Rapamycin directly activates lysosomal mucolipin TRP channels independent of mTOR

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 Ca 2+ 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.

TRPML1 links lysosomal calcium to autophagosome biogenesis through the activation of the CaMKKβ/VPS34 pathway

“…We found that acute pharmacological activation of TRPML1 rapidly induces AV formation and AV–lysosome fusion at early time points when TFEB is inactive being located predominantly in the cytosol. Our data are in agreement with previous work indicating that TRPML1 positively regulates membrane-trafficking processes such as vesicular fusion/fission events and autophagy 5,23,32,50,65,68,70–73 . There are also a few reports suggesting that TRPML1 modulation can block AV–lysosomal fusion 74,75 , although these observations might be explained by differences in the experimental conditions used and/or levels of TRPML1 overexpression.…”

Promoting tau secretion and propagation by hyperactive p300/CBP via autophagy-lysosomal pathway in tauopathy

“…For example, autophagy induction promotes the fusion of MVBs with lysosomes and inhibits exosome release [61]. It was recently found that rapamycin induces autophagic flux via TRPML1-TFEB pathway on lysosomes, independent of mTORC-ULK1 inhibition [46]. In line with this, we found that rapamycin induces autophagic flux and reduces tau secretion, both in WT cells and in cells with p300 activation.…”

“…We next examined if promoting autophagic flux affects tau secretion. Rapamycin treatment induces autophagic flux by promoting autophagic induction via mTOR inhibition [45] and enhancing lysosomal degradation [46] (Fig. 6a), resulting in increased LC3-II/I (reflected in reduced LC3-I) and reduced p62 ( Fig.…”

Immune Clearance of Senescent Cells to Combat Ageing and Chronic Diseases

“…Rapamycin decelerates cellular senescence in vitro and in vivo via mechanistic target of rapamycin (mTOR). Recently, rapamycin was reported to exert in vivo neuroprotective and anti-ageing effects via the activation of lysosomal mucolipin TRP channels, independent of mTOR [98]. Moreover, rapamycin, the US Food and Drug Administration-approved mTOR inhibitor, has been shown to extend the median and maximal lifespans of both male and female genetically heterogeneous mice [99].…”