ABSTRACT
Rapamycin (Rap) and its derivatives, called rapalogs, are being explored in clinical trials targeting cancer and neurodegeneration. The underlying mechanisms of Rap actions, however, are not well understood. Mechanistic target of rapamycin (mTOR), a lysosome-localized protein kinase that acts as a critical regulator of cellular growth, is believed to mediate most Rap actions. Here, we identified mucolipin 1 (transient receptor potential channel mucolipin 1 [TRPML1], also known as MCOLN1), the principle Ca2+ release channel in the lysosome, as another direct target of Rap. Patch-clamping of isolated lysosomal membranes showed that micromolar concentrations of Rap and some rapalogs activated lysosomal TRPML1 directly and specifically. Pharmacological inhibition or genetic inactivation of mTOR failed to mimic the Rap effect. In vitro binding assays revealed that Rap bound directly to purified TRPML1 proteins with a micromolar affinity. In both healthy and disease human fibroblasts, Rap and rapalogs induced autophagic flux via nuclear translocation of transcription factor EB (TFEB). However, such effects were abolished in TRPML1-deficient cells or by TRPML1 inhibitors. Hence, Rap and rapalogs promote autophagy via a TRPML1-dependent mechanism. Given the demonstrated roles of TRPML1 and TFEB in cellular clearance, we propose that lysosomal TRPML1 may contribute a significant portion to the in vivo neuroprotective and anti-aging effects of Rap via an augmentation of autophagy and lysosomal biogenesis.
Subject(s)
Lysosomes/metabolism , Sirolimus/pharmacology , TOR Serine-Threonine Kinases/metabolism , Transient Receptor Potential Channels/metabolism , Autophagy/drug effects , Basic Helix-Loop-Helix Leucine Zipper Transcription Factors/metabolism , Calcium/pharmacology , Cell Nucleus/drug effects , Cell Nucleus/metabolism , Fibroblasts/drug effects , Fibroblasts/metabolism , HEK293 Cells , HeLa Cells , Humans , Ion Channel Gating/drug effects , Lysosomes/drug effects , Models, Biological , Protein Binding/drug effects , Sirolimus/analogs & derivatives , Sirolimus/chemistryABSTRACT
BACKGROUND & OBJECTIVE: Increased level of reactive oxygen species is a hallmark of common neurodegenerative diseases such as Alzheimer's Disease and Parkinson's Disease. ROS can oxidize macromolecules including DNA, lipids and proteins and cause oxidative damage to the cell. Emerging evidence indicate that potassium channels in the central nervous system are no exceptions to these oxidative modifications. CONCLUSION: In this mini-review, we summarized recent reports on the oxidation of potassium channels in the CNS and the consequently resulted changes in cell functions and viability, with focus on its implications in neurodegenerative diseases.