When under pressure, get closer: PERKing up membrane contact sites during ER stress

The endoplasmic reticulum (ER) is the main hub of cellular Ca²⁺ signalling and protein synthesis and folding. The ER moreover is the central player in the formation of contact sites with other organelles and structures, including mitochondria, plasma membrane (PM) and endosomes. The most studied of these, the ER–mitochondria contact sites, are crucial regulators of cellular Ca²⁺ homoeostasis, metabolism and cell death signalling. Protein kinase RNA-like ER kinase (PERK), an ER stress kinase and crucial signalling protein in the unfolded protein response (UPR), was found to be able to orchestrate contact sites between the ER and mitochondria and to be indispensable for the pre-apoptotic trafficking of calreticulin (CRT) at the PM during immunogenic cell death (ICD). Furthermore, PERK has recently been linked with ER and PM contact sites through the mechanism of store-operated Ca²⁺ entry (SOCE). Here we discuss emerging findings disclosing novel roles of the ER stress sensor PERK in orchestrating inter-organellar communication in the context of ER stress.