Semaphorin3A (Sema3A) is a repulsive guidance molecule for axons, which acts by inducing growth cone collapse through phosphorylation of CRMP2 (collapsin response mediator protein 2). Here, we show a role for CRMP2 oxidation and thioredoxin (TRX) in the regulation of CRMP2 phosphorylation and growth cone collapse. Sema3A stimulation generated hydrogen peroxide (H2O2) through MICAL (molecule interacting with CasL) and oxidized CRMP2, enabling it to form a disulfide-linked homodimer through cysteine-504. Oxidized CRMP2 then formed a transient disulfide-linked complex with TRX, which stimulated CRMP2 phosphorylation by glycogen synthase kinase-3, leading to growth cone collapse. We also reconstituted oxidation-dependent phosphorylation of CRMP2 in vitro, using a limited set of purified proteins. Our results not only clarify the importance of H2O2 and CRMP2 oxidation in Sema3A-induced growth cone collapse but also indicate an unappreciated role for TRX in linking CRMP2 oxidation to phosphorylation.
Mammalian Ste20-like kinase-1 (MST1) kinase mediates H 2 O 2 -induced cell death by anticancer drugs such as cisplatin in a p53-dependent manner. However, the mechanism underlying MST1 activation by H 2 O 2 remains unknown. Here we show that peroxiredoxin-I (PRX-I) is an essential intermediate in H 2 O 2 -induced MST1 activation and cisplatin-induced cell death through p53. Cell stimulation with H 2 O 2 resulted in PRX-I oxidation to form homo-oligomers and interaction with MST1, leading to MST1 autophosphorylation and augmentation of kinase activity. In addition, RNA interference knockdown experiments indicated that endogenous PRX-I is required for H 2 O 2 -induced MST1 activation. Live-cell imaging showed H 2 O 2 generation by cisplatin treatment, which likewise caused PRX-I oligomer formation, MST1 activation and cell death. Cisplatin-induced PRX-I oligomer formation was not observed in embryonic fibroblasts obtained from p53-knockout mice, confirming the importance of p53. Indeed, ectopic expression of p53 induced PRX-I oligomer formation and cell death, both of which were cancelled by the antioxidant NAC. Moreover, we succeeded in reconstituting H 2 O 2 -induced MST1 activation in vitro, using purified PRX-I and MST1 proteins. Collectively, our results show a novel PRX-I function to cause cell death in response to high levels of oxidative stress by activating MST1, which underlies the p53-dependent cytotoxicity caused by anticancer agents.
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