No abstract

DNA topoisomerase II (TOP2) cleavable complexes represent an unusual type of DNA damage characterized by reversible TOP2-DNA cross-links and DNA double strand breaks. Many antitumor drugs and physiological stresses are known to induce TOP2 cleavable complexes leading to apoptotic cell death and genomic instability. However, the molecular mechanism(s) for repair of TOP2 cleavable complexes remains unclear. In the current studies, we show that TOP2 cleavable complexes induced by the prototypic TOP2 poison VM-26 are proteolytically degraded by the ubiquitin/26 S proteasome pathway. Surprisingly the TOP2␤ isozyme is preferentially degraded over TOP2␣ isozyme. In addition, transcription inhibitors such as 5,6-dichlorobenzimidazole riboside and camptothecin can substantially block VM-26-induced TOP2␤ degradation. These results are consistent with a model in which the repair of TOP2␤ cleavable complexes may involve transcription-dependent proteolysis of TOP2␤ to reveal the protein-concealed double strand breaks.DNA topoisomerases are double-edged swords. They are essential for many important processes of DNA such as DNA replication, RNA transcription, chromosome condensation/decondensation, and chromosome segregation (1). However, due to their delicate act on DNA, they are also highly vulnerable to xenobiotics and physiological stresses to produce topoisomerase-mediated DNA damage, mostly in the form of topoisomerase cleavable complexes (2-5). So far, five human DNA topoisomerases, topoisomerase I (TOP1), 1 TOP2␣, TOP2␤, TOP3␣, and TOP3␤, have been identified and characterized, and the first three have been demonstrated to be important molecular targets for antitumor drugs (1, 6 -10).Both hTOP2 isozymes have been demonstrated to be the cellular targets for many clinically useful anticancer drugs such as VP-16 (etoposide) and doxorubicin (11-13). In the presence of these TOP2-directed drugs (TOP2 poisons), TOP2 isozymes are trapped as their covalent reaction intermediates, the reversible TOP2 cleavable complexes in which each TOP2 subunit is covalently linked to the 5Ј-phosphoryl ends of the four-base staggered double strand breaks (14,15). While the double strand breaks within the TOP2 cleavable complexes are normally concealed by TOP2, many of the cellular effects of TOP2 cleavable complexes are clearly indicative of DNA damage. For example, TOP2 cleavable complexes induced by TOP2 poisons are known to induce DNA damage responses (e.g. G 2 arrest, elevation of sister-chromatid exchanges, NFB activation, and p53 stabilization) (16 -19). DNA repair mutant cells (e.g. ataxia telangiectasia, progeroid Werner's syndrome, and Rad52) are also known to be hypersensitive to TOP2 poisons (20 -22). However, how TOP2-concealed DNA strand breaks are converted to DNA damage signals is still unknown. Inhibitor studies have suggested that both DNA replication and RNA transcription may be important for processing TOP2 cleavable complexes into DNA damage signals (23-25).Repair of topoisomerase cleavable complexes is conceptually challe...

Long-term cytokine-mediated inflammation is a risk factor for obesity and type 2 diabetes mellitus (T2DM). Our previous studies reveal significant associations between promoter single nucleotide polymorphisms (SNPs) of interleukin (IL)-4 and T2DM, as well as between SNPs in genes encoding IL-4/IL-4 receptor and high density lipoproteins. Our animal study reveals that IL-4 regulates glucose/lipid metabolism by promoting glucose tolerance and inhibiting lipid deposits. The above results strongly suggest the involvement of IL-4 in energy homeostasis. In the present study, we focus on examining the regulatory mechanism of IL-4 to lipid metabolism. Our results show that IL-4 inhibits adipogenesis by downregulating the expression of peroxisome proliferator-activated receptor-γ and CCAAT/enhancer-binding protein-α. Additionally, IL-4 promotes lipolysis by enhancing the activity and translocation of hormone sensitive lipase (HSL) in mature adipocytes, which suggests that IL-4 plays a pro-lipolytic role in lipid metabolism by boosting HSL activity. Our results demonstrate that IL-4 harbors pro-lipolysis capacity by inhibiting adipocyte differentiation and lipid accumulation as well as by promoting lipolysis in mature adipocytes to decrease lipid deposits. The above findings uncover the novel roles of IL-4 in lipid metabolism and provide new insights into the interactions among cytokine/immune responses, insulin sensitivity, and metabolism.

In decerebrate, vagotomized, paralyzed, and ventilated cats, phrenic and respiratory-related hypoglossal discharges were evident at normocapnic normoxia or hyperoxia. Both increased progressively in hypercapnia or hypoxia. With increasing drive, onset of inspiratory hypoglossal activity began earlier relative to phrenic onset; an early expiratory hypoglossal burst was also observed. Following subanesthetic doses of chloralose, halothane, ketamine, or pentobarbital, hypoglossal activity was depressed much more than phrenic discharge. In moderate hypercapnia or hypoxia, phrenic activity increased more than hypoglossal, whereas, at high drive, the latter rose more sharply in some cats. Electromyograms of the diaphragm and genioglossus were recorded in intact awake cats to determine if their responses and those of decerebrates are comparable. Respiratory-related genioglossal discharge was evident in normocapnia. We conclude that anesthesia suppresses hypoglossal motor activities much more than those of the bulbospinal-phrenic system. Data for decerebrate cats and unanesthetized cats or humans provide no evidence of a differential distribution of chemoreceptor afferents on hypoglossal and bulbospinal-phrenic neurons, as suggested by results in anesthetized animals.

It has been proposed that the topoisomerase II (TOP2)␤-DNA covalent complex arrests transcription and triggers 26S proteasome-mediated degradation of TOP2␤. It is unclear whether the initial trigger for proteasomal degradation is due to DNA damage or transcriptional arrest. In the current study we show that the TOP2 catalytic inhibitor 4,4-(2,3-butanediyl)-bis(2,6-piperazinedione) (ICRF-193), which traps TOP2 into a circular clamp rather than the TOP2-DNA covalent complex, can also arrest transcription. Arrest of transcription, which is TOP2␤-dependent, is accompanied by proteasomal degradation of TOP2␤. Different from TOP2 poisons and other DNA-damaging agents, ICRF-193 did not induce proteasomal degradation of the large subunit of RNA polymerase II. These results suggest that proteasomal degradation of TOP2␤ induced by the TOP2-DNA covalent complex or the TOP2 circular clamp is due to transcriptional arrest but not DNA damage. By contrast, degradation of the large subunit of RNA polymerase II is due to a DNA-damage signal.

Chronic infection with hepatitis B virus (HBV) often causes chronic inflammation of the liver with an increased incidence of hepatocellular carcinoma (HCC). HBV-infected individuals may also have an increased incidence of nonliver cancers. Taking statin or metformin may decrease inflammation and infiltration, which may, as a result, reduce the risk of liver cancer or other major cancers in patients with HBV infection. The purpose of this study was to evaluate the hypothesis that statin and metformin could reduce the incidence of liver cancer (HCC) or nonliver cancers in patients with HBV.Using the Taiwan Longitudinal Health Insurance Database 2000 to 2008, this cohort study comprised patients with a recorded diagnosis of HBV (N = 71,847) between January 1, 2000 and December 31, 2008. Each patient was followed-up until the end of 2008. The occurrence of HCC or a nonliver cancer was evaluated in patients who either were or were not taking statin or metformin. Cox proportional hazard regressions were used to evaluate the cancer incidence after adjusting for known confounding factors.In total, 71,824 HBV-infected patients comprised the study cohort. Our study showed that either metformin or statin use was associated with a reduction in the incidence of cancer. This was most prominent in patients taking both statin and metformin. The adjusted hazard ratios (HRs) for patients using only statin were 0.52 (95% confidence interval [CI], 0.48–0.57) for all cancers, 0.28 (95% CI, 0.23–0.35) for liver cancer, and 0.63 (95% CI, 0.57–0.70) for nonliver cancers. Patients taking only metformin had risk-adjusted HRs of 0.82 (95% CI, 0.75–0.90) for all cancers, 0.97 (95% CI, 0.84–1.14) for liver cancer, and 0.75 (95% CI, 0.67–0.84) for nonliver cancers. A dose-dependent effect of statin use for chemoprevention was observed for all cancers, including both liver cancer and nonliver cancers. A dose-dependent effect of metformin was also seen in liver cancer and nonliver cancers without stratification into different cumulative daily doses of statin use.This population-based cohort study investigated the protective effect of statin and metformin against cancer events in patients with HBV infection. Our study demonstrated that either statin or metformin served as independent chemopreventive agents with a dose–response effect in reducing the incidence of cancer with a dose–response effect of the agents and an additive or synergistic effect of combining statin and metformin use in reducing the incidence of many cancers.

DNA tests in normal subjects and patients with ataxia and Parkinson's disease (PD) were carried out to assess the frequency of spinocerebellar ataxia (SCA) and to document the distribution of SCA mutations underlying ethnic Chinese in Taiwan. MJD/SCA3 (46%) was the most common autosomal dominant SCA in the Taiwanese cohort, followed by SCA6 (18%) and SCA1 (3%). No expansions of SCA types 2, 10, 12, or dentatorubropallidoluysian atrophy (DRPLA) were detected. The clinical phenotypes of these affected SCA patients were very heterogeneous. All of them showed clinical symptoms of cerebellar ataxia, with or without other associated features. The frequencies of large normal alleles are closely associated with the prevalence of SCA1, SCA2, MJD/SCA3, SCA6, and DRPLA among Taiwanese, Japanese, and Caucasians. Interestingly, abnormal expansions of SCA8 and SCA17 genes were detected in patients with PD. The clinical presentation for these patients is typical of idiopathic PD with the following characteristics: late onset of disease, resting tremor in the limbs, rigidity, bradykinesia, and a good response to levodopa. This study appears to be the first report describing the PD phenotype in association with an expanded allele in the TATA-binding protein gene and suggests that SCA8 may also be a cause of typical PD.

This study was designed to examine respiratory-related hypoglossal nerve activity in response to activation of pulmonary C-fibers by capsaicin. Rats were anesthetized with urethane (1.2 g/kg, i.p.). Tracheostomy was performed. Catheters were introduced into the femoral vein and artery. Another catheter was placed near the entrance of the right atrium via the right jugular vein. Rats were paralyzed with gallamine triethiodide (5 mg/kg, i.v.), and ventilated artificially. Activities of the phrenic nerve (PNA) and the hypoglossal nerve (HNA) were recorded simultaneously. Varied doses of capsaicin (0.625, 1.25, and 5 µg/kg) were delivered into the right atrium to activate pulmonary C-fibers. Before bilateral vagotomy, apnea, decreases in PNA and HNA were observed in response to pulmonary C-fiber activation by the low and moderate doses of capsaicin. The high dose of capsaicin evoked an increase in PNA, an immediate tonic discharge of the hypoglossal nerve, and a decrease in phasic HNA. The onset time of HNA preceding PNA was abolished and replaced by a time lagged pattern as pulmonary C-fibers were activated. Raising CO₂ concentration did not attenuate the inhibitory effect of pulmonary C-fiber activation upon PNA and HNA. After bilateral sectioning of the vagi, administration of the moderate dose of capsaicin to activate non-vagal C-fibers produced increases in PNA and HNA. These results suggest that pulmonary vagal C-fiber activation may narrow the diameter at the oropharyngeal level by a decrease in phasic HNA, which may be disadvantageous for the maintenance of a patent upper airway.