Fasexpressing

Fasexpressing refers to cells that express the Fas receptor (CD95) on their surface. Fas is a member of the tumor necrosis factor receptor (TNFR) superfamily and plays a central role in the extrinsic pathway of apoptosis when engaged by its ligand FasL (CD95L) or by agonistic anti-Fas antibodies.

The signaling mechanism of Fasexpressing cells involves the binding of FasL to Fas, which promotes trimerization of the receptor and recruitment of the adaptor protein FADD. This assembly forms the death-inducing signaling complex (DISC), leading to activation of initiator caspases such as caspase-8 and caspase-10 and the execution of apoptosis. In some cellular contexts, Fas signaling can also trigger non-apoptotic pathways, including NF-kB, MAPK, or PI3K/Akt signaling, potentially promoting survival, proliferation, or differentiation depending on factors like receptor density and the presence of regulatory proteins such as cFLIP.

Distribution and regulation of Fas expression vary by tissue and condition. Fas is constitutively expressed on many immune cells, particularly activated T cells, and on hepatocytes; inflammatory signals can upregulate Fas expression. In cancer, Fas expression can be altered in opposing ways: some tumors downregulate Fas to evade apoptosis, while others maintain or upregulate Fas but resist signaling through downstream inhibitors or mutations in caspases.

Detection and clinical relevance: Fas expression is typically measured by flow cytometry using anti-Fas (CD95) antibodies or by assessing CD95 mRNA levels via RT-PCR. Clinically, Fas expression and signaling integrity influence autoimmune disease susceptibility, transplant rejection, and tumor immune evasion. Therapeutic approaches may aim to modulate Fas–FasL interactions to induce tumor cell death or to protect normal tissues from unwanted apoptosis.