Apoptosis occurs daily in the human body for maintaining homeostasis by rapidly remove unwanted cells. Inefficient removal of apoptotic cells has been linked to inflammation, autoimmunity, cancer and infection. Apoptotic cells can generate smaller membrane-bound vesicles called apoptotic bodies (ApoBDs), which is a critical process for efficient clearance of apoptotic materials. Surprisingly, the machinery of ApoBD formation and importance of apoptotic cell disassembly are still poorly understood. The aim of current work is therefore to identify novel regulators of apoptotic cell disassembly to further understand the molecular mechanism of ApoBD formation and the importance of this process. To define new regulators of apoptotic cell disassembly, GSDME and Hook3, were examined in our study.
Recently, caspase-3 cleaved GSDME was shown to regulate the progression of apoptotic cells into secondary necrotic cells following membrane permeabilisation. So, there is a possibility that the occurrence of a downstream process of caspase-3 would drive membrane permeabilisation and negatively regulate apoptotic cell disassembly. Promoting cell disassembly could favour release the proinflammatory intracellular contents and interfere efficient clearance of ApoBDs. However, our results showed that loss of GSDME expression in both Jurkat T cells and THP-1 monocytes did not inhibit the progression of apoptotic cells into secondary necrotic cells or promote cell disassembly during apoptosis.
Another potential regulator, Hook3, a cytoplasmic protein that binds microtubules and organelles, was found to be enriched in ApoBDs and as caspase substrate during apoptosis. To examine whether Hook3 is essential for ApoBD formation, Hook3 knockout cells were generated. However, knockout of Hook3 in both human Jurkat T cells and monocytic THP-1 cells did not affect ApoBD formation.
Taken together, both GSDME and Hook3 are not regulators of cell disassembly in our cell models during apoptosis.