Responses to endoplasmic reticulum stress at a glance

The endoplasmic reticulum (ER) is the gateway to the eukaryotic protein secretory pathway. Beyond its role in protein biogenesis, it is central to Ca2+ homeostasis and lipid biosynthesis. This organelle, which can constitute more than 50% of the cellular membranes in secretory cells, is highly plastic and must adjust to intracellular or extracellular challenges to ensure proper protein secretion. ER stress, resulting from challenges such as accumulation, misfolding or aggregation of proteins or from disrupted ER lipid composition, can deleteriously affect cell function. Thus, the ER has evolved adaptive mechanisms that lead to cellular reprogramming to adjust its capacity to handle stress, including the unfolded protein response (UPR), which engages various ER quality control systems, protein degradation pathways and ER-organelle contacts. If this succeeds, the cell survives; but if it fails, cell death mechanisms are triggered. In this Cell Science at a Glance article and the accompanying poster, we summarize current knowledge on ER stress and control of the UPR in mammalian cells, highlighting aspects that require further attention. We also discuss recent insights that must be considered to better capture the full understanding of the ability of the ER to adjust to biological variation.