Phosphorylation of IκB-α inhibits its cleavage by caspase CPP32 in vitro

Abstract

IκB proteins function as direct regulators of Rel/NF-κB transcription complexes. We show that the cell-death protease CPP32 (caspase-3) in vitro specifically cleaved chicken and human IκB-α at a conserved Asp-Ser sequence. This cleavage site appears to be identical to the site at which chicken IκB-α is cleaved in vivo in temperature-sensitive v-Rel-transformed chicken spleen cells undergoing apoptosis. Other caspases, namely interleukin-1β converting enzyme (caspase-1) and Ich-1 (caspase-2), did not cleave IκB-α. CPP32 also cleaved mammalian IκB-β in vitro at the analogous Asp-Ser sequence. Cleavage of IκB-α by CPP32 was blocked by serine phosphorylation of IκB-α. Cleavage of IκB-α by a CPP32-like protease could generate a constitutive inhibitor of Rel transcription complexes. This report provides evidence for a direct biochemical interaction between the NF-κB signaling pathway and a cell-death protease signaling pathway.