Essential role of caspase-8 in p53/p73-dependent apoptosis induced by etoposide in head and neck carcinoma cells

<p>Abstract</p> <p>Background</p> <p>Caspase-8 is a key upstream mediator in death receptor-mediated apoptosis and also participates in mitochondria-mediated apoptosis via cleavage of proapoptotic Bid. However, the role of caspase-8 in p53- and p73-dependent apoptosis induced by genotoxic drugs remains unclear. We recently reported that the reconstitution of procaspase-8 is sufficient for sensitizing cisplatin- but not etoposide-induced apoptosis, in chemoresistant and caspase-8 deficient HOC313 head and neck squamous cell carcinoma (HNSCC) cells.</p> <p>Results</p> <p>We show that p53/p73-dependent caspase-8 activation is required for sensitizing etoposide-induced apoptosis by utilizing HOC313 cells carrying a temperature-sensitive p53G285K mutant. Restoration of wild-type p53 function under the permissive conditions, together with etoposide treatment, led to substantial transcriptional activation of proapoptotic Noxa and PUMA, but failed to induce apoptosis. In addition to p53 restoration, caspase-8 reconstitution was needed for sensitization to etoposide-induced apoptosis, mitochondria depolarization, and cleavage of the procaspases-3, and -9. In etoposide-sensitive Ca9-22 cells carrying a temperature-insensitive mutant p53, siRNA-based p73 knockdown blocked etoposide-induced apoptosis and procaspase-8 cleavage. However, induction of p73 protein and up-regulation of Noxa and PUMA, although observed in Ca9-22 cells, were hardly detected in etoposide-treated HOC313 cells under non-permissive conditions, suggesting a contribution of p73 reduction to etoposide resistance in HOC313 cells. Finally, the caspase-9 inhibitor Ac-LEHD-CHO or caspase-9 siRNA blocked etoposide-induced caspase-8 activation, Bid cleavage, and apoptosis in both cell lines, indicating that p53/p73-dependent caspase-8 activation lies downstream of mitochondria.</p> <p>Conclusions</p> <p>we conclude that p53 and p73 can act as upstream regulators of caspase-8, and that caspase-8 is an essential mediator of the p53/p73-dependent apoptosis induced by etoposide in HNSCC cells. Our data suggest the importance of caspase-8-mediated positive feedback amplification in the p53/p73-dependent apoptosis induced by etoposide in HNSCC cells.</p

Electronic Structures of N-doped Graphene with Native Point Defects

Nitrogen doping in graphene has important implications in graphene-based devices and catalysts. We have performed the density functional theory calculations to study the electronic structures of N-doped graphene with vacancies and Stone-Wales defect. Our results show that monovacancies in graphene act as hole dopants and that two substitutional N dopants are needed to compensate for the hole introduced by a monovacancy. On the other hand, divacancy does not produce any free carriers. Interestingly, a single N dopant at divacancy acts as an acceptor rather than a donor. The interference between native point defect and N dopant strongly modifies the role of N doping regarding the free carrier production in the bulk pi bands. For some of the defects and N dopant-defect complexes, localized defect pi states are partially occupied. Discussion on the possibility of spin polarization in such cases is given. We also present qualitative arguments on the electronic structures based on the local bond picture. We have analyzed the 1s-related x-ray photoemission and adsorption spectroscopy spectra of N dopants at vacancies and Stone-Wales defect in connection with the experimental ones. We also discuss characteristic scanning tunneling microscope (STM) images originating from the electronic and structural modifications by the N dopant-defect complexes. STM imaging for small negative bias voltage will provide important information about possible active sites for oxygen reduction reaction.Comment: 40 pages, 2 tables, 16 figures. The analysis of Clar sextets is added. This version is published on PHYSICAL REVIEW B 87, 165401(2013

Constraints on a vacuum energy from both SNIa and CMB temperature observations

We investigate the cosmic thermal evolution with a vacuum energy which decays into photon at the low-redshift. We assume that the vacuum energy is a function of the scale factor that increases toward the early universe. We put on the constraints using recent observations of both type Ia supernovae (SNIa) by Union-2 compilation and the cosmic microwave background (CMB) temperature at the range of the redshift 0.01 < z < 3. From SNIa, we find that the effects of a decaying vacuum energy on the cosmic expansion rate should be very small but could be possible for z < 1.5. On the other hand, we obtain the severe constraints for parameters from the CMB temperature observations. Although the temperature can be still lower than the case of the standard cosmological model, it should only affect the thermal evolution at the early epoch.Comment: 9 pages, 3 figures, 1 tables, submitted to Advances in Astronom

Interplay between Nitrogen Dopants and Native Point Defects in Graphene

To understand the interaction between nitrogen dopants and native point defects in graphene, we have studied the energetic stability of N-doped graphene with vacancies and Stone-Wales (SW) defect by performing the density functional theory calculations. Our results show that N substitution energetically prefers to occur at the carbon atoms near the defects, especially for those sites with larger bond shortening, indicating that the defect-induced strain plays an important role in the stability of N dopants in defective graphene. In the presence of monovacancy, the most stable position for N dopant is the pyridinelike configuration, while for other point defects studied (SW defect and divacancies) N prefers a site in the pentagonal ring. The effect of native point defects on N dopants is quite strong: While the N doping is endothermic in defect-free graphene, it becomes exothermic for defective graphene. Our results imply that the native point defect and N dopant attract each other, i.e., cooperative effect, which means that substitutional N dopants would increase the probability of point defect generation and vice versa. Our findings are supported by recent experimental studies on the N doping of graphene. Furthermore we point out possibilities of aggregation of multiple N dopants near native point defects. Finally we make brief comments on the effect of Fe adsorption on the stability of N dopant aggregation.Comment: 10 pages, 5 figures. Figure 4(g) and Figure 5 are corrected. One additional table is added. This is the final version for publicatio

Antioxidant and antiproliferative activities of Malaysian sea cucumber, (Holothuria edulis Lesson), extracts

Sea cucumber is a marine invertebrate of the phylum Echinodermata and the class Holothuroidea that found on the sea floor worldwide. In Asia, many of sea cucumber species are considered as traditional food items and have been used in featment of numerous diseases such as eczema, arthritis and hypertension. Previous scientific studies have shown multiple biological activities of sea cucumber species as antinociceptive, antimicrobial and antifungal properties. This study was conducted to investigate the antioxidant and antiproliferative activities of aqueous and organic extracts from sea cucumber, Holothuria edulis. Two different free radical systems were used to evaluate antioxidant activity of H. edulis, stable radical l,l-diphenyl-2- picrylhydrazyl (DPPH.) and linoleic acid free radical mediated p-carotene bleaching. In addition, Folin-Ciocalteau reagent was used to determine the total phenolic content of the exfacts. The inhibitory effect of the exfacts on proliferation of MCF-7 (human breast adenocarcinoma) and TEI (Human esophageal squamous cell carcinoma) human cancer cell lines were demonstrated by 3-(4,5- dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Our data showed that the gallic acid equivalent (GAE) of the total phenolic content in aqueous extract (GAE : 7.33 mglg) is higher than an organic extact (GAE = 2.17 mglg). An aqueous extract also exhibited higher.antioxidant capacity by using DPPH assay (ICso = 2.04 mg/ml vs. 8.73 mlmL in organic extract), as well as by using p-carotene bleaching assay (Antioxidant Activity : 42.69 %o vs. 28.52 % in organic extract). On the other hand, an organic extact showed higher antiproliferative effect against MCF-7 and TEI cancer cells, giving ICso : 28.0 and 17.5 pdmL, respectively than aqueous extract, that gave ICso : 133.0 pilmL against MCF- '7 and76.0 pgmL against TEl. In conclusion, frndings of this study revealed that H. edulis as a promising source ofnatural antioxidants and anticancer products

Effect of X-Irradiation at Different Stages in the Cell Cycle on Individual Cell?Based Kinetics in an Asynchronous Cell Population

Using an asynchronously growing cell population, we investigated how X-irradiation at different stages of the cell cycle influences individual cell-based kinetics. To visualize the cellcycle phase, we employed the fluorescent ubiquitination-based cell cycle indicator (Fucci). After 5 Gy irradiation, HeLa cells no longer entered M phase in an order determined by their previous stage of the cell cycle, primarily because green phase (S and G2) was less prolonged in cells irradiated during the red phase (G1) than in those irradiated during the green phase. Furthermore, prolongation of the green phase in cells irradiated during the red phase gradually increased as the irradiation timing approached late G1 phase. The results revealed that endoreduplication rarely occurs in this cell line under the conditions we studied. We next established a method for classifying the green phase into early S, mid S, late S, and G2 phases at the time of irradiation, and then attempted to estimate the duration of G2 arrest based on certain assumptions. The value was the largest when cells were irradiated in mid or late S phase and the smallest when they were irradiated in G1 phase. In this study, by closely following individual cells irradiated at different cell-cycle phases, we revealed for the first time the unique cell-cycle kinetics in HeLa cells that follow irradiation

Distinct and overlapping roles of ARID3A and ARID3B in regulating E2F‑dependent transcription via direct binding to E2F target genes

The AT-rich interacting domain (ARID) family of DNA-binding proteins is involved in various biological processes, including the regulation of gene expression during cell proliferation, differentiation and development. ARID3A and ARID3B are involved in chromatin remodeling and can bind to E2F1 and retinoblastoma tumor suppressor protein(RB), respectively. However, their role in regulating E2F target gene expression remains poorly understood. E2F transcription factors are critical regulators of cell cycle progression and are modulated by RB. Herein, putative ARID3-binding sites (BSs) in E2F target genes were identified, including Cdc2, cyclin E1 and p107, and it was found that ARID3A and ARID3B bound to these BSs in living cells. The mutation of ARID3 BSs reduced Cdc2 promoter activity, while ARID3A and ARID3B overexpression increased the promoter activity, depending on both ARID3 and E2F BSs. ARID3B knockdown blocked the transcription of Cdc2, cyclin E1 and p107 in normal human dermal fibroblasts (NHDFs), whereas the effects of ARID3A knockdown varied depending on the target genes. ARID3B overexpression, but not that of ARID3A, upregulated the transcription of E2F target genes, and activated cyclin E1 transcription and induced cell death with E2F1 assistance. Finally, ARID3A and ARID3B knockdown attenuated the cell cycle progression of NHDFs and T98G cells, and suppressed tumor cell growth. On the whole, these results indicate that ARID3A and ARID3B play distinct and overlapping roles in E2F-dependent transcription by directly binding to the E2F target genes. The present study provides novel insight into the mechanisms underlying the E2F dysregulation caused by ARID3A and ARID3B overexpression, which may have a significant influence on the progression of tumorigenesis

A Single Nucleotide Polymorphism within the Acetyl-Coenzyme A Carboxylase Beta Gene Is Associated with Proteinuria in Patients with Type 2 Diabetes

It has been suggested that genetic susceptibility plays an important role in the pathogenesis of diabetic nephropathy. A large-scale genotyping analysis of gene-based single nucleotide polymorphisms (SNPs) in Japanese patients with type 2 diabetes identified the gene encoding acetyl-coenzyme A carboxylase beta (ACACB) as a candidate for a susceptibility to diabetic nephropathy; the landmark SNP was found in the intron 18 of ACACB (rs2268388: intron 18 +4139 C > T, p = 1.4×10−6, odds ratio = 1.61, 95% confidence interval [CI]: 1.33–1.96). The association of this SNP with diabetic nephropathy was examined in 9 independent studies (4 from Japan including the original study, one Singaporean, one Korean, and two European) with type 2 diabetes. One case-control study involving European patients with type 1 diabetes was included. The frequency of the T allele for SNP rs2268388 was consistently higher among patients with type 2 diabetes and proteinuria. A meta-analysis revealed that rs2268388 was significantly associated with proteinuria in Japanese patients with type 2 diabetes (p = 5.35×10−8, odds ratio = 1.61, 95% Cl: 1.35–1.91). Rs2268388 was also associated with type 2 diabetes–associated end-stage renal disease (ESRD) in European Americans (p = 6×10−4, odds ratio = 1.61, 95% Cl: 1.22–2.13). Significant association was not detected between this SNP and nephropathy in those with type 1 diabetes. A subsequent in vitro functional analysis revealed that a 29-bp DNA fragment, including rs2268388, had significant enhancer activity in cultured human renal proximal tubular epithelial cells. Fragments corresponding to the disease susceptibility allele (T) had higher enhancer activity than those of the major allele. These results suggest that ACACB is a strong candidate for conferring susceptibility for proteinuria in patients with type 2 diabetes