Monitoring and manipulating mammalian unfolded protein response

The unfolded protein response (UPR) is a conserved, intracellular signaling pathway activated by endoplasmic reticulum (ER) stress. In mammalian cells, the UPR is controlled by three ER-resident transmembrane proteins: inositol-requiring enyzme-1 (IRE1), PKR-like ER kinase (PERK), and activating transcription factor-6 (ATF6), by which cytoprotective mechanisms are initiated to restore ER functions. However, if cellular homeostasis is not restored by the UPR's initial events, UPR signaling triggers apoptotic cell death, which correlates with the pathogenesis of a wide range of human diseases. The intrinsic function of the UPR in regulating cell survival and death suggests its importance as a mechanistic link between ER stress and disease pathogenesis. Understanding UPR regulatory molecules or signaling pathways involved in disease pathogenesis is critical to establishing therapeutic strategies. For this purpose, several experimental tools have been developed to evaluate individual UPR components. In this chapter, we present methods to monitor and quantify activation of individual UPR signaling pathways in mammalian cells and tissues, and we review strategies to artificially and selectively activate individual UPR signaling pathways using chemical-genetic approaches.