Regulation of apoptosis proteins in cancer cells by ubiquitin

Proteasome inhibition induces apoptosis through simultaneous inactivation of MCL-1/BCL-XL by NOXA independent of CHOP and JNK pathways

Proteasome inhibitors have been employed in the treatment of relapsed multiple myeloma and mantle cell lymphoma. The observed toxicity caused by proteasome inhibitors is a universal phenotype in numerous cancer cells with different sensitivity. In this study, we investigate the conserved mechanisms underlying the toxicity of the proteasome inhibitor bortezomib using gene editing approaches. Our findings utilizing different caspase knocking out cells reveal that bortezomib induces classic intrinsic apoptosis by activating caspase-9 and caspase-3/7, leading to pore-forming protein GSDME cleavage and subsequent lytic cell death or called secondary necrosis, a phenotype also observed in many apoptosis triggers like TNFα plus CHX, DTT and tunicamycin treatment in HeLa cells. Furthermore, through knocking out of nearly all BH3-only proteins including BIM, BAD, BID, BMF and PUMA, we demonstrate that NOXA is the sole BH3-only protein responsible for bortezomib-induced apoptosis. Of note, NOXA is well known for selectively binding to MCL-1 and A1, but our studies utilizing different BH3 mimetics as well as immunoprecipitation assays indicate that, except for the constitutive interaction of NOXA with MCL-1, the accumulation of NOXA after bortezomib treatment allows it to interact with BCL-XL, then simultaneous relieving suppression on apoptosis by both anti-apoptotic proteins BCL-XL and MCL-1. In addition, though bortezomib-induced significant ER stress and JNK activation were observed in the study, further genetic depletion experiments prove that bortezomib-induced apoptosis occurs independently of ER stress-related apoptosis factor CHOP and JNK. In summary, these results provide a solid conclusion about the critical role of NOXA in inactivation of BCL-XL except MCL-1 in bortezomib-induced apoptosis.

The entanglement of DNA damage and pattern recognition receptor signaling

Cells are under constant pressure to suppress DNA damage originating from both exogenous and endogenous sources. Cellular responses to DNA damage help to prevent mutagenesis and cell death that arises when DNA damage is either left unrepaired or repaired inaccurately. During the "acute phase" of DNA damage signaling, lesions are recognized, processed, and repaired to restore the primary DNA sequence whilst cell cycle checkpoints delay mitotic progression, cell death and the propagation of errors to daughter cells. Increasingly, there is recognition of a "chronic phase" of DNA damage signaling, exemplified by the secretion of dozens of cytokines days after the inciting damage event. In this review, we focus on the cellular origin of these chronic responses, the molecular pathways that control them and the increasing appreciation for the interconnection between acute and chronic DNA damage responses.

Systematic characterization of Brassica napus UBC13 genes involved in DNA-damage response and K63-linked polyubiquitination

BACKGROUND

Ubc13 is the only known ubiquitin conjugating enzyme (Ubc/E2) dedicated to promoting Lys (K)63-linked polyubiquitination, and this process requires a Ubc/E2 variant (UEV). Unlike conventional K48-linked polyubiquitination that targets proteins for degradation, K63-linked polyubiquitination, which is involved in several cellular processes, does not target proteins for degradation but alter their activities.

RESULTS

In this study we report the identification and functional characterization of 12 Brassica napus UBC13 genes. All the cloned UBC13 gene products were able to physically interact with AtUev1D, an Arabidopsis UEV, to form stable complexes that are capable of catalyzing K63-linked polyubiquitination in vitro. Furthermore, BnUBC13 genes functionally complemented the yeast ubc13 null mutant defects in spontaneous mutagenesis and DNA-damage responses, suggesting that BnUBC13s can replace yeast UBC13 in mediating K63-linked polyubiquitination and error-free DNA-damage tolerance.

CONCLUSION

Collectively, this study provides convincing data to support notions that B. napus Ubc13s promote K63-linked polyubiquitination and are probably required for abiotic stress response. Since plant Ubc13-UEV are also implicated in other developmental and stress responses, this systematic study sets a milestone in exploring roles of K63-linked polyubiquitination in this agriculturally important crop.

Functional antibody delivery: Advances in cellular manipulation

The current therapeutic antibody market in the U.S. consists of 100 antibody-based products and their market value is expected to explode beyond $300 billion by 2025. These therapies are presently limited to extracellular targets due to the innate inability of antibodies to transverse membranes. To expand the number of accessible therapeutic targets, intracellular antibody delivery is necessary. Many delivery vehicles for antibodies have been used with some promising results, such as nanoparticles and cell penetrating polymers. Despite the success of these delivery platforms using model antibody cargo, there is a surprisingly small number of studies that focus on functional antibody delivery into the cytosol that also measures a cellular response. Antibodies can be designed for essentially unlimited targets, including proteins and DNA, that will ultimately control cell function once delivered inside cells. Advancement in cellular manipulation depends on the application of intracellularly delivering functional antibodies to achieve a desired result. This review focuses on the emerging field of functional antibody delivery which enables various cellular responses and cell manipulation.

Upregulation of CRABP2 by TET1-mediated DNA hydroxymethylation attenuates mitochondrial apoptosis and promotes oxaliplatin resistance in gastric cancer

Oxaliplatin is the main chemotherapy drug for gastric cancer (GC), but quite a few patients are resistant to oxaliplatin, which contributes to the poor prognosis of GC patients. There is therefore an urgent need to identify potential targets for reversing chemotherapy resistance in GC patients. In this study, we analyzed the tumor samples of GC patients who received neoadjuvant chemotherapy based on oxaliplatin through quantitative proteomics and identified the potential chemoresistance-related protein cellular retinoic acid binding protein 2 (CRABP2). CRABP2 was significantly upregulated in the tumor tissues of chemoresistant GC patients and was closely related to prognosis. The results of cell function experiments showed that CRABP2 can promote the oxaliplatin resistance of GC cells in vitro. Coimmunoprecipitation and GST pulldown assays showed that CRAPB2 expedited the binding of BAX and PARKIN in GC cells and facilitated the ubiquitination-mediated degradation of BAX. Furthermore, both the in vitro assay and cell-derived xenograft (CDX) in vivo model verified that CRABP2 promoted oxaliplatin resistance by inhibiting BAX-dependent cell apoptosis. Further experiments proved that the abnormally high expression of CRABP2 in oxaliplatin-resistant GC cells was affected by TET1-mediated DNA hydroxymethylation. The patient-derived xenograft (PDX) model suggested that interference with CRABP2 reversed oxaliplatin resistance in GC in vivo. In conclusion, the results of our study show that CRABP2 was a key molecule in oxaliplatin resistance regulation and could be a new target for reversing the chemoresistance of GC.

Apoptosis and (in) Pain—Potential Clinical Implications

The deregulation of apoptosis is involved in the development of several pathologies, and recent evidence suggests that apoptosis may be involved in chronic pain, namely in neuropathic pain. Neuropathic pain is a chronic pain state caused by primary damage or dysfunction of the nervous system; however, the details of the molecular mechanisms have not yet been fully elucidated. Recently, it was found that nerve endings contain transient receptor potential (TRP) channels that sense and detect signals released by injured tissues and respond to these damage signals. TRP channels are similar to the voltage-gated potassium channels or nucleotide-gated channels that participate in calcium and magnesium homeostasis. TRP channels allowing calcium to penetrate into nerve terminals can activate apoptosis, leading to nerve terminal destruction. Further, some TRPs are activated by acid and reactive oxygen species (ROS). ROS are mainly produced in the mitochondrial respiratory chain, and an increase in ROS production and/or a decrease in the antioxidant network may induce oxidative stress (OS). Depending on the OS levels, they can promote cellular proliferation and/or cell degeneration or death. Previous studies have indicated that proinflammatory cytokines, such as tumor necrosis factor-α (TNF-α), play an important role in the peripheral mediation of neuropathic pain. This article aims to perform a review of the involvement of apoptosis in pain, particularly the role of OS and neuroinflammation, and the clinical relevance of this knowledge. The potential discovery of new biomarkers and therapeutic targets can result in the development of more effective and targeted drugs to treat chronic pain, namely neuropathic pain. Highlights: Oxidative stress and neuroinflammation can activate cell signaling pathways that can lead to nerve terminal destruction by apoptosis. These could constitute potential new pain biomarkers and targets for therapy in neuropathic pain.

Fucoidan Modulated Oxidative Stress and Caspase-3 mRNA Expression Induced by Sulfoxaflor in the Brain of Mice

The current study aimed to investigate the role of fucoidan in the oxidative and apoptotic effects of sulfoxaflor, a neonicotinoid sulfoximine insecticide, in the brain of Swiss albino mice (Mus musculus). Sulfoxaflor and fucoidan were administered to mice at doses of 15 mg/kg/day (1/50 oral LD50) and 50 mg/kg/day, respectively, by oral gavage for 24 h or 7 days. The tGSH, TBARS and protein levels, and GPx, GR, and GST enzyme activities were determined by spectrophotometric methods. Caspase-3 gene expression level was determined by RT-PCR. Data analysis showed that brains of sulfoxaflor-treated mice exhibited higher TBARS levels; GPx, GR, and GST enzyme activities; and caspase-3 expression levels, as well as lower levels of tGSH. Co-administration of fucoidan and sulfoxaflor reduced the TBARS levels, increased tGSH levels, and increased GPx, GR, and GST enzyme activities. Fucoidan also decreased the sulfoxaflor-induced up-regulation of caspase-3 mRNA expression. Results of the present study showed that sulfoxaflor caused oxidative stress by inducing lipid peroxidation and altering GSH-dependent antioxidants in the brain of mice. In addition, sulfoxaflor may trigger apoptotic cell death shown by the up-regulation of caspase-3. Fucoidan treatment modulated all the aforementioned alterations in the brain of mice. It was concluded that fucoidan might have antioxidant effects that support the GSH-dependent antioxidant system and can play a modulator role in oxidative stress and caspase-3 expression in the brain of sulfoxaflor treated-mice.

Inhibiting BCKDK in triple negative breast cancer suppresses protein translation, impairs mitochondrial function, and potentiates doxorubicin cytotoxicity

Triple-negative breast cancers (TNBCs) are characterized by poor survival, prognosis, and gradual resistance to cytotoxic chemotherapeutics, like doxorubicin (DOX). The clinical utility of DOX is limited by its cardiotoxic and chemoresistant effects that manifest over time. To induce chemoresistance, TNBC rewires oncogenic gene expression and cell signaling pathways. Recent studies have demonstrated that reprogramming of branched-chain amino acids (BCAAs) metabolism facilitates tumor growth and survival. Branched-chain ketoacid dehydrogenase kinase (BCKDK), a regulatory kinase of the rate-limiting enzyme of the BCAA catabolic pathway, is reported to activate RAS/RAF/MEK/ERK signaling to promote tumor cell proliferation. However, it remains unexplored if BCKDK action remodels TNBC proliferation and survival per se and influences susceptibility to DOX-induced genotoxic stress. TNBC cells treated with DOX exhibited reduced BCKDK expression and intracellular BCKAs. Genetic and pharmacological inhibition of BCKDK in TNBC cell lines also showed a similar reduction in intracellular and secreted BCKAs. BCKDK silencing in TNBC cells downregulated mitochondrial metabolism genes, reduced electron complex protein expression, oxygen consumption, and ATP production. Transcriptome analysis of BCKDK silenced cells confirmed dysregulation of mitochondrial metabolic networks and upregulation of the apoptotic signaling pathway. Furthermore, BCKDK inhibition with concurrent DOX treatment exacerbated apoptosis, caspase activity, and loss of TNBC proliferation. Inhibition of BCKDK in TNBC also upregulated sestrin 2 and concurrently decreased mTORC1 signaling and protein synthesis. Overall, loss of BCKDK action in TNBC remodels BCAA flux, reduces protein translation triggering cell death, ATP insufficiency, and susceptibility to genotoxic stress.

Proposed mechanism. A Doxorubicin (DOX) targets the BCAA catabolic pathway in TNBCs, by downregulating BCKDK and augmenting clearance of intracellular BCKAs. B Genetic or pharmacological (high BT2 concentration) inhibition of BCKDK results in increased cell death, decreased intracellular BCKAs, dysregulated mitochondrial function, ATP insufficiency, SESN2 activation, and inhibition of mTORC1 signaling and protein synthesis. C BCKDK inhibition (siRNA mediated or low-BT2 concentration) exacerbates DOX-induced cytotoxicity and caspase activity.

[Effect of DR5-mediated docetaxel-loaded lipid microbubble combined with ultrasoundtargeted microbubble destruction on HepG2 cell proliferation and apoptosis]

OBJECTIVE

To investigate the effect of DR5-mediated docetaxel-targeted lipid microbubbles (MBs) combined with ultrasound-targeted microbubble destruction on apoptosis and expressions of Bcl-2, nuclear factor-κB(NF-κB), caspase-8, and DR5 in human HepG2 cells.

METHODS

HepG2 cells were treated with docetaxel at its 50% inhibitory concentration (IC50) of 5 nmol/L, docetaxel combined with ultrasound, blank MBs, blank MBs combined with ultrasound (0.5 W/cm2 for 45 s), drugloaded lipid MBs (DLLM), DLLM combined with ultrasound, DR5-mediated DLLM (DR5-DLLM), or DR5-DLLM combined with ultrasound.After the treatments, the cells were further cultured for 24 h, and CCK-8 assay, TUNEL staining and flow cytometry were used to assess cell proliferation, apoptosis, and cell cycle changes; the changes in mRNA and protein expression levels of Bcl-2, NF-κB, caspase-8, and DR5 were detected with RT-qPCR and Western blotting.

RESULTS

Among all the treatments, DR5-DLLM combined with ultrasound produced the strongest effects to inhibit the proliferation (P < 0.001), promote apoptosis (P < 0.001), and cause G2/M cell cycle arrest (P < 0.001) in HepG2 cells.The combined treatment with DR5-DLLM and ultrasound also significantly downregulated Bcl-2 and NF-κB (P < 0.001) and upregulated DR5 and caspase-8 expressions (P < 0.001) at both the mRNA and protein levels.

CONCLUSION

DR5-DLLM combined with ultrasound-targeted microbubble destruction can induce G2/M cell cycle arrest, proliferation inhibition and apoptosis in HepG2 cells by downregulating Bcl-2 and NF-κB and upregulating DR5 and caspase-8 expressions, indicating its value as a novel ultrasoundtargeted therapy for liver cancer.

Enhancing the Effect of Tumor Necrosis Factor-Related Apoptosis-Inducing Ligand Signaling and Arginine Deprivation in Melanoma

Melanoma as a very aggressive type of cancer is still in urgent need of improved treatment. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and arginine deiminase (ADI-PEG20) are two of many suggested drugs for treating melanoma. Both have shown anti-tumor activities without harming normal cells. However, resistance to both drugs has also been noted. Studies on the mechanism of action of and resistance to these drugs provide multiple targets that can be utilized to increase the efficacy and overcome the resistance. As a result, combination strategies have been proposed for these drug candidates with various other agents, and achieved enhanced or synergistic anti-tumor effect. The combination of TRAIL and ADI-PEG20 as one example can greatly enhance the cytotoxicity to melanoma cells including those resistant to the single component of this combination. It is found that combination treatment generally can alter the expression of the components of cell signaling in melanoma cells to favor cell death. In this paper, the signaling of TRAIL and ADI-PEG20-induced arginine deprivation including the main mechanism of resistance to these drugs and exemplary combination strategies is discussed. Finally, factors hampering the clinical application of both drugs, current and future development to overcome these hurdles are briefly discussed.

Mechanisms of Apoptosis-Related Long Non-coding RNAs in Ovarian Cancer

Ovarian cancer is a health-threatening malignancy of ovary in female reproductive systems and one of the most common gynecological malignancies worldwide. Due to rare early symptoms, ovarian cancers are often diagnosed at advanced stages and exhibit poor prognosis. Thus, efforts have been paid to develop alternative diagnostic and therapeutic strategies for the disease. Recent studies have presented that some long non-coding RNAs (lncRNAs) play roles in apoptosis of ovarian cancer cells through various mechanisms involved in the regulation of transcription factors, histone modification complexes, miRNAs, and protein stability. Because evasion of apoptosis in cancer cells facilitates to promote tumor progression and therapy resistance, apoptosis regulatory mechanisms of lncRNAs may be promising new targets in ovarian cancer. In this review, we introduce the recent findings in regard to the molecular mechanisms of apoptosis-related lncRNAs in ovarian cancer cells.

Treating MCF7 breast cancer cell with proteasome inhibitor Bortezomib restores apoptotic factors and sensitizes cell to Docetaxel

Chemoresistance is the leading cause of limiting long-term treatment success in cancer cells. Anticancer drugs usually kill cells through apoptosis induction and defects in this signaling pathway lead to chemoresistance. Apoptotic protease activating factor 1 regulates cellular stress evoked by chemotherapeutic agents through facilitating apoptosome assembling but can be degraded by proteasome. This study examined the role of proteasome inhibitor Bortezomib in the cytotoxic effects of Docetaxel on MCF7 cells response and its correlation with Apaf-1 expression level. MTT assay, caspase 3/7 activity assay, propidium iodide staining, adenosine triphosphate and reactive oxygen species amount measurements were utilized to demonstrate the role of Bortezomib in Docetaxel efficacy with and without Apaf-1 overexpressing. Meanwhile, two-dimensional cell migration assay was performed by scratch wound assay. The combination of Docetaxel with Bortezomib was significantly more cytotoxic compared single drug, more effectively delayed cell growth, reduced ATP level and increased ROS production. In Apaf-1 overexpressing, Docetaxel was more efficient in preventing cell migration, however, Docetaxel plus Bortezomib were not significantly effective; and fluorescence images supported the interpretation. Our findings demonstrated MCF7 resistance to Docetaxel is due in part to low Apaf-1 level and Apaf-1 overexpression resulted in the increase of cell susceptibility to Docetaxel stimulus. We assume that proteasome inhibitor may restore apoptotic proteins like Apaf-1 and prevent the degradation of cytosolic cytochrome c released by Docetaxel, consequently triggering intrinsic apoptosis and promoting cancer cell death. Collectively, treating MCF7 breast cells with proteasome inhibitor sensitizes cells to Docetaxel-induced apoptosis and possibly overcomes chemoresistance.

Extracellular ubiquitin protects cardiomyocytes during ischemia/hypoxia by inhibiting mitochondrial apoptosis pathway through CXCR4

AIM

Acute myocardial infarction (AMI) is one of the deadliest diseases worldwide. The search for countermeasures to reduce cardiomyocytes death in the infarcted area has always been the focus of research. Ubiquitin (UB) is a small polypeptide mainly involved in proteasome-mediated protein degradation in cells, whereas extracellular UB in body fluids can also function through its receptor CXC chemokine receptor type 4 (CXCR4). This study aimed to explore the functional roles of extracellular UB in cardiomyocytes during ischemia/hypoxia (I/H).

METHODS

H9C2 cells were subjected to I/H treatment and cell injury was evaluated by cell viability, morphology changes and apoptosis rate. UB expression and levels of ubiquitinated proteins after I/H injury were measured. The effects of extracellular UB on I/H-induced cardiomyocytes apoptosis and the possible underlying mechanisms were studied.

RESULTS

I/H injury induced the decrease of cell viability as well as enhanced impaired cell morphology and apoptosis rate in H9C2 cells. Levels of UB mRNA and ubiquitinated proteins were significantly up-regulated after I/H treatment, whereas the concentration of extracellular UB in the conditioned media did not show significant change and the intracellular mono-UB levels in cells were down-regulated. Extracellular UB treatment protected cardiomyocytes from I/H injury by inhibiting the overactivation of mitochondria-dependent apoptosis pathway and up-regulating autophagy level. Inhibition of CXCR4 receptor using AMD3100 abolished cardioprotective effects of extracellular UB.

CONCLUSION

The up-regulation of UB was suggested to be an adaptive response to resist I/H-induced cardiomyocytes apoptosis, and additional extracellular UB treatment might serve as a new potential therapeutic drug for AMI.

Light spectra affect the in vitro shoot development of Cedrela fissilis Vell. (Meliaceae) by changing the protein profile and polyamine contents

The light spectrum quality is an important signal for plant growth and development. We evaluated the effects of different light spectra on the in vitro shoot development of Cedrela fissilis and its proteomic and polyamine (PA) profiles. Cotyledonary and apical nodal segments were grown under different light emitting diodes (LED) and fluorescent lamps. Shoots from cotyledonary nodal segments cultured with 6-benzyladenine (BA) that were grown under W_mB_dR LED showed increased length and higher fresh and dry matter compared to shoots grown under fluorescent lamps. A nonredundant protein databank generated by transcriptome sequencing and the de novo assembly of C. fissilis improved, and almost doubled, the protein identification compared to a Citrus sinensis databank. A total of 616 proteins were identified, with 23 up- and 103 down-accumulated in the shoots under W_mB_dR LEDs compared to fluorescent lamps. Most differentially accumulated proteins in shoots grown under the WmBdR LED lamp treatment compared to the fluorescent lamp treatment are involved in responding to metabolic processes, stress, biosynthetic and cellular protein modifications, and light stimulus processes. Among the proteins, the up-accumulation of argininosuccinate synthase was associated with an increase in the free putrescine content and, consequently, with higher shoot elongation under W_mB_dR LED. The down-accumulation of calreticulin, heat shock proteins, plastid-lipid-associated protein, ubiquitin-conjugating enzymes, and ultraviolet-B receptor UVR8 isoform X1 could be related to the longer shoot length noted under LED treatment. This study provides important data related to the effects of the light spectrum quality on in vitro morphogenesis through the modulation of specific proteins and free putrescine biosynthesis in C. fissilis, an endangered wood species from the Brazilian Atlantic Forest of economic and ecological relevance. The nonredundant protein databank of C. fissilis is available via ProteomeXchange under identifier PXD018020.

Molecular and Functional Characterization of Inhibitor of Apoptosis Proteins (IAP, BIRP) in Echinococcus granulosus

The larval stage of Echinococcus granulosus sensu lato, resulting in cystic echinococcosis, a parasitic zoonosis, causes huge economic losses to the livestock industry and poses a threat to public health. Inhibitor of apoptosis proteins (IAPs) is a class of endogenous anti-apoptotic family, which plays a significant functional role in the regulation of organism’s development. Herein, to explore potential functions of IAPs in E. granulosus, two members of IAPs from E. granulosus (Eg-IAP and Eg-BIRP) were cloned, expressed, and molecularly characterized. Eg-IAP and Eg-BIRP encoded putative 331 and 168 residue proteins, respectively. Bioinformatic analysis showed that both proteins contained a type II BIR domain-the essential functional domain of IAPs. Fluorescence immunohistochemistry revealed that both proteins were ubiquitously localized in all life-cycle stages of E. granulosus. Our fluorescent quantitative PCR (RT-qPCR) results revealed relatively higher transcription levels of two Eg-IAPs in protoscoleces (PSCs) compared to the 18-day strobilated worms. We further used different concentrations of LCL161, a Smac-mimetic pan-IAPs inhibitor, to induce the apoptosis in PSCs in vitro, and revealed that the survival rate of PSCs and transcription levels of both genes were negatively correlated with the concentration of LCL161. While the results of light microscopy, transmission electron microscopy (TEM), and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay also showed a higher apoptotic rate in PSCs with the increasing concentrations of LCL161. Taken together, our findings provide the reasonable evidence that both Eg-IAP and Eg-BIRP have potential implication in critical anti-apoptotic roles during the development of E. granulosus.

Honokiol Enhances TRAIL-Mediated Apoptosis through STAMBPL1-Induced Survivin and c-FLIP Degradation

Honokiol is a natural biphenolic compound extracted from traditional Chinese medicine Magnolia species, which have been known to display various biological effects including anti-cancer, anti-proliferative, anti-angiogenic, and anti-metastatic activities in cancer cells. Here, we found that honokiol sensitizes cancer cells to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis through downregulation of anti-apoptotic proteins survivin and c-FLIP. Ectopic expression of survivin and c-FLIP markedly abolished honokiol and TRAIL-induced apoptosis. Mechanistically, honokiol induced protein degradation of c-FLIP and survivin through STAMBPL1, a deubiquitinase. STAMBPL1 interacted with survivin and c-FLIP, resulted in reduction of ubiquitination. Knockdown of STAMBPL1 reduced survivin and c-FLIP protein levels, while overexpression of STAMBPL1 inhibited honokinol-induced survivin and c-FLIP degradation. Our findings provided that honokiol could overcome TRAIL resistance through survivin and c-FLIP degradation induced by inhibition of STAMBPL1 expression.

Tumor necrosis factor related apoptosis inducing ligand (TRAIL) regulates deubiquitinase USP5 in tumor cells

The tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) pathway has emerged as a cancer therapeutic target. However, clinical trials have proven that most human cancers are resistant to TRAIL. We show that exposure to recombinant TRAIL resulted in the accumulation of ubiquitinated proteins and free ubiquitin polymers, suggesting a link between TRAIL and the ubiquitin (Ub)-proteasome pathway. TRAIL treatment in cancer cells reduced the activity and cleavage of USP5, a deubiquitinase (DUB) previously shown to target unanchored Ub polymers and regulate p53-mediated transcription. TRAIL was effective in suppressing USP5 activity and cleavage in TRAIL-sensitive cells but not resistant cells. Knockdown of USP5 in TRAIL-resistant cells demonstrated that USP5 controls apoptotic responsiveness to TRAIL. USP5 cleavage and ubiquitination were blocked by caspase-8 specific inhibitors. A small-molecule USP5/9× inhibitor (G9) combined with TRAIL enhanced apoptosis and blocked colony growth in highly TRAIL-resistant cell lines. Finally, USP5 protein levels and activity were found to be frequently deregulated in TRAIL-resistant cells. Together, we conclude that activated TRAIL enhances USP5 activity and induces apoptosis in TRAIL-sensitive and -resistant cells. We also suggest that USP5 inhibition may be effective in inducing apoptotic thresholds to enhance responsiveness to TRAIL.

Molecular dynamics simulation revealed the intrinsic conformational change of cellular inhibitor of apoptosis protein-1

Inhibitor of apoptosis proteins (IAPs) are important regulators of apoptosis, and protein targets for the development of anti-cancer drugs. Cellular inhibitor of apoptosis protein-1 (cIAP1) is an important member of IAPs. Peptides or small-molecular antagonists can induce the dimerization, auto-ubiquitination, and proteasomal degradation of the cellular inhibitor of apoptosis protein-1 (cIAP1). While in the absence of antagonists, several mutations of the cIAP1 protein also lead to its dimerization and auto-ubiquitination. Even though the crystal structure of cIAP1 protein has been determined, the intrinsic mechanism of its dimerization remains unexplored. Accumulating evidence indicated that intrinsic conformational change existed during the binding of antagonists with cIAP1 protein, or introduction of mutations. To reveal this intrinsic conformational change, molecular dynamics simulations at microsecond scale were applied for the wild-type and mutant-type cIAP1 proteins. Compared to the crystal structure, significant conformational change was observed during the simulations, which could explain the importance of previously identified key mutations. To validate these findings revealed by our simulations, a new mutation D303A was constructed and the following native polyacrylamide gel electrophoresis (native-PAGE) assay observed a proportion of spontaneous dimerization, in comparison with the wild-type control. Taken together, these computational and experimental results revealed the intrinsic conformational change of cIAP1, which could not only explain previously identified key mutations, but also be exploited for further design and development of anti-tumor compounds that target the cIAP1 protein.Communicated by Ramaswamy H. Sarma.

Another look at phenolic compounds in cancer therapy the effect of polyphenols on ubiquitin-proteasome system

Inhibitors of the ubiquitin-proteasome system (UPS) have been the object of research interests for many years because of their potential as anti-cancer agents. Research in this field is aimed at improving the specificity and safety of known proteasome inhibitors. Unfortunately, in vitro conditions do not reflect the processes taking place in the human body. Recent reports indicate that the components of human plasma affect the course of many signaling pathways, proteasome activity and the effectiveness of synthetic cytostatic drugs. Therefore, it is believed that the key issue is to determine the effects of components of the human diet, including effects of chemically active polyphenols on the ubiquitin-proteasome system activity in both physiological and pathological (cancerous) states. The following article summarizes the current knowledge on the direct and indirect synergistic and antagonistic effects between polyphenolic compounds present in the human diet and the efficiency of protein degradation via the UPS.

Regulation of immune responses by E3 ubiquitin ligase Cbl-b

Casitas B lymphoma-b (Cbl-b), a RING finger E3 ubiquitin ligase, has been identified as a critical regulator of adaptive immune responses. Cbl-b is essential for establishing the threshold for T cell activation and regulating peripheral T cell tolerance through various mechanisms. Intriguingly, recent studies indicate that Cbl-b also modulates innate immune responses, and plays a key role in host defense to pathogens and anti-tumor immunity. These studies suggest that targeting Cbl-b may represent a potential therapeutic strategy for the management of human immune-related disorders such as autoimmune diseases, infections, tumors, and allergic airway inflammation. In this review, we summarize the latest developments regarding the roles of Cbl-b in innate and adaptive immunity, and immune-mediated diseases.

MG-132 treatment promotes TRAIL-mediated apoptosis in SEB-1 sebocytes

AIMS

This study aimed to identify the mechanism of how MG-132 stimulates cell death in SEB-1 sebocytes.

MATERIALS AND METHODS

TUNEL staining and annexin-FITC/PI flow cytometry were utilized to examine the apoptotic cell number of SEB-1 sebocytes and HaCaT keratinocytes upon MG-132 and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) treatment. MTT assay and CCK-8 assay monitored the proliferative rate and viability of both cell lines with different treatment. Western blotting (WB) and qPCR were performed to detect the expression of TRAIL and members of Bcl-2 family at protein and gene level. Additionally, RNA interfering was used to knockdown the mRNA transcription of TRAIL and BIK gene.

KEY FINDINGS

MG-132 treatment enhanced cell death in SEB-1 sebocytes but not in HaCaT keratinocytes. Meanwhile, TRAIL concentrations in SEB-1 sebocytes treated with MG-132 were markedly elevated. Furthermore, treatment with TRAIL or the TRAIL receptor-specific monoclonal antibody AY4 at various doses stimulated cell death in SEB-1 sebocytes in a time- and dose-dependent manner. Silencing of TRAIL restored the cell viability of SEB-1 cells to a normal level after MG-132 treatment. Combined treatment of SEB-1 sebocytes with TRAIL and MG-132 synergistically triggered cell death, suppressed cell proliferation and survival, and promoted BIK expression. Furthermore, BCL2 Interacting Killer (BIK) knockdown via RNA interference participated in the recovery of cell survival reduced by treatment with TRAIL and MG-132.

SIGNIFICANCE

These findings suggest that treatment with the selective proteasome suppressor MG-132 and TRAIL induces cell death in sebocytes through upregulation of BIK, a member of the Bcl-2 family.

Class I HDAC Inhibitors Display Different Antitumor Mechanism in Leukemia and Prostatic Cancer Cells Depending on Their p53 Status

Previously, we designed and synthesized a series of o-aminobenzamide-based histone deacetylase (HDAC) inhibitors, among which the representative compound 11a exhibited potent inhibitory activity against class I HDACs. In this study, we report the development of more potent hydrazide-based class I selective HDAC inhibitors using 11a as a lead. Representative compound 13b showed a mixed, slow, and tight binding inhibition mechanism for HDAC1, 2, and 3. The most potent compound 13e exhibited low nanomolar IC50s toward HDAC1, 2, and 3 and could down-regulate HDAC6 in acute myeloid leukemia MV4-11 cells. The EC50 of 13e against MV4-11 cells was 34.7 nM, which is 26 times lower than its parent compound 11a. In vitro responses to 13e vary significantly and interestingly based on cell type: in p53 wild-type MV4-11 cells, 13e induced cell death via apoptosis and G1/S cell cycle arrest, which is likely mediated by a p53-dependent pathway, while in p53-null PC-3 cells, 13e caused G2/M arrest and inhibited cell proliferation without inducing caspase-3-dependent apoptosis.

IAPs cause resistance to TRAIL-dependent apoptosis in follicular thyroid cancer

Follicular thyroid cancer's (FTC) excellent long-term prognosis is mainly dependent on postoperative radioactive iodine (RAI) treatment. However, once the tumour becomes refractory, the 10-year disease-specific survival rate drops below 10%. The aim of our study was to evaluate the prognostic and biological role of the TRAIL system in FTC and to elucidate the influence of small-molecule-mediated antagonisation of inhibitor of apoptosis proteins (IAPs) on TRAIL sensitivity in vitro Tissue microarrays were constructed from forty-four patients with histologically confirmed FTC. Expression levels of TRAIL and its receptors were correlated with clinicopathological data and overall as well as recurrence-free survival. Non-iodine-retaining FTC cell lines TT2609-bib2 and FTC133 were treated with recombinant human TRAIL alone and in combination with Smac mimetics GDC-0152 or Birinapant. TRAIL-R2/DR5 as well as TRAIL-R3/DcR1 and TRAIL-R4/DcR2 were significantly higher expressed in advanced tumour stages. Both decoy receptors were negatively associated with recurrence-free and overall survival. TRAIL-R4/DcR2 additionally proved to be an independent negative prognostic marker in FTC (HR = 1.446, 95% CI: 1.144-1.826; P < 0.001). In vitro, the co-incubation of Birinapant or GDC-0152 with rh-TRAIL-sensitised FTC cell lines for TRAIL-induced apoptosis, through degradation of cIAP1/2. The TRAIL system plays an important role in FTC tumour biology. Its decoy receptors are associated with poor prognosis as well as earlier recurrence. The specific degradation of cIAP1/2 sensitises FTC cells to TRAIL-induced apoptosis and might highlight a new point of attack in patients with RAI refractory disease.

Importance of immune monitoring approaches and the use of immune checkpoints for the treatment of diffuse intrinsic pontine glioma: From bench to clinic and vice versa (Review)

On the basis of immunological results, it is not in doubt that the immune system is able to recognize and eliminate transformed cells. A plethora of studies have investigated the immune system of patients with cancer and how it is prone to immunosuppression, due in part to the decrease in lymphocyte proliferation and cytotoxic activity. The series of experiments published following the demonstration by Dr Allison's group of the potential effect of anti-cytotoxic T lymphocyte-associated antigen-4 (CTLA-4) paved the way for a new perception in cancer immunotherapy: Immune checkpoints. Several T cell-co-stimulatory molecules including cluster of differentiation (CD)28, inducible T cell co-stimulatory, 4-1BB, OX40, glucocorticoid-induced tumor necrosis factor receptor-related gene and CD27, and inhibitory molecules including T cell immunoglobulin and mucin domain-containing-3, programmed cell death-1 (PD-1), programmed cell death ligand-1 (PD-L1), V-domain immunoglobulin suppressor of T cells activation, T cell immunoglobulin and immunoreceptor tyrosine-based inhibitory motif domain, and B and T lymphocyte attenuator have been described in regulating T cell functions, and have been demonstrated to be essential targets in immunotherapy. In preclinical studies, glioblastoma multiforme, a high-grade glioma, the monotherapy targeting PD-1/PD-L1 and CTLA-4 resulted in increased survival times. An improved understanding of the pharmacodynamics and immune monitoring on glioma cancers, particularly in diffuse intrinsic pontine glioma (DIPG), an orphan type of cancer, is expected to have a major contribution to the development of novel therapeutic approaches. On the basis of the recent preclinical and clinical studies of glioma, but not of DIPG, the present review makes a claim for the importance of investigating the tumor microenvironment, the immune response and the use of immune checkpoints (agonists or antagonists) in preclinical/clinical DIPG samples by immune monitoring approaches and high-dimensional analysis. Evaluating the potential predictive and correlative biomarkers in preclinical and clinical studies may assist in answering certain crucial questions that may be useful to improve the clinical response in patients with DIPG.

The Differential Regulation of Human Telomerase Reverse Transcriptase and Vascular Endothelial Growth Factor May Contribute to the Clinically More Aggressive Behavior of P63-Positive Breast Carcinomas

p63, a p53 homologue, is a myoepithelial cell marker in the normal mammary gland but p63-positive neoplastic cells may be found in up to 11% of invasive breast carcinomas. This study aims to verify the relationship between p63 expression and several clinicopathological features and tumor markers of clinical significance in breast pathology including key regulators of the cell cycle, oncogenes, apoptosis-related proteins, metalloproteinases and their inhibitors. Immunohistochemistry with 27 primary antibodies was performed in 100 formalin-fixed paraffin-embedded samples of invasive ductal carcinomas. p63-positive cells were found in 16% of carcinomas. p63-positive carcinomas were poorly differentiated, hormone receptor-negative neoplasms with a high proliferation rate. p63 also correlated with advanced pathological stage, tumor size, and the expression of human telomerase reverse transcriptase (hTERT), tissue inhibitor of matrix metalloproteinase 1 (TIMP1) and vascular endothelial growth factor (VEGF). The expression of TIMP1 suggests that the anti-proteolytic stimuli may be preponderant in p63-positive carcinomas. hTERT activity is associated with nodal metastases and cellular proliferation. VEGF regulates angiogenesis, which is also a fundamental event in the process of tumor growth and metastatic dissemination. Thus, the differential regulation of hTERT and VEGF in p63-positive breast carcinomas may contribute to the clinically more aggressive behavior of these neoplasms.

Niclosamide induces protein ubiquitination and inhibits multiple pro-survival signaling pathways in the human glioblastoma U-87 MG cell line

Glioblastoma is the most common and lethal malignant primary brain tumor for which the development of efficacious chemotherapeutic agents remains an urgent need. The anti-helminthic drug niclosamide, which has long been in use to treat tapeworm infections, has recently attracted renewed interest due to its apparent anticancer effects in a variety of in vitro and in vivo cancer models. However, the mechanism(s) of action remains to be elucidated. In the present study, we found that niclosamide induced cell toxicity in human glioblastoma cells corresponding with increased protein ubiquitination, ER stress and autophagy. In addition, niclosamide treatment led to down-regulation of Wnt/β-catenin, PI3K/AKT, MAPK/ERK, and STAT3 pro-survival signal transduction pathways to further reduce U-87 MG cell viability. Taken together, these results provide new insights into the glioblastoma suppressive capabilities of niclosamide, showing that niclosamide can target multiple major cell signaling pathways simultaneously to effectively promote cell death in U-87 MG cells. Niclosamide constitutes a new prospect for a therapeutic treatment against human glioblastoma.

MicroRNA-155 regulates the proliferation, cell cycle, apoptosis and migration of colon cancer cells and targets CBL

MicroRNA-155 (miR-155) is a well-studied miR and acts as an oncomiR in numerous cancer types. However, the biological functions of miR-155 in colon cancer as well as its target genes have remained to be fully elucidated. In order to investigate the biological functions of miR-155, MTT, colony formation and wound healing assays, cell cycle analysis and detection of apoptosis were performed. The results demonstrated that miR-155 promoted the proliferation of colon cancer cells and enhanced their colony formation capacity, promoted their cell cycle progression and inhibited apoptosis. miR-155 also promoted the migration of colon cancer cells. In the present study, casitas B-lineage lymphoma was identified as a novel target of miR-155. The present study suggested that miR-155 functions as an oncomiR in colon cancer cells and may become a promising therapeutic target for colon cancer therapy.

DBC2/RhoBTB2 functions as a tumor suppressor protein via Musashi-2 ubiquitination in breast cancer

The gene encoding ‘deleted in breast cancer 2' (DBC2), also referred to as RHOBTB2 (Rho-related BTB domain-containing protein 2), is classified as a tumor suppressor gene. DBC2 is a substrate-specific adaptor protein for a novel class of Cullin-3 (CUL3)-based E3 ubiquitin ligases; however, it is unclear if the substrate adaptor function of DBC2 is required for its tumor suppressor activity. Furthermore, the key substrates of DBC2-mediated ubiquitination have yet to be identified. In the present study, we established a genome-wide human cDNA library-based in vitro ubiquitination target screening assay and identified Musashi-2 (MSI2) as a novel ubiquitination target protein of DBC2. MSI2 directly interacted with DBC2, and this interaction promoted MSI2 polyubiquitination and proteasomal degradation in breast cancer cells. Overexpression and knockdown experiments demonstrated that DBC2 suppressed MSI2-associated oncogenic functions and induced apoptosis. Immunohistochemistry analysis of a breast cancer tissue microarray revealed that DBC2 and MSI2 protein levels are inversely correlated in both normal breast tissues and breast cancer tissues. Taken together, these findings provide evidence that DBC2 suppresses tumorigenesis in breast cancer by ubiquitinating MSI2.

Examining ubiquitinated peptide enrichment efficiency through an epitope labeled protein

Ubiquitination is a dynamic process that is responsible for regulation of cellular responses to stimuli in a number of biological systems. Previous efforts to study this post-translational modification have focused on protein enrichment; however, recent research utilizes the presence of the di-glycine (Gly-Gly) remnants following trypsin digestion to immuno-enrich ubiquitinated peptides. Monoclonal antibodies developed to the cleaved ubiquitin modification epitope, (tert-butoxycarbonyl) glycylglycine (Boc-Gly-Gly-NHS)(1), are used to identify the Gly-Gly signature. Here, we have successfully generated the Boc-Gly-Gly-NHS modification and showed that when conjugated to a lysine containing protein, such as lysozyme, it can be applied as a standard protein to examine ubiquitinated peptide enrichment within a complex background.

Functional polyesters enable selective siRNA delivery to lung cancer over matched normal cells

Conventional chemotherapeutics nonselectively kill all rapidly dividing cells, which produces numerous side effects. To address this challenge, we report the discovery of functional polyesters that are capable of delivering siRNA drugs selectively to lung cancer cells and not to normal lung cells. Selective polyplex nanoparticles (NPs) were identified by high-throughput library screening on a unique pair of matched cancer/normal cell lines obtained from a single patient. Selective NPs promoted rapid endocytosis into HCC4017 cancer cells, but were arrested at the membrane of HBEC30-KT normal cells during the initial transfection period. When injected into tumor xenografts in mice, cancer-selective NPs were retained in tumors for over 1 wk, whereas nonselective NPs were cleared within hours. This translated to improved siRNA-mediated cancer cell apoptosis and significant suppression of tumor growth. Selective NPs were also able to mediate gene silencing in xenograft and orthotopic tumors via i.v. injection or aerosol inhalation, respectively. Importantly, this work highlights that different cells respond differentially to the same drug carrier, an important factor that should be considered in the design and evaluation of all NP carriers. Because no targeting ligands are required, these functional polyester NPs provide an exciting alternative approach for selective drug delivery to tumor cells that may improve efficacy and reduce adverse side effects of cancer therapies.

Proteomic analysis of apoptosis induction by lariciresinol in human HepG2 cells

Lariciresinol (LA) is a traditional Chinese medicine possessing anticancer activity, but its mechanism of action remains unclear. The present study explored the effects of LA on human HepG2 cells and the underlying mechanism. Our data indicated that LA inhibited cell proliferation and induced cell cycle arrest in S phase, subsequently resulting in apoptosis in HepG2 cells. Using a proteomics approach, eight differentially expressed proteins were identified. Among them, three proteins, glyceraldehyde-3-phosphate, UDP-glucose 4-epimerase, and annexin A1, were upregulated, while the other five proteins, heat shock protein 27, haptoglobin, tropomodulin-2, tubulin alpha-1A chain, and brain acid soluble protein 1, were downregulated; all of these proteins are involved in cell proliferation, metabolism, cytoskeletal organization, and movement. Network analysis of these proteins suggested that the ubiquitin-conjugating enzyme (UBC) plays an important role in the mechanism of LA. Western blotting confirmed downregulation of heat shock protein 27 and upregulation of ubiquitin and UBC expression levels in LA-treated cells, consistent with the results of two-dimensional electrophoresis and a STRING software-based analysis. Overall, LA is a multi-target compound with anti-cancer effects potentially related to the ubiquitin-proteasome pathway. This study will increase our understanding of the anticancer mechanisms of LA.

Evidence for anti-apoptotic roles of proteasome activator 28γ via inhibiting caspase activity

Proteasome activator PA28γ (REGγ, Ki antigen) has recently been demonstrated to display anti-apoptotic properties via enhancing Mdm2-p53 interaction, thereby facilitating ubiquitination and down-regulation of the tumor suppressor p53. In this study we demonstrate a correlation between cellular PA28γ levels and the sensitivity of cells towards apoptosis in different cellular contexts thereby confirming a role of proteasome activator PA28γ as an anti-apoptotic regulator. We investigated the anti-apoptotic role of PA28γ upon UV-C stimulation in B8 mouse fibroblasts stably overexpressing the PA28γ-encoding PSME3 gene and upon butyrate-induced apoptosis in human HT29 adenocarcinoma cells with silenced PSME3 gene. Interestingly, our results demonstrate that PA28γ has a strong influence on different apoptotic hallmarks, especially p53 phosphorylation and caspase activation. In detail, PA28γ and effector caspases mutually restrict each other. PA28γ is a caspase substrate, if PA28γ levels are low. In contrast, PA28γ overexpression reduces caspase activities, including the caspase-dependent processing of PA28γ. Furthermore, overexpression of PA28γ resulted in a nuclear accumulation of transcriptional active p53. In summary, our findings indicate that even in a p53-dominated cellular context, pro-apoptotic signaling might be overcome by PA28γ-mediated caspase inhibition.

Phosphorylation Regulates the Bound Structure of an Intrinsically Disordered Protein: The p53-TAZ2 Case

Disordered regions and Intrinsically Disordered Proteins (IDPs) are involved in critical cellular processes and may acquire a stable three-dimensional structure only upon binding to their partners. IDPs may follow a folding-after-binding process, known as induced folding, or a folding-before-binding process, known as conformational selection. The transcription factor p53 is involved in the regulation of cellular events that arise upon stress or DNA damage. The p53 domain structure is composed of an N-terminal transactivation domain (p53TAD), a DNA Binding Domain and a tetramerization domain. The activity of TAD is tightly regulated by interactions with cofactors, inhibitors and phosphorylation. To initiate transcription, p53TAD binds to the TAZ2 domain of CBP, a co-transcription factor, and undergoes a folding and binding process, as revealed by the recent NMR structure of the complex. The activity of p53 is regulated by phosphorylation at multiple sites on the TAD domain and recent studies have shown that modifications at three residues affect the binding towards TAZ2. However, we still do not know how these phosphorylations affect the structure of the bound state and, therefore, how they regulate the p53 function. In this work, we have used computational simulations to understand how phosphorylation affects the structure of the p53TAD:TAZ2 complex and regulates the recognition mechanism. Phosphorylation has been proposed to enhance binding by direct interaction with the folded protein or by changing the unbound conformation of IDPs, for example by pre-folding the protein favoring the recognition mechanism. Here, we show an interesting turn in the p53 case: phosphorylation mainly affects the bound structure of p53TAD, highlighting the complexity of IDP protein-protein interactions. Our results are in agreement with previous experimental studies, allowing a clear picture of how p53 is regulated by phosphorylation and giving new insights into how post-translational modifications can regulate the function of IDPs.

Molecular modeling of structural and functional variance in the SAGA deubiquitinating module caused by Sgf73 Y57A mutation

Summary of the structural and dynamic impact caused by Sgf73 Y57A mutation.

Extracellular Ubiquitin: Role in Myocyte Apoptosis and Myocardial Remodeling

Ubiquitin (UB) is a highly conserved low molecular weight (8.5 kDa) protein. It consists of 76 amino acid residues and is found in all eukaryotic cells. The covalent linkage of UB to a variety of cellular proteins (ubiquitination) is one of the most common posttranslational modifications in eukaryotic cells. This modification generally regulates protein turnover and protects the cells from damaged or misfolded proteins. The polyubiquitination of proteins serves as a signal for degradation via the 26S proteasome pathway. UB is present in trace amounts in body fluids. Elevated levels of UB are described in the serum or plasma of patients under a variety of conditions. Extracellular UB is proposed to have pleiotropic roles including regulation of immune response, anti-inflammatory, and neuroprotective activities. CXCR4 is identified as receptor for extracellular UB in hematopoietic cells. Heart failure represents a major cause of morbidity and mortality in western society. Cardiac remodeling is a determinant of the clinical course of heart failure. The components involved in myocardial remodeling include-myocytes, fibroblasts, interstitium, and coronary vasculature. Increased sympathetic nerve activity in the form of norepinephrine is a common feature during heart failure. Acting via β-adrenergic receptor (β-AR), norepinephrine is shown to induce myocyte apoptosis and myocardial fibrosis. β-AR stimulation increases extracellular levels of UB in myocytes, and UB inhibits β-AR-stimulated increases in myocyte apoptosis and myocardial fibrosis. This review summarizes intracellular and extracellular functions of UB with particular emphasis on the role of extracellular UB in cardiac myocyte apoptosis and myocardial remodeling.

Inhibition on Proteasome β1 Subunit Might Contribute to the Anti-Cancer Effects of Fangchinoline in Human Prostate Cancer Cells

Fangchinoline is a bisbenzylisoquinoline alkaloid isolated from Radix Stephaniae tetrandrae S. Moore. Fangchinoline and its structure analogue, tetrandrine, exhibited direct binding affinity with recombinant human proteasome β1 subunit and also inhibited its activity in vitro. In cultured prostate PC-3 cells and LnCap cells, fangchinoline could dose-dependently inhibit cell proliferation and caspase-like activity of cellular proteasome which was mediated by proteasome β1 subunit. The inhibitive effect of fangchinoline on caspase-like activity of proteasome was also observed in purified human erythrocyte 20S proteasome. In PC-3 cells, fangchinoline induced cell cycle arrest at G0/G1 phase and apoptosis. Treatment of PC-3 tumor-bearing nude mice with fangchinoline inhibited tumor growth, induced apoptosis and also caused decrease in proteasome activities in tumor xenografts. Dose-dependent and time-dependent accumulation of ubiquitinated proteins and important proteasome substrates such as p27, Bax and IκB-α were observed in fangchinoline-treated cells. Over-expression of proteasome β1 subunit by plasmid transfection increased sensitivity of cells to the cytotoxicity of fangchinoline while knockdown of proteasome β1 subunit ameliorated cytotoxicity of fangchinoline in PC-3 cells. Results of the present study suggested that proteasome inhibition was involved in the anti-cancer effects of fangchinoline. Fangchinoline and its structure analogues might be new natural proteasome inhibitors targeting β1 subunit.

Vitamin D3 May Ameliorate the Ketoconazole Induced Adrenal Injury: Histological and Immunohistochemical Studies on Albino Rats

Ketoconazole (KZ) is used widely for treating the superficial, systemic fungal activities and hyperandrogenemic states. Its uses are limited by its deleterious effect on histological structure and function of the adrenal cortex. This study investigates whether vitamin D3 supplement can ameliorate the morphological changes induced by KZ. Thirty four adult male albino rats were randomized into control group (Group I) which was subdivided into: control 1 (n=7) and control 2 (n=7): In control 1, rats were intraperitoneal (I.P) injected once with 1 ml of polyethylene glycol-400 for 15 consecutive days and control 2 rats were injected I.P with (1 μg/kg) of vitamin D3 for the same period. Group II (n=10): rats were I.P injected with KZ (10 mg/100 g of body weight) once daily for 15 days; Group III (n=10): rats were I.P concomitantly injected with KZ and vitamin D3 similar doses to animals in groups II and control 2 respectively. Blood samples were collected to determine plasma ACTH, corticosterone and aldosterone levels. The right adrenal specimens sections were stained with Haematoxylin & Eosin and Masson Trichrome for histological studies and treated with Bax, Ubiquitin and vitamin D receptors for immunohistochemical studies. KZ induced adrenal cortical morphological changes in forms of disturbed adrenocorticocyte cytological architecture, nuclear changes, and intracellular lipid accumulation. KZ also increased adrenal Bax and Ub but decreased the vitamin D receptors immunopositive staining expression, in addition to increased plasma ACTH as well as decreased corticosterone and aldosterone levels. These changes were ameliorated by supplementing with vitamin D3.

New Insights into the Role of Ubiquitin Networks in the Regulation of Antiapoptosis Pathways

Ubiquitin is a small modifier protein that conjugates on lysine (Lys) residues of substrates, and it can be targeted by another ubiquitin molecule to form chains through conjugation on the intrinsic Lys residues and methionine (Met) 1 residue. Ubiquitination of substrates by such chains determines the fate of substrates, thereby influencing various biological processes. In this chapter, we focus on apoptosis with an emphasis on the regulation by ubiquitination. The signal transduction of apoptosis is governed not only by the classical function of ubiquitin, which is proteasome-dependent degradation of substrates, but also by the apoptosis signaling complex formation guided by different types of ubiquitin chains. Ubiquitinations of pro- and antiapoptotic proteins are tightly regulated by particular sets of enzymes, such as ubiquitin E3 ligases and deubiquitinases (DUBs). We further discuss ubiquitination in the tumor necrosis factor (TNF) signaling pathway as an example for the ubiquitin-dependent regulation of apoptosis and cell survival.

Trailing TRAIL Resistance: Novel Targets for TRAIL Sensitization in Cancer Cells

Resistance to chemotherapeutic drugs is the major hindrance in the successful cancer therapy. The tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a member of the tumor necrosis factor (TNF) family of ligands, which initiates apoptosis in cancer cells through interaction with the death receptors DR4 and DR5. TRAIL is perceived as an attractive chemotherapeutic agent as it specifically targets cancer cells while sparing the normal cells. However, TRAIL therapy has a major limitation as a large number of the cancer develop resistance toward TRAIL and escape from the destruction by the immune system. Therefore, elucidation of the molecular targets and signaling pathways responsible for TRAIL resistance is imperative for devising effective therapeutic strategies for TRAIL resistant cancers. Although, various molecular targets leading to TRAIL resistance are well-studied, recent studies have implicated that the contribution of some key cellular processes toward TRAIL resistance need to be fully elucidated. These processes primarily include aberrant protein synthesis, protein misfolding, ubiquitin regulated death receptor expression, metabolic pathways, epigenetic deregulation, and metastasis. Novel synthetic/natural compounds that could inhibit these defective cellular processes may restore the TRAIL sensitivity and combination therapies with such compounds may resensitize TRAIL resistant cancer cells toward TRAIL-induced apoptosis. In this review, we have summarized the key cellular processes associated with TRAIL resistance and their status as therapeutic targets for novel TRAIL-sensitizing agents.

Low-dose arsenic trioxide combined with aclacinomycin A synergistically enhances the cytotoxic effect on human acute myelogenous leukemia cell lines by induction of apoptosis

Acute myeloid leukemia (AML) is a common disorder in the elderly. Although remarkable progress has been made over recent decades, the outcome remains poor. Thus, the development of a more effective method to overcome this problem is necessary. In this study, we aimed to investigate the synergistic cytotoxic effect of low-dose arsenic trioxide (As2O3) combined with aclacinomycin A (ACM) on the human AML cell lines KG-1a and HL-60, and to clarify the underlying mechanism. Results showed that As2O3 combined with ACM exerted a synergistic cytotoxic effect by activation of the apoptosis pathway. Additionally, we found that the combination treatment decreased Bcl-2, c-IAP and XIAP expression but increased SMAC and caspase-3 expression more significantly than the single drug treatments. Furthermore, combination index (CI) values were < 1 in all matched combination groups. Additional evaluation of As2O3 combined with ACM as a potential therapeutic benefit for AML seems warranted.

Carfilzomib demonstrates broad anti-tumor activity in pre-clinical non-small cell and small cell lung cancer models

BACKGROUND

Carfilzomib (CFZ) is a proteasome inhibitor that selectively and irreversibly binds to its target and has been approved in the US for treatment of relapsed and refractory multiple myeloma. Phase 1B studies of CFZ reported signals of clinical activity in solid tumors, including small cell lung cancer (SCLC). The aim of this study was to investigate the activity of CFZ in lung cancer models.

METHODS

A diverse panel of human lung cancer cell lines and a SHP77 small cell lung cancer xenograft model were used to investigate the anti-tumor activity of CFZ.

RESULTS

CFZ treatment inhibited both the constitutive proteasome and the immunoproteasome in lung cancer cell lines. CFZ had marked anti-proliferative activity in A549, H1993, H520, H460, and H1299 non-small cell lung cancer (NSCLC) cell lines, with IC50 values after 96 hour exposure from <1.0 nM to 36 nM. CFZ had more variable effects in the SHP77 and DMS114 SCLC cell lines, with IC50 values at 96 hours from <1 nM to 203 nM. Western blot analysis of CFZ-treated H1993 and SHP77 cells showed cleavage of poly ADP ribose polymerase (PARP) and caspase-3, indicative of apoptosis, and induction of microtubule-associated protein-1 light chain-3B (LC3B), indicative of autophagy. In SHP77 flank xenograft tumors, CFZ monotherapy inhibited tumor growth and prolonged survival, while no additive or synergistic anti-tumor efficacy was observed for CFZ + cisplatin (CDDP).

CONCLUSIONS

CFZ demonstrated anti-proliferative activity in lung cancer cell lines in vitro and resulted in a significant survival advantage in mice with SHP77 SCLC xenografts, supporting further pre-clinical and clinical investigations of CFZ in NSCLC and SCLC.

Bortezomib sensitises TRAIL-resistant HPV-positive head and neck cancer cells to TRAIL through a caspase-dependent, E6-independent mechanism

Human papillomavirus (HPV) is causative for a new and increasing form of head and neck squamous cell carcinomas (HNSCCs). Although localised HPV-positive cancers have a favourable response to radio-chemotherapy (RT/CT), the impact of HPV in advanced or metastatic HNSCC remains to be defined and targeted therapeutics need to be tested for cancers resistant to RT/CT. To this end, we investigated the sensitivity of HPV-positive and -negative HNSCC cell lines to TRAIL (tumour necrosis factor-related apoptosis-inducing ligand), which induces tumour cell-specific apoptosis in various cancer types. A clear correlation was observed between HPV positivity and resistance to TRAIL compared with HPV-negative head and neck cancer cell lines. All TRAIL-resistant HPV-positive cell lines tested were sensitised to TRAIL-induced cell death by treatment with bortezomib, a clinically approved proteasome inhibitor. Bortezomib-mediated sensitisation to TRAIL was associated with enhanced activation of caspase-8, -9 and -3, elevated membrane expression levels of TRAIL-R2, cytochrome c release and G2/M arrest. Knockdown of caspase-8 significantly blocked cell death induced by the combination therapy, whereas the BH3-only protein Bid was not required for induction of apoptosis. XIAP depletion increased the sensitivity of both HPV-positive and -negative cells to TRAIL alone or in combination with bortezomib. In contrast, restoration of p53 following E6 knockdown in HPV-positive cells had no effect on their sensitivity to either single or combination therapy, suggesting a p53-independent pathway for the observed response. In summary, bortezomib-mediated proteasome inhibition sensitises previously resistant HPV-positive HNSCC cells to TRAIL-induced cell death through a mechanism involving both the extrinsic and intrinsic pathways of apoptosis. The cooperative effect of these two targeted anticancer agents therefore represents a promising treatment strategy for RT/CT-resistant HPV-associated head and neck cancers.

PhosphoPICK: modelling cellular context to map kinase-substrate phosphorylation events

MOTIVATION

The determinants of kinase-substrate phosphorylation can be found both in the substrate sequence and the surrounding cellular context. Cell cycle progression, interactions with mediating proteins and even prior phosphorylation events are necessary for kinases to maintain substrate specificity. While much work has focussed on the use of sequence-based methods to predict phosphorylation sites, there has been very little work invested into the application of systems biology to understand phosphorylation. Lack of specificity in many kinase substrate binding motifs means that sequence methods for predicting kinase binding sites are susceptible to high false-positive rates.

RESULTS

We present here a model that takes into account protein-protein interaction information, and protein abundance data across the cell cycle to predict kinase substrates for 59 human kinases that are representative of important biological pathways. The model shows high accuracy for substrate prediction (with an average AUC of 0.86) across the 59 kinases tested. When using the model to complement sequence-based kinase-specific phosphorylation site prediction, we found that the additional information increased prediction performance for most comparisons made, particularly on kinases from the CMGC family. We then used our model to identify functional overlaps between predicted CDK2 substrates and targets from the E2F family of transcription factors. Our results demonstrate that a model harnessing context data can account for the short-falls in sequence information and provide a robust description of the cellular events that regulate protein phosphorylation.

AVAILABILITY AND IMPLEMENTATION

The method is freely available online as a web server at the website http://bioinf.scmb.uq.edu.au/phosphopick.

CONTACT

m.boden@uq.edu.au

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Transcriptome profiling of expression changes during neuronal death by RNA-Seq

The molecular mechanisms underlying neuronal death are poorly understood. One of the most widely used models to study neuronal death are cultured cerebellar granule neurons (CGNs) which undergo apoptosis when switched from a medium containing depolarizing levels of potassium (HK) to a medium with low non-depolarizing levels of potassium (LK). Previously, other labs have used DNA microarray analysis to characterize gene expression changes in LK-treated CGNs. However, microarray analysis is only capable of measuring the status of known transcripts, and expression of low-abundance mRNAs is often not detected by the hybridization-based approach. We have used RNA-sequencing to conduct a more detailed and comprehensive analysis of gene expression changes in CGNs induced to die by LK treatment. RNA-seq investigates the status of both known transcripts as well as exploring new ones and is substantially more sensitive than the microarray approach. We have found that the expression of 4334 genes is significantly altered in LK-treated CGNs with 2199 being up-regulated while 2135 are down-regulated. Genes functioning in cell death and survival regulation, cell growth and proliferation and molecular transport were most affected by LK treatment. Further, a large number of genes involved in nervous system development and function were also deregulated. Analysis of signaling pathways that were affected in LK-induced death included but were not limited to mitochondrial dysfunction and oxidative phosphorylation, consistent with a number of studies showing perturbations of these pathways in neurodegenerative disorders. Thus, our study identifies a large number of new genes that are affected during the process of neuronal death. While a majority of these changes may reflect consequences of the induction of neuronal death, many of the genes that we have identified are likely to be critical and potentially novel mediators of neuronal death, including death associated with neurodegenerative disease.

Regulation of cardiac proteasomes by ubiquitination, SUMOylation, and beyond

The ubiquitin-proteasome system (UPS) is the major intracellular degradation system, and its proper function is critical to the health and function of cardiac cells. Alterations in cardiac proteasomes have been linked to several pathological phenotypes, including cardiomyopathies, ischemia-reperfusion injury, heart failure, and hypertrophy. Defects in proteasome-dependent cellular protein homeostasis can be causal for the initiation and progression of certain cardiovascular diseases. Emerging evidence suggests that the UPS can specifically target proteins that govern pathological signaling pathways for degradation, thus altering downstream effectors and disease outcomes. Alterations in UPS-substrate interactions in disease occur, in part, due to direct modifications of 19S, 11S or 20S proteasome subunits. Post-translational modifications (PTMs) are one facet of this proteasomal regulation, with over 400 known phosphorylation sites, over 500 ubiquitination sites and 83 internal lysine acetylation sites, as well as multiple sites for caspase cleavage, glycosylation (such as O-GlcNAc modification), methylation, nitrosylation, oxidation, and SUMOylation. Changes in cardiac proteasome PTMs, which occur in ischemia and cardiomyopathies, are associated with changes in proteasome activity and proteasome assembly; however several features of this regulation remain to be explored. In this review, we focus on how some of the less common PTMs affect proteasome function and alter cellular protein homeostasis. This article is part of a Special Issue entitled "Protein Quality Control, the Ubiquitin Proteasome System, and Autophagy".