Physical interaction of estrogen receptor with MnSOD: implication in mitochondrial O 2 .- upregulation and mTORC2 potentiation in estrogen-responsive breast cancer cells

• Published in: Oncogene 2017-03, Vol.36 (13), p.1829
• Main Authors: Lone, M-U-D, Baghel, K S, Kanchan, R K, Shrivastava, R, Malik, S A, Tewari, B N, Tripathi, C, Negi, M P S, Garg, V K, Sharma, M, Bhatt, M L B, Bhadauria, S
• Format: Article
• Language: English
• Subjects: Acetylation; Breast Neoplasms - genetics; Breast Neoplasms - metabolism; Catalysis - drug effects; Cell Line, Tumor; Estrogens - pharmacology; Female; Gene Silencing; Humans; Mechanistic Target of Rapamycin Complex 2; Mitochondria - drug effects; Mitochondria - metabolism; Models, Biological; Multiprotein Complexes - metabolism; Protein Binding; Reactive Oxygen Species - metabolism; Receptors, Estrogen - genetics; Receptors, Estrogen - metabolism; Sirtuin 3 - genetics; Sirtuin 3 - metabolism; Superoxide Dismutase - genetics; Superoxide Dismutase - metabolism; TOR Serine-Threonine Kinases - metabolism
• ISSN: 1476-5594
• DOI: 10.1038/onc.2016.346

Augmented reactive oxygen species levels consequential to functional alteration of key mitochondrial attributes contribute to carcinogenesis, either directly via oxidative DNA damage infliction or indirectly via activation of oncogenic signaling cascades. We previously reported activation of a key oncogenic signaling cascade via mammalian target of rapamycin (mTOR) signaling complex-2 (mTORC2) owing to estrogen receptor (ER-α)-dependent augmentation of O within the mitochondria of 17-β-estradiol (E2)-stimulated breast cancer cells. Manganese superoxide dismutase (MnSOD) is the principal mitochondrial attribute governing mitochondrial O homeostasis, raising the possibility that its functional alteration could be instrumental in augmenting mitochondrial O levels in breast cancer cells. Here we show ER-dependent transient inhibition of MnSOD catalytic function in breast cancer cells. Catalytic function of MnSOD is tightly regulated at the post-translational level. Post-translational modifications such as phosphorylation, nitration and acetylation represent key regulatory means governing the catalytic function of MnSOD. Acetylation at lysine-68 (K68) inhibits MnSOD catalytic activity and thus represents an important post-translational regulatory mechanism in human cells. Using reciprocal immunoprecipitation and proximity ligation assay, we demonstrate the occurrence of direct physical interaction between ER-α and MnSOD in human breast cancer cells, which in turn was associated with potentiated acetylation of MnSOD at K68. In addition, we also observed diminished interaction of MnSOD with sirtuin-3, the key mitochondrial deacetylase that deacetylates MnSOD at critical K68 and thereby activates it for scavenging O . Consequently, compromised deacetylation of MnSOD at K68 leading to its inhibition and a resultant buildup of O within the mitochondria culminated in the activation of mTORC2. In agreement with this, human breast cancer tissue specimen exhibited a positive correlation between acetyl-MnSOD levels and phospho-Ser mTOR levels. In addition to exposing the crosstalk of ER-α with MnSOD post-translational regulatory mechanisms, these data also unravel a regulatory role of ER/MnSOD interaction as an important control switch for redox regulation of ER-α-responsive oncogenic signaling cascades. Furthermore, our study provides a mechanistic link for ER-α-dependent O potentiation and resultant mTORC2 activation in breast cancer cells.