L-2,5-dihydrophenylalanine, an inducer of cathepsin-dependent apoptosis inhuman promyelocytic leukemia cells (HL-60)

L-2,5-Dihydrophenylalanine (DHPA), a phenylalanine analogue, induced apopto sis in human promyelocytic leukemia cells (HL-60). This apoptosis was demon strated by morphological changes of the cells, such as fragmentation of nuc lei and chromatin condensation, and by some evidence found in biochemical a nalysis, such as DNA ladder and activation of caspase 3. The DHPA-induced a poptosis was prevented by a pan-caspase inhibitor, Z-VAD-fmk, and a cystein e protease inhibitor, E-64d, which inhibits calpains and cathepsin B and L. A calpain inhibitor, Z-LL-H, did not affect this apoptosis. A cathepsin B specific inhibitor, CA074-Me, prevented only chromatin condensation. Howeve r, E-64d and a cathepsin L specific inhibitor, Z-FY(t-Bu)-dmk, protected th e cells from both chromatin condensation and oligonucleosomal DNA fragmenta tion. As proceeding to the apoptotic process, the activities of both cathep sin B and L increased gradually. These results indicated that DHPA was an i nducer of cathepsin-dependent apoptosis in HL-60 cells.