[Show abstract][Hide abstract] ABSTRACT: Mad2, a key component of the spindle checkpoint, is closely associated with chromosomal instability and poor prognosis in cancer. p31comet is a Mad2-interacting protein that serves as a spindle checkpoint silencer at mitosis. In this study, we showed that p31comet-induced apoptosis and senescence occur via counteraction of Mad2 activity. Upon retroviral transduction of p31comet, the majority of human cancer cell lines tested lost the ability to form colonies in a low-density seeding assay. Cancer cells with p31comet overexpression underwent distinct apoptosis and/or senescence, irrespective of p53 status, confirming the cytotoxicity of p31comet. Interestingly, both cytotoxic and Mad2 binding activities were eliminated upon deletion of the C-terminal 30 amino acids of p31comet. Point mutation or deletion of the region affecting Mad2 binding additionally abolished cytotoxic activity. Consistently, wild-type Mad2 interacting with p31comet, but not its non-binding mutant, inhibited cell death, indicating that the mechanism of p31comet-induced cell death involves Mad2 inactivation. Our results clearly suggest that the regions of p31comet affecting interactions with Mad2, including the C-terminus, are essential for induction of cell death. The finding that p31comet-induced cell death is mediated by interactions with Mad2 that lead to its inactivation is potentially applicable in anticancer therapy.
[Show abstract][Hide abstract] ABSTRACT: Despite the recent identification of several prognostic gene signatures, the lack of common genes among experimental cohorts has posed a considerable challenge in uncovering the molecular basis underlying hepatocellular carcinoma (HCC) recurrence for application in clinical purposes. To overcome the limitations of individual gene-based analysis, we applied a pathway-based approach for analysis of HCC recurrence.
By implementing a permutation-based semi-supervised principal component analysis algorithm using the optimal principal component, we selected sixty-four pathways associated with hepatitis B virus (HBV)-positive HCC recurrence (p < 0.01), from our microarray dataset composed of 142 HBV-positive HCCs. In relation to the public HBV- and public hepatitis C virus (HCV)-positive HCC datasets, we detected 46 (71.9%) and 18 (28.1%) common recurrence-associated pathways, respectively. However, overlap of recurrence-associated genes between datasets was rare, further supporting the utility of the pathway-based approach for recurrence analysis between different HCC datasets. Non-supervised clustering of the 64 recurrence-associated pathways facilitated the classification of HCC patients into high- and low-risk subgroups, based on risk of recurrence (p < 0.0001). The pathways identified were additionally successfully applied to discriminate subgroups depending on recurrence risk within the public HCC datasets. Through multivariate analysis, these recurrence-associated pathways were identified as an independent prognostic factor (p < 0.0001) along with tumor number, tumor size and Edmondson's grade. Moreover, the pathway-based approach had a clinical advantage in terms of discriminating the high-risk subgroup (N = 12) among patients (N = 26) with small HCC (<3 cm).
Using pathway-based analysis, we successfully identified the pathways involved in recurrence of HBV-positive HCC that may be effectively used as prognostic markers.
[Show abstract][Hide abstract] ABSTRACT: Glioblastoma multiforme (GBM) is the most malignant World Health Organization grade IV brain tumor. GBM patients have a poor prognosis because of its resistance to standard therapies, such as chemotherapy and radiation. Since stem-like cells have been associated with the treatment resistance of GBM, novel therapies targeting the cancer stem cell (CSC) population is critically required. However, GBM CSCs share molecular and functional characteristics with normal neural stem cells (NSCs). To elucidate differential therapeutic targets of GBM CSCs, we compared surface markers of GBM CSCs with adult human NSCs and found that GD2 and CD90 were specifically overexpressed in GBM CSCs. We further tested whether the GBM CSC specific markers are associated with the cancer stemness using primarily cultured patient-derived GBM cells. However, results consistently indicated that GBM cells with or without GD2 and CD90 had similar in vitro sphere formation capacity, a functional characteristics of CSCs. Therefore, GD2 and CD90, GBM specific surface markers, might not be used as specific therapeutic targets for GBM CSCs, although they could have other clinical utilities.
[Show abstract][Hide abstract] ABSTRACT: Standard treatment for glioblastoma comprises surgical resection, chemotherapy with temozolomide, and radiotherapy. Nevertheless, majority of glioblastoma patients have recurrence from resistance to the cytotoxic conventional therapies. We examined combinational effects of KML001, an arsenic compound targeting telomeres of chromosomes with temozolomide or irradiation, in glioblastoma cell lines and xenograft models, to overcome the therapeutic limitation of chemoradiation therapy for glioblastoma. Although KML001 alone showed little effects on in vitro survival of glioblastoma cells, cell death by in vitro temozolomide treatment or irradiation was synergistically potentiated by combination with KML001. Since phosphorylated γ-H2AX, cleaved casepase-3, and cleaved PARP were dramatically increased by KML001, the synergistic effects would be mediated by increased DNA damage and subsequent tumor cell apoptosis. Combinatorial effects of KML001 were observed not only in chemo- and radiosensitive glioblastoma cell line, U87MG, but also in the resistant cell line, U251MG. In the U87MG glioblastoma xenograft models, KML001 did not have systemic toxicity but showed synergistic therapeutic effects in combination with temozolomide or irradiation to reduce tumor volumes significantly. These data indicated that KML001 could be a candidate sensitizer to potentiate therapeutic effects of conventional cytotoxic treatment for glioblastoma.
[Show abstract][Hide abstract] ABSTRACT: β-Transducin repeat-containing protein (β-TrCP), an E3 ligase, promotes the degradation of substrate proteins in response to various stimuli. Even though several β-TrCP substrates have been identified to date, limited information of its upstream regulators is available. Here, we showed that SIRT1 suppresses β-TrCP protein synthesis via post-translational degradation. SIRT1 depletion led to a significant increase in the β-TrCP accumulation without affecting the mRNA level. Consistently, β-TrCP protein accumulation induced by resveratrol was further enhanced upon SIRT1 depletion. Rescue of SIRT1 reversed the effect of resveratrol, leading to reduced β-TrCP protein levels. Proteasomal inhibition led to recovery of β-TrCP in cells with SIRT1 overexpression. Notably, the recovered β-TrCP colocalized mostly with SIRT1. Thus, SIRT1 acts as a negative regulator of β-TrCP synthesis via promoting protein degradation.
Preview · Article · Nov 2013 · Biochemical and Biophysical Research Communications
[Show abstract][Hide abstract] ABSTRACT: The synthetic machinery of ATF4 (activating transcription factor 4) is activated in response to various stress conditions involved in nutrient restriction, endoplasmic reticulum homeostasis and oxidation. Stress-induced inhibition of proteasome activity triggers the unfolded protein response and endoplasmic reticulum stress where ATF4 is crucial for consequent biological events. In the current study, we showed that the NAD+-dependent deacetylase, SIRT1, suppresses ATF4 synthesis during proteasome inhibition. SIRT1 depletion via transfection of specific siRNA into HeLa cells resulted in a significant increase in ATF4 protein, which was observed specifically in the presence of the proteasome inhibitor, MG132. Consistent with SIRT1 depletion data, transient transfection of cells with SIRT1-overexpressing plasmid induced a decrease in the ATF4 protein level in the presence of MG132. Interestingly, however, ATF4 mRNA was not affected by SIRT1, even in the presence of MG132, indicating that SIRT1-induced suppression of ATF4 synthesis occurs under post-transcriptional control. Accordingly, we propose that SIRT1 serves as a negative regulator of ATF4 protein synthesis at the post-transcriptional level, which is observed during stress conditions, such as proteasome inhibition.
No preview · Article · Oct 2013 · Journal of Microbiology and Biotechnology
[Show abstract][Hide abstract] ABSTRACT: Upon apoptotic stimulation, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), a cytosolic enzyme normally active in glycolysis, translocates into the nucleus and activates an apoptotic cascade therein. In the present work, we show that SIRT1 prevents nuclear translocation of GAPDH via interaction with GAPDH. SIRT1 depletion triggered nuclear translocation of cytosolic GAPDH even in the absence of apoptotic stress. Such translocation was not, however, observed when SIRT1 enzymatic activity was inhibited, indicating that SIRT1 protein per se, rather than the deacetylase activity of the protein, is required to inhibit GAPDH translocation. Upon irradiation, SIRT1 prevented irradiation-induced nuclear translocation of GAPDH, accompanied by interaction of SIRT1 and GAPDH. Thus, SIRT1 functions to retain GAPDH in the cytosol, protecting the enzyme from nuclear translocation via interaction with these two proteins. This serves as a mechanism whereby SIRT1 regulates cell survival upon induction of apoptotic stress by means that include irradiation.
No preview · Article · Jul 2012 · Biochemical and Biophysical Research Communications
[Show abstract][Hide abstract] ABSTRACT: Chronic oxidative stress from reactive oxygen species (ROS) produced by the mitochondria promotes hepatocarcinogenesis and tumor progression. However, the exact mechanism by which mitochondrial ROS contributes to tumor cell invasion is not known. We investigated the role of ROS modulator 1 (Romo1) in hepatocellular carcinoma (HCC) development and tumor cell invasiveness.
We performed real-time, semi-quantitative, reverse transcriptase polymerase chain reaction; invasion and luciferase assays; and immunofluorescence and immunohistochemical analyses. The formation of pulmonary metastatic nodules after tumor cell injection was tested in severe combined immunodeficient mice. We analyzed Romo1 expression in HCC cell lines and tissues (n = 95).
Expression of Romo1 was increased in HCC cells, compared with normal human lung fibroblast cells. Exogenous expression of Romo1 in HCC cells increased their invasive activity, compared with control cells. Knockdown of Romo1 in Hep3B and Huh-7 HCC cells reduced their invasive activity in response to stimulation with 12-O-tetradecanoylphorbol-13-acetate. Levels of Romo1 were increased compared with normal liver tissues in 63 of 95 HCC samples from patients. In HCC samples from patients, there was an inverse correlation between Romo1 overexpression and patient survival times. Increased levels of Romo1 also correlated with vascular invasion by the tumors, reduced differentiation, and larger tumor size.
Romo1 is a biomarker of HCC progression that might be used in diagnosis. Reagents that inhibit activity of Romo1 and suppress mitochondrial ROS production, rather than eliminate up-regulated intracellular ROS, might be developed as cancer therapies.
No preview · Article · Jun 2012 · Gastroenterology
[Show abstract][Hide abstract] ABSTRACT: During genotoxic stress, reactive oxygen species hydrogen peroxide (H(2)O(2)) is a prime mediator of the DNA damage response. Telomeres function both to assist in DNA damage repair and to inhibit chromosomal end-to-end fusion. Here, we show that telomere dysfunction renders cells susceptible to H(2)O(2), via generation of multichromosomal fusion and chromosomal fragments. H(2)O(2) caused formation of multichromosomal end-to-end fusions involving more than three chromosomes, preferentially when telomeres were erosive. Interestingly, extensive chromosomal fragmentation (yielding small-sized fragments) occurred only in cells exhibiting such multichromosomal fusions. Telomeres were absent from fusion points, being rather present in the small fragments, indicating that H(2)O(2) cleaves chromosomal regions adjacent to telomeres. Restoration of telomere function or addition of the antioxidant N-acetylcysteine prevented development of chromosomal aberrations and rescued the observed hypersensitivity to H(2)O(2). Thus, chromosomal regions adjacent to telomeres become sensitive to reactive oxygen species hydrogen peroxide when telomeres are dysfunctional, and are cleaved to produce multichromosomal fusions and small chromosomal fragments bearing the telomeres.
No preview · Article · Nov 2011 · Biochemical and Biophysical Research Communications
[Show abstract][Hide abstract] ABSTRACT: Proteins involved in the G1 phase of the cell cycle are aberrantly expressed, sometimes in mutated forms, in human cancers including human hepatocellular carcinoma. Upon attack by a DNA-damaging anticancer drug, a cell arrests at the G1 phase; this is a safety feature prohibiting entry of DNA-damaged cells into S-phase. p21WAF1/CIP1 prevents damaged cells from progressing to the next cell cycle. Here, we show that, in response to mitomycin C and doxorubicin, human hepatocellular carcinoma cells generate conflicting signals, mediated by cyclin E and p21WAF1/CIP1, which respectively accelerates and represses cell cycle transition. Exposure to these anticancer drugs led to rapid accumulation of cyclin E in both p53-proficient HepG2 and p53-deficient Hep3B cells. Such anticancer drug-induced cyclin E accumulation influenced the G1-S-phase transition, but not DNA fragmentation-mediated death. In p53-proficient HepG2 cells, accumulation of cyclin E was followed by an increase in the level of p53-dependent p21WAF1/CIP1, thereby inhibiting further the G1-S-phase transition. Sublethal drug concentrations also induced rapid accumulation of cyclin E, but p21WAF1/CIP1 accumulation was delayed, further facilitating the G1-S-phase transition. Eventually, most cells arrested in G2/M. Thus, mitomycin C- or doxorubicin-induced conflicting signals, mediated by cyclin E and p21WAF1/CIP1, are in play in human hepatocellular carcinoma cells. Damaged G1 cells either immediately enter S-phase, or do not do so at all, depending on the extent of DNA damage.
No preview · Article · Sep 2011 · International Journal of Oncology
[Show abstract][Hide abstract] ABSTRACT: Protein arginine methylation is important for a variety of cellular processes including transcriptional regulation, mRNA splicing, DNA repair, nuclear/cytoplasmic shuttling and various signal transduction pathways. However, the role of arginine methylation in protein biosynthesis and the extracellular signals that control arginine methylation are not fully understood. Basic fibroblast growth factor (bFGF) has been identified as a potent stimulator of myofibroblast dedifferentiation into fibroblasts. We demonstrated that symmetric arginine dimethylation of eukaryotic elongation factor 2 (eEF2) is induced by bFGF without the change in the expression level of eEF2 in mouse embryo fibroblast NIH3T3 cells. The eEF2 methylation is preceded by ras-raf-mitogen-activated protein kinase kinase (MEK)-extracellular signal-regulated kinase (ERK1/2)- p21Cip/WAF1 activation, and suppressed by the mitogenactivated protein kinase (MAPK) inhibitor PD98059 and p21Cip/WAF1 short interfering RNA (siRNA). We determined that protein arginine methyltransferase 7 (PRMT7) is responsible for the methylation, and that PRMT5 acts as a coordinator. Collectively, we demonstrated that eEF2, a key factor involved in protein translational elongation is symmetrically arginine-methylated in a reversible manner, being regulated by bFGF through MAPK signaling pathway.
Preview · Article · Jul 2011 · Experimental and Molecular Medicine
[Show abstract][Hide abstract] ABSTRACT: The tissue environment in the region of hepatocellular carcinoma (HCC) influences both vascular invasion and recurrence. Thus, HCC patient prognosis depends on the characteristics not only of the tumor but also those of adjacent surrounding liver tissue.
Expression profiles of both tumor and adjacent liver tissue following curative resection were measured to discriminate 56 hepatitis B virus-positive HCC patients into subgroups based on survival risk. This approach was further tested in 40 patients.
Expression profiles of both tumor and adjacent liver tissue successfully discriminated 56 training samples into 2 subgroups, those at low- or high-risk for survival and recurrence. However, the prognostic gene set selected for tumor tissue was quite different from that for adjacent tissues. This variation in prognostic genes resulted in a change in allocation of patients within each low- or high-risk group. Combination of survival subgroups from tumor and adjacent liver tissue significantly improved the prediction of prognostic outcome. This integrative approach was confirmed to be effective in a further 40 test patients. A clinicopathological study showed that survival subgroups divided by tumor and adjacent liver tissue gene expression were also statistically associated with UICC stage and extent of cell differentiation, respectively.
Variation in gene expression during the nontumor stage as well as the tumor stage may affect the prognosis of HCC patients, and integration of the gene expression profiles of HCC and adjacent liver tissue increases discriminatory effectiveness between patient groups, predicting clinical outcomes with enhanced statistical reliability.
No preview · Article · Apr 2011 · Annals of Surgical Oncology
[Show abstract][Hide abstract] ABSTRACT: The anticancer effect of paclitaxel is attributable principally to irreversible promotion of microtubule stabilization and is hampered upon development of chemoresistance by tumor cells. Telomere shortening, and eventual telomere erosion, evoke chromosomal instability, resulting in particular cellular responses. Using telomerase-deficient cells derived from mTREC-/-p53-/- mice, here we show that, upon telomere erosion, paclitaxel propagates chromosomal instability by stimulating chromosomal end-to-end fusions and delaying the development of multinucleation. The end-to-end fusions involve both the p- and q-arms in cells in which telomeres are dysfunctional. Paclitaxel-induced chromosomal fusions were accompanied by prolonged G2/M cell cycle arrest, delayed multinucleation, and apoptosis. Telomere dysfunctional cells with mutlinucleation eventually underwent apoptosis. Thus, as telomere erosion proceeds, paclitaxel stimulates chromosomal fusion and instability, and both apoptosis and chemosensitization eventually develop.
No preview · Article · Jan 2011 · Biochemical and Biophysical Research Communications
[Show abstract][Hide abstract] ABSTRACT: A combination of a radiotherapeutic regimen with telomerase inhibition is valuable when tumor cells are to be sensitized to radiation. Here, we describe cell clones unresponsive to radiosensitization after telomere shortening. After extensive division of individual transformed clones of mTERC-/- cells, about 22% of clones were unresponsive to radiosensitization even though telomerase action was inhibited. The telomere lengths of unsensitized mTERC-/- clones were reduced, as were those of most sensitized clones. However, the unsensitized clones did not exhibit chromosomal end-to-end fusion to the extent noted in all sensitized clones. Thus, a defense mechanism preventing telomere erosion is operative even when telomeres become shorter under conditions of telomerase deficiency, and results in unresponsiveness to the radiosensitization generally mediated by telomere shortening.
No preview · Article · Sep 2010 · Biochemical and Biophysical Research Communications