PHOSPHORYLATION OF I-KAPPA-B-ALPHA INHIBITS ITS CLEAVAGE BY CASPASE CPP32 IN-VITRO

I kappa B proteins function as direct regulators of Rel/NF-kappa B tra nscription complexes. We show that the cell-death protease CPP32 (casp ase-3) in vitro specifically cleaved chicken and human I kappa B-alpha at a conserved Asp-Ser sequence. This cleavage site appears to be ide ntical to the site at which chicken I kappa B-alpha is cleaved in vivo in temperature-sensitive v-Rel-transfarmed chicken spleen cells under going apoptosis. Other caspases, namely interleukin-1 beta-converting enzyme (caspase-1) and Ich-1 (caspase-2), did not cleave I kappa B-alp ha. CPP32 also cleaved mammalian I kappa B-beta in vitro at the analog ous Asp-Ser sequence. Cleavage of I kappa B-alpha by CPP32 was blocked by serine phosphorylation of I kappa B-alpha. Cleavage of I kappa B-a lpha by a CPP32-like protease could generate a constitutive inhibitor of Rel transcription complexes. This report provides evidence for a di rect biochemical interaction between the NF-kappa B signaling pathway and a cell-death protease signaling pathway.