Apoptotic cells detach due to the inactivation of this

The correct option is FAK.

To understand why this is the correct answer, let us break down the molecular mechanisms of cell adhesion and how apoptosis affects these processes step-by-step:

1. What is FAK (Focal Adhesion Kinase)?
Focal Adhesion Kinase (FAK) is a cytoplasmic tyrosine kinase that plays a pivotal role in integrating signals from integrins (cell surface receptors) and the extracellular matrix (ECM). It is localized at focal adhesions, which are specialized sub-cellular structures that physically anchor a cell to its surrounding extracellular substrate.

2. The Role of FAK in Cell Survival and Adherence
Under normal physiological conditions, active FAK transmits survival signals (often referred to as anchorage-dependent survival signaling) into the cell. This signaling prevents a form of programmed cell death known as anoikis, which is apoptosis induced by the loss of cell attachment. As long as FAK remains active, the cell maintains its cytoskeletal structure and remains firmly attached to the substrate.

3. FAK Inactivation during Apoptosis
When a cell undergoes apoptosis (programmed cell death), executioner caspases (such as caspase-3 and caspase-6) are activated. These caspases target and cleave key structural and signaling proteins to dismantle the cell in an orderly fashion. FAK is a major substrate for caspase-mediated cleavage during early apoptosis. Cleavage of FAK leads to its functional inactivation and disassembly from focal adhesion complexes.

4. The Consequence: Cell Detachment
Once FAK is inactivated and cleaved, the anchorage-dependent signaling cascade is disrupted. The focal adhesion complexes break down, causing the actin cytoskeleton to reorganize and retract. Consequently, the apoptotic cell loses its physical connection to the extracellular matrix, rounds up, and detaches from the substrate or neighboring cells. This detachment is a classic morphological hallmark of apoptotic cells in culture.