Hsp40 Couples with the CSPα Chaperone Complex upon Induction of the Heat Shock Response

Abstract

In response to a conditioning stress, the expression of a set of molecular chaperones called heat shock proteins is increased. In neurons, stress-induced and constitutively expressed molecular chaperones protect against damage induced by ischemia and neurodegenerative diseases, however the molecular basis of this protection is not known. Here we have investigated the crosstalk between stress-induced chaperones and cysteine string protein (CSPα). CSPα is a constitutively expressed synaptic vesicle protein bearing a J domain and a cysteine rich “string” region that has been implicated in the long term functional integrity of synaptic transmission and the defense against neurodegeneration. We have shown previously that the CSPα chaperone complex increases isoproterenol-mediated signaling by stimulating GDP/GTP exchange of Gαs. In this report we demonstrate that in response to heat shock or treatment with the Hsp90 inhibitor geldanamycin, the J protein Hsp40 becomes a major component of the CSPα complex. Association of Hsp40 with CSPα decreases CSPα-CSPα dimerization and enhances the CSPα-induced increase in steady state GTP hydrolysis of Gαs. This newly identified CSPα-Hsp40 association reveals a previously undescribed coupling of J proteins. In view of the crucial importance of stress-induced chaperones in the protection against cell death, our data attribute a role for Hsp40 crosstalk with CSPα in neuroprotection.

The Large Conductance, Calcium-activated K+ (BK) Channel is regulated by Cysteine String Protein

“…Functionally, mutation of the HPD motif (residues 43-45) in CSPα disrupts the integrity of the highly conserved J domain, thereby preventing CSPα from activating Hsp70/Hsc70 to carry out conformational protein folding44. Expression of the loss-of-function mutant CSPα HPD-AAA is thus expected to override the activity of endogenous CSPα in CAD cells and act in a dominant-negative fashion45. Figures 2A and B show Western blot analysis and corresponding mean data of BK channel expression in the stable CAD cell line 48 h following transient transfection with myc-tagged CSPα, CSPα HPD-AAA or pCMV plasmid (negative control).…”

CSPα: the neuroprotective J proteinThis paper is one of a selection of papers published in this special issue entitled “Canadian Society of Biochemistry, Molecular & Cellular Biology 52nd Annual Meeting — Protein Folding: Principles and Diseases” and has undergone the Journal's usual peer review process.

“…The consequence of C-terminal alternative splicing to yield full-length CSP1 and truncated CSP2 is not yet understood. Finally, it is important to note that CSPa has been shown to undergo oligomerization, which could affect its overall function; 70 kDa detergent-resistant CSPa dimers have been extensively reported in rat brain (Braun and Scheller 1995;Chamberlain and Burgoyne 1997;Magga et al 2000), rat pancreas (Braun and Scheller 1995), and various transiently transfected cell lines (Gibbs et al 2009;Bai et al 2007;Chamberlain and Burgoyne 1998;Swayne et al 2003). The hydrophobic linker and cysteine string region are key elements in CSPa oligomerization (Swayne et al 2003).…”

“…Hsp40 is a cytosolic J protein whose levels are up-regulated in response to stress. Following a conditioning heat shock or treatment with the Hsp90 inhibitor geldanamycin, the J protein Hsp40 becomes a major component of the CSPa complex (Gibbs et al 2009). Association of Hsp40 with CSPa decreases CSPaCSPa dimerization and increases CSPa GEF (guanine nucleotide exchange factor) activity (see below).…”

Multifaceted Role of Heat Shock Protein 70 in Neurons

“…The homologue of Dna-J1, Hsp40, is involved in repairing damaged proteins in a complex with Hsc70/Hsp70 [86]. Furthermore, in response to heat shock, Hsp40 forms a complex with CSP at the synapse, disrupting CSP dimerization and promoting CSP-mediated GTP hydrolysis on G a subunit, in a manner that is similar to that of Hsc70 [87]. Given the expression level and functions of Hsp83 and Dna-J/Hsp40, these heat shock proteins can provide significant thermoprotection in the absence of inducible Hsp70.…”