TRPML1-induced autophagy inhibition triggers mitochondrial mediated apoptosis.

Previous studies have demonstrated that autophagy tightly regulates apoptosis. However, the underlying mechanism whereby autophagy regulates apoptosis remains unclear. Here, we discover a "autophagy inhibition-mitochondrial turnover disruption-ROS elevation-DNA damage-p53 transactivation-apoptosis" axis that explicates the process of autophagy modulating apoptosis. We found that autophagy inhibition induced by TRPML1, a cationic channel localized in the lysosome, results in accumulation of damaged mitochondria via blocking the mitophagic flux to lysosomes in human melanoma and glioblastoma cells. The disrupted mitochondria turnover leads to ROS elevation, which in turn causes severe damage to DNA in these cancer cells. Damage to DNA resulted from TRPML1-mediated autophagy inhibition subsequently activates p53, which ultimately triggers mitochondrial mediated apoptosis by modulating pro- and anti-apoptosis proteins in these cancer cells. As a result, by triggering apoptosis, TRPML1-induced autophagy inhibition greatly suppresses growth of human melanoma and glioma both in vitro and in vivo. In summary, our findings define the mechanism underling the regulation of autophagy inhibition in apoptosis and represent TRPML1 as a novel target for potentially treating melanoma and glioblastoma in the clinical setting.

Autophagy inhibition mediated by MCOLN1/TRPML1 suppresses cancer metastasis via regulating a ROS-driven TP53/p53 pathway.

Compelling evidence has demonstrated that macroautophagy/autophagy plays an important role in regulating multiple steps of metastatic cascades; however, the precise role of autophagy in metastasis remains unclear. This study demonstrates that autophagy inhibition induced by MCOLN1/TRPML1 suppresses cancer metastasis by evoking the ROS-mediated TP53/p53 pathway. First, we found that MCOLN1-mediated autophagy inhibition not only profoundly inhibits both migration and invasion in malignant melanoma and glioma cell lines in vitro, but also suppresses melanoma metastasis in vivo. Second, our study reveals that autophagy inhibition induced by MCOLN1 leads to damaged mitochondria accumulation followed by large quantities of ROS release. Third, we demonstrate that the elevated ROS resulting from autophagy inhibition subsequently triggers TP53 activity, which in turn modulates expression of its downstream targets that are involved in a broad spectrum of the metastatic cascade to suppress metastasis including MMP members and TWIST. In summary, our findings have established a mechanism by which autophagy inhibition suppresses metastasis via the ROS-TP53 signaling pathway. More importantly, our study demonstrates that autophagy inhibition through stimulation of MCOLN1 could evidently be one of the therapeutic potentials for combating cancer metastasis.Abbreviations: 3-MA: 3-methyladenine; AA: amino acid; ATG5: autophagy related 5; ATG12: autophagy-related 12; Baf-A1: bafilomycin A1; CCCP: carbonyl cyanide m-chlorophenylhydrazone; CQ: chloroquine; DMEM: Dulbecco's Modified Eagle Medium; EMT: epithelial-mesenchymal transition; FBS: fetal bovine serum; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; HEK: human embryonic kidney; LAMP1: lysosomal-associated membrane protein 1; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; MCOLN1/TRPML1: mucolipin TRP cation channel 1; MMP: matrix metallopeptidase; NC: negative control; NRK: normal rat kidney; PBS: phosphate-buffered saline; shRNA: short hairpin RNA; siRNA: short interfering RNA; SQSTM1/p62: sequestosome 1; ULK1: unc-51 like autophagy-activating kinase 1.