ERK/ribosomal S6 kinase (RSK) signaling positively regulates death receptor 5 expression through co-activation of CHOP and Elk1

MiR-29 and MiR-140 regulate TRAIL-induced drug tolerance in lung cancer

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has chemotherapeutic potential as a regulator of an extrinsic apoptotic ligand, but its effect as a drug is limited by innate and acquired resistance. Recent findings suggest that an intermediate drug tolerance could mediate acquired resistance, which has made the main obstacle for limited utility of TRAIL as an anti-cancer therapeutics. We propose miRNA-dependent epigenetic modification drives the drug tolerant state in TRAIL-induced drug tolerant (TDT). Transcriptomic analysis revealed miR-29 target gene activation in TDT cells, showing oncogenic signature in lung cancer. Also, the restored TRAIL-sensitivity was associated with miR-29ac and 140-5p expressions, which is known as tumor suppressor by suppressing oncogenic protein RSK2 (p90 ribosomal S6 kinase), further confirmed in patient samples. Moreover, we extended this finding into 119 lung cancer cell lines from public data set, suggesting a significant correlation between TRAIL-sensitivity and RSK2 mRNA expression. Finally, we found that increased RSK2 mRNA is responsible for NF-κB activation, which we previously showed as a key determinant in both innate and acquired TRAIL-resistance. Our findings support further investigation of miR-29ac and -140-5p inhibition to maintain TRAIL-sensitivity and improve the durability of response to TRAIL in lung cancer.

ALK inhibitors downregulate the expression of death receptor 4 in ALK-mutant lung cancer cells via facilitating Fra-1 and c-Jun degradation and subsequent AP-1 suppression

The successful treatment of patients with advanced non-small cell lung cancer (NSCLC) harboring chromosomal rearrangements of anaplastic lymphoma kinase (ALK) with ALK tyrosine kinase inhibitors (ALK-TKIs) represents a promising targeted therapy. As a result, various ALK-TKIs have been rapidly developed, some of which are approved while some are being tested in clinical trials. Death receptor 4 (DR4; also called TNFRSF10A or TRAIL-R1) is a cell surface protein, which functions as a pro-apoptotic protein that transduces TRAIL death signaling to trigger apoptosis. DR4 expression is positively regulated by MEK/ERK signaling and thus can be downregulated by MEK/ERK inhibition. This study thus focused on determining the effects of AKL-TKIs on DR4 expression and the underlying mechanisms. Three tested ALK-TKIs including APG-2449, brigatinib and alectinib effectively and preferentially inhibited Akt/mTOR as well as MEK/ERK signaling and decreased cell survival in ALK-mutant (ALKm) NSCLC cells with induction of apoptosis. This was also true for DR4 downregulation, which occurred even at 2 h post treatment. These ALK-TKIs did not affect DR4 protein stability, rather decreased DR4 mRNA expression. In parallel, they promoted degradation and reduced the levels of Fra-1 and c-Jun, two critical components of AP-1, and suppressed AP-1 (Fra-1/c-Jun)-dependent transcription/expression of DR4. Hence, it appears that ALK-TKIs downregulate DR4 expression in ALKm NSCLC cells via facilitating Fra-1 and c-Jun degradation and subsequent AP-1 suppression. Our findings thus warrant further investigation of the biological significance of DR4 downregulation in ALK-targeted cancer therapy.

Asprosin inhibits macrophage lipid accumulation and reduces atherosclerotic burden by up-regulating ABCA1 and ABCG1 expression via the p38/Elk-1 pathway

Background

Asprosin, a newly discovered adipokine, is a C-terminal cleavage product of profibrillin. Asprosin has been reported to participate in lipid metabolism and cardiovascular disease, but its role in atherogenesis remains elusive.

Methods

Asprosin was overexpressed in THP-1 macrophage-derived foam cells and apoE^−/− mice using the lentiviral vector. The expression of relevant molecules was determined by qRT-PCR and/or western blot. The intracellular lipid accumulation was evaluated by high-performance liquid chromatography and Oil red O staining. HE and Oil red O staining was employed to assess plaque burden in vivo. Reverse cholesterol transport (RCT) efficiency was measured using [³H]-labeled cholesterol.

Results

Exposure of THP-1 macrophages to oxidized low-density lipoprotein down-regulated asprosin expression. Lentivirus-mediated overexpression of asprosin promoted cholesterol efflux and inhibited lipid accumulation in THP-1 macrophage-derived foam cells. Mechanistic analysis revealed that asprosin overexpression activated p38 and stimulated the phosphorylation of ETS-like transcription factor (Elk-1) at Ser383, leading to Elk-1 nuclear translocation and the transcriptional activation of ATP binding cassette transporters A1 (ABCA1) and ABCG1. Injection of lentiviral vector expressing asprosin diminished atherosclerotic lesion area, increased plaque stability, improved plasma lipid profiles and facilitated RCT in apoE^−/− mice. Asprosin overexpression also increased the phosphorylation of p38 and Elk-1 as well as up-regulated the expression of ABCA1 and ABCG1 in the aortas.

Conclusion

Asprosin inhibits lipid accumulation in macrophages and decreases atherosclerotic burden in apoE^−/− mice by up-regulating ABCA1 and ABCG1 expression via activation of the p38/Elk-1 signaling pathway.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-022-03542-0.

CSC-3436 sensitizes triple negative breast cancer cells to TRAIL-induced apoptosis through ROS-mediated p38/CHOP/death receptor 5 signaling pathways

Tumor necrosis factor-related apoptosis-induced ligand (TRAIL) shows little or no toxicity in most normal cells and preferentially induces apoptosis in a variety of malignant cells. However, patients develop resistance to TRAIL, therefore, sensitizing agents that can sensitize the tumor cells to TRAIL-mediated apoptosis are necessary. In this study, we investigated the effect of 2-(3-hydroxyphenyl)-5-methylnaphthyridin-4-one (CSC-3436), an useful flavonoid, to overcome the TRAIL-resistant triple negative breast cancer (TNBC) cells. We found that CSC-3436 potentiated TRAIL-induced apoptosis in TRAIL-resistant TNBC cells and this correlated with the upregulation of death receptors (DR)-5 and down-regulation of decreased decoy receptor (DcR)-1 expression. When examined for its mechanism, we found that the decreased expression of anti-apoptotic proteins c-FLIPS/L, Bcl-Xl, Bcl-2, Survivin, and XIAP. CSC-3436 would increase the expression of Bax and promoted the cleavage of bid. In addition, the induction of DR5 by CSC-3436 was found to be dependent on the modulation of reactive oxygen species (ROS)/p38/C/EBP-homologous protein (CHOP) signaling pathways. Overall, our results indicated that CSC-3436 could potentiate the apoptotic effects of TRAIL through down-regulation of cell survival proteins and upregulation of DR5 via the ROS-mediated upregulation of CHOP protein.

Differential effects of cyclooxygenase-2 (COX-2) inhibitors on endoplasmic reticulum (ER) stress in human coronary artery endothelial cells

Selective cyclooxygenase-2 (COX-2) inhibitor rofecoxib was pulled off the market because of its association with increased risk of adverse cardiovascular effects. The precise underlying mechanism for the differential effects of COX-2 inhibitors on cardiovascular risk is not known. Since endoplasmic reticulum (ER) stress is implicated in atherogenesis, we examined the effects of COX-2 inhibitors on ER stress in primary human coronary artery endothelial cells (HCAEC), human umbilical vein endothelial cells (HUVEC), and human pulmonary artery endothelial cells (HPAEC). ER stress was measured in HCAEC treated with either tunicamycin (TM) or high-concentrations (27.5 mM) of dextrose (HD) using the secreted alkaline phosphatase (ES-TRAP) assay. Markers of the unfolded protein response (UPR) such as activating transcription factor 6 (ATF6), glucose-regulated protein 78 (GRP78), inositol-requiring enzyme 1α (IRE1α), phospho-IRE1α, protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK), and phospho-PERK were measured by Western blot. Treatment of HCAEC with TM and HD decreased secreted alkaline phosphatase activity indicating increased ER stress. Treatment of cells exposed to TM or HD with celecoxib, meloxicam, ibuprofen, and acetylsalicylic acid, but not rofecoxib, resulted in a dose-dependent decrease in ER stress. High-dextrose and TM increased IRE1α and PERK phosphorylation and ATF6 and GRP78 expression. Treatment with celecoxib, but not rofecoxib, inhibited these markers of the UPR. Treatment with selective COX-2 inhibitors, with the exception of rofecoxib, suppressed ER stress as measured with both alkaline phosphatase activity assays and markers for the UPR. The inability of rofecoxib to inhibit ER stress, unlike the other cyclooxygenase inhibitors tested, may have contributed to its unfavorable effects on cardiovascular outcomes.

Targeting c-Myc to overcome acquired resistance of EGFR mutant NSCLC cells to the third generation EGFR tyrosine kinase inhibitor, osimertinib

Osimertinib (AZD9291 or TAGRISSOTM) is a promising and approved third-generation epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (TKI) for treating patients with advanced non-small cell lung cancer (NSCLC) harboring EGFR-activating mutations or the resistant T790M mutation. However, the inevitable emergence of acquired resistance limits its long-term efficacy. A fuller understanding of the mechanism of action of osimertinib and its linkage to acquired resistance will enable the development of more efficacious therapeutic strategies. Consequently, we have identified a novel connection between osimertinib or other EGFR TKI and c-Myc. Osimertinib rapidly and sustainably decreased c-Myc levels primarily via enhancing protein degradation in EGFR-mutant (EGFRm) NSCLC cell lines and xenograft tumors. c-Myc levels were substantially elevated in different EGFRm NSCLC cell lines with acquired resistance to osimertinib in comparison with their corresponding parental cell lines and could not be reduced any further by osimertinib. Consistently, c-Myc levels were elevated in the majority of EGFRm NSCLC tissues relapsed from EGFR-TKI treatment compared to their corresponding untreated baseline c-Myc levels. Suppression of c-Myc through knockdown or pharmacological targeting with BET inhibitors restored the response of resistant cell lines to osimertinib. These findings indicate that c-Myc modulation mediates the therapeutic efficacy of osimertinib and the development of osimertinib-acquired resistance. Furthermore, they establish c-Myc as a potential therapeutic target and warrant clinical testing of BET inhibition as a potential strategy to overcome acquired resistance to osimertinib or other EGFR inhibitors.

MET inhibition downregulates DR4 expression in MET-amplified lung cancer cells with acquired resistance to EGFR inhibitors through suppressing AP-1-mediated transcription

Death receptor 4 (DR4) is a cell surface protein that is generally thought to mediate apoptosis upon binding to its ligand named TRAIL. However, its contribution to apoptosis resistance has also been reported. MET (or c-MET) gene amplification represents an important mechanism for acquired resistance to EGFR tyrosine kinase inhibitors (EGFR-TKIs) against EGFR mutant non-small cell lung cancer (NSCLC). This study focuses on demonstrating the impact of MET inhibition on DR4 modulation in MET-amplified EGFR mutant NSCLC cell lines and the underlying mechanisms. Several MET inhibitors decreased DR4 levels in MET-amplified HCC827 cell lines resistant to EGFR-TKIs with no or limited effects on modulating DR5 levels, while increasing DR4 levels in HCC827 parental cells and other NSCLC cell lines. MET inhibitors did not affect DR4 stability, but decreased DR4 mRNA levels with suppression of AP-1-dependent DR4 promoter transactivation. Moreover, these inhibitors suppressed ERK and c-Jun phosphorylation accompanied with decreasing c-Jun levels. Hence, it is likely that MET inhibition downregulates DR4 expression in MET-amplified EGFR mutant NSCLC cells through suppressing AP-1-mediated DR4 transcription. Osimertinib combined with MET inhibition synergistically induces apoptosis in the MET-amplified EGFR mutant NSCLC cells accompanied with augmented DR4 reduction both in vitro and in vivo. Furthermore, MET inhibition combined with TRAIL enhanced killing of MET-amplified EGFR mutant HCC827/AR cells, but not HCC827 parental cells. These data collectively suggest that DR4 may possess an unrecognized anti-apoptotic function, contributing to apoptosis resistance under given conditions.

Downregulation of death receptor 4 is tightly associated with positive response of EGFR mutant lung cancer to EGFR-targeted therapy and improved prognosis

Death receptor 4 (DR4), a cell surface receptor, mediates apoptosis or induces inflammatory cytokine secretion upon binding to its ligand depending on cell contexts. Its prognostic impact in lung cancer and connection between EGFR-targeted therapy and DR4 modulation has not been reported and thus was the focus of this study. Methods: Intracellular protein alterations were measured by Western blotting. Cell surface protein was detected with antibody staining and flow cytometry. mRNA expression was monitored with qRT-PCR. Gene transactivation was analyzed with promoter reporter assay. Drug dynamic effects in vivo were evaluated using xenografts. Gene modulations were achieved with gene overexpression and knockdown. Proteins in human archived tissues were stained with immunohistochemistry. Results: EGFR inhibitors (e.g., osimertinib) decreased DR4 levels only in EGFR mutant NSCLC cells and tumors, being tightly associated with induction of apoptosis. This modulation was lost once cells became resistant to these inhibitors. Increased levels of DR4 were detected in cell lines with acquired osimertinib resistance and in NSCLC tissues relapsed from EGFR-targeted therapy. DR4 knockdown induced apoptosis and augmented apoptosis when combined with osimertinib in both sensitive and resistant cell lines, whereas enforced DR4 expression significantly attenuated osimertinib-induced apoptosis. Mechanistically, osimertinib induced MARCH8-mediated DR4 proteasomal degradation and suppressed MEK/ERK/AP-1-dependent DR4 transcription, resulting in DR4 downregulation. Moreover, we found that DR4 positive expression in human lung adenocarcinoma was significantly associated with poor patient survival. Conclusions: Collectively, we suggest that DR4 downregulation is coupled to therapeutic efficacy of EGFR-targeted therapy and predicts improved prognosis, revealing a previously undiscovered connection between EGFR-targeted therapy and DR4 modulation.

P53-independent partial restoration of the p53 pathway in tumors with mutated p53 through ATF4 transcriptional modulation by ERK1/2 and CDK9

A long-term goal in the cancer-field has been to develop strategies for treating p53-mutated tumors. A novel small-molecule, PG3-Oc, restores p53 pathway-signaling in tumor cells with mutant-p53, independently of p53/p73. PG3-Oc partially upregulates the p53-transcriptome (13.7% of public p53 target-gene dataset; 15.2% of in-house dataset) and p53-proteome (18%, HT29; 16%, HCT116-p53^−/−). Bioinformatic analysis indicates critical p53-effectors of growth-arrest (p21), apoptosis (PUMA, DR5, Noxa), autophagy (DRAM1), and metastasis-suppression (NDRG1) are induced by PG3-Oc. ERK1/2- and CDK9-kinases are required to upregulate ATF4 by PG3-Oc which restores p53 transcriptomic-targets in cells without functional-p53. PG3-Oc represses MYC (ATF4-independent), and upregulates PUMA (ATF4-dependent) in mediating cell death. With largely nonoverlapping transcriptomes, induced-ATF4 restores p53 transcriptomic targets in drug-treated cells including functionally important mediators such as PUMA and DR5. Our results demonstrate novel p53-independent drug-induced molecular reprogramming involving ERK1/2, CDK9, and ATF4 to restore upregulation of p53 effector genes required for cell death and tumor suppression.

Stress-induced TRAILR2 expression overcomes TRAIL resistance in cancer cell spheroids

The influence of 3D microenvironments on apoptosis susceptibility remains poorly understood. Here, we studied the susceptibility of cancer cell spheroids, grown to the size of micrometastases, to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). Interestingly, pronounced, spatially coordinated response heterogeneities manifest within spheroidal microenvironments: In spheroids grown from genetically identical cells, TRAIL-resistant subpopulations enclose, and protect TRAIL-hypersensitive cells, thereby increasing overall treatment resistance. TRAIL-resistant layers form at the interface of proliferating and quiescent cells and lack both TRAILR1 and TRAILR2 protein expression. In contrast, oxygen, and nutrient deprivation promote high amounts of TRAILR2 expression in TRAIL-hypersensitive cells in inner spheroid layers. COX-II inhibitor celecoxib further enhanced TRAILR2 expression in spheroids, likely resulting from increased ER stress, and thereby re-sensitized TRAIL-resistant cell layers to treatment. Our analyses explain how TRAIL response heterogeneities manifest within well-defined multicellular environments, and how spatial barriers of TRAIL resistance can be minimized and eliminated.

CXXC finger protein 4 inhibits the CDK18-ERK1/2 axis to suppress the immune escape of gastric cancer cells with involvement of ELK1/MIR100HG pathway

Gastric cancer, is the fourth most common tumour type yet, ranks second in terms of the prevalence of cancer‐related deaths worldwide. CXXC finger protein 4 (CXXC4) has been considered as a novel cancer suppressive factor, including gastric cancer. This study attempted to investigate the possible function of CXXC4 in gastric cancer and the underlying mechanism. The binding of the ETS domain‐containing protein‐1 (ELK1) to the long non‐coding RNA MIR100HG promoter region was identified. Then, their expression patterns in gastric cancer tissues and cells (SGC7901) were detected. A CCK‐8 assay was used to detect SGC7901 cell proliferation. Subsequently, SGC7901 cells were co‐cultured with CD3+ T cells, followed by measurement of CD3+ T cell proliferation, magnitude of IFN‐γ+ T cell population and IFN‐γ secretion. A nude mouse model was subsequently developed for in vivo validation of the in vitro results. Low CXXC4 expression was found in SGC7901 cells. Nuclear entry of ELK1 can be inhibited by suppression of the extent of ELK1 phosphorylation. Furthermore, ELK1 is able to bind the MIR100HG promoter. Overexpression of CXXC4 resulted in weakened binding of ELK1 to the MIR100HG promoter, leading to a reduced proliferative potential of SGC7901 cells, and an increase in IFN‐γ secretion from CD3+ T cells. Moreover, in vivo experiments revealed that CXXC4 inhibited immune escape of gastric cancer cells through the ERK1/2 axis. Inhibition of the CXXC4/ELK1/MIR100HG pathway suppressed the immune escape of gastric cancer cells, highlighting a possible therapeutic target for the treatment of gastric cancer.

TRAIL receptor signaling: From the basics of canonical signal transduction toward its entanglement with ER stress and the unfolded protein response

The cytokine tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is a member of the large TNF superfamily that can trigger apoptosis in transformed or infected cells by binding and activating two receptors, TRAIL receptor 1 (TRAILR1) and TRAIL receptor 2 (TRAILR2). Compared to other death ligands of the same family, TRAIL induces apoptosis preferentially in malignant cells while sparing normal tissue and has therefore been extensively investigated for its suitability as an anti-cancer agent. Recently, it was noticed that TRAIL receptor signaling is also linked to endoplasmic reticulum (ER) stress and the unfolded protein response (UPR). The role of TRAIL receptors in regulating cellular apoptosis susceptibility therefore is broader than previously thought. Here, we provide an overview of TRAIL-induced signaling, covering the core signal transduction during extrinsic apoptosis as well as its link to alternative outcomes, such as necroptosis or NF-κB activation. We discuss how environmental factors, transcriptional regulators, and genetic or epigenetic alterations regulate TRAIL receptors and thus alter cellular TRAIL susceptibility. Finally, we provide insight into the role of TRAIL receptors in signaling scenarios that engage the unfolded protein response and discuss how these findings might be translated into new combination therapies for cancer treatment.

ERK inhibition effectively overcomes acquired resistance of epidermal growth factor receptor-mutant non-small cell lung cancer cells to osimertinib

BACKGROUND

Osimertinib (AZD9291), a third-generation, mutation-selective epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (EGFR-TKI), is an approved drug for patients who have non-small cell lung cancer (NSCLC) with activating EGFR mutations or those harboring a resistant T790M mutation. Unfortunately, all patients eventually relapse and develop resistance to osimertinib. The current study addressed whether ERK inhibition exerts effects similar to those produced by MEK inhibition in overcoming acquired resistance to osimertinib.

METHODS

Drug effects on cell and tumor growth were assessed by measuring cell number alterations and colony formation in vitro and with xenografts in nude mice in vivo. Apoptosis was assessed with annexin V/flow cytometry and protein cleavage. Protein alterations in cells were detected with Western blot analysis. Gene overexpression and knockout were achieved with lentiviral infection and CRISPR/Cas9, respectively.

RESULTS

The combination of osimertinib with an ERK inhibitor synergistically decreased the survival of osimertinib-resistant cell lines with enhanced induction of apoptosis and effectively inhibited the growth of osimertinib-resistant xenografts in nude mice. Moreover, the combination of an MEK or ERK inhibitor with a first-generation (eg, erlotinib) or second-generation (eg, afatinib) EGFR-TKI also very effectively inhibited the growth of osimertinib-resistant cells in vitro and of tumors in vivo, although these cell lines were cross-resistant to first-generation or second-generation EGFR-TKIs.

CONCLUSIONS

The current findings emphasize the importance of targeting MEK/ERK signaling in maintaining the long-term benefit of osimertinib through overcoming acquired resistance to osimertinib, warranting further investigation of this therapeutic strategy to improve the therapeutic efficacy of osimertinib in the clinic.

The Third-Generation EGFR Inhibitor, Osimertinib, Promotes c-FLIP Degradation, Enhancing Apoptosis Including TRAIL-Induced Apoptosis in NSCLC Cells with Activating EGFR Mutations

The third-generation EGFR inhibitor, osimertinib (AZD9291), selectively and irreversibly inhibits EGFR activating and T790 M mutants while sparing wild-type EGFR. Osimertinib is now an approved drug for non-small cell lung cancer (NSCLC) patients with activating EGFR mutations (first-line) or those who have become resistant to 1st generation EGFR inhibitors through the T790 M mutation (second-line). Unfortunately, all patients eventually relapse and develop resistance to osimertinib. Hence, it is essential to fully understand the biology underlying the development of resistance to osimertinib in order to improve its therapeutic efficacy and overcome resistance. Cellular FLICE-inhibitory protein (c-FLIP) is a truncated form of caspase-8 and functions as a key inhibitor of the extrinsic apoptotic pathway. The current study has demonstrated that osimertinib reduces c-FLIP levels via facilitating its degradation and enhances apoptosis induced by tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) primarily in NSCLC with activating EGFR mutations. Moreover, modulation of c-FLIP expression levels, to some degree, also alters the sensitivities of EGFR mutant NSCLC cells to undergo osimertinib-induced apoptosis, suggesting that c-FLIP suppression is an important event contributing to the antitumor activity of osimertinib against EGFR mutant NSCLC.

Involvement of ERK1/2-mediated ELK1/CHOP/DR5 pathway in 6-(methylsulfinyl)hexyl isothiocyanate-induced apoptosis of colorectal cancer cells

6-(Methylsulfinyl)hexyl isothiocyanate (6-MSITC) is a major bioactive compound in Wasabi. Although 6-MSITC is reported to have cancer chemopreventive activities in rat model, the molecular mechanism is unclear. In this study, we investigated the anticancer mechanisms using two types of human colorectal cancer cells (HCT116 p53^+/+ and p53^-/-). 6-MSITC caused cell cycle arrest in G₂/M phase and induced apoptosis in both types of cells in the same fashion. Signaling data revealed that the activation of ERK1/2, rather than p53, is recruited for 6-MSITC-induced apoptosis. 6-MSITC stimulated ERK1/2 phosphorylation, and then activated ERK1/2 signaling including ELK1 phosphorylation, and upregulation of C/EBP homologous protein (CHOP) and death receptor 5 (DR5). The MEK1/2 inhibitor U0126 blocked all of these molecular events induced by 6-MSITC, and enhanced the cell viability in both types of cells in the same manner. These results indicated that ERK1/2-mediated ELK1/CHOP/DR5 pathway is involved in 6-MSITC-induced apoptosis in colorectal cancer cells. Abbreviations: CHOP: C/EBP homologous protein; DR5: death receptor 5; ELK1: ETS transcription factor; ERK1/2: extracellular signal-regulated kinase 1/2; JNK: Jun-N-terminal kinase; MAPK: mitogen-activated protein kinase; MEK1/2: MAP/ERK kinase 1/2; 6-MSITC: 6-(methylsulfinyl)hexyl isothiocyanate; MTT: 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide; PARP: poly(ADP-ribose) polymerase.

Oleandrin synergizes with cisplatin in human osteosarcoma cells by enhancing cell apoptosis through activation of the p38 MAPK signaling pathway

Purpose

Our previous studies have reported the antitumor effect of oleandrin on osteosarcoma; however, its chemosensitizing effect in osteosarcoma treatment is still unknown. Therefore, we explored the sensitizing effects of oleandrin to cisplatin in osteosarcoma and investigated the potential mechanisms.

Methods

After exposure to oleandrin and/or cisplatin, CCK-8 and colony formation assays, DAPI staining and flow cytometry were performed to detect cell proliferation and apoptosis in 143B, U-2OS and MG-63 osteosarcoma cells. The median-effect analysis was applied to evaluate the combined effect. Western blot was used to determine the expression of related proteins. Osteosarcoma xenografts and histological observations were applied to confirm the combined effect in vivo.

Results

Compared with cisplatin or oleandrin alone, the combined treatment significantly inhibited cell proliferation and induced cell apoptosis. The median-effect analysis indicated a synergistic cytotoxic effect. The combined treatment downregulated Bcl-2 and upregulated Bax and cleaved caspase-3, -8 and -9. And the suppression of caspases reduced cell death. Furthermore, oleandrin alone or with cisplatin, activated the p38 MAPK/Elk-1 pathway. The inhibition of the p38 MAPK pathway increased cell viability and reduced apoptosis. In vivo, the combined treatment was also verified to significantly inhibit tumor growth, induce apoptosis and activate the p38 MAPK pathway.

Conclusions

The combination of oleandrin with cisplatin exerts a synergistic antitumor effect in osteosarcoma, which relates to the activation of the p38 MAPK pathway.

Monocyte chemotactic protein-induced protein-1 enhances DR5 degradation and negatively regulates DR5 activation-induced apoptosis through its deubiquitinase function

Monocyte chemotactic protein-induced protein-1 (MCPIP1; also called Regnase-1) encoded by the ZC3H12A gene critically regulates inflammatory responses and immune homeostasis primarily by RNase-dependent and -independent mechanisms. However, the relationship of MCPIP1 with apoptosis and cancer and the underlying mechanisms are largely unclear. The current study has demonstrated a previously uncovered connection between MCPIP1 and the negative regulation of death receptor 5 (DR5; also known as TRAIL-R2 or killer/DR5), a cell surface receptor for tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), which is produced endogenously by various immune cells such as T cells. Our findings have revealed that MCPIP1 decreases both total cellular and cell surface DR5, primarily through modulating DUB-mediated protein autophagic/lysosomal degradation. Suppression of MCPIP1 by gene knockdown induces the formation of death-induced signaling complex (DISC) and enhances TRAIL or DR5 activation-induced apoptosis in cancer cells. Moreover, we demonstrated an inverse correlation between MCPIP1 expression and DR5 expression/cell sensitivity to DR5 activation-induced apoptosis in cancer cells. Our findings warrant future investigation of the roles of negative regulation of DR5 by MCPIP1 in cancer and in T-cell immunity.

Identification of key genes and long non‑coding RNAs in celecoxib‑treated lung squamous cell carcinoma cell line by RNA‑sequencing

Celecoxib is an inhibitor of cyclooxygenase-2, a gene that is often aberrantly expressed in the lung squamous cell carcinoma (LSQCC). The present study aims to provide novel insight into chemoprevention by celecoxib treatment. The human LSQCC cell line SK‑MES‑1 was treated with or without celecoxib and RNA‑sequencing (RNA‑seq) was performed on the Illumina HiSeq 2000 platform. Expression levels of genes or long non‑coding RNAs (lncRNAs) were calculated by Cufflinks software. Subsequently, differentially expressed genes (DEGs) and differentially expressed lncRNAs (DE‑LNRs) between the two groups were selected using the limma package and LNCipedia 3.0, respectively; followed by co‑expression analysis based on their expression correlation coefficient (CC). Enrichment analysis for the DEGs and co‑expressed DE‑LNRs were performed. Protein‑protein interaction (PPI) network analysis for DEGs was performed using STRING database. A set of 317 DEGs and 25 DE‑LNRs were identified between celecoxib‑treated and non‑treated cell lines. A total of 12 pathways were enriched by the DEGs, including 'protein processing in endoplasmic reticulum' for activating transcription factor 4 (ATF4), 'mammalian target of rapamycin (mTOR) signaling pathway' for vascular endothelial growth factor A (VEGFA) and 'ECM‑receptor interaction' for fibronectin 1 (FN1). Genes such as VEGFA, ATF4 and FN1 were highlighted in the PPI network. VEGFA was linked with lnc‑AP000769.1‑2:10 (CC= ‑0.99227), whereas ATF4 and FN1 were closely correlated with lnc‑HFE2‑2:1 (CC=0.996159 and ‑0.98714, respectively). lncRNAs were also enriched in pathways such as 'mTOR signaling pathway' for lnc‑HFE2‑2:1. Several important molecules were identified in celecoxib‑treated LSQCC cell lines, such as VEGFA, ATF4, FN1, lnc‑AP000769.1‑2:10 and lnc‑HFE2‑2:1, which may enhance the anti‑cancer effects of celecoxib on LSQCC.

Concomitant activation of ETS-like transcription factor-1 and Death Receptor-5 via extracellular signal-regulated kinase in withaferin A-mediated inhibition of hepatocarcinogenesis in mice

Hepatocellular carcinoma (HCC) has the second lowest 5-year survival rate (~16%) of all tumor types partly owing to the lack of effective therapeutic agents. Withaferin A (WA) is a bioactive molecule derived from Withania somnifera and the present study is designed to systemically investigate the anti-HCC efficacy of WA. WA inhibited growth, migration and invasion of HCC cells. Using a phospho-kinase screening array, we discovered that WA increased phosphorylation of ERK and p38 in HCC. Further analyses revealed a key role of ERK leading to increased phosphorylation of p90-ribosomal S6 kinase (RSK) and a concomitant activation of ETS-like transcription factor-1(ELK1) and Death Receptor protein-5 (DR5) in HCC. Importantly, oral administration of WA effectively inhibited HepG2-xenografts and DEN-induced-HCC in C57BL/6 mice. Analyses of WA-treated HepG2-xenografts and DEN-induced-HCC tumors showed elevated levels of ERK, RSK, ELK1 and DR5 along with decreased expression of Ki67. In silico analyses of HCC, utilizing published profiling studies showed an inverse correlation between DR5 and Ki67. These data showed the efficacy of WA as an effective agent for HCC inhibition and provided first in vitro and in vivo evidence supporting the key role of a novel crosstalk between WA, ERK/RSK, ELK1, and DR5 in HCC inhibition.

ONC201 activates ER stress to inhibit the growth of triple-negative breast cancer cells

ONC201 was previously identified as a first-in-class antitumor agent and small-molecule inducer of the TRAIL (tumor necrosis factor-related apoptosis-inducing ligand) gene that induces apoptosis in cancer cells. ONC201 has a safety profile and is currently in phase II clinical trials for the treatment of various malignancies. In the current study, we examine the effect of ONC201 on triple-negative breast cancer cells (TNBC), a subtype of breast cancer that is sensitive to TRAIL. We find that ONC201 inhibits the growth of TNBC cells including TNBC cells that have developed acquired TRAIL resistance. However, TNBC cells that have developed acquired ONC201 resistance are cross-resistant to TRAIL. Mechanistically, ONC201 triggers an integrated stress response (ISR) involving the activation of the transcription factor ATF4. Knockdown of ATF4 impairs ONC201-induced apoptosis of TNBC cells. Importantly, the activation of ATF4 is compromised in ONC201-resistant TNBC cells. Thus, our results indicate that ONC201 induces an ISR to cause TNBC cell death and suggest that TNBC patients may benefit from ONC201-based therapies.

The proteasome deubiquitinase inhibitor b-AP15 enhances DR5 activation-induced apoptosis through stabilizing DR5

b-AP15 and its derivatives block proteasome deubiquitinase (DUB) activity and have been developed and tested in the clinic as potential cancer therapeutic agents. b-AP15 induces apoptosis in cancer cells, but the underlying mechanisms are largely undefined. The current study focuses on studying the modulatory effects of b-AP15 on death receptor 5 (DR5) levels and DR5 activation-induced apoptosis as well as on understanding the underlying mechanisms. Treatment with b-AP15 potently increased DR5 levels including cell surface DR5 in different cancer cell lines with limited or no effects on the levels of other related proteins including DR4, c-FLIP, FADD, and caspase-8. b-AP15 substantially slowed the degradation of DR5, suggesting that it stabilizes DR5. Moreover, b-AP15 effectively augmented apoptosis when combined with TRAIL or the DR5 agonistic antibody AMG655; these effects are DR5-dependent because DR5 deficiency abolished the ability of b-AP15 to enhance TRAIL- or AMG655-induced apoptosis. Therefore, it is clear that b-AP15, and possibly its derivatives, can stabilize DR5 and increase functional cell surface DR5 levels, resulting in enhancement of DR5 activation-induced apoptosis. Our findings suggest that b-AP15 and its derivatives may have potential in sensitizing cancer cells to DR5 activation-based cancer therapy.

Miconazole induces apoptosis via the death receptor 5-dependent and mitochondrial-mediated pathways in human bladder cancer cells

Miconazole (MIC), an antifungal agent, diplays anti‑tumorigenic activity in various types of human cancers, including bladder cancer, yet its mechanism of antitumor action is not well understood. In the present study, we demonstrated that, in a cell viability assay, MIC had a cytotoxic effect on human T24, J82 and TSGH-8301 bladder cancer cells in a dose- and time‑dependent manner, but did not exhibit significant toxicity toward human peripheral blood mononuclear cells. Cell cycle analysis revealed that MIC at concentrations of 25 and 50 µM significantly caused G0/G1 arrest in the TSGH-8301 and T24 cells, respectively. DNA fragmentation, mitochondrial membrane potential and western blot analyses showed that MIC inhibited the growth of these cells by both mitochondrial‑mediated and death receptor (DR5)‑mediated apoptosis pathways. Specifically, MIC increased the protein levels of p21 and p27, but decreased the expression of cyclin E1, CDK2 and CDK4. MIC augmented the expression of DR5, cleaved forms of caspase-3 -8 and -9, poly(ADP‑ribose) polymerase and Bax, decreased the expression of Bcl-2 but increased cytosol levels of cytochrome c. Our results suggest that MIC inhibits the growth of bladder cancer cells through induction of G0/G1 arrest and apoptosis via activation of both the extrinsic and intrinsic apoptotic pathways. MIC is a potential chemotherapeutic agent for treating bladder cancer in humans.

Intracellular localization of DR5 and related regulatory pathways as a mechanism of resistance to TRAIL in cancer

TNF-related apoptosis-inducing ligand (TRAIL) is a prominent cytokine capable of inducing apoptosis. It can bind to five different cognate receptors, through which diverse intracellular pathways can be activated. TRAIL's ability to preferentially kill transformed cells makes it a promising potential weapon for targeted tumor therapy. However, recognition of several resistance mechanisms to TRAIL-induced apoptosis has indicated that a thorough understanding of the details of TRAIL biology is still essential before this weapon can be confidently unleashed. Critical to this aim is revealing the functions and regulation mechanisms of TRAIL's potent death receptor DR5. Although expression and signaling mechanisms of DR5 have been extensively studied, other aspects, such as its subcellular localization, non-signaling functions, and regulation of its membrane transport, have only recently attracted attention. Here, we discuss different aspects of TRAIL/DR5 biology, with a particular emphasis on the factors that seem to influence the cell surface expression pattern of DR5, along with factors that lead to its nuclear localization. Disturbance of this balance apparently affects the sensitivity of cancer cells to TRAIL-mediated apoptosis, thus constituting an eligible target for potential new therapeutic agents.

Calreticulin Promotes Proliferation and Migration But Inhibits Apoptosis in Schwann Cells

Background

Previous studies indicated that calreticulin (CRT) regulated various biological processes. This study was aimed to investigate the function of CRT in Schwann cells (SCs).

Material/Methods

SCs were separated from sciatic nerves of mice and were transfected with pcDNA3.1-CRT (pc-CRT), small interfering RNA targets CRT (siCRT), or their corresponding negative controls. The expression of CRT was determined by quantitative reverse transcription PCR (qRT-PCR) and Western blot analysis. Then, cell proliferation, migration, and apoptosis were measured by 3-(4, 5-dimethylhiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay, modified 2-chamber migration assay, and flow cytometry, respectively. Finally, the phosphorylation levels of key kinases in the phosphatidylinositol-3-kinase (PI3K)/AKT and the extracellular signal-regulated kinase/ribosomal S6 kinase 2 (ERK/S6) pathways were detected by Western blot analysis.

Results

Overexpression of CRT remarkably increased viability (P<0.05, P<0.01 or P<0.001) and migration (P<0.001), but inhibited apoptosis (P<0.05). The CRT-knockdown showed the inverse impacts on viability (P<0.05 or P<0.001), migration (P<0.001), and apoptosis (P<0.001). Additionally, the phosphorylation levels of AKT (Thr³⁰⁸ and Ser⁴⁷³), ERK, and S6 were all up-regulated in CRT-overexpressed cells (P<0.001), and were down-regulated in CRT-knockdown cells (P<0.05, P<0.01 or P<0.001).

Conclusions

Overexpression of CRT in SCs promoted cell proliferation and migration but suppressed cell apoptosis. The PI3K/AKT and ERK/S6 pathways might be involved in the functional effects of CRT on SCs.

Expression of Death Receptor 4 Is Positively Regulated by MEK/ERK/AP-1 Signaling and Suppressed upon MEK Inhibition

Death receptor 4 (DR4) is a cell surface receptor for tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and triggers apoptosis upon ligation with TRAIL or aggregation. MEK/ERK signaling is a well known and the best-studied effector pathway downstream of Ras and Raf. This study focuses on determining the impact of pharmacological MEK inhibition on DR4 expression and elucidating the underlying mechanism. We found that several MEK inhibitors including MEK162, AZD6244, and PD0325901 effectively decreased DR4 protein levels including cell surface DR4 in different cancer cell lines. Accordingly, pre-treatment of TRAIL-sensitive cancer cell lines with a MEK inhibitor desensitized them to TRAIL-induced apoptosis. These results indicate that MEK inhibition negatively regulates DR4 expression and cell response to TRAIL-induced apoptosis. MEK inhibitors did not alter DR4 protein stability, rather decreased its mRNA levels, suggesting a transcriptional regulation. In contrast, enforced activation of MEK/ERK signaling by expressing ectopic B-Raf (V600E) or constitutively activated MEK1 (MEK1-CA) or MEK2 (MEK2-CA) activated ERK and increased DR4 expression; these effects were inhibited when a MEK inhibitor was present. Promoter analysis through deletion and mutation identified the AP-1 binding site as an essential response element for enhancing DR4 transactivation by MEK1-CA. Furthermore, inhibition of AP-1 by c-Jun knockdown abrogated the ability of MEK1-CA to increase DR4 promoter activity and DR4 expression. These results suggest an essential role of AP-1 in mediating MEK/ERK activation-induced DR4 expression. Our findings together highlight a previously undiscovered mechanism that positively regulates DR4 expression through activation of the MEK/ERK/AP-1 signaling pathway.

Paradoxical activation of MEK/ERK signaling induced by B-Raf inhibition enhances DR5 expression and DR5 activation-induced apoptosis in Ras-mutant cancer cells

B-Raf inhibitors have been used for the treatment of some B-Raf–mutated cancers. They effectively inhibit B-Raf/MEK/ERK signaling in cancers harboring mutant B-Raf, but paradoxically activates MEK/ERK in Ras-mutated cancers. Death receptor 5 (DR5), a cell surface pro-apoptotic protein, triggers apoptosis upon ligation with tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) or aggregation. This study focused on determining the effects of B-Raf inhibition on DR5 expression and DR5 activation-induced apoptosis in Ras-mutant cancer cells. Using chemical and genetic approaches, we have demonstrated that the B-Raf inhibitor PLX4032 induces DR5 upregulation exclusively in Ras-mutant cancer cells; this effect is dependent on Ras/c-Raf/MEK/ERK signaling activation. PLX4032 induces DR5 expression at transcriptional levels, largely due to enhancing CHOP/Elk1-mediated DR5 transcription. Pre-exposure of Ras-mutated cancer cells to PLX4032 sensitizes them to TRAIL-induced apoptosis; this is also a c-Raf/MEK/ERK-dependent event. Collectively, our findings highlight a previously undiscovered effect of B-Raf inhibition on the induction of DR5 expression and the enhancement of DR5 activation-induced apoptosis in Ras-mutant cancer cells and hence may suggest a novel therapeutic strategy against Ras-mutated cancer cells by driving their death due to DR5-dependent apoptosis through B-Raf inhibition.

The novel proteasome inhibitor carfilzomib activates and enhances extrinsic apoptosis involving stabilization of death receptor 5

Carfilzomib (CFZ) is a second generation proteasome inhibitor approved for the treatment of patients with multiple myeloma. It induces apoptosis in human cancer cells; but the underlying mechanisms remain undefined. In the present study, we show that CFZ decreases the survival of several human cancer cell lines and induces apoptosis. Induction of apoptosis by CFZ occurs, at least in part, due to activation of the extrinsic apoptotic pathway, since FADD deficiency protected cancer cells from undergoing apoptosis. CFZ increased total and cell surface levels of DR5 in different cancer cell lines; accordingly it enhanced TRAIL-induced apoptosis. DR5 deficiency protected cancer cells from induction of apoptosis by CFZ either alone or in combination with TRAIL. These data together convincingly demonstrate that DR5 upregulation is a critical mechanism accounting for CFZ-induced apoptosis and enhancement of TRAIL-induced apoptosis. CFZ inhibited the degradation of DR5, suggesting that DR5 stabilization contributes to CFZ-induced DR5 upregulation. In summary, the present study highlights the important role of DR5 upregulation in CFZ-induced apoptosis and enhancement of TRAIL-induced apoptosis in human cancer cells.

Tanshinone IIA induces TRAIL sensitization of human lung cancer cells through selective ER stress induction

Although tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a promised anticancer medicine targeting only the tumor, most cancers show resistance to TRAIL-induced apoptosis. For this reason, new therapeutic strategies to overcome the TRAIL resistance are required for more effective tumor treatment. In the present study, potential of tanshinone IIA as a TRAIL sensitizer was evaluated in human non-small cell lung cancer (NSCLC) cells. NSCLC cells showed resistance to TRAIL-mediated cell death, but combination treatment of Tanshinone IIA and TRAIL synergistically decreased cell viability and increased apoptosis in TRAIL-resistant NSCLC cells. Tanshinone IIA greatly induced death receptor 5 (DR5), but not death receptor 4 (DR4). Furthermore, DR5 knockdown attenuated the combination treatment of tanshinone IIA with TRAIL-mediated cell death in human NSCLC cells. Tanshinone IIA also increased CHOP and activated the PERK-ATF4 pathway suggesting that tanshinone IIA increased DR5 and CHOP by activating the PERK-ATF4 pathway. Tanshinone IIA also downregulated phosphorylation of STAT3 and expression of survivin. Taken together, these results indicate that tanshinone IIA increases TRAIL-induced cell death via upregulating DR5 and downregulating survivin mediated by, respectively, selective activation of PERK/ATF4 and inhibition of STAT3, suggesting combinatorial intervention of tanshinone IIA and TRAIL as a new therapeutic strategy for human NSCLC.

Decursin enhances TRAIL-induced apoptosis through oxidative stress mediated- endoplasmic reticulum stress signalling in non-small cell lung cancers

BACKGROUND AND PURPOSE

The TNF-related apoptosis-inducing ligand (TRAIL) is a promising anticancer agent due to its remarkable ability to selectively kill tumour cells. However, because most tumours exhibit resistance to TRAIL-induced apoptosis, the development of combination therapies to overcome resistance to TRAIL is required for effective cancer therapy.

EXPERIMENTAL APPROACH

Cell viability and possible synergy between the plant pyranocoumarin decursin and TRAIL was measured by MTT assay and calcusyn software. Reactive oxygen species (ROS) and apoptosis were measured using dichlorodihydrofluorescein and annexin/propidium iodide in cell flow cytometry. Changes in protein levels were assessed with Western blotting.

KEY RESULTS

Combining decursin and TRAIL markedly decreased cell viability and increased apoptosis in TRAIL-resistant non-small-cell lung cancer (NSCLC) cell lines. Decursin induced expression of the death receptor 5 (DR5). Inhibition of DR5 attenuated apoptotic cell death in decursin + TRAIL treated NSCLC cell lines. Interestingly, induction of DR5 and CCAAT/enhancer-binding protein homologues protein by decursin was mediated through selective induction of the pancreatic endoplasmic reticulum kinase (PERK)/activating transcription factor 4 (ATF4) branch of the endoplasmic reticulum stress response pathway. Furthermore, enhancement of PERK/ATF4 signalling by decursin was mediated by ROS generation in NSCLC cell lines, but not in normal human lung cells. Decursin also markedly down-regulated expression of survivin and Bcl-xL in TRAIL-resistant NSCLC cells.

CONCLUSIONS AND IMPLICATIONS

ROS generation by decursin selectively activated the PERK/ATF4 axis of the endoplasmic reticulum stress signalling pathway, leading to enhanced TRAIL sensitivity in TRAIL-resistant NSCLC cell lines, partly via up-regulation of DR5.

Enhanced expression of c-myc in hepatocytes promotes initiation and progression of alcoholic liver disease

BACKGROUND & AIMS

Progression of alcoholic liver disease (ALD) can be influenced by genetic factors, which potentially include specific oncogenes and tumor suppressors. In the present study, we tested the hypothesis that aberrant expression of the proto-oncogene c-myc might exert a crucial role in the development of ALD.

METHODS

Expression of c-myc was measured in biopsies of patients with ALD by quantitative real-time PCR and immunohistochemistry. Mice with transgenic expression of c-myc in hepatocytes (alb-myc(tg)) and wild-type (WT) controls were fed either control or ethanol (EtOH) containing Lieber-DeCarli diet for 4weeks to induce ALD.

RESULTS

Hepatic c-myc was strongly upregulated in human patients with advanced ALD and in EtOH-fed WT mice. Transcriptome analysis indicated deregulation of pathways involved in ER-stress, p53 signaling, hepatic fibrosis, cell cycle regulation, ribosomal synthesis and glucose homeostasis in EtOH-fed alb-myc(tg) mice. Transgenic expression of c-myc in hepatocytes with simultaneous EtOH-uptake led to early ballooning degeneration, increased liver collagen deposition and hepatic lipotoxicity, together with excessive CYP2E1-derived reactive oxygen species (ROS) production. Moreover, EtOH-fed alb-myc(tg) mice exhibited substantial changes in mitochondrial morphology associated with energy dysfunction. Pathway analysis revealed that elevated c-myc expression and ethanol uptake synergistically lead to strong AKT activation, Mdm2 phosphorylation and as a consequence to inhibition of p53.

CONCLUSIONS

Expression of c-myc and EtOH-uptake synergistically accelerate the progression of ALD most likely due to loss of p53-dependent protection. Thus, c-myc is a new potential marker for the early detection of ALD and identification of risk patients.

Marine Drugs Regulating Apoptosis Induced by Tumor Necrosis Factor-Related Apoptosis-Inducing Ligand (TRAIL)

Marine biomass diversity is a tremendous source of potential anticancer compounds. Several natural marine products have been described to restore tumor cell sensitivity to TNF-related apoptosis inducing ligand (TRAIL)-induced cell death. TRAIL is involved during tumor immune surveillance. Its selectivity for cancer cells has attracted much attention in oncology. This review aims at discussing the main mechanisms by which TRAIL signaling is regulated and presenting how marine bioactive compounds have been found, so far, to overcome TRAIL resistance in tumor cells.

FLLL12 induces apoptosis in lung cancer cells through a p53/p73-independent but death receptor 5-dependent pathway

Unlike chemotherapy drugs, the safety of natural compounds such as curcumin has been well established. However, the potential use of curcumin in cancer has been compromised by its low bioavailability, limited tissue distribution and rapid biotransformation leading to low in vivo efficacy. To circumvent these problems, more potent and bioavailable analogs have been synthesized. In the current study, we investigated the mechanism of anti-tumor effect of one such analog, FLLL12, in lung cancers. IC50 values measured by sulforhodamine B (SRB) assay at 72 h and apoptosis assays (annexin V staining, cleavage of PARP and caspase-3) suggest that FLLL12 is 5-10-fold more potent than curcumin against a panel of premalignant and malignant lung cancer cell lines, depending on the cell line. Moreover, FLLL12 induced the expression of death receptor-5 (DR5). Ablation of the expression of the components of the extrinsic apoptotic pathway (DR5, caspase-8 and Bid) by siRNA significantly protected cells from FLLL12-induced apoptosis (p < 0.05). Analysis of mRNA expression revealed that FLLL-12 had no significant effect on the expression of DR5 mRNA expression. Interestingly, inhibition of global phosphatase activity as well as protein tyrosine phosphatases (PTPs), but not of alkaline phosphatases, strongly inhibited DR5 expression and significantly inhibited apoptosis (p < 0.05), suggesting the involvement of PTPs in the regulation of DR5 expression and apoptosis. We further showed that the apoptosis is independent of p53 and p73. Taken together, our results strongly suggest that FLLL12 induces apoptosis of lung cancer cell lines by posttranscriptional regulation of DR5 through activation of protein tyrosine phosphatase(s).

Inhibition of B-Raf/MEK/ERK signaling suppresses DR5 expression and impairs response of cancer cells to DR5-mediated apoptosis and T cell-induced killing

Inhibition of B-Raf/MEK/ERK signaling is an effective therapeutic strategy against certain types of cancers such as melanoma and thyroid cancer. While demonstrated to be effective anticancer agents, B-Raf or MEK inhibitors have also been associated with early tumor progression and development of secondary neoplasms. The ligation of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) with its receptor, death receptor 5 (DR5), leading to induction of apoptosis, offers a promising anticancer strategy. Importantly, this is also a natural immunosurveillance mechanism against cancer development. We previously demonstrated that activated B-Raf/MEK/ERK signaling positively regulates DR5 expression. Hence, our current work sought to address whether B-Raf/MEK/ERK inhibition and the consequent suppression of DR5 expression impede cancer cell response to DR5 activation-induced apoptosis and activated immune cell-induced killing. We found that both B-Raf (for example, PLX4032) and MEK inhibitors (for example, AZD6244 and PD0325901) effectively inhibited ERK1/2 phosphorylation and reduced DR5 levels in both human thyroid cancer and melanoma cells. Similar to the observed effect of genetic knockdown of the B-Raf gene, pre-treatment of cancer cell lines with either B-Raf or MEK inhibitors attenuated or abolished cellular apoptotic response induced by TRAIL or the DR5 agonistic antibody AMG655 or cell killing by activated T cells. Our findings clearly show that inhibition of B-Raf/MEK/ERK signaling suppresses DR5 expression and impairs DR5 activation-induced apoptosis and T cell-mediated killing of cancer cells. These findings suggest a potential negative impact of B-Raf or MEK inhibition on TRAIL- or DR5-mediated anticancer therapy and on TRAIL/DR5-mediated immune-clearance of cancer cells.

PDE5 inhibitors enhance celecoxib killing in multiple tumor types

The present studies determined whether clinically relevant phosphodiesterase 5 (PDE5) inhibitors interacted with a clinically relevant NSAID, celecoxib, to kill tumor cells. Celecoxib and PDE5 inhibitors interacted in a greater than additive fashion to kill multiple tumor cell types. Celecoxib and sildenafil killed ex vivo primary human glioma cells as well as their associated activated microglia. Knock down of PDE5 recapitulated the effects of PDE5 inhibitor treatment; the nitric oxide synthase inhibitor L-NAME suppressed drug combination toxicity. The effects of celecoxib were COX2 independent. Over-expression of c-FLIP-s or knock down of CD95/FADD significantly reduced killing by the drug combination. CD95 activation was dependent on nitric oxide and ceramide signaling. CD95 signaling activated the JNK pathway and inhibition of JNK suppressed cell killing. The drug combination inactivated mTOR and increased the levels of autophagy and knock down of Beclin1 or ATG5 strongly suppressed killing by the drug combination. The drug combination caused an ER stress response; knock down of IRE1α/XBP1 enhanced killing whereas knock down of eIF2α/ATF4/CHOP suppressed killing. Sildenafil and celecoxib treatment suppressed the growth of mammary tumors in vivo. Collectively our data demonstrate that clinically achievable concentrations of celecoxib and sildenafil have the potential to be a new therapeutic approach for cancer.

Spatial dynamics of TRAIL death receptors in cancer cells

TNF-related apoptosis inducing ligand (TRAIL) selectively induces apoptosis in cancer cells without harming most normal cells. Currently, multiple clinical trials are underway to evaluate the antitumor activity of recombinant human TRAIL (rhTRAIL) and agonistic antibodies that target death receptors (DRs) 4 or 5. It is encouraging that these products have shown a tolerated safety profile in early phase studies. However, their therapeutic potential is likely limited by the emergence of tumor drug resistance phenomena. Increasing evidence indicates that TRAIL DRs are deficient on the plasma membrane of some cancer cells despite their total protein expression. Notably, the lack of surface DR4/DR5 is sufficient to render cancers resistant to TRAIL-induced apoptosis, regardless of the status of other apoptosis signaling components. The current review highlights recent findings on the dynamic expression of TRAIL death receptors, including the regulatory roles of endocytosis, autophagy, and Ras GTPase-mediated signaling events. This information could aid in the identification of novel predictive biomarkers of tumor response as well as the development of combinational drugs to overcome or bypass tumor drug resistance to TRAIL receptor-targeted therapies.

Id3 induces an Elk-1-caspase-8-dependent apoptotic pathway in squamous carcinoma cells

Inhibitor of differentiation/DNA-binding (Id) proteins are helix–loop–helix (HLH) transcription factors. The Id protein family (Id1–Id4) mediates tissue homeostasis by regulating cellular processes including differentiation, proliferation, and apoptosis. Ids typically function as dominant negative HLH proteins, which bind other HLH proteins and sequester them away from DNA promoter regions. Previously, we have found that Id3 induced apoptosis in immortalized human keratinocytes upon UVB exposure, consistent with its role as a tumor suppressor. To investigate the role of Id3 in malignant squamous cell carcinoma (SCC) cells (A431), a tetracycline-regulated inducible system was used to induce Id3 in cell culture and mouse xenograft models. We found that upon Id3 induction, there was a decrease in cell number under low serum conditions, as well as in soft agar. Microarray, RT-PCR, immunoblot, siRNA, and inhibitor studies revealed that Id3 induced expression of Elk-1, an E-twenty-six (ETS)-domain transcription factor, inducing procaspase-8 expression and activation. Id3 deletion mutants revealed that 80 C-terminal amino acids, including the HLH, are important for Id3-induced apoptosis. In a mouse xenograft model, Id3 induction decreased tumor size by 30%. Using immunofluorescent analysis, we determined that the tumor size decrease was also mediated through apoptosis. Furthermore, we show that Id3 synergizes with 5-FU and cisplatin therapies for nonmelanoma skin cancer cells. Our studies have shown a molecular mechanism by which Id3 induces apoptosis in SCC, and this information can potentially be used to develop new treatments for SCC patients.

Targeting cannabinoid receptor-2 pathway by phenylacetylamide suppresses the proliferation of human myeloma cells through mitotic dysregulation and cytoskeleton disruption

Cannabinoid receptor-2 (CB2) is expressed dominantly in the immune system, especially on plasma cells. Cannabinergic ligands with CB2 selectivity emerge as a class of promising agents to treat CB2-expressing malignancies without psychotropic concerns. In this study, we found that CB2 but not CB1 was highly expressed in human multiple myeloma (MM) and primary CD138+ cells. A novel inverse agonist of CB2, phenylacetylamide but not CB1 inverse agonist SR141716, inhibited the proliferation of human MM cells (IC50 : 0.62 ∼ 2.5 μM) mediated by apoptosis induction, but exhibited minor cytotoxic effects on human normal mononuclear cells. CB2 gene silencing or pharmacological antagonism markedly attenuated phenylacetylamide's anti-MM effects. Phenylacetylamide triggered the expression of C/EBP homologous protein at the early treatment stage, followed by death receptor-5 upregulation, caspase activation, and β-actin/tubulin degradation. Cell cycle related protein cdc25C and mitotic regulator Aurora A kinase were inactivated by phenylacetylamide treatment, leading to an increase in the ratio inactive/active cdc2 kinase. As a result, phosphorylation of CDK substrates was decreased, and the MM cell mitotic division was largely blocked by treatment. Importantly, phenylacetylamide could overcome the chemoresistance of MM cells against dexamethasone or melphalan. Thus, targeting CB2 may represent an attractive approach to treat cancers of immune origin.

Targeting death receptors for TRAIL by agents designed by Mother Nature

Selective killing of cancer cells is one of the major goals of cancer therapy. Although chemotherapeutic agents are being used for cancer treatment, they lack selectivity toward tumor cells. Among the six different death receptors (DRs) identified to date, DR4 and DR5 are selectively expressed on cancer cells. Therefore, unlike chemotherapeutic agents, these receptors can potentially mediate selective killing of tumor cells. In this review we outline various nutraceuticals derived from 'Mother Nature' that can upregulate DRs and thus potentiate apoptosis. These nutraceuticals increase tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL)-induced apoptosis of cancer cells through different mechanisms. First, nutraceuticals have been found to induce DRs through the upregulation of various signaling molecules. Second, nutraceuticals can downregulate tumor cell-survival pathways. Third, nutraceuticals alone have been found to activate cell-death pathways. Although both TRAIL and agonistic antibodies against DR4 and DR5 are in clinical trials, combination with nutraceuticals is likely to boost their anticancer potential.

Role of activating transcription factor 3 (ATF3) in endoplasmic reticulum (ER) stress-induced sensitization of p53-deficient human colon cancer cells to tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL)-mediated apoptosis through up-regulation of death receptor 5 (DR5) by zerumbone and celecoxib

Death receptor 5 (DR5) is a death domain-containing transmembrane receptor that triggers cell death upon binding to its ligand, TNF-related apoptosis-inducing ligand (TRAIL), and a combination of TRAIL and agents that increase the expression of DR5 is expected to be a novel anticancer therapy. In this report, we demonstrate that the stress response gene ATF3 is required for endoplasmic reticulum stress-mediated DR5 induction upon zerumbone (ZER) and celecoxib (CCB) in human p53-deficient colorectal cancer cells. Both agents activated PERK-eIF2α kinases and induced the expression of activating transcription factor 4 (ATF4)-CCAAT enhancer-binding protein (C/EBP) homologous protein, which were remarkably suppressed by reactive oxygen species scavengers. In the absence of ATF3, the induction of DR5 mRNA and protein was abrogated significantly, and this was associated with reduced cell death by cotreatment of TRAIL with ZER or CCB. By contrast, exogenous expression of ATF3 caused a more rapid and elevated expression of DR5, resulting in enhanced sensitivity to apoptotic cell death by TRAIL/ZER or TRAIL/CCB. A reporter assay demonstrated that at least two ATF/cAMP response element motifs as well as C/EBP homologous protein motif at the proximal region of the human DR5 gene promoter were required for ZER-induced DR5 gene transcription. Taken together, our results provide novel insights into the role of ATF3 as an essential transcription factor for p53-independent DR5 induction upon both ZER and CCB treatment, and this may be a useful biomarker for TRAIL-based anticancer therapy.

Ilimaquinone induces death receptor expression and sensitizes human colon cancer cells to TRAIL-induced apoptosis through activation of ROS-ERK/p38 MAPK-CHOP signaling pathways

TRAIL induces apoptosis in a variety of tumor cells. However, development of resistance to TRAIL is a major obstacle to more effective cancer treatment. Therefore, novel pharmacological agents that enhance sensitivity to TRAIL are necessary. In the present study, we investigated the molecular mechanisms by which ilimaquinone isolated from a sea sponge sensitizes human colon cancer cells to TRAIL. Ilimaquinone pretreatment significantly enhanced TRAIL-induced apoptosis in HCT 116 cells and sensitized colon cancer cells to TRAIL-induced apoptosis through increased caspase-8, -3 activation, PARP cleavage, and DNA damage. Ilimaquinone also reduced the cell survival proteins Bcl2 and Bcl-xL, while strongly up-regulating death receptor (DR) 4 and DR5 expression. Induction of DR4 and DR5 by ilimaquinone was mediated through up-regulation of CCAAT/enhancer-binding protein homologous protein (CHOP). The up-regulation of CHOP, DR4 and DR5 expression was mediated through activation of extracellular-signal regulated kinase (ERK) and p38 mitogen-activated protein kinase (MAPK) signaling pathways. Finally, the generation of ROS was required for CHOP and DR5 up-regulation by ilimaquinone. These results demonstrate that ilimaquinone enhanced the sensitivity of human colon cancer cells to TRAIL-induced apoptosis through ROS-ERK/p38 MAPK-CHOP-mediated up-regulation of DR4 and DR5 expression, suggesting that ilimaquinone could be developed into an adjuvant chemotherapeutic drug.

Quercetin enhances apoptotic effect of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) in ovarian cancer cells through reactive oxygen species (ROS) mediated CCAAT enhancer-binding protein homologous protein (CHOP)-death receptor 5 pathway

Although tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has shown efficacy in a phase 2 clinical trial, development of resistance to TRAIL by tumor cells is a major roadblock. We investigated whether quercetin, a flavonoid, can sensitize human ovarian cancer cells to TRAIL. Results indicate that quercetin sensitized cancer cells to TRAIL. The quercetin induced expression of death receptor DR5 but did not affect expression of DR4 in cancer cells. The induction of DR5 was mediated through activation of JNK and through upregulation of a transcription factor CCAAT enhancer-binding protein homologous protein (CHOP); as silencing of these signaling molecules abrogated the effect of quercetin. Upregulation of DR5 was mediated through the generation of reactive oxygen species (ROS), as ROS scavengers reduced the effect of quercetin on JNK activation, CHOP upregulation, DR induction, TRAIL sensitization, downregulated the expression of cell survival proteins and upregulated the proapoptotic proteins. Furthermore, quercetin enhances TRAIL mediated inhibition of tumor growth of human SKOV-3 xenograft was associated with induction of apoptosis, activation of caspase-3, CHOP and DR5. Overall, our data suggest that quercetin enhances apoptotic death of ovarian cancer cells to TRAIL through upregulation of CHOP-induced DR5 expression following ROS mediated endoplasmic reticulum-stress.

Regulation of the microRNA 200b (miRNA-200b) by transcriptional regulators PEA3 and ELK-1 protein affects expression of Pin1 protein to control anoikis

MicroRNA (miRNA) 200s regulate E-cadherin by directly targeting ZEB1/ZEB2, which are transcriptional repressors of E-cadherin. Decreased expression of E-cadherin results in cancer cells losing interaction with the extracellular matrix and detaching from the primary tumor. Normally, cells will undergo anoikis after losing interaction with the extracellular matrix. Cancer cells must, therefore, possess the ability to resist anoikis during the process of metastasis. Here we show that miRNA-200b regulates anoikis by directly targeting the 3' UTR of Pin1 mRNA and regulating Pin1 expression at the translational level. We found that down-regulation of miRNA-200b promotes cancer cells survival during metastasis, and the homeless state of these cells resulted in decreased expression of miRNA-200b in the MCF-7 cell line. We also found that expression of miRNA-200b is down-regulated in human breast cancer during lymph node metastasis, which has a significant negative correlation with Pin1 expression. Two members of the ETS (E-26) family (PEA3 and ELK-1) regulate the expression of miRNA-200b. PEA3 promotes the expression of miRNA-200b, and ELK-1 is a transcriptional repressor of miRNA-200b. In addition, miRNA-200b regulates the activity of PEA3 and ELK-1 via the Pin1-pERK pathway and forms self-regulated feedback loops. This study characterizes the role of miRNA-200b in the regulation of anoikis and demonstrates the regulation of its own expression in the process of metastasis.

High throughput transcriptome profiling of lithium stimulated human mesenchymal stem cells reveals priming towards osteoblastic lineage

Human mesenchymal stem cells (hMSCs) present in the bone marrow are the precursors of osteoblasts, chondrocytes and adipocytes, and hold tremendous potential for osteoregenerative therapy. However, achieving directed differentiation into osteoblasts has been a major concern. The use of lithium for enhancing osteogenic differentiation has been documented in animal models but its effect in humans is not clear. We, therefore, performed high throughput transcriptome analysis of lithium-treated hMSCs to identify altered gene expression and its relevance to osteogenic differentiation. Our results show suppression of proliferation and enhancement of alkaline phosphatase (ALP) activity upon lithium treatment of hMSCs under non-osteogenic conditions. Microarray profiling of lithium-stimulated hMSC revealed decreased expression of adipogenic genes (CEBPA, CMKLR1, HSD11B1) and genes involved in lipid biosynthesis. Interestingly, osteoclastogenic factors and immune responsive genes (IL7, IL8, CXCL1, CXCL12, CCL20) were also downregulated. Negative transcriptional regulators of the osteogenic program (TWIST1 and PBX1) were suppressed while genes involved in mineralization like CLEC3B and ATF4 were induced. Gene ontology analysis revealed enrichment of upregulated genes related to mesenchymal cell differentiation and signal transduction. Lithium priming led to enhanced collagen 1 synthesis and osteogenic induction of lithium pretreated MSCs resulted in enhanced expression of Runx2, ALP and bone sialoprotein. However, siRNA-mediated knockdown of RRAD, CLEC3B and ATF4 attenuated lithium-induced osteogenic priming, identifying a role for RRAD, a member of small GTP binding protein family, in osteoblast differentiation. In conclusion, our data highlight the transcriptome reprogramming potential of lithium resulting in higher propensity of lithium "primed" MSCs for osteoblastic differentiation.

Salermide up-regulates death receptor 5 expression through the ATF4-ATF3-CHOP axis and leads to apoptosis in human cancer cells

Sirtuins (a class III histone deacetylase) have emerged as novel targets for cancer therapy. Salermide, a reverse amide compound that inhibits Sirtuin 1 (Sirt1) and Sirtuin 2 (Sirt2), has been shown to induce apoptosis in human cancer cells. The mechanism underlying cellular apoptotic signalling by salermide remains unclear. In this study, we show that salermide up-regulates the expression of death receptor 5 (DR5) in human non-small cell lung cancer (NSCLC) cells. Blocking DR5 expression by gene silencing technology results in a decrease in activated forms of several pro-apoptotic proteins (caspase-8, caspase-9, caspase-3, PARP). Increasing DR5 protein expression correlates with salermide-induced apoptosis in human NSCLC cells. We discovered that IRE-1α, Bip, activating transcription factor 3 (ATF4), activating transcription factor 3 (ATF3) and C/EBP homologous protein (CHOP) are induced by salermide, which suggests that DR5-dependent apoptosis is induced by endoplasmic reticulum stress. Moreover, knockdown of Sirt1 and Sirt2 expression resulted in up-regulation of ATF4, CHOP and DR5. Transfected NSCLC cells with ATF4, ATF3 or CHOP siRNA results in a decline in pro-apoptotic proteins (such as caspase-8, caspase-9, caspase-3 and PARP) despite salermide treatment. We demonstrate that salermide induces expression of ATF4, and ATF4 up-regulates ATF3 and subsequently modulates CHOP. This suggests that DR5 is modulated by the ATF4-ATF3-CHOP axis in NSCLC after Sirt1/2 inhibition or salermide treatment. This study highlights the importance of DR5 up-regulation in apoptosis induced by Sirt1/2 inhibition and elucidates the underlying mechanism in human NSCLC cells.