J-domain proteins: From molecular mechanisms to diseases.

J-domain proteins (JDPs) are the largest family of chaperones in most organisms, but much of how they function within the network of other chaperones and protein quality control machineries is still an enigma. Here, we report on the latest findings related to JDP functions presented at a dedicated JDP workshop in Gdansk, Poland. The report does not include all (details) of what was shared and discussed at the meeting, because some of these original data have not yet been accepted for publication elsewhere or represented still preliminary observations at the time.

Extracellular chaperone networks and the export of J-domain proteins.

An extracellular network of molecular chaperones protects a diverse array of proteins that reside in or pass through extracellular spaces. Proteins in the extracellular milieu face numerous challenges that can lead to protein misfolding and aggregation. As a checkpoint for proteins that move between cells, extracellular chaperone networks are of growing clinical relevance.

Cysteine String Protein Controls Two Routes of Export for Misfolded Huntingtin.

Extracellular vesicles (EVs) are secreted vesicles of diverse size and cargo that are implicated in the cell-to-cell transmission of disease-causing-proteins in several neurodegenerative diseases. Mutant huntingtin, the disease-causing entity in Huntington's disease, has an expanded polyglutamine track at the N terminus that causes the protein to misfold and form toxic intracellular aggregates. In Huntington's disease, mutant huntingtin aggregates are transferred between cells by several routes.

Neurons Export Extracellular Vesicles Enriched in Cysteine String Protein and Misfolded Protein Cargo.

The fidelity of synaptic transmission depends on the integrity of the protein machinery at the synapse. Unfolded synaptic proteins undergo refolding or degradation in order to maintain synaptic proteostasis and preserve synaptic function, and buildup of unfolded/toxic proteins leads to neuronal dysfunction. Many molecular chaperones contribute to proteostasis, but one in particular, cysteine string protein (CSPα), is critical for proteostasis at the synapse.

Increased Expression of the Large Conductance, Calcium-Activated K+ (BK) Channel in Adult-Onset Neuronal Ceroid Lipofuscinosis.

Cysteine string protein (CSPα) is a presynaptic J protein co-chaperone that opposes neurodegeneration. Mutations in CSPα (i.e.

J protein mutations and resulting proteostasis collapse.

Despite a century of intensive investigation the effective treatment of protein aggregation diseases remains elusive. Ordinarily, molecular chaperones ensure that proteins maintain their functional conformation. The appearance of misfolded proteins that aggregate implies the collapse of the cellular chaperone quality control network.

CSPα-chaperoning presynaptic proteins.

Synaptic transmission relies on precisely regulated and exceedingly fast protein-protein interactions that involve voltage-gated channels, the exocytosis/endocytosis machinery as well as signaling pathways. Although we have gained an ever more detailed picture of synaptic architecture much remains to be learned about how synapses are maintained. Synaptic chaperones are "folding catalysts" that preserve proteostasis by regulating protein conformation (and therefore protein function) and prevent unwanted protein-protein interactions.

Cysteine string protein limits expression of the large conductance, calcium-activated K⁺ (BK) channel.

Large-conductance, calcium-activated K(+) (BK) channels are widely distributed throughout the nervous system and play an essential role in regulation of action potential duration and firing frequency, along with neurotransmitter release at the presynaptic terminal. We have previously demonstrated that select mutations in cysteine string protein (CSPα), a presynaptic J-protein and co-chaperone, increase BK channel expression. This observation raised the possibility that wild-type CSPα normally functions to limit neuronal BK channel expression.

The large conductance, calcium-activated K+ (BK) channel is regulated by cysteine string protein.

Large-conductance, calcium-activated-K(+) (BK) channels are widely distributed throughout the nervous system, where they regulate action potential duration and firing frequency, along with presynaptic neurotransmitter release. Our recent efforts to identify chaperones that target neuronal ion channels have revealed cysteine string protein (CSPα) as a key regulator of BK channel expression and current density. CSPα is a vesicle-associated protein and mutations in CSPα cause the hereditary neurodegenerative disorder, adult-onset autosomal dominant neuronal ceroid lipofuscinosis (ANCL).

Cell line specific modulation of extracellular aβ42 by Hsp40.

Heat shock proteins (Hsps) are a set of molecular chaperones involved in cellular repair. They provide protective mechanisms that allow cells to survive potentially lethal insults, In response to a conditioning stress their expression is increased. Here we examined the connection between Hsps and Aβ(42), the amyloid peptide involved in the pathological sequence of Alzheimer's disease (AD).

Mitochondrial chaperone DnaJA3 induces Drp1-dependent mitochondrial fragmentation.

Mitochondrial morphology is dynamic and controlled by coordinated fusion and fission pathways. The role of mitochondrial chaperones in mitochondrial morphological changes and pathology is currently unclear. Here we report that altered levels of DnaJA3 (Tid1/mtHsp40) a mitochondrial member of the DnaJ protein family, and heat shock protein (Hsp) co-chaperone of matrix 70 kDa Hsp70 (mtHsp70/mortalin/HSPA9), induces mitochondrial fragmentation.

Identification of bilateral changes in TID1 expression in the 6-OHDA rat model of Parkinson's disease.

Parkinson's disease (PD) is a common neurodegenerative disease characterized by the loss of dopaminergic neurons in the substantia nigra and the aggregation of α-synuclein into Lewy bodies. Existing therapies address motor dysfunction but do not halt progression of the disease. A still unresolved question is the biochemical pathway that modulates the outcome of protein misfolding and aggregation processes in PD.

Quercetin targets cysteine string protein (CSPalpha) and impairs synaptic transmission.

Background: Cysteine string protein (CSPalpha) is a synaptic vesicle protein that displays unique anti-neurodegenerative properties. CSPalpha is a member of the conserved J protein family, also called the Hsp40 (heat shock protein of 40 kDa) protein family, whose importance in protein folding has been recognized for many years. Deletion of the CSPalpha in mice results in knockout mice that are normal for the first 2-3 weeks of life followed by an unexplained presynaptic neurodegeneration and premature death.

CSPalpha: the neuroprotective J protein.

Cysteine string protein (CSPalpha, also called DnaJC5) is unique among J proteins. Similar to other J proteins, CSPalpha interacts with and activates the ATPase of Hsc70s (heat shock proteins of 70 kDa), thereby harnessing the ATPase activity for conformational work on client proteins. In contrast to other J proteins, CSPalpha is anchored to synaptic vesicles, as well as to exocrine, endocrine and neuroendocrine secretory granules, and has been shown to have an essential anti-neurodegenerative role.

Reduction of PrP(C) in human cerebrospinal fluid after spinal cord injury.

It has been estimated that cerebrospinal fluid (CSF) contains approximately 80 proteins that significantly increase or decrease in response to various clinical conditions. Here we have evaluated the CSF protein PrP(C) (cellular prion protein) for possible increases or decreases following spinal cord injury. The physiological function of PrP(C) is not yet completely understood; however, recent findings suggest that PrP(C) may have neuroprotective properties.

Functional role of J domain of cysteine string protein in Ca2+-dependent secretion from acinar cells.

The heat shock protein 70 family members Hsc70 and Hsp70 are known to play a protective role against the onset of experimental pancreatitis, yet their molecular function in acini is unclear. Cysteine string protein (CSP-alpha) is a zymogen granule (ZG) membrane protein characterized by an NH(2)-terminal "J domain" and a central palmitoylated string of cysteine residues. The J domain functions as a cochaperone by modulating the activity of Hsc70/Hsp70 family members.

Hsp40 couples with the CSPalpha chaperone complex upon induction of the heat shock response.

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 (CSPalpha).

Emerging roles of J proteins in neurodegenerative disorders.

Several families of proteins called molecular chaperones comprise the cellular machinery that has evolved to maintain protein structure and eliminate misfolded proteins in the cell. In experimental animal models, chaperones have been shown to be powerful inhibitors of neurodegeneration. As such, molecular chaperones represent exciting pharmaceutical targets that potentially eliminate aberrant cellular proteins and slow disease progression.

RDJ2 (DNAJA2) chaperones neural G protein signaling pathways.

A number of structurally divergent proteins with J domains, called J proteins, interact with and activate the ATPase of Hsp70s, thereby harnessing the ATPase activity for conformational work on target proteins. The precise role of most mammalian J proteins remains undefined. In this paper, we demonstrate that transient expression of the J protein, Rdj2, in HEK 293 cells increased cellular cyclic adenosine monophosphate (cAMP) levels in the presence of the beta-adrenergic agonist isoproterenol.

Aggregate-centered redistribution of proteins by mutant huntingtin.

Huntingtin is a widely expressed 350-kDa cytosolic multidomain of unknown function. Aberrant expansion of the polyglutamine tract located in the N-terminal region of huntingtin results in Huntington's disease. The presence of insoluble huntingtin inclusions in the brains of patients is one of the hallmarks of Huntington's disease.

The CSPalpha/G protein complex in PC12 cells.

Cysteine string proteinalpha (CSPalpha) is a regulated vesicle protein and molecular chaperone that has been found to be critical for continuous synaptic transmission and is implicated in the defense against neurodegeneration. Previous work has revealed links between CSPalpha and heterotrimeric GTP binding protein (G protein) signal transduction pathways. We have shown that CSPalpha is a guanine nucleotide exchange factor (GEF) for Galphas.

The cysteine string protein multimeric complex.

Cysteine string protein (CSPalpha) is a member of the cellular folding machinery that is located on regulated secretory vesicles. We have previously shown that CSPalpha in association with Hsc70 (70kDa heat shock cognate protein) and SGT (small glutamine-rich tetratricopeptide repeat domain protein) is a guanine nucleotide exchange factor (GEF) for G(alphas). Association of this CSPalpha complex with N-type calcium channels, a channel key in coupling calcium influx with synaptic vesicle exocytosis, triggers tonic G protein inhibition of the channels.