SCO2 Induces p53-Mediated Apoptosis by Thr⁸⁴⁵ Phosphorylation of ASK-1 and Dissociation of the ASK-1–Trx Complex

Abstract

p53 prevents cancer via cell cycle arrest, apoptosis, and the maintenance of genome stability. p53 also regulates energy-generating metabolic pathways such as oxidative phosphorylation (OXPHOS) and glycolysis via transcriptional regulation of SCO2 and TIGAR. SCO2, a cytochrome c oxidase assembly factor, is a metallochaperone which is involved in the biogenesis of cytochrome c oxidase subunit II. Here we have shown that SCO2 functions as an apoptotic protein in tumor xenografts, thus providing an alternative pathway for p53-mediated apoptosis. SCO2 increases the generation of reactive oxygen species (ROS) and induces dissociation of the protein complex between apoptosis signal-regulating kinase 1 (ASK-1) (mitogen-activated protein kinase kinase kinase [MAPKKK]) and its cellular inhibitor, the redox-active protein thioredoxin (Trx). Furthermore, SCO2 induces phosphorylation of ASK-1 at the Thr⁸⁴⁵ residue, resulting in the activation of the ASK-1 kinase pathway. The phosphorylation of ASK-1 induces the activation of mitogen-activated protein kinase kinases 4 and 7 (MAP2K4/7) and MAP2K3/6, which switches the c-Jun N-terminal protein kinase (JNK)/p38-dependent apoptotic cascades in cancer cells. Exogenous addition of the SCO2 gene to hypoxic cancer cells and hypoxic tumors induces apoptosis and causes significant regression of tumor xenografts. We have thus discovered a novel apoptotic function of SCO2, which activates the ASK-1 kinase pathway in switching “on” an alternate mode of p53-mediated apoptosis. We propose that SCO2 might possess a novel tumor suppressor function via the ROS–ASK-1 kinase pathway and thus could be an important candidate for anticancer gene therapy.

SUPPLEMENTAL MATERIAL

Supplemental material for this article may be found at http://dx.doi.org/10.1128/MCB.06798-11.

ACKNOWLEDGMENTS

We thank the University Grant Commission, India, Capacity Build Up Fund (to U.P.), Indian Council of Medical Research (grant to A.A.M.), and NIH (RO1 grant NIH EB004031 to P.K.).

We thank Muzzammill Sayyid and Shally Awasthi (faculty in charge, Research Cell, CSMMU) for their contributions.

We declare no conflict of interest.

E.M. participated in the conceptualization of the study, conducted the majority of the experiments, analyzed the data, interpreted the results, and prepared the manuscript. R.G. helped in conceptualization, conducted some key experiments, helped to analyze the data, interpreted the results, and equally participated in the preparation of the manuscript. P.K. helped in the fine-tuning of the experimental design, interpretation, and preparation of the manuscript. M.B. provided technical editing of the manuscript. A.A.M. provided the design of the study. U.P. provided the design of the study and manuscript.