bluuebunny/crossref_metadata_2025_split huggingface dataset:
Regulation of DNA Methyltransferase 1 by the pRb/E2F1 Pathway
Authors: McCabe Michael T. , Davis Joanne N. , Day Mark L. 
Published: September 2005

Abstract
Tumor suppressor gene silencing by DNA hypermethylation contributes to tumorigenesis in many tumor types. This aberrant methylation may be due to increased expression and activity of DNA methyltransferases, which catalyze the transfer of methyl groups from S-adenosylmethionine to cytosines in CpG dinucleotides. Elevated expression of the maintenance DNA methyltransferase, DNA methyltransferase 1 (DNMT-1), has been shown in carcinomas of the colon, lung, liver, and prostate. Based on the nearly ubiquitous alterations of both DNA methylation and the retinoblastoma protein (pRb) pathway found in human cancer, we investigated a potential regulatory pathway linking the two alterations in murine and human prostate epithelial cells. Analysis of DNA methyltransferase levels in Rb−/− murine prostate epithelial cell lines revealed elevated Dnmt-1 levels. Genomic DNA sequence analysis identified conserved E2F consensus binding sites in proximity to the transcription initiation points of murine and human Dnmt-1. Furthermore, the Dnmt-1 promoter was shown to be regulated by the pRb/E2F pathway in murine and human cell lines of epithelial and fibroblast origin. In the absence of pRb, Dnmt-1 transcripts exhibited aberrant cell cycle regulation and Rb−/− cells showed aberrant methylation of the paternally expressed gene 3 (Peg3) tumor suppressor gene. These findings show a link between inactivation of the pRb pathway and induction of DNA hypermethylation of CpG island–containing genes in tumorigenesis.
Tachyplesin Activates the Classic Complement Pathway to Kill Tumor Cells
Authors: Chen Jinguo , Xu Xue-Ming , Underhill Charles B. , Yang Shanmin , Wang Luping , Chen Yixin , Hong Shuigen , Creswell Karen , Zhang Lurong 
Published: September 2005

Abstract
Tachyplesin is a small, cationic peptide that possesses antitumor properties. However, little is known about its action mechanism. We used phage display to identify a protein that interacted with tachyplesin and isolated a sequence corresponding to the collagen-like domain of C1q, a key component in the complement pathway. Their interaction was subsequently confirmed by both ELISA and affinity precipitation. Tachyplesin seemed to activate the classic complement cascade because it triggered several downstream events, including the cleavage and deposition of C4 and C3 and the formation of C5b-9. When TSU tumor cells were treated with tachyplesin in the presence of serum, activated C4b and C3b could be detected on tumor cells by flow cytometry, Western blotting, and confocal microscopy. However, this effect was blocked when the tumor cells were treated with hyaluronidase or a large excess of hyaluronan, indicating that hyaluronan or related glycosaminoglycans were involved in this process. Treatment of cells with tachyplesin and serum increased in membrane permeability as indicated by the ability of FITC-dextran to enter the cytoplasm. Finally, the combination of tachyplesin and human serum markedly inhibited the proliferation and caused death of TSU cells, and these effects were attenuated if the serum was heat-inactivated or if hyaluronidase was added. Taken together, these observations suggest that tachyplesin binds to both hyaluronan on the cell surface and C1q in the serum and activates the classic complement cascade, which damages the integrity of the membranes of the tumor cells resulting in their death.
Development of Magnetic Resonance Imaging Contrast Material for In vivo Mapping of Tissue Transglutaminase Activity
Authors: Mazooz Galit , Mehlman Tevie , Lai Thung-Shen , Greenberg Charles S. , Dewhirst Mark W. , Neeman Michal 
Published: September 2005

Abstract
Transglutaminases are a family of enzymes that play an important role in tissue remodeling by catalyzing covalent cross-links between proteins of the extracellular matrix. Elevated activity of transglutaminase was shown at the boundaries of invading tumors, in association with angiogenesis, in stabilization of atherosclerotic plaques, and in generation of blood clots. The aim of this work was to develop a low molecular weight substrate of transglutaminase that could serve for noninvasive magnetic resonance and optical mapping of transglutaminase-mediated cross-linking activity. A 2 kDa contrast material was generated which showed cross-linking by either tissue transglutaminase or factor XIII in the context of multicellular tumor spheroids or fibrin clots, respectively. Successful detection by nuclear magnetic resonance microscopy of transglutaminase-mediated cross-linking of the contrast material to MCF7 multicellular spheroids provides hope that this approach could potentially be developed for clinical demarcation of sites of transglutaminase activity.
Tumor Suppressor VDUP1 Increases p27kip1 Stability by Inhibiting JAB1
Authors: Jeon Jun-Ho , Lee Kee-Nyung , Hwang Chae Young , Kwon Ki-Sun , You Kwan-Hee , Choi Inpyo 
Published: September 2005

Abstract
Vitamin D3 up-regulated protein 1 (VDUP1) is a stress-response gene that is up-regulated by 1,25(OH)2D3 in many cells. It has been reported that VDUP1 expression is reduced in many tumor cells and the enforced expression of VDUP1 inhibits cell proliferation by arresting cell cycle progression. Here, we found that VDUP1−/− fibroblast cells proliferated more rapidly compared with wild-type cells with reduced expression of p27kip1, a cyclin-dependent kinase inhibitor. JAB1 is known to interact with p27kip1 and to decrease the stability of p27kip1. VDUP1 interacted with JAB1 and restored JAB1-induced suppression of p27kip1 stability. In this process, VDUP1 blocked the JAB1-mediated translocation of p27kip1 from the nucleus to the cytoplasm. In addition, VDUP1 inhibited JAB1-mediated activator protein-1 activation and cell proliferation. Taken together, these results indicate that VDUP1 is a novel factor of p27kip1 stability via regulating JAB1.
Kaposi's Sarcoma–Associated Herpesvirus Viral IFN Regulatory Factor 1 Inhibits Transforming Growth Factor-β Signaling
Authors: Seo Taegun , Park Junsoo , Choe Joonho 
Published: September 2005

AbstractKaposi's sarcoma–associated herpesvirus, also called human herpesvirus 8, has been implicated in the pathogenesis of Kaposi's sarcoma, body cavity–based primary effusion lymphoma, and some forms of multicentric Castleman's disease. The Kaposi's sarcoma–associated herpesvirus open reading frame K9 encodes viral IFN regulatory factor 1 (vIRF1), which functions as a repressor of IFN-mediated signal transduction. vIRF1 expression in NIH 3T3 cells leads to transformation and consequently induces malignant fibrosarcoma in nude mice, suggesting that vIRF1 is a strong oncoprotein. Here, we show that vIRF1 inhibited transforming growth factor-β (TGF-β) signaling via its targeting of Smad proteins. vIRF1 suppressed TGF-β-mediated transcription and growth arrest. vIRF1 directly interacted with both Smad3 and Smad4, resulting in inhibition of their transactivation activity. Studies using vIRF1 deletion mutants showed that the central region of vIRF1 was required for vIRF1 association with Smad3 and Smad4 and that this region was also important for inhibition of TGF-β signaling. In addition, we found that vIRF1 interfered with Smad3-Smad4 complex formation and inhibited Smad3/Smad4 complexes from binding to DNA. These results indicate that vIRF1 inhibits TGF-β signaling via interaction with Smads. In addition, the data indicate the TGF-β pathway is an important target for viral oncoproteins.
Mutant V599EB-Raf Regulates Growth and Vascular Development of Malignant Melanoma Tumors
Authors: Sharma Arati , Trivedi Nishit R. , Zimmerman Melissa A. , Tuveson David A. , Smith Charles D. , Robertson Gavin P. 
Published: September 2005

Abstract
Activating mutations of the B-RAF gene are observed in &gt;60% of human melanomas. Approximately 90% of these mutations occur in the activation segment of the kinase domain as a single-base substitution that converts a valine to glutamic acid at codon 599 (V599E) in exon 15. This mutation causes activation of the kinase as well as downstream effectors of the mitogen-activated protein kinase–signaling cascade, leading to melanoma tumor development by an as yet unknown mechanism. In this study, we have identified the role of V599EB-Raf in melanoma tumor development by characterizing the mechanism by which this mutant protein promotes melanoma tumorigenesis. Small interfering RNA targeted against B-Raf or a Raf kinase inhibitor (BAY 43-9006) was used to reduce expression and/or activity of V599EB-Raf in melanoma tumors. This inhibition led to reduced activity of the mitogen-activated protein kinase–signaling cascade and inhibited tumor development in animals. Targeted reduction of mutant V599EB-Raf expression (activity) in melanoma cells before tumor formation inhibited tumorigenesis by reducing the growth potential of melanoma cells. In contrast, reduction of mutant V599EB-Raf activity in preexisting tumors prevented further vascular development mediated through decreased vascular endothelial growth factor secretion, subsequently increasing apoptosis in tumors. These effects in combination with reduced proliferative capacity halted growth, but did not shrink the size of preexisting melanoma tumors. Thus, these studies identify the mechanistic underpinnings by which mutant V599EB-RAF promotes melanoma development and show the effectiveness of targeting this protein to inhibit melanoma tumor growth.
Knockdown of STAT3 Expression by RNA Interference Inhibits the Induction of Breast Tumors in Immunocompetent Mice
Authors: Ling Xiaoyang , Arlinghaus Ralph B. 
Published: September 2005

Abstract
Constitutively activated STAT3 is involved in the formation of multiple types of tumors including breast cancer. We examined the effects of Stat3 protein knockdown by RNA interference using a dicistronic lentivirus small hairpin (shRNA) delivery system on the growth of mammary tumors in BALB/c mice induced by the 4T1 cell line. A single exposure of 4T1 cells to shRNA/STAT3 lentivirus transduced 75% of the cells with green fluorescent protein (GFP) within 96 hours. In cells selected for GFP expression, neither Stat3 protein nor phosphotyrosine Stat3 was detected. Tumor formation induced by injecting 4T1 cells into the mammary fat pad was blocked by expression of the shRNA for STAT3 whereas all mice injected with 4T1 cells expressing only GFP efficiently formed tumors. c-Myc expression was reduced 75% in cells expressing greatly reduced levels of Stat3 compared with the GFP control. Of interest, the level of activated Src, which is known to activate Stat3, was virtually eliminated but the level of the Src protein itself remained the same. Importantly, expression of Twist protein, a metastatic regulator, was eliminated in STAT3 knockdown cells. Invasion activity of STAT3 knockdown cells was strongly inhibited. However, the proliferation rate of cells in Stat3 knockdown cells was similar to that of the GFP control; the cell cycle was also not affected. We conclude from these studies that activated Stat3 protein plays a critical role in the induction of breast tumors induced by 4T1 cells by enhancing the expression of several important genes including c-Myc and the metastatic regulator Twist. These studies suggest that stable expression of small interfering RNA for STAT3 has potential as a therapeutic strategy for breast cancer.
An Expression Signature Classifies Chemotherapy-Resistant Pediatric Osteosarcoma
Authors: Mintz Michelle B. , Sowers Rebecca , Brown Kevin M. , Hilmer Sara C. , Mazza BethAnne , Huvos Andrew G. , Meyers Paul A. , LaFleur Bonnie , McDonough Wendy S. , Henry Michael M. , Ramsey Keri E. , Antonescu Cristina R. , Chen Wen , Healey John H. , Daluski Aaron , Berens Michael E. , MacDonald Tobey J. , Gorlick Richard , Stephan Dietrich A. 
Published: September 2005

Abstract
Osteosarcoma is the most common malignant bone tumor in children. Osteosarcoma patients who respond poorly to chemotherapy are at a higher risk of relapse and adverse outcome. Therefore, it was the aim of this study to identify prognostic factors at the time of diagnosis to characterize the genes predictive of poor survival outcome and to identify potential novel therapeutic targets. Expression profiling of 30 osteosarcoma diagnostic biopsy samples, 15 with inferior necrosis following induction chemotherapy (Huvos I/II) and 15 with superior necrosis following induction chemotherapy (Huvos III/IV), was conducted using Affymetrix U95Av2 oligonucleotide microarrays. One hundred and four genes were found to be statistically significant and highly differentially expressed between Huvos I/II and III/IV patients. Statistically significant genes were validated on a small independent cohort comprised of osteosarcoma xenograft tumor samples. Markers of Huvos I/II response predominantly were gene products involved in extracellular matrix (ECM) microenvironment remodeling and osteoclast differentiation. A striking finding was the significant decrease in osteoprotegerin, an osteoclastogenesis inhibitory factor. Additional genes involved in osteoclastogenesis and bone resorption, which were statistically different, include annexin 2, SMAD, PLA2G2A, and TGFβ1. ECM remodeling genes include desmoplakin, SPARCL1, biglycan, and PECAM. Gene expression of select genes involved in tumor progression, ECM remodeling, and osteoclastogenesis were validated via quantitative reverse transcription-PCR in an independent cohort. We propose that osteosarcoma tumor–driven changes in the bone microenvironment contribute to the chemotherapy-resistant phenotype and offer testable hypotheses to potentially enhance therapeutic response.
Role of Glycogen Synthase Kinase 3β in Rapamycin-Mediated Cell Cycle Regulation and Chemosensitivity
Authors: Dong JinJiang , Peng Junying , Zhang Haixia , Mondesire Wallace H. , Jian Weiguo , Mills Gordon B. , Hung Mien-Chie , Meric-Bernstam Funda 
Published: September 2005

Abstract
The mammalian target of rapamycin is a serine-threonine kinase that regulates cell cycle progression. Rapamycin and its analogues inhibit the mammalian target of rapamycin and are being actively investigated in clinical trials as novel targeted anticancer agents. Although cyclin D1 is down-regulated by rapamycin, the role of this down-regulation in rapamycin-mediated growth inhibition and the mechanism of cyclin D1 down-regulation are not well understood. Here, we show that overexpression of cyclin D1 partially overcomes rapamycin-induced cell cycle arrest and inhibition of anchorage-dependent growth in breast cancer cells. Rapamycin not only decreases endogenous cyclin D1 levels but also decreases the expression of transfected cyclin D1, suggesting that this is at least in part caused by accelerated proteolysis. Indeed, rapamycin decreases the half-life of cyclin D1 protein, and the rapamycin-induced decrease in cyclin D1 levels is partially abrogated by proteasome inhibitor N-acetyl-leucyl-leucyl-norleucinal. Rapamycin treatment leads to an increase in the kinase activity of glycogen synthase kinase 3β (GSK3β), a known regulator of cyclin D1 proteolysis. Rapamycin-induced down-regulation of cyclin D1 is inhibited by the GSK3β inhibitors lithium chloride, SB216763, and SB415286. Rapamycin-induced G1 arrest is abrogated by nonspecific GSK3β inhibitor lithium chloride but not by selective inhibitor SB216763, suggesting that GSK3β is not essential for rapamycin-mediated G1 arrest. However, rapamycin inhibits cell growth significantly more in GSK3β wild-type cells than in GSK3β-null cells, suggesting that GSK3β enhances rapamycin-mediated growth inhibition. In addition, rapamycin enhances paclitaxel-induced apoptosis through the mitochondrial death pathway; this is inhibited by selective GSK3β inhibitors SB216763 and SB415286. Furthermore, rapamycin significantly enhances paclitaxel-induced cytotoxicity in GSK3β wild-type but not in GSK3β-null cells, suggesting a critical role for GSK3β in rapamycin-mediated paclitaxel-sensitization. Taken together, these results show that GSK3β plays an important role in rapamycin-mediated cell cycle regulation and chemosensitivity and thus significantly potentiates the antitumor effects of rapamycin.
A Noninvasive Approach for Assessing Tumor Hypoxia in Xenografts: Developing a Urinary Marker for Hypoxia
Authors: Nelson Daniel W. , Cao Hongbin , Zhu Yonghua , Sunar-Reeder Bulbin , Choi Clara Y.H. , Faix James D. , Brown J. Martin , Koong Albert C. , Giaccia Amato J. , Le Quynh-Thu 
Published: September 2005

AbstractTumor hypoxia modifies the efficacy of conventional anticancer therapy and promotes malignant tumor progression. Human chorionic gonadotropin (hCG) is a glycoprotein secreted during pregnancy that has been used to monitor tumor burden in xenografts engineered to express this marker. We adapted this approach to use urinary β-hCG as a secreted reporter protein for tumor hypoxia. We used a hypoxia-inducible promoter containing five tandem repeats of the hypoxia-response element (HRE) ligated upstream of the β-hCG gene. This construct was stably integrated into two different cancer cell lines, FaDu, a human head and neck squamous cell carcinoma, and RKO, a human colorectal cancer cell line. In vitro studies showed that tumor cells stably transfected with this plasmid construct secrete β-hCG in response to hypoxia or hypoxia-inducible factor 1α (HIF-1α) stabilizing agents. The hypoxia responsiveness of this construct can be blocked by treatment with agents that affect the HIF-1α pathways, including topotecan, 1-benzyl-3-(5′-hydroxymethyl-2′-furyl)indazole (YC-1), and flavopiridol. Immunofluorescent analysis of tumor sections and quantitative assessment with flow cytometry indicate colocalization between β-hCG and 2-(2-nitro-1H-imidazol-1-yl)-N-(2,2,3,3,3-pentafluoropropyl)acetamide (EF5) and β-hCG and pimonidazole, two extrinsic markers for tumor hypoxia. Secretion of β-hCG from xenografts that contain these stable constructs is directly responsive to changes in tumor oxygenation, including exposure of the animals to 10% O2 and tumor bed irradiation. Similarly, urinary β-hCG levels decline after treatment with flavopiridol, an inhibitor of HIF-1 transactivation. This effect was observed only in tumor cells expressing a HRE-regulated reporter gene and not in tumor cells expressing a cytomegalovirus-regulated reporter gene. The 5HRE β-hCG reporter system described here enables serial, noninvasive monitoring of tumor hypoxia in a mouse model by measuring a urinary reporter protein.
Inhibition of c-Jun-N-terminal-Kinase Sensitizes Tumor Cells to CD95-Induced Apoptosis and Induces G2/M Cell Cycle Arrest
Authors: Kuntzen Christian , Sonuc Nilüfer , De Toni Enrico N. , Opelz Christine , Mucha Simon R. , Gerbes Alexander L. , Eichhorst Sören T. 
Published: September 2005

Abstract
Loss of susceptibility to apoptosis signals is a crucial step in carcinogenesis. Therefore, sensitization of tumor cells to apoptosis is a promising therapeutic strategy. c-Jun-N-terminal-kinases (JNK) have been implicated in stress-induced apoptosis, but may also contribute to survival signaling. Here we show that CD95-induced apoptosis is augmented by the JNK inhibitor SP600125 and small interfering RNA directed against JNK1/2. SP600125 potently inhibited methyl methane sulfonate–induced phosphorylation of c-Jun, but had minimal effect on apoptosis alone. In contrast, it strongly enhanced CD95-mediated apoptosis in six of eight tumor cell lines and led to a G2/M phase arrest in all cell lines. SP600125 enhanced cleavage of caspase 3 and caspase 8, the most upstream caspase in the CD95 pathway. JNK inhibition up-regulates p53 and its target genes p21Cip1/Waf1 and CD95. However, although HCT116 p53−/− cells and p21+/+ cells were less sensitive to CD95 stimulation than their p53+/+ and p21−/− counterparts, p53 and p21 were not involved in the JNK-mediated effect. JunD, which was described to be protective in tumor necrosis factor–induced apoptosis, was not regulated by JNK inhibition on the protein level. When transcription was blocked by actinomycin D, JNK inhibition still enhanced apoptosis to a comparable extent. We conclude that JNK inhibition has antitumor activity by inducing growth arrest and enhancing CD95-mediated apoptosis by a transcription-independent mechanism.
Antiangiogenic Concentrations of Paclitaxel Induce an Increase in Microtubule Dynamics in Endothelial Cells but Not in Cancer Cells
Authors: Pasquier Eddy , Honore Stéphane , Pourroy Bertrand , Jordan Mary Ann , Lehmann Maxime , Briand Claudette , Braguer Diane 
Published: September 2005

AbstractMicrotubule-targeted drugs such as paclitaxel exhibit potent antiangiogenic activity at very low concentrations, but the mechanism underlying such an effect remains unknown. To understand the involvement of microtubules in angiogenesis, we analyzed the dynamic instability behavior of microtubules in living endothelial cells [human microvascular endothelial cells (HMEC-1) and human umbilical vascular endothelial cells (HUVEC)] following 4 hours of paclitaxel treatment. Unexpectedly, antiangiogenic concentrations of paclitaxel (0.1-5 nmol/L) strongly increased microtubule overall dynamicity in both HMEC-1 (86-193%) and HUVEC (54-83%). This increase was associated with increased microtubule growth and shortening rates and extents and decreased mean duration of pauses. The enhancement of microtubule dynamics by paclitaxel seemed to be specific to antiangiogenic concentrations and to endothelial cells. Indeed, cytotoxic concentration (100 nmol/L) of paclitaxel suppressed microtubule dynamics by 40% and 54% in HMEC-1 and HUVECs, respectively, as observed for all tested concentrations in A549 tumor cells. After 4 hours of drug incubation, antiangiogenic concentrations of paclitaxel that inhibited endothelial cell proliferation without apoptosis (1-5 nmol/L) induced a slight decrease in anaphase/metaphase ratio, which was more pronounced and associated with increased mitotic index after 24 hours of incubation. Interestingly, the in vitro antiangiogenic effect also occurred at 0.1 nmol/L paclitaxel, a concentration that did not alter mitotic progression and endothelial cell proliferation but was sufficient to increase interphase microtubule dynamics. Altogether, our results show that paclitaxel mediates antiangiogenesis by an increase in microtubule dynamics in living endothelial cells and suggest that the impairment of interphase microtubule functions is responsible for the inhibition of angiogenesis.