Combined action of extracellular signal-regulated kinase and p38 kinase rescues Molt4 T cells from nitric oxide-induced apoptotic and necrotic cell death

Regulatory Differences in Natal Down Development between Altricial Zebra Finch and Precocial Chicken

Birds can be classified into altricial and precocial. The hatchlings of altricial birds are almost naked, whereas those of precocial birds are covered with natal down. This regulatory divergence is thought to reflect environmental adaptation, but the molecular basis of the divergence is unclear. To address this issue, we chose the altricial zebra finch and the precocial chicken as the model animals. We noted that zebra finch hatchlings show natal down growth suppressed anterior dorsal (AD) skin but partially down-covered posterior dorsal (PD) skin. Comparing the transcriptomes of AD and PD skins, we found that the feather growth promoter SHH (sonic hedgehog) was expressed higher in PD skin than in AD skin. Moreover, the data suggested that the FGF (fibroblast growth factor)/Mitogen-activated protein kinase (MAPK) signaling pathway is involved in natal down growth suppression and that FGF16 is a candidate upstream signaling suppressor. Ectopic expression of FGF16 on chicken leg skin showed downregulation of SHH, upregulation of the feather growth suppressor FGF10, and suppression of feather bud elongation, similar to the phenotype found in zebra finch embryonic AD skin. Therefore, we propose that FGF16-related signals suppress natal down elongation and cause the naked AD skin in zebra finch. Our study provides insights into the regulatory divergence in natal down formation between precocial and altricial birds.

(-)-Epigallocatechin-3-gallate protects against NO-induced ototoxicity through the regulation of caspase- 1, caspase-3, and NF-κB activation

Excessive nitric oxide (NO) production is toxic to the cochlea and induces hearing loss. However, the mechanism through which NO induces ototoxicity has not been completely understood. The aim of this study was to gain further insight into the mechanism mediating NO-induced toxicity in auditory HEI-OC1 cells and in ex vivo analysis. We also elucidated whether and how epigallocatechin-3-gallate (EGCG), the main component of green tea polyphenols, regulates NO-induced auditory cell damage. To investigate NO-mediated ototoxicity, S-nitroso-N-acetylpenicillamine (SNAP) was used as an NO donor. SNAP was cytotoxic, generating reactive oxygen species, releasing cytochrome c, and activating caspase-3 in auditory cells. NO-induced ototoxicity also mediated the nuclear factor (NF)-κB/caspase-1 pathway. Furthermore, SNAP destroyed the orderly arrangement of the 3 outer rows of hair cells in the basal, middle, and apical turns of the organ of Corti from the cochlea of Sprague-Dawley rats at postnatal day 2. However, EGCG counteracted this ototoxicity by suppressing the activation of caspase-3/NF-κB and preventing the destruction of hair cell arrays in the organ of Corti. These findings may lead to the development of a model for pharmacological mechanism of EGCG and potential therapies against ototoxicity.

Dose-dependent dual effect of HTLV-1 tax oncoprotein on p53-dependent nucleotide excision repair in human T-cells

In this study we investigated the effect of Tax on nucleotide excision repair (NER) in human T-cell lines by using the host cell repair analysis of UVC-irradiated reporter plasmid. This analysis revealed a p53-dependent NER activity in wild type (w.t.) p53-containing T-cells and p53-independent NER in w.t. p53-lacking T-cells. Notably, in the w.t. p53-containing cells Tax exerted a dose-dependent dual effect on NER. While low Tax doses markedly stimulated this repair, high Tax doses strongly reduced it. Further experiments demonstrated that the low Tax doses enhanced, in these cells, the level and the transcriptional function of their w.t. p53 protein. On the other hand, although the high Tax doses further increased the level of p53, they functionally inactivated its accumulating molecules. Both of these Tax effects on p53 proved to be mediated by Tax-induced NF-kappaB-related mechanisms. Together, these data suggest that by NF-kappaB activation Tax elevates the level of the cellular w.t. p53. However, while at low Tax doses the elevating w.t. p53 molecules are functionally active and capable of stimulating NER, intensifying further the NF-kappaB activation by the high Tax doses concomitantly evokes certain mechanism(s) which functionally inactivates the accumulating p53 protein. In contrast to this dual effect on the p53-dependent NER, Tax displayed only an inhibitory effect on the p53-independent NER by its high doses, whereas its low doses had no effect on this repair. The mechanisms of the NF-kappaB-associated effects on the level and function of the cellular w.t.p53 and of the p53-independent NER noted in our experimental systems are further investigated in our laboratory.

Iron chelator induces THP-1 cell differentiation potentially by modulating intracellular glutathione levels

Iron chelators have been implicated to modulate certain inflammatory mediators and regulate inflammatory processes. Here we report that iron chelator deferoxamine (DFO) induces differentiation of monocytic THP-1 cells into functional macrophages. DFO rapidly phosphorylated both extracellular signal-regulated kinase (ERK) and p38 kinase. Blockade of ERK signaling by the MEK1/2 inhibitor PD098059 abolished DFO-induced class A scavenger receptor (SR-A) expression and phagocytic activity, indicating that ERK cascades mediate the induction of THP-1 differentiation. In contrast, in cells treated with the p38 inhibitor SB203580 or transfected with the dominant-negative variant of p38 kinase, DFO-mediated ERK activation became more prominent, and the induction of SR-A expression and phagocytic activity were significantly increased. Interestingly, differentiation by DFO was associated with decrease in cellular glutathione (GSH) level. Both MAPK inhibitors did not influence the GSH level; however, treatment with ferric citrate (Fe3+) or N-acetyl-cysteine, a major precursor of GSH, markedly recovered GSH level to a normal extent, along with the significant decrease of differentiation. Collectively, these results indicate that oxidative stress by DFO and the resulting activation of ERK cascade play dominant roles in the process of THP-1 differentiation, while p38 acts as a negative signal transmitter.

A novel lignan composition from Cedrus deodara induces apoptosis and early nitric oxide generation in human leukemia Molt-4 and HL-60 cells

AP9-cd, a standardized lignan composition from Cedrus deodara consisting of (-)-wikstromal, (-)-matairesinol, and dibenzyl butyrolactol, showed cytotoxicity in several human cancer cell lines reported earlier. An attempt was made in this study to investigate the mechanism of cell death in human leukemia Molt-4 and HL-60 cells. It inhibited Molt-4 cell proliferation with 48-h IC(50) of approximately 15 microg/ml, increased sub-G0 cell fraction with no mitotic block, produced apoptotic bodies and induced DNA ladder formation. Flow cytometric analysis of annexinV-FITC/PI-stained cells showed time-related increase in apoptosis and post-apoptotic necrosis. All these biological end-points indicated cell death by apoptosis. Further, initial events involved massive nitric oxide (NO) formation within 4 h with subsequent late appearance of peroxides in cells; measured by flow cytometry using specific fluorescent probes. Persistently high levels of NO and peroxide appeared to decrease mitochondrial membrane potential (Psi(mt)) which was recovered by cyclosporin A in Molt-4 cells. AP9-cd caused 2-fold activation of caspase-3 in Molt-4 and 5-fold activation in HL-60 cells. Also caspases-8 and -9 were activated in HL-60 cells. Ascorbate suppressed the enhanced caspases activities indicating a pro-oxidant effect of AP9-cd. Further, caspase-3 activation correlated with NO generation that was partially impaired by nitric oxide synthase (NOS) inhibitors and ascorbate suggesting a role of pro-oxidant species in caspase-3 activation. AP9-cd produced no cytotoxicity in primary rat hepatocyte culture at the concentrations used. The studies indicated that AP9-cd mediated early NO formation leads to caspases activation, peroxide generation, and mitochondrial depolarization which may be responsible for mitochondrial-dependent and -independent apoptotic pathways involved in the killing of leukemia cells by AP9-cd.

Nitric oxide contributes to the development of a post-injury Th2 T-cell phenotype and immune dysfunction

Severe injury induces immune dysfunction resulting in increased susceptibility to opportunistic infections. Previous studies from our laboratory have demonstrated that post-burn immunosuppression is mediated by nitric oxide (NO) due to the increased expression of macrophage inducible nitric oxide synthase (iNOS). In contrast, others suggest that injury causes a phenotypic imbalance in the regulation of Th1- and Th2 immune responses. It is unclear whether or not these apparently divergent mediators of immunosuppression are interrelated. To study this, C57BL/6 mice were subjected to major burn injury and splenocytes were isolated 7 days later and stimulated with antiCD3. Burn injury induced NO-mediated suppression of proliferative responses that was reversed in the presence of the NOS inhibitor L-monomethyl-L-arginine and subsequently mimicked by the addition of the NO donor, S-nitroso-N-acetyl-penicillamine (SNAP). SNAP also dose-dependently suppressed IFN-gamma and IL-2 (Th1), but not IL-4 and IL-10 (Th2) production. Delaying the addition of SNAP to the cultures by 24 h prevented the suppression of IFN-gamma production. The Th2 shift in immune phenotype was independent of cGMP and apoptosis. The addition of SNAP to cell cultures also induced apoptosis, attenuated mitochondrial oxidative metabolism and induced mitochondrial membrane depolarization. However, these detrimental cellular effects of NO were observed only at supra-physiologic concentrations (>250 microM). In conclusion, these findings support the concept that NO induces suppression of cell-mediated immune responses by selective action on Th1 T cells, thereby promoting a Th2 response.

Hypoxia and serum deprivation-induced apoptosis in mesenchymal stem cells

In recent years, the understanding that regeneration progresses at the level of the myocardium has placed stem cell research at the center stage in cardiology. Despite an increasing interest in cell transplant research, relatively little is known about the biochemical regulation of the stem cell itself after transplantation into an ischemic heart. We demonstrated here, using rat mesenchymal stem cells (MSCs), that cells undergo caspase-dependent apoptosis in response to hypoxia and serum deprivation (SD), which are both components of ischemia in vivo. In particular, the treated cells exhibited mitochondrial dysfunction, including cytochrome C release, loss in DeltaPsim, and Bax accumulation, but in a p53-independent manner. Although the cells treated by hypoxia/SD possess the activity of caspase-8, zIEDT-fmk, a specific caspase-8 inhibitor, failed to inhibit cell apoptosis induced in our system. Taken together, our findings indicate that MSCs are sensitive to hypoxia/SD stimuli that involve changes in mitochondrial integrity and function but are potentially independent of caspase-8.