Assays for induction of the unfolded protein response and selective activation of the three major pathways

The endoplasmic reticulum (ER) is responsible for the proper folding and processing of secreted and transmembrane proteins within the cell. Stimuli that disrupt ER function cause an accumulation of misfolded proteins within the ER lumen, a condition termed ER stress. The unfolded protein response (UPR) is activated in response to ER stress in an attempt to restore ER homeostasis. UPR is initiated by three transmembrane sensors that activate three signaling pathways which lead to the activation of transcription factors and production of chaperones. The coordinated action of these three pathways attempt to restore homeostasis. However, if the ER homeostasis cannot be restored, it initiates apoptosis. Deregulated or compromised functions of these pathways can therefore lead to the pathogenesis of disease. In order to understand the molecular mechanisms involved, it is important to study each pathway independently. Here, we describe a number of approaches to selectively target each arm of UPR and investigate the functional significance of the UPR pathway involved.