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Macrophage-mediated clearance of cells undergoing caspase-3-independent death
Abstract:
Little is known of the functions of caspases in mediating the surface changes required for phagocytosis of dying cells. Here we investigate the role played by the effector caspase, caspase-3 in this process using the caspase-3-defective MCF-7 breast carcinoma line and derived caspase-3-expressing transfectants. Our results indicate that, while certain typical features of apoptosis induced by etoposide--namely classical morphological changes and the ability to degrade DNA into oligonucleosomal fragments - are caspase-3-dependent, loss of cell adhesion to plastic and the capacity to interact with, and to be phagocytosed by, human monocyte-derived macrophages - both by CD14-dependent and CD14-independent mechanisms--do not require caspase-3. Furthermore, both etoposide-induced caspase-3-positive and -negative MCF-7 cells suppressed proinflammatory cytokine release by macrophages. These results demonstrate directly that cell surface changes that are sufficient for anti-inflammatory clearance by human macrophages can be regulated independently of stereotypical features of the apoptosis programme that require caspase-3.
Insights
Caspase-3 is not required for dying cells to lose adhesion or be phagocytosed by macrophages. This suggests anti-inflammatory clearance mechanisms can operate independently of typical apoptosis features.
Area of Science:
- Cell Biology
- Immunology
- Biochemistry
Background:
- Caspases are key mediators of apoptosis, but their role in cell surface changes for phagocytosis is unclear.
- Understanding these mechanisms is crucial for regulating immune responses to dying cells.
Purpose of the Study:
- To investigate the role of effector caspase-3 in mediating surface changes for phagocytosis of dying cells.
- To determine if caspase-3 is essential for macrophage interaction and phagocytosis of apoptotic cells.
Main Methods:
- Utilized caspase-3-defective MCF-7 breast carcinoma cells and caspase-3-expressing transfectants.
- Analyzed etoposide-induced apoptosis features, including morphological changes, DNA fragmentation, cell adhesion, and interaction with macrophages.
- Assessed the impact of MCF-7 cells on proinflammatory cytokine release by macrophages.
Main Results:
- Caspase-3 was essential for classical apoptosis features like DNA fragmentation and morphological changes.
- Loss of cell adhesion and phagocytosis by macrophages (CD14-dependent and -independent) did not require caspase-3.
- Both caspase-3-positive and -negative MCF-7 cells suppressed macrophage proinflammatory cytokine release.
Conclusions:
- Cell surface changes facilitating anti-inflammatory clearance by macrophages can be regulated independently of caspase-3-dependent apoptosis.
- These findings decouple stereotypical apoptosis from efferocytosis and anti-inflammatory signaling.