Human Molecular Genetics Advance Access published online on November 14, 2008
Human Molecular Genetics, doi:10.1093/hmg/ddn389
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Positive and negative feedback regulates the transcription factor FOXL2 in response to cell stress: evidence for a regulatory imbalance induced by disease-causing mutations
1 INSERM U567, Team 21, Department of Genetics and Development, Institut Cochin, 75014 Paris, France 2 CNRS UMR8104, Institut Cochin, 75014 Paris, France 3 Université Paris Descartes, Faculté de Médecine Cochin-Port-Royal, Paris 75014, France 4 Université Denis Diderot, Paris VII, 75013 Paris, France 5 École Normale Supérieure, 75005 Paris, France 6 Paris-Sud, Paris XI, 91400 Orsay, France 7 INRA/Université de Limoges, UMR 1061, Unité de Génétique Moléculaire Animale, Université de Limoges, Limoges, France 8 Center for Medical Genetics, Ghent University Hospital, 9000 Ghent, Belgium
* Corresponding author. INSERM E21-GDPM, Institut Cochin, 24, Rue du Faubourg Saint-Jacques, 75014 Paris, France. Tel: +33144412301 Fax: +33144412302 Email: reiner.veitia{at}inserm.fr
Received September 30, 2008; Revised November 13, 2008; Accepted November 13, 2008
FOXL2 is a Forkhead transcription factor, essential for ovarian function, whose mutations are responsible for the Blepharophimosis Syndrome, characterized by craniofacial defects, often associated with premature ovarian failure. Here, we show that cell stress upregulates FOXL2 expression in an ovarian granulosa cell model. Increased FOXL2 transcription might be mediated at least partly by self-activation. Moreover, using 2D-western blot, we show that the response of FOXL2 to stress correlates with a dramatic remodeling of its post-translational modification profile. Upon oxidative stress, we observe an increased recruitment of FOXL2 to several stress-response promoters, notably that of the mitochondrial Superoxide Dismutase (MnSOD). Using several reporter systems, we show that FOXL2 transactivation is enhanced in this context. Models predict that gene upregulation in response to a signal should eventually be counterbalanced to restore the initial steady state. In line with this, we find that FOXL2 activity is repressed by the SIRT1 deacetylase. Interestingly, we demonstrate that SIRT1 transcription is, in turn, directly upregulated by FOXL2, which closes a negative-feedback loop. The regulatory relationship between FOXL2 and SIRT1 prompted us the test action of nicotinamide, an inhibitor of sirtuins, on FoxL2 expression/activity. According to our expectations, nicotinamide treatment increases FoxL2 transcription. Finally, we show that 11 disease-causing mutations in the ORF of FOXL2 induce aberrant regulation of FOXL2 and/or regulation of the FOXL2 stress-response target gene MnSOD. Taken together, our results establish that FOXL2 is an actor of the stress response, and provide new insights into the pathogenic consequences of FOXL2 mutations.
The authors wish it to be known that, in their opinion, the second, third and fourth authors contributed equally to this work.
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