ICF-LIKE PROTEASE (CASPASE) IS INVOLVED IN TRANSFORMING-GROWTH-FACTORBETA-1-MEDIATED APOPTOSIS IN FAO RAT HEPATOMA-CELL LINE

Transforming growth factor-beta(1) (TGF-beta(1)) arrests growth and/or stimulates apoptosis of a variety of cells. The biochemical pathways involved in the apoptotic processes, however, remain poorly defined. T GF-beta(1) induces DNA fragmentation together with morphological chang es, which are characteristic of apoptosis in the FaO rat hepatoma cell line. Histones were remarkably enriched in lysates of these cells dur ing TGF beta(1)-induced apoptosis. We identified U1-70 kd as a death s ubstrate which is cleaved following TGF-beta(1) treatment. The tetrape ptide caspase inhibitor valyl-alanly-aspartyl-(beta-O-methyl)-fluorome thyl ketone (ZVAD-FMK) prevented TGF beta(1)-induced apoptotic DNA fra gmentation and cleavage of the U1-70 kd protein, showing that caspase( s) are involved in TGF beta(1)-mediated apoptosis. To identify specifi c caspases involved in apoptosis induced by TGF-beta(1) in FaO cells, proteolytic activation of several of these caspases and their substrat es were studied as a function of time following TGF beta(1)-treatment. TGF beta(1)-treatment induced the progressive proteolytic processing of caspase-2 (ICH-1L/Nedd-2), whereas caspase-1 itself did not show an y cleavage from the precursor. Pretreatment with ZVAD-FMK abrogated th e maturation of caspase-2 and blocked the apoptotic progress. These re sults suggest that caspase-2, but not caspase-1, may play a crucial ro le in TGF beta(1)-induced apoptosis in these cells.