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2008-01-21 - Colloque/Présentation - communication orale - Français - 1 page(s)

Tassin Alexandra , Ansseau Eugénie , Vanderplanck Céline, Cloet S, Barro Marietta, Laoudj-Chenivesse Dalila, Chen Yi-Wen, Belayew Alexandra , Coppée Frédérique , "DUX4 and DUX4c activate different pathways in Facioscapulohumeral dystrophy " in Colloque « Myogenese IX », Institut de Myologie, Paris, France, 2008

  • Codes CREF : Biologie moléculaire (DI3111), Pathologies particulières (DI3370)
  • Unités de recherche UMONS : Biologie moléculaire (M122)
  • Instituts UMONS : Institut des Sciences et Technologies de la Santé (Santé)

Abstract(s) :

(Anglais) Facioscapulohumeral muscular dystrophy (FSHD) is a dominant disease genetically linked to contractions of a repeat array in the 4q35 subtelomeric region. In non-affected individuals the array comprises 11-100 tandem copies of a 3.3-kb element named D4Z4. Patients only have 1-10 copies left, and the disease is more severe with smaller copy numbers. We have characterized a double homeobox gene (DUX4) within each D4Z4 unit. It expresses a toxic protein in FSHD but not control myoblasts. DUX4 activates transcription of the paired-like homeodomain transcription factor 1 gene (PITX1) in 5q26. PITX1 is specifically up-regulated in FSHD muscles as compared to 11 other neuromuscular disorders. It is associated to muscle atrophy and left/right asymmetry. Our data provided a direct link between the genetic defect in 4q35 and the pathophysiology of the disease (Dixit et al 2007). Since DUX4 forced expression activates the endogenous Pitx1 gene in transfected C2C12 cells (mouse myoblasts), we checked by co-immunofluorescence whether the endogenous DUX4 protein could activate the endogenous PITX1 gene in cultures of FSHD primary myotubes. We could indeed observe DUX4 positive nuclei, some of which were also stained for PITX1. By Western blot, we detected high levels of 52-kDa DUX4 in muscle biopsies from 3 patients with FSHD but not 2 controls. We could only detect the PITX1 protein in a severely affected FSHD muscle biopsy with atrophic fibers. We have also characterized the homologous DUX4c gene mapped 42 kb of the D4Z4 repeat array. DUX4c mRNA and protein were detected in control primary myoblasts and induced upon differentiation. The protein level was increased 1.5-2-fold in FSHD versus control and DMD (Duchenne Muscular dystrophy) myotubes. In muscle biopsies, DUX4c expression was increased in FSHD (2-10-fold) as compared to controls. Higher levels were detected in FSHD samples with shorter D4Z4 arrays that usually correlate with a worse clinical outcome. DUX4c expression was increased 3-4-fold in muscle biopsies of patients with DMD as compared to controls: this increase might result from the multiple degeneration/regeneration cycles characteristic of the disease. In a functional study we transfected human TE671 rhabdomyosarcoma cells with pCINeo expression vectors for either DUX4, DUX4c, DUX1 or without insert. By immunofluorescence we observed a strong up-regulation of PCNA (proliferating cell nuclear antigen) 24h post-transfection in DUX4c expressing cells only. When we added a differentiation medium (2% horse serum), DUX4c expressing cells continued to proliferate instead of aligning to fuse into myotubes like the other transfected cells. We had previously showed that DUX4c specifically induced the MYF5 transcription factor. In aggregate these findings suggested a role for DUX4c in muscle regeneration not restricted to FSHD. We propose that as well an excess (in patients with low D4Z4 copy number) as a reduced amount (in families where the D4Z4 deletion removes the DUX4c gene) of DUX4c expression could affect muscle regeneration and contribute to the FSHD pathology. Reference: Dixit et al, 2007, Proc Natl Acad Sci U S A. 104:18157-18162.