bims-lypmec 2022-09-04 papers

Issue of 2022‒09‒04
two papers selected by
Satoru Kobayashi
New York Institute of Technology

Mol Cell. 2022 Aug 23. pii: S1097-2765(22)00761-4. [Epub ahead of print]

Ubiquitination of phosphatidylethanolamine in organellar membranes.

Jun-Ichi Sakamaki, Koji L Ode, Yoshitaka Kurikawa, Hiroki R Ueda, Hayashi Yamamoto, Noboru Mizushima.

The covalent conjugation of ubiquitin family proteins is a widespread post-translational protein modification. In the ubiquitin family, the ATG8 subfamily is exceptional because it is conjugated mainly to phospholipids. However, it remains unknown whether other ubiquitin family proteins are also conjugated to phospholipids. Here, we report that ubiquitin is conjugated to phospholipids, mainly phosphatidylethanolamine (PE), in yeast and mammalian cells. Ubiquitinated PE (Ub-PE) accumulates at endosomes and the vacuole (or lysosomes), and its level increases during starvation. Ub-PE is also found in baculoviruses. In yeast, PE ubiquitination is catalyzed by the canonical ubiquitin system enzymes Uba1 (E1), Ubc4/5 (E2), and Tul1 (E3) and is reversed by Doa4. Liposomes containing Ub-PE recruit the ESCRT components Vps27-Hse1 and Vps23 in vitro. Ubiquitin-like NEDD8 and ISG15 are also conjugated to phospholipids. These findings suggest that the conjugation to membrane phospholipids is not specific to ATG8 but is a general feature of the ubiquitin family.

Keywords: Doa4; Tul1; endosome; lysosome; phosphatidylethanolamine; phospholipids; ubiquitin; ubiquitin-like proteins; vacuole

DOI: https://doi.org/10.1016/j.molcel.2022.08.008

Mol Cell. 2022 Aug 25. pii: S1097-2765(22)00758-4. [Epub ahead of print]

Life in lockdown: Orchestrating endoplasmic reticulum and lysosome homeostasis for quiescent cells.

Andrew Murley, Kevin Wickham, Andrew Dillin.

Cellular quiescence-reversible exit from the cell cycle-is an important feature of many cell types important for organismal health. Quiescent cells activate protective mechanisms that allow their persistence in the absence of growth and division for long periods of time. Aging and cellular dysfunction compromise the survival and re-activation of quiescent cells over time. Counteracting this decline are two interconnected organelles that lie at opposite ends of the secretory pathway: the endoplasmic reticulum and lysosomes. In this review, we highlight recent studies exploring the roles of these two organelles in quiescent cells from diverse contexts and speculate on potential other roles they may play, such as through organelle contact sites. Finally, we discuss emerging models of cellular quiescence, utilizing new cell culture systems and model organisms, that are suited to the mechanistic investigation of the functions of these organelles in quiescent cells.

Keywords: ER; aging; lysosome; quiescence; stem cells

DOI: https://doi.org/10.1016/j.molcel.2022.08.005