Physical interaction of estrogen receptor with MnSOD: implication in mitochondrial O2.− upregulation and mTORC2 potentiation in estrogen-responsive breast cancer cells

Abstract

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.

Role of TXNIP/NLRP3 in sepsis-induced myocardial dysfunction

“…SOD has three subtypes, Cu/ZnSOD, FeSOD and MnSOD, among which MnSOD accounts for 70% of the total SOD in the heart and up to 90% in cardiomyocytes (14). The expression of MnSOD in mitochondria regulates the production of O 2 − during oxidative phosphorylation, thus, MnSOD serves a key role in ROS (15).…”

Mitochondrial Hormone Receptors - an Emerging Field of Signaling in the Cell’s Powerhouse

“…As MnSOD is activated by the mitochondrially localized sirtuin SIRT3 by deacetylation at K68, an interference with the acetylation status of K68 was studied. These experiments revealed a correlation of ERα/MnSOD association with acetylation of this regulatory lysine [8]. Another recent finding of high actuality concerns the role of long noncoding RNAs (lncRNAs) in mitochondrial ER actions [9], results that may find parallels in the regulation of other mitochondrial steroid receptors.…”

“…In addition to modulation of bioenergetics [6], effects on mitochondrial gene expression were assumed [7]. Moreover, translocation of the usually genomically acting ERα was reported [8]. A more specific and, to a certain degree unexpected, nongenomic action has been recently described for this other estrogen receptor.…”

“…In breast cancer cells, ERα was shown to physically interact with the mitochondrial superoxide dismutase (MnSOD) [8]. As MnSOD is activated by the mitochondrially localized sirtuin SIRT3 by deacetylation at K68, an interference with the acetylation status of K68 was studied.…”

Overview of Current Findings about the Role of Oestrogen Receptor α in Cancer Cell Signalling Pathways

“…Ta kóduje především proteiny, které jsou součástí elektronového transportního řetězce (electron transport chain -ETC) [26,27]. Bylo prokázáno, že ERα může také vstupovat do mitochodrií a plnit zde roli transkripčního faktoru [2,28]. Nicméně v současné literatuře není tak často s mitochondriemi spojován samotný ERα jako spíše jeho inhibitor TAM.…”