Fas receptor (TNFRSF6) (CD95)

The Fas receptor (TNFRSF6/CD95), also known as APO-1, is a type I transmembrane protein in the tumor necrosis factor receptor superfamily that primarily mediates programmed cell death (apoptosis) upon binding its trimeric ligand, FasL (CD95L). It features an extracellular cysteine-rich domain for ligand binding, a transmembrane domain enabling homotrimerization via proline motifs, and an intracellular death domain that recruits the adaptor FADD to form the death-inducing signaling complex (DISC), activating caspase-8 and downstream effectors like caspase-3/7 or mitochondrial pathways via Bid. Beyond apoptosis, Fas signaling can trigger non-canonical pathways including necroptosis (via RIPK1/3-MLKL), NF-κB for inflammation and survival, JNK/MAPK for stress responses, and PI3K/AKT for proliferation and migration, with context-dependent outcomes influenced by regulators like c-FLIP or XIAP. Encoded by the FAS gene on chromosome 10q24.1, it plays key roles in immune homeostasis, such as peripheral tolerance and T-cell regulation, but dysregulation contributes to cancer (as suppressor or promoter), autoimmune diseases, and immune pathologies. Therapeutically, agonistic antibodies targeting Fas aim to induce apoptosis in tumors but face challenges like hepatotoxicity from off-target cell death and variable potency due to affinity effects on clustering. Overall, Fas represents a prototypical death receptor with complex signaling balancing cell survival and death.

Other names

FasFasRAPO-1APTAPO-1 antigenapoptosis antigen 1tumor necrosis factor receptor superfamily member 6TNFRSF6

Ligand-induced trimerization leading to DISC formation with FADD and caspase-8 activation for apoptosis; antibody-mediated clustering mimicking FasL to trigger apoptosis; inverse affinity-potency correlation in some agonist antibodies