Selective expression of FLIP in malignant melanocytic skin lesions

The tumor immune microenvironment in primary cutaneous melanoma

Melanoma is an immunogenic tumor. The melanoma tumor immune microenvironment (TIME) is made up of a heterogenous mix of both immune and non-immune cells as well as a multitude of signaling molecules. The interactions between tumor cells, immune cells and signaling molecules affect tumor progression and therapeutic responses. Understanding the composition and function of the TIME in primary cutaneous melanoma is useful for prognostication and therapeutic decisions. This review provides an overview of the components of the TIME in primary cutaneous melanoma, and their influence on clinical outcomes.

The molecular crosstalk between innate immunity and DNA damage repair/response: Interactions and effects in cancers

DNA damage can lead to erroneous alterations and mutations which in turn can result into wide range of disease condition including aging, severe inflammation, and, most importantly, cancer. Due to the constant exposure to high-risk factors such as exogenous and endogenous DNA-damaging agents, cells may experience DNA damage impairing stability and integrity of the genome. These perturbations in DNA structure can arise from several mutations in the genome. Therefore, DNA Damage Repair/Response (DDR) detects and then corrects these potentially tumorigenic problems by inducing processes such as DNA repair, cell cycle arrest, apoptosis, etc. Additionally, DDR can activate signaling pathways related to immune system as a protective mechanism against genome damage. These protective machineries are ignited and spread through a network of molecules including DNA damage sensors, transducers, kinases and downstream effectors. In this review, we are going to discuss the molecular crosstalk between innate immune system and DDR, as well as their potential effects on cancer pathophysiology.

The Identification of New c-FLIP Inhibitors for Restoring Apoptosis in TRAIL-Resistant Cancer Cells

The catalytically inactive caspase-8-homologous protein, c-FLIP, is a potent antiapoptotic protein highly expressed in various types of cancers. c-FLIP competes with caspase-8 for binding to the adaptor protein FADD (Fas-Associated Death Domain) following death receptors' (DRs) activation via the ligands of the TNF-R family. As a consequence, the extrinsic apoptotic signaling pathway involving DRs is inhibited. The inhibition of c-FLIP activity in tumor cells might enhance DR-mediated apoptosis and overcome immune and anticancer drug resistance. Based on an in silico approach, the aim of this work was to identify new small inhibitory molecules able to bind selectively to c-FLIP and block its anti-apoptotic activity. Using a homology 3D model of c-FLIP, an in silico screening of 1880 compounds from the NCI database (National Cancer Institute) was performed. Nine molecules were selected for in vitro assays, based on their binding affinity to c-FLIP and their high selectivity compared to caspase-8. These molecules selectively bind to the Death Effector Domain 2 (DED2) of c-FLIP. We have tested in vitro the inhibitory effect of these nine molecules using the human lung cancer cell line H1703, overexpressing c-FLIP. Our results showed that six of these newly identified compounds efficiently prevent FADD/c-FLIP interactions in a molecular pull-down assay, as well as in a DISC immunoprecipitation assay. The overexpression of c-FLIP in H1703 prevents TRAIL-mediated apoptosis; however, a combination of TRAIL with these selected molecules significantly restored TRAIL-induced cell death by rescuing caspase cleavage and activation. Altogether, our findings indicate that new inhibitory chemical molecules efficiently prevent c-FLIP recruitment into the DISC complex, thus restoring the caspase-8-dependent apoptotic cascade. These results pave the way to design new c-FLIP inhibitory molecules that may serve as anticancer agents in tumors overexpressing c-FLIP.

Regulation of extrinsic apoptotic signaling by c-FLIP: towards targeting cancer networks

The extrinsic pathway is mediated by death receptors (DRs), including CD95 (APO-1/Fas) or TRAILR-1/2. Defects in apoptosis regulation lead to cancer and other malignancies. The master regulator of the DR networks is the cellular FLICE inhibitory protein (c-FLIP). In addition to its key role in apoptosis, c-FLIP may exert other cellular functions, including control of necroptosis, pyroptosis, nuclear factor κB (NF-κB) activation, and tumorigenesis. To gain further insight into the molecular mechanisms of c-FLIP action in cancer networks, we focus on the structure, isoforms, interactions, and post-translational modifications of c-FLIP. We also discuss various avenues to target c-FLIP in cancer cells for therapeutic benefit.

Cytotoxic Efficacy and Resistance Mechanism of a TRAIL and VEGFA-Peptide Fusion Protein in Colorectal Cancer Models

TNF-related apoptosis-inducing ligand (TRAIL) is a type II transmembrane protein capable of selectively inducing apoptosis in cancer cells by binding to its cognate receptors. Here, we examined the anticancer efficacy of a recently developed chimeric AD-O51.4 protein, a TRAIL fused to the VEGFA-originating peptide. We tested AD-O51.4 protein activity against human colorectal cancer (CRC) models and investigated the resistance mechanism in the non-responsive CRC models. The quantitative comparison of apoptotic activity between AD-O51.4 and the native TRAIL in nine human colorectal cancer cell lines revealed dose-dependent toxicity in seven of them; the immunofluorescence-captured receptor abundance correlated with the extent of apoptosis. AD-O51.4 reduced the growth of CRC patient-derived xenografts (PDXs) with good efficacy. Cell lines that acquired AD-O51.4 resistance showed a significant decrease in surface TRAIL receptor expression and apoptosis-related proteins, including Caspase-8, HSP60, and p53. These results demonstrate the effectiveness of AD-O51.4 protein in CRC preclinical models and identify the potential mechanism underlying acquired resistance. Progression of AD-O51.4 to clinical trials is expected.

Cutaneous Malignant Melanoma: A Review of Early Diagnosis and Management

Cutaneous melanoma (CM) is a malignant tumor formed from pigment-producing cells called melanocytes. It is one of the most aggressive and fatal forms of skin malignancy. In the last decades, CM's incidence has gradually risen, with 351,880 new cases in 2015. Since the 1960s, its incidence has increased steadily, in 2019, with approximately 96,000 new cases. A greater understanding of early diagnosis and management of CM is urgently needed because of the high mortality rates due to metastatic melanoma. Timely detection of melanoma is crucial for successful treatment, but diagnosis with histopathology may also pose a significant challenge to this objective. Early diagnosis and management are essential and contribute to better survival rates of the patient. To better control this malignancy, such information is expected to be particularly useful in the early detection of possible metastatic lesions and the development of new therapeutic approaches. This article reviews the available information on the early diagnosis and management of CM and discusses such information's potential in facilitating the future prospective.

The NLRP3 Inflammasome as a Critical Actor in the Inflammaging Process

As a consequence of the considerable increase in the human lifespan over the last century, we are experiencing the appearance and impact of new age-related diseases. The causal relationships between aging and an enhanced susceptibility of suffering from a broad spectrum of diseases need to be better understood. However, one specific shared feature seems to be of capital relevance for most of these conditions: the low-grade chronic inflammatory state inherently associated with aging, i.e., inflammaging. Here, we review the molecular and cellular mechanisms that link aging and inflammaging, focusing on the role of the innate immunity and more concretely on the nucleotide-binding oligomerization domain (NOD)-like receptor family pyrin domain containing 3 (NLRP3) inflammasome, as well as how the chronic activation of this inflammasome has a detrimental effect on different age-related disorders.

The Histone Deacetylase Inhibitor Entinostat/Syndax 275 in Osteosarcoma

The prognosis for metastatic osteosarcoma (OS) is poor and has not changed in several decades. Therapeutic paradigms that target and exploit novel molecular pathways are desperately needed. Recent preclinical data suggests that modulation of the Fas/FasL pathway may offer benefit in the treatment of refractory osteosarcoma. Fas and FasL are complimentary receptor-ligand proteins. Fas is expressed in multiple tissues, whereas FasL is restricted to privilege organs, such as the lung. Fas expression has been shown to inversely correlate with the metastatic potential of OS cells; tumor cells which express high levels of Fas have decreased metastatic potential and the ones that reach the lung undergo cell death upon interaction with constitutive FasL in the lung. Agents such as gemcitabine and the HDAC inhibitor, entinostat/Syndax 275, have been shown to upregulate Fas expression on OS cells, potentially leading to decreased OS pulmonary metastasis and improved outcome. Clinical trials are in development to evaluate this combination as a potential treatment option for patients with refractory OS.

Immune surveillance in melanoma: From immune attack to melanoma escape and even counterattack

Pharmacologic inhibition of the cytotoxic T lymphocyte antigen 4 (CTLA4) and the programmed death receptor-1 (PD1) has resulted in unprecedented durable responses in metastatic melanoma. However, resistance to immunotherapy remains a major challenge. Effective immune surveillance against melanoma requires 4 essential steps: activation of the T lymphocytes, homing of the activated T lymphocytes to the melanoma microenvironment, identification and episode of melanoma cells by activated T lymphocytes, and the sensitivity of melanoma cells to apoptosis. At each of these steps, there are multiple factors that may interfere with the immune surveillance machinery, thus allowing melanoma cells to escape immune attack and develop resistance to immunotherapy. We provide a comprehensive review of the complex immune surveillance mechanisms at play in melanoma, and a detailed discussion of how these mechanisms may allow for the development of intrinsic or acquired resistance to immunotherapeutic modalities, and potential avenues for overcoming this resistance.

Lesser-Known Molecules in Ovarian Carcinogenesis

Currently, the deciphering of the signaling pathways brings about new advances in the understanding of the pathogenic mechanism of ovarian carcinogenesis, which is based on the interaction of several molecules with different biochemical structure that, consequently, intervene in cell metabolism, through their role as regulators in proliferation, differentiation, and cell death. Given that the ensemble of biomarkers in OC includes more than 50 molecules the interest of the researchers focuses on the possible validation of each one's potential as prognosis markers and/or therapeutic targets. Within this framework, this review presents three protein molecules: ALCAM, c-FLIP, and caveolin, motivated by the perspectives provided through the current limited knowledge on their role in ovarian carcinogenesis and on their potential as prognosis factors. Their structural stability, once altered, triggers the initiation of the sequences characteristic for ovarian carcinogenesis, through their role as modulators for several signaling pathways, contributing to the disruption of cellular junctions, disturbance of pro-/antiapoptotic equilibrium, and alteration of transmission of the signals specific for the molecular pathways. For each molecule, the text is built as follows: (i) general remarks, (ii) structural details, and (iii) particularities in expression, from different tumors to landmarks in ovarian carcinoma.

NF-κB Regulation of c-FLIP Promotes TNFα-Mediated RAF Inhibitor Resistance in Melanoma

Targeted inhibitors elicit heterogeneous clinical responses in genetically stratified groups of patients. Although most studies focus on tumor intrinsic properties, factors in the tumor microenvironment were recently found to modulate the response to inhibitors. Here, we show that in cutaneous BRAF V600E melanoma, the cytokine tumor necrosis factor-α (TNFα) blocks RAF inhibitor-induced apoptosis via activation of NF-κB. Several NF-κB-dependent factors are upregulated following TNFα and RAF inhibitor treatment. Of these factors, we show that death receptor inhibitor cellular caspase 8 (FLICE)-like inhibitory protein (c-FLIP) is required for TNFα-induced protection against RAF inhibitor. Overexpression of c-FLIP_S or c-FLIP_L isoform decreased RAF inhibitor-induced apoptosis in the absence of TNFα. Importantly, targeting NF-κB enhances response to RAF inhibitor in vitro and in vivo. Together, our results show mechanistic evidence for cytokine-mediated resistance to RAF inhibitor and provide a preclinical rationale for the strategy of cotargeting the RAF/MEK/ERK1/2 pathway and the TNFα/NF-κB axis to treat mutant BRAF melanomas.

Co-acting gene networks predict TRAIL responsiveness of tumour cells with high accuracy

Background

Identification of differentially expressed genes from transcriptomic studies is one of the most common mechanisms to identify tumor biomarkers. This approach however is not well suited to identify interaction between genes whose protein products potentially influence each other, which limits its power to identify molecular wiring of tumour cells dictating response to a drug. Due to the fact that signal transduction pathways are not linear and highly interlinked, the biological response they drive may be better described by the relative amount of their components and their functional relationships than by their individual, absolute expression.

Results

Gene expression microarray data for 109 tumor cell lines with known sensitivity to the death ligand cytokine tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) was used to identify genes with potential functional relationships determining responsiveness to TRAIL-induced apoptosis. The machine learning technique Random Forest in the statistical environment “R” with backward elimination was used to identify the key predictors of TRAIL sensitivity and differentially expressed genes were identified using the software GeneSpring. Gene co-regulation and statistical interaction was assessed with q-order partial correlation analysis and non-rejection rate. Biological (functional) interactions amongst the co-acting genes were studied with Ingenuity network analysis. Prediction accuracy was assessed by calculating the area under the receiver operator curve using an independent dataset. We show that the gene panel identified could predict TRAIL-sensitivity with a very high degree of sensitivity and specificity (AUC = 0 · 84). The genes in the panel are co-regulated and at least 40% of them functionally interact in signal transduction pathways that regulate cell death and cell survival, cellular differentiation and morphogenesis. Importantly, only 12% of the TRAIL-predictor genes were differentially expressed highlighting the importance of functional interactions in predicting the biological response.

Conclusions

The advantage of co-acting gene clusters is that this analysis does not depend on differential expression and is able to incorporate direct- and indirect gene interactions as well as tissue- and cell-specific characteristics. This approach (1) identified a descriptor of TRAIL sensitivity which performs significantly better as a predictor of TRAIL sensitivity than any previously reported gene signatures, (2) identified potential novel regulators of TRAIL-responsiveness and (3) provided a systematic view highlighting fundamental differences between the molecular wiring of sensitive and resistant cell types.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-1144) contains supplementary material, which is available to authorized users.

Synergistic anti-tumor activity and inhibition of angiogenesis by cotargeting of oncogenic and death receptor pathways in human melanoma

Improving treatment of advanced melanoma may require the development of effective strategies to overcome resistance to different anti-tumor agents and to counteract relevant pro-tumoral mechanisms in the microenvironment. Here we provide preclinical evidence that these goals can be achieved in most melanomas, by co-targeting of oncogenic and death receptor pathways, and independently of their BRAF, NRAS, p53 and PTEN status. In 49 melanoma cell lines, we found independent susceptibility profiles for response to the MEK1/2 inhibitor AZD6244, the PI3K/mTOR inhibitor BEZ235 and the death receptor ligand TRAIL, supporting the rationale for their association. Drug interaction analysis indicated that a strong synergistic anti-tumor activity could be achieved by the three agents and the AZD6244–TRAIL association on 20/21 melanomas, including cell lines resistant to the inhibitors or to TRAIL. Mechanistically, synergy was explained by enhanced induction of caspase-dependent apoptosis, mitochondrial depolarization and modulation of key regulators of extrinsic and intrinsic cell death pathways, including c-FLIP, BIM, BAX, clusterin, Mcl-1 and several IAP family members. Moreover, silencing experiments confirmed the central role of Apollon downmodulation in promoting the apoptotic response of melanoma cells to the combinatorial treatments. In SCID mice, the AZD6244–TRAIL association induced significant growth inhibition of a tumor resistant to TRAIL and poorly responsive to AZD6244, with no detectable adverse events on body weight and tissue histology. Reduction in tumor volume was associated not only with promotion of tumor apoptosis but also with suppression of the pro-angiogenic molecules HIF1α, VEGFα, IL-8 and TGFβ1 and with inhibition of tumor angiogenesis. These results suggest that synergistic co-targeting of oncogenic and death receptor pathways can not only overcome melanoma resistance to different anti-tumor agents in vitro but can also promote pro-apoptotic effects and inhibition of tumor angiogenesis in vivo.

c-FLIPp43 induces activation of the nuclear factor‑κB signaling pathway in a dose-dependent manner in the A375 melanoma cell line

In order to investigate the role of c‑FLIPp43 in the regulation of the nuclear factor (NF)‑κB signaling pathway in melanoma cell lines, a eukaryotic expression vector for c‑FLIPp43 was constructed with the pCMV‑Tag2B plasmid. The monoclonal A375 cells with stable expression of c‑FLIPp43 were obtained by G418 selection and were identified with western blot analysis. The protein level of NF‑κBp65 in the A375 cell line with stable expression of c‑FLIPp43 was examined by western blot analysis. The translocation of NF‑κBp65 was examined using immunofluorescence. The A375 cell lines were transfected with the pCMV‑Tag2B‑cFLIPp43 vector at different doses and the activation of the NF‑κB signaling pathway was examined by the dual‑luciferase reporter assay system. The stable expression of c‑FLIPp43 in the A375 cell lines transfected with the pCMV‑Tag2B‑cFLIPp43 vector increased the protein level of NF‑κBp65 compared with in the A375 cell lines transfected with the empty vector. Transfection of the cells using the pCMV‑Tag2B‑cFLIPp43 vector increased the amount of NF‑κBp65 in the nucleus in a dose‑dependent manner. In conclusion, the transfection of the c‑FLIPp43 expression vector induces the protein expression of NF‑κBp65 and promotes the activation of the NF‑κB signaling pathway in the A375 melanoma cell line.

Class I-specific histone deacetylase inhibitor MS-275 overrides TRAIL-resistance in melanoma cells by downregulating c-FLIP

Tumor-necrosis factor-related apoptosis-inducing ligand (TRAIL) has selective killing effect toward malignant cells; however some human melanomas are intrinsically resistant. In this study, we have shown that class I-specific histone deacetylase inhibitor (HDACi) MS-275 can synergize with TRAIL to induce apoptosis in TRAIL-resistant cell lines and to enhance susceptibility of sensitive cells. Conversely, class II-selective HDACi MC1575 has shown no effect on the resistance of melanoma cells and was able exclusively to increase TRAIL-induced cell death in responsive cells. Both the HDACis variably increased DR4, DR5, and procaspase 8 expression, regardless whether cells were TRAIL-sensitive or TRAIL-resistant. However, only MS-275 markedly decreased the expression levels of both the long and short c-FLIP isoforms. RNAi-mediated c-FLIP silencing resulted in caspase 8-dependent apoptosis in survivor cells which was comparable to that observed following MS-275 treatment. Accordingly, enforced expression of ectopic c-FLIP has abolished the cooperative induction of apoptosis by the combination of MS-275 and TRAIL. These data indicate that c-FLIP is a critical regulator of death ligand sensitivity in melanoma. Inhibition of class I HDAC isoenzymes 1, 2 and 3 has resulted to be functionally important for c-FLIP downregulation by MS-275. In contrast, knockdown of class II HDACs has had no effect on c-FLIP expression, thus explaining the dual incapacity of MC1575 to inhibit c-FLIP expression and sensitize cells resistant to TRAIL. The data reported here suggest that MS-275 represents a promising therapeutic approach in combination with TRAIL for treatment of cutaneous and uveal melanoma due to its ability to reduce c-FLIP expression.

Cutaneous malignant melanoma: update on diagnostic and prognostic biomarkers

The incidence of cutaneous malignant melanoma has rapidly increased in recent years in all parts of the world, and melanoma is a leading cause of cancer death. As even relatively small melanomas may have metastatic potential, accurate assessment of progression is critical. Although diagnosis of cutaneous malignant melanoma is usually based on histopathologic criteria, these criteria may at times be inadequate in differentiating melanoma from certain types of benign nevi. As for prognosis, tumor (Breslow) thickness, mitotic rate, and ulceration have been considered the most important prognostic indicators among histopathologic criteria. However, there are cases of thin primary melanomas that have ultimately developed metastases despite complete excision. Given this, an accurate assessment of melanoma progression is critical, and development of molecular biomarkers that identify high-risk melanoma in its early phase is urgently needed. Large-scale genomic profiling has identified considerable heterogeneity in melanoma and suggests subgrouping of tumors by patterns of gene expression and mutation will ultimately be essential to accurate staging. This subgrouping in turn may allow for more targeted therapy. In this review, we aim to provide an update on the most promising new biomarkers that may help in the identification and prognostication of melanoma.

The histone deacetylase inhibitor, MS-275 (entinostat), downregulates c-FLIP, sensitizes osteosarcoma cells to FasL, and induces the regression of osteosarcoma lung metastases

The purpose of this study was to determine the effects of the histone deacetylase inhibitor, MS-275, on the Fas signaling pathway and susceptibility of osteosarcoma (OS) to Fas ligand (FasL)-induced cell death. OS metastasizes almost exclusively to the lungs. We have shown that Fas expression in OS cells is inversely correlated with their metastatic potential. Fas(+) cells are rapidly eliminated when they enter the lungs via interaction with FasL, which is constitutively expressed in the lungs. Fas(-) OS cells escape this FasL-induced apoptosis and survive in the lung microenvironment. Moreover, upregulation of Fas in established OS lung metastases results in tumor regression. Therefore, agents that upregulate Fas expression or activate the Fas signaling pathway may have therapeutic potential. Treatment of Fas(-) metastatic OS cell lines with 2 µM MS-275 sensitized cells to FasL-induced cell death in vitro. We found that MS-275 did not alter the expression of Fas on the cell surface; rather it resulted in the downregulation of the anti-apoptotic protein, c-FLIP (cellular FLICE-inhibitory protein), by inhibiting c-FLIP mRNA. Downregulation of c- FLIP correlated with caspase activation and apoptosis induction. Treatment of nu/nu-mice with established OS lung metastases with oral MS-275 resulted in tumor regression, increased apoptosis and a significant inhibition of c-FLIP expression in tumors. Histopathological examination of mice showed no evidence of significant toxicity. Overall, these results suggest that the mechanism by which MS-275 sensitizes OS cells and lung metastases to FasL-induced cell death may be by a direct reduction in the expression of c-FLIP.

Absence of FLICE-inhibitory protein is a novel independent prognostic marker for very short survival in pancreatic ductal adenocarcinoma

OBJECTIVES

Evading apoptosis is a hallmark of pancreatic cancer. In pancreatic cancer models, chemotherapy down-regulates the antiapoptotic protein cellular FLICE inhibitory protein (c-FLIP), which renders cells sensitive to apoptosis. Currently, the relevance of c-FLIP expression as a biomarker in pancreatic cancer is unknown, and here we assessed the prognostic significance of the c-FLIP expression status in a large cohort of pancreatic cancer patients with clinical follow-up.

METHODS

Cellular FLICE inhibitory protein expression levels were determined by immunohistochemistry in 120 surgically resected ductal pancreatic adenocarcinomas. Survival analysis by c-FLIP status was compared with established clinicopathologic biomarkers as well as Ki-67 and cyclooxygenase 2 expression levels as 2 other established independent prognostic biomarkers in pancreatic cancer.

RESULTS

Of 120 tumors, 111 (91%) were c-FLIP positive, whereas 9 (9%) were completely c-FLIP negative. Cyclooxygenase 2 was positive in 59 cases (52%), and Ki-67 was positive in more than 10% of tumor cells in 51 cases (44%). Univariate and multivariate survival analysis (correcting for stage, grade, and proliferation index) showed that c-FLIP is an independent prognostic factor. Specifically, c-FLIP negativity identifies 9% of patients with a highly aggressive disease course (P = 0.0001).

CONCLUSIONS

Cellular FLICE inhibitory protein expression status is a valuable prognostic biomarker in pancreatic cancer.

Anti-apoptotic proteins on guard of melanoma cell survival

Apoptosis plays a pivotal role in sustaining proper tissue development and homeostasis. Evading apoptosis by cancer cells is a part of their adaption to microenvironment and therapies. Cellular integrity is predominantly maintained by pro-survival members of Bcl-2 family and IAPs. Melanoma cells are characterized by a labile and stage-dependent phenotype. Pro-survival molecules can protect melanoma cells from apoptosis and mediate other processes, thus enhancing aggressive phenotype. The essential role of Bcl-2, Mcl-1, Bcl-X(L), livin, survivin and XIAP was implicated for melanoma, often in a tumor stage-dependent fashion. In this review, the current knowledge of pro-survival machinery in melanoma is discussed.

Predictive value of Sp1/Sp3/FLIP signature for prostate cancer recurrence

Prediction of prostate cancer prognosis is challenging and predictive biomarkers of recurrence remain elusive. Although prostate specific antigen (PSA) has high sensitivity (90%) at a PSA level of 4.0 ng/mL, its low specificity leads to many false positive results and considerable overtreatment of patients and its performance at lower ranges is poor. Given the histopathological and molecular heterogeneity of prostate cancer, we propose that a panel of markers will be a better tool than a single marker. We tested a panel of markers composed of the anti-apoptotic protein FLIP and its transcriptional regulators Sp1 and Sp3 using prostate tissues from 64 patients with recurrent and non-recurrent cancer who underwent radical prostatectomy as primary treatment for prostate cancer and were followed with PSA measurements for at least 5 years. Immunohistochemical staining for Sp1, Sp3, and FLIP was performed on these tissues and scored based on the proportion and intensity of staining. The predictive value of the FLIP/Sp1/Sp3 signature for clinical outcome (recurrence vs. non-recurrence) was explored with logistic regression, and combinations of FLIP/Sp1/Sp3 and Gleason score were analyzed with a stepwise (backward and forward) logistic model. The discrimination of the markers was identified by sensitivity-specificity analysis and the diagnostic value of FLIP/Sp1/Sp3 was determined using area under the curve (AUC) for receiver operator characteristic curves. The AUCs for FLIP, Sp1, Sp3, and Gleason score for predicting PSA failure and non-failure were 0.71, 0.66, 0.68, and 0.76, respectively. However, this increased to 0.93 when combined. Thus, the “biomarker signature” of FLIP/Sp1/Sp3 combined with Gleason score predicted disease recurrence and stratified patients who are likely to benefit from more aggressive treatment.

Cell surface adhesion molecules and adhesion-initiated signaling: understanding of anoikis resistance mechanisms and therapeutic opportunities

Cells express various cell surface adhesion molecules (receptors) that not only mechanically serve as contacting sites between the cell and extracellular matrix (ECM) or adjacent cells, but also initiate intracellular signaling pathways modulating important cellular events including survival and proliferation. Normal cells undergo apoptosis when lacking ECM attachment. This type of cell death has been termed anoikis. Anoikis can be viewed as a normal process which ensures tissue homeostasis and failure to execute the anoikis program or resistance to anoikis could result in adherent cells surviving under suspension condition and proliferating at ectopic sites where the matrix proteins are different from those the cells originally contact. Resistance to anoikis is emerging as a hallmark of metastatic cancers which enables cancer cells to disseminate to distant organs through systemic circulation. In this review, we will discuss the molecular basis of adhesion-initiated signaling, the impact of loss of cell-ECM adhesion on normal cell survival, the role of cancer cell aggregate formation via intercellular adhesion under non-adherent condition, and mechanisms of anoikis resistance developed in metastatic cancer cells. Understanding of these aspects will provide opportunities to find new potential molecular targets, and therapeutic strategies based on these findings will likely prove to be more specific and effective.

Inhibition of SREBP1 sensitizes cells to death ligands

Evasion of death receptor ligand-induced apoptosis contributs to cancer development and progression. To better understand mechanisms conferring resistance to death ligands, we screened an siRNA library to identify sequences that sensitize resistant cells to fas activating antibody (CH-11). From this screen, we identified the Sterol-Regulatory Element-Binding Protein 1 (SREBP1), a transcription factor, which regulates genes involved in cholesterol and fatty acid synthesis including fatty acid synthase. Inhibition of SREBP1 sensitized PPC-1 and HeLa to the death receptor ligands CH-11 and TRAIL. In contrast, DU145 prostate cancer cells that are resistant to death ligands despite expressing the receptors on their cell surface remained resistant to CH-11 and TRAIL after knockdown of SREBP1. Consistent with the effects on cell viability, the addition of CH-11 activated caspases 3 and 8 in HeLa but not DU145 cells with silenced SREBP1. We demonstrated that knockdown of SREBP1 produced a marked decrease in fatty acid synthase expression. Furthermore, genetic or chemical inhibition of fatty acid synthase with shRNA or orlistat, respectively, recapitulated the effects of SREBP1 inhibition and sensitized HeLa but not DU145 cells to CH-11 and TRAIL. Sensitization to death receptor ligands by inhibition of fatty acid synthase was associated with activation of caspase 8 prior to caspase 9. Neither silencing of SREBP1 or fatty acid synthase changed basal expression of the core death receptor components Fas, caspase 8, FADD, caspase 3 or FLIP. Thus, inhibition of SREBP1 or its downstream target fatty acid synthase sensitizes resistant cells to death ligands.

Targeting c-FLIP in cancer

Cellular-FLICE inhibitory protein (c-FLIP) is a key anti-apoptotic regulator that inhibits cell death mediated by the death receptors Fas, DR4, DR5, and TNF-R1. Three splice variants of c-FLIP function at the DISC level by blocking the processing and activation of procaspase-8 and -10. Overexpression of c-FLIP has been identified in many different tumour types, and its downregulation in vitro has been shown to restore apoptosis mediated by CD95L and TRAIL. c-FLIP therefore represents a promising target for cancer therapy. This review focuses on the molecular mechanisms that control c-FLIP expression and current research into inhibitors of the protein. Increasing evidence supports the investigation of c-FLIP as a therapeutic target to restore an apoptotic response in cancer cells.

TAK1 is required for survival of mouse fibroblasts treated with TRAIL, and does so by NF-kappaB dependent induction of cFLIPL

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is known as a “death ligand”—a member of the TNF superfamily that binds to receptors bearing death domains. As well as causing apoptosis of certain types of tumor cells, TRAIL can activate both NF-κB and JNK signalling pathways. To determine the role of TGF-β-Activated Kinase-1 (TAK1) in TRAIL signalling, we analyzed the effects of adding TRAIL to mouse embryonic fibroblasts (MEFs) derived from TAK1 conditional knockout mice. TAK1−/− MEFs were significantly more sensitive to killing by TRAIL than wild-type MEFs, and failed to activate NF-κB or JNK. Overexpression of IKK2-EE, a constitutive activator of NF-κB, protected TAK1−/− MEFs against TRAIL killing, suggesting that TAK1 activation of NF-κB is critical for the viability of cells treated with TRAIL. Consistent with this model, TRAIL failed to induce the survival genes cIAP2 and cFlipL in the absence of TAK1, whereas activation of NF-κB by IKK2-EE restored the levels of both proteins. Moreover, ectopic expression of cFlipL, but not cIAP2, in TAK1−/− MEFs strongly inhibited TRAIL-induced cell death. These results indicate that cells that survive TRAIL treatment may do so by activation of a TAK1–NF-κB pathway that drives expression of cFlipL, and suggest that TAK1 may be a good target for overcoming TRAIL resistance.

Angiogenin protects motoneurons against hypoxic injury

Cells can adapt to hypoxia through the activation of hypoxia-inducible factor-1 (HIF-1), which in turn regulates the expression of hypoxia-responsive genes. Defects in hypoxic signaling have been suggested to underlie the degeneration of motoneurons in amyotrophic lateral sclerosis (ALS). We have recently identified mutations in the hypoxia-responsive gene, angiogenin (ANG), in ALS patients, and have shown that ANG is constitutively expressed in motoneurons. Here, we show that HIF-1alpha is sufficient and required to activate ANG in cultured motoneurons exposed to hypoxia, although ANG expression does not change in a transgenic ALS mouse model or in sporadic ALS patients. Administration of recombinant ANG or expression of wild-type ANG protected motoneurons against hypoxic injury, whereas gene silencing of ang1 significantly increased hypoxia-induced cell death. The previously reported ALS-associated ANG mutations (Q12L, K17I, R31K, C39W, K40I, I46V) all showed a reduced neuroprotective activity against hypoxic injury. Our data show that ANG plays an important role in endogenous protective pathways of motoneurons exposed to hypoxia, and suggest that loss of function rather than loss of expression of ANG is associated with ALS.

Involvement of FLIP in 2-methoxyestradiol-induced tumor regression in transgenic adenocarcinoma of mouse prostate model

PURPOSE

The purpose of this study is to investigate whether Fas-associated death domain interleukin-1 converting enzyme like inhibitory protein (FLIP) inhibition is a therapeutic target associated with 2-methoxyestradiol (2-ME2)-mediated tumor regression.

EXPERIMENTAL DESIGN

Expression and levels of FLIP were analyzed using (a) real-time PCR and immunoblot analysis in androgen-independent PC-3 cells treated with the newly formulated 2-ME2 and (b) immunohistochemistry in different Gleason pattern human prostate tumors. Transient transfections and chromatin immunoprecipitation (ChIP) assays were used to identify the transcription factors that regulate FLIP. Involvement of FLIP in 2-ME2-induced tumor regression was evaluated in transgenic adenocarcinoma mouse prostate (TRAMP) mice.

RESULTS

High Gleason pattern (5+5) human prostate tumors exhibit significant increase in FLIP compared with low Gleason pattern 3+3 (P=or<0.04). 2-ME2 reduced the levels and promoter activity of FLIP (P=0.001) in PC-3 cells. Transient expression assays show sequences between -503/+242 being sufficient for 2-ME2-induced inhibition of FLIP promoter activity. Cotransfection experiments show that overexpression of Sp1 activated, whereas Sp3 inhibited, Sp1 transactivation of FLIP promoter activity (P=0.0001). 2-ME2 treatment reduced binding of Sp1 to the FLIP promoter as evidenced by ChIP. Further, levels of FLIP associated with Fas or FADD decreased, whereas cleavage of caspase-8, levels of Bid, and apoptosis increased in response to 2-ME2 treatment in PC-3 cells. Administration of 2-ME2 regressed established prostate tumors in TRAMP mice that were associated with reduced expression of FLIP and Sp1.

CONCLUSION

Targeting Sp1-mediated FLIP signaling pathway may provide a novel approach for prostate cancer management.

Short hairpin RNA targeting c-FLIP sensitizes human cervical adenocarcinoma Hela cells to chemotherapy and radiotherapy

c-FLIP inhibits caspase-8 activation and cell apoptosis mediated by death receptors. The present study aims at determining the effects of c-FLIP targeted vector-based short hairpin RNA (shRNA) on cell growth and evaluating its modulation of responsiveness to drugs and radiotherapy in cervical adenocarcinoma Hela cells. cFLIP expression of the cells transfected with shRNA against c-FLIP was significantly down-regulated after 72 h. c-FLIP silencing markedly suppressed cell proliferation and increased cell apoptosis. The activation of caspase-8 and caspase-3 was induced with shRNA targeting cFLIP with the passage of time after transfection. Furthermore, Vector-based shRNA against c-FLIP subsequently increased the sensitivity to cisplatin, iritican and Co60 radiotherapy by about 4- to 6-folds in Hela cells. Our data suggest that vector-based shRNA effectively inhibited c-FLIP expression, enhanced the expression level of caspase-8 and caspase-3 to induce cell apoptosis, probably with the higher efficacy in combination therapies with conventional chemotherapy and radiotherapy in cervical adenocarcinoma.

Caspase-8 and its inhibitors in RCCs in vivo: the prominent role of ARC

Activation of the initiator-caspase, caspase-8 is under tight control of multiple antiapoptotic regulators including ARC, cFlip(S), cFlip(L) and PED/PEA-15. Since there is little data regarding the expression of caspase-8 and its antiapoptotic regulators in human tumours in vivo, we analysed their expression in renal cell carcinomas (RCCs) to identify which of these genes might be crucial for the well known impaired apoptosis and--as a result--resistance towards chemotherapy and ionizing radiation of RCCs. Caspase-8, cFlip(S), cFlip(L) and PED/PEA-15 mRNA expression was significantly increased only in early stages of RCCs compared to non-neoplastic renal tissue. In contrast, ARC mRNA expression was significantly increased in RCCs of all stages without differences between the tumour stages and grades. Importantly, the relative mRNA expression ratio between ARC and caspase-8 was significantly increased during carcinogenesis and tumour progression. In contrast, the relative mRNA expression ratio between cFlip(S), cFlip(L) or PED/PEA-15 and caspase-8 remained constant during all tumour stages. In conclusion, our analysis revealed that ARC is the only caspase-8 inhibiting regulator being constantly overexpressed in RCCs. Furthermore, the balance between antiapoptotic ARC and proapoptotic caspase-8 is the only one to be disturbed during carcinogenesis and tumour progression of RCCs. This inhibition of Caspase-8 might therefore be one example for the multiple antiapoptotic functions of ARC in RCCs possibly contributing to the marked resistance of RCCs towards radio- and chemotherapy and reflects a shift of gene expression towards a more antiapoptotic context in RCCs.

FLIP ing the coin? Death receptor-mediated signals during skin tumorigenesis

Keratinocyte skin cancer is a multi-step process, during which a number of obstacles have to be overcome by the tumor cell to allow the development of a manifest tumor. Beside proliferation and immortality, apoptosis resistance is one additional and critical step during skin carcinogenesis. Over the past two decades, much has been learned about the prototypical membrane-bound inducers of apoptosis, namely the death receptors and their ligands, and the apoptosis signalling pathways activated by death receptors have been elucidated in great detail. In contrast, much less is known about the tissue-specific role of the death receptor/ligands systems during the development of skin cancer. Here, we summarize and discuss the role of this intriguing receptor family and the potential mechanistical impact of the intracellular caspase-8 inhibitor cFLIP for keratinocyte skin cancer. Given more recent data about cFLIP and its isoforms, a more complex regulatory role of cFLIP can be suspected. Indeed, cFLIP may not solely interfere with death receptor-mediated apoptosis signalling pathways, but may positively or negatively influence other, potential harmful signalling pathways such as the production of inflammatory cytokines, tumor cell migration or the activation of transcription factors such as NF-kappaB, considered crucial during skin tumorigenesis. In this respect, cFLIP may act to 'FLIP the coin' during the development of keratinocyte skin cancer.

Dysregulation of apoptotic signaling in cancer: molecular mechanisms and therapeutic opportunities

Apoptosis is a tightly regulated cell suicide program that plays an essential role in the maintenance of tissue homeostasis by eliminating unnecessary or harmful cells. Defects in this native defense mechanism promote malignant transformation and frequently confer chemoresistance to transformed cells. Indeed, the evasion of apoptosis has been recognized as a hallmark of cancer. Given that multiple mechanisms function at many levels to orchestrate the regulation of apoptosis, a multitude of opportunities for apoptotic dysregulation are present within the intricate signaling network of cell. Several of the molecular mechanisms by which cancer cells are protected from apoptosis have been elucidated. These advances have facilitated the development of novel apoptosis-inducing agents that have demonstrated single-agent activity against various types of cancers cells and/or sensitized resistant cancer cells to conventional cytotoxic therapies. Herein, we will highlight several of the central modes of apoptotic dysregulation found in cancer. We will also discuss several therapeutic strategies that aim to reestablish the apoptotic response, and thereby eradicate cancer cells, including those that demonstrate resistance to traditional therapies.

Epithelial human leukocyte antigen-DR expression predicts reduced recurrence rates and prolonged survival in rectal cancer patients

PURPOSE

The development of local and distant recurrences is a major problem in the treatment of rectal cancer patients. In this study, we investigated whether epithelial human leukocyte antigen-DR (HLA-DR) expression allowed discrimination between high and low tumor recurrence rates, and analyzed the mechanism behind its expression.

EXPERIMENTAL DESIGN

The role of IFNgamma in HLA-DR expression was studied in rectal cancer cell lines and tumors by promoter-specific analyses of class II transactivator (CIITA). The predictive value of epithelial HLA-DR expression was investigated by immunohistochemical evaluation of 1,016 rectal tumors, obtained from a large prospective trial. Associations with recurrences and survival were determined by univariate and multivariate log-rank testing.

RESULTS

HLA-DR was induced by IFNgamma in rectal cancer cell lines. Activity of the IFNgamma-inducible pIV-CIITA promoter correlated with epithelial HLA-DR expression in rectal tumors. Patients with HLA-DR-positive tumors developed less frequent local and distant recurrences [1.6% versus 9.1% (P = 0.0015) and 15.3% versus 29.9% (P < 0.0001), respectively, after 5 years of follow-up] and had better survival (78.6% versus 61.3%; P < 0.0001) than patients with HLA-DR-negative tumors. Epithelial HLA-DR was more often found in lower tumor-node-metastasis (TNM) stages. Next to TNM and circumferential resection margin, HLA-DR expression was independently associated with lower distant recurrence rates and prolonged survival.

CONCLUSIONS

Epithelial HLA-DR expression can be used as a marker to discriminate patients with high or low risk of developing recurrences. The possible involvement of IFNgamma, the relationship with lower TNM stages, and the independent effect on recurrence development together suggest that the host immune response plays an important role in controlling tumor cells.

Immunohistochemical characteristics of melanoma

Melanoma has a wide spectrum of histologic features which mimic epithelial, hematologic, mesenchymal, and neural tumors. Immunohistochemistry has been the primary tool to distinguish melanomas from these other tumors; it has also been studied for use as an adjunct to distinguish benign and malignant melanocytic tumors and to elucidate prognosis. Furthermore, there has been extensive effort to find a suitable marker to differentiate spindle cell and desmoplastic melanoma from other tumors. We have reviewed the literature investigating melanocytic differentiation markers, proliferation markers, immunomodulatory markers, signaling molecules, and nerve growth factors and receptors. Despite the proliferation of immunohistochemical markers, S-100 remains the most sensitive marker for melanocytic lesions, while markers such as HMB-45, MART-1/Melan-A, tyrosinase, and MITF demonstrate relatively good specificity but not as good sensitivity as S-100. No marker has proven useful in distinguishing spindle cell and desmoplastic melanomas from other tumors. Ki67 remains the most useful adjunct in distinguishing benign from malignant melanocytic tumors. None of the markers reviewed has been shown conclusively to have prognostic value for melanocytic neoplasms.

FLIP as an anti-cancer therapeutic target

Suppression of apoptosis is one of the hallmarks of carcinogenesis. Tumor cells endure apoptotic pressure by overexpressing several antiapoptotic proteins, and FLICE inhibitory protein (FLIP) is one of the important antiapoptotic proteins that have been shown to be overexpressed in various primary tumor cells. FLIP has two death-effector domains in tandem, mimicking the prodomain of procaspase-8. It is recruited to Fadd in death-inducing signaling complex, thereby preventing the activation of procaspase-8. To date, three isoforms of human cytosolic FLIP (c-FLIP) and six viral homologs (v-FLIP) have been identified. Recently, the crystal structure of v-FLIP MC159 was determined for the first time as an atomic-detail FLIP structure, which revealed that two death effector domains are packed tightly against each other mainly through conserved hydrophobic interactions. The overexpression of c-FLIP in tumor cells has been shown to be the determinant of the tumor's resistance to death ligands such as FasL and TRAIL. It has also been shown that the down-regulation of c-FLIP results in sensitizing resistant tumor cells. Therefore, the agents directly targeting c-FLIP at mRNA and protein levels are expected to be developed in near future and tested for the potential as a new class of anti-cancer drugs.

Resistance to FasL and tumor necrosis factor-related apoptosis-inducing ligand-mediated apoptosis in Sezary syndrome T-cells associated with impaired death receptor and FLICE-inhibitory protein expression

Because of the low proliferative potential of tumor cells in patients with Sézary syndrome (SzS), their accumulation has been suggested to be due to defective regulation of apoptosis. We analyzed the sensitivity to soluble Fas-ligand (FasL) and tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL), 2 members of the TNF superfamily in peripheral blood leukocytes (PBL) from patients with SzS. Compared with healthy donors, CD4(+) cells from patients with SzS were completely resistant to FasL in 9 of 16 cases. Of these 9 FasL-resistant cases, 4 revealed a loss in Fas (CD95) expression, whereas the remaining 5 exhibited normal or enhanced Fas expression. In the latter 5 cases, the apoptosis inhibitor cFLIP was overexpressed in CD4(+)/CD26(-) tumor cells compared with CD4(+)/CD26(-) cells from Fas-expressing FasL-sensitive patients and healthy donors. Furthermore, resistance to TRAIL and tumor cell-restricted loss of TRAIL-receptor 2 were observed in 16 of 16 SzS PBLs. It is noteworthy that resistance to FasL could be overcome by the use of a hexameric FasL or upon exposure of SzS cells to interferon-alpha (IFN-alpha) or IFN-gamma, the latter by an increase of Fas expression. Our data on primary SzS lymphocytes reveal frequent resistance to apoptosis induced by FasL and TRAIL, which may contribute to their accumulation in patients with SzS and be relevant at a therapeutic level.

Apoptosis pathways and oncolytic adenoviral vectors: promising targets and tools to overcome therapy resistance of malignant melanoma

In the last decades melanoma incidence has been increasing worldwide, while mortality remained on a high level. Until now, there is no suitable therapy for metastasized melanoma, which could lead to a significant increase in overall survival. Apoptosis deficiency is supposed to be a critical factor for therapy resistance, and previous work has characterized the basic mechanisms of apoptosis regulation in melanoma. Genes and strategies suitable for efficient induction of apoptosis in melanoma cells were identified, which are based on proapoptotic Bcl-2 proteins (Bcl-x(S), Bcl-x(AK), Bik/Nbk and Bax) as well as on tumor necrosis factor (TNF)-related death ligands (CD95L/Fas ligand and TNF-related apoptosis-inducing ligand, TRAIL). Proapoptotic genes may be employed in improved gene therapeutic strategies, based on conditional oncolytic adenoviral vectors.

Death receptors and apoptosis

Interactions between death receptors from the tumor necrosis factor superfamily and their ligands play a crucial role in the development and the integrity of the epidermis. The major consequence resulting from death receptor targeting is apoptosis. Evidence for dysregulation of death receptor signaling associated with the pathogenesis of selected cutaneous diseases, including toxic epidermal necrolysis, graft versus host disease, and skin cancer, are reviewed herein.

NF-kappaB-dependent expression of the antiapoptotic factor c-FLIP is regulated by calpain 3, the protein involved in limb-girdle muscular dystrophy type 2A

Limb-girdle muscular dystrophy type 2A (LGMD2A) is a recessive genetic disorder caused by mutations in the cysteine protease calpain 3 (CAPN3) that leads to selective muscle wasting. We previously showed that CAPN3 deficiency is associated with a profound perturbation of the NF-kappaB/IkappaB alpha survival pathway. In this study, the consequences of altered NF-kappaB/IkappaB alpha pathway were investigated using biological materials from LGMD2A patients. We first show that the antiapoptotic factor cellular-FLICE inhibitory protein (c-FLIP), which is dependent on the NF-kappaB pathway in normal muscle cells, is down-regulated in LGMD2A biopsies. In muscle cells isolated from LGMD2A patients, NF-kappaB is readily activated on cytokine induction as shown by an increase in its DNA binding activity. However, we observed discrepant transcriptional responses depending on the NF-kappaB target genes. IkappaB alpha is expressed following NF-kappaB activation independent of the CAPN3 status, whereas expression of c-FLIP is obtained only when CAPN3 is present. These data lead us to postulate that CAPN3 intervenes in the regulation of the expression of NF-kappaB-dependent survival genes to prevent apoptosis in skeletal muscle. Deregulations in the NF-kappaB pathway could be part of the mechanism responsible for the muscle wasting resulting from CAPN3 deficiency.

Toll-like receptor 3 expressed by melanoma cells as a target for therapy?

PURPOSE

The immunomodulatory properties of Toll-like receptors (TLR) agonists have inspired their use as experimental adjuvants for vaccination of cancer patients. However, it is now well recognized that TLR expression is not restricted to immune cells but can also be found in many cell types, including those giving rise to tumors. It is therefore mandatory to explore the potential effects of TLR triggering directly on tumor cells.

EXPERIMENTAL DESIGN

In the present work, we have investigated TLR3 protein expression in melanoma cell lines derived from patients, and analyzed the effects of TLR3 agonists on tumor cell survival. Moreover, we used RNA interference to stably knock down TLR3 expression and study the involvement of this receptor in dsRNA-induced effects on melanoma cells viability.

RESULTS

Human melanoma cells can express functional TLR3 protein. Interestingly, the engagement of the receptor by TLR3 agonists can directly inhibit cell proliferation and induce tumor cell death when combined to treatment with either type I IFN or protein synthesis inhibitors. These effects were shown by RNA interference to be largely dependent on TLR3. Moreover, TLR3-mediated cell death involves the activation of caspases and engages both extrinsic and intrinsic apoptotic pathways.

CONCLUSION

TLR3 protein can be expressed in human melanoma cells, where it can deliver proapoptotic and antiproliferative signaling. Altogether, these results suggest that TLR3 agonists represent very promising adjuvants for cancer vaccines not only based on their well-described immunostimulatory properties, but also due to their newly identified cytostatic and cytotoxic effects directly on tumor cells.

Impairment of the ubiquitin-proteasome system by cellular FLIP

Cellular FLIP (cFLIP) is a homologue of caspase-8 without protease activity that inhibits the apoptosis signaling initiated by death receptor ligation. We previously reported that a long form of cFLIP (cFLIP-L) inhibits ubiquitylation of beta-catenin and enhances Wnt signaling. Here we show that cFLIP-L impairs the function of the ubiquitin-proteasome system (UPS), and increases the accumulation of various short-lived proteins, such as GFP conjugated with destabilization sequence, beta-catenin and HIF1 alpha, that are subjected to rapid ubiquitylation and degradation by proteasomes. Accordingly, beta-catenin- and HIF1 alpha-mediated gene expressions are induced in the cFLIP-L-expressing cells. Exogenously expressed cFLIP-L accumulates in aggregates at the peri-nuclear region in the cells, and the cFLIP-L aggregates are refractory to solubilization. Like exogenously expressed cFLIP-L, the endogenous cFLIP in A549 lung cancer cells displays particulate distribution in the cells and more than 60% of cFLIP-L is refractory to solubilization. Down-regulation of cFLIP in A549 cells by RNA-mediated interference reduced beta-catenin- and HIF1 alpha-mediated gene expression. These results suggest that cFLIP-L is prone to aggregate and impairs UPS function, which could be involved in the pathological function of cFLIP-L expressed in certain cancer cells.

c-FLIP expression in colorectal carcinomas: association with Fas/FasL expression and prognostic implications

AIMS

Disruption of apoptotic cell death has been implicated in tumour aggressiveness in colonic carcinogenesis. The Fas-Fas ligand (FasL) system is involved in the execution of apoptosis induced by the immune system. c-FLIP protein constitutes an inhibitor of Fas and other (TRAIL) death receptor-mediated apoptosis. The aim of this study was to investigate the simultaneous expression of Fas, FasL and c-FLIP in relation to standard clinicopathological parameters and patients' outcome in colorectal cancer.

METHODS AND RESULTS

Levels of Fas, FasL and c-FLIP protein expression were quantified immunohistochemically in paraffin-embedded tissues from 90 patients. Immunopositivity was detected for Fas, FasL and c-FLIP in 71%, 35.5% and 68.8% of cases, respectively. Concurrent expression of Fas/FasL was seen in 28 samples (31%), of which 24 (85.7%) also displayed c-FLIP positivity (P = 0.04). c-FLIP overexpression (> 10%) tended to prevail marginally in higher stage tumours (P = 0.09). Additionally, FasL and c-FLIP adversely affected survival on both univariate (P = 0.001 and P = 0.0024, respectively) and multivariate analysis [hazard ratio (HR) 3.491, P = 0.005 and HR 2.960, P = 0.036, respectively].

CONCLUSIONS

The frequent expression and coexpression of Fas, FasL and c-FLIP in colorectal carcinoma implicates c-FLIP as an inhibitor of the Fas-FasL-induced death pathway in these tumours. Moreover, c-FLIP conveys independent prognostic information in the presence of classical prognosticators.

Critical role for Fas-associated death domain-like interleukin-1-converting enzyme-like inhibitory protein in anoikis resistance and distant tumor formation

BACKGROUND

Normal epithelial cells undergo anoikis, or apoptosis on loss of anchorage to the extracellular matrix, by initiating the death receptor pathway of caspase activation. However, malignant epithelial cells with metastatic potential resist anoikis and can survive in an anchorage-independent fashion. We hypothesized that c-Fas-associated death domain-like interleukin-1-converting enzyme-like inhibitory protein (FLIP), an endogenous inhibitor of death receptor signaling, may suppress anoikis.

METHODS

We assessed viability and apoptosis of PPC-1 prostate cancer cells cultured in adherent and suspension conditions using 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium inner salt and Annexin V staining assays. Expression of the death receptor Fas and activation of caspase 8 were measured using flow cytometry. Expression of Fas ligand was measured by reverse transcription-polymerase chain reaction. FLIP protein expression was measured by immunoblotting. Small-molecule inhibitors of FLIP (including the death receptor sensitizer 5809354) and small-interfering (si) RNA directed against FLIP were used to assess the effects of FLIP inhibition on anoikis of prostate cancer cells in vitro and in vivo. All statistical tests were two-sided.

RESULTS

PPC-1 cells cultured in suspension resisted anoikis, despite increased expression of Fas (0 versus 8 hours, mean relative percent expression = 100% versus 135%, difference = 35%, 95% confidence interval [CI] = 10% to 61%; P = .02) and Fas L (0 versus 24 hours, mean relative percent expression = 100% versus 208%, difference = 108%, 95% CI = 18% to 197%; P = .02). Knockdown of FLIP expression by siRNA or treatment with 5809354 sensitized prostate cancer cells to anoikis (control siRNA versus FLIP siRNA at 10 nM, mean relative percent viability = 95% versus 51%, difference = 44%, 95% CI = 34% to 54%; P<.001; control versus 5809354 at 20 microM, mean relative percent viability = 96% versus 52%, difference = 44%, 95% CI = 13% to 75%; P = .015). Inhibition of FLIP expression specifically activated caspase 8 in PPC-1 cells grown in suspension but not adherent conditions and decreased the metastatic potential of circulating PPC-1 cells in vivo.

CONCLUSIONS

FLIP may be a suppressor of anoikis and therefore a possible target for antimetastatic therapeutic strategies.

The role of death receptor ligands in shaping tumor microenvironment

Death receptor ligands (FasL, TRAIL) activate apoptosis in cells expressing the cognate receptors. Evidence suggests that these ligands also deliver pro-inflammatory signals. In the tumor microenvironment, "Fas counterattack" mounted by tumors against immune cells is mediated by tumor-associated FasL. But death ligands crosslinking their receptors also induce inhibition of apoptosis and activation of the transcription factor, NFkappaB, with a subsequent burst of pro-inflammatory cytokine production and tumor growth promotion. NFkappaB, a key link between inflammation and cancer, regulates dual activities of death ligands, depending on molecular signals in the tumor microenvironment. This paper focuses on death ligands as an example of the extensive repertoire of strategies devised by tumors for escape from immune control.

Troglitazone sensitizes tumor cells to TRAIL-induced apoptosis via down-regulation of FLIP and Survivin

Induction of apoptosis by the death ligand TRAIL might be a promising therapeutic approach in cancer therapy. However, since not all tumor cells are sensitive to TRAIL, there is a need for the development of strategies to overcome TRAIL-resistance. The results of the present study show that the anti-diabetic drug troglitazone sensitizes human glioma and neuroblastoma cells to TRAIL-induced apoptosis. This process is accompanied by a substantial increase of active caspase 8 and active caspase 3, but it is independent of troglitazone's effects on the nuclear receptor PPAR-gamma. Troglitazone induces a pronounced reduction in protein expression levels of the anti-apoptotic FLICE-inhibitory protein (FLIP) without affecting FLIP mRNA levels. Further, protein and mRNA expression levels of the anti-apoptotic protein Survivin significantly decrease upon treatment with troglitazone. Moreover, sensitization to TRAIL is partly accompanied by an up-regulation of the TRAIL receptor, TRAIL-R2. A combined treatment with troglitazone and TRAIL might be a promising experimental therapy because troglitazone sensitizes tumor cells to TRAIL-induced apoptosis via various mechanisms, thereby minimizing the risk of acquired tumor cell resistance.

Mechanism of ASC-mediated apoptosis: bid-dependent apoptosis in type II cells

Apoptosis-associated speck-like protein containing a CARD (ASC) is an adaptor molecule that mediates apoptotic and inflammatory signals, and implicated in tumor suppression. However, the mechanism of ASC-mediated apoptosis has not been well elucidated. Here, we investigated the molecular mechanisms of ASC-mediated apoptosis in several cell lines using a caspase recruitment domain 12-Nod2 chimeric protein that transduces the signal from muramyl dipeptide into ASC-mediated apoptosis. Experiments using dominant-negative mutants, small-interfering RNAs and peptide inhibitors for caspases indicated that caspase-8 was generally required for ASC-mediated apoptosis, whereas a requirement for caspase-9 depended on the cell type. In addition, caspase-like apoptosis-regulatory protein (CLARP)/Fas-like inhibitor protein, a natural caspase-8 inhibitor, suppressed ASC-mediated apoptosis, and Clarp-/- mouse embryonic fibroblasts were highly sensitive to ASC-mediated apoptosis. Bax-deficient HCT116 cells were resistant to ASC-mediated apoptosis as reported previously, although we failed to observe colocalization of ASC and Bax in cells. Like Fas-ligand-induced apoptosis, the ASC-mediated apoptosis was inhibited by Bcl-2 and/or Bcl-XL in type-II but not type-I cell lines. Bid was cleaved upon ASC activation, and suppression of endogenous Bid expression using small-interfering RNAs in type-II cells reduced the ASC-mediated apoptosis. These results indicate that ASC, like death receptors, mediates two types of apoptosis depending on the cell type, in a manner involving caspase-8.

“Bak (and Bax) to the Future” — of Primary Melanoma Prognosis?

Bcl-2 proteins either block or activate the "intrinsic" mitochondrial apoptosis pathway. Loss of expression of proapoptotic Bcl-2 proteins, namely Bax and Bak, in primary melanomas is associated with a worse long-term prognosis. Consequently, inactivation of mitochondrial signaling pathways of apoptosis may not only be a prerequisite for melanoma progression but may also hamper therapeutic efforts with chemotherapeutic drugs.

Pathologic Reporting and Special Diagnostic Techniques for Melanoma

Pathologists play a central role in the management of cutaneous melanoma in determining that a tumor is a melanoma, whether or not it is primary or metastatic, and whether or not the margins of excision are tumor free and in evaluating prognostic indicators from examination of the primary tumor and, where appropriate, lymph nodes, including the sentinel nodes.