Encyclopedia of Signaling Molecules

2018 Edition
| Editors: Sangdun Choi

C-FLIP

Reference work entry
DOI: https://doi.org/10.1007/978-3-319-67199-4_101547

Synonyms

Integration of the Mitochondrial and Death Receptors (DRs) Pathways and Role of c-FLIP

Two major signaling pathways, the intrinsic or mitochondrial pathway and the extrinsic or cell surface DRs pathway, regulate apoptosis (Fig. 1) (Lavrik et al. 2005; Micheau and Tschopp 2003; Safa et al. 2008). In the intrinsic pathway, various anti- and pro-apoptotic members of the Bcl-2 family form an interactive network that finally regulates the release of apoptosis-triggering factors such as cytochrome c, apoptosis-inducing factors including Smac/DIABLO, HtrA2/Omi, and Endonuclease G (endoG) from the mitochondria to the cytosol (Vaux 2011; Plati et al. 2011). Upon release, cytochrome c and dATP bind to apoptotic proteinase-activating factor-1 (Apaf-1), and this complex along with adenine nucleotides forms the apoptosome and promotes procaspase-9 autoactivation (Plati et al. 2011; Liu et al. 1996; Yuan et al. 2013). Apoptosome assembly is a crucially important point in the mitochondrial pathway of apoptosis, consisting of a wheel-like heptamer of seven Apaf-1 molecules and seven cytochrome c molecules that bind and activate the initiator caspase-9, which in turn activates caspases-2, -3, -6, -7, -8, and -10 (Liu et al. 1996; Yuan et al. 2013). Apoptosis induced by different death stimuli requires direct activation of Bax and BAK at the mitochondria by a member of the Bcl-2 homology domain-3 (BH3)-only family of proteins including Bid, Bim, or PUMA (Reubold and Eschenburg 2012). Cytochrome c release is associated with opening the permeability transition pore (PTP) and a collapse of mitochondrial transmembrane potential (Δψm) due to the intake of Ca2+ following its release from the endoplasmic reticulum (ER) (Grimm 2012; Cain et al. 2000) into the cytosol.
C-FLIP, Fig. 1

Graphical scheme illustrating c-FLIP variants as anti-apoptotic proteins. Interaction of TRAIL with its receptors DR4 and DR5 or binding of Fas ligand (CD95L) to Fas receptor (CD95) initiates the death receptor (extrinsic) and subsequently mitochondrial apoptosis signaling (intrinsic) pathways through FADD-dependent autocatalytic activation of caspases-8 and -10 and Bid cleavage to truncated Bid. c-FLIPL and c-FLIPS isoforms suppress caspase-8 and -10 activation, therefore preventing the downstream apoptosis cascade. c-FLIPL and c-FLIPS isoforms also activate the cytoprotective and survival signaling pathways including ErbB-2/MAPK, Erk, Wnt/β-catenin, NF-κB, and PI3K/AKT/mTOR

In the death receptor (DR)-mediated or extrinsic apoptosis pathway, Fas/Fas Ligand (FasL) [(CD95/CD95 Ligand, CD95L)] interaction, TRAIL/DR4, or TRAIL/DR5 interaction, or binding of tumor necrosis factor α (TNF-α) with its receptor, TNF receptor 1 (TNFR1), initiates apoptosis (Figs. 1 and 2). Similarly, binding of the agonistic antibodies to these respective receptors also initiates the apoptotic signaling cascade. Following the interactions of the DR ligands or DR agonistic antibodies with their respective trimerized DRs, the adaptor molecule Fas-Associated Death Domain (FADD) is recruited to the DRs via death domain (DD) interactions, whereas procaspase-8, procaspase-10, and c-FLIP are recruited to the death-inducing signaling complex (DISC) via death effector domain (DED) interactions (Krammer et al. 2007; Scaffidi et al. 1998). Therefore, the DISC consists of trimerized DRs, FADD, procaspase-8/-10, and c-FLIP. Procaspase-8 or procaspase-10 is autocatalytically activated and forms the active initiator caspase-8 [(FADD-like interleukin-1 beta-converting enzyme (FLICE)] and caspase-10 which in turn activate the downstream caspases including caspases-3, -6, and -7 (Safa et al. 2008; Yuan et al. 2013; Lavrik and Krammer 2012). c-FLIP also known as Casper, iFLICE, FLAME-1, CASH, CLARP, MRIT, or usurpin (Micheau 2003) was initially shown to robustly inhibit death receptor-mediated apoptosis (Irmler et al. 1997). At high expression levels, the three splice variants of c-FLIP [c-FLIP long (c-FLIPL), c-FLIP short (c-FLIPS), and c-FLIP Raji (c-FLIPR)] are recruited to the DISC through DED interactions and subsequently abolish death receptor-induced apoptotic signaling by blocking the activation of caspase-8 and caspase-10 (Irmler et al. 1997; Day et al. 2006; Bagnoli et al. 2010; Golks et al. 2005; Peter 2004). Nevertheless, at low expression levels, c-FLIPL may mediate apoptosis by enhancing caspase-8/-10 activation at the DISC (Chang et al. 2002; Peter 2004). While c-FLIPL may function as a pro- or anti-apoptotic factor in normal tissues, it has generally been demonstrated to function as a critical anti-apoptotic regulator of apoptosis in cancer cells (Bagnoli et al. 2010; Safa et al. 2008). Furthermore, silencing c-FLIP expression sensitizes tumor cells to death ligands and chemotherapy in experimental models (Safa et al. 2008; Safa and Pollok 2011). In addition to its function as an apoptosis modulator, c-FLIP exerts other cellular functions including increased cell proliferation and tumorigenesis (Safa et al. 2008; Safa 2013)
C-FLIP, Fig. 2

Apoptosis signaling pathways and roles of c-FLIP in preventing apoptosis. TNFR1 mediated apoptosis, roles of c-FLIP in preventing apoptosis, and NF-κB signaling pathways. The binding of the TNF-α to its receptor TNFR1 results in formation of the Complex I which consists of TNFR1, TRADD, TRAF2 and RIP. NF-κB activation pathway is mediated by Complex I and occur through the MEKK3-IKK-IκB-NF-κB cascade, which leads to expression of a many antiapoptotic factors such as IAP and c-FLIP isoforms. TNF-α treatment through Complex I also activates the JNK and ERK through MAPK signaling pathway. USP2 stabilizes the ubiquitin-E3-ligase ITCH and decreases NF-κB basal activity which leads to reduction of c-FLIP isoforms mRNA production, and proteasomal degradation of c-FLIP isoforms is elevated by the proteasome ITCH. Therefore, levels of c-FLIP protein isoforms decrease. The internalization of the TNFR1 complex leads to formation of Complex II that consists of RIP, TRADD, FADD, and procaspase 8. Caspase-8 is autoactivated and activates the caspases-3 and -7, resulting in induction of apoptosis. Cleavage of the proapoptotic protein Bid by caspase-8 activates the mitochondrial apoptosis pathway that involves release of cytochrome c and Smac/DIABLO from mitochondria. Cytochrome c binds Apaf1 to activate caspase-9-mediated activation of executor caspases. The NF-κB activated factor c-FLIP suppresses caspase-8 activation, while IAPs inhibit executor caspases. Smac released from the mitochondria suppresses IAP to release the apoptosis brake

.

In TNF-α-triggered apoptosis, the internalization of the TNFR1 complex induces formation of Complex II that contains RIP, TRADD, FADD, and caspase-8. Caspase-8 is autoactivated to trigger activation of the executor caspases-3 and -7, resulting in apoptosis, and c-FLIP inhibits capsase-8 activation and apoptosis (Safa et al. 2008; Wang and Lin 2008). Active caspases-8 and -10 are known to cleave a pro-apoptotic Bcl-2 family member, Bid, and the truncated Bid (tBid) induces mitochondrial cytochrome c release, thereby linking the two pathways. After activation, both caspases-8 and -9 activate caspase-3, which in turn cleaves other caspases and many cellular proteins leading to apoptosis.

Mitochondria play a critical role in maintaining cellular respiration and homeostasis in the cells and transfer various signals to the cytosol necessary for survival and cell death. Recent data (Ranjan and Pathak 2016a) demonstrated that FADD and c-FLIP expression participates in balancing redox potential by regulating antioxidant levels. Further, we noticed that knockdown of c-FLIPL and induced expression of FADD results in rapid accumulation of intracellular ROS accompanied by JNK1 activation to substantiate apoptosis. Therefore, apart from their death receptor signaling, c-FLIPL and FADD play important roles in preventing mitochondrial-mediated apoptosis.

The binding of the TNF-α trimer to TNF receptor 1 (TNFR1) also triggers trimerization of TNFR1, resulting in Complex I formation which is involved in inducing the antiapoptotic proteins (Fig. 2). This complex consists of TNFR1, TRADD, TRAF2, and RIP and mediates activation of the NF-κB signaling pathway through the MEKK3-IKK-IκB-NF-κB cascade and subsequent transcription activation and expression of a number of genes including the antiapoptotic factors such as IAPs, Bcl-2, and c-FLIP (Safa et al. 2008; Wang and Lin 2008). As shown in Fig. 3, TNF-α treatment through Complex I can also cause activation of JNK and ERK through the MAPK signaling pathway. The ubiquitin-proteasome system (USP2) stabilizes the ubiquitin-E3-ligase ITCH and lowers NF-κB basal activity, which leads to reduced c-FLIP mRNA production, and proteasomal degradation of c-FLIP isoforms is elevated by its negative regulator proteasome ITCH (Haimerl et al. 2009). Therefore, levels of c-FLIP protein isoforms decrease and apoptosis increase.
C-FLIP, Fig. 3

Structures of c-FLIP variants and cleavage products. c-FLIP isoforms (c-FLIPL, c-FLIPS, and c-FLIPR) contain two death effector domains (DED1 and DED2) at their N termini which are required for DISC recruitment. In addition to two DEDs, c-FLIPL has a significant similarity to caspase-8 and has a large (p20) and a small (p12) caspase-like domain which are catalytically inactive. c-FLIPS and c-FLIPR consist of two DEDs and a small C terminus. c-FLIPL can be cleaved by caspase-8 generating the N-terminal fragment p43-FLIP or p22-FLIP. The phosphorylation (P) sites and ubiquitination (U) sites are indicated (Bagnoli et al. 2010; Safa and Pollok 2011; Oztürk et al. 2012). The p20/p12 regions interact with TRAF2 and RIP1, respectively, and Ku70 bind to DED2 (Kerr et al. 2012) (Modified from Safa 2013)

The TRAIL receptors, DR4 or DR5, can also promote alternative signaling pathways such as JNK, MAPK, or NF-κB by recruiting RIP1 and TRAF2 or TRAF5 to form secondary signaling complex (Yang et al. 2010; Trivedi and Mishra 2015). Activation of NF-κB in this pathway also results in increased expression of c-FLIP (Fig. 2). Studies with TRADD-deficient mouse embryo fibroblasts (MEFs) have documented that RIP1 was also recruited to the TRAIL receptor by interacting with TRADD and both RIP1 and TRADD protect against TRAIL-induced apoptosis (Cao et al. 2011). In these TRADD-deficient MEFs, MAPK and NF-κB pathway activation was impaired, confirming the role of TRADD as the key adaptor protein mediating nonapoptotic signaling by DRs (Cao et al. 2011). Indeed, Human T-Cell Leukemia Virus Type 1 Tax induces c-FLIP expression through DR4/DR5-dependent activation of the IKK-I-κBα-NF-κB pathway (Wang et al. 2014). It is also known that TNF-α and Fas trigger the cleavage of mitogen-activated protein kinase/ERK kinase kinase (MEKK)1, resulting in production of a constitutive active form of MEKK1 and leading to JNK activation in c-FLIP knockdown cells (Nakajima et al. 2008).

In the absence of caspase-8 activity, the death receptors can promote death by programmed necrosis (necroptosis) which requires the kinases receptor-interacting kinase 1 (RIPK1), RIPK3, and mixed-lineage kinase-like protein (MLKL) (Silke and Strasser 2013).

c-FLIP Spliced Variants

Thome et al. (1997) initially identified viral FLICE-inhibitory proteins (v-FLIPs) by a bioinformatic search for novel death effector domains (DED-containing virus-encoded apoptotic regulatory proteins). These authors described six v-FLIPs and showed that cells expressing v-FLIPs were resistance to Fas (CD95/APO-1)- ,TRAILR1-, and TNFR1-induced apoptosis (Thome et al. 1997). v-FLIPs contain two DEDs, bind to the DED of FADD and interfere with the FADD-procaspase-8 interaction, leading to suppressed recruitment of procaspase-8 to the DISC and its activation (Thome et al. 1997). Shortly after the characterization of v-FLIPs, the mammalian cellular homologue was identified and termed c-FLIP (Irmler et al. 1997). c-FLIP consists of 13 distinct spliced variants, three of which are expressed as proteins: the 26 kDa short form (c-FLIPS), the 24 kDa form of c-FLIP (c-FLIPR), and the 55 kDa long form (c-FLIPL) (Lavrik and Krammer 2012; Safa 2013) (Fig. 3). The three c-FLIP variants can interact with the adaptor protein FADD. c-FLIPR is smaller than c-FLIPS and has a similar pattern of expression as c-FLIPS during activation of primary human T cells and is strongly induced in T cells upon CD3/CD28 costimulation (Golks et al. 2005).

Roles of c-FLIP in Necroptosis and Autophagy

In addition to its role in apoptosis, c-FLIPL also plays an important role in necroptotic cell death and autophagy (He and He 2013; Safa 2013). Recent results have demonstrated that necroptosis is a programed receptor-interacting protein-1/receptor-interacting protein-3 (RIP-1/RIP-3)-dependent necrotic cell death induced when caspase-8 activation is inhibited (Walsh and Edinger 2010). c-FLIPL is known to regulate necroptosis through the formation of the signaling platform Ripoptosome, a RIP1/caspase-8-containing intracellular cell death complex (Tenev et al. 2011; Feoktistova et al. 2011). While c-FLIPL prevents Ripoptosome formation, interestingly, c-FLIPS promotes its assembly (Feoktistova et al. 2011; Safa 2013). Therefore, c-FLIP isoforms in the Ripoptosome determine whether cell death occurs by RIP3-dependent necroptosis or caspase-dependent apoptosis (Feoktistova et al. 2011). c-FLIPL mediates the regulation of autophagic signaling and suppresses autophagic stress as well as regulating the activation of p53 and JNK1 to maintain the interaction of Bcl-2 and Beclin-1, a primary protein involved in the autophagic process (Ranjan and Pathak 2016b). To maintain the integrity of the autophagic process, c-FLIPL also simultaneously regulates oxidative stress and proautophagic accumulation of high-mobility group box 1 (HMGB1), a protein that can promote the pathogenesis of inflammatory reaction (Ranjan and Pathak 2016b).

Normal Function of c-FLIP

Animal models provide evidence that c-FLIP plays a critical role in T-cell proliferation and heart development (Micheau 2003). Abnormal c-FLIP expression has been identified in various diseases such as multiple sclerosis, Alzheimer’s disease, diabetes mellitus, rheumatoid arthritis, and various cancers (Micheau 2003). c-FLIP overexpression is known to evade the natural immunity mediated by TRAIL-induced cell death as well as by augmenting cell motility and invasion in vivo (El-Gazzar et al. 2010). Elevated expression of c-FLIP is also seen in Alzheimer disease (Mezache et al. 2015), systemic lupus erythematosus (SLE) (Tao et al. 2009), inflammation diseases (Kang et al. 2009), and lung miofibrosis (Golan-Gerstl et al. 2012). c-FLIPL plays an important antinecroptotic role and is a key regulator of apoptosis, autophagy, and necroptosis in T lymphocytes (He and He 2013). Moreover, recent data suggest that c-FLIPR is an important modulator of apoptosis and enforced expression leads to autoimmunity (Ewald et al. 2014). Experiments with c-FLIP-deficient mice demonstrated that c-FLIP has two distinct roles: (1) cooperates with FADD and caspase-8 during embryonic development and (2) cytoprotects against death-factor triggered apoptosis (Yeh et al. 2000). c-FLIP also has a role in cardiac remodeling following myocardial infarction (MI). c-FLIP also protects against the development of postinfarction cardiac remodeling (Xiao et al. 2012). Furthermore, c-FLIP is essential for myofibroblast accumulation and may serve as a potential target to manipulate tissue fibrosis (Golan-Gerstl et al. 2012). Recent results demonstrated that expression of c-FLIPR in hematopoietic cells supports an efficient immune response against bacterial infections (Telieps et al. 2013).

Upregulation of c-FLIP in Human Cancers

Overexpression of c-FLIP has been found in various types of malignancies and could be associated with cancer progression due to its ability to inhibit cancer cell death. Elevated expression levels of c-FLIP have been reported in several tumor types (Du et al. 2009; Pallares et al. 2009; Safa and Pollok 2011; Tian et al. 2012) including melanoma, hepatocellular carcinoma (HCC), nonsmall cell lung carcinoma, endometrial, colon, breast cancer, bladder cancer (BC), and prostate cancer. Significantly, increased c-FLIP expression was an independent negative prognostic indicator for disease-free survival (DFS) in cervical squamous cell carcinoma (CSCC) (Yao et al. 2016). c-FLIP overexpression has been found to be associated with disease progression and/or poor prognosis in BL, HCC, ovarian, endometrial, colon, prostate, and head and neck squamous cell carcinoma (HNSCC) (Safa et al. 2008; Korkolopoulou et al. 2007; Du et al. 2009). c-FLIPL is highly expressed in invasive breast carcinomas, and its expression level is closely related to the molecular subtypes and clinical prognosis of breast cancer patients (Zang et al. 2014). In addition to blocking apoptotic signaling pathways, c-FLIP has been implicated in contributing to tumor promotion through its influence on several critical cellular survival signaling mechanisms (Safa et al. 2008; Safa 2012).

Structure of c-FLIP Isoforms

In humans, three isoforms of c-FLIP, FLIPL (55 kDa), c-FLIPS (27 kDa) and c-FLIPR (25 kDa) have been identified (Oztürk et al. 2012; Safa 2013). All c-FLIP isoforms contain two DEDs that are structurally similar to the N-terminal part of procaspase-8 (Fig. 1). c-FLIPL contains additional caspase-like domains (p20 and p12) that are catalytically inactive. Moreover, c-FLIPS has an additional isoform-specific C-terminal tail of 19 amino acids. c-FLIPR also contains two DEDs but lacks the additional carboxy (C)-terminal amino acids that are present in c-FLIPS. Moreover, c-FLIPL has a caspase-8 cleavage site at position Asp-376 (LEVD); c-FLIPL cleavage at this site produces the proteolytic fragment variant p43c-FLIP, p43-FLIP, and p22-FLIP, respectively (Oztürk et al. 2012; Safa 2013). The C-terminal region of c-FLIPS and c-FLIPR plays a crucial role in ubiquitination and degradation as well as the antiapoptotic function of these isoforms (Oztürk et al. 2012; Safa 2013).

c-FLIP Activates Cytoprotective and Proliferation Pathways

Several cytoprotective and survival signaling pathways with crucial roles in regulating cell survival, proliferation, and carcinogenesis are activated by c-FLIP (Oztürk et al. 2012; Safa et al. 2008; Safa and Pollak 2011; Safa 2012; Seidelin et al. 2013). Increased expression of c-FLIPL activates NF-κB and ERK signaling by binding to adaptor proteins in each pathway, such as TNFR-associated factors 1 (TRAF1) and 2 (TRAF2), receptor-interacting protein 1 (RIP), and Raf-1 (Fig. 2). The caspase-8 cleaved N-terminal fragment of c-FLIPL (p43-cFLIP) is more efficient than c-FLIPL at recruiting TRAF2 and RIP1, leading to more robust NF-κB activation (Kataoka and Tschopp 2004; Yu and Shi 2008). Interestingly, c-FLIP may also provide the molecular switch from Fas-triggered apoptosis to Fas-promoting cell proliferation (Gilot et al. 2005).

It is known that interaction between Akt and c-FLIPL enhances the antiapoptotic functions of Akt by modulating Gsk3β activity (Quintavalle et al. 2010) and that c-FLIPL overexpression interferes with Gsk3-β phosphorylation levels and induces resistance to TRAIL in cancer cells. DNA-PK/Akt pathway is also reported to play a role in expression of c-FLIP (Kim et al. 2012). Interestingly, siRNA-mediated silencing of DNA-PK or treatment with its inhibitor 4,5-dimethoxy-2-nitrobenzaldehyde (DMNB) led to decreased phosphorylation of Akt and Bad (a target molecule of Akt), elevated expression of DR4/DR5, and decreased expression of c-FLIP (Mizushima and Levine 2010). Furthermore, c-FLIPL directly interacts with a JNK activator, MAP kinase kinase 7 (MKK7), in a TNFα-dependent manner and inhibits the interactions of MKK7 with MAP/ERK kinase kinase 1 (MEKK1), apoptosis signal-regulating kinase 1 (ASK1), and TGF-β-activated kinase 1. This interaction of c-FLIPL with MKK7 might selectively suppress JNK activation (Nakajima et al. 2006).

In addition to its role as a critical regulator of apotosis, necroptosis, and autophagy, c-FLIP may also regulate potentially harmful signaling pathways regulating the production of inflammatory cytokines, tumor cell migration and metastasis, and the activation of transcription factors critical during tumorigenesis (Naito et al. 2004; Gilot et al. 2005; Leverkus et al. 2008). Furthermore, overexpression of c-FLIP can alter cell cycle progression and enhance cell proliferation and carcinogenesis (Safa 2013).

Summary

c-FLIP is a master antiapoptotic protein and an important protein in causing resistance to cytokines and chemotherapeutic agents. It regulates apoptosis, necroptosis, autophagy, and cytoprotective signaling pathways. c-FLIP is expressed as c-FLIPL, c-FLIPS, and c-FLIPR isoforms in human cells. c-FLIP isoforms bind to FADD and caspase-8 or -10 and TRAIL receptor 5 (DR5), which prevents autocatalytic activation of these caspases and DISC formation. c-FLIPL and c-FLIPS are also known to have multifunctional activities in various cellular signaling pathways, as well as activating and/or upregulating several cytoprotective and pro-survival signaling proteins including Akt, ERK, β-catenin, and NF-κB. 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. Moreover, since elevated expression of c-FLIP has been documented in Alzheimer disease, systemic lupus erythematosus (SLE), inflammation diseases, and lung fibrosis, it is a potentially important target for identifying therapeutic agents for treating these diseases.

Notes

Acknowledgment

I would like to thank Dr. Mary D. Kraeszig for her editorial assistance. The work in the author’s laboratory was supported by research grants from the National Cancer Institute (CA 080734, CA 90878, and CA 101743), Department of Defense (DOD) (OC 06095), and the Indiana University Cancer Center Translational Research Acceleration Collaboration (ITRAC) initiative.

References

  1. Bagnoli M, Canevari S, Mezzanzanica D. Cellular FLICE-inhibitory protein (c-FLIP) signalling: a key regulator of receptor-mediated apoptosis in physiologic context and in cancer. Int J Biochem Cell Biol. 2010;42:210–3. doi: 10.1016/j.biocel.2009.11.015.CrossRefPubMedGoogle Scholar
  2. Cain K, Bratton SB, Langlais C, Walker G, Brown DG, Sun XM, Cohen GM. Apaf-1 oligomerizes into biologically active approximately 700-kDa and inactive approximately 1.4-MDa apoptosome complexes. J Biol Chem. 2000;275:6067–70.CrossRefPubMedGoogle Scholar
  3. Chang DW1, Xing Z, Pan Y, Algeciras-Schimnich A, Barnhart Bc, Yaish-Ohad S. et al. c-FLIOL is a dual function regulator for caspase-8 activation and CD95-mediated apoptosis. EMBO J. 2002;21:3704–14.Google Scholar
  4. Cao X, Pobezinskaya YL, Morgan MJ, Liu ZG. The role of TRADD in TRAIL-induced apoptosis and signaling. FASEB J. 2011;4:1353–8. doi: 10.1096/fj.10-170480.CrossRefGoogle Scholar
  5. Day TW, Najafi F, Wu CH, Safa AR. Cellular FLICE-like inhibitory protein (c-FLIP): a novel target for Taxol-induced apoptosis. Biochem Pharmacol. 2006;71:1551–61.CrossRefPubMedGoogle Scholar
  6. Du X, Bao G, He X, Zhao H, Yu F, Qiao Q, et al. Expression and biological significance of c-FLIP in human hepatocellular carcinomas. J Exp Clin Cancer Res. 2009;28:24. doi: 10.1186/1756-9966-28-24.CrossRefPubMedPubMedCentralGoogle Scholar
  7. El-Gazzar A, Wittinger M, Perco P, Anees M, Horvat R, Mikulits W, et al. The role of c-FLIP(L) in ovarian cancer: chaperoning tumor cells from immunosurveillance and increasing their invasive potential. Gynecol Oncol. 2010;117:451–9. doi: 10.1016/j.ygyno.2010.02.024.CrossRefPubMedGoogle Scholar
  8. Ewald F, Annemann M, Pils MC, Plaza-Sirvent C, Neff F, Erck C, Reinhold D, Schmitz I. Constitutive expression of murine c-FLIPR causes autoimmunity in aged mice. Cell Death Dis. 2014;5:e1168. doi: 10.1038/cddis.2014.138.CrossRefPubMedPubMedCentralGoogle Scholar
  9. Feoktistova M, Geserick P, Kellert B, Dimitrova DP, Langlais C, Hupe M, et al. cIAPs block Ripoptosome formation, a RIP1/caspase-8 containing intracellular cell death complex differentially regulated by cFLIP isoforms. Mol Cell. 2011;43:449–63. doi: 10.1016/j.molcel.2011.06.011.CrossRefPubMedPubMedCentralGoogle Scholar
  10. Gilot D, Serandour AL, Ilyin GP, Lagadic-Gossmann D, Loyer P, Corlu A, et al. A role for caspase-8 and c-FLIPL in proliferation and cell-cycle progression of primary hepatocytes. Carcinogenesis. 2005;26:2086–94.CrossRefPubMedGoogle Scholar
  11. Golan-Gerstl R, Wallach-Dayan SB, Zisman P, Cardoso WV, Goldstein RH, Breuer R. Cellular FLICE-like inhibitory protein deviates myofibroblast Fas-induced apoptosis toward proliferation during lung fibrosis. Am J Respir Cell Mol Biol. 2012;47:271–9.Google Scholar
  12. Golks A, Brenner D, Fritsch C, Krammer PH, Lavrik IN. c-FLIPR, a new regulator of death receptor-induced apoptosis. J Biol Chem. 2005;280:14507–13.CrossRefPubMedGoogle Scholar
  13. Golks A, Brenner D, Krammer PH, Lavrik IN. The c-FLIP-NH2 terminus (p22-FLIP) induces NF-κB activation. J Exp Med. 2006;203:1295–305.CrossRefPubMedPubMedCentralGoogle Scholar
  14. Grimm S. The ER-mitochondria interface: the social network of cell death. Biochim Biophys Acta. 2012;1823:327–34. doi: 10.1016/j.bbamcr.2011.11.018.CrossRefPubMedGoogle Scholar
  15. Haimerl F, Erhardt A, Sass G, Tiegs G. Down-regulation of the de-ubiquitinating enzyme ubiquitin-specific protease 2 contributes to tumor necrosis factor-alpha-induced hepatocyte survival. J Biol Chem. 2009;284:495–4. doi: 10.1074/jbc.M803533200.CrossRefPubMedGoogle Scholar
  16. He MX, He YW. A role for c-FLIPL in the regulation of apoptosis, autophagy, and necroptosis in T lymphocytes. Cell Death Differ. 2013;2:188–97. doi: 10.1038/cdd.2012.148.CrossRefGoogle Scholar
  17. Irmler M, Thome M, Hahne M, Schneider P, Hofmann K, Steiner V, et al. Inhibition of death receptor signals by cellular FLIP. Nature. 1997;388:190–5.CrossRefPubMedGoogle Scholar
  18. Kang HK, Ecklund D, Liu M, Datta SK. Apigenin, a non-mutagenic dietary flavonoid, suppresses lupus by inhibiting autoantigen presentation for expansion of autoreactive Th1 and Th17 cells. Arthritis Res Ther. 2009;11:R59. doi: 10.1186/ar2682.CrossRefPubMedPubMedCentralGoogle Scholar
  19. Kataoka T, Tschopp J. N-terminal fragment of c-FLIP(L) processed by caspase 8 specifically interacts with TRAF2 and induces activation of the NF-kappaB signaling pathway. Mol Cell Biol. 2004;24:2627–36.CrossRefPubMedPubMedCentralGoogle Scholar
  20. Kerr E, Holohan C, McLaughlin KM, Majkut J, Dolan S, Redmond K, et al. Identification of an acetylation-dependant Ku70/FLIP complex that regulates FLIP expression and HDAC inhibitor-induced apoptosis. Cell Death Differ. 2012;19:1317–27. doi: 10.1038/cdd.2012.8.CrossRefPubMedPubMedCentralGoogle Scholar
  21. Kim MJ, Kim HB, Bae JH, Lee JW, Park SJ, et al. Sensitization of human K562 leukemic cells to TRAIL-induced apoptosis by inhibiting the DNA-PKcs/Akt-mediated cell survival pathway. Biochem Pharmacol. 2009;78:573–82.CrossRefPubMedGoogle Scholar
  22. Korkolopoulou P, Saetta AA, Levidou G, Gigelou F, Lazaris A, Thymara I, et al. c-FLIP expression in colorectal carcinomas: association with Fas/FasL expression and prognostic implications. Histopathology. 2007;51:150–6. doi: 10.1038/cdd.2012.8.CrossRefPubMedGoogle Scholar
  23. Krammer PH, Kamiński M, Kiessling M, Gülow K. No life without death. Adv Cancer Res. 2007;97:111–38.CrossRefPubMedGoogle Scholar
  24. Lavrik IN, Krammer PH. Regulation of CD95/Fas signaling at the DISC. Cell Death Differ. 2012;19:36–41.CrossRefPubMedGoogle Scholar
  25. Lavrik I, Golks A, Krammer PH. Death receptor signaling. J Cell Sci. 2005;118:265–67.Google Scholar
  26. Leverkus M, Diessenbacher P, Geserick P. FLIPing the coin? Death receptor-mediated signals during skin tumorigenesis. Exp Dermatol. 2008;17:614–22.Google Scholar
  27. Liu X, Kim CN, Yang J, Jemmerson R, Wang X. Induction of apoptotic program in cell-free extracts: Requirement for dATP and cytochrome c. Cell. 1996;86:147–57.CrossRefPubMedGoogle Scholar
  28. Mezache L, Mikhail M, Garofalo M, Nuovo GJ. Reduced miR-512 and the elevated expression of its targets cFLIP and MCL1 localize to neurons with hyperphosphorylated tau protein in Alzheimer disease. Appl Immunohistochem Mol Morphol. 2015;23:615–23.CrossRefPubMedGoogle Scholar
  29. Micheau O. Cellular FLICE-inhibitory protein: an attractive therapeutic target? Expert Opin Ther Targets. 2003;7:559–73.CrossRefPubMedPubMedCentralGoogle Scholar
  30. Micheau O, Tschopp J. Induction of TNF receptor I-mediated apoptosis via two sequential signaling complexes. Cell. 2003;114:181–90.CrossRefPubMedGoogle Scholar
  31. Mizushima N, Levine B. Autophagy in mammalian development and differentiation. Nat Cell Biol. 2010;12:823–30.CrossRefPubMedPubMedCentralGoogle Scholar
  32. Naito M, Katayama R, Ishioka T, Takada R, Fujita N, Tsuruo T, et al. Cellular FLIP inhibits β-catenin ubiquitylation and enhances Wnt signaling. Mol Cell Biol. 2004;24:8418–27. doi: 10.1242/jcs.058602.CrossRefPubMedPubMedCentralGoogle Scholar
  33. Nakajima A, Komazawa-Sakon S, Takekawa M, Sasazuki T, Yeh WC, Yagita H, et al. An antiapoptotic protein, c-FLIPL, directly binds to MKK7 and inhibits the JNK pathway. EMBO J. 2006;25:5549–59.CrossRefPubMedPubMedCentralGoogle Scholar
  34. Nakajima A, Kojima Y, Nakayama M, Yagita H, Okumura K, Nakano H. Downregulation of c-FLIP promotes caspase-dependent JNK activation and reactive oxygen species accumulation in tumor cells. Oncogene. 2008;27:76–84.CrossRefPubMedGoogle Scholar
  35. Oztürk S, Schleich K, Lavrik IN. Cellular FLICE-like inhibitory proteins (c-FLIPs): fine-tuners of life and death decisions. Exp Cell Res. 2012;318:1324–31. doi: 10.1016/j.yexcr.2012.01.019.CrossRefPubMedGoogle Scholar
  36. Pallares J, Llobet D, Santacana M, Eritja N, Velasco A, Cuevas D, Lopez S, Palomar-Asenjo V, Yeramian A, Dolcet X. Matias-Guiu X. CK2beta is expressed in endometrial carcinoma and has a role in apoptosis resistance and cell proliferation. Am J Pathol. 2009;174:287–96. doi: 10.2353/ajpath.2009.080552.
  37. Peter ME. The flip side of FLIP. Biochem J. 2004;382(Pt 2):e1–3.CrossRefPubMedPubMedCentralGoogle Scholar
  38. Plati J, Bucur O, Khosravi-Far R. Apoptotic cell signaling in cancer progression and therapy. Integr Biol (Camb). 2011;2011(3):279–96.CrossRefGoogle Scholar
  39. Quintavalle C, Incoronato M, Puca L, Acunzo M, Zanca C, Romano G, et al. c-FLIPL enhances anti-apoptotic Akt functions by modulation of Gsk3β activity. Cell Death Differ. 2010;17:1908–16.Google Scholar
  40. Ranjan K, Pathak C. Expression of FADD and cFLIPL balances mitochondrial integrity and redox signaling to substantiate apoptotic cell death. Mol Cell Biochem. 2016a;422:135–50.CrossRefPubMedGoogle Scholar
  41. Ranjan K, Pathak C. Expression of cFLIPL determines the basal interaction of Bcl-2 with Beclin-1 and regulates p53 dependent ubiquitination of Beclin-1 during autophagic stress. J Cell Biochem. 2016b;117:1757–68. doi: 10.1002/jcb.25474.CrossRefPubMedGoogle Scholar
  42. Reubold TF, Eschenburg S. A molecular view on signal transduction by the apoptosome. Cell Signal. 2012;24:1420–5.CrossRefPubMedGoogle Scholar
  43. Safa AR. c-FLIP, a master anti-apoptotic regulator. Exp Oncol. 2012;34:176–84.PubMedPubMedCentralGoogle Scholar
  44. Safa AR. Roles of c-FLIP in apoptosis, necroptosis, and autophagy. J Carcinog Mutagen. 2013; Suppl 6. pii: 003. doi: 10.4172/2157-2518.S6-003.PubMedPubMedCentralGoogle Scholar
  45. Safa AR, Pollok KE. Targeting the anti-apoptotic protein c-FLIP for cancer therapy. Cancers (Basel). 2011;3:1639–71. doi: 10.3390/cancers3021639.CrossRefGoogle Scholar
  46. Safa AR, Day TW, Wu CH. Cellular FLICE-like inhibitory protein (c-FLIP): a novel target for cancer therapy. Curr Cancer Drug Targets. 2008;8:37–46.CrossRefPubMedPubMedCentralGoogle Scholar
  47. Scaffidi C, Fulda S, Srinivasan A, Friesen C, Li F, Tomaselli KJ, Debatin KM, et al. Two CD95 (APO-1/Fas) signaling pathways. EMBO J. 1998;17:1675–87.CrossRefPubMedPubMedCentralGoogle Scholar
  48. Seidelin JB, Coskun M, Vainer B, Riis L, Soendergaard C, Nielsen OH. ERK controls epithelial cell death receptor signalling and cellular FLICE-like inhibitory protein (c-FLIP) in ulcerative colitis. J Mol Med (Berl). 2013;91:839–49. doi: 10.1007/s00109-013-1003-7. Epub 2013 Feb 1.CrossRefGoogle Scholar
  49. Silke J, Strasser A. The FLIP side of life. Sci Signal. 2013;6:pe2. doi: 10.1126/scisignal.2003845.PubMedGoogle Scholar
  50. Tao J, Dong J, Li Y, Liu YQ, Yang J, Wu Y, et al. Up-regulation of cellular FLICE-inhibitory protein in peripheral blood B lymphocytes in patients with systemic lupus erythematosus is associated with clinical characteristics. J Eur Acad Dermatol Venereol. 2009;23:433–7.CrossRefPubMedGoogle Scholar
  51. Telieps T, Ewald F, Gereke M, Annemann M, Rauter Y, Schuster M, et al. c-FLIPR modulates cell death induction upon T-cell activation and infection. Eur J Immunol. 2013;43:1499–510. doi: 10.1002/eji.201242819.CrossRefPubMedGoogle Scholar
  52. Tenev T, Bianchi K, Darding M, Broemer M, Langlais C, Wallberg F, et al. The Ripoptosome, a signaling platform that assembles in response to genotoxic stress and loss of IAPs. Mol Cell. 2011;43:432–48. doi: 10.1016/j.molcel.2011.06.006.CrossRefPubMedGoogle Scholar
  53. Thome M, Schneider P, Hofmann K, Fickenscher H, Meinl E, Neipel F, et al. Viral FLICE-inhibitory proteins (FLIPs) prevent apoptosis induced by death receptors. Nature. 1997;386:517–21.CrossRefPubMedGoogle Scholar
  54. Tian F, Lu JJ, Wang L, Li L, Yang J, Li Y, et al. Expression of c-FLIP in malignant melanoma, and its relationship with the clinicopathological features of the disease. Clin Exp Dermatol. 2012;37:259–65. doi: 10.1111/j.1365-2230.2011.04238.x.CrossRefPubMedGoogle Scholar
  55. Trivedi R, Mishra DP. Trailing TRAIL resistance: novel targets for TRAIL sensitization in cancer cells. Front Oncol. 2015;5:69. doi: 10.3389/fonc.2015.00069.CrossRefPubMedPubMedCentralGoogle Scholar
  56. Vaux DL. Apoptogenic factors released from mitochondria. Biochim Biophys Acta. 2011;13:546–50. doi: 10.1016/j.bbamcr.2010.08.002.CrossRefGoogle Scholar
  57. Walsh CM, Edinger AL. The complex interplay between autophagy, apoptosis, and necrotic signals promotes T-cell homeostasis. Immunol Rev. 2010;236:95–109. doi: 10.1111/j.1600-065X.2010.00919.x.CrossRefPubMedPubMedCentralGoogle Scholar
  58. Wang X, Lin Y. Tumor necrosis factor and cancer, buddies or foes? Acta Pharmacol Sin. 2008;29:1275–88.CrossRefPubMedPubMedCentralGoogle Scholar
  59. Wang W, Zhou J, Shi J, Zhang Y, Liu S, Liu Y, et al. Human T-cell leukemia virus type 1 Tax-deregulated autophagy pathway and c-FLIP expression contribute to resistance against death receptor-mediated apoptosis. J Virol. 2014;88:2786–98. doi: 10.1128/JVI.03025-13.
  60. Xiao J, Moon M, Yan L, Nian M, Zhang Y, Liu C, et al. Cellular FLICE-inhibitory protein protects against cardiac remodelling after myocardial infarction. Basic Res Cardiol. 2012;107:239. doi: 10.1007/s00395-011-0239-z.CrossRefPubMedGoogle Scholar
  61. Yang A, Wilson NS, Ashkenazi A. Proapoptotic DR4 and DR5 signaling in cancer cells: toward clinical translation. Curr Opin Cell Biol. 2010;22:837–44. doi: 10.1016/j.ceb.2010.08.001.CrossRefPubMedGoogle Scholar
  62. Yao Q, Du J, Lin J, Luo Y, Wang Y, Liu Y, et al. Prognostic significance of TRAIL signalling molecules in cervical squamous cell carcinoma. J Clin Pathol. 2016;69:122–7. doi: 10.1136/jclinpath-2014-202811.CrossRefPubMedGoogle Scholar
  63. Yeh WC, Itie A, Elia AJ, Ng M, Shu HB, Wakeham A, et al. Requirement for Casper (c-FLIP) in regulation of death receptor-induced apoptosis and embryonic development. Immunity. 2000;12:633–42.CrossRefPubMedGoogle Scholar
  64. Yu JW, Shi Y. FLIP and the death effector domain family. Oncogene. 2008;27:6216–27. doi: 10.1038/onc.2008.299.CrossRefPubMedGoogle Scholar
  65. Yuan S, Topf M, Reubold TF, Eschenburg S, Akey CW. Changes in apaf-1 conformation that drive apoptosome assembly. Biochemistry. 2013;52:2319–27.CrossRefPubMedPubMedCentralGoogle Scholar
  66. Zang F, Wei X, Sun B. Relationship of c-FLIPL protein expression with molecular subtyping and clinical prognosis in invasive breast cancer. Zhonghua Bing Li Xue Za Zhi. 2014;43:442–6.Google Scholar

Copyright information

© Springer International Publishing AG 2018

Authors and Affiliations

  1. 1.Department of Pharmacology and ToxicologyIndiana University School of MedicineIndianapolisUSA
  2. 2.Indiana University Simon Cancer CenterIndiana University School of MedicineIndianapolisUSA