Regulated cell death is essential both for maintaining healthy tissue as well as fighting infection and disease. Caspases are cysteine-aspartic acid endopeptidases that are involved in regulating cell death. One such caspase enzyme, called caspase-8, controls the entry of cells into two forms of regulated cell death: apoptosis and necroptosis. When caspase-8 is active, the cell will undergo apoptosis, while when inactive, the cell will undergo necroptosis. Both cell death types are highly‑ordered processes, but they differ in subsequent immune response. Biological factors that control the switch between these two processes are poorly understood. Our group recently discovered that caspase-8 can be inactivated by oxidation through the biological oxidant HOSCN; oxidation leads to cells undergoing necroptosis.1 Moreover, we found that caspase-8 oxidation leads to a dramatic structural transformation into large, ordered, fibrillar structures.
Using recombinant protein, we are studying the structural transition that occurs upon oxidation. Preliminary data shows that oxidized caspase-8 is Thioflavin-T positive which is indicative of beta‑amyloid fibrillar structures. Amyloid fibrils are a particular type of ordered protein aggregate that are known to be involved in many neurodegenerative diseases. More recently, aggregates of this kind have been found to be involved in normal cell signaling processes.2 Using a combination of biophysical techniques and human cell-based models we have found that this oxidation is highly specific and resistant to reduction. This suggests a functional role for caspase-8 aggregation in allowing necroptosis to occur at sites of inflammation.