The lysosome-associated apoptosis-inducing protein containing the pleckstrin homology (PH) and FYVE domains (LAPF), representative of a novel family of PH and FYVE domain-containing proteins, induces caspase-independent apoptosis via the lysosomal-mitochondrial pathway (Publication with Expression of Concern. See vol. 295, pg. 8877, 2020) (Withdrawn Publication. See vol. 296, 2021) (Withdrawn Publication. See vol. 296, 2021)

Lysosomes have recently been identified as important apoptotic signal integrators in response to various stimuli. Here we report the functional characterization of LAPF, a novel lysosome-associated apoptosis-inducing protein containing PH and FYVE domains. LAPF is a representative of a new protein family, the Phafins (protein containing both PH and FYVE domains), which consists of 14 unidentified proteins from various species. Overexpression of LAPF in L929 cells induces apoptosis and also increases cell sensitivity to TNF alpha-induced apoptosis, concomitant with its translocation to lysosomes. Two mutants of LAPF, either lacking the PH or FYVE domain, failed to induce cell death and translocate to lysosomes, suggesting that both domains are required for its apoptosis- inducing activity and relocation. We demonstrate that LAPF may induce apoptosis via the following steps: LAPF translocation to lysosomes, lysosomal membrane permeabilization (LMP), release of cathepsin (cath) D and L, mitochondrial membrane permeabilization (MMP), release of apoptosis- inducing factor (AIF), and caspase-independent apoptosis. The cath D-specific inhibitor attenuates LAPF-induced apoptosis, indicating a pivotal role of lysosomes in LAPFinitiated apoptosis. We also demonstrate that the lysosomal pathway was employed in the typical apoptotic model in which high dose TNF alpha was used to stimulate L929 cells. Silencing of LAPF expression by small RNA interference protected L929 cells from hTNF alpha-induced apoptosis by impairing hTNF alpha-triggered LMP and MMP. Therefore, LAPF may launch caspase-independent apoptosis through the lysosomal-mitochondrial pathway.