Endothelial protein disulfide isomerase (EndoPDI) is a thioredoxin member of the protein disulfide isomerase family of chaperones. This enzyme has been localized to the endoplasmic reticulum in primary endothelial cells, but colocalizes with nucleoli in the nuclei of breast, colon, and renal cancer cells. EndoPDI mRNA and protein expression is induced by hypoxia and exhibits a protective effect on endothelial cells during hypoxia (1).