Proapoptotic BAX and BAK control multiple initiator caspases

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• The intrinsic apoptotic pathway is crucial for programmed cell death.
• BAX and BAK proteins are key regulators of this pathway, acting at mitochondria and the endoplasmic reticulum (ER).
• The necessity of BAX and BAK for caspase activation under intrinsic stress remains unclear.

Purpose of the Study:

• To investigate whether caspases can be activated by intrinsic apoptotic signals independently of BAX and BAK.
• To determine the role of BAX and BAK in initiating the intrinsic apoptotic cascade.

Main Methods:

• Utilized Bax(-/-)Bak(-/-) doubly deficient (DKO) cells.
• Applied organelle-specific intrinsic stress signals, including DNA damage and ER stress.
• Monitored the activation of CARD-containing initiator caspases (CASP-1, -2, -9, -11, -12) and effector caspases (CASP-3, -7).
• Assessed the effect of BCL-2 overexpression in DKO cells.

Main Results:

• No activation of initiator caspases (CASP-1, -2, -9, -11, -12) was detected in DKO cells following intrinsic stress.
• No activation of effector caspases (CASP-3, -7) was observed in DKO cells.
• BCL-2 overexpression did not alter the inherent resistance of DKO cells to DNA damage and ER stress.
• Results indicate that BAX and BAK are indispensable for initiating caspase activation in the intrinsic apoptotic pathway.

Conclusions:

• BAX and BAK are essential gateways for caspase activation in the intrinsic apoptotic pathway.
• Intrinsic apoptotic signals do not appear to activate caspases in the absence of BAX and BAK.
• The study refutes a BAX, BAK-independent intrinsic apoptotic pathway for initiator caspase activation.