Loss of Lysosomal Ion Channel Transient Receptor Potential Channel Mucolipin-1 (TRPML1) Leads to Cathepsin B-dependent Apoptosis

Grace A Colletti,Mark T Miedel,James Quinn,Neel Andharia,Ora A Weisz,Kirill Kiselyov

doi:10.1074/jbc.m111.285536

Grace A Colletti, Mark T Miedel + Show 4 more

Open Access

https://doi.org/10.1074/jbc.m111.285536

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Abstract

Mucolipidosis type IV (MLIV) is a lysosomal storage disease caused by mutations in the gene MCOLN1, which codes for the transient receptor potential family ion channel TRPML1. MLIV has an early onset and is characterized by developmental delays, motor and cognitive deficiencies, gastric abnormalities, retinal degeneration, and corneal cloudiness. The degenerative aspects of MLIV have been attributed to cell death, whose mechanisms remain to be delineated in MLIV and in most other storage diseases. Here we report that an acute siRNA-mediated loss of TRPML1 specifically causes a leak of lysosomal protease cathepsin B (CatB) into the cytoplasm. CatB leak is associated with apoptosis, which can be prevented by CatB inhibition. Inhibition of the proapoptotic protein Bax prevents TRPML1 KD-mediated apoptosis but does not prevent cytosolic release of CatB. This is the first evidence of a mechanistic link between acute TRPML1 loss and cell death.

Highlights

Mechanisms of cell death in mucolipidosis type IV, a lysosomal storage disease caused by mutations in gene coding for ion channel TRPML1, are unknown
Cellular inclusions have been previously shown to accumulate in the same TRPML1 KD model, further confirming that this model represents the early stages of Mucolipidosis type IV (MLIV) [13]
cathepsin B (CatB) Buildup in TRPML1 KD Cells—CatB is a ubiquitous lysosomal protease, which has previously been implicated in cell death upon lysosomal permeabilization

Summary

Background

Mechanisms of cell death in mucolipidosis type IV, a lysosomal storage disease caused by mutations in gene coding for ion channel TRPML1, are unknown. Inhibition of the proapoptotic protein Bax prevents TRPML1 KD-mediated apoptosis but does not prevent cytosolic release of CatB This is the first evidence of a mechanistic link between acute TRPML1 loss and cell death. We believe that the key to identifying the cell death pathways in lysosomal storage diseases lies in deconstructing the early events accompanying the loss of TRPML1 or other components of the endocytic pathway. Inhibition of Bax activity did not prevent CatB release, suggesting that this protein lies downstream of CatB or in a separate apoptotic pathway These results illustrate, for the first time, the early events leading to cell death in TRPML1-deficient cells

EXPERIMENTAL PROCEDURES

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DISCUSSION