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

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 O2.- within the mitochondria of 17-ß-estradiol (E2)-stimulated breast cancer cells. Manganese superoxide dismutase (MnSOD) is the principal mitochondrial attribute governing mitochondrial O2.- homeostasis, raising the possibility that its functional alteration could be instrumental in augmenting mitochondrial O2.- 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 O2.-. Consequently, compromised deacetylation of MnSOD at K68 leading to its inhibition and a resultant buildup of O2.- within the mitochondria culminated in the activation of mTORC2. In agreement with this, human breast cancer tissue specimen exhibited a positive correlation between acetyl-MnSODK68 levels and phospho-Ser2481 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 O2.- potentiation and resultant mTORC2 activation in breast cancer cells.

Cyclooxygenase-2 inhibition attenuates hypoxic cancer cells induced m2-polarization of macrophages.

Tumor-associated macrophages (TAMs), represent a major subpopulation of tumor infiltrating immune cells. These alternatively activated M2-polarized macrophages are well known for their pro-tumor functions. Owing to their established role in potentiating tumor-neovasculogenesis and metastasis, TAMs have emerged as promising target for anti-cancer immunotherapy. One of the key TAMs related phenomenon that is amenable to therapeutic intervention is their phenotype switching into alternatively activated M2-polarized macrophages. Hindering macrophage polarization towards a pro-tumor M2 phenotype, or better still reprogramming the M2 like TAMs towards M1 subtype is being considered a beneficial anti-cancer strategy. Hypoxic tumor milieu has been proposed as one of the most plausible factor governing M2-polarization of macrophages. We recently demonstrated that hypoxic tumor cells imparted a pro­angiogenic M2 skewed phenotype to macrophages. Furthermore, sizeable body of data indicates for participation of cyclooxygenase-2 (COX-2) in macrophage polarization. Concordantly, inhibition of COX-2 is associated with impaired macrophage polarization. Prompted by this in the current study we decided to explore if inhibition of COX-2 activity via chemical inhibitors may prevent hypoxic cancer cell induced M2-polarization of macrophages. We observed that treatment with Flunixin meglumine, an established preferential inhibitor of COX-2 activity markedly inhibited hypoxic cancer cell induced of M2-polarization of macrophages thereby indicating for usage of COX-2 inhibition as possible anti-cancer treatment modality.