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1.
Mol Biol Cell ; 33(13): ar125, 2022 11 01.
Article in English | MEDLINE | ID: mdl-36044348

ABSTRACT

Huntington's disease is characterized by accumulation of the aggregation-prone mutant Huntingtin (mHTT) protein. Here, we show that expression of exon 1 of mHTT in mouse cultured cells activates IRE1, the transmembrane sensor of stress in the endoplasmic reticulum, leading to degradation of the Blos1 mRNA and repositioning of lysosomes and late endosomes toward the microtubule organizing center. Overriding Blos1 degradation results in excessive accumulation of mHTT aggregates in both cultured cells and primary neurons. Although mHTT is degraded by macroautophagy when highly expressed, we show that before the formation of large aggregates, mHTT is degraded via an ESCRT-dependent, macroautophagy-independent pathway consistent with endosomal microautophagy. This pathway is enhanced by Blos1 degradation and appears to protect cells from a toxic, less aggregated form of mHTT.


Subject(s)
Protein Aggregates , Protein Serine-Threonine Kinases , Animals , Endoribonucleases , Endosomal Sorting Complexes Required for Transport , Huntingtin Protein/genetics , Mice , RNA, Messenger/genetics
2.
J Cell Biol ; 218(4): 1118-1127, 2019 04 01.
Article in English | MEDLINE | ID: mdl-30787040

ABSTRACT

Cells respond to stress in the ER by initiating the widely conserved unfolded protein response. Activation of the ER transmembrane nuclease IRE1 leads to the degradation of specific mRNAs, but how this pathway affects the ability of cells to recover from stress is not known. Here, we show that degradation of the mRNA encoding biogenesis of lysosome-related organelles 1 subunit 1 (Blos1) leads to the repositioning of late endosomes (LEs)/lysosomes to the microtubule-organizing center in response to stress in mouse cells. Overriding Blos1 degradation led to ER stress sensitivity and the accumulation of ubiquitinated protein aggregates, whose efficient degradation required their independent trafficking to the cell center and the LE-associated endosomal sorting complexes required for transport. We propose that Blos1 regulation by IRE1 promotes LE-mediated microautophagy of protein aggregates and protects cells from their cytotoxic effects.


Subject(s)
Endoplasmic Reticulum Stress , Endosomes/enzymology , Fibroblasts/enzymology , Lysosomes/enzymology , Membrane Proteins/metabolism , Nerve Tissue Proteins/metabolism , Protein Serine-Threonine Kinases/metabolism , RNA Stability , RNA, Messenger/metabolism , 3T3 Cells , Animals , Endosomes/genetics , Endosomes/pathology , Fibroblasts/pathology , Lysosomes/genetics , Lysosomes/pathology , Membrane Proteins/genetics , Mice , Microautophagy , Mitochondrial Proteins , Nerve Tissue Proteins/genetics , Protein Aggregates , Protein Serine-Threonine Kinases/genetics , RNA, Messenger/genetics , Ubiquitination
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