus indicating that an intact CRE was necessary for pristane activation. In P+ cells, pristane repressed phosphodiesterase activity. However, protein kinase A was activated by pristance in P+ and P‐cells. Taken together, these results indicated pristane induced novel changes in P+cells that in turn may facilitate neoplastic transformation.©1994 Wiley‐Liss, Inc.
Cytogenetic analysis of malignant skin tumors induced in chemically treated TG.AC transgenic mice
Authors: French John E. , Libbus Bisharah L. , Hansen Laura , Spalding Judson , Tice Raymond R. , Mahler Joel , Tennant Raymond W. 
Published: February 2007

AbstractTG.AC mice (which carry a v‐Ha‐ras transgene) rapidly develp papillomas in response to 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA). Approximately 30% of the papilomas are associated with subsequent development of maliganancies. Early‐passage spindle‐shaped tumor cells arising from explant cultures of TPA‐induced tumors in TG‐AC mice were tumorigenic when transplanted to syngeneic recipients. The v‐Ha‐ras transgene in the transplanted tumors was expressed at a high level. To identify possible genetic changes associated with the development of malignant tumors, explanted cells were cultured in vitro and assessed for karyotypic changes between the second and third passages by analyzing G‐banded metaphase chromosomes. For comparison, skin malignancies were induced in nontransgenic FVB/N mice (parent strain) by 7, 12‐dimethylbenz[a] anthracene (DMBA) Initiation and TPA promotion, and their G‐banded metaphase chromosomes were analyzed. Trisomy (in at least 50% of about 30 metaphases) of chromosome 15 (in five of 15 tumors) and chromosome 6 (four of 15 tumors) was observed in TG.AC mice, independent of chemical treatment or tumor type. Of six tumors from DMBA/TPA‐treated FVB/N mice, three had trisomy 10 or 15 (or both), and two appeared normal. The absence of trisomy 7 is notable because c‐Ha‐ras maps to that chromosome. The absence of trisomy 7 in the six FVB/N DMBA/TPA‐induced skin malignancies contrasts with DMBA/TPA‐ induced karyotypic effects in SENCAR mice. Expression of the v‐Ha‐ras transgene may have precluded the requirement for endogenous mutant ras and allelic imbalance involving chromosome 7 in TG.AC mice, but it could not have in FVB/N mice. These results suggest the possibility that the observed trissmies are consequential, rather than causal, events in the development of TG.AC or FVB/N skin malignancies. Molecular genetic analysis will be required to understand the changes associated with tumorigenesis in this transgenic line as well as in the parent mouse line. ©1994 Wiley‐Liss, Inc.