Necroptosis | TNF-Alpha Signalling

Summary

This video explains the necroptosis signaling pathway, a programmed form of cell death independent of caspases. It begins with the binding of TNF-alpha to TNFR1 receptors on the cell membrane, triggering trimerization and activation of downstream signaling. Proteins like RIPK1 and CIAP play key roles in activating NF-kB, while C-FLIP inhibits apoptosis by inactivating Caspase-8. If apoptosis is blocked, RIPK3 activates MLKL, leading to membrane disruption and cell death. The video also highlights how TNFR1 interacts with riboflavin kinase to produce ROS, further contributing to necroptosis.

Takeaways

• 😀 Necroptosis is a programmed form of cell death, similar to apoptosis but independent of gas, and is mediated through the tumor necrosis factor receptor 1 (TNFR1).
• 😀 TNF alpha molecules bind to TNFR1 on the cell membrane, causing the receptors to trimerize, which initiates downstream signaling.
• 😀 The 'death domain' of TNFR1 is initially inhibited by a protein called SODD (silencer of death domain), but once TNF alpha binds, SODD leaves, allowing the signaling pathway to proceed.
• 😀 The activated death domain recruits several key proteins, including TRAF, RIPK1, and TRADD, which facilitate the next steps in the signaling cascade.
• 😀 Ubiquitination of RIPK1 and other proteins like CIAP (cellular inhibitor of apoptosis protein) takes place, which is essential for further activation of the pathway.
• 😀 The complex then recruits the LUBAC complex, which performs extended ubiquitination of RIPK1, RIPK3, and TRADD, ultimately leading to the activation of NF-κB pathway.
• 😀 NF-κB activation leads to the expression of c-FLIP, which plays a crucial role in regulating the necroptosis pathway.
• 😀 The c-FLIP molecule prevents apoptosis by inhibiting caspase-8, which otherwise would trigger the apoptotic pathway.
• 😀 If c-FLIP does not inhibit caspase-8, RIPK3 levels increase, which directly inactivates caspase-8 and proceeds the signaling toward necroptosis.
• 😀 In the final stages of necroptosis, RIPK1 and RIPK3 activate MLKL monomers, which oligomerize and form pores in the plasma membrane, leading to cell death.
• 😀 The process of necroptosis is further enhanced by the generation of reactive oxygen species (ROS) through interactions between TNFR1 and riboflavin kinase, which ultimately contribute to cell death.

Q & A

What is necroptosis and how does it differ from apoptosis?

Necroptosis is a programmed form of cell death that occurs independently of caspase activity, unlike apoptosis, which is a caspase-dependent process. Both are forms of regulated cell death, but necroptosis is triggered by different signaling pathways.

What role does TNFR1 play in necroptosis?

TNFR1 (Tumor Necrosis Factor Receptor 1) is essential for initiating the necroptosis pathway. It binds to TNF-alpha molecules, which triggers receptor trimerization and the activation of the death domain within the receptor, starting the signaling cascade.

What is the function of SODD in the TNFR1 signaling pathway?

SODD (Silencer of Death Domain) inhibits the death domain of TNFR1 in the resting state. When TNF-alpha binds to TNFR1, SODD is displaced, allowing the activation of the death domain and the initiation of downstream signaling in necroptosis.

How does cIAP contribute to necroptosis signaling?

cIAP (Cellular Inhibitor of Apoptosis Protein) binds to the receptor complex and promotes the ubiquitination of proteins like RIPK1 and cIAP itself. This leads to the activation of the NF-kB pathway, which plays a role in regulating apoptosis and necroptosis.

What is the role of NF-kB in necroptosis?

The NF-kB pathway, activated by the ubiquitination of RIPK1, promotes the expression of cFLIP-s proteins, which help inhibit apoptosis by preventing the activation of caspase-8, a crucial protein for apoptotic cell death.

How does cFLIP-s inhibit apoptosis in necroptosis?

cFLIP-s binds with caspase-8 and renders it inactive, thereby preventing apoptosis. This inhibition is crucial for allowing the necroptosis pathway to proceed instead of the apoptotic pathway.

What happens when cFLIP-s fails to inhibit caspase-8?

If cFLIP-s does not adequately inhibit caspase-8, higher levels of RIPK3 can phosphorylate and activate caspase-8, leading to apoptosis. In the case of necroptosis, the inhibition of caspase-8 is necessary to proceed with the cell death process.

What is the role of RIPK3 in necroptosis?

RIPK3 (Receptor Interacting Protein Kinase 3) is recruited and activated by RIPK1. It phosphorylates MLKL, causing MLKL monomers to oligomerize and translocate to the plasma membrane, where they form pores that lead to cell death.

How does MLKL contribute to cell death in necroptosis?

MLKL (Mixed-Lineage Kinase Domain-Like protein) is phosphorylated and oligomerizes, forming pores in the plasma membrane. These pores disrupt the membrane, allowing DAMPs and ROS to enter the cell, ultimately causing cell death.

What is the role of ROS in necroptosis?

ROS (Reactive Oxygen Species) are generated during necroptosis, contributing to cell damage. ROS production is facilitated by interactions between TNFR1 and proteins like NOX, and ROS further amplify the necroptotic process by damaging cellular structures.