| Fas (CD95/Apo‑1) is a type‑I transmembrane death receptor that belongs to the TNF receptor superfamily and transduces extrinsic apoptotic signals when engaged by its trimeric ligand FasL (CD95L). Fas contains an extracellular ligand‑binding domain, a transmembrane segment, and an intracellular death domain that serves as a recruitment platform for homotypic interactions with the adaptor FADD, which in turn nucleates assembly of the death‑inducing signaling complex (DISC) through its own death domain and downstream death‑effector‑domain‑mediated recruitment of procaspase‑8. Ligand‑induced clustering of Fas brings multiple Fas molecules into close proximity, enabling formation of an oligomeric Fas–FADD death‑domain network that promotes caspase‑8 dimerization and activation within the DISC, initiating a downstream caspase cascade that includes cleavage and activation of effector caspases such as caspase‑3, ultimately leading to execution of apoptosis. In lymphocytes, this pathway is a key negative regulator of cell numbers, and loss‑of‑function mutations in Fas (lpr) or FasL (gld) result in accumulation of CD4‑CD8‑ double‑negative T cells, lymphadenopathy, and splenomegaly, underscoring the physiological role of Fas‑FasL signaling in immune homeostasis and lymphocyte turnover. Fas also contributes to non‑apoptotic outputs such as T‑cell activation and cytokine modulation in certain contexts, and its dysregulation is implicated in autoimmune and lymphoproliferative disorders as well as in tumor immune‑evasion strategies where FasL expression on malignant cells can delete Fas‑expressing lymphocytes. |
Lane 1: ACHN, Lane 2: HT1080
