Serial in vivo loss and in vitro gain of Fas expression and function in human cancerous pancreatic duct cells

Abstract

Recent studies have shown the involvement of the Fas system (Fas receptor and its ligand FasL) in cancerous processes. The absence or downregulation of Fas, reported in the majority of human tumors, conflicts with its presence in cancerous cells from the same tumors but maintained in vitro. Recently, the eventual role of environmental factors in the loss of Fas expression, or in the in vivo selection of a Fas-negative cell population has been suggested. We determined the Fas expression and function in the Capan-1 human cancerous pancreatic duct cells over 2 successive passages in vivo separated by a period of 10-20 passages in vitro. We showed that Capan-1 cells express Fas and are sensitive to Fas-mediated apoptosis when maintained in vitro. When these cells were xenografted into nude mice the expression of Fas was lost in the majority of the tumors. Culture of tumor-derived cells exhibited that they became Fas-positive and sensitive to Fas-mediated apoptosis after a short period in vitro. The loss/gain of Fas was reproduced after re-explantation and re-culture of these Fasexpressing cells. Key words: Fas; Fas-mediated apoptosis; human pancreatic cancer; cell culture; xenograft The Fas/FasL system constitutes one of the main systems mediating the cytotoxicity of T cells and regulating immune responses, tissue development and homeostasis. 1 FasL and its receptor Fas (APO-1, CD95) are members of the tumor necrosis factor and tumor necrosis factor receptor family, respectively. Activation of Fas by its ligand 2 or by an agonistic antibody 3 induces programmed cell death (apoptosis) in functional Fas-bearing cells through a distinct cytoplasmic motif called 'Death Domain' (DD), 4,5 which interacts with FADD. 6,7 The recruitment of FADD allows the connection of the Fas receptor to cysteine proteases (Caspases) via FLICE. 8,9 Fas and FasL are highly expressed in activated T lymphocytes and natural killer cells. 1 However, these proteins are also constitutively expressed in many non-lymphoid tissues including several epithelial cell types. 10,11 Malignant cells possess several strategies to evade immune surveillance such as (i) low level expression of target antigens recognized by cytotoxic T lymphocytes, 12 (ii) decrease or loss of HLA (human leukocyte antigen) Class I or Class II molecule expression, which is required for antigen presentation 13,14 and (iii) suppression of immune cell function by secreting factors such as transforming growth factor-b. 15 Interestingly, tumor cells have developed another strategy (the Fas-counter-attack), 16 whereby loss of Fas expression or function and aberrant expression of FasL by tumor cells may contribute to the evasion of host immune surveillance by triggering apoptosis of tumor-specific T lymphocytes. 17,18 The loss or downregulation of Fas expression leading to Fasmediated apoptosis resistance has been reported in a variety of malignancies including cancers from: lung, 19,20 colon, 21 Human pancreatic cancer is the fourth (male) and fifth (female) leading cause of cancer de...

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“…FAS is a member of the TNF-receptor superfamily and contains a death domain. FAS has been shown to play a central role in the physiological regulation of programmed cell death, and has been implicated in the pathogenesis of various malignancies and diseases of the immune system (Hiraide et al 2005;Radfar et al 2005).…”

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New Aspects of Regulatory Signaling Pathways and Novel Therapies in Pancreatic Cancer

“…Fas expression and the sensitivity to Fas-mediated apoptosis in human pancreatic cell lines maintained in vitro, however, conflicts with recent findings indicating the mentioned absence or downregulation of Fas expression and function in most human solid tumors, including pancreatic malignancies [21]. There is also reduction in the Fas mRNAs expression in these tumor cells [21]. Thus, they are resistant to Fas-mediated apoptosis, due to absence or weakness in membrane-Fas expression.…”

“…These Fas positive cells are sensitive to Fas-mediated apoptosis when maintained in monolayer cultures, in vitro [21]. Fas expression and the sensitivity to Fas-mediated apoptosis in human pancreatic cell lines maintained in vitro, however, conflicts with recent findings indicating the mentioned absence or downregulation of Fas expression and function in most human solid tumors, including pancreatic malignancies [21]. Specifically, when these cells are xenografted into nude mice, the expression of Fas is lost in the majority of the tumors.…”