2017/07/29 by Urška Repnik, Marita Borg Distefano, Martin Speth +5 · 1 voice
Biochemistry, Genetics and Molecular Biology · Immunology and Microbiology · Medicine · #Autophagy in Disease and Therapy #Cell death mechanisms and regulation #Toxoplasma gondii Research Studies
paper · doi:10.1242/jcs.204529
openalex publication_date 2017/07/29 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/31
L-leucyl-L-leucine methyl ester (LLOMe) induces apoptosis, which is thought to be mediated by release of lysosomal cysteine cathepsins from permeabilized lysosomes into the cytosol. Here, we demonstrated in HeLa cells that apoptotic as well as sub-apoptotic concentrations of LLOMe caused rapid and complete lysosomal membrane permeabilization (LMP), as evidenced by loss of the proton gradient and release into the cytosol of internalized lysosomal markers below a relative molecular mass of 10,000. However, there was no evidence for the release of cysteine cathepsins B and L into the cytosol; rather they remained within lysosomes, where they were rapidly inactivated and degraded. LLOMe-induced adverse effects, including LMP, loss of cysteine cathepsin activity, caspase activation and cell death could be reduced by inhibition of cathepsin C, but not by inhibiting cathepsins B and L. When incubated with sub-apoptotic LLOMe concentrations, lysosomes transiently lost protons but annealed and re-acidified within hours. Full lysosomal function required new protein synthesis of cysteine cathepsins and other hydrolyses. Our data argue against the release of lysosomal enzymes into the cytosol and their proposed proteolytic signaling during LLOMe-induced apoptosis.