Cycling hypoxia up-regulates thioredoxin levels in human MDA-MB-231 breast cancer cells

► ROS decreases during hypoxia, but increases during reoxygenation in MDA-MB-231 cells. ► Thioredoxin protein levels are increased during reoxygenation following hypoxia. ► Pre-conditioning with hypoxia and reoxygenation upregulates thioredoxin and Ref-1. ► High thioredoxin cell surface levels occur after reoxygenation and pre-conditioning. ► The thioredoxin gene promoter is activated during reoxygenation by Nrf-2.