Abstract
IntroductionProtein denitrosylation by thioredoxin reductase (TrxR) is key for maintaining S-nitrosothiol (SNO) homeostasis, although its role in tumor progression is unknown. Therefore, the present study aimed to assess the role of altered SNO homeostasis in breast cancer cells.MethodsThe impairment of SNO homeostasis in breast cancer cells was achieved with the highly specific TrxR inhibitor auranofin and/or exposure to S-nitroso-L-cysteine. S-nitrosylated proteins were detected using the biotin switch assay. Estrogen receptor (ER) alpha knockdown was achieved using RNA silencing technologies and subcellular localization of ERα was analyzed by confocal microscopy. The Oncomine database was explored for TrxR1 (TXNRD1) expression in breast tumors and TrxR1, ER and p53 expression was analyzed by immunohistochemistry in a panel of breast tumors.ResultsThe impairment of SNO homeostasis enhanced cell proliferation and survival of ER+ MCF-7 cells, but not of MDA-MB-231 (ER-, mut p53) or BT-474 (ER+, mut p53) cells. This enhanced cell growth and survival was associated with Akt, Erk1/2 phosphorylation, and augmented cyclin D1 expression and was abolished by the ER antagonist fulvestrant or the p53 specific inhibitor pifithrin-α. The specific silencing of ERα expression in MCF-7 cells also abrogated the growth effect of TrxR inhibition. Estrogenic deprivation in MCF-7 cells potentiated the pro-proliferative effect of impaired SNO homeostasis. Moreover, the subcellular distribution of ERα was altered, with a predominant nuclear localization associated with phosphorylation at Thr311 in those cells with impaired SNO homeostasis. The impairment of SNO homeostasis also expanded a cancer stem cell-like subpopulation in MCF-7 cells, as indicated by the increase of percentage of CD44+ cells and the augmented capability to form mammospheres in vitro. Notably, ER+ status in breast tumors was significantly associated with lower TXNDR1 mRNA expression and immunohistochemical studies confirmed this association, particularly when p53 abnormalities were absent.ConclusionThe ER status in breast cancer may dictate tumor response to different nitrosative environments. Impairment of SNO homeostasis confers survival advantages to ER+ breast tumors, and these molecular mechanisms may also participate in the development of resistance against hormonal therapies that arise in this type of mammary tumors.
Highlights
Protein denitrosylation by thioredoxin reductase (TrxR) is key for maintaining S-nitrosothiol (SNO) homeostasis, its role in tumor progression is unknown
To determine the effect that impaired SNO homeostasis may have on cancer cell growth, breast cancer cells were subjected to treatment with the nitrosothiol CSNO in the absence of or in the presence of the TrxR specific inhibitor auranofin
Despite the antiproliferative effect obtained by a severe alteration of SNO homeostasis, the inhibition of TrxR with auranofin in MCF-7 cells induced a proproliferative effect
Summary
Protein denitrosylation by thioredoxin reductase (TrxR) is key for maintaining S-nitrosothiol (SNO) homeostasis, its role in tumor progression is unknown. A broad spectrum of pathologies, including cardiovascular diseases [10], respiratory diseases [11,12], hepatic diseases [13], neurodegenerative diseases [14,15] and neoplasic diseases [16], has been associated with impaired SNO homeostasis and aberrant S-nitrosylation of proteins. In this regard, we have recently reported that the inhibition of NO synthesis during induced cholestasis ameliorates hepatocellular injury, and that this therapeutic effect is in part mediated by the improvement of liver proficiency in maintaining SNO homeostasis [13]
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