Signal transduction: Splicing together the unfolded-protein response

Cells respond to the accumulation of unfolded proteins in the endoplasmic reticulum (ER) by increasing the production of ER-resident chaperones, such as BiP and protein disulfide isomerase (PDI), that expedite protein folding and assembly in the ER lumen. In organisms as diverse as yeast and humans, this is accomplished by increasing the transcription of the genes that encode these chaperones. The response, which involves a signal-transduction cascade from the ER to the nucleus, is called the unfolded-protein response (UPR).