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Many tumor cells, including hepatocellular carcinoma (HCC), express both Fas and its ligand on their surfaces, and it has remained a mystery why such cells do not spontaneously become apoptotic. In the current study, we analyzed the alterations of Fas structure and the expression of Fas and Fas ligand (FasL) and of Fas pathway inhibitors, including soluble Fas (sFas), Fas-associated phosphatase-1 (FAP-1), and bcl-2, in 50 cases of human HCC. Monoallelic loss of the Fas gene, as determined by loss of heterozygosity with intragenic polymorphisms, was observed in 5 of the 34 informative cases (15%), but none of the 50 cases showed Fas gene mutation. Expression of Fas and FasL was detected in 44 (88%) and 50 (100%) cases, respectively. sFas messenger RNA, as analyzed by in situ reverse-transcription polymerase chain reaction was expressed in 42 of the 50 cases (84%), and FAP-1 expression was observed in 40 of the 50 cases (80%). In contrast, none of the 50 cases showed bcl-2 expression. Our results showed that the majority of the HCCs (88%) coexpressed a death receptor, Fas and its cognate ligand, FasL, but all HCCs showed one or more alterations of the Fas pathway molecules known to inhibit Fas-mediated apoptosis. These findings suggest that the expression of sFas and FAP-1 and, in part, loss of Fas expression, rather than Fas gene alteration or bcl-2 expression, may be involved in the Fas resistance of HCC in vivo and that these mechanisms may play important roles in the pathogenesis of human HCC. HUM PATHOL 32:250-256., (Copyright 2001 by W.B. Saunders Company)

Fas (Apo-1/CD95) is a cell-surface receptor involved in cell death signaling, and recent reports have suggested that defects within the Fas receptor pathway such as Fas mutation play an important part in the development and progression of human tumors. Burn scar-related squamous cell carcinoma of skin is a unique subtype of cutaneous squamous cell carcinoma, and tends to be more aggressive in nature than conventional squamous cell carcinoma. The molecular mechanisms underlying the development and progression of burn scar-related squamous cell carcinoma, however, are not clear. In this study, we analyzed the entire coding region and all splice sites of the Fas gene for the detection of the somatic mutations in a series of 50 conventional squamous cell carcinomas and 21 burn scar-related squamous cell carcinomas by polymerase chain reaction, single strand conformation polymorphism, and DNA sequencing. We detected mis-sense mutations in three of 21 burn scar-related squamous cell carcinomas (14.3%), whereas no mutation was detected in 50 conventional squamous cell carcinomas. Of the three Fas mutations detected in the burn scar-related squamous cell carcinomas, one was found in Fas ligand-binding domain, another one was identified in the death domain known to be involved in the transduction of an apoptotic signal, and the other one was found in the transmembrane domain. Our data show that some burn scar-related squamous cell carcinomas have Fas gene mutations in important regions for the apoptosis function and suggest that these mutations might be involved in the pathogenesis of burn scar-related squamous cell carcinomas. In addition, our results provide an important clue to understanding the difference between burn scar-related squamous cell carcinoma and conventional squamous cell carcinoma at the molecular level.

Fas, a death receptor, is widely expressed in human tissue, but its expression, although a prerequisite for the induction of apoptosis, does not predict its biological function. To understand the mechanisms of Fas resistance in human tissues in vivo, we performed immunohistochemistry using an antibody against Fas-associated phosphatase-1 (FAP-1), which interacts with the cytosolic domain of Fas and inhibits Fas-mediated apoptosis. In normal human tissues, FAP-1 immunostaining was easily detected, for example, in renal tubules, skeletal muscle, myocardiocytes, pituitary gland, parathyroid gland, pancreatic islets, hepatocytes, testicular germ cells, prostatic glands, neurons, epithelium of fallopian tube, endometrial glands, trophoblasts, bronchial epithelial cells, and some types of gastrointestinal epithelial cells. In 123 (78%) of 158 cancers of various origins, including breast carcinomas, stomach carcinomas, colon carcinomas, lung carcinomas and several types of sarcomas, variable intensities of FAP-1 expression were evident. Taken together, these findings demonstrated that FAP-1 is widely expressed in normal human tissues and partly overlapped with Fas expression described in earlier reports, suggesting that FAP-1 may have an important role in the regulation of apoptosis in vivo. In addition, FAP-1 expression in cancers suggests that many cancers may be resistant to Fas-mediated apoptosis through the action of FAP-1 in vivo.

Fas (Apo-1/CD95) is a cell-surface receptor involved in cell death signaling. The key role of the Fas system in negative growth regulation has been studied mostly within the immune system, and somatic mutations of Fas in cancer patients have been described solely in lymphoid-lineage malignancies. We analyzed somatic mutations and loss of heterozygosity of Fas gene in 43 transitional cell carcinomas of urinary bladder. Overall, 12 tumors (28%) were found to have Fas mutations, including 11 missense mutations and 1 frameshift mutation. Ten of the 12 mutations were located in the death domain known to be involved in the transduction of an apoptotic signal, and 8 of these 10 mutations showed an identical G to A transition at bp 993, indicating a potential hotspot in bladder cancers. Three of eight (38%) informative tumors carrying Fas mutations showed LOH at polymorphic sites in the promoter region. This is the first report on the Fas gene mutations in nonlymphoid malignancies, and our data suggest that alterations of the Fas gene might lead to the loss of its apoptotic function and contribute to the pathogenesis of some bladder cancers.

Many tumour cells express both Fas and its ligand (FasL) on their surface and it has remained a mystery why such cells do not simply kill themselves. It remains to be determined whether Fas and FasL are expressed in human hepatoblastomas and if so, what is responsible for the possible Fas resistance of these tumours. In this study, the expression of Fas and FasL was examined in 23 cases of human hepatoblastoma by immunohistochemical staining. To elucidate possible Fas resistance in hepatoblastomas, Fas-resistance pathways including the expression of bcl-2 and Fas-associated phosphatase-1 (FAP-1), and the expression of soluble Fas (sFas) mRNA, were analysed by immunohistochemistry and in situ reverse transcription-polymerase chain reaction (in situ RT-PCR). Fas gene mutation in the death domain was also examined. Fas and FasL were expressed in all hepatoblastomas analysed. Twenty (87 per cent) and 18 (78 per cent) cases of hepatoblastoma were positive for sFas mRNA and FAP-1, respectively, but none of the hepatoblastomas expressed bcl-2. Mutation in the death domain of the Fas gene was not found in hepatoblastomas. Taken together, these findings demonstrated that Fas, a death receptor, and its ligand are co-expressed in hepatoblastomas in vivo, but some inhibitors of Fas-mediated apoptosis are also expressed in these tumours. These results suggest that it is probably due to the action of inhibitory molecules of the Fas pathway that the tumour cells of hepatoblastomas do not kill themselves in an autocrine-driven cycle and that in this manner hepatoblastomas avoid apoptosis., (Copyright 1999 John Wiley & Sons, Ltd.)

Objective: To characterize the Fas-Fas ligand system, a main apoptotic pathway, in transitional cell carcinoma (TCC) of the urinary bladder, by analysing the expression of Fas and Fas ligand (FasL) in TCC samples., Materials and Methods: Archival paraffin-embedded tissues from 37 patients with TCC were analysed by immunohistochemistry to determine Fas and FasL expression., Results: Fas and FasL were detected on the cell surface and cytoplasm of respectively 34 (92%) and all cases analysed. The expression of Fas and FasL did not differ with the cytological grade of TCC., Conclusion: The high expression of FasL in TCC, reported for the first time in the present study, suggests that FasL may contribute to the immune escape of TCC through killing Fas-bearing lymphocytes. Co-expression of Fas with FasL also suggests that TCC may have pathways resistant to Fas-mediated autocrine cell suicide.

Fas, a cell surface receptor and member of the tumour necrosis factor receptor superfamily, induces apoptosis upon oligomerization by its ligand (Fas ligand: FasL). Detailed studies have revealed that Fas is broadly expressed in normal human tissues, but relatively little is known about the range of cell types capable of expressing FasL. The aim of this study was to determine the in vivo patterns of expression of Fas and FasL in human skin tissues. Immunohistochemistry was performed using paraffin-embedded samples of normal and neoplastic skin tissues. In normal skin, FasL was expressed in the epidermis, sebaceous glands, sweat glands and outer root sheath of the hair. In squamous cell carcinomas (SCC), all cases analysed expressed FasL at high levels, whereas 60% of basal cell carcinomas (BCC) were positive for FasL. Expression of Fas in normal skin was observed in the basal and spinous layers of the epidermis, the outer root sheath of the hair, and the sebaceous glands. Expression of Fas was observed in all the SCC tested and none of the BCC tested. Expression of FasL by normal cells and tumour cells in skin tissue, demonstrated for the first time in the present study, may provide an important clue to understanding skin physiology, and immune evasion of skin tumours.