bluuebunny/crossref_metadata_2025_split huggingface dataset:
Factors influencing the expression of endogenous retrovirus‐like sequences in rat 6 cells
Authors: Hsieh Ling‐Ling , Weinstein I. Bernard 
Published: February 2007

AbstractPrevious studies from this laboratory have demonstrated increased levels of expression of endogenous rat leukemia virus (RaLV) and 30S retrovirus‐like sequences in liver and colon tumors induced by chemical carcinogens in rats. During the process of normal liver regeneration, the levels of RaLV RNA were dramatically increased, whereas the levels of 30S RNA did not change. The present study examined several factors that might influence the expression of these sequences in the Rat 6 embryo fibroblast cell line. Rat 6 cells in either log‐phase or confluent cultures were treated with cycloheximide, the tumor promoter 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA), or the activated carcinogen benzo[a]pyrene diol epoxide (BPDE) for various periods of time up to 48 h. Northern blot analyses of total RNA indicated that cells in untreated cultures in log phase had higher levels of RaLV and 30S RNAs than did confluent cells. Within 10 h cycloheximide (2 or 10 μg/mL) markedly increased the levels of RaLV and 30S RNAs in both log‐phase and confluent cells. BPDE (100 μg/mL) induced a marked increase in the levels of RaLV RNA at 4 to 10 h, which returned to the basal level by 24 h in the log‐phase cells; but no significant change was seen in the confluent cells. The level of 30S RNA also increased moderately in the BPDE‐treated log‐phase cells and was maximal at 24 h; but no change was seen in confluent cells. Treatment with TPA (100 ng/mL) induced no significant increase in either RaLV or 30S RNA levels in the log‐phase or confluent cells. The exposure of Rat 6 cells to 5‐azacytidine (3 μM for 24 h) led to a marked increase in the levels of both RaLV and 30S RNAs, which persisted during at least 15 subsequent passages in the absence of the drug. Thus, inhibition of protein synthesis, DNA damage, or hypomethylation can increase the expression of certain endogenous retrovirus‐like sequences, but an activator of protein kinase C does not.
The v‐ras oncogene inhibits the expression of differentiation markers and facilitates expression of cytokeratins 8 and 18 in mouse keratinocytes
Authors: Cheng Christina , Kilkenny Anne E. , Roop Dennis , Yuspa Stuart H. 
Published: February 2007

AbstractCultured mouse keratinocytes can be initiated in vitro by the introduction of a v‐rasHa gene by viral transduction. Previous studies indicated that v‐rasHa‐transduced keratinocytes have a high proliferation rate in medium with 0.05 mM Ca2+ and resist terminal differentiation in medium with > 0.1 mM Ca2+, a culture condition in which normal cells mature into squames. The current studies demonstrate that v‐rasHa keratinocytes do not express transcripts or protein for epidermal early differentiation markers keratins 1 and 10 when cells are challenged with 0.12 mM Ca2+, which is a signal for expression of these genes in normal cells. Both transcript and protein for the late differentiation marker loricrin are also diminished in v‐ras keratinocytes, but filaggrin, also a late differentiation‐related gene product, is expressed in nearly normal amounts but at a different Ca2+ optimum. Modification of intracellular Ca2+ with ionomycin failed to restore the expression of any suprabasal keratinocyte markers. In contrast to the effects on normal products of keratinocyte differentiation, the introduction of the v‐rasHa gene facilitated the expression of keratins 8 (K8) and 18 (K18). These keratins are characteristic of embryonic cells and cells of simple adult epithelia but not stratified squamous epithelia such as skin. Like normal differentiation markers, the expression of K8 and K18 was dependent both on the v‐ras oncogene and the Ca2+ concentration of the culture medium, with > 0.1 mM Ca2+ being optimal. At the optimal Ca2+ level, the majority of v‐ras keratinocytes expressed K8 and K18 after 96 h, and many cells had reduced amounts of the normal keratinocyte cytokeratin K14. These studies indicate that the v‐ras gene causes substantial reprogramming of epidermal physiology, producing an unusual phenotype devoid of early suprabasal markers but at least partially permissive for late marker expression. Furthermore, the Ca2+‐dependent expression of K8 and K18 suggests that a normal signalling pathway used in keratinocyte differentiation is diverted to an abnormal endpoint.
Expression of c‐myc, c‐raf‐1, and c‐Ki‐ras in azaserine‐induced pancreatic carcinomas and growing pancreas in rats
Authors: Silverman Jeffrey A. , Kuhlmann Elna T. , Zurlo Joanne , Yager James D. , Longnecker Daniel S. 
Published: February 2007

AbstractWe examined the pattern of expression of several proto‐oncogenes during nonneoplastic growth and in acinar cell neoplasms in the rat pancreas. The levels of c‐myc, c‐raf‐1, and c‐Ki‐ras mRNAs were increased in regenerating pancreata following surgical partial pancreatectomy and following administration of camostat. We also investigated proto‐oncogene expression associated with the progression of pancreatic cancers in azaserine‐treated rats. Injection of a single dose (30 mg/kg) of azaserine (O‐diazoacetyl‐L‐serine) to 14‐d‐old rats leads to a variety of neoplastic lesions in the rat pancreas. Total RNA was isolated from lesions in various stages of tumor progression, including adenomas, carcinomas in situ, and invasive carcinomas. We observed increased expression of c‐myc, c‐raf‐1, and c‐Ki‐ras in azaserine‐induced adenomas and carcinomas. Actin expression was also increased in these tissues, whereas amylase expression was variable. However, when compared to the normal growing pancreas, the level of proto‐oncogene expression in the adenomas and carcinomas was disproportionate to the degree of cellular division in those tissues. Thus, the alterations induced by azaserine apparently caused a deregulated increase in expression of cellular oncogenes associated with growth regulation.
Tissue‐specific expression of p53 in transgenic mice is regulated by intron sequences
Authors: Lozano Guillermina , Levine Arnold J. 
Published: February 2007

AbstractTransgenic mice were produced harboring the p53 murine cDNA clone regulated by the SV40 enhancer‐promoter region 5′ to the cDNA and the small t antigen splice sites, and poly(A) addition signals 3′ to the cDNA. This construction was not expressed in these mice. The presence of several murine p53 introns in the cDNA, however, permitted expression of the transgene mRNA in several tissues of transgenic mice. The insertion of intron 4 led to the preferential expression of the transgene mRNA in spleen cells, where the endogenous p53 gene is also expressed at high levels. While intron 4 promoted high levels of p53mRNA expression in a tissue‐preferred manner in transgenic mice, there was no evidence that intron 4 could act as an enhancer of transcription in cell culture or in transgenic animals. The presence of some p53 introns appears to be critical for the regulation of this gene in vivo.
The moloney murine leukemia virus enhancer and its flanking sequences collaborate to determine virulence in T‐cell lymphomagenesis
Authors: Yuen Pick‐Hoong , Khang Yong‐Ho , Kumar Abhay , Szurek Paul F. , Maull Elizabeth A. 
Published: February 2007

AbstractA panel of recombinant virus genomes was constructed by exchanging homologous genome fragments between the potent T‐cell lymphoma inducer Moloney murine leukemia virus (MoMuLV) and its closely related but significantly less virulent relative MoMuLV‐TB. Testing of these recombinant viruses in BALB/c mice established that only nucleotide changes within the Clal(‐590)‐Kpnl(36) fragment altered virulence. Fine analysis of this fragment showed that while mutations within the enhancer of MoMuLV‐TB attenuated the latency period most, mutations within the MoMuLV‐TB fragments flanking the enhancer also helped reduce the virulence of MoMuLV. The present study also suggests that the small difference in the relative number of lymphomas that developed primarily in the spleens of MoMuLV‐ or MoMuLV‐TB‐infected mice may correlate with nucleotide differences between the Clal‐Kpnl fragments of the two viruses. However, the significantly greater proportion of premature deaths observed in MoMuLV‐TB‐ relative to MoMuLV‐infected mice could not be correlated with nucleotide differences in a specific genome fragment.
Tyrosine phosphorylation of three cellular proteins correlates with transformation of rat 1 cells by pp60src
Authors: Bouton Amy H. , Kanner Steven B. , Vines Richard R. , Parsons J. Thomas 
Published: February 2007

AbstractThe analysis of phosphotyrosine‐containing proteins in Rat 1 cells overexpressing either the tyrosine kinase pp60c−src or genetic variants containing alterations in functional and structural domains has led to the identification of three proteins whose tyrosine phosphorylation correlated with pp60src‐induced cellular transformation. The tyrosine phosphorylation of one of these proteins, p120, has been previously shown by us and others to coincide with the presence of kinase‐activated, membrane‐associated pp60src‐in chicken embryo cells. The second protein was identified as the ras‐associated GTPase‐activating protein (GAP). The third protein whose tyrosine phosphorylation was markedly elevated in Rat 1 cells expressing activated, membrane‐bound forms of pp60src‐had an apparent molecular mass of 64–67 kDa. The electrophoretic mobility of this protein varied in cells expressing different pp60src variants. The tyrosine‐phosphorylated form of p64–67 was present in immune complexes containing GAP, suggesting a stable interaction between these two cellular proteins.
Effect of myogenic determination on tumorigenicity of chemically transformed 10T1/2 cells
Authors: Hustad Carolyn Marziasz , Jones Peter A. 
Published: February 2007

AbstractTransforming agents have been postulated to interfere with cellular differentiation programs, thus causing uncontrolled growth. Inducing transformed cells to differentiate can result in loss of the transformed phenotype since many end‐stage differentiated cells are unable to divide. We attempted to bypass or suppress the tumorigenic phenotype of 3‐methylcholanthrene (MCA)‐transformed 10T1/2 cells (MCA CI 15C1) by induction of myogenic determination. MCA CI 15C1 cells were either treated with the hypomethylating drug 5‐azacytidine (5‐aza‐CR) or were transfected with the muscle determination gene MyoD1, both of which induce a myogenic phenotype in 10T1/2 cells. Colonies containing myoblast‐like cells were isolated and examined. Muscle markers were detected both in 5‐aza‐CR‐treated and in MyoD1‐transfected myogenic clones by immunofluorescence and northern analyses. The myogenic clones did not show decreased tumorigenicities relative to that of the parental cells upon subcutaneous injection in nude mice. Some of the resulting tumors, however, were classified as rhabdomyosarcomas rather than fibrosarcomas. Although induction of myogenic determination was not sufficient to abolish the tumorigenic phenotype of MCA CI 15C1 cells, several tumors showed decreased levels of MyoD1 mRNA, suggesting that growth in vivo either selected for or caused decreased determination gene expression.
Preferential mutagenesis at G·C base pairs by the anti 3,4‐dihydrodiol 1,2‐epoxide of 7‐methylbenz[a]anthracene
Authors: Bigger C. Anita H. , Flickinger Denise J. , John Judith St. , Harvey Ronald G. , Dipple Anthony 
Published: February 2007

AbstractThe racemic anti‐dihydrodiol epoxide of 7‐methylbenz[a]anthracene preferentially induced mutations at G·C base pairs in the pS 189 shuttle vector. Mutations were not randomly distributed throughout the supF target gene, but were concentrated at five hotspots. The hotspots for this agent did not correspond exactly to those produced by any other dihydrodiol epoxide examined to date, indicating that dihydrodiol epoxide structure and reactivity play a major role in determining mutagenic hotspots.
DNA methylation and oncogene expression in methapyrilene‐induced rat liver tumors and in treated hepatocytes in culture
Authors: Hernandez Lidia , Petropoulos Christos J. , Hughes Stephen H. , Lijinsky William 
Published: February 2007

AbstractContinued exposure of rats to carcinogenic doses of methapyrilene (MP) leads to elevated levels of 5‐methyl‐deoxycytidine (5MC) in liver DNA. Since gene expression often correlates with DNA methylation, we investigated these parameters in the MP‐induced hepatocellular carcinomas of Fischer 344 rats. DNA was hypermethylated in liver tissue surrounding the tumors relative to liver tissue of untreated controls of the same age, while tumor DNA was not; DNA methylation declined to normal levels when MP treatment ceased. Gene expression analysis showed measurable levels of mRNA for c‐Ki‐ras, erb‐B, erb‐B2, hck, src, lyn, vav, trk, raf‐1, l‐myc, c‐jun, c‐yes, c‐myc, c‐abl, and p53. No significant differences in expression for these and other oncogenes were seen between tumors and surrounding livers, although erb‐B2 and vav showed visible decreases compared with normal liver. Hypermethylation of DNA and expression of these oncogenes in MP‐treated tissues were not correlated. Levels of mRNA for the same genes in MP‐treated hepatocytes in culture were similar to in vivo levels; analysis of DNA synthesis levels showed that this gene expression pattern occurred in the absence of proliferation bursts or toxicity in these cells, thus suggesting that treatment in vivo may produce the same results.
Topological properties of bovine papillomavirus type 1 (BPV‐1) DNA in episomal nucleoprotein complexes: A model system for chromatin organization in higher eukaryotes
Authors: Rösl Frank , Waldeck Waldemar 
Published: February 2007

AbstractSedimentation analysis of isolated episomal bovine papillomavirus type 1 (BPV‐1) nucleoprotein complexes in sucrose gradients and subsequent separation of the purified DNA in chloroquine gels revealed different classes of molecules, varying in their degree of superhelicity. Since torsionally stressed DNA favors the adoption of secondary structures, we employed the single‐strand‐specific S1 nuclease to detect such structural alterations in both naked DNA and native chromatin. Direct examination of nuclease digestion products in chloroquine gels showed that neither the naked DNA nor the BPV‐1 nucleoprotein complexes in isolated nuclei were cleaved randomly by the enzyme. Instead, there was a strict dependence on nuclease susceptibility and the degree of supercoiling, strongly suggesting that the structural features detected by S1 nuclease are due to the occurrence of torsionally stressed viral chromatin. Mapping analysis using the indirect end‐labeling method demonstrated an S1‐nuclease cleavage site adjacent to 20 homopurine residues known to be hypersensitive to S1 attack. Furthermore, direct methylation experiments with viral chromatin in isolated nuclei indicated that only circular, covalently closed nucleoprotein complexes served as substrate, whereas linearized BPV‐1 chromatin was not susceptible to exogenously added Hhal methylase. This observation raises the possibility that the modulation of topology in nucleosomally organized DNA might also play a role in eukaryotic DNA methylation.
Elevation of glucose transporter, c‐myc, and transin RNA levels by Ha‐rasT24 is independent of its effect on the cell cycle
Authors: Godwin Andrew K. , Lieberman Michael W. 
Published: February 2007

AbstractElevation of the steady‐state mRNA levels of glucose transporter and c‐myc are among the earliest changes in gene expression observed after Ha‐rasT24 stimulation of Rat‐1 fibroblasts to enter the cell cycle. Since the expression of these genes may be the result of either increased cell proliferation or a specific response to rasT24, we evaluated the expression of glucose transporter and c‐myc and their induction during the cell cycle in both parental Rat‐1 cells and cell lines bearing a metallothionein rasT24 fusion gene (MTrasT24). We showed that, although levels of glucose transporter and c‐myc mRNAs in Rat‐1 cells underwent a transient increase within hours of the addition of serum, epidermal growth factor, or 12‐O‐tetradecanoylphorbol‐13‐acetate to quiescent (G0) cells, the levels of glucose transporter and c‐myc mRNA otherwise remained constant throughout the normal cell cycle. In cells carrying MTrasT24 (MR5 cells), induction of rasT24 expression by ZnSO4 led to a rapid induction of glucose transporter and c‐myc mRNA expression in both quiescent (density‐arrested) and G1/S‐synchronized (aphidicolin‐blocked) cells. These increases exceeded the constitutive levels expressed in rapidly proliferating Rat‐1 cells, indicating that the ras oncogene has an effect on these genes that is independent of growth status. In addition, the transin gene, which is not expressed in proliferating Rat‐1 cells in the continuous presence of serum growth factors, was also induced after increased expression of the mutant ras gene. These results suggest that the induction of glucose transporter, c‐myc, and transin is the direct result of rasT24‐mediated alterations in cellular gene expression and is distinct from normal cell‐cycle events.
Isolation and partial characterization of a transformation‐associated sequence from human nasopharyngeal carcinoma
Authors: Cao Ya , Sun Yi , Poirier Sylvie , Winterstein Dolores , Hegamyer Glenn , Seed John , Malin Sacha , Colburn Nancy H. 
Published: February 2007

AbstractA transforming activity associated with Chinese nasopharyngeal carcinoma (NPC) cell line CNE2 DNA has been identified by transfer into nontransformed promotion‐sensitive mouse JB6(P+) C141 cells. To clone this transformation‐associated sequence, we carried out three cycles of transfection, followed by cloning of anchorage‐independent transformants in soft agar. A tertiary CNE/JB6 clonal transfectant cell line 625 whose DNA showed transforming activity, as indicated in both soft‐agar assay and nude‐mice implantation, was used to make a genomic library in the vector λ dash. Using the human repeated sequence Blur 8 to screen the library, we obtained 10 human Alu‐positive clones. A cloned Alu‐positive insert of 16 kbp, CNE 323, was characterized in detail. CNE 323 transferred moderate transforming activity when introduced into JB6 P+ cells and showed no homology to Ha‐, Ki‐, or N‐ras genes; human promotion sensitivity genes; src, myb, jun, myc, fos, raf, or int‐2 oncogenes; or epidermal growth factor receptor. The isolated CNE 323 DNA sequence appeared to preserve the genomic structure of the original sequence found in CNE2 cells and in nude mouse tumors induced by CNE2 cells or by CNE/JB6 transfectant cells, indicating that the cloned NPC sequence was activated during NPC carcinogenesis and not during transfection or construction of the library, and that the cloned sequence or a larger sequence of which it was part played a role in tumor formation. Finally, we identified a 1.3‐kb mRNA that hybridizes to a subclone of the 16‐kb NPC sequence in CNE2 cell poly (A)+ RNA.
A monoclonal antibody to rat liver cytochrome P450 IIC11 strongly and regiospecifically inhibits constitutive benzo[a]pyrene metabolism and DNA binding
Authors: Todorovic Rosa , Devanesan Prabhaker D. , Cavalieri Ercole L. , Rogan Eleanor G. , Park Sang S. , Gelboin Harry V. 
Published: February 2007

AbstractThe monoclonal antibody MAb 1‐68‐11, prepared to constitutive cytochrome P450 IIC11 (2c/RLM5) from male Sprague‐Dawley rat liver, was used to study the contribution of the class of cytochrome P450s epitopically related to P450 IIC11 to the regiospecific metabolism of benzo[a]pyrene (BP) and its binding to DNA. The effect of MAb 1‐68‐11 was determined on the conversion of BP to BP‐9,10‐dihydrodiol, BP‐7,8‐dihydrodiol, BP‐4,5‐dihydrodiol, BP phenols, and BP quinones, and on the P450‐dependent DNA binding catalyzed by P450 in microsomes from uninduced male and female Wistar and Sprague‐Dawley rat livers, as well as 3‐methylcholanthrene‐ and phenobarbital (PB)‐induced male Wistar rat livers. In liver microsomes from untreated male rats, MAb 1‐68‐11 inhibited BP‐9,10‐dihydrodiol formation by 80%; in liver microsomes from untreated female rats, the inhibition was 100%. BP‐7,8‐dihydrodiol formation was inhibited from 38 to 77% in microsomes from males and 50% in those from females. In microsomes from PB‐induced rats, inhibition of the 9,10‐dihydrodiol and the 7,8‐dihydrodiol was 90% and 73%, respectively, whereas BP‐4,5‐dihydrodiol formation was enhanced 80%. In microsomes from 3‐methylcholanthrene‐treated rats, no inhibition of MAb 1‐68‐11 was observed on either the metabolism of BP or its binding to DNA. In contrast, the binding of BP to DNA was completely inhibited by MAb 1‐68‐11 in microsomes from uninduced male Wistar rats and 70% in PB‐induced microsomes. 32P‐postlabeling analysis showed that formation of the major stable adduct, BP diol epoxide bound at C‐10 to the 2‐amino of deoxyguanosine, was strongly inhibited in uninduced and PB‐induced microsomes. Formation of the major labile BP‐DNA adduct 7‐(benzo[a]pyren‐6‐yl) guanine (BP‐N7Gua) was inhibited about 60% in microsomes from untreated male Wistar rats. These results show that MAb 1‐68‐11 regiospecifically inhibits cytochrome P450 IIC11 and epitopically related P450s that metabolize BP at the 7,8 and 9,10 positions. MAb 1‐68‐11 also inhibits enzyme‐catalyzed binding of BP to DNA in the specific formation of BP‐N7Gua and adducts detected by the 32P‐postlabeling technique.
Molecular mechanisms of TPA‐mediated inhibition of Gap‐junctional intercellular communication: Evidence for action on the assembly or function but not the expression of connexin 43 in rat liver epithelial cells
Authors: Asamoto Makoto , Oyamada Masahito , Aoumari Abdelhakim El , Gros Daniel , Yamasaki Hiroshi 
Published: February 2007

AbstractWe found that a rat liver epithelial cell line (IAR 20) expresses connexin 43, the major cardiac gap‐junction protein, but not connexin 26 or connexin 32, major liver gap‐junction proteins. The effects of TPA on connexin 43 expression in IAR 20 were investigated using northern blot analysis, western blot analysis, and an immuno‐fluorescence technique. Gap‐junctional intercellular communication (GJIC) in this cell line decreased within 60 min of 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA) treatment and recovered after 24 h. The number of immu‐nofluorescence spots of connexin 43 on IAR 20 was closely related to the change in GJIC induced by TPA. However, TPA did not change the level of mRNA measured by northern blot analysis. Moreover, connexin 43 protein expression analyzed by western blotting suggests that connexin 43 proteins were still present in TPA‐treated cells at a similar level. These results suggest that GJIC of these rat liver epithelial cells was mediated by connexin 43 protein and that TPA inhibited GJIC by inhibiting posttranslational processing of connexin 43 proteins, e.g., localization or assembly.
Coordinate activation of multidrug‐resistance (P‐glycoprotein) genes mdr2 and mdr3 during mouse liver regeneration
Authors: Teeter Larry D. , Chan John Y. , Kuo M. Tien 
Published: February 2007

AbstractWe previously reported that only one of the three mouse multidrug‐resistance (mdr) genes, mdr3, is activated in hepatocellular carcinomas (HCCs). The present study examined the expression of mdr family members during mouse liver regeneration after partial hepatectomy to determine whether the regeneration that occurs during hepatic tumorigenesis is responsible for mdr3 elevation in HCC. We demonstrated that in both C3H/HeN and B6C3/F1 mice strains, the levels of both mdr2 and mdr3 mRNAs coordinately increased five‐ to sevenfold 24 h after partial hepatectomy, whereas the levels of mdr1 mRNA were not statistically different from those in the controls. Forty‐eight hours after partial hepatectomy, mdr mRNA levels decreased and in most cases returned to normal levels after 72 h. These results indicate that mdr3 induction during hepatocarcinogenesis is not due to liver regeneration alone.