execution phase of apoptosis

Definition

Target type: biologicalprocess

A stage of the apoptotic process that starts with the controlled breakdown of the cell through the action of effector caspases or other effector molecules (e.g. cathepsins, calpains etc.). Key steps of the execution phase are rounding-up of the cell, retraction of pseudopodes, reduction of cellular volume (pyknosis), chromatin condensation, nuclear fragmentation (karyorrhexis), plasma membrane blebbing and fragmentation of the cell into apoptotic bodies. When the execution phase is completed, the cell has died. [GOC:mtg_apoptosis, PMID:21760595]

The execution phase of apoptosis is a tightly regulated cascade of events that leads to the dismantling of the cell. It is characterized by the activation of a family of cysteine proteases called caspases, which cleave specific proteins within the cell, ultimately leading to its death. Here's a detailed breakdown of the process:

**Initiation:**

* The execution phase is initiated by activation of initiator caspases (caspase-8 and -9), typically triggered by the upstream apoptotic signaling pathways (intrinsic or extrinsic).

**Caspase Cascade:**

* Activated initiator caspases activate executioner caspases (caspase-3, -6, and -7) through proteolytic cleavage. This creates a cascading effect, amplifying the apoptotic signal.

**Executioner Caspase Activity:**

* Executioner caspases cleave numerous cellular substrates, leading to the dismantling of the cell. Some key targets include:
* **Nuclear lamins:** This disrupts the nuclear envelope and leads to the fragmentation of DNA.
* **Cytoskeletal proteins:** This results in cell shrinkage and the formation of apoptotic bodies.
* **Inhibitors of DNase:** This allows the activation of DNase, leading to DNA fragmentation.
* **Other proteins:** Executioner caspases can also cleave other proteins involved in cell signaling, adhesion, and other vital functions, contributing to the cell's demise.

**Cell Morphology Changes:**

* Apoptosis is characterized by distinct morphological changes:
* **Cell shrinkage:** The cell shrinks in size due to the breakdown of the cytoskeleton.
* **Nuclear fragmentation:** The nucleus condenses and fragments into smaller bodies.
* **Formation of apoptotic bodies:** The cell breaks down into membrane-bound vesicles called apoptotic bodies, containing fragments of cytoplasm and organelles.

**Phagocytosis:**

* Apoptotic bodies are recognized and engulfed by neighboring cells or phagocytes, ensuring that the cell's components are safely disposed of without triggering an inflammatory response.

**Overall, the execution phase of apoptosis is a highly orchestrated process that results in the controlled and silent removal of cells. It is essential for maintaining tissue homeostasis and eliminating damaged or unwanted cells.**'
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Proteins (10)

Compounds (504)