C-termini of P/Q-type Ca2+ channel alpha1A subunits translocate to nuclei and promote polyglutamine-mediated toxicity.
P/Q-type voltage-gated calcium channels are regulated, in part, through the cytoplasmic C-terminus of their alpha1A subunit. Genetic absence or alteration of the C-terminus leads to abnormal channel function and neurological disease. Here, we show that the terminal 60-75 kDa of the endogenous alpha1A C-terminus is cleaved from the full-length protein and is present in cell nuclei. Antiserum to the C-terminus (CT-2) labels both wild-type mouse and human Purkinje cell nuclei, but not leaner mouse cerebellum. Human embryonic kidney cells stably expressing beta3 and alpha2delta subunits and transiently transfected with full-length human alpha1A contain a 75 kDa CT-2 reactive peptide in their nuclear fraction. Primary granule cells transfected with C-terminally Green fluorescent protein (GFP)-tagged alpha1A exhibit GFP nuclear labeling. Nuclear translocation depends partly on the presence of three nuclear localization signals within the C-terminus. The C-terminal fragment bears a polyglutamine tract which, when expanded (Q33) as in spinocerebellar ataxia type 6 (SCA6), is toxic to cells. Moreover, polyglutamine-mediated toxicity is dependent on nuclear localization. Finally, in the absence of flanking sequence, the Q33 expansion alone does not kill cells. These results suggest a novel processing of the P/Q-type calcium channel and a potential mechanism for the pathogenesis of SCA6.
Kordasiewicz
Holly B
HB
Department of Neuroscience, Unviersity of Minnesota, 420 Delaware Street SE, Minneapolis, 55455, USA.
Thompson
Randall M
RM
Clark
H Brent
HB
Gomez
Christopher M
CM
D021581:Active Transport, Cell Nucleus; D020816:Amino Acid Motifs; D000818:Animals; D015220:Calcium Channels / Q000235:genetics / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D002470:Cell Survival; D002478:Cells, Cultured; D002531:Cerebellum / Q000378:metabolism; D006801:Humans; D051379:Mice; D009154:Mutation; D019913:Nuclear Localization Signals / Q000502:physiology; D010455:Peptides / Q000502:physiology*; D021122:Protein Subunits / Q000378:metabolism; D011689:Purkinje Cells / Q000378:metabolism; D020864:Calcium Channels, N-Type
D015220:Calcium Channels; D019913:Nuclear Localization Signals; D010455:Peptides; D021122:Protein Subunits; C105656:CACNA1A protein, human; D020864:Calcium Channels, N-Type; C097188:polyglutamine