PRDX5 and cancer: In the same vein, although increase in thioredoxin reductase (TR) seems to play a role in protecting against oxidative stress, other studies show that thioredoxin in reduced form may support the growth of cancer cells by complexing with apoptosis signaling kinase 1 (ASK1), which then prevents apoptosis (Arnér and Holmgren, 2000).