Cellular FLICE-like inhibitory protein long form (c-FLIPL) overexpression is related to cervical cancer progression

Non-apoptotic cell death programs in cervical cancer with an emphasis on ferroptosis

BACKGROUND

Cervical cancer, a pernicious gynecological malignancy, causes the mortality of hundreds of thousands of females worldwide. Despite a considerable decline in mortality, the surging incidence rate among younger women has raised serious concerns. Immortality is the most important characteristic of tumor cells, hence the carcinogenesis of cervical cancer cells pivotally requires compromising with cell death mechanisms.

METHODS

The current study comprehensively reviewed the mechanisms of non-apoptotic cell death programs to provide possible disease management strategies.

RESULTS

Comprehensive evidence has stated that focusing on necroptosis, pyroptosis, and autophagy for disease management is associated with significant limitations such as insufficient understanding, contradictory functions, dependence on disease stage, and complexity of intracellular pathways. However, ferroptosis represents a predictable role in cervix carcinogenesis, and ferroptosis-related genes demonstrate a remarkable correlation with patient survival and clinical outcomes.

CONCLUSION

Ferroptosis may be an appropriate option for disease management strategies from predicting prognosis to treatment.

The dual role of the CD95 and CD95L signaling pathway in glioblastoma

Binding of CD95, a cell surface death receptor, to its homologous ligand CD95L, transduces a cascade of downstream signals leading to apoptosis crucial for immune homeostasis and immune surveillance. Although CD95 and CD95L binding classically induces programmed cell death, most tumor cells show resistance to CD95L-induced apoptosis. In some cancers, such as glioblastoma, CD95-CD95L binding can exhibit paradoxical functions that promote tumor growth by inducing inflammation, regulating immune cell homeostasis, and/or promoting cell survival, proliferation, migration, and maintenance of the stemness of cancer cells. In this review, potential mechanisms such as the expression of apoptotic inhibitor proteins, decreased activity of downstream elements, production of nonapoptotic soluble CD95L, and non-apoptotic signals that replace apoptotic signals in cancer cells are summarized. CD95L is also expressed by other types of cells, such as endothelial cells, polymorphonuclear myeloid-derived suppressor cells, cancer-associated fibroblasts, and tumor-associated microglia, and macrophages, which are educated by the tumor microenvironment and can induce apoptosis of tumor-infiltrating lymphocytes, which recognize and kill cancer cells. The dual role of the CD95-CD95L system makes targeted therapy strategies against CD95 or CD95L in glioblastoma difficult and controversial. In this review, we also discuss the current status and perspective of clinical trials on glioblastoma based on the CD95-CD95L signaling pathway.

Multiple Functions of Cellular FLIP Are Essential for Replication of Hepatitis B Virus

Hepatitis B virus (HBV) infection is a leading cause of liver diseases; however, the host factors which facilitate the replication and persistence of HBV are largely unidentified. Cellular FLICE inhibitory protein (c-FLIP) is a typical antiapoptotic protein. In many cases of liver diseases, the expression level of c-FLIP is altered, which affects the fate of hepatocytes. We previously found that c-FLIP and its cleaved form interact with HBV X protein (HBx), which is essential for HBV replication, and regulate diverse cellular signals. In this study, we investigated the role of endogenous c-FLIP in HBV replication and its underlying mechanisms. The knockdown of endogenous c-FLIP revealed that this protein regulates HBV replication through two different mechanisms. (i) c-FLIP interacts with HBx and protects it from ubiquitin-dependent degradation. The N-terminal DED1 domain of c-FLIP is required for HBx stabilization. (ii) c-FLIP regulates the expression or stability of hepatocyte nuclear factors (HNFs), which have critical roles in HBV transcription and maintenance of hepatocytes. c-FLIP regulates the stability of HNFs through physical interactions. We verified our findings in three HBV infection systems: HepG2-NTCP cells, differentiated HepaRG cells, and primary human hepatocytes. In conclusion, our results identify c-FLIP as an essential factor in HBV replication. c-FLIP regulates viral replication through its multiple effects on viral and host proteins that have critical roles in HBV replication.IMPORTANCE Although the chronic hepatitis B virus (HBV) infection still poses a major health concern, the host factors which are required for the replication of HBV are largely uncharacterized. Our studies identify cellular FLICE inhibitory protein (c-FLIP) as an essential factor in HBV replication. We found the dual roles of c-FLIP in regulation of HBV replication: c-FLIP interacts with HBx and enhances its stability and regulates the expression or stability of hepatocyte nuclear factors which are essential for transcription of HBV genome. Our findings may provide a new target for intervention in persistent HBV infection.

FLIP as a therapeutic target in cancer

One of the classic hallmarks of cancer is disruption of cell death signalling. Inhibition of cell death promotes tumour growth and metastasis, causes resistance to chemo- and radiotherapies as well as targeted agents, and is frequently due to overexpression of antiapoptotic proteins rather than loss of pro-apoptotic effectors. FLIP is a major apoptosis-regulatory protein frequently overexpressed in solid and haematological cancers, in which its high expression is often correlated with poor prognosis. FLIP, which is expressed as long (FLIP(L)) and short (FLIP(S)) splice forms, achieves its cell death regulatory functions by binding to FADD, a critical adaptor protein which links FLIP to the apical caspase in the extrinsic apoptotic pathway, caspase-8, in a number of cell death regulating complexes, such as the death-inducing signalling complexes (DISCs) formed by death receptors. FLIP also plays a key role (together with caspase-8) in regulating another form of cell death termed programmed necrosis or 'necroptosis', as well as in other key cellular processes that impact cell survival, including autophagy. In addition, FLIP impacts activation of the intrinsic mitochondrial-mediated apoptotic pathway by regulating caspase-8-mediated activation of the pro-apoptotic Bcl-2 family member Bid. It has been demonstrated that FLIP can not only inhibit death receptor-mediated apoptosis, but also cell death induced by a range of clinically relevant chemotherapeutic and targeted agents as well as ionizing radiation. More recently, key roles for FLIP in promoting the survival of immunosuppressive tumour-promoting immune cells have been discovered. Thus, FLIP is of significant interest as an anticancer therapeutic target. In this article, we review FLIP's biology and potential ways of targeting this important tumour and immune cell death regulator.

Metformin-induced apoptosis facilitates degradation of the cellular caspase 8 (FLICE)-like inhibitory protein through a caspase-dependent pathway in human renal cell carcinoma A498 cells

Renal cell carcinoma (RCC) is one of the most common types of cancer in adults. Previous studies have reported that the survival rate was significantly lower for renal cancer patients with diabetes than for those without diabetes. Metformin is a well-known anti-diabetic agent used for the treatment of type 2 diabetes mellitus (T2DM). It also inhibits cell proliferation and angiogenesis and is known to possess antitumor effects. However, the molecular mechanism for metformin-induced apoptosis in renal cell carcinoma is not understood. In the present study, treatment with metformin induced apoptosis in A498 cells in a dose-dependent manner. It was revealed that degradation of cellular caspase 8 (FLICE)-like inhibitory protein (c-FLIP) and activation of procaspase-8 were associated with metformin-mediated apoptosis. By contrast, treatment with metformin did not affect the mRNA level of c-FLIP_L in A498 cells. Treatment with benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone (z-VAD-fmk, a pan-caspase inhibitor) almost completely blocked metformin-induced apoptosis and degradation of c-FLIP_L protein. However, N-acetyl-L-cysteine (NAC), a reactive oxygen species (ROS) scavenger, did not inhibit metformin-mediated apoptosis in A498 cells. Taken together, the results of the present study demonstrated that metformin-induced apoptosis involved degradation of the c-FLIP_L protein and activation of caspase-8 in human renal cell carcinoma A498 cells and suggested that metformin could be potentially used for the treatment of renal cancer.

Cell death and restoration of TRAIL-sensitivity by ciglitazone in resistant cervical cancer cells

Known activators of the Peroxisome Proliferator-Activated Receptor γ (PPARγ), thiazolidinediones (TZD) induce apoptosis in a variety of cancer cells through dependent and/or independent mechanisms of the receptor. We tested a panel of TZD (Rosiglitazone, Pioglitazone, Ciglitazone) to shed light on their potential therapeutic effects on three cervical cancer cell lines (HeLa, Ca Ski, C-33 A). In these cells, only ciglitazone triggered apoptosis through PPARγ-independent mechanisms and in particular via both extrinsic and intrinsic pathways in Ca Ski cells containing Human PapillomaVirus (HPV) type 16. It also inhibits cervical cancer xenograft development in nude mice. Ciglitazone kills cervical cancer cells by activating death receptor signalling pathway, caspase cascade and BH3 interacting-domain death agonist (Bid) cleavage through the up-regulation of Death Receptor 4 (DR4)/DR5 and soluble and membrane-bound TNF related apoptosis inducing ligand (TRAIL). Importantly, the drug let TRAIL-resistant Ca Ski cells to respond to TRAIL through the downregulation of cellular FLICE-Like Inhibitory Protein (c-FLIP) level. For the first time, we revealed that ciglitazone is able to decrease E6 viral oncoprotein expression known to block TRAIL pathway and this was associated with cell death. Our results highlight the capacity of ciglitazone to restore TRAIL sensitivity and to prevent E6 blocking action to induce apoptosis in cervical cancer cells.

Immunohistopathological Study of c-FLIP Protein in Mycosis Fungoides

Background:

Mycosis fungoides (MF) is the commonest variant of primary cutaneous T cell lymphoma with several clinicopathologic variants. Defective apoptotic mechanism may be important in the pathogenesis and progression of MF. c-FLIP protein is an important anti-apoptotic marker and chemotherapeutic resistant factor. This study aimed to evaluate the c-FLIP expression in MF and its role in the pathogenesis of MF.

Methods:

Twenty patients of MF and ten normal persons were included in this study. Skin biopsies were obtained from both patients and controls. They were studied and examined immunohistochemically for the expression of CD4 and c-FLIP.

Results:

c-FLIP expression was significantly increased in patients when compared to controls in both epidermis and dermis. There were positive correlations between c-FLIP expression and CD4+ expression in both epidermal and dermal lesions of patients group. There were statistically significant positive correlations between c-FLIP expression (in both dermal and epidermal lesions) and the age of patients. c-FLIP expression increased with the tumor progression but with no statistical significance.

Conclusion:

Defective regulation of apoptosis has been considered as a main cause for accumulation of clonal T cells, and it was related to an increased expression of c-FLIP which may have a role in the pathogenesis of MF. Also, c-FLIP may have prognostic information in MF as its level increased with both age of the patients and tumor progression.

Apoptotic Caspases in Promoting Cancer: Implications from Their Roles in Development and Tissue Homeostasis

Apoptosis, a major form of programmed cell death, is an important mechanism to remove extra or unwanted cells during development. In tissue homeostasis apoptosis also acts as a monitoring machinery to eliminate damaged cells in response to environmental stresses. During these processes, caspases, a group of proteases, have been well defined as key drivers of cell death. However, a wealth of evidence is emerging which supports the existence of many other non-apoptotic functions of these caspases, which are essential not only in proper organism development but also in tissue homeostasis and post-injury recovery. In particular, apoptotic caspases in stress-induced dying cells can activate mitogenic signals leading to proliferation of neighbouring cells, a phenomenon termed apoptosis-induced proliferation. Apparently, such non-apoptotic functions of caspases need to be controlled and restrained in a context-dependent manner during development to prevent their detrimental effects. Intriguingly, accumulating studies suggest that cancer cells are able to utilise these functions of caspases to their advantage to enable their survival, proliferation and metastasis in order to grow and progress. This book chapter will review non-apoptotic functions of the caspases in development and tissue homeostasis with focus on how these cellular processes can be hijacked by cancer cells and contribute to tumourigenesis.

Prognostic significance of TRAIL signalling molecules in cervical squamous cell carcinoma

AIM

Tumour necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is a member of the TNF superfamily that preferentially induces apoptosis in cancer cells while exhibiting little or no toxicity in normal cells. In this study, we evaluated the clinicopathological significance of TRAIL signalling members' expression profiles in cervical squamous cell carcinoma (CSCC).

METHODS

TRAIL, DR5, caspase-8 and cellular FLICE-inhibitory protein (c-FLIP) protein expression was investigated in 72 stage IA2-IIIA CSCC patients using immunohistochemistry. Correlation between protein expression and clinicopathological features, radiotherapy response and survival was statistically analysed.

RESULTS

Positive c-FLIP expression was an independent negative indicator for disease-free survival (DFS) (p=0.015) in multivariate Cox regression analysis. The DR5 nuclear positive group (p=0.069 by log rank test) showed some advantage of radiotherapy for overall survival (OS) compared with the DR5 nuclear negative cohort (p=0.568 by log rank test). In addition, loss of TRAIL expression was associated with worse differentiation (p=0.004), while absence of caspase-8 staining was more frequently observed in cases with lymphovascular invasion (p=0.035).

CONCLUSIONS

High c-FLIP expression is shown to be an independent prognostic variable, DR5 nuclear expression may serve as a predictive biomarker for radiotherapy, and TRAIL as well as caspase-8 loss may be associated with malignant progression.

Expression of Apoptotic vs Antiapoptotic Proteins in Middle Ear Cholesteatoma

Objectives

To explore the role of antiapoptotic and apoptotic processes in the development of cholesteatoma by investigating the expression of an antiapoptotic (c-FLIP) and apoptotic (p53) protein relative to the expression of a proliferation marker (Ki-67).

Study Design

Basic science study.

Setting

Tertiary referral center.

Subjects and Methods

An immunohistochemical investigation was performed on 35 cholesteatoma specimens (21 acquired, 14 congenital) and 10 normal retroauricular skins to evaluate the expression of c-FLIP, p53, and Ki-67. The expression rate of each marker was measured to assess the difference between retroauricular skin and cholesteatoma, as well as between congenital and acquired cholesteatoma.

Results

c-FLIP expression was significantly higher in the cholesteatoma specimens than in retroauricular skin ( P < .05), while the expression of p53 did not significantly differ between the two. Ki-67 expression in cholesteatoma was significantly higher than in retroauricular skin ( P < .001). The c-FLIP expression rate was positively correlated with that of Ki-67 ( r = 0.47, P = .001), and there was no significant correlation between the expression level of p53 and that of Ki-67 ( r = 0.152, P = .319). In addition, no differences in c-FLIP, p53, and Ki-67 expression rates were evident between congenital and acquired cholesteatoma.

Conclusions

The upregulation of c-FLIP together with unchanged p53 suggests an altered equilibrium between apoptosis and antiapoptosis, favoring antiapoptosis, and may play a role in the pathogenesis of cholesteatoma.

Regulation of TRAIL-receptor expression by the ubiquitin-proteasome system

The tumor necrosis factor (TNF)-related apoptosis-inducing ligand- receptor (TRAIL-R) family has emerged as a key mediator of cell fate and survival. Ligation of TRAIL ligand to TRAIL-R1 or TRAIL-R2 initiates the extrinsic apoptotic pathway characterized by the recruitment of death domains, assembly of the death-inducing signaling complex (DISC), caspase activation and ultimately apoptosis. Conversely the decoy receptors TRAIL-R3 and TRAIL-R4, which lack the pro-apoptotic death domain, function to dampen the apoptotic response by competing for TRAIL ligand. The tissue restricted expression of the decoy receptors on normal but not cancer cells provides a therapeutic rational for the development of selective TRAIL-mediated anti-tumor therapies. Recent clinical trials using agonistic antibodies against the apoptosis-inducing TRAIL receptors or recombinant TRAIL have been promising; however the number of patients in complete remission remains stubbornly low. The mechanisms of TRAIL resistance are relatively unexplored but may in part be due to TRAIL-R down-regulation or shedding of TRAIL-R by tumor cells. Therefore a better understanding of the mechanisms underlying TRAIL resistance is required. The ubiquitin-proteasome system (UPS) has been shown to regulate TRAIL-R members suggesting that pharmacological inhibition of the UPS may be a novel strategy to augment TRAIL-based therapies and increase efficacies. We recently identified b-AP15 as an inhibitor of proteasome deubiquitinase (DUB) activity. Interestingly, exposure of tumor cell lines to b-AP15 resulted in increased TRAIL-R2 expression and enhanced sensitivity to TRAIL-mediated apoptosis and cell death in vitro and in vivo. In conclusion, targeting the UPS may represent a novel strategy to increase the cell surface expression of pro-apoptotic TRAIL-R on cancer cells and should be considered in clinical trials targeting TRAIL-receptors in cancer patients.

BAI, a novel Cdk inhibitor, enhances farnesyltransferase inhibitor LB42708-mediated apoptosis in renal carcinoma cells through the downregulation of Bcl-2 and c-FLIP (L)

Previously, we reported the potential of a novel Cdk inhibitor, 2-[1,1'-biphenyl]-4-yl-N-[5-(1,1-dioxo-1λ6-isothiazolidin-2-yl)-1H-indazol-3-yl]acetamide (BAI) as a cancer chemotherapeutic agent. In this study, we investigated mechanisms by which BAI modulates FTI-mediated apoptosis in human renal carcinoma Caki cells. BAI synergizes with FTI to activate DEVDase, cleavage of poly ADP-ribose polymerase (PARP), and degradation of various anti-apoptotic proteins in Caki cells. BAI plus LB42708-induced apoptosis was inhibited by pretreatment with pan-caspase inhibitor, z-VAD-fmk, but not by overexpression of CrmA. The ROS scavenger, N-acetylcysteine (NAC) did not reduce BAI plus LB4270-induced apoptosis. Co-treatment of BAI and LB42708 reduced the mitochondrial membrane potential (MMP, ∆Ψm) in a time-dependent manner, and induced release of AIF and cytochrome c from mitochondria in Caki cells. Furthermore, BAL plus LB42708 induced downregulation of anti-apoptotic proteins [c-FLIP (L), c-FLIP (s), Bcl-2, XIAP, and Mcl-1 (L)]. Especially, we found that BAI plus LB42708-induced apoptosis was significantly attenuated by overexpression of Bcl-2 and partially blocked by overexpression of c-FLIP (L). Taken together, our results show that the activity of BAI plus LB42708 modulate multiple components in apoptotic response of human renal Caki cells, and indicate a potential as combinational therapeutic agents for preventing cancer such as renal carcinoma.

Roles of c-FLIP in Apoptosis, Necroptosis, and Autophagy

Cellular FLICE (FADD-like IL-1β-converting enzyme)-inhibitory protein (c-FLIP) is a major antiapoptotic protein and an important cytokine and chemotherapy resistance factor that suppresses cytokine- and chemotherapy-induced apoptosis. c-FLIP is expressed as long (c-FLIPL), short (c-FLIPS), and c-FLIPR splice variants in human cells. c-FLIP binds to FADD and/or caspase-8 or -10 and TRAIL receptor 5 (DR5). This interaction in turn prevents Death-Inducing Signaling Complex (DISC) formation and subsequent activation of the caspase cascade. c-FLIPL and c-FLIPS are also known to have multifunctional roles in various signaling pathways, as well as activating and/or upregulating several cytoprotective and pro-survival signaling proteins including Akt, ERK, and NF-κB. In addition to its role in apoptosis, c-FLIP is involved in programmed necroptosis (necrosis) and autophagy. Necroptosis is regulated by the Ripoptosome, which is a signaling intracellular cell death platform complex. The Ripoptosome contains receptor-interacting protein-1/Receptor-Interacting Protein-3 (RIP1), caspase-8, caspase-10, FADD, and c-FLIP isoforms involved in switching apoptotic and necroptotic cell death. c-FLIP regulates the Ripoptosome; in addition to its role in apoptosis, it is therefore also involved in necrosis. c-FLIPL attenuates autophagy by direct acting on the autophagy machinery by competing with Atg3 binding to LC3, thereby decreasing LC3 processing and inhibiting autophagosome formation. Upregulation of c-FLIP has been found in various tumor types, and its silencing has been shown to restore apoptosis triggered by cytokines and various chemotherapeutic agents. Hence, c-FLIP is an important target for cancer therapy. This review focuses on (1) the anti-apoptotic role of c-FLIP splice variants in preventing apoptosis and inducing cytokine and chemotherapy drug resistance, as well as its roles in necrosis and autophagy, and (2) modulation of c-FLIP expression as a means to enhance apoptosis and modulate necrosis and autophagy in cancer cells.