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Introduction to Apoptosis (Part Five)

By: Lionel Valenzuela Perez

activation of caspases

Apoptosis triggered by external signals: extrinsic or receptor pathway death

Fas and TNF receptors (receptor of tumor necrosis factor) are integral membrane proteins with receptor function domains exposed on the cell surface .

Binding of FasL death signaling molecules (Fas ligand) and TNF (tumor necrosis factor) to their respective receptors transmit a signal to the cytoplasm, which determines the activation of caspase 8 (an initiator caspase as caspase 9), which initiates a proteolytic cascade activating caspases that leads to phagocytosis of the cell.

When cytotoxic T cells, bind to target cells (eg virus infected cells or tumor cells to be destroyed), produce more FasL on their surface. By increasing the number FasL, increased binding to the Fas receptor on the target cell. The Fas receptor, activated by binding to FasL, triggers a signal that causes apoptosis.