bluuebunny/crossref_metadata_2025_split huggingface dataset:
Overexpression of an elongation factor‐1 γ‐hybridizing rna in colorectal adenomas
Authors: Ender Bulent , Lynch Patrick , Kim Yeul Hong , Inamdar Nikhil V. , Cleary Karen R. , Frazier Marsha L. 
Published: February 2007

AbstractWhile it is apparent that colorectal carcinogenesis results from a series of genetic alterations manifested phenotypically by the adenoma‐to‐carcinoma sequence, the early events that occur in the process of tumorigenesis have not been elucidated. We previously demonstrated that human elongation factor‐1 (EF‐1)γ‐hybridizing RNA was overexpressed in 25 of 29 colorectal carcinomas. To determine if the overexpression of this mRNA occurs early in tumor development, we examined 25 adenomas and corresponding normal‐appearing distant mucosae from 20 patients without familial adenomatous polyposis (FAP). We observed overexpression at a level of twofold or more in 14 (56%) of the 25 adenomas, indicating that overexpression of EF‐1γ RNA is often a relatively early event in the development of non‐FAP colorectal cancer.
Different levels of v‐Ha‐ras p21 expression in primary keratinocytes transformed with harvey sarcoma virus correlate with benign versus malignant behavior
Authors: Brissette Janice L. , Missero Caterina , Yuspa Staurt H. , Dotto G. Paolo 
Published: February 2007

AbstractPrimary mouse keratinocytes transformed with an activated ras oncogene transduced by helper‐free Harvey sarcoma virus (HaSV) form predominantly benign tumors. In contrast, keratinocytes transformed with helper‐associated HaSV form malignant tumors. We report here that this different tumorigenic behavior correlated with a much higher level of v‐Ha‐ras p21 protein in cells transformed with the helper‐associated virus. The high level of v‐ras expression in these cells was due to viral spread beyond the initial infection. The low level of v‐ras p21 expression that resulted from single‐hit infection with helper‐free virus, together with the intrinsic heterogeneity of primary keratinocytes, explains, at least in part, the different tumorigenic behavior of keratinocytes transformed by the two types of viruses.
Expression pattern of proteins that bind to the ultraviolet‐responsive element (TGACAACA) in human keratinocytes
Authors: Yang Yang‐Ming , Rutberg Susan E. , Foiles Peter G. , Ronai Zeev 
Published: February 2007

AbstractWe previously identified an ultraviolet (UV)‐responsive element (URE; TGACAACA) that plays a role in both transcription and replication of polyoma sequences. Mouse polyclonal antibodies were raised against affinitypurified URE‐bound proteins to characterize their expression patterns. These antibodies specifically recognized two of four URE‐bound proteins, of 40 and 68 kDa. The 68‐kDa protein was constitutively expressed in human keratinocytes, while the expression of the 40‐kDa protein was induced by UV irradiation. Of the two, the 68‐kDa protein bound to the URE with greater affinity than the 40‐kDa protein, as determined by southwestern analysis. The expression of the 40‐kDa protein increased as early as 1 h after UV irradiation of both rat fibroblasts and human keratinocytes and correlated with increased binding to the URE in an electrophoretic mobility shift assay. Other types of damage, as well as heat shock and serum stimulation, also induced the expression of this protein, suggesting that it may play a role in cellular response to stress or damage. The 40‐kDa protein was expressed at the highest levels in the S phase of the cell cycle and was induced by aphidicolin, suggesting that it has a role in DNA replication. All together, these results suggest that exposure of human keratinocytes to damage‐ and stress‐inducing agents modulates the expression of proteins that may play a role in regulating cellular response to DNA damage.
Differential activity of the RVF enhancer element in the decreased expression of the neu oncogene in NR‐6 cells versus parental Swiss Webster 3T3 cells
Authors: Yan Duen‐Hwa , Hung Mien‐Chie 
Published: February 2007

AbstractThe rat neu oncogene encodes a growth factor receptor—like glycoprotein, termed p185, that shares structural similarity with epidermal growth factor receptor (EGFR), particularly in the tyrosine‐kinase domain. The Swiss Webster 3T3 murine embryo fibroblast (SW3T3) variant NR‐6, in contrast to the parental cell line, does not express EGFR mRNA. After transfection of an activated rat neu cosmid clone, we demonstrated in this report that whereas SW3T3 cells readily expressed the exogenous rat p 185 protein, NR‐6 cells did not express detectable levels of this protein product. By transfection of plasmids containing the chloramphenicol acetyltransferase (CAT) gene driven by the neu promoter and subsequent CAT assays, we also showed that neu gene promoter activity was significantly less in NR‐6 cells than in SW3T3 cells and that the neu promoter sequence responsible for this decreased transcription was a previously identified RVF enhancer element (Yan D‐H, Hung M‐C, Mol Cell Biol 11:1875–1882, 1991). That is to say, the RVF enhancer element of the neu promoter did not function as an enhancer in NR‐6 cells. To investigate the mechanism responsible for the inactivation of RVF in NR‐6 cells, we used southwestern blot analyses and demonstrated that the 60‐kDa RVF polypeptide was present in both NR‐6 and SW3T3 cell nuclear extracts. This result indicates that the DNA‐binding activity of RVF was similar in these two cell lines; therefore, loss of RVF enhancer activity in NR‐6 cells is probably due to inactivation of the trans‐activating function and not DNA binding activity of RVF.
Reversal of ras‐induced inhibition of gap‐junctional intercellular communication, transformation, and tumorigenesis by lovastatin
Authors: Ruch Randall J. , Madhukar Burra V. , Trosko James E. , Klaunig James E. 
Published: February 2007

AbstractThe plasma‐membrane association and transforming activity of the ras oncoprotein p21 are dependent upon posttranslational farnesylation. Farneslyl synthesis and p21 ras farnesylation are inhibited by hydroxmethylglutaryl‐CoA reductase inhibitors such as lovastatin. In this study, we examined whether lovastatin could reverse the transformed phenotype of a v‐Ha‐ras‐transformed rat liver epithelial cell line (WB‐ras cells) and if changes were associated with the enhancement of gap‐junctional intercellular communication (GJIC). WB‐ras cells grow in soft agar, have reduced GJIC, and are highly tumorigenic. Membrane association of p21 ras in these cells was inhibited after in vitro treatment with lovastatin (0.1–0.5 μM) for 48 h. Concomitantly, the cells displayed a more normal morphology, decreased growth in soft agar, and enhanced GJIC. These changes were prevented by cotreatment with mevalonic acid. The morphology and GJIC of rat liver epithelial cells transformed with other oncogenes (src, neu, and raf/myc) were not affected by lovastatin. Intrahepatic WB‐ras tumors were induced in male rats by intraportal‐vein injection of WB‐ras cells. The size and DNA labeling index of these tumors were decreased approximately 75% by administration of lovastatin (5 mg/kg orally twice daily for 2 wk). These results suggest that lovastatin reversed the transformed phenotype of WB‐ras cells by inhibiting p21 ras plasma membrane association. Furthermore, the concomitant enhancement of GJIC in lovastatin‐treated cells suggests a role for reduced GJIC in the expression of the transformed phenotype.
Creation of an active estrogen‐responsive element by a single base change in the flanking sequence of a cellular oncogene: A possible mechanism for hormonal carcinogenesis?
Authors: Nawaz Zafar , Stancel George M. , McDonnell Donald P. , Hyder Salman M. 
Published: February 2007

AbstractEstrogens are considered to act as promoters in a multistep process of hormonal carcinogenesis, although the molecular mechanisms by which these hormones act in tumorigenesis are unclear at present. Estradiol is known to induce expression of certain proto‐oncogenes, and this led us to examine potential regulatory regions of the cellular c‐fos oncogene. The 5′‐flanking region of the murine c‐fos contains a 13‐bp palindromic sequence (GGTCTnnnAGACC) with striking homology to the consensus estrogen‐responsive element (ERE) GGTCAnnnTGACC. However, the c‐fos sequence did not bind the human estrogen receptor or confer hormonal responsiveness in a yeast‐based transcriptional test system. Importantly, a single base change in the fifth position of the c‐fos sequence (GGTCTnnnAGACC to GGTCA/GnnnAGACC) produced an element that bound the estrogen receptor and conferred estrogen‐dependent transcriptional activation of a reporter gene. This suggests a specific hypothesis by which estrogens could act as tumor promoters. In this paradigm, the regulatory region of the cellular oncogenes, tumor suppressor genes, and growth‐factor genes contain inactive sequences with close homologies to hormone‐responsive elements. Initiation occurs when some agent (e.g., a chemical carcinogen) causes a mutation in such a sequence to create a functional hormone‐responsive element. Estrogens, acting through their receptors and the mutated element, can then activate the target gene to stimulate cell proliferation and increase the population of initiated cells.
Direct growth stimulation of normal human epithelial cells by mutant p53
Authors: Wyllie Fiona S. , Lemoine Nick R. , Barton Claire M. , Dawson Tim , Bond Jane , Wynford‐Thomas David 
Published: February 2007

AbstractWe developed a high‐titer amphotropic retroviral vector that expresses mutant (Ala 143) human p53 to test directly the response of genetically normal human epithelial cells to p53 mutation. Contrary to our prediction, we found that in pancreatic epithelium (whose tumors display a high frequency of p53 mutation) but not in thyroid (whose tumors show an exceptionally low mutation frequency), expression of mutant p53 induced a dramatic, though self‐limiting, proliferative response. This result questions the assumption that p53 mutation is relevant only to the later stages of tumorigenesis.
Quantitation of 2‐amino‐3‐methylimidazo[4,5‐f]quinoline and 2‐amino‐3,8‐dimethylimidazo[4,5‐f]quinoxaline DNA adducts in specific sequences using alkali or uvrABC excinuclease
Authors: Nouso Kazuhiro , Bohr Vilhelm A. , Schut Herman A. J. , Snyderwine Elizabeth G. 
Published: February 2007

Abstract2‐Amino‐3‐methylimidazo[4,5‐f]quinoline (IQ) and 2‐amino‐3,8‐dimethylimidazo[4,5‐f]quinoxaline (MelQx) are carcinogens found in cooked meats that form DNA adducts upon metabolic activation. Purified DNA from Chinese hamster ovary (CHO) cells was reacted in vitro with the active metabolites N‐acetoxy‐lQ or N‐acetoxy‐MelQx, and the adduct levels in the 5′ dihydrofolate reductase (DHFR) gene and downstream region were quantitated by Southern hybridization. Adducted and restricted DNA was treated with Escherichia coli uvrABC excinuclease or alkali (0.1 N NaOH, 37°C, 60 min) to incise DNA at IQ and MeIQx adduct sites. The DNA was then denatured with formamide, electrophoresed on a neutral agarose gel, transferred to a support membrane, and hybridized with sequence‐specific DNA probes. Both uvrABC and alkali reduced the intensity of Southern hybridization in proportion to the number of IQ or MeIQx adducts in DNA, indicating that these adducts are substrates for uvrABC and that they form alkali‐labile lesions in DNA. IQ and MeIQx adduct levels were the same in the 5′ DHFR gene and in the downstream region. Southern hybridization analysis of pBR322 containing known levels of IQ or MeIQx adducts showed that the efficiency of cutting IQ or MeIQx adducts by uvrABC excinuclease and alkali was approximately 30% and 15%, respectively. 32P‐postlabeling studies examining adduct level in bulk DNA further showed that the adduct profiles were identical in pBR322, CHO DNA, and cultured CHO cells exposed to the reactive metabolites of IQ or MeIQx. The results indicate that IQ and MeIOx adducts can be quantitated in specific genomic sequences and that this method should be directly applicable to studies of gene‐specific repair of these adducts in cultured cells.
Suppression of tumorigenicity of A549 lung adenocarcinoma cells by human chromosomes 3 and 11 introduced via microcell‐mediated chromosome transfer
Authors: Satoh Hitoshi , Lamb Patricia W. , Dong Jin‐Tang , Everitt Jeff , Boreiko Craig , Oshimura Mitsuo , Barrett J. Carl 
Published: February 2007

AbstractTo map tumor suppressor genes for lung adenocarcinomas, we introduced normal human chromosomes 3, 7, and 11 into the A549 tumor cell line by microcell‐mediated chromosome transfer to test which chromosomes had the ability to suppress tumorigenicity. These human chromosomes, which contain the neomycin gene as a selectable marker, were transferred into A549 lung adenocarcinoma cells at frequencies of 0.3–1.8 × 10−6. Two microcell hybrid clones with an introduced chromosome 3, two with an introduced chromosome 7, and six with an introduced chromosome 11 were isolated and examined for their growth properties and tumorigenicity in nude mice. Whereas parental A549 cells formed tumors with an average latency of 68 d, both microcell hybrids with an introduced chromosome 3 failed to form tumors for over 360 d. Similar tumorigenicity results were obtained when the clones were implanted into denuded tracheas, a more orthotopic transplantation site. The two clones with an introduced chromosome 7 were still tumorigenic; they formed tumors within 100–123 d after injection and grew progressively, although the tumors grew slightly slower than the parental cells did. Among the six clones with an introduced chromosome 11, one clone was still highly tumorigenic but did not contain an extra copy of an intact introduced chromosome 11. Three clones with a single intact copy of introduced chromosome 11 formed tumors with latency periods significantly longer than those of the parental cells. Two clones had two copies of the introduced chromosome 11, and both failed to form tumors within 1 yr of injection. These results indicate that chromosomes 3 and 11 can suppress the tumorigenicity of A549 lung adenocarcinoma cells.
High variability of nitrosamine metabolism among individuals: Role of cytochromes P450 2A6 and 2E1 in the dealkylation of N‐nitrosodimethylamine and N‐nitrosodiethylamine in mice and humans
Authors: Camus Anne‐Marie , Geneste Olivier , Honkakoski Paavo , Béréziat Jean‐Claude , Henderson Colin J. , Wolf Roland C. , Bartsch Helmut , Lang Matti A. 
Published: February 2007

AbstractWe undertook this study to answer several questions regarding nitrosamine metabolism. Kinetics of nitrosamine metabolism showed the involvement of at least two enzymes in the dealkylation of N‐nitrosodiethylamine (NDEA) and N‐nitrosodimethylamine (NDMA) in mouse liver microsomes. Coumarin inhibited both reactions competitively. On the other hand, microsomal coumarin 7‐hydroxylase was inhibited by NDMA (Ki 2.7 mM) and NDEA (Ki 0.013 mM). The big difference in the Ki values suggests a higher affinity of NDEA than NDMA to Cyp2a‐5 (mouse cytochrome P450coh). A specific antibody against Cyp2a‐5 inhibited more of the microsomal NDEA (up to 90%) than NDMA (up to 40%) dealkylation. The converse was true with anti‐Cyp2e‐1 antibody. These results suggest that the primary substrate for Cyp2a‐5 is NDEA and for Cyp2e‐1, NDMA. Western blot analysis of human liver microsomes showed a great interindividual variation in the amounts of CYP2A6 (human cytochrome P450coh) and CYP2E1. Also, courmarin 7‐hydroxylation and nitrosamine dealkylation varied greatly among individuals. A high correlation (r = 0.93, P < 0.001) was found between NDEA and coumarin metabolism. Both activities were associated with CYP2A6. On the other hand, little or no correlation was found between microsomal CYP2A6 and CYP2E1 or between CYP2E1 and NDEA dealkylation. Immunoinhibition of human microsomal NDEA metabolism by CYP2a‐5 antibody varied greatly among individuals (10–90%), suggesting, as in the case of mice, that NDEA is metabolized primarily by CYP2A6, at least in some individuals. Taken together the data suggest that (1) the metabolic activation of nitrosamines in humans varies greatly among individuals; (2) different nitrosamines may partially be metabolized by different cytochrome P450 isozymes; and (3) because of similarities between nitrosamine metabolism in mice and humans, inbred strains of mice would be relevant experimental models for studying nitrosamine activation.
Nucleotide sequence analysis of c‐raf‐1 cDNA and promoter from a radiation‐resistant human squamous carcinoma cell line: Deletion within exon 17
Authors: Patel Bharvin K. R. , Kasid Usha 
Published: February 2007

AbstractThe c‐raf‐1 proto‐oncogene is the cellular homologue of v‐raf, the oncogene of the acutely transforming retrovirus 3611‐MSV. The product of c‐raf‐1 (raf‐1) is a 74‐kDa cytoplasmic serine/threonine protein kinase. We previously reported that antisense human c‐raf‐1 cDNA transfection results in reduction of the endogenous c‐raf‐1 transcript, decreased tumor growth rate, and enhanced radiation sensitivity of SQ‐20B tumor cells established from a radiation‐resistant laryngeal squamous cell carcinoma. In the study reported here, we used cDNA‐linked polymerase chain reaction amplification and nucleotide sequencing to examine the structure of the 3233‐bp SQ‐20B c‐raf‐1 cDNA. The 812‐bp c‐raf‐1 promoter region was analyzed by genomic DNA amplification followed by cloning and sequencing. Sequence comparison with a previously published c‐raf‐1 sequence indicated no structural changes within the coding region of SQ‐20B c‐raf‐1. However, a 4‐bp deletion was observed in the 3′ untranslated region within exon 17. This deletion was also present in a c‐raf‐1 cDNA clone isolated from a SQ‐20B cDNA library. While the possibility of a 3′ transcriptional control mechanism cannot be ruled out, it appears that the raf‐1 protein kinase may regulate the development of radioresistant malignancies via interaction with other molecules in the damage and repair—related signal transduction pathways. © 1993 Wiley‐Liss, Inc.
Timing of replication of differentially transcribed genes in syrian hamster embryo fibroblasts
Authors: Sorscher David H. , Barrett J. Carl , Cordeiro‐Stone Marila 
Published: February 2007

AbstractSyrian hamster embryo cell lines have been used as models of neoplastic progression in vitro. Changes in phenotype and biological properties have been observed in these cell lines in association with modulation of gene transcription. We explored this natural evolution of cells in culture to investigate the reported relationship between transcriptional activity and replication in early S phase. In this study we used two nontumorigenic cell lines that had either retained (supB+) or lost (supB‐) the ability to suppress tumorigenicity of malignantly transformed hamster fibroblasts (BP6T). In association with the loss of suppressor gene function, supB‐ cells have downregulated the expression of the H19 and tropomyosin‐I (TM‐I) genes, which are actively transcribed in supB+ cells. Synchronous populations of supB+ and supB‐ cells were pulse‐labeled with [3H]thymidine and bromodeoxyuridine at 1‐h intervals during S phase; the replicating DNA was isolated by centrifugation in cesium chloride gradients and hybridized to 32P‐labeled gene probes. No correlation was found between the timing of gene replication and the status of expression of these two genes. TM‐I replicated during the first hour and H19 replicated between the second and third hours of the S phase in the expressing and nonexpressing cell lines. Immunoglobulin gene sequences, known to be late‐replicating in fibroblasts, replicated at the end of the S phase. These results suggest that downregulation of transcription is not always accompanied by a concomitant change in time of gene replication from early to late S phase. © 1993 Wiley‐Liss, Inc.
Preferential incorporation of 3′‐azido‐2′,3′‐dideoxythymidine into telomeric DNA and Z‐DNA—containing regions of chinese hamster ovary cells
Authors: Olivero Ofelia A. , Poirier Miriam C. 
Published: February 2007

Abstract3′‐Azido‐2′,3′‐dideoxythymidine (azidothymidine; AZT) induces bone marrow toxicity in patients chronically given therapeutic doses of drug and is tumorigenic in rodents, inducing squamous cell tumors in vaginal tissues of mice and rats. In the study reported here, we explored the incorporation of AZT into specific regions of mammalian chromosomal DNA. CHO cells were exposed to AZT for 4 h, allowed to complete at least one cell cycle, and then arrested in metaphase with colchicine. Regions of concentrated AZT incorporation were identified in individual metaphase chromosomes by immunohistochemistry using antiserum specific for AZT and a secondary antiserum with a streptavidin—Texas red end point. These studies demonstrated that most of the intensely staining regions were chromosomal ends or telomeres. When 18 metaphases were examined, all telomeres but one (39 of 40) were positive at least once. Using an anti—Z‐DNA antibody, chromosomal regions containing DNA in Z conformation were also localized by immunohistochemistry using a rhodamine‐conjugated secondary antibody. When metaphase chromosome spreads were stained for either AZT or Z‐DNA, ideograms showing localization of AZT (18 metaphases) and DNA in Z configuration (26 metaphases) were drawn for every chromosome of each metaphase examined. These ideograms demonstrated that 60% of the regions that stained positive for AZT were also positive for Z‐DNA. Furthermore, slides incubated with both antibodies, using streptavidin—Texas red to identify AZT and fluorescein to identify Z‐DNA, confirmed colocalization of the two markers. Additional experiments exploring the induction of chromatin bridges in AZT‐treated cells suggest that the analogue may be able to bind to and disrupt the normal functioning of telomeric DNA.
Effect of retroviral integration on control of expression of a tumor marker in hela cells
Authors: Gross Monika M. , Janiaud Paul , Stanbridge Eric J. 
Published: February 2007

AbstractFusion between HeLa cells and normal human fibroblasts results in the suppression of tumorigenicity. Under prolonged culture conditions, rare tumorigenic segregants arise and have been shown to reexpress a cell surface antigen, p75, which is also present in the HeLa parent but not in the fibroblast parent or in the nontumorigenic HeLa x fibroblast hybrid. Expression of p75 strictly correlates with tumorigenicity in HeLa and human somatic cell hybrids, as has been shown by chromosomal segregation and after γ‐irradiation. Using insertional mutagenesis, we induced expression of p75 in the nontumorigenic hybrid. Three cell clones were isolated that expressed p75 at different levels. Two of these clones exhibited a high level of p75 expression and displayed an altered morphology similar to that of the previously characterized tumorigenic segregants and consistent with the appearance of tumorigenicity. When injected into athymic nude mice, two clones were found to be tumorigenic, one from the onset of subculturing and the second only after further propagation for approximately 50 population doublings. The third clone showed very low p75 expression, had no altered morphology, and was nontumorigenic.