bluuebunny/crossref_metadata_2025_split huggingface dataset:
Altered levels of endogenous retrovirus‐like sequence (VL30) RNA during mouse epidermal cell carcinogenesis
Authors: Han Kyung‐An , Rothberg Paul , Kulesz‐Martin Molly 
Published: February 2007

AbstractGene expression during mouse keratinocyte carcinogenesis was examined in a clonal cell model. Tumor cells from three separate initiated cell lineages were compared with their nontumorigenic precursors and with the progenitor cell strain prior to treatment with 7,12‐dimethylbenz[a]anthracene (DMBA). The steady‐state levels of VL30 RNA in normal and papilloma cells were regulated by extracellular Ca2+ (which controls proliferation and differentiation in normal epidermal keratinocytes) and culture density. In contrast, steady‐state levels of VL30 RNA were not regulated by these factors in the squamous cell carcinoma or the anaplastic carcinoma cells. VL30 expression was Ca2+ dependent in the initiated cell precursors within each tumor cell lineage, suggesting that the loss of response to extracellular Ca2+ was associated with the malignant conversion stage of carcinogenesis. No differences between normal and tumor cells were found in the cellular RNA levels of five additional proto‐oncogenes. The mouse epidermal cell model should provide a means for direct assessment of a potential functional role of VL30 sequences in cancer development.
A single mutation in one of the core elements of moloney murine leukemia virus reduced binding of a 42‐kDa T lymphoma cell nuclear factor but did not affect lymphomagenesis
Authors: Case Roger S. , Khang Yong‐Ho , Kumar Abhay , Yuen Pick‐Hoong 
Published: February 2007

AbstractThe genetic determinant responsible for virulence in Moloney murine leukemia virus (MoMuLV) induced T‐cell lymphomagenesis has recently been mapped [J Virol 63:471–480, 1989] by homologous genomic fragment exchange between MoMuLV and MoMuLV‐TB to the Clal/Xbal at the 3' end of the genome. This region of MoMuLV and MoMuLV‐TB differs in 11 nucleotides. Of these 11 nucleotide differences, 9 are distributed within the two CORE, the two distal NF1, and the two GRE/LVa elements of the enhancer. Since both the CORE binding sites of MoMuLV‐TB are mutated with respect to those of MoMuLV, we compared nuclear proteins of a thymusbone marrow cell line and a T‐lymphoma cell line (EMT), which bind to the wild‐type and mutant CORE binding sites. Using both the bandshift assay and southwestern analysis with labeled synthetic deoxyoligonucleotides, we showed that a 42‐kDa protein from TB and EMT cells bound specifically to the MoMuLV CORE element. The T SSC transversion of nucleotide 6 of the CORE consensus, TGTGGT/CTAA, significantly reduced binding of the 42‐kDa TB and EMT cell factors. However, the transversion of nucleotide 3 from T →C had little effect on the binding of the 42‐kDa protein to the CORE element. In addition, the 42‐kDa protein bound weakly to the CCAAT element of MoMuLV. A recombinant virus, NwtTB‐6, was generated by introducing the two CORE mutations of MoMuLV‐TB into the MoMuLV genome. Although the latency period of NwtTB‐6 in the induction of lymphoma was not significantly different from that of MoMuLV, preliminary findings suggest that the lymphoma induced by NwtTB‐6 may be more widely distributed.
Partial characterization of epidermal protein kinase C in mice sensitive or resistant to phorbol ester
Authors: Hirabayashi Naoki , Warren Barbour S. , Wang Xiao‐Jing , Petersen‐Marht Svend , Beltran Linda , Davis Melika M. , Ashendel Curtis L. , Digiovanni John 
Published: February 2007

AbstractThe present study has characterized several aspects of the mouse epidermal protein kinase C (PKC) system and compared phorbol ester‐sensitive and‐resistant mice. Protein immunoblots of partially purified epidermal PKC preparations from SENCAR and C57BL/6 mice indicated the presence of the γ‐, β‐, and α‐isozymes of PKC in both strains. Hydroxylapatite chromatography profiles of epidermal PKC isozymes from SENCAR and C57BL/6 mice revealed three major peaks of PKC activity eluting in fractions similar to those observed in chromatograms of brain tissue and corresponding to PKC‐γ, ‐β, and ‐α. Further analyses of hydroxylapatite chromatography fractions revealed that PKC‐γ and ‐β were present in approximately similar proportions and were much more abundant than PKC‐α. This distribution of epidermal PKC isozymes was similar in both strains. After a single topical application of 3.4 nmol 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA) to SENCAR mouse epidermis, total PKC activity in the cytosol fraction decreased rapidly to about 50% of control within 15 min and was accompanied by an increase (∼150% of control) of PKC activity in the membrane fraction. At 4 h, PKC activities were significantly lower than the control levels and remained downregulated through 96 h with a maximal decrease (to ∼25–30% of the control) in both cytosol and membrane fractions at 48 h. PKC activity returned to control levels by 168 h. Ca++/phospholipid‐independent kinase activity was the same as control levels at 15 min, 1 h, and 4 h after TPA treatment but was elevated above control levels at 24 h, 48 h, and 96 h, and by 168 h returned essentially to control levels. No differences were found in the magnitude or kinetics of TPA‐induced translocation and downregulation of total PKC or appearance of Ca++/phospholipid‐independent kinase activity between SENCAR, DBA/2, and C57BL/6 mice. Scatchard analyses using a two binding site model revealed that the apparent Kd and Bmax values for binding of PDBu to epidermal cytosol and membrane fractions were similar between SSIn, SENCAR, DBA/2, and C57BL/6 mice. The present results demonstrate for the first time that mouse epidermis contains significant amounts of the three major PKC isozymes that are present in brain, especially PKC‐γ. In addition, topical application of a promoting dose of TPA did not lead to complete loss of PKC activity in either the membrane or cytosol fractions of mouse epidermis. In conclusion, no differences were observed between phorbol ester‐sensitive and ‐resistant mice in any aspect of epidermal PKC examined.
Relationship between chemically induced ha‐ras mutation and transformation of BALB/c 3T3 cells: Evidence for chemical‐specific activation and cell type—specific recruitment of oncogene in transformation
Authors: Nakazawa Hisayoshi , Aguelon Anne‐Marie , Yamasaki Hiroshi 
Published: February 2007

AbstractBALB/c 3T3 cells were exposed to 7, 12‐dimethylbenz[a]anthracene (DMBA) and resultant transformed foci were analyzed for the presence of A182 → T mutation at codon 61 of Ha‐ras (a mutation found in many DMBA‐induced animal tumors). None of the 30 independently cloned transformed cell lines contained such a mutation. In order to see whether DMBA is able to induce this mutation in BALB/c 3T3 cells, we developed a method sensitive enough to detect this specific mutation at the frequency of 10–6. Employing this assay, we found time‐and dose‐dependent induction by DMBA of Ha‐ras A182 → T mutation in BALB/c 3Tc cells; for example, 2 wk after exposure to 100 μg/mL DMBA, 1.4 in 1 × 104 cells contained this specific mutation. On the other hand, other agents that also induce BALB/c 3T3 cell transformation, such as 3‐methylcholanthrene (MCA), 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA), N‐methyl‐N'‐nitro‐N‐nitrosoguanidine (MNNG), or ultraviolet light, did not induce the mutation at detectable frequency (< 10–6). These results suggest that DMBA efficiently induces Ha‐ras mutation in BALB/c 3T3 cells but that this mutation is not recruited in the process of cell transformation. A hypothesis of carcinogen‐specific mutation of Ha‐ras gene and its tissue (cell type)‐specific recruitment in carcinogenesis is proposed.
Nickel mutagenesis: Alteration of the MuSVts 110 thermosensitive splicing phenotype by a nickel‐induced duplication of the 3′ splice site
Authors: Chiocca Susanna M. , Sterner Deborah A. , Biggart Neal W. , Murphy Edwin C. 
Published: February 2007

AbstractWe investigated DNA damage caused by carcinogenic metals in a murine sarcoma virus (MuSV)‐based mutagenicity assay in which mutations targeted to v‐mos expression can be selected. Nickel chloride treatment of NRK cells (termed 6m2 cells) infected with MuSVts110, a retrovirus conditionally defective in viral RNA splicing and cell transformation, caused the outgrowth of transformed “revertants” with changes in the MuSVts110 RNA splicing phenotype. Cadmium and chromium treatment of 6m2 cells resulted in the selection of a second class of revertants with what appeared to be frameshift mutations allowing the translation of a readthrough gag‐mos protein. In both classes of metal‐induced revertants, viral gene expression was distinct from that observed in revertants arising in untreated 6m2 cultures, arguing that metal treatment did not simply enhance the rate of spontaneous reversion. In one representative nickel revertant line the operative nickel‐induced mutation affecting MuSVts110 RNA splicing was a duplication of 70 bases surrounding the 3′ splice site. The effect of this mutation was to direct splicing to the most downstream of the duplicated 3′ sites and concomitantly relax its characteristic thermosensitivity. These data establish the mutagenic potential of nickel and provide the first example of a defined nickel‐induced mutation in a mammalian gene.
Expression of retinoic acid α and β receptor genes in liver and hepatocellular carcinoma
Authors: Sever Cordelia E. , Locker Joseph 
Published: February 2007

AbstractcDNA probes for human retinoic acid receptors α and β (RARα and RARβ) were modified for use as specific hybridization probes to study hepatocellular carcinomas (HCC) and cell lines, liver regeneration, and fetal development. RARβ mRNA was detected at low levels in adult liver and rose markedly during the early phase of liver regeneration. RARβ mRNA was present at very low levels in HCC and was not detected in fetal liver. In contrast, RARα mRNA was present at low levels in normal liver, but showed a marked elevation in several HCCs and cell lines. Growth of cell lines was altered by retinoic acid (RA), but the effects could not be predicted by the levels of either RARα or RARβ mRNA. However, the response correlated with cell phenotype. Three cell lines with an adult phenotype (high albumin and low α‐fetoprotein) were inhibited by RA, two undifferentiated lines showed moderate growth stimulation, and two of three cell lines that had high levels of α‐fetoprotein were markedly stimulated by RA.
Role of growth hormone in the regulation of the c‐myc gene during progression of sex‐differentiated rat liver carcinogenesis in the resistant hepatocyte model
Authors: Hällström I. Porsch , Gustafsson Jan‐Åke , Blanck Agneta 
Published: February 2007

AbstractIn this study, we extended the previous observations of a growth hormone‐regulated sex difference in hepatic c‐myc expression in the resistant hepatocyte model during the selection/promotion phase, when sex differences in growth rate of enzyme‐altered foci are first identified, to studies of the regulation of this gene during later stages of hepatocarcinogenesis. The expression of the c‐myc gene was studied in preneoplastic nodules, hepatocellular carcinomas, and the corresponding surrounding livers of male and female Wistar rats treated according to the resistant hepatocyte model. In males, nodules isolated 8 and 11‐12 mo after initiation and hepatocellular carcinomas exhibited a 2.5‐ to threefold higher c‐myc expression than the surrounding liver. In females, no increase in c‐myc expression was observed in nodules 8 mo after initiation, while nodules isolated after 11‐14 mo and tumors snowed a twofold and threefold increase, respectively, when compared with the surrounding tissue. Increased transcription of the c‐myc gene was observed in nuclei from male nodules isolated 11 mo after initiation compared with nuclei from the surrounding liver. The difference in transcription between male nodules and surrounding tissue is similar for the first and second exon of the gene. Continuous infusion of growth hormone to nodule‐bearing male rats 8 and 11 mo after initiation decreased c‐myc expression in the surrounding tissue and downregulated the expression in 8‐mo nodules to the level in the surrounding liver. No significant decrease in response to growth hormone treatment was seen in 11‐mo nodules. In hypophysectomized nodule‐bearing males, nodular c‐myc remained upregulated. Taken together, the data showed that the sex difference in c‐myc expression was maintained during a large part of the progression period. Furthermore, the loss of growth hormone regulation of the c‐myc gene in advanced male nodules indicated an escape from normal regulatory mechanisms during progression. These findings might reflect a role for the c‐myc gene in sex‐differentiated rat liver carcinogenesis.
Ki‐ras mutations in spontaneous and chemically induced renal tumors of the rat
Authors: Ohgaki Hiroko , Kleihues Paul , Hard Gordon C. 
Published: February 2007

AbstractA high frequency of point mutations at codon 12 of the Ki‐ras gene has previously been reported for rat kidney mesenchymal tumors induced by methylating N‐nitroso compounds. In this study, we analyzed renal tumors with divergent histogenesis, i.e., mesenchymal tumors (sarcomas), cortical epithelial tumors (carcinomas), and embryonal tumors (nephroblastomas). Renal mesenchymal tumors and carcinomas were induced in juvenile or young adult Wistar rats by a single dose of N‐nitrosodimethylamine (NDMA) while nephroblastomas were induced in Nb hooded rats by a single transplacental dose of N‐nitrosoethylurea (NEU). Nephroblastomas developing spontaneously in WAB/Not rats were also examined. Amplification of Ki‐ras sequences from formalin‐fixed, paraffin‐embedded tissue by the polymerase chain reaction was followed by direct DNA sequencing. GGT GAT point mutations at codon 12 of the Ki‐ras gene were found in 9 of 12 (75%) renal mesenchymal tumors and in 9 of 12 (75%) cortical epithelial tumors induced by NDMA. Even higher incidences were observed in nephroblastomas (8/8; 100%) induced by NEU and in spontaneous nephroblastomas (10/11; 91%). These results indicate that Ki‐ras mutations are frequent events during the development of kidney tumors irrespective of their histogenesis and suggest that they may play an important role in renal carcinogenesis in rats. These data further indicate that mutational activation of Ki‐ras proto‐oncogenes in carcinogen‐induced rat kidney tumors occurs in a tissue‐specific, rather than cell‐specific, manner.
Correlation of increased levels of Ha‐ras T24 protein with extent of loss of gap junction function in rat liver epithelial cells
Authors: de Feijter Adriaan W. , Trosko James E. , Krizman David B. , Lebovitz Russell M. , Lieberman Michael W. 
Published: February 2007

AbstractAlthough it is known that cells transformed by ras and other oncogenes show reduced gap junction function, to date there has been no investigation of the quantitative relationship between intracellular levels of ras oncoprotein and loss of cell‐cell communication. Using the rat liver epithelial cell line MTR6, which carries a zinc‐inducible metallothionein ras T24 (MT ras T24) fusion gene, we showed a direct correlation between the accumulation of ras T24 protein and the loss of dye transfer as measured by interactive laser cytometry. After stimulation with zinc sulfate, changes in both parameters were rapid and measurable by 24 h. Similarly, there was a dose‐response relationship between loss of gap junction function and increase in ras T24 protein. Northern analysis of two gap junction proteins (connexins 43 and 32) showed no differences between cells that expressed high levels of ras and control cells. These data demonstrate that the degree of loss of gap junction function is dependent on the amount of increase in ras T24 protein levels, but the mechanism by which these changes are effected remains unclear. © 1992 Wiley‐Liss, Inc.
Rare frequency of activation of the ki‐ras gene in rat colon tumors induced by heterocyclic amines: Possible alternative mechanisms of human colon carcinogenesis
Authors: Kakiuchi Hideki , Ushijima Toshikazu , Ochiai Masako , Sugimura Takashi , Nagao Minako , Imai Kozo , Yachi Akira , Ito Nobuyuki 
Published: February 2007

AbstractHeterocyclic amines present in cooked foods are known to produce colon tumors in F344 rats at a high incidence, indicating the possibility of involvement of ras gene activation in colon carcinogenesis in rats as in humans. We examined mutations at codons 12, 13, and 61 of the Ki‐ras, Ha‐ras, and N‐ras genes by polymerase chain reaction—direct sequencing in seven colon tumors in F344 rats induced by 2‐amino‐6‐methyldipyrido‐[1,2‐a:3′,2′‐d]imidazole (Glu‐P‐1), 11 induced by 2‐amino‐3‐methylimidazo[4,5‐f]quinoline, and nine induced by 2‐amino‐1‐methyl‐6‐phenylimidazo[4,5‐b]pyridine. A Ki‐ras gene mutation (G → T at the second position in codon 12) was found in one Glu‐P‐1—induced colon adenocarcinoma. None of the other 26 tumors had mutations in any of these three ras family genes. These results indicate that in rats, colon carcinogenesis induced by heterocyclic amines may be induced by alterations of other oncogenes or tumor suppressor genes. We think this experimental system using carcinogens to which humans are exposed is a good model for studying alterations of other genes in human colon tumors in which no Ki‐ras alterations are observed. © 1993 Wiley‐Liss, Inc.
No point mutation of ha‐ras or p53 genes expressed in preneoplastic‐to‐neoplastic progression as modeled in mouse JB6 cell variants
Authors: Sun Yi , Nakamura Kazuki , Hegamyer Glenn , Dong Zigang , Colburn Nancy 
Published: February 2007

AbstractAlterations of the p53 gene have been found in many human and animal tumors, and ras mutations have been seen somewhat less frequently. Loss of p53 tumor suppressor activity has been implicated in multistage tumor promotion/progression after initiation by Ha‐ras or Ki‐ras activation. Whether p53 or ras alterations occur during promotion of neoplastic transformation in JB6 cells has not been reported. Using a series of mouse JB6 variants representing different stages of progression toward the tumor‐cell phenotype, we investigated whether mutational activation of Ha‐ras and mutational inactivation and altered expression of the p53 gene occurred during progression. We report here that neither point mutations of the Ha‐ras or p53 genes nor p53 structural alterations were involved in this process. Although there was no significant difference in steady‐state levels of p53 mRNA, an elevated level of immunoprecipitable p53 protein was observed in a subset of transformed cells. We also report the detection of a second 2.2‐kb p53‐hybridizing transcript. This transcript was not translated into p53 protein and may be a nuclear precursor of the mature message. Both p53‐hybridizing transcripts were downregulated by prolonged 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA) treatment (24 h) regardless of the stage of progression. We conclude from this study that in JB6 variants (1) mutational activation of Ha‐ras and inactivation of p53are unlikely to be involved in preneoplastic progression; (2) increased amounts of p53 protein may be involved in a subset of transformed cells, possibly reflecting a longer half‐life, as demonstrated in other systems; and (3) late downregulation of p53 mRNA but not protein expression may be a secondary response in the TPA‐mediated signal transduction pathway. © 1993 Wiley‐Liss, Inc.
Genetic analysis of carcinogen enhancement of type 5 adenovirus transformation of cloned fischer rat embryo fibroblast cells
Authors: Su Zao‐Zhong , Shen Ruoqian , Young C. S. H. , Fisher Paul B. 
Published: February 2007

AbstractPretreatment of CREF cells with methyl methanesulfonate (MMS) before infection with the host‐range cold‐sensitive type 5 adenovirus (Ad5) mutant H5hr1 results in a dose‐dependent carcinogen enhancement of viral transformation (CET). The properties of CET observed with H5hr1, which include both an MMS dose‐dependent enhancement in the number of transformed foci and an increase in transformation frequency after correction for cell toxicity, are not observed in carcinogen‐pretreated wild‐type (wt) Ad5 (H5wt)‐infected CREF cells. This study was conducted to determine the role of the viral E1A and E1B transforming genes of H5hr1 in mediating the unique CET phenotype of H5hr1. Coinfection of MMS‐pretreated CREF cells with H5wt or H5sub309 (which displays a wt Ad5 phenotype) and H5hr1 resulted in a suppression of the unique CET phenotype that was directly related to the multiplicity of infection with wt Ad5. Suppression of the unique H5hr1 CET phenotype was also apparent in MMS‐pretreated CREF cells coinfected with H5hr1 and an Ad5 mutant expressing either a wt 13S E1A‐encoded 289 amino‐acid (aa) protein and an intact wt E 1B gene or a wt 13S E1A‐encoded 289‐aa protein and a 22S E1B‐encoded 495‐aa protein. In contrast, the unique H5hr1 CET phenotype was not suppressed in MMS‐pretreated CREF cells coinfected with H5hr1 and Ad5 or Ad2 mutants expressing either a wt 12S E1A‐encoded 243‐aa protein and both wt E1B gene products or an intact wt E1A gene and a wt E1B 13S‐encoded 175‐aa protein. That genetic changes in both the E1A and E1B viral regions of H5hr1 were required to induce the unique CET phenotype was also indicated by the inability of a recombinant Ad5 containing the 0—4.5 map‐unit region of H5hr1 and the 4.5–100 map‐unit region of H5sub309 to display the H5hr1 unique CET phenotype. Direct confirmation of the requirement for both gene regions of H5hr1 to mediate its unique CET was obtained by generating CREF cells stably expressing a wt Ad5 E1A 13S‐encoded 289‐aa protein and a wt E1B 22S‐encoded 495‐aa protein. In these CREF transformants (which displayed a CREF‐like morphology), transformation by H5hr1 was not reduced, but the unique CET phenotype after MMS pretreatment was eliminated. These results suggest that alterations in both the 13S‐encoded E1A and 22S‐encoded E1B gene products of H5hr1 contribute to its unique CET.
Association of tumorigenic and nontumorigenic (immunogenic) variants in a mouse t‐cell lymphoma with two distinct p53 mutations
Authors: Bergel Michael , Hochman Jacob , Siwarski David , Huppi Konrad , Bhatia Kishor , Gutierrez Marina 
Published: February 2007

AbstractAn in vitro model system for xenogenization has been developed in which an immunogenic, nonmalignant phenotype was selected from a highly malignant T‐cell line (S49). We showed by single‐strand conformation polymorphism and DNA sequence analysis that specific point mutations in the p53 tumor suppressor gene correlated with a change from a tumorigenic to a nontumorigenic (immunogenic) phenotype. Specifically, we found that the highly malignant S49 cell line T‐60 contains an Arg→Gln substitution at residue 246 in exon 7 of p53. In contrast, nontumorigenic (immunogenic) variants (T‐25‐Adh and Rev‐1) exhibited a Gly→Ser substitution at residue 242 of p53. In two subsequent tumorigenic revertants derived from Rev‐1, we again found the Arg→Gln substitution at residue 246 that was found initially in the T‐60 cells. Thus, mutation at residue 246 of p53 was associated with a highly malignant phenotype, whereas a novel mutation at residue 242 of p53 appeared to be associated with a nonmalignant phenotype and may have actually protected the host through immunization. We conclude that mutation of residue 242 may represent a new class of permissive (nonmalignant) mutations in the mouse that are analogous to the Li‐Fraumeni mutation in humans. © 1993 Wiley‐Liss, Inc.