Protein kinase C-δ isoform mediates lysosome labilization in DNA damage-induced apoptosis

Abstract

Abstract.A lysosomal pathway, characterized by the partial rupture or labilization of lysosomal membranes (LLM) and cathepsin release into the cytosol, is evoked during the early events of 20-S-camptothecin lactone (CPT)-induced apoptosis in human cancer cells, including human histiocytic lymphoma U-937 cells. These lysosomal events begin rapidly and simultaneously with mitochondrial permeabilization and caspase activation within 3 h after drug treatment. Recently, in a comparative proteomics analysis performed on highlyenriched lysosomal extracts, we identified proteins whose translocation to lysosomes correlated with LLM induction after CPT treatment, including protein kinase C-‰ (PKC-‰).In this study, we show that the PKC-‰ translocation to lysosomes is required for LLM, as silencing its expression with RNA interference or suppressing its activity with the inhibitor, rottlerin, prevents CPT-induced LLM. PKC-‰ translocation to lysosomes is associated with lysosomal acidic sphingomyelinase (ASM) phosphorylation and activation, which in turn leads to an increase in ceramide (CER) content in lysosomes. The accumulation of endogenous CER in lysosomes is a critical event for CPT-induced LLM as suppressing PKC-‰ or ASM activity reduces both the CPTmediated CER generation in lysosomes and CPT-induced LLM. These findings reveal a novel mechanism by which PKC-‰ mediates ASM phosphorylation/activation and CER accumulation in lysosomes in CPT-induced LLM, rapidly activating the lysosomal pathway of apoptosis after CPT treatment.

The Neutral Sphingomyelinase 2 Is Required to Polarize and Sustain T Cell Receptor Signaling

“…Novel (PKCθ and PKCδ) and atypical (PKCζ) PKC isoforms are important in T cell polarization ( 14 ) and both PKCδ and PKCζ are ceramide effectors ( 52 ). To reveal whether they are generally subjected to NSM-dependent regulation (independently of TCR signaling) in T cells, their activation after PMA/ionomycin stimulation was analyzed in parental and Jurkat-ΔNSM cells.…”