bluuebunny/crossref_metadata_2025_split huggingface dataset:
Increased expression of and sensitivity to transforming growth factor‐α: A promotive role during rat liver carcinogenesis
Authors: Strömblad Staffan , Eriksson Lennart C. , Andersson Göran 
Published: February 2007

AbstractThe influence of the tumor promoter 2‐acetylaminofluorene (2‐AAF) on cell proliferation and on the epidermal growth factor receptor (EGFR) system was assessed in normal and nodular rat livers. DNA replication in vivo was inhibited below the detection level after 8 d of dietary 2‐AAF treatment of previously unexposed rats. The 2‐AAF‐induced growth inhibition was accompanied by downregulation of the number of epidermal growth factor (EGF)‐binding sites and decreased levels of EGFR transcripts, whereas no changes in the transforming growth factor‐α (TGF‐α) mRNA levels were observed. The persistent liver nodules generated by intermittent 2‐AAF feeding had a 30‐ to 35‐fold higher replicating cell fraction than normal liver. Treatment with 2‐AAF in vivo reduced the replicating cell fraction to one third in nodules after 14 d of 2‐AAF treatment. The initial EGFR mRNA levels and number of EGF binding sites in nodules before 2‐AAF administration was about 60% that of control livers and was slightly reduced by 2‐AAF feeding. The levels of EGFR mRNA after 14 d of 2‐AAF feeding were thus similar in the nodules and in the 2‐AAF‐treated control livers, whereas the fraction of proliferating cells in nodules after the 2‐AAF treatment was much larger than in normal liver. The TGF‐α mRNA level in the nodules Was found to be 1.4‐fold and in malignant hepatomas 1.7‐fold the level in normal liver. Primary hepatocytes isolated from control livers were four to five times more sensitive to replicative stimulation with EGF than with TGF‐α, whereas nodular cells responded at lower concentrations than control cells and equally well to both EGF and TGF‐α. We conclude that the decreased amounts of EGFR in the nodular cells with respect to proliferate stimulation could be more than compensated for by elevated synthesis of TGF‐α combined with an increased TGF‐α sensitivity. Collectively, these changes implicate TGF‐α in sustaining cell proliferation during chemically induced rat liver carcinogenesis. © 1994 Wiley‐Liss, Inc.
Preferential repair of ultraviolet light‐induced dna damage in the transcribed strand of the human p53 gene
Authors: Ford James M. , Lommel Lori , Hanawalt Philip C. 
Published: February 2007

AbstractMutations in the p53 tumor suppressor gene have been found in most human tumors. Analyses of the spectrum of p53 mutations in certain tumor types have shown a bias for mutations originating from lesions presumed to be in the untranscribed strand of the gene. This implies strand specificity for the formation or repair of DNA damage. We measured the induction and repair of ultraviolet light‐induced cyclobutane pyrimidine dimers (CPD) in each strand of the human p53 gene in a normal human lung fibroblast cell line using quantitative Southern hybridization. We found that the removal of CPD from the transcribed strand was more rapid than that from the untranscribed strand of this gene, although the frequency of CPD induction was similar in both strands. Preferential repair of the transcribed strand of the p53 gene may account for the mutational spectra of this gene in human tumors. © 1994 Wiley‐Liss, Inc.
Cellular control of human papillomavirus oncogene transcription
Authors: Hoppe‐Seyler Felix , Butz Karin 
Published: February 2007

AbstractSpecific types of human papillomaviruses (HPVs) are closely associated with the development of cervical cancer. The transforming ability of these high‐risk HPV types depends on the expression of the viral E6 and E7 oncogenes. It is therefore of particular interest to elucidate the molecular mechanisms that result in the activation of E6/E7 expression during HPV‐associated tumorigenesis. Recently, much progress has been made in characterizing the proteins involved in the regulation of HPV oncogene transcription. This review describes the functional significance of cellular factors involved in the transcriptional control of the E6/E7 promoter for the two most common HPV types associated with cervical cancer, HPV16 and HPV18. In addition, we discuss regulatory pathways that may contribute to the epithelial cell specificity of E6/E7 transcription. The definition of the factors that regulate HPV oncogene transcription could provide new insights into the molecular mechanisms activating viral oncogene expression during cervical carcinogenesis and forms an experimental basis for investigating the specific biochemical pathways that contribute to HPV‐associated malignant cell transformation. © 1994 Wiley‐Liss, Inc.
Non‐Ap‐1 tumor promoter 12‐O‐tetradecanoylphorbol‐13‐acetate‐responsive sequences in the human ornithine decarboxylase gene
Authors: Kim Yong‐Joo , Pan Huichin , Verma Ajit K. 
Published: February 2007

AbstractTo define the mechanisms of 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA)‐induced transcription of the ornithine decarboxylase (ODC) gene, we isolated a genomic clone (hODC41 B) of ODC from a human leukocyte genomic DNA library. The restriction endonuclease map, in comparison with the previously published sequences of the human ODC gene, indicated that hODC41B contained a 15.7‐kb sequence that extended from the sixth exon to about 10 kb upstream of the ODC gene. A 2.5‐kb genomic fragment containing the 5′ flanking region and the first exon was subcloned and sequenced. Sequence analysis revealed multiple putative promoter/enhancer elements (a TATA box, a CAAT box, 17 GC boxes, and a cAMP‐responsive element) but no consensus AP‐1 sequences (TGAGTCA) in the 2.5‐kb 5 flanking region. However, three AP‐1 sequences were located in introns 3, 5, and 11. We constructed aseries of chimeric genes containing part of the first exon and increasingly longer 5′ flanking sequences of the ODC gene fused to either bacterial chloramphenicol acetyltransferase (CAT) or luciferase reporter genes. TPA inducibility was determined by transient transfection and measurement of CAT or luciferase expression in HeLa cells. The induction of CAT activity by TPA decreased with decreasing lengths of the 5′ flanking sequences up to nt‐82. The TPA induction from the construct‐72 ODC CAT was threefold to sevenfold, and the TPA inducibility of the same fragment was about ninefold to 30‐fold with the luciferase reporter gene. Further deletion analysis revealed TPA‐responsive sequences in ODC nt‐42 to +54. Gel mobility shift assays using α‐32P‐end labeled ODC nt‐42 to +60 revealed that nt‐42 to +60 specifically bound HeLa cell nuclear proteins. HeLa cell nuclear protein binding to ODC nt‐42 to +60 could not be completely competed by AP‐1‐, AP‐2‐, AP‐3‐, or SP1‐responsive sequences. © 1994 Wiley‐Liss, Inc.
Effects of the genotoxic carcinogen chromium(VI) on basal and hormone‐inducible phosphoenolpyruvate carboxykinase gene expression in vivo: Correlation with glucocorticoid‐and developmentally regulated expression
Authors: McCaffrey Jennifer , Wolf Chad M. , Hamilton Joshua W. 
Published: February 2007

AbstractPrevious studies have shown that a number of different genotoxic carcinogens that induce different types of DNA damage preferentially alter the expression of inducible genes in vivo. To investigate further the mechanistic basis for these effects, we examined the effects of the human lung carcinogen chromium(VI) on expression of the hormone‐inducible cytosolic phosphoenolpyruvate carboxykinase (PEPCK) gene in chick embryo liver. Chromium(VI) pretreatment had significant effects on both basal and glucocorticoid‐inducible PEPCK expression in 14‐d‐old embryo liver. These effects were principally a result of changes in PEPCK transcription. In contrast, treatment with chromium(VI) 1 h after treatment with glucocorticoid had no effect on PEPCK induction, suggesting that an early event in the induction process is the target for carcinogen effects. In 16‐d‐old liver, in which PEPCK expression is no longer responsive to glucocorticoid induction, both basal and inducible PEPCK expression were also refractory to chromium(VI) effects, indicating that carcinogen responsiveness is a phenotypic rather than an inherent property of inducible genes and is related to their competence for induction. Chromium(VI) had no effect on cAMP induction of PEPCK expression, demonstrating that carcinogens target their effects to specific regulatory pathways. Comparison of the effects of chromium(VI) with those of cycloheximide suggests that chromium(VI) targets its effects to a labile, constitutively expressed repressor involved in PEPCK gene regulation. © 1994 Wiley‐Liss, Inc.
Differences in the regulation of phosphatidylinositol‐specific phospholipase C in normal and neoplastic keratinocytes
Authors: Punnonen Kari , Denning Mitchell F. , Rhee Sue Goo , Yuspa Stuart H. 
Published: February 2007

AbstractThe induction of epidermal differentiation by Ca2+ in vitro is associated with enhanced activity of phosphatidylinositol‐specific phospholipase C (PLC). Neoplastic keratinocyte cell lines expressing a mutant c‐Ha‐ras gene and normal keratinocytes transformed to the neoplastic phenotype by transduction with the v‐Ha‐ras gene (v‐Ha‐ras keratinocytes) have elevated constitutive activity of PLC that increases further in response to Ca2+, but the cells do not differentiate normally. PLC‐γ1 (145 kDa) is the major isoform detected by immuno‐blotting of extracts from control, v‐Ha‐ras, and neoplastic keratinocyte cell lines cultured in 0.05 mM Ca2+ medium. The amount of PLC‐γ1 protein was higher in neoplastic cell lines than in normal and v‐Ha‐ras keratinocytes that had similar PLC‐γ1 protein levels. Thus, higher PLC‐γ1 protein levels cannot account for the elevated constitutive activity PLC in v‐Ha‐ras keratinocytes. After induction of differentiation by Ca2+, the amount of PLC‐γ1 protein increased in all cell types, and PLC‐δ1 (85 kDa), barely detectable in 0.05 mM Ca2+, increased. PLC‐β1 was not detected at any Ca2+ concentration. PLC‐γ1 and PLC‐δ1 mRNA did not increase after elevation of extracellular Ca2+, suggesting that posttranscriptional mechanisms can regulate PLC‐γ1 and PLC‐δ1 protein levels in normal and neoplastic keratinocytes. Activation of protein kinase C by treatment with 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA) inhibited the stimulation of inositol phosphate (InsP) formation by Ca2+ but did not alter basal InsP levels in normal keratinocytes. In contrast, TPA treatment reduced both Ca2+‐stimulated and basal InsP formation in neoplastic cells lines and v‐Ha‐ras keratinocytes. In both normal and v‐Ha‐ras keratinocytes labeled with [32P]orthophosphate, antibodies against PLC‐γ1 immunoprecipitated a complex of 32 P‐labeled proteins. The relative labeling of the PLC‐γ1 band was greater in normal than in v‐Ha‐ras keratinocytes. Furthermore, treatment with TPA specifically increased the relative phosphorylation of PLC‐γ1 in v‐Ha‐ras keratinocytes but not in normal keratinocytes. These results suggest that the negative regulation of constitutive activity of PLC by protein kinase C differs in normal and neoplastic keratinocytes and that this could be the mechanism of increased PLC activity produced by an oncogenic ras gene in keratinocytes. © 1994 Wiley‐Liss, Inc.
Use of representational difference analysis for the identification of mdm2 oncogene amplification in diethylstilbestrol‐induced murine uterine adenocarcinomas
Authors: Risinger John I. , Terry Lori A. , Boyd Jeff 
Published: February 2007

AbstractExposure in utero to the synthetic estrogen diethylstilbestrol (DES) is associated with the subsequent development of reproductive‐tract malignancies in female offspring. To search for the genetic targets of DES, representational difference analysis was used to compare genomic DNA from DES‐associated mouse uterine adenocarcinoma cells with genomic DNA from normal CD‐1 mouse tissue. Several difference clones were obtained, all of which recognized rearranged and amplified sequences in tumor compared with normal DNA. One of these difference fragments mapped to a region of mouse chromosome 10 that includes the mdm2 oncogene. Amplification and overexpression of mdm2 was found in all three early‐passage cell lines established from independent DES‐associated cancers. These findings demonstrate the potential power of representational difference analysis in cancer research and suggest a genetic mechanism for DES‐induced carcinogenesis. ©1994 Wiley‐Liss, Inc.
Differences in the expression of connexin genes in rat hepatomas in vivo and in vitro
Authors: Neveu Mark J. , Sattler Carol A. , Sattler Gerald L. , Hully Jim R. , Hertzberg Elliot L. , Paul David L. , Nicholson Bruce J. , Pitot Henry C. 
Published: February 2007

AbstractGap‐junctional intercellular communication (GJIC) in normal rat liver cells involves at least three different connexins (Cxs)—Cx32, Cx26, Cx43—depending on the cell type, position in the lobule, or both. Whereas rat hepatocyte primary cultures expressed Cx32 and Cx26 as observed in vivo, cell lines derived from normal rat liver (WB‐F344, Clone 9, RLEC, and BRL) expressed Cx43 and to a lesser extent Cx26. Hepatoma cells propagated in vitro were either deficient in GJIC and Cx expression (7777, 8994, H4IIE‐C3) or communicated via gap junctions composed of Cx43 protein (N1S1‐67, 9618A). Analysis of neoplasms that resulted from injection of hepatoma cells into rat femoral muscle showed differences in Cx expression when compared with cells grown in vitro. Whereas hepatoma cells 7777 and H4IIE‐C3 failed to express Cx mRNAs in culture, these cells transplanted in vivo expressed levels of Cx32 mRNA comparable to those in normal liver. However, detectable Cx32 immunostaining was observed in less than 5% of the neoplastic cells in vivo. These results indicate that Cx32 protein was posttranscriptionally downregulated in 7777 and H4IIE‐C3 tumor cells. Unexpectedly, 9618A cells expressed Cx43 mRNA and protein in cell culture but expressed Cx32 mRNA in vivo. In contrast, N1S1 transplants continued to express Cx43 mRNA and protein in vivo. Unlike the punctate Cx43 staining observed in suspension cultures of N1S1 cells, diffuse intracellular Cx43 staining was observed in N1S1‐derived neoplasms in vivo, although the electrophoretic pattern of Cx43 isolated from N1S1 tumors grown in vivo (43 kDa) was different from that observed in suspension cell cultures (43 and 45 kDa). Thus, the findings reported here demonstrate that Cx expression in hepatoma cells depends on the environment, whether in vivo or in vitro, in which the cells are propagated.©1994 Wiley‐Liss, Inc.
Augmented expression of cytokines in mouse epidermal tumor cells and its possible involvement in the induction of hematopoietic alterations
Authors: Bauluz Cristina , Larcher Fernando , Ballestin Claudio , Grande Teresa , Jorcano José L. 
Published: February 2007

AbstractMice with skin tumors induced either by 7,12‐dimethylbenz[a]anthracene complete carcinogenesis or subcutaneous injection of a carcinogenic keratinocyte cell line showed moderate to severe splenomegaly as a result of an increase in splenic granulocyte‐macrophage and erythroid (erythroid burst‐forming unit) progenitors. To test whether the observed alterations involve the release of soluble factors by the epidermal component of skin tumors, we used an in vitro approach. A series of mouse keratinocyte cell lines resembling progressive stages of skin carcinogenesis and carrying either normal or activated Ha‐ras genes were assayed for their ability to produce the factors required for colony growth of hematopoietic‐committed progenitors. Only the conditioned media of keratinocytes harboring activated Ha‐ras genes were able to support the growth of granulocyte‐macrophage colony‐forming units. In addition, preincubation of normal bone‐marrow cells with conditioned media from the transformed epidermal cell lines stimulated in vitro amplification of the hematopoietic granulocyte‐macrophage progenitor compartment. To identify the possible factors responsible for the activities detected in the keratinocyte‐conditioned media, we performed northern blot analysis using the cytokine probes granulocyte colony‐stimulating factor, macrophage colony‐stimulating factor, granulocyte‐macrophage colony‐stimulating factor, stem cell factor, interleukin‐1α, interleukin‐3, and tumor necrosis factor‐α. The cell lines expressed different cytokine mRNA combinations that positively correlated with the colony‐stimulating activity detected in the corresponding conditioned medium. These results suggest that transformed epidermal tumor cells in vivo may alter normal hematopoiesis as a consequence of the production of cytokines that act in autocrine or paracrine loops probably related to tumor growth. ©1994 Wiley‐Liss, Inc.
Brief communications oncogene amplification per se: An independent prognostic factor in human breast cancer
Authors: Champème Marie‐Hélène , Biéche Ivan , Hacéne Kamel , Lidereau Rosette 
Published: February 2007

AbstractAs the prognostic significance of the three most frequently amplified oncogenes in breast cancer (c‐myc, int‐2IFGF3, and c‐erbB‐2lnew) is still unclear, and as the amplification of these genes appears to be mutually exclusive, we investigated the prognostic significance of oncogene amplification per se by multivariate analysis in a group of 112 primary human breast cancer cases. Amplification of at least one gene (c‐myc, int‐2lFGF3, or c‐erbB‐2Ineu), progesterone receptor status, and pathological tumor size were the only independent variables predictive of metastasis‐free survival. Moreover, We constructed prognostic profilles by computing risks associated with the three parameters predictive of poor survival and disciminated high‐,moderate‐, and low‐risk categories. ©1994 Wiley‐Liss, Inc.
Reduced expression of phospholipase c‐δ, a signal‐transducing enzyme, in rat colon neoplasms induced by methylazoxymethanol acetate
Authors: Yoshimi Naoki , Wang Aijin , Makita Hiroki , Suzui Masumi , Mori Hideki , Okano Yukio , Banno Yoshiko , Nozawa Yoshinori 
Published: February 2007

AbstractPhospholipase C (PLC), Which hydrolyzes phosphoinositides, has been implicated as a key enzyme in signal transduction. We examined the expression of an isozyme of PLC, PLC,‐δ, in rat colon neoplasms induced by methylazoxymethanol (MAM) acetate. Large‐bowel neoplasms were observed in five of 10 rats given MAM acetate (25 mg/kg body weight, by interperitoneal injection at 6 and 7 wk of age) 40 wk after treatment. Expression of PLC‐δ in the neoplasms was not detected by northern blot analysis, and a low level of expression was detected by immunoblot analysis, although PLC‐δ expression was apparent in the non‐neoplastic colon mucosae of MAM acetate‐treated rats as well as in the colon mucosae of control rats. Furthermore, analysis by reverse transcriptase‐polymerase chain reaction revealed that the ratio of the expression of PLC‐δ to that of β‐action in the neoplasms was significantly lower than the ratios in the non‐neoplastic colon mucosae of carcinogen‐treated and control rats (P<0.01) However, the ornithine decarboxylase (ODC) activity in the neoplsms was significantly greater than that of the non‐neoplastic and control mucosae (P<0.001). The differences in the levels of PLC‐δ expression in neoplastic and non‐neoplastic tissues and the inverse correlation of PLC‐δ expression with ODC activity may suggest that PLC‐δ has little effect on the PLC‐mediated mitogenic signaling system, at least in MAM acetate‐induced colon neoplasms in rats.
DNA recombination induced by aflatoxin B1 activated by cytochrome P450 1A enzymes
Authors: Sengstag Christian , Würgler Friedrich E. 
Published: February 2007

AbstractMutations in tumor suppressor genes are intricately associated with the etiology of neoplasia. Often, such mutations are followed by the second, functional alleles of tumor suppressor genes, a phenomenon known as loss of heterozygosity. Loss of heterozygosity may occur by different molecular mechanisms, including mitotic recombination, and it is conceivable that these molecular events are influenced by endogenous as well as exogenous factors. To test whether mitotic recombination is induced by certain carcinogens, we genetically engineered a Saccharomyces cerevisiae tester strain so that it metabolized two important classes of carcinogens, polycyclic aromatic hydrocarbons and heterocyclic arylamines. This was accomplished by expressing human cDNA's coding for the cytochrome P450 (CYP) enzymes CYP1A1 or CYP1A2 in combination with NADPH‐CYP oxidoreductase in a strain heterozygous for two mutations in the trp5 gene. Microsomes isolated form the transformed yeast strains activated various xenobiotics to powerful mutagens that were detected in the were detected in the Ames test. Of these, the mycotoxin aflatoxin B1, when activated intracellularly in the strains containing either human CYP enzyme, significantly induced mitotic recombination. These results are discussed in light of possible mechanisms that are involved in aflatoxin B1‐mediated hepatocarcinogenesis. Similarly, benzo[a]pyrene‐trans‐7,8‐dihydrodiol and 3‐amino‐1‐methyl‐5H‐pyrido [4,3‐b]indole were activated to recombinagenic products, whereas benozo[a]pyrene and 2‐amino‐3,8‐dimethylimidazo[4,5‐f] quinoxaline were negative in this assay. Our results argue that the contstructed yeast strains may be a valuable tool for the investigation of drug‐induced mitotic recombination. ©1994 Wiley‐Liss, Inc.
Frequent P53 mutation in mouse tumors induced by repeated β‐irradiation
Authors: Ootsuyama Akira , Makino Hiroshi , Nagao Minako , Ochiai Atsushi , Yamauchi Yuko , Tanooka Hiroshi 
Published: February 2007

AbstractOn examination of cDNA of the p53 gene in 65 murine tumors of the skin and bone produced by repeated exposure to a suprathreshold dose of 1–8 Gy of 90Sr‐90Y β‐radiation per exposure, we found 20 cases of mutation: 11 minute deletions (loss of 1‐24bp), including two cases possibly due to aberrant splicing: three insertions of 4–8 bp; and six base‐pair substitutions, including four at CpG sites, three being identical changes at codon 122 (a p53 hot spot). All but one of these mutations were confined to the central region of the p53 gene. From frameshifts created by deletions and insertions, the minimum size of the mutant p53 proteins found in these tumors was estimated to be 55% of the intact size. Cells of 17 of 19 tested tumors with p53 mutation were positive for immunostaining of p53 proteins accumulated in the nuclei and so were clearly different from nonneoplastic cells. Ha‐ras mutation was absent in these tumors, indicating that repeated β‐irradiation created a cell‐growth stimulating effect similar to that of ras mutation.