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: Béatrice Marquèze-Pouey, Nicole Martin-Moutot, Marie Sakkou-Norton, Christian Lévêque, Yong Ji, Véronique Cornet, Wendy L Hsiao, Michael Seagar
• Journal: Traffic (Copenhagen, Denmark) (Traffic) Vol. 9 Issue 7 Pg. 1088-100 (Jul 2008) ISSN: 1600-0854 [Electronic] England
• PMID: 18384641 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• CD4 Antigens
• Calcium Channels
• Peptides
• polyglutamine
• Glutathione Transferase
• Nonmuscle Myosin Type IIB

Topics

• Amino Acid Sequence
• Animals
• CD4 Antigens (biosynthesis)
• COS Cells
• Calcium Channels (chemistry)
• Chlorocebus aethiops
• Endocytosis
• Glutathione Transferase (metabolism)
• Humans
• Mice
• Molecular Sequence Data
• Neurodegenerative Diseases (metabolism)
• Nonmuscle Myosin Type IIB (chemistry, physiology)
• Peptides (chemistry)
• Protein Structure, Tertiary
• Rats
• Sequence Homology, Amino Acid
• Spinocerebellar Ataxias (metabolism)