FRG1P-mediated aggregation of proteins involved in pre-mRNA processing

Abstract

FRG1 is considered a candidate gene for facioscapulohumeral muscular dystrophy (FSHD) based on its location at chromosome 4qter and its upregulation in FSHD muscle. The FRG1 protein (FRG1P) localizes to nucleoli, Cajal bodies (and speckles), and has been suggested to be a component of the human spliceosome but its exact function is unknown. Recently, transgenic mice overexpressing high levels of FRG1P in skeletal muscle were described to present with muscular dystrophy. Moreover, upregulation of FRG1P was demonstrated to correlate with missplicing of specific pre-mRNAs. In this study, we have combined colocalization studies with yeast two-hybrid screens to identify proteins that associate with FRG1P. We demonstrate that artificially induced nucleolar aggregates of VSV-FRG1P specifically sequester proteins involved in pre-mRNA processing. In addition, we have identified SMN, PABPN1, and FAM71B, a novel speckle and Cajal body protein, as binding partners of FRG1P. All these proteins are, or seem to be, involved in RNA biogenesis. Our data confirm the presence of FRG1P in protein complexes containing human spliceosomes and support a potential role of FRG1P in either splicing or another step in nuclear RNA biogenesis. Intriguingly, among FRG1P-associated proteins are SMN and PABPN1, both being involved in neuromuscular disorders, possibly through RNA biogenesis-related processes.

Facioscapulohumeral muscular dystrophy (FSHD): an enigma unravelled?

“…Consistent with a putative role in FSHD, several functional studies of the FRG1 protein have shown it to have a role in both angiogenesis and muscle development by utilising quite different biochemical functions, i.e. alternative RNA splicing and actin bundling (Gabellini et al 2006;van Koningsbruggen et al 2007;Hanel et al 2009;Wuebbles et al 2009;Liu et al 2010;Sun et al 2011). Furthermore, a recent analysis of myoblasts isolated from affected muscle of a transgenic mouse overexpressing FRG1 reported a significant loss of cell proliferation and an increased doubling time not observed in unaffected muscle .…”

A nuclear matrix attachment site in the 4q35 locus has an enhancer-blocking activity in vivo: Implications for the facio-scapulo-humeral dystrophy

“…gene which encodes a putative splicing factor (Gabellini et al 2005;van Koningsbruggen et al 2006) found overexpressed in myoblasts from FSHD patients (Gabellini et al 2002;Rijkers et al 2004;Laoudj-Chenivesse et al 2005). A 577-bp fragment from the FRG1 gene promoter region was transferred into the promoterless pGL3-Basic plasmid for transfection into human primary myoblasts and HeLa cells.…”

Comprehensive Analysis of Yeast Surface Displayed cDNA Library Selection Outputs by Exon Microarray to Identify Novel Protein-Ligand Interactions

“…Nuclear speckles are subnuclear structures enriched in pre-mRNA splicing factors (44). Three of the novel phosphatidylinositide-binding protein fragments we identified (FAM71B, RNPS1, and SFRS4) and one unverified candidate (SRRP35) are from proteins that localize to nuclear speckles (45)(46)(47)(48). Phosphatidylinositide binding by the PDZ domains of syntenin-2 and zonula occludens-1 and -2 regulates their localization to nuclear speckles (37,38).…”