Quercetin accumulates in nuclear structures and triggers specific gene expression in epithelial cells☆ George Notas a,1 , Artemisia-Phoebe Nifli a,1,2 , Marilena Kampa a , Vassiliki Pelekanou a,3 , Vasileia-Ismini Alexaki a , Panayiotis Theodoropoulos b , Joseph Vercauteren c , Elias Castanas a, ⁎ a Laboratory of Experimental Endocrinology, University of Crete, School of Medicine, P.O. Box 2208, Heraklion GR-71003, Greece b Laboratory of Biochemistry, University of Crete, School of Medicine, P.O. Box 2208, Heraklion GR-71003, Greece c Laboratoire de Pharmacognosie, Université de Montpellier I, 34093, France Received 7 October 2010; received in revised form 25 February 2011; accepted 11 March 2011 Abstract Quercetin is a flavonol modifying a number of cell processes in different cell lines. Here, we present evidence that nonconjugated quercetin enters cells possibly via organic anion transporter polypeptides and quickly accumulates in the nucleus where it concentrates at distinct foci. Furthermore, it induces major transcriptional events with a high number of transcripts being modified over time and about 2200 transcripts being continuously influenced by the agent. The latter transcripts are related to cell cycle and adhesion, xenobiotic metabolism, immune-related factors and transcription. In addition, quercetin up-regulates the expression of estrogen receptors α and β. The overall outcome on cell fate is reflected by an inhibition of cell proliferation, cell cycle arrest in the G1 phase and reduction of the cells' migratory potential due to actin cytoskeleton disorganization. Finally, we report that the flavonol modifies the transcription and/or activity of numerous transcription factors. In conclusion, our data support the idea that quercetin may actively accumulate in discrete cell structures and exert more than just antioxidant actions on epithelial cells by regulating mechanisms related to gene transcription. © 2011 Elsevier Inc. All rights reserved. Keywords: Cell adhesion; Cell cycle; Transcriptional analysis; Cell lines (HepG2; T47D); Quercetin 1. Introduction Polyphenols (more than 8000 identified molecules containing a phenolic scaffold) constitute a large family of plant-derived com- pounds, incorporated in animals through dietary absorption of vegetal foods. Besides their powerful antioxidant properties, they exert a large number of biological actions, depending on their absorption and metabolism [1,2]. One of the most widely represented polyphenol in the human diet is the flavonol quercetin [3,4]. It is present in different fruits and vegetables, and its daily consumption, in a balanced diet, varies between 3 and 38 mg/day, resulting in circulating concentrations of 0.3–7.6 μM of the nonconjugated form [4,5]. After absorption, the major part of quercetin undergoes glucuronidation, methylation or sulfation in the liver (critically discussed in Refs. [3] and [6]) before its release to the circulation. Interestingly, a number of studies have shown that conjugated quercetin quickly enters the cell where it regains its active, nonconjugated form [7]. Classically, the main attributed activity of quercetin was related to its antioxidant effect. However, recent data are indicative of additional effects by direct interaction with plasma membranes [8] and accumulation to the nucleus [9] and mitochondria [10], affecting a number of cell functions. Indeed, quercetin interacts with steroid and aryl-hydrocarbon receptors in breast and prostate cancer cell lines [11,12], decreases cell proliferation and modulates several signal transduction pathways involving MEK/ERK and Nrf2/keap1 [13]. Rodent studies additionally suggest that dietary administration of quercetin may prevent chemically induced colon carcinogenesis, while epidemiological studies indicate that its reasonable food intake may be associated with the prevention of lung cancer [13]. The intracellular transport of the agent and its action in the nucleus have not been examined in detail until now. In the present work, we explore the kinetics and potential mechanisms involved in quercetin cellular internalization and nuclear accumulation. Addi- tionally, through a kinetic transcriptome analysis, we investigated the effects of the flavonol on the transcriptional activity of the cell. We Available online at www.sciencedirect.com Journal of Nutritional Biochemistry xx (2011) xxx – xxx ☆ Grants: Work was partially supported by EU (COOP-CT-2003-508649 Project PARADOX and EL-0075-2008, project ICC) grant. ⁎ Corresponding author. Laboratory of Experimental Endocrinology University of Crete, School of Medicine P.O. Box 2208, Heraklion GR-71003, Greece. Tel.: +30 2810 394580, fax: +30 2810 394581. E-mail address: castanas@med.uoc.gr (E. Castanas). 1 Authors have equally contributed to this work. 2 Present address: Artemisia-Phoebe Nifli: University of Thesaly, School of Medicine, Larissa, Greece. 3 Present address: Vassiliki Pelekanou, Laboratoire d’Anatomie Patholo- gique, Institut Jules Bordet, Brussels, 1000, Belgium. 0955-2863/$ - see front matter © 2011 Elsevier Inc. All rights reserved. doi:10.1016/j.jnutbio.2011.03.010