Estrogen interferes with DUX4 nuclear import

DUX4 (Double Homeobox Protein 4) pathogenic activity is developed through transcriptional function and is associated with its nuclear localization. Three monopartite nuclear localization signals (NLS) are present in DUX4, but their function has not been completely defined in myoblasts (Corona et al., 2013). Recently, we demonstrated that in vitro differentiation of myoblasts from FSHD patients is improved by estrogen treatments. Estrogen through estrogen receptor β (ERβ) reduce DUX4 transcriptional activity and impair its nuclear localization (Teveroni et al., 2017). To understand how estrogen interferes with DUX4 activity, we analysed the interactome of DUX4 in myoblasts grown for three days in differentiation medium in presence or absence of estrogen. Interactome analysis revealed that DUX4 binds some Nuclear Pore Complex (NPC) proteins. Estrogen treatment decreases such binding without altering these NPC protein levels. Preliminary immunofluorescence experiments confirmed increased co-localization of DUX4 with these proteins during myoblast differentiation. Overexpression of these proteins increases DUX4 transcriptional activity, supporting the relevance of such interaction for the development of DUX4 activity. Finally, a loss of function mutant in one of the three NLS showed decreased transcriptional function compared to wild-type DUX4. Overall these data suggest that the nuclear import of DUX4 is an active process and that estrogen can impair it.