IDENTIFICATION OF AN INTERLEUKIN-1-BETA CONVERTING ENZYME-LIKE ACTIVITY THAT INCREASES UPON TREATMENT OF P19 CELLS WITH RETINOIC ACID AS THE PROTEASOME

We examined changes in proteinase activities in P19 embryonal carcinom a cells during retinoic acid-induced differentiation. The interleukin- 1 beta converting enzyme (ICE)-like Ac-YVAD-MCA hydrolytic activity wa s increased about 6-fold by treatment with retinoic acid, This activit y was inhibited by N-ethylmaleimide and Ac-WAD-H but not by E-64, EDTA , PIMSF, or amastatin. The ICE-like activity in P19 cells eluted as a single peak just after the void volume on gel filtration. No ICE-like activity was observed at a molecular mass of 30-50 kDa. Enzymatic puri fication, Western blot analysis, and an immunoabsorption study demonst rated that the ICE-like activity in P19 cells is caused by the proteas ome, and is stimulated during retinoic acid-induced differentiation, T he proteasome purified from mouse liver also cleaved Ac-YVAD-MCA. Thes e results strongly suggest that the proteasome is a major ICE-like pro teinase in P19 cells and may be involved in the neural differentiation and the apoptotic pathway.