Cycloheximide suppresses radiation-induced apoptosis in MOLT-4 cells with Arg72 variant of p53 through translational inhibition of p53 accumulation

Chronic Oxidative Stress and Stress Granule Formation in UBQLN2 ALS Neurons: Insights into Neuronal Degeneration and Potential Therapeutic Targets

The pathogenesis of neurodegenerative diseases results from the interplay between genetic and environmental factors. Aging and chronic oxidative stress are critical contributors to neurodegeneration. UBQLN2, a ubiquitin-related protein, aids in protein degradation and protects against oxidative stress. In ALS neurons harboring UBQLN2 mutations, oxidative stress accelerates pathological changes, yet the precise mechanisms remain unclear. Using induced motor neurons (iMNs) derived from UBQLN2 P497H iPSCs, we observed ALS-like phenotypes, including TDP-43 mislocalization, increased cell death, and reduced viability. Sodium arsenite (SA)-induced oxidative stress triggered stress granule formation, while autophagy dysfunction exacerbated neuronal degeneration. CHX and bosutinib treatments reduced ubiquitinated protein accumulation and alleviated degeneration, highlighting potential therapeutic pathways. These findings emphasize the role of chronic oxidative stress and stress granule formation in UBQLN2 ALS, offering insights into novel therapeutic targets.

Antitumor activity of α-pinene in T-cell tumors

T-cell acute leukemia and lymphoma have a poor prognosis. Although new therapeutic agents have been developed, their therapeutic effects are suboptimal. α-Pinene, a monoterpene compound, has an antitumor effect on solid tumors; however, few comprehensive investigations have been conducted on its impact on hematologic malignancies. This report provides a comprehensive analysis of the potential benefits of using α-pinene as an antitumor agent for the treatment of T-cell tumors. We found that α-pinene inhibited the proliferation of hematologic malignancies, especially in T-cell tumor cell lines EL-4 and Molt-4, induced mitochondrial dysfunction and reactive oxygen species accumulation, and inhibited NF-κB p65 translocation into the nucleus, leading to robust apoptosis in EL-4 cells. Collectively, these findings suggest that α-pinene has potential as a therapeutic agent for T-cell malignancies, and further investigation is warranted.

A Novel RNA Synthesis Inhibitor, STK160830, Has Negligible DNA-Intercalating Activity for Triggering A p53 Response, and Can Inhibit p53-Dependent Apoptosis

RNA synthesis inhibitors and protein synthesis inhibitors are useful for investigating whether biological events with unknown mechanisms require transcription or translation; however, the dependence of RNA synthesis has been difficult to verify because many RNA synthesis inhibitors cause adverse events that trigger a p53 response. In this study, we screened a library containing 9600 core compounds and obtained STK160830 that shows anti-apoptotic effects in irradiated wild-type-p53-bearing human T-cell leukemia MOLT-4 cells and murine thymocytes. In many of the p53-impaired cells and p53-knockdown cells tested, STK160830 did not show a remarkable anti-apoptotic effect, suggesting that the anti-apoptotic activity is p53-dependent. In the expression analysis of p53, p53-target gene products, and reference proteins by immunoblotting, STK160830 down-regulated the expression of many of the proteins examined, and the downregulation correlated strongly with its inhibitory effect on cell death. mRNA expression analyses by qPCR and nascent RNA capture kit revealed that STK160830 showed a decreased mRNA expression, which was similar to that induced by the RNA synthesis inhibitor actinomycin D but differed to some extent. Furthermore, unlike other RNA synthesis inhibitors such as actinomycin D, p53 accumulation by STK160830 alone was negligible, and a DNA melting-curve analysis showed very weak DNA-intercalating activity, indicating that STK160830 is a useful inhibitor for RNA synthesis without triggering p53-mediated damage responses.

A Chemical Modulator of p53 Transactivation that Acts as a Radioprotective Agonist

Inhibiting p53-dependent apoptosis by inhibitors of p53 is an effective strategy for preventing radiation-induced damage in hematopoietic lineages, while p53 and p21 also play radioprotective roles in the gastrointestinal epithelium. We previously identified some zinc(II) chelators, including 8-quinolinol derivatives, that suppress apoptosis in attempts to discover compounds that target the zinc-binding site in p53. We found that 5-chloro-8-quinolinol (5CHQ) has a unique p53-modulating activity that shifts its transactivation from proapoptotic to protective responses, including enhancing p21 induction and suppressing PUMA induction. This p53-modulating activity also influenced p53 and p53-target gene expression in unirradiated cells without inducing DNA damage. The specificity of 5CHQ for p53 and p21 was demonstrated by silencing the expression of each protein. These effects seem to be attributable to the sequence-specific alteration of p53 DNA-binding, as evaluated by chromatin immunoprecipitation and electrophoretic mobility shift assays. In addition, 5-chloro-8-methoxyquinoline itself had no antiapoptotic activity, indicating that the hydroxyl group at the 8-position is required for its antiapoptotic activity. We applied this remarkable agonistic activity to protecting the hematopoietic and gastrointestinal system in mouse irradiation models. The dose reduction factors of 5CHQ in total-body and abdominally irradiated mice were about 1.2 and 1.3, respectively. 5CHQ effectively protected mouse epithelial stem cells from a lethal dose of abdominal irradiation. Furthermore, the specificity of 5CHQ for p53 in reducing the lethality induced by abdominal irradiation was revealed in Trp53-KO mice. These results indicate that the pharmacologic upregulation of radioprotective p53 target genes is an effective strategy for addressing the gastrointestinal syndrome. Mol Cancer Ther; 17(2); 432-42. ©2017 AACRSee all articles in this MCT Focus section, "Developmental Therapeutics in Radiation Oncology."

A Small Molecule Screen Exposes mTOR Signaling Pathway Involvement in Radiation-Induced Apoptosis

Individuals are at risk of exposure to acute ionizing radiation (IR) from a nuclear accident or terrorism, but we lack effective therapies to mitigate the lethal IR effects. In the current study, we exploited an optimized, cell-based, high throughput screening assay to interrogate a small molecule library comprising 3437 known pharmacologically active compounds for mitigation against IR-induced apoptosis. Thirty-three library compounds significantly reduced apoptosis when administered 1 h after 4 Gy IR. Two- or three-dimensional computational structural analyses of the compounds indicated only one or two chemical clusters with most of the compounds being unique structures. The mechanistic target of rapamycin complex 1 (mTORC1) inhibitor, rapamycin, was the most potent compound, and it mitigated apoptosis by 50% at 200 ± 50 pM. Other mTOR inhibitors, namely everolimus, AZD8055, and torin 1, also suppressed apoptosis, providing additional pharmacological evidence for mTOR pathway involvement in regulating cell death after IR. Everolimus and torin 1 treatment after IR decreased the S phase population and enforced both G1 and G2 phase arrest. This prorogation of cell cycle progression was accompanied by decreased IR-induced DNA damage measured by γH2AX phosphorylation at Ser139. RNA interference-mediated knockdown of the respective mTORC1 and mTORC2 subunits, Raptor or Rictor, also mitigated IR-induced apoptosis. Collectively, this study suggests a central role for the mTOR signaling in the cytotoxic response to IR and offers a useful platform to probe for additional agents.

Comparative cytotoxicity of chelidonine and homochelidonine, the dimethoxy analogues isolated from Chelidonium majus L. (Papaveraceae), against human leukemic and lung carcinoma cells

BACKGROUND

The search for new anticancer compounds is a crucial element of natural products research.

PURPOSE

In this study the effects of naturally occurring homochelidonine in comparison to chelidonine on cell cycle progression and cell death in leukemic T-cells with different p53 status are described.

METHODS

The mechanism of cytotoxic, antiproliferative, apoptosis-inducing effects and the effect on expressions of cell cycle regulatory proteins was investigated using XTT assay, Trypan blue exclusion assay, flow cytometry, Western blot analysis, xCELLigence, epi-fluorescence and 3D super resolution microscopy. A549 cells were used for xCELLigence, clonogenic assay and for monitoring microtubule stability.

RESULTS

We found that homochelidonine and chelidonine displayed significant cytotoxicity in examined blood cancer cells with the exception of HEL 92.1.7 and U-937 exposed to homochelidonine. Unexpectedly, homochelidonine and chelidonine-induced cytotoxicity was more pronounced in Jurkat cells contrary to MOLT-4 cells. Homochelidonine showed an antiproliferative effect on A549 cells but it was less effective compared to chelidonine. Biphasic dose-depended G1 and G2/M cell cycle arrest along with the population of sub-G1 was found after treatment with homochelidonine in MOLT-4 cells. In variance thereto, an increase in G2/M cells was detected after treatment with homochelidonine in Jurkat cells. Treatment with chelidonine induced cell cycle arrest in the G2/M cell cycle in both MOLT-4 and Jurkat cells. MOLT-4 and Jurkat cells treated with homochelidonine and chelidonine showed features of apoptosis such as phosphatidylserine exposure, a loss of mitochondrial membrane potential and an increase in the caspases -3/7, -8 and -9. Western blots indicate that homochelidonine and chelidonine exposure activates Chk1 and Chk2. Studies conducted with fluorescence microscopy demonstrated that chelidonine and homochelidonine inhibit tubulin polymerization in A549 cells.

CONCLUSION

Collectively, the data indicate that chelidonine and homochelidonine are potent inducers of cell death in cancer cell lines, highlighting their potential relevance in leukemic cells.

Evaluation of zinc (II) chelators for inhibiting p53-mediated apoptosis

In a previous study, we reported that sodium orthovanadate (vanadate) is the first known inhibitor that is capable of protecting mice from death from the radiation-induced gastrointestinal syndrome via its ability to block both transcription-dependent and transcription-independent p53 apoptotic pathways. In this paper, we report that vanadate has a unique activity for inducing the denaturation of p53 relative to other known radioprotective p53 inhibitors, pifithrin-α (PFTα) and pifithrin-µ (PFTµ). This potent radioprotective effect of vanadate prompted us to undertake a more extensive search for p53 inhibitors that can induce p53 denaturation. Based on the fact that p53 denaturation can be induced by the dissociation of a zinc ion, which is used as a structural factor of p53, we screened some zinc (II) chelators for the suppression of the DNA binding activity of p53 in vitro and the inhibition of radiation-induced p53-dependent apoptosis in MOLT-4 cells. The findings indicate that two of five zinc (II) chelators also suppressed apoptosis. Among the inhibitors tested, Bispicen (N,N'-Bis(2-pyridylmethyl)-1,2-ethanediamine) had the highest inhibition activity. A mechanistic study using cells bearing different p53 status or functions (i.e., p53-knockdown MOLT-4 transformant and its revertants, p53 mutant cells, p53-null cells), and p53-independent apoptotic stimuli revealed that the suppressive effect of Bispicen on apoptosis is specifically mediated through p53. Moreover, Bispicen, similar to vanadate, induces the denaturation of p53 as well as the blocking of both transcription-dependent and -independent apoptotic pathways. Our findings indicate that the use of zinc (II) chelators represent a new approach for protecting against radiation-induced p53-dependent apoptosis through the inhibition of p53-dependent apoptotic pathways.

AS-2, a novel inhibitor of p53-dependent apoptosis, prevents apoptotic mitochondrial dysfunction in a transcription-independent manner and protects mice from a lethal dose of ionizing radiation

In a previous study, we reported that some tetradentate zinc(II) chelators inhibit p53 through the denaturation of its zinc-requiring structure but a chelator, Bispicen, a potent inhibitor of in vitro apoptosis, failed to show any efficient radioprotective effect against irradiated mice because the toxicity of the chelator to mice. The unsuitability of using tetradentate chelators as radioprotectors prompted us to undertake a more extensive search for p53-inhibiting agents that are weaker zinc(II) chelators and therefore less toxic. Here, we show that an 8-hydroxyquinoline (8HQ) derivative, AS-2, suppresses p53-dependent apoptosis through a transcription-independent mechanism. A mechanistic study using cells with different p53 characteristics revealed that the suppressive effect of AS-2 on apoptosis is specifically mediated through p53. In addition, AS-2 was less effective in preventing p53-mediated transcription-dependent events than pifithrin-μ (PFTμ), an inhibitor of transcription-independent apoptosis by p53. Fluorescence visualization of the extranuclear distribution of AS-2 also supports that it is ineffective on the transcription-dependent pathway. Further investigations revealed that AS-2 suppressed mitochondrial apoptotic events, such as the mitochondrial release of intermembrane proteins and the loss of mitochondrial membrane potential, although AS-2 resulted in an increase in the mitochondrial translocation of p53 as opposed to the decrease of cytosolic p53, and did not affect the apoptotic interaction of p53 with Bcl-2. AS-2 also protected mice that had been exposed to a lethal dose of ionizing radiation. Our findings indicate that some types of bidentate 8HQ chelators could serve as radioprotectors with no substantial toxicity in vivo.

Radio-sensitization of human leukaemic MOLT-4 cells by DNA-dependent protein kinase inhibitor, NU7441

We studied the effect of pre-incubation with NU7441, a specific inhibitor of DNA-dependent protein kinase (DNA-PK), on molecular mechanisms triggered by ionizing radiation (IR). The experimental design involved four groups of human T-lymphocyte leukaemic MOLT-4 cells: control, NU7441-treated (1 μM), IR-treated (1 Gy), and combination of NU7441 and IR. We used flow cytometry for apoptosis assessment, Western blotting and ELISA for detection of proteins involved in DNA repair signalling and epifluorescence microscopy for detection of IR-induced phosphorylation of histone H2A.X. We did not observe any major changes in the amount of DNA-PK subunits Ku70/80 caused by the combination of NU7441 and radiation. Their combination led to an increased phosphorylation of H2A.X, a hallmark of DNA damage. However, it did not prevent up-regulation of neither p53 (and its phosphorylation at Ser 15 and 392) nor p21. We observed a decrease in the levels of anti-apoptotic Mcl-1, cdc25A phosphatase, cleavage of PARP and a significant increase in apoptosis in the group treated with combination. In conclusion, the combination of NU7441 with IR caused increased phosphorylation of H2A.X early after irradiation and subsequent induction of apoptosis. It was efficient in MOLT-4 cells in 10× lower concentration than the inhibitor NU7026. NU7441 proved as a potent radio-sensitizing agent, and it might provide a platform for development of new radio-sensitizers in radiotherapy.

Mitochondria are required for ATM activation by extranuclear oxidative stress in cultured human hepatoblastoma cell line Hep G2 cells

Ataxia-telangiectasia mutated (ATM) is a serine/threonine protein kinase that plays a central role in DNA damage response (DDR). A recent study reported that oxidized ATM can be active in the absence of DDR. However, the issue of where ATM is activated by oxidative stress remains unclear. Regarding the localization of ATM, two possible locations, namely, mitochondria and peroxisomes are possible. We report herein that ATM can be activated when exposed to hydrogen peroxide without inducing nuclear DDR in Hep G2 cells, and the oxidized cells could be subjected to subcellular fractionation. The first detergent-based fractionation experiment revealed that active, phosphorylated ATM was located in the second fraction, which also contained both mitochondria and peroxisomes. An alternative fractionation method involving homogenization and differential centrifugation, which permits the light membrane fraction containing peroxisomes to be produced, but not mitochondria, revealed that the light membrane fraction contained only traces of ATM. In contrast, the heavy membrane fraction, which mainly contained mitochondrial components, was enriched in ATM and active ATM, suggesting that the oxidative activation of ATM occurs in mitochondria and not in peroxisomes. In Rho 0-Hep G2 cells, which lack mitochondrial DNA and functional mitochondria, ATM failed to respond to hydrogen peroxide, indicating that mitochondria are required for the oxidative activation of ATM. These findings strongly suggest that ATM can be activated in response to oxidative stress in mitochondria and that this occurs in a DDR-independent manner.

Allele-specific behavior of molecular networks: understanding small-molecule drug response in yeast

The study of systems genetics is changing the way the genetic and molecular basis of phenotypic variation, such as disease susceptibility and drug response, is being analyzed. Moreover, systems genetics aids in the translation of insights from systems biology into genetics. The use of systems genetics enables greater attention to be focused on the potential impact of genetic perturbations on the molecular states of networks that in turn affects complex traits. In this study, we developed models to detect allele-specific perturbations on interactions, in which a genetic locus with alternative alleles exerted a differing influence on an interaction. We utilized the models to investigate the dynamic behavior of an integrated molecular network undergoing genetic perturbations in yeast. Our results revealed the complexity of regulatory relationships between genetic loci and networks, in which different genetic loci perturb specific network modules. In addition, significant within-module functional coherence was found. We then used the network perturbation model to elucidate the underlying molecular mechanisms of individual differences in response to 100 diverse small molecule drugs. As a result, we identified sub-networks in the integrated network that responded to variations in DNA associated with response to diverse compounds and were significantly enriched for known drug targets. Literature mining results provided strong independent evidence for the effectiveness of these genetic perturbing networks in the elucidation of small-molecule responses in yeast.

p53 codon 72 polymorphism and hematological cancer risk: an update meta-analysis

Background

Previous studies on the association of p53 codon 72 (Arg72Pro) polymorphism with hematological malignancies risk have produced conflicting results. The purpose of this meta-analysis is to define the effect of p53 Arg72Pro polymorphism on hematological malignancies risk.

Methodology/Principal Findings

Through searching PubMed databases (or hand searching) up to April 2012 using the following MeSH terms and keywords: “p53”, “codon 72” “polymorphism” and “leukemia”, or “lymphoma”, or “myeloma”, thirteen were identified as eligible articles in this meta-analysis for p53 Arg72Pro polymorphism (2,731 cases and 7, 356 controls), including nine studies on leukemia (1,266 cases and 4, 474 controls), three studies on lymphoma (1,359 cases and 2,652 controls), and one study on myeloma. The overall results suggested that p53 Arg72Pro polymorphism was not associated with hematological malignancies risk. In stratified analyses, significantly increased non-Hodgkin lymphomas risk was found in p53 Arg72Pro polymorphism heterozygote model (Arg/Pro vs. Arg/Arg: OR = 1.18, 95%CI: 1.02–1.35) and dominant model (Arg/Pro+Pro/Pro vs. Arg/Arg: OR = 1.18, 95%CI: 1.03–1.34), but no significant association was found between leukemia risk and p53 Arg72Pro polymorphism. Further studies showed no association between leukemia risk and p53 Arg72Pro polymorphism when stratified in subtypes of leukemias, ethnicities and sources of controls.

Conclusions/Significance

This meta-analysis indicates that the p53 Arg72Pro polymorphism may contribute to susceptibility to non-Hodgkin lymphomas.

miRNA-125b regulates TNF-α production in CD14+ neonatal monocytes via post-transcriptional regulation

Neonates, although deficient in cell immunity, frequently reveal sepsis with augmented proinflammatory reactions. Here, we found that neonatal monocytes produced significantly higher TNF-α mRNA and protein than adult monocytes. Assessment of the transcriptional factor found no significant difference of NF-κB p65 level between neonatal and adult monocytes. Addition of Act D to access the half-life of TNF-α mRNA revealed no significant difference of the LPS-induced TNF-α mRNA half-life between them, whereas CHX increased neonatal TNF-α mRNA significantly. This suggests that a post-transcriptional mechanism involves the augmentation of TNF-α production by neonatal monocytes. To examine whether miRNA was involved in the post-transcriptional regulation, differential displays of miRNA array between neonatal and adult MNCs were performed, along with the discovery of hsa-miR-103, hsa-miR-125b, hsa-miR-130a, hsa-miR-454-3p, and hsa-miR-542-3p, which were greater than a twofold decrease or increase after LPS treatment for 4 h. The functional validation identified that miR-125b decreased significantly in association with higher TNF-α expression by neonatal monocytes after LPS stimulation. Transfection of the miR-125b precursor into neonatal monocytes significantly repressed the TNF-α mRNA and protein expression, suggesting that miR-125b negatively regulates TNF-α expression in neonatal monocytes. Modulation of miRNA expression may be used to regulate TNF-α production in newborns with altered proinflammatory reactions.