Polyalanine expansion mutations in the X-linked hypopituitarism gene SOX3 result in aggresome formation and impaired transactivation.
Polyalanine expansion mutations have been identified in eight transcription factors that are associated with a range of congenital disorders. While some of these mutant proteins have been shown to generate cellular aggregates in heterologous cell lines, little is known about the mechanism by which these aggregates cause disease. Here we examine the aggregation and functional properties of the two known polyalanine expansion mutations associated with X-linked Hypopituitarism (XH), SOX3(22Ala) and SOX3(26Ala), which contain an additional seven and eleven alanine residues, respectively. SOX3(22Ala) and SOX3(26Ala) proteins form cytoplasmic aggregates and nuclear inclusions in transiently transfected COS-7 and CHO K1 cells, and in transfected explant cultures of chick neural epithelium. SOX3(26Ala) exhibits a more potent aggregation phenotype, resulting in significantly more cells with dispersed cytoplasmic and large perinuclear aggregates. SOX3(22Ala) and SOX3(26Ala) protein aggregates exhibit the key properties of aggresomes including vimentin redistribution, colocalisation with the Microtubule Organising Centre and sensitivity to microtubule disruption. This is the first time that aggresomes have been implicated in the aetiology of a polyalanine expansion disorder, suggesting that XH and protein conformation disorders may become manifest through similar pathological mechanisms. Further, we show that mutant SOX3 proteins have impaired transcriptional activity and reduced capacity to inhibit beta-catenin/TCF-mediated transcription. These data suggest that deregulation of SOX3 target genes and inappropriate canonical Wnt signaling in central nervous system (CNS) progenitors may also contribute to dysfunction of the hypothalamic-pituitary axis in XH patients.
Wong
Jacqueline
J
Pituitary Research Unit, Murdoch Childrens Research Institute, Royal Childrens Hospital, Melbourne, Australia.
Farlie
Peter
P
Holbert
Sebastien
S
Lockhart
Paul
P
Thomas
Paul Q
PQ
D000818:Animals; D019556:COS Cells; D022003:Cell Nucleus Structures / Q000737:chemistry; D002642:Chick Embryo; D002522:Chlorocebus aethiops; D022083:Cytoplasmic Structures / Q000737:chemistry; D042622:DNA Repeat Expansion; D004268:DNA-Binding Proteins / Q000032:analysis / Q000235:genetics* / Q000378:metabolism; D040181:Genetic Diseases, X-Linked / Q000235:genetics*; D006609:High Mobility Group Proteins / Q000032:analysis / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D007018:Hypopituitarism / Q000235:genetics*; D008297:Male; D010455:Peptides / Q000737:chemistry / Q000235:genetics*; D055748:SOXB1 Transcription Factors; D014157:Transcription Factors / Q000032:analysis / Q000235:genetics* / Q000378:metabolism; D015533:Transcriptional Activation; D051176:beta Catenin / Q000378:metabolism
D004268:DNA-Binding Proteins; D006609:High Mobility Group Proteins; D010455:Peptides; C527785:SOX3 protein, human; D055748:SOXB1 Transcription Factors; D014157:Transcription Factors; D051176:beta Catenin; C019529:polyalanine