Which initiator caspase is activated first in the EXTRINSIC (death receptor) pathway of apoptosis after ligand binding to its receptor?
- A Caspase-9
- B Caspase-8 ✓
- C Caspase-3
- D Caspase-12
Correct answer: B. Caspase-8
Explanation
Binding of Fas ligand or TNF to death receptors recruits FADD and procaspase-8 to form the death-inducing signaling complex (DISC). Procaspase-8 is activated by induced proximity and then cleaves executioner caspases such as caspase-3. Caspase-9 is the initiator of the intrinsic mitochondrial pathway activated within the apoptosome, and caspase-3 is an executioner, not an initiator.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.