Caspase 1 degrades p40. (A) Schematic
representation of caspase 1 cleavage site in p40. (B)
p53-expressing lysates contain caspase 1, which cleaves p40 in
vitro. Total lysates from SaOs2 cells infected with Ad-p53 were
incubated with [35S]p40 or 35S-labeled
mutated p40 (YVEA185) in the absence or presence of 5 μM
each caspase substrate–inhibitors (for caspase 1, Ac-YVAD-CHO; caspase
3, Ac-DEVD-CHO; caspase 6, Ac-VEID-CHO; caspase 8, Ac-IETD-CHO).
(C) Purified caspase 1 cleaves p40 in
vitro. For protease cleavage, [35S]p40 or
35S-labeled mutated p40 (YVEA) polypeptides were incubated
with purified caspases for 2 h at 37°C and analyzed by
SDS/PAGE followed by autoradiography. p40 (residues 1–356, 44 kDa)
is cleaved in half, generating two fragments (residues 1–184 and
185–356) with an apparent molecular mass of 20 kDa.