@article {69351, title = {COPII with ALG2 and ESCRTs control lysosome-dependent microautophagy of ER exit sites.}, journal = {Dev Cell}, year = {2024}, month = {2024 Apr 06}, abstract = {

Endoplasmic reticulum exit sites (ERESs) are tubular outgrowths of endoplasmic reticulum that serve as the earliest station for protein sorting and export into the secretory pathway. How these structures respond to different cellular conditions remains unclear. Here, we report that ERESs undergo lysosome-dependent microautophagy when Ca\ is released by lysosomes in response to nutrient stressors such as mTOR inhibition or amino acid starvation in mammalian cells. Targeting and uptake of ERESs into lysosomes were observed\ by\ super-resolution live-cell imaging and focus ion beam scanning electron microscopy (FIB-SEM). The mechanism\ was ESCRT dependent and required\ ubiquitinated SEC31, ALG2, and ALIX, with a knockout of ALG2 or function-blocking mutations of ALIX preventing engulfment of ERESs by lysosomes. In\ vitro, reconstitution of the pathway was possible using lysosomal lipid-mimicking giant unilamellar vesicles and purified recombinant components. Together, these findings demonstrate a pathway of lysosome-dependent ERES microautophagy mediated by COPII, ALG2, and ESCRTS induced by nutrient stress.

}, issn = {1878-1551}, doi = {10.1016/j.devcel.2024.03.027}, author = {Liao, Ya-Cheng and Pang, Song and Li, Wei-Ping and Shtengel, Gleb and Choi, Heejun and Schaefer, Kathy and Xu, C Shan and Lippincott-Schwartz, Jennifer} } @article {68935, title = {Lysosomal release of amino acids at ER three-way junctions regulates transmembrane and secretory protein mRNA translation.}, journal = {bioRxiv}, year = {2023}, month = {2023 Aug 03}, abstract = {

One-third of the mammalian proteome is comprised of transmembrane and secretory proteins that are synthesized on endoplasmic reticulum (ER). Here, we investigate the spatial distribution and regulation of mRNAs encoding these membrane and secretory proteins (termed "secretome" mRNAs) through live cell, single molecule tracking to directly monitor the position and translation states of secretome mRNAs on ER and their relationship to other organelles. Notably, translation of secretome mRNAs occurred preferentially near lysosomes on ER marked by the ER junction-associated protein, Lunapark. Knockdown of Lunapark reduced the extent of secretome mRNA translation without affecting translation of other mRNAs. Less secretome mRNA translation also occurred when lysosome function was perturbed by raising lysosomal pH or inhibiting lysosomal proteases. Secretome mRNA translation near lysosomes was enhanced during amino acid deprivation. Addition of the integrated stress response inhibitor, ISRIB, reversed the translation inhibition seen in Lunapark knockdown cells, implying an eIF2 dependency. Altogether, these findings uncover a novel coordination between ER and lysosomes, in which local release of amino acids and other factors from ER-associated lysosomes patterns and regulates translation of mRNAs encoding secretory and membrane proteins.

}, doi = {10.1101/2023.08.01.551382}, author = {Choi, Heejun and Liao, Ya-Cheng and Yoon, Young J and Grimm, Jonathan and Lavis, Luke D and Singer, Robert H and Lippincott-Schwartz, Jennifer} } @article {68300, title = {Organization of translating secretome mRNAS on endoplasmic reticulum}, journal = {Biophysical Journal}, volume = {121}, year = {2022}, month = {2022 Feb 01}, pages = {33a}, abstract = {

The endoplasmic reticulum (ER) has a complex morphology comprised of stacked sheets, tubules, and three-way junctions, which together function as a platform for protein synthesis of membrane and secretory proteins. Specific ER subdomains are thought to be spatially organized to enable protein synthesis activity, but precisely where these domains are localized is unclear, especially relative to the plethora of organelle interactions taking place on the ER. Here, we use single-molecule tracking of ribosomes and mRNA in combination with simultaneous imaging of ER to assess the sites of membrane protein synthesis on the ER. We found that ribosomes were widely distributed throughout different ER morphologies, but the synthesis of membrane proteins (including Type I, II, and multi-spanning) and an ER luminal protein (Calreticulin) occurred primarily at three-way junctions. Lunapark played a key role in stabilizing transmembrane protein mRNA at three-way junctions. We additionally found that translating mRNAs coding for transmembrane proteins are in the vicinity of lysosomes and translate through a cap-independent but eIF2-dependent mechanism. These results support the idea that discrete ER subdomains co-exist with lysosomes to support specific types of protein synthesis activities, with ER-lysosome interactions playing an important role in the translation of secretome mRNAs.

}, issn = {00063495}, doi = {10.1016/j.bpj.2021.11.2550}, url = {https://linkinghub.elsevier.com/retrieve/pii/S0006349521035256}, author = {Choi, Heejun and Liao, Ya-Cheng and Yoon, Young J. and Grimm, Jonathan and Lavis, Luke D. and Singer, Robert H. and Lippincott-Schwartz, Jennifer} } @article {65156, title = {RNA granules hitchhike on lysosomes for long-distance transport, Using annexin A11 as a molecular tether.}, journal = {Cell}, volume = {179}, year = {2019}, month = {2019 Sep 19}, pages = {147-164.e20}, abstract = {

Long-distance RNA transport enables local protein synthesis at metabolically-active sites distant from the nucleus. This process ensures an appropriate spatial organization of proteins, vital to polarized cells such as neurons. Here, we present a mechanism for RNA transport in which RNA granules "hitchhike" on moving lysosomes. In\ vitro biophysical modeling, live-cell microscopy, and unbiased proximity labeling proteomics reveal that annexin A11 (ANXA11), an RNA granule-associated phosphoinositide-binding protein, acts as a molecular tether between RNA granules and lysosomes. ANXA11 possesses an N-terminal low complexity domain, facilitating its phase separation into membraneless RNA granules, and a C-terminal membrane binding domain, enabling interactions with lysosomes. RNA granule transport requires ANXA11, and amyotrophic lateral sclerosis (ALS)-associated mutations in ANXA11 impair RNA granule transport by disrupting their interactions with lysosomes. Thus, ANXA11 mediates neuronal RNA transport by tethering RNA granules to actively-transported lysosomes, performing a critical cellular function that is disrupted in ALS.

}, issn = {1097-4172}, doi = {10.1016/j.cell.2019.08.050}, author = {Liao, Ya-Cheng and Fernandopulle, Michael S and Wang, Guozhen and Choi, Heejun and Hao, Ling and Drerup, Catherine M and Patel, Rajan and Qamar, Seema and Nixon-Abell, Jonathon and Shen, Yi and Meadows, William and Vendruscolo, Michele and Knowles, Tuomas P J and Nelson, Matthew and Czekalska, Magdalena A and Musteikyte, Greta and Gachechiladze, Mariam A and Stephens, Christina A and Pasolli, H Amalia and Forrest, Lucy R and St George-Hyslop, Peter and Lippincott-Schwartz, Jennifer and Ward, Michael E} }