Expression of Fas and Fas-related molecules in human hepatocellular carcinoma

Activation of transcription factors NF-kappaB and AP-1 and their relations with apoptosis-associated proteins in hepatocellular carcinoma

AIM: To study the distribution pattern of transcription factors NF-κB and AP-1 and their relations with the expression of apoptosis associated-proteins Fas/FasL and ICH-1L/S in human hepatocellular carcinoma (HCC).

METHODS: We performed in situ hybridization and immunohistochemical techniques for NF-κB, AP-1, Fas/FasL and ICH-1 in 40 cases of human HCC along with corresponding nontumoral tissues and 7 cases of normal liver tissues.

RESULTS: Twenty-two (55%) and 25 (62.5%) of 40 cases for NF-κB and AP-1 were presented for nuclear or both nuclear and cytoplastic staining respectively, while less cases were presented for only cytoplastic staining for NF-κB (18%) and AP-1 (10%) in adjacent nontumoral tissues and negative staining in normal liver tissues. There was no statistically significant difference of NF-κB or AP-1 activation between well differentiated tumors and poorly differentiated tumors (P > 0.05). NF-κB activity is positively corresponded to AP-1 activation. The expression of ICH-1L/S was associated with the activation of NF-κB and AP-1 (P < 0.05), but no significant relationship was found between Fas/FasL and NF-κB or AP-1(P > 0.05).

CONCLUSION: Activation of both NF-κB and AP-1 may be required for ICH-1L/S-induced apoptosis in HCC, but not for Fas/FasL-mediated apoptosis. NF-κB and AP-1 may play important roles in the pathogenesis of human HCC.

Apoptotic effects of extract from Antrodia camphorata fruiting bodies in human hepatocellular carcinoma cell lines

The fruiting body of Antrodia camphorata is well known in Taiwan as a traditional medicine for treating cancer and inflammation. The purpose of this study was to evaluate the apoptotic effects of ethylacetate extract from A. camphorata (EAC) fruiting bodies in two human liver cancer cell lines, Hep G2 and PLC/PRF/5. Treatment with EAC decreased the cell growth of Hep G2 and PLC/PRF/5 cells in a dose dependent manner. In Fas/APO-1 positive-Hep G2 cells, EAC increased the expression level of Fas/APO-1 and its two forms of ligands, membrane-bound Fas ligand (mFasL) and soluble Fas ligand (sFasL), in a p53-indenpendent manner. In addition, EAC also initiated mitochondrial apoptotic pathway through regulation of Bcl-2 family proteins expression, release of cytochrome c, and activation of caspase-9 both in Hep G2 and PLC/PRF/5 cells. Furthermore, EAC also inhibited the cell survival signaling by enhancing the amount of IkappaBalpha in cytoplasm and reducing the level and activity of NF-kappaB in the nucleus, and subsequently attenuated the expression of Bcl-X(L) in Hep G2 and PLC/PRF/5 cells. EAC therefore decreased the cell growth and induced apoptosis both in Hep G2 and PLC/PRF/5 cells.

Alpha-fetoprotein triggers hepatoma cells escaping from immune surveillance through altering the expression of Fas/FasL and tumor necrosis factor related apoptosis-inducing ligand and its receptor of lymphocytes and liver cancer cells

AIM: To investigate the mechanism of α-fetoprotein (AFP) in escaping from the host immune surveillance of hepatoc-ellular carcinoma.

METHODS: AFP purified from human umbilical blood was administrated into the cultured human lymphoma Jurkat T cell line or hepatoma cell line, Bel7402 in vitro. The expression of tumor necrosis factor related apoptosis-inducing ligand (TRAIL) and its receptor (TRAILR) mRNA were analyzed by Northern blot and Western blot was used to detect the expression of Fas and Fas ligand (FasL) protein.

RESULTS: AFP (20 mg/L) could promote the expression of FasL and TRAIL, and inhibit the expression of Fas and TRAILR of Bel7402 cells. For Jurkat cell line, AFP could suppress the expression of FasL and TRAIL, and stimulate the expression of Fas and TRAILR. AFP also could synergize with Bel7402 cells to inhibit the expression of FasL protein and TRAIL mRNA in Jurkat cells. The monoclonal antibody against AFP (anti-AFP) could abolish these functions of AFP.

CONCLUSION: AFP is able to promote the expression of FasL and TRAIL in hepatoma cells and enhance the expression of Fas and TRAILR in lymphocytes. These could elicit the escape of hepatocellular carcinoma cells from the host’s lymphocytes immune surveillance.

Role of the Fas/Fas ligand death receptor pathway in ginseng saponin metabolite-induced apoptosis in HepG2 cells

This research team found in previous studies, that the ginseng saponin metabolite IH901 induces apoptosis in HepG2 cells via a mitochondrial-mediated pathway, which resulted in the activation of caspase-9 and subsequently of caspase-3 and -8. Based on these results, the involvement of the Fas/Fas ligand (FasL) death-receptor pathway, in IH901-induced apoptosis in HepG2 cells, was investigated. Levels of Fas and the Fas ligand (FasL) mRNA or protein were not increased by IH901, rather they were decreased significantly at 18 h post treatment. Soluble FasL (sFasL) was detectable by immunoprecipitation analysis in the medium of HepG2 cells treated with IH901. Increased levels of sFasL were inversely correlated with the levels of FasL. Preincubation of HepG2 cells with antagonistic anti-Fas antibody showed little protective effect, if any, on IH901-induced cell death. At a 30 microM (24 and 48 h) and 40 microM (24 h) concentration of IH901, the cytotoxic effect of IH901 was less then 50%, anti-Fas antibody prevented IH901-induced cell death. However, at a 60 microM (24 and 48 h) and 40 microM (48 h) concentration of IH901, cell death rates were about 80% or more and most of the chemopreventive and chemotherapeutic effects of IH901 were manifested. Blocking the Fas receptor did not influence IH901-induced cell death. These results indicate that the Fas/FasL system is engaged, but not required for IH901-induced cell death, at pharmacologically significant concentrations.

Eicosapentaenoic Acid Induces Fas-Mediated Apoptosis Through a p53-Dependent Pathway in Hepatoma Cells

Eicosapentaenoic acid (EPA) has been demonstrated to induce apoptosis and cell cycle arrest in various cancer cell lines in vitro. In this study, we investigated the anti-tumor effects of EPA on hepatoma cell lines and the mechanisms responsible for induced cell death. Three hepatoma cell lines tested had different p53 status: HepG2 with a wild-type p53; Hep3B, of which the endogenous p53 was deleted; and Huh7 with its p53 mutated. MTT assay showed reduced viability of HepG2 cells after exposure to EPA, and the cytotoxicity of EPA was time and dose dependent. However, EPA had no effect on the viability and cell death in the two other hepatoma cell lines containing dysfunctional p53. DNA fragmentation analysis and TUNEL (terminal deoxynucleotidyl transferase [TdT]-mediated deoxyuridine diphosphate [dUTP] nick end labeling) staining showed a typical pattern of DNA laddering and DNA breaks staining, respectively, in wild-type p53-containing HepG2 cells after EPA treatment. We also observed that EPA induced transient nuclear accumulation of P53 protein that subsequently up-regulated the expression of Fas messenger RNA and protein in HepG2 cells. In contrast, these findings were not observed in Hep3B and Huh7 cells exposed to EPA. Most notably, EPA-induced apoptosis in HepG2 cells could be reduced almost completely by treatment with FasL antisense oligonucleotides. We conclude that EPA inhibits the growth of HepG2 cells and mediates its effect, at least in part, via the Fas-mediated apoptosis. It appears that the effects of EPA on hepatoma cells are determined by the status of p53 and that wild-type p53 is a prerequisite for the anticancer effect of EPA.

Acacetin inhibits the proliferation of Hep G2 by blocking cell cycle progression and inducing apoptosis

Flavonoids are a broadly distributed class of plant pigments, universally present in vascular plants and responsible for much of the coloring in nature. They are strong antioxidants that occur naturally in foods and can inhibit carcinogenesis in rodents. In this study, we examined acacetin (5,7-dihydroxy-4'-methoxyflavone), a flavonoid compound, for its effect on proliferation in a human liver cancer cell line, Hep G2. The results showed that acacetin inhibited the proliferation of Hep G2 by inducing apoptosis and blocking cell cycle progression in the G1 phase. Enzyme-linked immunosorbent assay showed that acacetin significantly increased the expression of p53 and p21/WAF1 protein, contributing to cell cycle arrest. An enhancement in Fas/APO-1 and its two form ligands, membrane-bound Fas ligand and soluble Fas ligand, as well as Bax protein, was responsible for the apoptotic effect induced by acacetin. Taken together, our study suggests that the induction of p53 and activity of the Fas/Fas ligand apoptotic system may participate in the antiproliferative activity of acacetin in Hep G2 cells.

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Induction of FAS ligand expression in a human hepatoblastoma cell line by HCV core protein

Tumour cells and virus infected cells expressing Fas ligand (FasL) can evade immune surveillance by inducing apoptosis in T cells expressing Fas. In order to characterise a possible role of hepatitis C virus (HCV) core protein in similar mechanisms during HCV infection, we investigated Fas ligand expression and activity in a human hepatoblastoma cell line (HepG2) constitutively expressing this protein. Strong FasL induction was detected by immunoblotting and flow cytometry analysis in the core expressing cell lines Hep39. In contrast, vector transfected cells or cell lines expressing HCV E1-E2 proteins did not show FasL expression. Co-cultivation experiments of Hep39 cells with a Fas-sensitive T cell line indicated that FasL induced by the core protein had apoptotic activity toward target cells. Effect of the core protein on induction of FasL promoter was further examined by co-transfection of HepG2 cells with core-bearing plasmid and a vector in which luciferase gene expression is driven by human FasL promoter. Results of the luciferase assay indicated a positive regulation of FasL promoter by the core protein. In conclusion, HCV core protein plays a role in the induction of functional FasL in hepatoblastoma cell line and apoptosis in a target T cell line expressing Fas. Similar mechanisms may contribute, in vivo, to establishment of chronic infection and development of hepatocellular carcinoma (HCC).

Sodium butyrate enhances Fas-mediated apoptosis of human hepatoma cells

BACKGROUND/AIMS

Human hepatoma cells have been reported to be resistant to Fas-mediated apoptosis. Sodium butyrate (SB) induced apoptosis of several cancer cells. We investigated the effects of SB on Fas-mediated apoptosis of hepatoma cells.

METHODS

In hepatoma cells (HuH-6, HuH-7, Hep-G2, and PLC/PRF/5), susceptibility to Fas-mediated apoptosis and Fas expression were assessed. Caspase-3 activation and cell cycle progression were evaluated in HuH-6. A cDNA microarray assay was performed to screen the changes in the expression of mRNAs.

RESULTS

Pretreatment with SB caused an enhancement of the sensitivity to anti-Fas-mediated cytotoxicity, though it did not increase the expression of Fas. The cDNA microarray assay revealed up-regulation of pro-apoptotic Bik, Bak, Bid and c-Jun N-terminal protein kinase-1, and down-regulation of anti-apoptotic Bag-1 and cellular Fas-associated death domain-like interleukin-1beta-converting enzyme inhibitor protein. In some molecules, expression of the proteins was confirmed by Western blotting. An increase in truncated-Bid accompanying the reduction in Bid was also observed.

CONCLUSIONS

SB enhances the susceptibility of hepatoma cells to anti-Fas-mediated cytotoxicity by altering the mRNA and protein expression and/or the activation status of proteins that could be involved in the Fas signaling pathway. SB may have an important role in the elimination of hepatoma cells.

Fas-mediated pathway and apoptosis in normal, hyperplastic, and neoplastic endometrium

OBJECTIVES

Abnormalities in the control of cell proliferation and apoptosis have been suggested to contribute to the development and progression of neoplasia. There are at least two pathways that activate apoptosis. The first is a mitochondria-dependent route governed by bcl-2 family proteins. The second is a parallel mechanism which involves the activation of a group of tumor necrosis factor (TNF) receptors, such as Fas.

METHODS

The aim of this study was to examine the distribution and interrelation between the expression patterns of apoptosis-related proteins such as Fas, caspase-3 (CPP32), and M30, and to investigate the role of Fas-mediated apoptosis in the pathogenesis and progression of endometrial neoplasms.

RESULTS

Using specific antibodies for Fas, caspase-3, and M30, we examined protein expressions in 29 endometrial carcinomas, 30 endometrial hyperplasias, and 21 normal cyclic endometria. The results of immunostaining for Fas and caspase-3 were analyzed semiquantitatively by using an immunohistochemical scoring system (HSCORE) that incorporated both the intensity and the distribution of specific staining. For M30, positive staining cells and extracellular particles were analyzed semiquantitatively per 10 high-power fields.HSCOREs of Fas and caspase-3 were slightly higher in the secretory endometria than in the proliferative endometria. Similarly, M30 reactivity seemed to increase in the late secretory phase of the cycle. HSCOREs of Fas and caspase-3 and the reactivity of M30 were significantly higher in the carcinoma group than in the simple hyperplasia group (P < 0.05). Complex hyperplasias, however, expressed quite similar HSCOREs of Fas and caspase-3 as carcinomas. M30 reactivity was also significantly higher in complex hyperplasias than in simple hyperplasias, and in carcinomas positivity increased significantly (P < 0.05) as the grade progressed.

CONCLUSIONS

The significant increase observed in Fas, caspase-3, and M30 expression in carcinomas as compared with simple hyperplasias may suggest that the Fas-related apoptotic pathway is also involved in the regulation of apoptosis in the endometrial tissue and promotes the development and progression of endometrial neoplasia.

The protein tyrosine phosphatase PTP-Basophil/Basophil-like

The protein tyrosine phosphatase PTP-Basophil (PTP-Bas) and its mouse homologue, PTP-Basophil-like (PTP-BL), are high molecular mass protein phosphatases consisting of a number of diverse protein-protein interaction modules. Several splicing variants of these phosphatases are known to exist thus demonstrating the complexity of these molecules. PTP-Bas/BL serves as a central scaffolding protein facilitating the assembly of a multiplicity of different proteins mainly via five different PDZ domains. Many of these interacting proteins are implicated in the regulation of the actin cytoskeleton. However, some proteins demonstrate a nuclear function of this protein tyrosine phosphatase. PTP-Bas is involved in the regulation of cell surface expression of the cell death receptor, Fas. Moreover, it is a negative regulator of ephrinB phosphorylation, a receptor playing an important role during development. The phosphorylation status of other proteins such as RIL, IkappaBalpha and beta-catenin can also be regulated by this phosphatase. Finally, PTP-BL has been shown to be involved in the regulation of cytokinesis, the last step in cell division. Although the precise molecular function of PTP-Bas/BL is still elusive, current data suggest clearly that PTP-Bas/BL belongs to the family of PDZ domain containing proteins involved in the regulation of the cytoskeleton and of intracellular vesicular transport processes.

Oligomerization of soluble Fas antigen induces its cytotoxicity

Soluble Fas antigen can protect cells against Fas-mediated apoptosis. High level soluble Fas antigen characteristic for blood of patients with autoimmune disease or cancer is believed to prevent the elimination of autoimmune lymphocytes or tumor cells. Here we first report that human recombinant FasDeltaTM, i.e. soluble Fas generated by alternative splicing of the intact exon 6, is capable of inducing death of transformed cells by "reverse" apoptotic signaling via transmembrane Fas ligand. FasDeltaTM, as well as transmembrane Fas antigen, can be either monomeric or oligomeric, and both its forms are efficient in blocking Fas-mediated apoptosis, although the cytotoxic activity is exhibited solely by the latter. An in vivo analysis of soluble Fas antigen showed that unlike in healthy controls, nearly the total FasDeltaTM present in sera of rheumatoid arthritis patients was oligomeric. This resulted in suppression of cell proliferation in the experimental sera and in its promotion in controls. Thus, oligomerization/depolymerization of soluble Fas antigen can regulate its activity and contribute to the pathogenesis of autoimmune diseases and cancer.

Tetrandrine-induced cell cycle arrest and apoptosis in Hep G2 cells

The effects of tetrandrine in the human hepatoblastoma G2 (Hep G2) cell line were investigated in this study. The results showed that tetrandrine not only inhibited Hep G2 growth but also induced apoptosis and blocked cell cycle progression in the G1 phase. ELISA assay demonstrated that tetrandrine significantly increased the expression of p53 and p21/WAF1 protein, which caused cell cycle arrest. An enhancement in Fas/APO-1 and its two form ligands, membrane-bound Fas ligand (mFasL) and soluble Fas ligand (sFasL), might be responsible for the apoptotic effect induced by tetrandrine. Taken together, p53 and Fas/FasL apoptotic system possibly participated in the antiproliferative activity of tetrandrine in Hep G2 cells.

Clinicopathologic relevance of apoptotic and proliferative factors in human lung adenocarcinoma: Fas expression correlates with the histologic subtype, but not with the degree of apoptosis

We immunohistochemically examined 141 surgically resected peripheral lung adenocarcinomas for the expression of Fas, single stranded (ss-) DNA and Ki-67, and statistically evaluated the relationship of these parameters with other clinicopathologic variables, including clinical stage, nodal involvement, and histopathologic subtypes classified according to WHO criteria. Fas expression by cancer cells was characteristically localized in the cytoplasm, and the extent of expression correlated well with the degree of Ki-67 reactivity (p = 0.0004), but not with the degree of apoptic occurrence, as assessed by ss-DNA reactivity. Cancer cells of the bronchioloalveolar carcinoma (BAC) subtype without invasive growth exhibited a significantly lower Fas expression than those of other subtypes (p < 0.0001). Positive expression of Fas was frequently associated with a high incidence of nodal involvement and advanced clinical stage, as compared with cases of negative expression (p = 0.0111 and p = 0.0439, respectively). Multivariate analysis revealed that Fas expression significantly correlated with the histologic subtype, but not with tumor size, nodal involvement, or clinical stage. Survival analysis determined by the log-rank test revealed that clinical stage and Ki-67 reactivity were poor prognostic variables, and Fas expression was not statistically significant. Based on these data, intracytoplasmic expression of Fas in cancer cells may participate in the development of resistance to fas-mediated apoptosis.

Modified apoptotic molecule (BID) reduces hepatitis C virus infection in mice with chimeric human livers

Hepatitis C virus (HCV) encodes a polyprotein consisting of core, envelope (E1, E2, p7), and nonstructural polypeptides (NS2, NS3, NS4A, NS4B, NS5A, NS5B). The serine protease (NS3/NS4A), helicase (NS3), and polymerase (NS5B) constitute valid targets for antiviral therapy. We engineered BH3 interacting domain death agonist (BID), an apoptosis-inducing molecule, to contain a specific cleavage site recognized by the NS3/NS4A protease. Cleavage of the BID precursor molecule by the viral protease activated downstream apoptotic molecules of the mitochondrial pathway and triggered cell death. We extended this concept to cells transfected with an infectious HCV genome, hepatocytes containing HCV replicons, a Sindbis virus model for HCV, and finally HCV-infected mice with chimeric human livers. Infected mice injected with an adenovirus vector expressing modified BID exhibited HCV-dependent apoptosis in the human liver xenograft and considerable declines in serum HCV titers.

FAP-1 association with Fas (Apo-1) inhibits Fas expression on the cell surface

As revealed by intracellular pools of nonactive Fas (Apo-1), export of Fas to the cell surface is often impaired in human tumors, thereby inactivating Fas ligand-mediated apoptosis. Here, we demonstrate that association with Fas-associated phosphatase 1 (FAP-1) attenuates Fas export to the cell surface. Forced expression of FAP-1 reduces cell surface Fas levels and increases the intracellular pool of Fas within the cytoskeleton network. Conversely, expression of dominant-negative forms of FAP-1, or inhibition of FAP-1 expression by short interfering RNA, efficiently up-regulates surface expression of Fas. Inhibition of Fas surface expression by FAP-1 depends on its association with the C terminus of Fas. Mutation within amino acid 275 results in decreased association with FAP-1 and greater export of Fas to the cell surface in melanomas, normal fibroblasts, or Fas null cells. Identifying the role of FAP-1 in binding to, and consequently inhibition of, Fas export to the cell surface provides novel insight into the mechanism underlying the regulation of Fas trafficking, which is commonly impaired in advanced tumors with FAP-1 overexpression.

Increased expression of FLIP, an inhibitor of Fas-mediated apoptosis, in stomach cancer

Despite the cell surface expression of Fas (Apo-1/CD95), many types of tumor cells, including stomach cancer cells, are resistant to Fas-mediated apoptosis, indicating the presence of inactivating mechanisms of Fas signaling. Expression of FLICE-like inhibitory protein (FLIP), one of the inhibitory proteins of Fas-mediated apoptosis, has been reported in several cancer types, but not in stomach cancer. In the present study, we analyzed the expression of Fas and FLIP in 60 advanced gastric adenocarcinomas by immunohistochemistry using a tissue microarray approach. Immunopositivity (defined as >/=30% of the neoplastic cells) was observed for Fas in 58 (97%) and FLIP in 54 (90%) of the 60 cancers. All of the tumors with FLIP immunostaining also showed Fas immunostaining. Loss of cell surface Fas immunostaining, another mechanism of Fas resistance, was observed in 45 tumors (75%). By contrast, normal gastric mucosal cells showed no or weak expression of both Fas and FLIP. Taken together, these results indicate that increased expression of FLIP is a frequent event in stomach carcinomas, and suggest that for evading apoptosis stomach carcinoma cells in vivo may need FLIP expression, which might contribute to tumor development.

Apoptosis and the liver: relation to autoimmunity and related conditions

Apoptosis is a normal physiologic form of cell death that follows activation of either an intrinsic or extrinsic pathway. In the intrinsic, various stimuli, such as oxidative stress, lead to mitochondrial dysfunction and the release of pro-apoptotic factors. Ligand binding to cell surface death receptors, such as Fas, activates the extrinsic pathway. Due to the rapid clearance of apoptotic cells, detection and quantification of apoptotic cells is prone to underestimation. In the liver, the importance of apoptosis is evident both during development and homeostasis of the biliary tree. Apoptosis also plays a prominent role in liver pathogenesis. Induction of the extrinsic apoptotic pathway by cytotoxic lymphocytes predominates in autoimmune liver diseases, viral hepatitis, and liver allograft rejection. Biliary cell apoptosis is highly regulated by bcl-2 family members. Both the extrinsic and intrinsic pathways are active in alcohol-related liver disease. Overexpression of anti-apoptotic proteins and FasL allow liver tumor cells to evade tumor specific cytotoxic lymphocytes. Agents that modulate apoptosis may be of future therapeutic benefit in a number of liver diseases.

Hepatocellular carcinoma with an unusual medullary-like histology and signs of regression ("medullary-like hepatocellular carcinoma")

The case of a variant of hepatocellular carcinoma is described, which, based on its unique histology, we propose to term, medullary-like hepatocellular carcinoma. It developed in a 56-year-old male patient with liver cirrhosis, and consisted of large, amphophilic cells with a solid growth pattern. The tumour was densely infiltrated with lymphocytes and plasma cells. Lymphocytes formed a mixture of B and T cells, and plasma cells were polytypic. In addition, numerous S-100 protein-reactive stellate cells were observed at the tumour border, where marked apoptosis of hepatocellular carcinoma cells was evident. In areas of dense lymphoplasmacytic infiltration, part of the tumour cells had lost their intercellular connections and their beta-catenin reactivity. Some tumour cells expressed FasL, but not Fas. The tumour exhibited several foci of regression, showing small remnants of damaged tumour cells within dense infiltrations. The patient is alive without evidence of disease 25 months after resection. Medullary-like hepatocellular carcinoma is a lesion which mimics several features known for other medullary carcinomas, including a marked immune response which may be responsible for partial regression of this tumour.

Transforming growth factor alpha protects against Fas-mediated liver apoptosis in mice

The Fas/Fas ligand interaction plays a crucial role in various liver diseases, and administration of agonistic anti-Fas antibody to mice causes massive hepatic apoptosis and fulminant hepatic failure. Several growth factors have recently been found to function in preventing apoptosis. In this study, we demonstrated that overexpression of transforming growth factor alpha (TGFalpha) has a dramatic protective effect on Fas-mediated hepatic apoptosis at the biochemical and histological levels. Moreover, 85.7% (six out of seven) of TGFalpha transgenic mice survived the lethal liver damage, whereas all wild-type mice died. Expression of Bcl-xL, an anti-apoptotic protein, was greatly increased in the transgenic mice. Taken together, our findings suggest that TGFalpha protects against Fas-mediated liver apoptosis in vivo and up-regulation of Bcl-xL may participate in protective effect of TGFalpha.

Peroxisome proliferator-activated receptor gamma augments tumor necrosis factor family-induced apoptosis in hepatocellular carcinoma

Proliferator-activated receptor gamma (PPARgamma) is a nuclear receptor, which mainly associates with adipogenesis, but also appears to facilitate cell differentiation or apoptosis in certain malignant cells. This apoptosis induction by PPARgamma is increased by co-stimulation with tumor necrosis factor (TNF)-alpha-related apoptosis-inducing ligand (TRAIL), a member of the TNF family. In this study, we investigated the effect of PPARgamma on Fas-mediated apoptosis in hepatocellular carcinoma (HCC) cell lines. PPARgamma was expressed on all seven HCC cell lines and located in their nuclei. 15-Deoxy-Delta-12,14-prostaglandin J2 (15d- PGJ2), a PPARgamma ligand, inhibited cellular proliferation in HepG2, SK-Hep1 or HLE cells, unlike pioglitazone, another PPARgamma ligand, which did not have a significant influence on proliferation of these cells. However, 15d-PGJ2 facilitated Fas-mediated HCC apoptosis that could not be induced by Fas alone. These results suggest that PPARgamma can augment TNF-family-induced apoptosis.