SIRT1 suppresses cellular accumulation of ß-TrCP E3 ligase via protein degradation.

ß-Transducin repeat-containing protein (ß-TrCP), an E3 ligase, promotes the degradation of substrate proteins in response to various stimuli. Even though several ß-TrCP substrates have been identified to date, limited information of its upstream regulators is available. Here, we showed that SIRT1 suppresses ß-TrCP protein synthesis via post-translational degradation. SIRT1 depletion led to a significant increase in the ß-TrCP accumulation without affecting the mRNA level. Consistently, ß-TrCP protein accumulation induced by resveratrol was further enhanced upon SIRT1 depletion. Rescue of SIRT1 reversed the effect of resveratrol, leading to reduced ß-TrCP protein levels. Proteasomal inhibition led to recovery of ß-TrCP in cells with SIRT1 overexpression. Notably, the recovered ß-TrCP colocalized mostly with SIRT1. Thus, SIRT1 acts as a negative regulator of ß-TrCP synthesis via promoting protein degradation.

Cells with dysfunctional telomeres are susceptible to reactive oxygen species hydrogen peroxide via generation of multichromosomal fusions and chromosomal fragments bearing telomeres.

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.

Paclitaxel stimulates chromosomal fusion and instability in cells with dysfunctional telomeres: implication in multinucleation and chemosensitization.

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.

p31comet Induces cellular senescence through p21 accumulation and Mad2 disruption.

Functional suppression of spindle checkpoint protein activity results in apoptotic cell death arising from mitotic failure, including defective spindle formation, chromosome missegregation, and premature mitotic exit. The recently identified p31(comet) protein acts as a spindle checkpoint silencer via communication with the transient Mad2 complex. In the present study, we found that p31(comet) overexpression led to two distinct phenotypic changes, cellular apoptosis and senescence. Because of a paucity of direct molecular link of spindle checkpoint to cellular senescence, however, the present report focuses on the relationship between abnormal spindle checkpoint formation and p31(comet)-induced senescence by using susceptible tumor cell lines. p31(comet)-induced senescence was accompanied by mitotic catastrophe with massive nuclear and chromosomal abnormalities. The progression of the senescence was completely inhibited by the depletion of p21(Waf1/Cip1) and partly inhibited by the depletion of the tumor suppressor protein p53. Notably, p21(Waf1/Cip1) depletion caused a dramatic phenotypic conversion of p31(comet)-induced senescence into cell death through mitotic catastrophe, indicating that p21(Waf1/Cip1) is a major mediator of p31(comet)-induced cellular senescence. In contrast to wild-type p31(comet), overexpression of a p31 mutant lacking the Mad2 binding region did not cause senescence. Moreover, depletion of Mad2 by small interfering RNA induced senescence. Here, we show that p31(comet) induces tumor cell senescence by mediating p21(Waf1/Cip1) accumulation and Mad2 disruption and that these effects are dependent on a direct interaction of p31(comet) with Mad2. Our results could be used to control tumor growth.

Clonal cell populations unresponsive to radiosensitization induced by telomerase inhibition.

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.

Proteomic identification of cytosolic proteins that undergo arginine methylation during rat liver regeneration.

Protein arginine methylation plays a crucial role in signal transduction, protein-protein interactions, and transcriptional regulation. Previously, we showed that protein arginine methyltransferase activity increased significantly during rat liver regeneration. In the present study, in vivo arginine methylation during liver regeneration was investigated. The presence of symmetric or asymmetric dimethylarginine in proteins varied significantly at the early stage of regeneration after partial hepatectomy. The nature of the 31 proteins that showed significant variations in arginine methylation were identified using 2-DE and MS. Many of these proteins were oxidative stress-related or oxidation-prone proteins that exhibited significant variations in arginine methylation without changes in their expression levels. The oxidation of some of the oxidation-prone proteins under oxidative stress such as carbonic anhydrase 3 decreased with increased levels of arginine methylation, whereas normal levels of protein oxidation were recovered as arginine methylation subsided. Taken together, this study demonstrated that time-dependent methylation events in hepatocytes during the early period of rat liver regeneration may participate in the regulation or protection of protein activities, thus presenting a significant new insight into the biology of proliferating cells at the post-translational modification level and into a key population of proteins involved in these processes.

Inhibition of ß-site amyloid precursor protein cleaving enzyme 1 and cholinesterases by pterosins via a specific structure-activity relationship with a strong BBB permeability.

We extracted 15 pterosin derivatives from Pteridium aquilinum that inhibited ß-site amyloid precursor protein cleaving enzyme 1 (BACE1) and cholinesterases involved in the pathogenesis of Alzheimer's disease (AD). (2R)-Pterosin B inhibited BACE1, acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) with an IC50 of 29.6, 16.2 and 48.1 µM, respectively. The Ki values and binding energies (kcal/mol) between pterosins and BACE1, AChE, and BChE corresponded to the respective IC50 values. (2R)-Pterosin B was a noncompetitive inhibitor against human BACE1 and BChE as well as a mixed-type inhibitor against AChE, binding to the active sites of the corresponding enzymes. Molecular docking simulation of mixed-type and noncompetitive inhibitors for BACE1, AChE, and BChE indicated novel binding site-directed inhibition of the enzymes by pterosins and the structure-activity relationship. (2R)-Pterosin B exhibited a strong BBB permeability with an effective permeability (Pe) of 60.3×10-6 cm/s on PAMPA-BBB. (2R)-Pterosin B and (2R,3 R)-pteroside C significantly decreased the secretion of Aß peptides from neuroblastoma cells that overexpressed human ß-amyloid precursor protein at 500 µM. Conclusively, our study suggested that several pterosins are potential scaffolds for multitarget-directed ligands (MTDLs) for AD therapeutics.

Benzylideneacetone Derivatives Inhibit Osteoclastogenesis and Activate Osteoblastogenesis Independently Based on Specific Structure-Activity Relationship.

(E)-3,4-Dihydroxybenzylideneacetone (compound 1) inhibited receptor activator of NF-κB ligand-induced osteoclastogenesis of C57BL/6 bone marrow monocyte/macrophages with IC50 of 7.8 µM (IC50 of alendronate, 3.7 µM) while stimulating the differentiation of MC3T3-E1 osteoblastic cells, accompanied by the induction of Runt-related transcription factor 2, alkaline phosphatase, and osteocalcin. (E)-4-(3-Hydroxy-4-methoxyphenyl)-3-buten-2-one (compound 2c) showed a dramatically increased osteoclast-inhibitory potency with IC50 of 0.11 µM while sustaining osteoblast-stimulatory activity. (E)-4-(4-Hydroxy-3-methoxyphenyl)-3-buten-2-one (compound 2g) stimulated alkaline phosphatase production 2-fold at 50 µM without changing osteoclast-inhibitory activity, compared with compound 1. Oral administration of compounds 1, 2c, and 2g prevented ovariectomy-induced osteoporosis in ddY mice to a degree proportional to their osteoclastogenesis-inhibitory potencies. The administration of 1 (mg/kg)/d compound 2c ameliorated histomorphometry of osteoporotic bone to a degree comparable with 10 (mg/kg)/d alendronate. Conclusively, the in vitro capacity of a few benzylideneacetone derivatives to inhibit osteoclastogenesis supported by independent osteoblastogenesis activation was convincingly reflected in in vivo management of osteoporosis, suggesting a potential novel therapeutics for osteopenic diseases.

Arginine deiminase enhances MCF-7 cell radiosensitivity by inducing changes in the expression of cell cycle-related proteins.

After successful clinical application, arginine deiminase (ADI) has been proposed to be a new cancer therapeutic. In the present study, we examined the effect of ADI in combination with ionizing radiation (IR) on MCF-7 cell growth and clonogenic cell death. Cell growth was inhibited by IR in a dose-dependent manner and ADI enhanced the radiosensitivity. ADI itself did not suppress the growth of MCF-7 cells due to the high level of expression of argininosuccinate synthetase (ASS), which convert citrulline, a product of arginine degradation by ADI, to arginine. Previously, it was suggested that ammonia, another product of arginine degradation by ADI, is the main cause of the growth inhibition of irradiated hepatoma cells contaminated with ADI-expressing mycoplasma [van Rijn et al. (2003)]. However, we found that ammonia is not the only factor that enhances radiosensitivity, as enhancement was also observed in the absence of ammonia. In order to identify the enhancing effect, levels of ASS and proteins related to the cell cycle were examined. ASS was unchanged by ADI plus IR, but p21 (a CDK inhibitor) was upregulated and c-Myc downregulated. These findings indicate that changes in the expressions of cell cycle proteins are involved in the enhancement of radiosensitivity by ADI. We suggest that ADI is a potential adjunct to cancer therapy.

Gamma-irradiation enhances RECK protein levels in Panc-1 pancreatic cancer cells.

Radiotherapy is an important treatment for many malignant tumors, but there are recent reports that radiation may increase the malignancy of cancer cells by stimulating expression of type IV collagenases. In this study, we examined changes in matrix metalloproteinase (MMP) inhibitors, such as the tissue inhibitors of metalloproteinase (TIMP)-1, TIMP-2 and RECK, in response to irradiation in Panc-1 pancreatic cancer cells. Irradiation increased RECK protein levels but not mRNA levels, whereas no significant changes were found in TIMP-1 and TIMP-2. The enhanced RECK protein levels were associated with an increase in MMP inhibitory activity. However, irradiation slightly but reproducibly increased the invasiveness of the Panc-1 cells. Like irradiation, treatment of Panc-1 cells with transforming growth factor (TGF)-Beta1 led to a 2-fold increase in RECK protein levels. Transient transfection with Smad3 also increased RECK protein levels, but transfection with Smad7 markedly reduced them. Stable expression of Smad7 and treatment with SB431542, an inhibitor of TGF-Beta receptor I kinase, abolished TGF-Beta1- and radiation-mediated effects on RECK. Furthermore, irradiation increased levels of phosphorylated Smad3. We conclude that radiation post-transciptionally enhances RECK protein levels in Panc-1 cells, at least in part, via TGF-Beta signaling, and that irradiation increases Panc-1 invasiveness via a mechanism that may not be linked to MMP-2 activity.

MicroRNA-196b enhances the radiosensitivity of SNU-638 gastric cancer cells by targeting RAD23B.

Gastric cancer is characterized by resistance to ionizing radiation. The development of resistance to radiotherapy in gastric cancer patients is one of the obstacles to effective radiotherapy. MicroRNAs are small well-conserved non-coding RNA species that regulate post-transcriptional activation. Our study aimed to investigate the role of miR-196b in radiation-induced gastric cancer. In the present study, we found that miR-196b expression was significantly reduced following radiation. The ectopic miR-196b expression sensitized SNU-638 gastric cancer cells and increased γ-H2AX foci upon radiation treatment. Bioinformatics analysis suggested that the DNA repair protein RAD23B was a putative target gene of miR-196b. Overexpression of miR-196b suppressed RAD23B expression in SNU-638 cells. Reporter assays further showed that miR-196b inhibited RAD23B 3'-UTR luciferase activity. Knockdown of RAD23B by small interfering RNA transfection closely mimicked the outcomes of miR-196b transfection, leading to impaired DNA damage repair in gastric cancer cells. Our results show that miR-196b improved radiosensitivity of SNU-638 cells by targeting RAD23B. Our data indicate that miR-196b is a potential target to enhance the effect of radiation treatment on gastric cancer cells. These findings will provide evidence for a new therapeutic target in radiotherapy.

SIRT1 promotes DNA repair activity and deacetylation of Ku70.

Human SIRT1 controls various physiological responses including cell fate, stress, and aging, through deacetylation of its specific substrate protein. In processing DNA damage signaling, SIRT1 attenuates a cellular apoptotic response by deacetylation of p53 tumor suppressor. The present study shows that, upon exposure to radiation, SIRT1 could enhance DNA repair capacity and deacetylation of repair protein Ku70. Ectopically over-expressed SIRT1 resulted in the increase of repair of DNA strand breakages produced by radiation. On the other hand, repression of endogenous SIRT1 expression by SIRT1 siRNA led to the decrease of this repair activity, indicating that SIRT1 can regulate DNA repair capacity of cells with DNA strand breaks. In addition, we found that SIRT1 physically complexed with repair protein Ku70, leading to subsequent deacetylation. The dominant-negative SIRT1, a catalytically inactive form, did not induce deacetylation of Ku70 protein as well as increase of DNA repair capacity. These observations suggest that SIRT1 modulates DNA repair activity, which could be regulated by the acetylation status of repair protein Ku70 following DNA damage.

Mutation analysis of p31comet gene, a negative regulator of Mad2, in human hepatocellular carcinoma.

Failure of mitotic checkpoint machinery leads to the chromosomal missegregation and nuclear endoreduplication, thereby driving the emergence of aneuploidy and tetraploidy population. Although abnormal nuclear ploidy and the resulting impairment of mitotic checkpoint function are typical physiological event leading to human hepatocellular carcinoma, any mutational change of mitotic checkpoint regulators has not yet been discovered. Therefore, we investigated the mutation of p31(comet), a recently identified mitotic checkpoint regulator, in human hepatocellular carcinoma. Of 51 human hepatocellular carcinoma tissue and 6 cell lines tested, five samples exhibited nucleotide sequence variations dispersed on four sites within the entire coding sequence. Among these sites with sequence substitutions, three were found to be missense mutation accompanied with amino acid change but one was a silent mutation. Of these sequence substitutions, two were present in both tumor and non-tumor liver tissues, suggesting the possibility of polymorphism. The present findings indicate that p31(comet) does not have an impact on the formation of aneuploidy and tetraploidy found in human hepatocellular carcinoma.

Chromosomal end fusion resulting from telomere erosion increases susceptibility to radiation via multinucleation: effect of p53.

Loss of p53 tumor suppressor facilitates acquisition of telomerase activity. In fact, both p53 inactivation and telomerase activation are frequently found in human cancers. p53 inactivation, however, eliminates or attenuates the biological responses to telomerase inhibition and the eventual telomere erosion. We show that telomere erosion can increase the susceptibility to radiation, irrespective of p53 status. Both telomerase inhibition and critically shortened telomere with significant change of chromosomal end-to-end fusion were essential for the enhancement of radiosensitivity. The enhancement was correlated with greater formation of multinucleated cells. p53 inactivation did not eliminate the observed generation of chromosomal fusion and multinucleation, and the resulting increased susceptibility to radiation, as opposed to the previously proved role of p53 in mediating cellular responses to telomere dysfunction. The present findings suggest the importance of chromosomal end fusion in modulating radiosensitivity rather than p53 DNA damage signaling. Thus, the suggested anticancer radiotherapeutic strategy combined with telomerase inhibition could clinically be applicable to cancers, irrespective of p53 status.

Decreased expression of DNA repair proteins Ku70 and Mre11 is associated with aging and may contribute to the cellular senescence.

The gradual loss of telomeric DNA can contribute to replicative senescence and thus, having longer telomeric DNA is generally considered to provide a longer lifespan. Maintenance and stabilization of telomeric DNA is assisted by binding of multiple DNA-binding proteins, including those involved in double strand break (DSB) repair. We reasoned that declining DSB repair capacity and increased telomere shortening in aged individuals may be associated with decreased expression of DSB repair proteins capable of telomere binding. Our data presented here show that among the DSB repair proteins tested, only the expression of Ku70 and Mre11 showed statistically significant age-dependent changes in human lymphocytes. Furthermore, we found that expressions of Ku70 and Mre11 are statistically correlated, which indicate that the function of Ku70 and Mre11 may be related. All the other DSB repair proteins tested, Sir2, TRF1 and Ku80, did not show any significant differences upon aging. In line with these data, people who live in the regional community (longevity group), which was found to have statistically longer average life span than the rest area, shows higher level of Ku70 expression than those living in the neighboring control community. Taken together, our data show, for the first time, that Ku70 and Mre11 may represent new biomarkers for aging and further suggest that maintenance of higher expression of Ku70 and Mre11 may be responsible for keeping longer life span observed in the longevity group.

Genome-wide expression profiling of 8-chloroadenosine- and 8-chloro-cAMP-treated human neuroblastoma cells using radioactive human cDNA microarray.

Previous reports raised question as to whether 8-chloro-cyclic adenosine 3,5-monophosphate (8-Cl-cAMP) is a prodrug for its metabolite, 8-Cl-adenosine which exerts growth inhibition in a broad spectrum of cancer cells. The present study was carried out to clarify overall cellular affects of 8-Cl-cAMP and 8-Cl-adenosine on SK-N-DZ human neuroblastoma cells by systematically characterizing gene expression using radioactive human cDNA microarray. Microarray was prepared with PCR-amplified cDNA of 2,304 known genes spotted on nylon membranes, employing (33)P-labeled cDNAs of SK-N-DZ cells as a probe. The expression levels of approximately 100 cDNAs, representing about 8% of the total DNA elements on the array, were altered in 8-Cl-adenosine- or 8-Cl-cAMP-treated cells, respectively. The genome-wide expression of the two samples exhibited partial overlaps; different sets of up-regulated genes but the same set of down-regulated genes. 8-Cl-adenosine treatment up-regulated genes involved in differentiation and development (LIM protein, connexin 26, neogenin, neurofilament triplet L protein and p21(WAF1/CIP1)) and immune response such as natural killer cells protein 4, and down-regulated ones involved in proliferation and transformation (transforming growth factor-beta, DYRK2, urokinase-type plasminogen activator and proteins involved in transcription and translation) which were in close parallel with those by 8-Cl-cAMP. Our results indicated that the two drugs shared common genomic pathways for the down-regulation of certain genes, but used distinct pathways for the up-regulation of different gene clusters. Based on the findings, we suggest that the anti-cancer activity of 8-Cl-cAMP results at least in part through 8-Cl-adenosine. Thus, the systematic use of DNA arrays can provide insight into the dynamic cellular pathways involved in anticancer activities of chemotherapeutics.

Increased methylation of the cytosolic 20-kD protein is accompanied by liver regeneration in a hepatectomized rat.

Arginine methylation has been implicated in the signal transduction pathway leading to cell growth. Here we show that a regenerating rat liver following partial hepatectomy exhibited elevated methyltransferase activity as shown by increased methylation of a subset of endogenous proteins in vitro. The 20-kDa protein was shown to be a major cytosolic protein undergoing methylation in regenerating hepatocytes. Methylation of the 20-kDa protein peaked at 1 d following partial hepatectomy, which gradually declined to a basal level within the next 14 d. Likewise, methylation of exogenously added bulk histones followed the similar time kinetics as the 20-kDa protein, reflecting time-dependent changes in methyltransferase activity in regenerating hepatocytes. Presence of exogenously added bulk histone in the in vitro methylation assay resulted in dose-dependent inhibition of methylation of the 20-kDa protein. All the histone subtypes tested, histone 1, 2A, 2B, 3 or 4, were able to inhibit methylation of the 20-kDa protein while addition of cytochrome C, a-lactalbumin, carbonic anhydrase, bovine serum albumin, and g globulin minimally affected methylation of the 20-kDa protein. Since methylation of the 20-kDa protein preceded proliferation of hepatocytes upon partial hepatectomy, it is tempting to speculate that the methylated 20-kDa protein by activated histone-specific methyltransferase may be involved in an early signal critical for liver regeneration.

The nuclear 16-kD protein methylation increases in the early period of liver regeneration in a hepatectomized rat.

Methylation events play a critical role in various cellular processes including regulation of gene transcription and proliferation. We observed that methyltransferase activity underwent time-dependent changes in the cytosol of the rat hepatocytes upon partial hepatectomy. However,any change in the methylation of nuclear proteins is not clear during hepatocyte proliferation. The nuclear fraction possesses basal level of methyltransferase to catalyze methylation of several proteins ranging from 7 to 70 kD prior to any hepatecmony. The specific p16 (16 kD)band was transiently and heavily methylated post 1 day hepatectomy, and then became non-detectable, but not in the control liver. Methylation of p16 band was completely inhibited by exogenously added histones, particularly 2AS, 1,2A and 2B subtypes. The methylated p16 protein remains stable in either acid or alkali- induced demethylation conditions, indicating that methylation is not likely to occur on isoaspartyl or C-terminal cysteinyl residues. Exogenous addition of non-hydrolyzable GTP caused a dose-dependent suppression of a p16 methylation suggesting that G-proteins might play a role as an endogenous methylation inhibitor in vivo. Taken together, we have identified the proliferation event associated-methylation of the nuclear p16 protein in the hepatocytes undergoing liver regeneration.

Gene expression profiling of oxidative stress on atrial fibrillation in humans.

Atrial Fibrillation (AF) is thought be caused by oxidative stress. Oxidative stress at the cellular level results from many factors, including exposure to alcohol, medications, cold, toxins or radiation. In this study we investigated gene transcriptional profiles on the human myocardial tissues from AF and oxidative stress conditions. Right atrial appendages were obtained from AF patients (n = 26) undergoing the Maze procedure, and from control patients (n = 26) who were in normal sinus rhythm and undergoing coronary artery bypass graft operation. To examine the effects of oxidative stress on AF, we used radioactive complementary DNA (cDNA) microarrays to evaluate changes in the expression of 1,152 known genes. This technology, which monitors thousands of genes simultaneously, gives us a better picture of the interactions between AF and oxidative stress. Total RNAs prepared from the retrieved tissues were used to synthesize 33P-labeled cDNAs by reverse transcription and hybridized to cDNA microarrays. Gene expression profiles showed that 30 genes were upregulated and 25 were downregulated in AF patients compared with control patients. Moreover, comparison rank analysis revealed that the expression of five genes related to reactive oxygen species (ROS)-including flavin containing monooxygenase 1, monoamine oxidase B, ubiquitin specific protease 8, tyrosinase-related protein 1, and tyrosine 3-monooxygenase-increased by more than 2.0 of the Z-ratio, and two genes related to antioxidants including glutathione peroxidase 1, and heme oxygenase 2-decreased to the Z-ratio levels of < or = -2.0. Apparently, a balanced regulation of pro- and anti-oxidation can be shifted toward pro-oxidation and can result in serious damage similar to that of human AF. Western blotting analysis confirmed the upregulation of tyrosinase-related protein 1 and tyrosine 3-monooxygenase and the downregulation of heme oxygenase 2. These results suggested that the gene expression pattern of myocardial tissues in AF patients can be associated with oxidative stress, resulting in a significant increase in ROS. Thus, the cDNA microarray technique was useful for investigating transcription profiles in AF. It showed that the intracellular mechanism of oxidative stress plays a pivotal role in the pathologic progression of AF and offers novel insight into potential treatment with antioxidants.

Induction of adaptive response by low-dose radiation in RIF cells transfected with Hspb1 (Hsp25) or inducible Hspa (Hsp70).

An adaptive response results in a reduced effect of a high challenging dose of a stressor after a smaller, inducing dose has been applied a few hours earlier. Radiation-induced fibrosarcoma (RIF) cells did not show an adaptive response, i.e. a reduced effect from a high challenging dose (2 Gy) of a radiation after a priming dose (1 cGy) had been applied 4 or 7 h earlier, but cells of a thermoresistant clone (TR) derived from RIF cells did. Since the expression of inducible Hspa (also known as Hsp70) and Hspb1 (also known as Hsp25) was different in these two cell lines, the role of inducible Hspa and Hspb1 in the adaptive response was examined. When RIF cells were transfected with inducible Hspa or Hspb1, both radioresistance measured by clonogenic assays and a reduction of apoptosis were detected. The adaptive response was also acquired by these two cell lines. The inducible Hspa transfectant showed a more pronounced adaptive response than the Hspb1 transfectant. Based on these results, it appears that inducible Hspa and Hspb1 are at least partly responsible for the induction of the adaptive response in these cells. Moreover, when inducible Hspa or Hspb1 was transfected into RIF cells, co-regulation of the two genes was detected. Heat-shock factor (Hsf) was found to be at least partially responsible for the induction of the adaptive response in these cells.