Activation of lysosomal function in the course of autophagy via mTORC1 suppression and autophagosome-lysosome fusion

Abstract

Lysosome is a key subcellular organelle in the execution of the autophagic process and at present little is known whether lysosomal function is controlled in the process of autophagy. In this study, we first found that suppression of mammalian target of rapamycin (mTOR) activity by starvation or two mTOR catalytic inhibitors (PP242 and Torin1), but not by an allosteric inhibitor (rapamycin), leads to activation of lysosomal function. Second, we provided evidence that activation of lysosomal function is associated with the suppression of mTOR complex 1 (mTORC1), but not mTORC2, and the mTORC1 localization to lysosomes is not directly correlated to its regulatory role in lysosomal function. Third, we examined the involvement of transcription factor EB (TFEB) and demonstrated that TFEB activation following mTORC1 suppression is necessary but not sufficient for lysosomal activation. Finally, Atg5 or Atg7 deletion or blockage of the autophagosome-lysosome fusion process effectively diminished lysosomal activation, suggesting that lysosomal activation occurring in the course of autophagy is dependent on autophagosome-lysosome fusion. Taken together, this study demonstrates that in the course of autophagy, lysosomal function is upregulated via a dual mechanism involving mTORC1 suppression and autophagosome-lysosome fusion.

Looking at the metabolic consequences of the colchicine-based in vivo autophagic flux assay

“…However, the increase of lysosomal transcripts was not followed by an increase of the lysosomal function (as evidenced by the activity of CTSD), in line with the demonstrated inhibition of the autophagic flux in our samples and the recently published data showing that activation of lysosomal function depends on autophagosome-lysosome fusion. 41 Thus, the observed induction of autophagyand lysosome-related transcripts in colchicine-treated fish could result from a compensatory mechanism to rescue a dysfunctional autophagic-lysosomal function. Finally, while we cannot account for all the cellular and metabolic perturbations induced by the long term use of colchicine, we speculate that induction of ER stress may also affect major cellular functions, such as apoptosis or chaperone-mediated autophagy (CMA), that crosstalk with autophagic flux.…”

Restoration of autophagic flux in myocardial tissues is required for cardioprotection of sevoflurane postconditioning in rats

“…Impaired autophagic flux at the late stage is closely related with lysosomal dysfunction. A previous study demonstrated that lysosomal function was activated in the course of autophagy via mTORC1 suppression and autophagosome-lysosome fusion [31] . In this study, SpostC activated lysosomal function in the autophagy process, which was characterized by a decrease in p62 levels as well as increased expression and activation of cathepsin B ( Figure 3D-3F and Figure 5D-5F).…”

Pharmacological inhibition of lysosomes activates the MTORC1 signaling pathway in chondrocytes in an autophagy-independent manner

“…9,[26][27][28][29][30][31][32] The role of the v-ATPase in MTORC1 activation is unequivocal and well described for multiple cell lines. 4 However, mutations in genes encoding GATOR1 proteins, makes MTORC1 signaling resistant to a v-ATPase inhibitor, thereby providing a possibility that v-ATPase-dependent MTORC1 regulation might differ in different cellular settings.…”