Phosphorylation of Rad9 at serine 328 by cyclin A-Cdk2 triggers apoptosis via interfering Bcl-xL

GasPhos: Protein Phosphorylation Site Prediction Using a New Feature Selection Approach with a GA-Aided Ant Colony System

Protein phosphorylation is one of the most important post-translational modifications, and many biological processes are related to phosphorylation, such as DNA repair, transcriptional regulation and signal transduction and, therefore, abnormal regulation of phosphorylation usually causes diseases. If we can accurately predict human phosphorylation sites, this could help to solve human diseases. Therefore, we developed a kinase-specific phosphorylation prediction system, GasPhos, and proposed a new feature selection approach, called Gas, based on the ant colony system and a genetic algorithm and used performance evaluation strategies focused on different kinases to choose the best learning model. Gas uses the mean decrease Gini index (MDGI) as a heuristic value for path selection and adopts binary transformation strategies and new state transition rules. GasPhos can predict phosphorylation sites for six kinases and showed better performance than other phosphorylation prediction tools. The disease-related phosphorylated proteins that were predicted with GasPhos are also discussed. Finally, Gas can be applied to other issues that require feature selection, which could help to improve prediction performance. GasPhos is available at http://predictor.nchu.edu.tw/GasPhos.

Naturally Occurring Level of Aflatoxin B1 Injures Human, Canine and Bovine Leukocytes Through ATP Depletion and Caspase Activation

Aflatoxin (AF) B₁ is a potent hepatotoxic, mutagenic, teratogenic mycotoxin and may cause immune suppression/dysregulation in humans and animals. Toxic effects of AFB₁ on key mammalian immune cells (ie, leukocytes) needs to be mechanistically elucidated. In this study, along with the determination of AFB₁'s LC₅₀ for certain leukocytes, we analyzed the effect of naturally occurring levels of AFB₁ on apoptosis/necrosis of neutrophils, lymphocytes, and monocytes from healthy young humans (20- to 25-year-old male), dogs (1- to 2-year-old Persian/herd breed), and cattle (1- to 2-year-old cattle). Leukocytes were incubated for approximately 24 hours with naturally occurring levels of AFB₁ (10 ng/mL). Intracellular adenosine triphosphate (ATP) depletion and caspase-3/7 activity were then determined by luciferase-dependent bioluminescence (BL). Furthermore, the necrotic leukocytes were measured using propidium iodide (PI)-related flow cytometry. A significant decrease (24%-45%, 33.2% ± 2.7%) in intracellular ATP content was observed in AFB₁-treated neutrophils, lymphocytes, and monocytes in all studied mammals. Also, with such a low level (10 ng/mL) of AFB₁, BL-based caspase-3/7 activity (BL intensity) in all 3 tested mammalian leukocyte lineages was noticeably increased (∼>2-fold). Flow cytometry-based PI staining (for viability assay) of the AFB₁-treated leukocytes showed slightly/insignificantly more increase of necrotic (PI⁺) neutrophils, lymphocytes, and monocytes in human, dogs, and cattle. Even though in vitro LC₅₀s for AFB_1' (∼20,000-40,000 ng/mL) were approximately 2,000 to 4,000 times higher than background, these studies demonstrate leukocytes from human and farm/companion animals are sensitive to naturally occurring levels of AFB₁. The observed in vitro ATP depletion and caspase activation in AFB₁-exposed leukocytes can partially explain the underlying mechanisms of AFB₁-induced immune disorders in mammals.

Pathogenic Salmonella weakens avian enriched blood monocytes through ATP depletion, apoptosis induction and phagocytosis inefficiency

Salmonella enterica Subsp enterica serovar Typhimurium (S. Typhimurium, ST) is one of the most important serovars of the genus Salmonella in human and animals. Because of its intracellular tropism, monocytes/macrophages are pivotal in killing of Salmonella serovars; they are also responsible for transporting of ST to extra-intestinal organs. To investigate the effect of the ST on the functions of avian innate immune cells, almost homogeneous enriched monocytes (EMo) were isolated from peripheral blood mononuclear cells of 2-3 weeks-old of healthy broilers. The EMo were then divided in three groups: control (media only), treatments (challenged with ST clinical isolates) and [doxorubicin (Dox), specifically as positive control for EMo apoptosis] groups. Cellular-molecular damage caused by ST in EMo was assessed with bioluminescence (for caspase-3, 7, and 9 activities and intracellular ATP content), chemiluminescence (for pro/anti-oxidant capacities) and flow cytometry (for apoptosis/necrosis). Further, phagocytosis capacity of post-ST challenged EMo was assessed using a flow cytometry-based internalisation of FITC-loaded polystyrene microparticles. Like the effects of Dox, in post-ST challenged EMo much higher caspase-3, 7 and 9 activities and ATP depletion along with decreased phagocytosis capacity and anti-oxidant load were observed. The results herein indicate that ST weakens EMo particularly through caspases activation/apoptosis. These findings can open a new window on the molecular aspects of Salmonella-macrophage interactions and immunopathology/pathogenicity of salmonellosis in animals especially avian species.

Palbociclib triggers apoptosis in bladder cancer cells by Cdk2-induced Rad9-mediated reorganization of the Bak.Bcl-xl complex

Palbociclib is a Cdk4/6 inhibitor approved for metastatic estrogen receptor-positive breast cancer. The drug is also under clinical evaluation for metastatic urothelial cancer and other solid tumors. Preclinical studies from multiple tumor types suggest that other factors also affect the sensitivity of individual tumors to Cdk4/6 inhibitor. We show here that Cdk2 has an essential role in palbociclib antitumor effect against bladder cancers. We found that palbociclib induced apoptosis instead of cell cycle arrest to exhibit its anticancer activity in T24 cells, as was evidenced by membrane blebbing, caspase-3 activation and AIF release from mitochondria. Cdk2 activation was important to palbociclib-induced apoptotic triggering activity, since depletion of Cdk2 significantly inhibited caspase-3 activation and cell apoptosis. Cdk2 activation caused p-Rad9 translocation to the mitochondria and subsequently interaction with Bcl-xl, leading to conformational activation of Bak and cell apoptosis. The anticancer activity and Cdk2 activation of palbociclib-treated mice were finally validated in a T24 xenograft model. Collectively, these results together demonstrate that palbociclib exerts its anticancer effect in T24 cells mainly through Cdk2 activation. Our findings provide new insights into the molecular interactions and anticancer mechanisms of Cdk4/6 inhibitors.

Synergistic anti-tumor effect of bullfrog sialic acid-binding lectin and pemetrexed in malignant mesothelioma

Malignant mesothelioma is an aggressive cancer with limited therapeutic options. Sialic acid-binding lectin isolated from Rana catesbeiana oocytes (cSBL) is a multifunctional protein with anti-cancer activity. The effects of pemetrexed, cisplatin, and cSBL were evaluated in mesothelioma and normal mesothelial cell lines. We evaluated cytotoxicity, apoptosis, caspase-3 cleavage and activation, cell proliferation, cell cycle arrest, and levels of cell cycle proteins in H28 cells treated with pemetrexed, cisplatin, and cSBL alone or in combination. Treatment with cSBL alone was cytotoxic to mesothelioma cells. The anti-cancer effect of cSBL was observed in a broader range of cell lines and exhibited greater cancer cell selectivity than pemetrexed or cisplatin. Combination treatment with pemetrexed + cSBL resulted in greater dose-dependent cytotoxicity than pemetrexed + cisplatin, the standard of care in mesothelioma. The synergistic effect of pemetrexed + cSBL was mediated by the cytostatic effect of pemetrexed and the cytotoxic effect of cSBL. It thus appears that cSBL has therapeutic potential for the treatment of mesothelioma.

Venetoclax Synergizes with Radiotherapy for Treatment of B-cell Lymphomas

Constitutive B-cell receptor signaling leads to overexpression of the antiapoptotic BCL-2 protein and is implicated in the pathogenesis of many types of B-cell non-Hodgkin lymphoma (B-NHL). The BCL-2 small-molecule inhibitor venetoclax shows promising clinical response rates in several lymphomas, but is not curative as monotherapy. Radiotherapy is a rational candidate for combining with BCL-2 inhibition, as DNA damage caused by radiotherapy increases the activity of pro-apoptotic BCL-2 pathway proteins, and lymphomas are exquisitely sensitive to radiation. We tested B-NHL responses to venetoclax combined with either external beam radiotherapy or radioimmunotherapy (RIT), which joins the selectivity of antibody targeting with the effectiveness of irradiation. We first tested cytotoxicity of cesium-137 irradiation plus venetoclax in 14 B-NHL cell lines representing five lymphoma subtypes. Combination treatment synergistically increased cell death in 10 of 14 lines. Lack of synergy was predicted by resistance to single-agent venetoclax and high BCL-XL expression. We then assessed the efficacy of external beam radiotherapy plus venetoclax in murine xenograft models of mantle cell (MCL), germinal-center diffuse large B-cell (GCB-DLBCL), and activated B-cell (ABC-DLBCL) lymphomas. In each model, external beam radiotherapy plus venetoclax synergistically increased mouse survival time, curing up to 10%. We finally combined venetoclax treatment of MCL and ABC-DLBCL xenografts with a pretargeted RIT (PRIT) system directed against the CD20 antigen. Optimal dosing of PRIT plus venetoclax cured 100% of mice with no detectable toxicity. Venetoclax combined with radiotherapy may be a promising treatment for a wide range of lymphomas Cancer Res; 77(14); 3885-93. ©2017 AACR.

Inside the biochemical pathways of thymidylate synthase perturbed by anticancer drugs: Novel strategies to overcome cancer chemoresistance

Our current understanding of the mechanisms of action of antitumor agents and the precise mechanisms underlying drug resistance is that these two processes are directly linked. Moreover, it is often possible to delineate chemoresistance mechanisms based on the specific mechanism of action of a given anticancer drug. A more holistic approach to the chemoresistance problem suggests that entire metabolic pathways, rather than single enzyme targets may better explain and educate us about the complexity of the cellular responses upon cytotoxic drug administration. Drugs, which target thymidylate synthase and folate-dependent enzymes, represent an important therapeutic arm in the treatment of various human malignancies. However, prolonged patient treatment often provokes drug resistance phenomena that render the chemotherapeutic treatment highly ineffective. Hence, strategies to overcome drug resistance are primarily designed to achieve either enhanced intracellular drug accumulation, to avoid the upregulation of folate-dependent enzymes, and to circumvent the impairment of DNA repair enzymes which are also responsible for cross-resistance to various anticancer drugs. The current clinical practice based on drug combination therapeutic regimens represents the most effective approach to counteract drug resistance. In the current paper, we review the molecular aspects of the activity of TS-targeting drugs and describe how such mechanisms are related to the emergence of clinical drug resistance. We also discuss the current possibilities to overcome drug resistance by using a molecular mechanistic approach based on medicinal chemistry methods focusing on rational structural modifications of novel antitumor agents. This paper also focuses on the importance of the modulation of metabolic pathways upon drug administration, their analysis and the assessment of their putative roles in the networks involved using a meta-analysis approach. The present review describes the main pathways that are modulated by TS-targeting anticancer drugs starting from the description of the normal functioning of the folate metabolic pathway, through the protein modulation occurring upon drug delivery to cultured tumor cells as well as cancer patients, finally describing how the pathways are modulated by drug resistance development. The data collected are then analyzed using network/netwire connecting methods in order to provide a wider view of the pathways involved and of the importance of such information in identifying additional proteins that could serve as novel druggable targets for efficacious cancer therapy.

Effect of sun ginseng potentiation on epirubicin and paclitaxel-induced apoptosis in human cervical cancer cells

Background

Sun ginseng (SG), a specific formulation of quality-controlled red ginseng, contains approximately equal amounts of three major ginsenosides (RK1, Rg3, and Rg5), which reportedly has antitumor-promoting activities in animal models.

Methods

MTT assay was used to assess whether SG can potentiate the anticancer activity of epirubicin or paclitaxel in human cervical adenocarcinoma HeLa cells, human colon cancer SW111C cells, and SW480 cells; apoptosis status was analyzed by annexin V-FITC and PI and analyzed by flow cytometry; and apoptosis pathway was studied by analysis of caspase-3, -8, and -9 activation, mitochondrial accumulation of Bax and Bak, and cytochrome c release.

Results

SG remarkably enhances cancer cell death induced by epirubicin or paclitaxel in human cervical adenocarcinoma HeLa cells, human colon cancer SW111C cells, and SW480 cells. Results of the mechanism study highlighted the cooperation between SG and epirubicin or paclitaxel in activating caspase-3 and -9 but not caspase-8. Moreover, SG significantly increased the mitochondrial accumulation of both Bax and Bak triggered by epirubicin or paclitaxel as well as the subsequent release of cytochrome c in the targeted cells.

Conclusion

SG significantly potentiated the anticancer activities of epirubicin and paclitaxel in a synergistic manner. These effects were associated with the increased mitochondrial accumulation of both Bax and Bak that led to an enhanced cytochrome c release, caspase-9/-3 activation, and apoptosis. Treating cancer cells by combining epirubicin and paclitaxel with SG may prove to be a novel strategy for enhancing the efficacy of the two drug types.

Pemetrexed induces S-phase arrest and apoptosis via a deregulated activation of Akt signaling pathway

Pemetrexed is approved for first-line and maintenance treatment of patients with advanced or metastatic non-small-cell lung cancer (NSCLC). The protein kinase Akt/protein kinase B is a well-known regulator of cell survival which is activated by pemetrexed, but its role in pemetrexed-mediated cell death and its molecular mechanisms are unclear. This study showed that stimulation with pemetrexed induced S-phase arrest and cell apoptosis and a parallel increase in sustained Akt phosphorylation and nuclear accumulation in the NSCLC A549 cell line. Inhibition of Akt expression by Akt specific siRNA blocked S-phase arrest and protected cells from apoptosis, indicating an unexpected proapoptotic role of Akt in the pemetrexed-mediated toxicity. Treatment of A549 cells with pharmacological inhibitors of phosphatidylinositol 3-kinase (PI₃K), wortmannin and Ly294002, similarly inhibited pemetrexed-induced S-phase arrest and apoptosis and Akt phosphorylation, indicating that PI₃K is an upstream mediator of Akt and is involved in pemetrexed-mediated cell death. Previously, we identified cyclin A-associated cyclin-dependent kinase 2 (Cdk2) as the principal kinase that was required for pemetrexed-induced S-phase arrest and apoptosis. The current study showed that inhibition of Akt function and expression by pharmacological inhibitors as well as Akt siRNA drastically inhibited cyclin A/Cdk2 activation. These pemetrexed-mediated biological and molecular events were also observed in a H1299 cell line. Overall, our results indicate that, in contrast to its normal prosurvival role, the activated Akt plays a proapoptotic role in pemetrexed-mediated S-phase arrest and cell death through a mechanism that involves Cdk2/cyclin A activation.

Tousled-like kinase-dependent phosphorylation of Rad9 plays a role in cell cycle progression and G2/M checkpoint exit

Genomic integrity is preserved by checkpoints, which act to delay cell cycle progression in the presence of DNA damage or replication stress. The heterotrimeric Rad9-Rad1-Hus1 (9-1-1) complex is a PCNA-like clamp that is loaded onto DNA at structures resulting from damage and is important for initiating and maintaining the checkpoint response. Rad9 possesses a C-terminal tail that is phosphorylated constitutively and in response to cell cycle position and DNA damage. Previous studies have identified tousled-like kinase 1 (TLK1) as a kinase that may modify Rad9. Here we show that Rad9 is phosphorylated in a TLK-dependent manner in vitro and in vivo, and that T355 within the C-terminal tail is the primary targeted residue. Phosphorylation of Rad9 at T355 is quickly reduced upon exposure to ionizing radiation before returning to baseline later in the damage response. We also show that TLK1 and Rad9 interact constitutively, and that this interaction is enhanced in chromatin-bound Rad9 at later stages of the damage response. Furthermore, we demonstrate via siRNA-mediated depletion that TLK1 is required for progression through S-phase in normally cycling cells, and that cells lacking TLK1 display a prolonged G2/M arrest upon exposure to ionizing radiation, a phenotype that is mimicked by over-expression of a Rad9-T355A mutant. Given that TLK1 has previously been shown to be transiently inactivated upon phosphorylation by Chk1 in response to DNA damage, we propose that TLK1 and Chk1 act in concert to modulate the phosphorylation status of Rad9, which in turn serves to regulate the DNA damage response.