Targeting the Fas/FasL signaling pathway in cancer therapy

Ceramide targets xIAP and cIAP1 to sensitize metastatic colon and breast cancer cells to apoptosis induction to suppress tumor progression

Background

Ceramide is a bioeffector that mediates various cellular processes, including apoptosis. However, the mechanism underlying ceramide function in apoptosis is apparently cell type-dependent and is not well-understood. We aimed at identifying molecular targets of ceramide in metastatic human colon and breast cancer cells, and determining the efficacy of ceramide analog in suppression of colon and breast cancer metastasis.

Methods

The activity of and mechanism underlying ceramide as a cytotoxic agent, and as a sensitizer for Fas-mediated apoptosis was analyzed in human cell lines established from primary or metastatic colon and breast cancers. The efficacy of ceramide analog LCL85 in suppression of metastasis was examined in preclinical mouse tumor models.

Results

Exposure of human colon carcinoma cells to ceramide analog LCL85 results in apoptosis in a dose-dependent manner. Interestingly, a sublethal dose of LCL85 increased C16 ceramide content and overcame tumor cell resistance to Fas-mediated apoptosis. Subsequently, treatment of tumor cells with exogenous C16 ceramide resulted in increased tumor cell sensitivity to Fas-mediated apoptosis. LCL85 resembles Smac mimetic BV6 in sensitization of colon carcinoma cells to Fas-mediated apoptosis by inducing proteasomal degradation of cIAP1 and xIAP proteins. LCL85 also decreased xIAP1 and cIAP1 protein levels and sensitized metastatic human breast cancer cells to Fas-mediated apoptosis. Silencing xIAP and cIAP1 with specific siRNAs significantly increased the metastatic human colon carcinoma cell sensitivity to Fas-mediated apoptosis, suggesting that IAP proteins mediate apoptosis resistance in metastatic human colon carcinoma cells and ceramide induces IAP protein degradation to sensitize the tumor cells to apoptosis induction. Consistent with its apoptosis sensitization activity, subtoxic doses of LCL85 suppressed colon carcinoma cell metastatic potential in an experimental lung metastasis mouse model, as well as breast cancer growth and spontaneous lung metastasis in an orthotopic breast cancer mouse model.

Conclusion

We have identified xIAP and cIAP1 as molecular targets of ceramide and determined that ceramide analog LCL85 is an effective sensitizer in overcoming resistance of human cell lines established from metastatic colon and breast cancers to apoptosis induction to suppress metastasis in vivo.

FASLG T844C polymorphism and susceptibility to breast cancer: a meta-analysis

Many studies were published to assess the association between FASLG T844C polymorphism and susceptibility to breast cancer, but the data were controversial. A meta-analysis was performed to assess the association comprehensively. We performed a comprehensive search in PubMed, Embase, and Web of Science to find eligible studies. Six studies with a total of 6,784 participants were finally included into the meta-analysis. There were a total of 3,382 cases with breast cancer and 3,402 controls in those six studies. Odds ratio (OR) with 95 % confidence interval (95 %CI) was used to evaluate the association. Overall, there was an obvious association between FASLG T844C polymorphism and breast cancer under all four contrast models (for C versus T: OR = 1.26, 95 %CI 1.05-1.50, P OR = 0.011; for CC versus TT: OR = 1.42, 95 %CI 1.11-1.81, P OR = 0.005; for CC versus TT/TC: OR = 1.41, 95 %CI 1.06-1.88, P OR = 0.019; for CC/TC versus TT: OR = 1.16, 95 %CI 1.01-1.33, P OR = 0.038). In the subgroup analysis by ethnicity, there was an obvious association between FASLG T844C polymorphism and breast cancer in Asians, but there was no obvious association in Caucasians. The meta-analysis suggests that there is an association between FASLG T844C polymorphism and susceptibility to breast cancer, especially in Asians.

Nanotechnology for the detection and kill of circulating tumor cells

Circulating tumor cells (CTCs) represent a surrogate biomarker of hematogenous metastases and thus could be considered as a 'liquid biopsy' which reveals metastasis in action. But it is absolutely a challenge to detect CTCs due to their extreme rarity. At present, the most common principle is to take advantage of the epithelial surface markers of CTCs which attach to a specific antibody. Antibody-magnetic nanobeads combine with the epithelial surface markers, and then the compound is processed by washing, separation, and detection. However, a proportion of CTC antigen expressions are down-regulated or lost in the process of epithelial-mesenchymal transition (EMT), and thus, this part of CTCs cannot be detected by classical detection methods such as CellSearch. To resolve this problem, some multiple-marker CTC detections have been developed rapidly. Additionally, nanotechnology is a promising approach to kill CTCs with high efficiency. Implantable nanotubes coated with apoptosis-promoting molecules improve the disease-free survival and overall survival. The review introduces some novel CTC detection techniques and therapeutic methods by virtue of nanotechnology to provide a better knowledge of the progress about CTC study.

Fas gene variants in childhood acute lymphoblastic leukemia and association with prognosis

Fas molecule is one of the main important molecules involved in apoptotic cell death. Single nucleotide polymorphisms in the promoter of Fas gene at positions -1377G/A and -670 A/G may affect its expression and play an important role in the pathology of leukemia. In the present study the association between these polymorphisms and risk of the development of acute lymphoblastic leukemia (ALL) in children with ALL compared to cancer-free control subjects was examined by polymerase chain reaction- based restriction fragment length polymorphism. The relationship between the polymorphisms and clinical and laboratory features of the patients and response to therapy were determined. No significant differences in genotype and allele frequencies between the patients and the control subjects at positions -670 and -1377 were detected. Evaluation of the prognostic factors revealed an association between the GG genotype at position -670 and liver involvement in ALL patients (p < 0.04). Although patients with -1377 AA genotype showed shorter mean complete remission duration, the result of survival analysis did not reach to be significant. In conclusion, results of this study showed no contribution of Fas genotypes at positions -670 and -1377 to risk of ALL in children. The association of Fas GG genotype at position -670 with liver involvement in the patients may show its important role in prognosis of ALL.

Down-regulation of Fas-mediated apoptosis by plasma transglutaminase factor XIII that catalyzes fetal-specific cross-link of the Fas molecule

The Fas antigen, also designated as APO-1 or CD95, is a member of the tumor necrosis factor receptor superfamily and can mediate apoptotic cell death in various cells. We report here that blood coagulation factor XIII (plasma transglutaminase, fibrin stabilizing factor) inhibits apoptosis induced by a cytotoxic anti-Fas monoclonal antibody in Jurkat cells. When cells were treated with the antibody in fetal calf serum-containing media, higher-molecular-weight (180K) polypeptides containing Fas molecule were detected by immunoblotting. Under conditions where the transglutaminase activity was eliminated or suppressed, the cross-link of Fas was not observed, and concurrently cell death was hastened. Moreover, an antibody against factor XIII strongly accelerated the Fas-mediated apoptosis. Furthermore, addition of partially purified factor XIII neutralized the apoptosis-promoting effect of anti-factor XIII antibody, indicating that this enzyme is involved in cross-link of Fas and down-regulates Fas-mediated apoptotic cell death. Significantly, the cross-link of Fas was seen only in fetal calf serum but not in newly-born calf serum, 1-year-old calf serum or adult bovine serum. These data suggest that plasma transglutaminase factor XIII may play a key role in fetal development of vertebrates via cross-link of Fas antigen.

FASL rs763110 polymorphism contributes to cancer risk: an updated meta-analysis involving 43,295 subjects

Background

Published studies investigating the association between genetic polymorphism -884C/T (rs763110) of the FAS ligand (FASL) promoter and cancer risk reported inconclusive results. To derive a more precise estimation of the relationship, we performed an updated meta-analysis of all eligible studies.

Methodology/Principal Findings

We carried out a meta-analysis, including 47 studies with 19,810 cases and 23,485 controls, to confirm a more conclusive association between the FASL rs763110 polymorphism and cancer susceptibility. Overall, significantly reduced cancer risk was associated with the variant -884T when all studies were pooled (TC vs. CC: OR = 0.83, 95%CI = 0.75–0.92; P_{heterogeneity}<0.001; TT+TC vs. CC: OR = 0.85, 95%CI = 0.77–0.94; P_{heterogeneity}<0.001). Stratified analysis revealed that there was a statistically reduced cancer risk in Asians (TC vs. CC: OR = 0.76, 95%CI = 0.67–0.87; P_{heterogeneity}<0.001; TT+TC vs. CC: OR = 0.79, 95%CI = 0.70–0.90; P_{heterogeneity}<0.001) and in patients with cancers of head and neck (TC vs. CC: OR = 0.87, 95%CI = 0.77–0.99; P_{heterogeneity} = 0.118; TT+TC vs. CC: OR = 0.88, 95%CI = 0.78–0.99; P_{heterogeneity} = 0.168) and ovarian cancer (TC vs. CC: OR = 0.67, 95%CI = 0.49–0.90; P_{heterogeneity} = 0.187; TT+TC vs. CC: OR = 0.64, 95%CI = 0.48–0.86; P_{heterogeneity} = 0.199). Meta-regression showed that ethnicity (p = 0.029) and genotyping method (p = 0.043) but not cancer types (p = 0.772), sample size (p = 0.518), or source of controls (p = 0.826) were the source of heterogeneity in heterozygote comparison.

Conclusion

Our results suggest that the FASL polymorphism rs763110 is associated with a significantly reduced risk of cancer, especially in Asian populations.

Artesunate possesses anti-leukemia properties that can be enhanced by arsenic trioxide

Artesunate (ART), an effective and safe anti-malaria drug, also exhibits anticancer activity. We studied the effects of ART on proliferation and apoptosis of human K562 and U937 leukemia cell lines. MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay demonstrated that ART inhibits cell growth in a dose- and time-dependent manner. Based on the findings obtained from light, fluorescence and transmission electron microscopy and propidium iodide staining, the effect of ART was shown to be mediated through apoptosis. In parallel, ART treatment increased Fas expression, while it decreased the c-Fos level in K562 cells. Furthermore, co-treatment with arsenic trioxide (ATO) significantly facilitated ART-induced K562 cell apoptosis. These findings demonstrated that ART had an antitumor activity against K562 and U937 leukemia cells, largely due to inhibition of proliferation and induction of apoptosis via the intrinsic pathway; and this tumoricidal function could be enhanced by ATO.

Study on Apoptosis of Human Promyelocytic Leukemia HL-60 Cells Induced by Fucosterol via Death Receptor Pathway

The purpose of this study is to investigate the effect of fucosterol on the induction of apoptosis and the molecular mechanism involved in Human promyelocytic leukemia HL-60 Cells. HL-60 Cells were treated with different concentrations of fucosterol at different time. MTT method was used to study fucosterol anti-tumor activity. Morphology observation was performed to determine the effects of fucosterol on apoptosis of HL-60 cells. Flow cytometry (FCM) was used to detect the cell cycle. Laser scanning confocal microscope (LSCM) was used to analyze the expressions of Fas, FasL, Fadd and Caspase-8. Caspase activity kits were used to determine the activity of Caspase-8 and Caspase-3. The results showed fucosterol could inhibit the growth of HL-60 cells, and the apoptosis morphology for 48 h treatment was obvious, which showed cell protuberance, cytoplasm concentrated and apoptotic body. Fucosterol treatment for 24 h increased the protein expression of Fas, FasL, Fadd and Caspase-8. It also showed that the activity of Caspase-3 and Caspase-8 has increased significantly. In conclusion, Fucosterol could induce HL-60 cells apoptosis via death receptor pathway.

Enhancing production and cytotoxic activity of polymeric soluble FasL-based chimeric proteins by concomitant expression of soluble FasL

Membrane FasL is the natural trigger of Fas-mediated apoptosis. A soluble homotrimeric counterpart (sFasL) also exists which is very weakly active, and needs oligomerization beyond its trimeric state to induce apoptosis. We recently generated a soluble FasL chimera by fusing the immunoglobulin-like domain of the leukemia inhibitory factor receptor gp190 to the extracellular region of human FasL, which enabled spontaneous dodecameric homotypic polymerization of FasL. This polymeric soluble human FasL (pFasL) displayed anti-tumoral activity in vitro and in vivo without systemic cytotoxicity in mouse. In the present work, we focused on the improvement of pFasL, with two complementary objectives. First, we developed more complex pFasL-based chimeras that contained a cell-targeting module. Secondly, we attempted to improve the production and/or the specific activity of pFasL and of the cell-targeting chimeras. We designed two chimeras by fusing to pFasL the extracellular portions of the HLA-A2 molecule or of a human gamma-delta TCR, and analyzed the consequences of co-expressing these molecules or pFasL together with sFasL on their heterotopic cell production. This strategy significantly enhanced the production of pFasL and of the two chimeras, as well as the cytotoxic activity of the two chimeras but not of pFasL. These results provide the proof of concept for an optimization of FasL-based chimeric proteins for a therapeutic use.

Antagonistic functional duality of cancer genes

Cancer evolution is a stochastic process both at the genome and gene levels. Most of tumors contain multiple genetic subclones, evolving in either succession or in parallel, either in a linear or branching manner, with heterogeneous genome and gene alterations, extensively rewired signaling networks, and addicted to multiple oncogenes easily switching with each other during cancer progression and medical intervention. Hundreds of discovered cancer genes are classified according to whether they function in a dominant (oncogenes) or recessive (tumor suppressor genes) manner in a cancer cell. However, there are many cancer "gene-chameleons", which behave distinctly in opposite way in the different experimental settings showing antagonistic duality. In contrast to the widely accepted view that mutant NADP(+)-dependent isocitrate dehydrogenases 1/2 (IDH1/2) and associated metabolite 2-hydroxyglutarate (R)-enantiomer are intrinsically "the drivers" of tumourigenesis, mutant IDH1/2 inhibited, promoted or had no effect on cell proliferation, growth and tumorigenicity in diverse experiments. Similar behavior was evidenced for dozens of cancer genes. Gene function is dependent on genetic network, which is defined by the genome context. The overall changes in karyotype can result in alterations of the role and function of the same genes and pathways. The diverse cell lines and tumor samples have been used in experiments for proving gene tumor promoting/suppressive activity. They all display heterogeneous individual karyotypes and disturbed signaling networks. Consequently, the effect and function of gene under investigation can be opposite and versatile in cells with different genomes that may explain antagonistic duality of cancer genes and the cell type- or the cellular genetic/context-dependent response to the same protein. Antagonistic duality of cancer genes might contribute to failure of chemotherapy. Instructive examples of unexpected activity of cancer genes and "paradoxical" effects of different anticancer drugs depending on the cellular genetic context/signaling network are discussed.

mTOR plays a critical role in p53-induced oxidative kidney cell injury in HIVAN

Oxidative stress has been implicated to contribute to HIV-induced kidney cell injury; however, the role of p53, a modulator of oxidative stress, has not been evaluated in the development of HIV-associated nephropathy (HIVAN). We hypothesized that mammalian target of rapamycin (mTOR) may be critical for the induction of p53-mediated oxidative kidney cell injury in HIVAN. To test our hypothesis, we evaluated the effect of an mTOR inhibitor, rapamycin, on kidney cell p53 expression, downstream signaling, and kidney cell injury in both in vivo and in vitro studies. Inhibition of the mTOR pathway resulted in downregulation of renal tissue p53 expression, associated downstream signaling, and decreased number of sclerosed glomeruli, tubular microcysts, and apoptosed and 8-hydroxy deoxyguanosine (8-OHdG)-positive (+ve) cells in Tg26 mice. mTOR inhibition not only attenuated kidney cell expression of p66ShcA and phospho-p66ShcA but also reactivated the redox-sensitive stress response program in the form of enhanced expression of manganese superoxide dismutase (MnSOD) and catalase. In in vitro studies, the mTOR inhibitor also provided protection against HIV-induced podocyte apoptosis. Moreover, mTOR inhibition downregulated HIV-induced podocyte (HP/HIV) p53 expression. Since HP/HIV silenced for mTOR displayed a lack of expression of p53 as well as attenuated podocyte apoptosis, this suggests that mTOR is critical for kidney cell p53 activation and associated oxidative kidney cell injury in the HIV milieu.

Activation of hepatocyte growth factor receptor, c-met, in renal tubules is required for renoprotection after acute kidney injury

Hepatocyte growth factor is a pleiotrophic protein that promotes injury repair and regeneration in multiple organs. Here, we show that after acute kidney injury (AKI), the HGF receptor, c-met, was induced predominantly in renal tubular epithelium. To investigate the role of tubule-specific induction of c-met in AKI, we generated conditional knockout mice, in which the c-met gene was specifically disrupted in renal tubules. These Ksp-met−/−mice were phenotypically normal and had no appreciable defect in kidney morphology and function. However, in AKI induced by cisplatin or ischemia-reperfusion injury, the loss of tubular c-met substantially aggravated renal injury. Compared with controls, Ksp-met−/−mice displayed higher serum creatinine, more severe morphologic lesions, and increased apoptosis, which was accompanied by an increased expression of Bax and Fas ligand and decreased phosphorylation-activation of Akt. In addition, ablation of c-met in renal tubules promoted chemokine expression and renal inflammation after AKI. Consistently, ectopic expression of hepatocyte growth factor in vivo protected the kidneys against AKI in control mice, but not in Ksp-met−/−counterparts. Thus, our results suggest that tubule-specific c-met signaling is crucial in conferring renal protection after AKI, primarily by its anti-apoptotic and anti-inflammatory mechanisms.

Functional polymorphisms of FAS and FASL gene and risk of breast cancer - pilot study of 134 cases

Fas/Fas ligand (FasL) system is one of the key apoptotic signaling entities in the extrinsic apoptotic pathway. De-regulation of this pathway, i.e. by mutations may prevent the immune system from the removal of newly-formed tumor cells, and thus lead to tumor formation. The present study investigated the association between −1377 G/A (rs2234767) and −670 A/G (rs1800682) polymorphisms in Fas as well as single nucleotide polymorphisms INV2nt −124 A/G (rs5030772) and −844 C/T (rs763110) in FasL in a sample of Iranian patients with breast cancer. This case-control study was done on 134 breast cancer patients and 152 normal women. Genomic DNA was extracted from whole blood samples. The polymorphisms were determined by using tetra-ARMS-PCR method. There was no significant difference in the genotype distribution of FAS rs2234767 polymorphism between cases and controls. FAS rs1800682, FASL rs5030772, and FASL rs763110 genotypes showed significant associations with an increasing risk of breast cancer (odds ratio OR = 3.18, P = 0.019; OR = 5.08, P = 0.012; OR = 2.40, P = 0.024, respectively). In conclusion, FAS rs2234767 was not associated with breast cancer risk. Though, FAS rs1800682, FASL rs5030772, and FASL rs763110 polymorphisms were associated with the risk of breast cancer in the examined population.

Rab25 Small GTPase Mediates Secretion of Tumor Necrosis Factor Receptor Superfamily Member 11b (osteoprotegerin) Protecting Cancer Cells from Effects of TRAIL

BACKGROUND

Expression of Rab25, which is located in the 1q amplicon present at high frequency in many cancer lineages, promotes cancer cell survival under multiple stress conditions. While Rab proteins play essential roles in all stages of vesicle trafficking, the functions and endogenous cargoes for Rab25 remain to be fully elucidated. Osteoprotegerin (OPG) is a secreted glycoprotein that binds the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) thus preventing it from activating the TNF-family death receptors. In the present study, we demonstrated that Rab25 regulates OPG at both the transcription and secretion level.

METHODS

The effect of Rab25 on OPG expression and its effect on TRAIL-induced cell were examined in both ovarian and breast cells. Signal transduction pathways regulation of OPG expression was examined in cells using pharmacogenetic approaches.

RESULTS

Expression of Rab25 to levels similar to those in tumors with RAB25 amplification, increased OPG mRNA expression and secretion from ovarian and breast cancer cell lines, whereas down regulation with Rab25 specific siRNA decreased OPG secretion and sensitized cells to TRAIL-induced cell death. Critically, exogenous OPG mimicked the effects of Rab25 on cell death supporting the contention that Rab25-induced accumulation of OPG protects cancer cells from the effects of TRAIL. Rab25 cooperates with EGFR-mediated MAPK signaling to increase TRAIL production and release. Importantly, priming cells with EGFR inhibitors increased sensitivity to TRAIL-induced cells death regardless of the Rab25 background.

CONCLUSION

Increased OPG expression induced by Rab25 may provide a mechanistic advantage for cancer development and progression.

Unphosphorylated STAT1 promotes sarcoma development through repressing expression of Fas and bad and conferring apoptotic resistance

STAT1 exists in phosphorylated (pSTAT1) and unphosphorylated (uSTAT1) forms each regulated by IFN-γ. Although STAT1 is a key mediator of the IFN-γ signaling pathway, an essential component of the host cancer immunosurveillance system, STAT1 is also overexpressed in certain human cancers where the functions of pSTAT1 and uSTAT1 are ill defined. Using a murine model of soft tissue sarcoma (STS), we show that disruption of the IFN effector molecule IRF8 decreases pSTAT1 and increases uSTAT1 in STS cells, thereby increasing their metastatic potential. We determined that the IRF8 gene promoter was hypermethylated frequently in human STS. An analysis of 123 human STS specimens revealed that high uSTAT1 levels in tumor cells was correlated with a reduction in disease-specific survival (DSS), whereas high pSTAT1 levels in tumor cells were correlated with an increase in DSS. In addition, uSTAT1 levels were negatively correlated with pSTAT1 levels in these STS specimens. Mechanistic investigations revealed that IRF8 suppressed STAT1 transcription by binding the STAT1 promoter. RNAi-mediated silencing of STAT1 in STS cells was sufficient to increase expression of the apoptotic mediators Fas and Bad and to elevate the sensitivity of STS cells to Fas-mediated apoptosis. Together, our findings show how the phosphorylation status of pSTAT1 determines its function as a tumor suppressor, with uSTAT1 acting as a tumor promoter that acts by elevating resistance to Fas-mediated apoptosis to promote immune escape.