Does calcium contribute to the CD95 signaling pathway? Pierre Vacher a,b , Nadine Khadra c,d , Anne-Marie Vacher a,b , Emilie Charles a,b , Laurence Bresson-Bepoldin a,b and Patrick Legembre c,d Death receptors play a crucial role in immune surveillance and cellular homeostasis, two processes circumvented by tumor cells. CD95 (also termed Fas or APO1) is a transmembrane receptor, which belongs to the tumor necrosis factor receptor superfamily, and induces a potent apoptotic signal. Initial steps of the CD95 signal take place through protein/protein interactions that bring zymogens such as caspase-8 and caspase-10 closer. Aggregation of these procaspases leads to their autoprocessing, to the release of activated caspases in the cytosol, which causes a caspase cascade, and to the transmission of the apoptotic signal. In parallel, CD95 engagement drives an increase in the intracellular calcium concentration (Ca 2+ ) i whose origin and functions remain controversial. Although Ca 2+ ions play a central role in apoptosis/necrosis induction, recent studies have highlighted a protective role of Ca 2+ in death receptor signaling. By the light of these findings, we discuss the role of Ca 2+ ions as modulators of CD95 signaling. Anti-Cancer Drugs 00:000–000  c 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins. Anti-Cancer Drugs 2011, 00:000–000 Keywords: apoptosis, calcium, CD95, immunology, signaling a INSERM U916, Institut Bergonie ´, 229 cours de l’Argonne, Cedex, b University of Bordeaux-2, 146 rue Le ´ o Saignat, Bordeaux, c IRSET/EA 4427 and d University of Rennes-1, 2 Avenue du Professeur Le ´ on Bernard, Rennes, France Correspondence to Dr Patrick Legembre, Universite ´ de Rennes-1, IRSET, (Institut de Recherche en Sante ´, Environnement et Travail)/EA-4427, 2 av Prof Le ´ on Bernard, Rennes, Cedex 35043, France Tel: +33 2 2323 4807; fax: +33 2 2323 4794; e-mail: patrick.legembre@inserm.fr Received 27 September 2010 Revised form accepted 30 December 2010 So-called death receptor CD95 CD95 (APO1/Fas) has been initially cloned as a death receptor [1]. The receptor CD95 is resolved in an SDS- polyacrylamide gel electrophoresis weighing approxi- mately 40 and 50 kDa and this transmembrane receptor belongs to the tumor necrosis factor receptor superfamily [2]. In contrast to the ubiquitously expressed CD95, its cognate ligand, CD95L shows a restricted pattern of expression and is expressed at the surface of activated T-lymphocytes [3] and natural killer cells [4] in which it plays a pivotal role in the elimination of transformed and infected cells and in immune homeostasis. This ligand can be cleaved by metalloproteases, such as MMP3 [5], MMP7 [6], MMP9 [7], or ADAM10 [8,9] and is released in the connective tissue and blood circulation. In contrast to the membrane-bound CD95L, cleaved CD95L, which is found increased in certain patients affected by cancers, does not trigger any apoptotic signal [10,11] and its physiopathological role remains unknown. Recently, it has been shown using a knock-in mouse model, which cleaved CD95L, may aggravate autoimmune disorders and tumor occurrence through the activation of the nuclear factor-kB proinflammatory signal [12]. In agree- ment with the notion that the couple CD95L/CD95 may exert nonapoptotic functions, a recent study pinpointed that CD95 engagement contributed to liver and ovarian carcinogenesis through the activation of the c-Jun N- terminal kinase (JNK) signaling pathway in mouse xenograft models and tissue-specific CD95 knockout mice [13]. In addition, CD95 stimulation promotes liver regeneration after partial hepatectomy [14], raising the possibility that in a certain context, CD95 may exert dominant pro-proliferative activities. At present, the main challenges remain to decipher how the death receptor CD95 can be converted into a pro-oncogenic receptor and to show that this process can occur in humans. The CD95-mediated apoptotic signal: protein/protein interactions CD95 is a type I transmembrane protein whose intracellular region encompasses a domain termed death domain (DD). Similar to the death receptors belonging to the tumor necrosis factor receptor family, CD95 does not exhibit any enzymatic activity and the transmitted signal is ignited through the formation of a plasma mem- brane platform that promotes protein/protein interactions [1,15]. Indeed, on the binding of membrane-bound CD95L, CD95 is clustered to form nanometer-scaled structures called signaling protein oligomerization trans- duction structures [16] and/or SDS-stable microaggre- gates [17,18] and then, to constitute micrometer-sized platform called CD95-CAP [19]. Meanwhile, CD95 manifests modifications of its DD conformation, which allows the recruitment of the adapter protein Fas- associating protein with DD (FADD) [20], which in turn recruits zymogens named caspase-8 and caspase-10. This complex is called the death-inducing signaling complex (DISC) [21] and it includes factors such as cellular FADD-like interleukin-1 b-converting enzyme-inhibitory protein (c-FLIP) [22,23] and PED/PEA-15 [24], which hamper the ignition of the apoptotic signal. According to the efficiency of the DISC formation, cells have been Review article 1 0959-4973  c 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins DOI: 10.1097/CAD.0b013e32834433ea CE: Lasya ED: Asra Op: CSR CAD: LWW_CAD_200821