UFM1 at the endoplasmic reticulum: linking ER stress, ribosome quality control, and ER-phagy.

Ubiquitin-fold modifier 1 (UFM1) is a small protein that functions as a ubiquitin-like modifier attached to other proteins to alter their behavior. Although less famous than ubiquitin, UFM1 has gained attention as a key regulator of proteostasis (protein homeostasis) in the cell. Notably, the endoplasmic reticulum (ER) has emerged as the central stage for UFM1's activity. UFM1 was initially recognized for its role in the ER stress response, and we now know it orchestrates two critical quality-control processes at the ER: ribosome-associated quality control and selective autophagy of the ER. Together, these mechanisms ensure that the cell can cope with misfolded proteins and stalled ribosomes, maintaining the health of the ER and the proteins it produces. In this review, we will explore how UFM1 works at the ER, how its components are regulated during stress, how it facilitates both immediate quality control and longer-term ER turnover, and how disruptions in this system lead to disease, especially in the nervous system.