Cysteine string protein (CSP) inhibition of N-type calcium channels is blocked by mutant huntingtin.
Cysteine string protein (CSP), a 34-kDa molecular chaperone, is expressed on synaptic vesicles in neurons and on secretory vesicles in endocrine, neuroendocrine, and exocrine cells. CSP can be found in a complex with two other chaperones, the heat shock cognate protein Hsc70, and small glutamine-rich tetratricopeptide repeat domain protein (SGT). CSP function is vital in synaptic transmission; however, the precise nature of its role remains controversial. We have previously reported interactions of CSP with both heterotrimeric GTP-binding proteins (G proteins) and N-type calcium channels. These associations give rise to a tonic G protein inhibition of the channels. Here we have examined the effects of huntingtin fragments (exon 1) with (huntingtin(exon1/exp)) and without (huntingtin(exon1/nonexp)) expanded polyglutamine (polyQ) tracts on the CSP chaperone system. In vitro huntingtin(exon1/exp) sequestered CSP and blocked the association of CSP with G proteins. In contrast, huntingtin(exon1/nonexp) did not interact with CSP and did not alter the CSP/G protein association. Similarly, co-expression of huntingtin(exon1/exp) with CSP and N-type calcium channels eliminated CSP's tonic G protein inhibition of the channels, while coexpression of huntingtin(exon1/nonexp) did not alter the robust inhibition promoted by CSP. These results indicate that CSP's modulation of G protein inhibition of calcium channel activity is blocked in the presence of a huntingtin fragment with expanded polyglutamine tracts.
Cellular and Molecular Neurobiology Research Group, Department of Physiology and Biophysics, University of Calgary, Calgary, Alberta T2N 4N1, Canada.
Linda C
LC
Miller
Leigh Anne
LA
Swayne
Lina
L
Chen
Zhong-Ping
ZP
Feng
Jennifer L
JL
Wacker
Paul J
PJ
Muchowski
Gerald W
GW
Zamponi
Janice E A
JE
Braun
D000818:Animals; D015153:Blotting, Western; D015220:Calcium Channels / Q000737:chemistry / Q000378:metabolism; D020864:Calcium Channels, N-Type / Q000378:metabolism*; D002460:Cell Line; D019281:Dimerization; D004591:Electrophoresis, Polyacrylamide Gel; D004594:Electrophysiology; D005091:Exons; D005982:Glutathione Transferase / Q000378:metabolism; D049452:Green Fluorescent Proteins; D050956:HSP40 Heat-Shock Proteins; D006624:Hippocampus / Q000378:metabolism; D006801:Humans; D000071058:Huntingtin Protein; D015151:Immunoblotting; D008164:Luminescent Proteins / Q000378:metabolism; D008565:Membrane Proteins / Q000502:physiology*; D008856:Microscopy, Fluorescence; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D009687:Nuclear Proteins / Q000378:metabolism*; D010455:Peptides / Q000737:chemistry / Q000378:metabolism; D017434:Protein Structure, Tertiary; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D015398:Signal Transduction; D009435:Synaptic Transmission; D013696:Temperature; D013997:Time Factors; D014162:Transfection
D015220:Calcium Channels; D020864:Calcium Channels, N-Type; D050956:HSP40 Heat-Shock Proteins; C086055:HTT protein, human; C499524:Htt protein, rat; D000071058:Huntingtin Protein; D008164:Luminescent Proteins; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D010455:Peptides; D011993:Recombinant Fusion Proteins; C088460:cysteine string protein; D049452:Green Fluorescent Proteins; C097188:polyglutamine; D005982:Glutathione Transferase