Involvement of caspase-4 in endoplasmic reticulum stress-induced apoptosis and Abeta-induced cell death

Recent studies have suggested that neuronal death in Alzheimer's disease or ischemia could arise from dysfunction of the endoplasmic reticulum (ER). Although caspase-12 has been implicated in ER stress-induced Apoptosis and amyloid-beta (Abeta)-induced Apoptosis in rodents, it is controversial whether similar mechanisms operate in humans. We found that human caspase-4, a member of Caspase-1 subfamily that includes caspase-12, is localized to the ER membrane, and is cleaved when cells are treated with ER stress-inducing reagents, but not with other apoptotic reagents. Cleavage of caspase-4 is not affected by overexpression of Bcl-2, which prevents signal transduction on the mitochondria, suggesting that caspase-4 is primarily activated in ER stress-induced Apoptosis. Furthermore, a reduction of caspase-4 expression by small interfering RNA decreases ER stress-induced Apoptosis in some cell lines, but not other ER stress-independent Apoptosis. Caspase-4 is also cleaved by administration of Abeta, and Abeta-induced Apoptosis is reduced by small interfering RNAs to caspase-4. Thus, caspase-4 can function as an ER stress-specific Caspase in humans, and may be involved in pathogenesis of Alzheimer's disease.