title: Toxicity and endocytosis of spinocerebellar ataxia type 6 polyglutamine domains: role of myosin IIb.
abstract: Spinocerebellar ataxia type 6 (SCA6) is a dominantly inherited neurodegenerative disease caused by a small expansion of CAG repeats in the sequence coding for the cytoplasmic C-terminal region of the Ca(v)2.1 subunit of P/Q-type calcium channels. We have tested the toxicity of mutated Ca(v)2.1 C-terminal domains expressed in the plasma membrane. In COS-7 cells, CD4-green fluorescent protein fused to Ca(v)2.1 C-terminal domains containing expanded 24 polyglutamine (Q) tracts displayed increased toxicity and stronger expression at the cell surface relative to 'normal' 12 Q tracts, partially because of reduced endocytosis. Glutathione S-transferase pull-down and proteomic analysis indicated that Ca(v)2.1 C-termini interact with the heavy and light chains of cerebellar myosin IIB, a molecular motor protein. This interaction was confirmed by coimmunoprecipitation from rat cerebellum and COS-7 cells and shown to be direct by binding of in vitro-translated (35)S-myosin IIB heavy chain. In COS-7 cells, incremented polyglutamine tract length increased the interaction with myosin IIB. Furthermore, the myosin II inhibitor blebbistatin reversed the effects of polyglutamine expansion on plasma membrane expression. Our findings suggest a key role of myosin IIB in promoting accumulation of mutant Ca(v)2.1Ct at the plasma membrane and suggest that this gain of function might contribute to the pathogenesis of SCA6.
authors.affiliation: INSERM U641, Marseille F-13916, France. marqueze@ciml.univ-mrs.fr
authors.forename: Béatrice
authors.initials: B
authors.lastname: Marquèze-Pouey
authors.forename: Nicole
authors.initials: N
authors.lastname: Martin-Moutot
authors.forename: Marie
authors.initials: M
authors.lastname: Sakkou-Norton
authors.forename: Christian
authors.initials: C
authors.lastname: Lévêque
authors.forename: Yong
authors.initials: Y
authors.lastname: Ji
authors.forename: Véronique
authors.initials: V
authors.lastname: Cornet
authors.forename: Wendy L
authors.initials: WL
authors.lastname: Hsiao
authors.forename: Michael
authors.initials: M
authors.lastname: Seagar
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D015704:CD4 Antigens / Q000096:biosynthesis; D019556:COS Cells; D015220:Calcium Channels / Q000737:chemistry; D002522:Chlorocebus aethiops; D004705:Endocytosis; D005982:Glutathione Transferase / Q000378:metabolism; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D019636:Neurodegenerative Diseases / Q000378:metabolism; D024501:Nonmuscle Myosin Type IIB / Q000737:chemistry* / Q000502:physiology*; D010455:Peptides / Q000737:chemistry*; D017434:Protein Structure, Tertiary; D051381:Rats; D017386:Sequence Homology, Amino Acid; D020754:Spinocerebellar Ataxias / Q000378:metabolism*
chemical_list: D015704:CD4 Antigens; D015220:Calcium Channels; D010455:Peptides; C097188:polyglutamine; D005982:Glutathione Transferase; D024501:Nonmuscle Myosin Type IIB