Death receptors are cell surface receptors that belong to the tumor necrosis factor receptor superfamily, the most well known members of which are tumor necrosis factor receptor 1, the CD95/Fas receptor, and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) 1 receptors DR4/TRAIL-R1 and DR5/TRAIL-R2 (for a review, see Ref. 1). Upon ligand-mediated oligomerization of CD95/Fas or TRAIL receptors, the Fas-associated death domain protein (FADD) attaches to the death receptor via homophilic death domain interactions. The death effector domain (DED) of FADD is in turn linked to the apoptotic machinery due to its affinity for the initiator caspases, procaspase-8 and procaspase-10. The close proximity of procaspase-8 molecules results in dimerization of the procaspases, the assembly of which forms an enzymatically active site (2, 3). This enzymatic activity induces serial cleavages converting the zymogen into p10 and p18 fragments, forming the proteolytically active caspase-8 heterotetramer. In responsive cells, activated caspase-8 is then able to activate effector caspases thereby initiating apoptosis (for a review, see Ref. 4). In addition to the initiator caspases, the DED in FADD also interacts with the apoptosis modulator cellular FLICE-inhibitory protein (c-FLIP; Ref. 5), which exists as two splice variants, the long splice form of FLIP (FLIP L ) and the short splice form of FLIP (FLIP S ). Together with the activated death receptor, FADD, and caspase-8 and -10, the FLIP proteins form the core of the death-inducing signaling complex (DISC; Ref. 6), which also contains a number of other proteins, many of which seem to be involved in modulating death receptor signals (for a review, see Ref. 1). The DISC assembly with pro-and antiapoptotic proteins allows for control of death receptor signaling through a number of different routes. Consequently in addition to apoptosis, stimulation of the receptors may also lead to cell survival and proliferation. Modulation of the apoptotic pathway at the level of the activated receptor is required in situations when the extrinsic, but not the intrinsic, apoptosis pathway needs to be inhibited or when localized initiator caspase activity is required for specialized signaling functions. For example, caspase-8 activity is necessary for normal T cell development (7,8) and is probably acquired through complex regulation of anti-and proapoptotic proteins in the DISC. In addition, some malignant cells are able to convert death receptor stimulation into proliferative signals (9, 10). Therefore, active regulation of the DISC proteins, both transcriptional and post-translational, determines the outcome of death receptor stimulation.c-FLIP L and c-FLIP S have been characterized as specific inhibitors of death receptor-mediated apoptosis (for a review, see Ref. 11). c-FLIP L is homologous to caspase-8, consisting of two tandemly repeated DEDs and a catalytically inactive caspase-like domain. Although c-FLIP S shares most of its se-* This work was supported by the Academy of Finlan...

Invasive migration of carcinoma cells is a prerequisite for the metastatic dissemination of solid tumours. Numerous mechanisms control the ability of cancer cells to acquire a motile and invasive phenotype, and subsequently degrade and invade the basement membrane. Several genes that are up-regulated in breast carcinoma are responsible for mediating the metastatic cascade. Recent studies have revealed that the NFAT (nuclear factor of activated T-cells) is a transcription factor that is highly expressed in aggressive breast cancer cells and tissues, and mediates invasion through transcriptional induction of pro-invasion and migration genes. In the present paper we demonstrate that NFAT promotes breast carcinoma invasion through induction of GPC (glypican) 6, a cell-surface glycoprotein. NFAT transcriptionally regulates GPC6 induction in breast cancer cells and binds to three regulatory elements in the GPC6 proximal promoter. Expression of GPC6 in response to NFAT signalling promotes invasive migration, whereas GPC6 silencing with shRNA (small-hairpin RNA) potently blocks this phenotype. The mechanism by which GPC6 promotes invasive migration involves inhibition of canonical β-catenin and Wnt signalling, and up-regulation of non-canonical Wnt5A signalling leading to the activation of JNK (c-Jun N-terminal kinase) and p38 MAPK (mitogen-activated protein kinase). Thus GPC6 is a novel NFAT target gene in breast cancer cells that promotes invasive migration through Wnt5A signalling.