title: Mechanism of apoptosis induced by a lysosomotropic agent, L-Leucyl-L-Leucine methyl ester.
abstract: Lysosomes are fundamental for cell growth, and thus inhibition of the lysosomal function often leads to cell death. L-Leucyl-L-leucine methyl ester (LeuLeuOMe) is a lysosomotropic agent that induces apoptosis of certain immune cells. LeuLeuOMe is taken up through receptor-mediated endocytosis, and then converted into (LeuLeu)n-OMe (n>3) by dipeptidyl peptidase I (DPPI) in lysosomes, which reportedly causes rupture of the lysosomes and DNA fragmentation. In this study we examined how lysosomal damage causes DNA fragmentation in LeuLeuOMe-treated HL-60 cells. When acridine orange was employed to monitor lysosomal membrane integrity, orange or red granular fluorescence was seen in normal cells. In contrast, LeuLeuOMe-treated cells showed orange, yellow or green cellular fluorescence all over the cytoplasm, suggesting that LeuLeuOMe induced a loss of lysosomal membrane integrity. The loss was inhibited by a DPPI inhibitor, GlyPheCHN2 (GFCHN2), but not by a caspase-3 inhibitor, Ac-DEVD-CHO, indicating that a condensation product was responsible for the loss. LeuLeuOMe also induced the activation of caspase-3-like protease and DNA fragmentation, both of which were inhibited by either GFCHN2 or Ac-DEVD-CHO. Therefore, the activation of caspase-3-like protease links the loss of lysosomal membrane integrity to DNA fragmentation during apoptosis induced by LeuLeuOMe.
authors.affiliation: Department of Biomolecular Science, Faculty of Science, Toho University, Funabashi, Chiba 274-8510, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Uchimoto
authors.forename: H
authors.initials: H
authors.lastname: Nohara
authors.forename: R
authors.initials: R
authors.lastname: Kamehara
authors.forename: M
authors.initials: M
authors.lastname: Iwamura
authors.forename: N
authors.initials: N
authors.lastname: Watanabe
authors.forename: Y
authors.initials: Y
authors.lastname: Kobayashi