CONICET | Buscador de Institutos y Recursos Humanos

The retro-transposed gene DUX4, at the human chromosome 4q35, encodes a transcription factor that regulates the expression of zygote activated genes in placental mammals. Our laboratory has demonstrated that DUX4 is a toxic pro-apoptotic protein underlying the pathogenesis of facioscapulohumeral muscular dystrophy (FSHD), the third most common form of inherited myopathy in humans. FSHD females, less affected than males, dramatically deteriorate after menopause or pharmacological treatment with tamoxifen. Interestingly, the C-terminal region of DUX4 possess a LLXXL amino acid motif, present in co-regulators of hormone nuclear receptors, suggesting a potential endocrine function of DUX4. In this report we explored if DUX4 is a co-regulator of the progesterone nuclear receptor (PNR). The activity of PNR was studied on cultured T47D cells, which endogenously expresses PNR, as well as in a reconstituted system in cultured HepG2 cells, transfected with a plasmid expressing the PNR. Two alternative reporters of the activity of the PNR were used: MMTV-Luc and 2XPRE-Luc. The potential co-repressor activity of DUX4 in these experimental systems was assayed using co-transfection with a plasmid expressing either wild-type, GFP fusions or mutant versions of DUX4. We found that DUX4 dramatically inhibits the transcriptional activating function of PNR in T47D and HepG2 cells expressing PNR. DUX4 mutants affecting its nuclear localization signals (NLS-1-2), or its homeodomains 1 and 2 (H1/H2-IWF), loose the repressor activity on the PNR. Taken together, our results indicate that DUX4 is a strong co-repressor of the PNR and that its nuclear location and/or its N-terminal region contribute to this activity. Although DUX4 is mostly considered a transcriptional activator, our results indicate that this protein could indirectly modulate gene expression by repressing the activity of a sex hormone NR.