Control of FLIP(L) expression and TRAIL resistance by the extracellular signal-regulated kinase1/2 pathway in breast epithelial cells

GINS1 promotes the initiation and progression of bladder cancer by activating the AKT/mTOR/c-Myc signaling pathway

Bladder cancer(BC) is one of the most prevalent cancers in the urinary tract, with high recurrence and fatality rates. Research indicates that go-ichi-ni-san complex subunit 1 (GINS1) crucially influences cancer progression by regulating DNA replication through cell cycle modulation. Thus, suppressing the active proliferation of cells in tumor tissues may require silencing GINS1. However, the consequences of GINS1 in bladder cancer aren't to be determined. In this paper, we examine the role and mechanism of GINS1 in the development of bladder cancer. GINS1 expression levels and prognostic relevance in bladder cancer were validated using Western blotting, immunohistochemistry, and Kaplan-Meier survival analysis. The influence of GINS1 on bladder cancer was investigated using a variety of approaches, including cell transfection, cell counts, transwell migrations, colony formation, and flow cytometry. Immunohistochemistry studies demonstrate that GINS1 expression is increased in bladder cancer tissues. GINS1 silencing resulted in an arrest of the cell cycle at the phase of G0/G1, which inhibited BC cell growth both in vitro and in vivo. GINS1 knockdown also hindered the AKT/mTOR pathway. Furthermore, increased GINS1 expression affects the cell cycle and stimulates the AKT/mTOR pathway, allowing BC to develop more quickly. Consequently, GINS1 occurs as a latent therapeutic target, particularly for individuals with BC.

CD13 inhibition augments DR4-induced tumor cell death in a p-ERK1/2-independent manner

OBJECTIVE

Death receptor 4 (DR4; TRAIL-R1) critically mediates extrinsic apoptosis cascades via binding to TNF-related apoptosis-inducing ligand (TRAIL). However, intrinsic and/or acquired resistance are observed in the clinical application of TRAIL. The aim of this study was to investigate the function and molecular mechanism of CD13 in the TRAIL/DR4 pathway against tumor cells, and provide a new strategy for improving therapeutic efficacy or overcoming TRAIL-resistance.

METHODS

TRAIL protein was expressed as a secretory protein in a Pichia pastoris expression system and was isolated and purified by affinity chromatography. The cell viability and apoptosis were evaluated with MTT (thiazolyl blue tetrazolium bromide) assays and annexin V-FITC/PI staining with flow cytometry analysis, respectively. Western blot analysis was used to detect the levels of the indicated proteins in tumor cells. DR4 degradation or stability was examined with cycloheximide chase assays, and cell surface DR4 was assessed with flow cytometric analysis after staining with a FITC-conjugated antibody. The effects of cell migration were determined with Transwell and gelatin zymography assays. A xenograft nude mouse model was used to detect the anti-tumor effect in vivo, and the proliferation in tumor tissues was examined with immunohistochemical staining.

RESULTS

CD13 inhibition potently sensitized tumor cells to TRAIL-induced killing, including proliferation inhibition, increased apoptosis, and migration suppression. In addition, the inhibition of CD13 elevated both total cellular expression and cell surface DR4 through stabilizing DR4 by suppressing its degradation. DR4 siRNA attenuated the enhanced anti-tumor effects of TRAIL plus CD13 inhibition. Interestingly, these phenomena were p-ERK1/2 independent, although p-ERK1/2 down-regulation was tightly correlated with the cooperation of TRAIL and CD13 inhibition. Moreover, a synergistic decrease in tumor growth was surprisingly achieved in the xenograft model by treatment of TRAIL with a CD13 inhibitor (**P < 0.01, CDI = 0.47).

CONCLUSIONS

CD13 inhibition cooperates with TRAIL in enhancing DR4-mediated cell death, through the up-regulation and stabilization of DR4 in a p-ERK1/2-independent manner. Thus CD13 inhibition has emerged as an effective strategy for TRAIL/DR4-based therapy.

The oncogenic role of ubiquitin specific peptidase (USP8) and its signaling pathways targeting for cancer therapeutics

USP8 is a deubiquitinating enzyme in the family of ubiquitin-specific proteases (USPs) which can remove ubiquitin from the substrate and protect the substrate from degradation. The upregulated or mutated USP8 becomes hyperactivated and stabilizes numerous oncogenes or proto-oncogenes leading to cancer progression and survival by activating multiple signaling pathways. Moreover, USP8 inhibition is also important to overcome anticancer drug-resistant. This review is the first study to find, combine, analyze, and represent the multiple oncogenic signaling pathways with their downstream and upstream regulation activated or enhanced by USP8, which will help the researchers to find any therapeutic strategy for drug discovery by inhibiting or suppressing the multi-targeted USP8.

Revisiting the role of TRAIL/TRAIL-R in cancer biology and therapy

TNF-related apoptosis-inducing ligand (TRAIL), a member of the TNF superfamily, can induce apoptosis in cancer cells, sparing normal cells when bound to its associated death receptors (DR4/DR5). This unique mechanism makes TRAIL a potential anticancer therapeutic agent. However, clinical trials of recombinant TRAIL protein and TRAIL receptor agonist monoclonal antibodies have shown disappointing results due to its short half-life, poor pharmacokinetics and the resistance of the cancer cells. This review summarizes TRAIL-induced apoptotic and survival pathways as well as mechanisms leading to apoptotic resistance. Recent development of methods to overcome cancer cell resistance to TRAIL-induced apoptosis, such as protein modification, combination therapy and TRAIL-based gene therapy, appear promising. We also discuss the challenges and opportunities in the development of TRAIL-based therapies for the treatment of human cancers.

Glucosamine Enhances TRAIL-Induced Apoptosis in the Prostate Cancer Cell Line DU145

Background: Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) selectively kills tumor cells in cancer patients. However, patients often develop TRAIL resistance; thus, agents that can sensitize cells to TRAIL therapy would be beneficial clinically. Methods: Immunoblotting, flow cytometry, confocal microscopy, qPCR and caspase 8 activity assays were used to investigate whether glucosamine (GlcN) can sensitize cancer cells to TRAIL thereby enhancing apoptosis and potentially improving clinical response. Results: GlcN sensitized DU145 cells to TRAIL-induced apoptosis but did not increase death receptor 5 (DR5) cell surface expression. Once treated, these cells responded to TRAIL-induced apoptosis through both extrinsic and intrinsic apoptotic pathways as evidenced by the cleavage of both caspases 8 and 9. The combination of GlcN and TRAIL suppressed the expression of key anti-apoptotic factors cFLIP, BCL-X_L, MCL-1 and XIAP and translocated BAK to the mitochondrial outer membrane thereby facilitating cytochrome C and SMAC release. In addition to the activation of apoptotic pathways, TRAIL-mediated inflammatory responses were attenuated by GlcN pretreatment reducing nuclear NF-kB levels and the expression of downstream target genes IL-6 and IL-8. Conclusions: GlcN/TRAIL combination could be a promising strategy for treating cancers by overcoming TRAIL resistance and abrogating TRAIL-induced inflammation.

Developing TRAIL/TRAIL death receptor-based cancer therapies

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is a member of the TNF superfamily that can initiate the apoptosis pathway by binding to its associated death receptors DR4 and DR5. The activation of the TRAIL pathway in inducing tumor-selective apoptosis leads to the development of TRAIL-based cancer therapies, which include recombinant forms of TRAIL, TRAIL receptor agonists, and other therapeutic agents. Importantly, TRAIL, DR4, and DR5 can all be induced by synthetic and natural agents that activate the TRAIL apoptosis pathway in cancer cells. Thus, understanding the regulation of the TRAIL apoptosis pathway can aid in the development of TRAIL-based therapies for the treatment of human cancer.

Oncogenic p95HER2/611CTF primes human breast epithelial cells for metabolic stress-induced down-regulation of FLIP and activation of TRAIL-R/Caspase-8-dependent apoptosis

Oncogenic transformation triggers reprogramming of cell metabolism, as part of the tumorigenic process. However, metabolic reprogramming may also increase the sensitivity of transformed cells to microenvironmental stress, at the early stages of tumor development. Herein, we show that transformation of human breast epithelial cells by the p95HER2/611CTF oncogene markedly sensitizes these cells to metabolic stress induced by the simultaneous inhibition of glucose and glutamine metabolism. In p95HER2/611CTF-transformed cells, metabolic stress activates a TNF related apoptosis-inducing ligand (TRAIL)-R and caspase-8-dependent apoptotic process that requires prior down-regulation of cellular FLICE-like inhibitor protein (c-FLIP) levels. Importantly, sustained mTOR activation is involved in FLIP down-regulation and apoptosis induced by metabolic stress. In vivo experiments in immunodeficient mice demonstrate a requirement for caspase-8 in restraining primary tumor growth of xenografts with p95HER2/611CTF-transformed cells. Collectively, these data define a critical role of the extrinsic pathway of apoptosis in the control of tumor initiation by microenvironmental cues.

USP8 suppresses death receptor-mediated apoptosis by enhancing FLIPL stability

FLICE-like inhibitory protein (FLIP) is a critical regulator of death receptor-mediated apoptosis. Here, we found ubiquitin-specific peptidase 8 (USP8) to be a novel deubiquitylase of the long isoform of FLIP (FLIP_L). USP8 directly deubiquitylates and stabilizes FLIP_L, but not the short isoform. USP8 depletion induces FLIP_L destabilization, promoting anti-Fas-, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)- and tumor necrosis factor alpha-induced extrinsic apoptosis by facilitating death-inducing signaling complex or TNFR1 complex II formation, which results in the activation of caspase-8 and caspase-3. USP8 mRNA levels are elevated in melanoma and cervical cancers, and the protein levels of USP8 and FLIP_L are positively correlated in these cancer cell lines. Xenograft analyses using ME-180 cervical cancer cells showed that USP8 depletion attenuated tumor growth upon TRAIL injection. Taken together, our data indicate that USP8 functions as a novel deubiquitylase of FLIP_L and inhibits extrinsic apoptosis by stabilizing FLIP_L.

Opposing roles of TGF-β and EGF in the regulation of TRAIL-induced apoptosis in human breast epithelial cells

Transforming growth factor-beta (TGF-β) induces the epithelial to mesenchymal transition (EMT) in breast epithelial cells and plays an important role in mammary morphogenesis and breast cancer. In non-transformed breast epithelial cells TGF-β antagonizes epidermal growth factor (EGF) action and induces growth inhibition. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has been reported to participate in lumen formation during morphogenesis of human breast epithelial cells. Our previous work indicated that sensitivity of human breast epithelial cells to TRAIL can be modulated through the activation of the epidermal growth factor receptor-1 (EGFR). Here, we show that TGF-β opposes EGF-mediated sensitization to TRAIL-induced caspase-8 activation and apoptosis in non-transformed breast epithelial cells. Death-inducing signalling complex (DISC) formation by TRAIL was significantly reduced in cells treated with TGF-β. TGF-β treatment activates cytoprotective autophagy and down-regulates TRAIL-R2 expression at the cell surface by promoting the intracellular accumulation of this receptor. Lastly, we demonstrate that EMT is not involved in the inhibitory effect of TGF-β on apoptosis by TRAIL. Together, the data reveal a fine regulation by EGF and TGF-β of sensitivity of human breast epithelial cells to TRAIL which may be relevant during morphogenesis.

Paclitaxel enhances tumoricidal potential of TRAIL via inhibition of MAPK in resistant gastric cancer cells

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) holds promise for cancer therapy due to its unique capacity to selectively trigger apoptosis in cancer cells. However, TRAIL therapy is greatly hampered by its resistance. A preclinical successful strategy is to identify combination treatments that sensitize resistant cancers to TRAIL. In the present study, we fully assessed TRAIL sensitivity in 9 gastric cancer cell lines. We found combined administration of paclitaxel (PTX) markedly enhanced TRAIL-induced apoptosis in resistant cancer cells both in vitro and in vivo. The sensitization to TRAIL was accompanied by activation of mitochondrial apoptotic pathway, upregulation of TRAIL receptors and downregulation of anti-apoptotic proteins including C-IAP1, C-IAP2, Livin and Mcl-1. Noticeably, we found PTX could suppress the activation of mitogen-activated protein kinases (MAPKs). Inhibition of MAPKs using specific inhibitors (ERK inhibitor U0126, JNK inhibitor SP600125 and P38 inhibitor SB202190) facilitated TRAIL-mediated apoptosis and cytotoxicity. Additionally, SP600125 upregulated TRAL receptors as well as downregulated C-IAP2 and Mcl-1 suggesting the anti-apoptotic role of JNK. Thus, PTX-induced suppression of MAPKs may contribute to restoring TRAIL senstitivity. Collectively, our comprehensive analyses gave new insight into the role of PTX on enhancing TRAIL sensitivity, and provided theoretical references on the development of combination treatment in TRAIL-resistant gastric cancer.

RAD001 (everolimus) enhances TRAIL cytotoxicity in human leukemic Jurkat T cells by upregulating DR5

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), either alone or in combination with other anti-cancer agents, is a promising new strategy for the treatment of cancer. However, aberrant PI3K/Akt/mTOR survival signaling may confer TRAIL resistance by altering the balance between pro- and anti-apoptotic proteins. In the present study, we showed that the Akt/mTOR inhibitor RAD001 (everolimus) induced cell death in a dose-dependent manner and enhanced TRAIL-induced apoptosis in human leukemic Jurkat T cells, which show PI3K/Akt/mTOR pathway activation and basal expression levels of death receptor (DR) 5 (TRAIL-R2). Investigation of the effect of RAD001 treatment on the expression of TRAIL receptors (TRAIL-Rs) in Jurkat T cells showed that RAD001 significantly upregulated DR5 by up to 51.22%, but not other TRAIL-Rs such as DR4 (TRAIL-R1), decoy receptor (DcR) 1 (TRAIL-R3), and DcR2 (TRAIL-R4). Pretreatment with DR5:Fc chimera abrogated the RAD001-induced increase of TRAIL cytotoxicity, indicating that the upregulation of DR5 by RAD001 plays a role in enhancing the susceptibility of Jurkat T cells to TRAIL. Our results indicate that combination treatment with RAD001 and TRAIL may be a novel therapeutic strategy in leukemia.

TRAIL combinations: The new 'trail' for cancer therapy (Review)

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) therapy is anticipated to be one of the most effective cancer treatments. However, resistance to TRAIL therapy remains a challenge facing the development of anticancer strategies. To circumvent this problem, TRAIL combinations have been experimented with for over ten years to induce synergism or sensitize resistant cancer cells. By analyzing the signaling pathways triggered by these combinations, this review has defined a set of core targets for novel combinatorial treatments. The review suggests specific pathways to be targeted together with TRAIL for more efficient treatment, including cellular FLICE inhibitory protein and its downstream survival factors, the Bcl-2 family and other prominent targets. The suggested pathways provide new avenues for more effective TRAIL-based cancer therapy.