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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. J-domain proteins (JDPs) are ubiquitous molecular chaperones that are known for their essential roles in a wide array of fundamental cellular processes through their regulation of heat shock protein 70s. As the largest molecular chaperone family, JDPs have long been recognized for their diverse functions within cells. Some JDPs are elegantly selective for their "client proteins," some do not discriminate among substrates and others act cooperatively on the same target. The realization that JDPs are exported through both classical and unconventional secretory pathways has fueled investigation into the roles that JDPs play in protein quality control and intercellular communication. The proposed functions of exported JDPs are diverse. Studies suggest that export of DnaJB11 enhances extracellular proteostasis, that intercellular movement of DnaJB1 or DnaJB6 enhances the proteostasis capacity in recipient cells, whereas the import of DnaJB8 increases resistance to chemotherapy in recipient cancer cells. In addition, the export of DnaJC5 and concurrent DnaJC5- dependent ejection of dysfunctional and aggregation-prone proteins are implicated in the prevention of neurodegeneration. This review provides a brief overview of the current understanding of the extracellular chaperone networks and outlines the first wave of studies describing the cellular export of JDPs. [ABSTRACT FROM AUTHOR]

In this study, we have systematically evaluated the signaling mechanisms underlying stimulated nitric oxide (NO) synthesis by estrogen ([E.sub.2]) and other vasoactive agents at the level of a single endothelium-derived cell. To do so, we have characterized and contrasted rapid [E.sub.2]-evoked NO synthesis with that of ATP using single-cell microfluorimetry and patch-clamp recordings to monitor stimulated changes in cellular NO synthesis (via 4-amino-5-methylamino-2',7'-difluorofluorescein), [Ca.sup.2+] transients (via Fluo-3), and membrane hyperpolarization in cultured human EA.hy926 cells. Ez-evoked NO synthesis in single cells ([EC.sub.50] ~0.3 nM) was blocked by the E2 receptor antagonist ICI 182,780 and the NO synthase inhibitor [N.sup.[omega]]-nitro-L-arginine methyl ester. Although both [E.sub.2] and ATP stimulated comparable [Ca.sup.2+] transients, [E.sub.2]-induced NO synthesis was insensitive to intracellular BAPTA-AM or removal of external [Ca.sup.2+]. In contrast, ATP-evoked NO production was abolished by either one of these treatments. ATP-evoked hyperpolarizations (~20 mV) and NO production were both inhibited by the respective small-conductance and intermediate-conductance calciumactivated [K.sup.+] channel blockers apamin and charybdotoxin. [E.sub.2] minimally affected membrane potential, and stimulated NO synthesis was insensitive to calcium-activated [K.sup.+] channel blockers. Exposure to either the phosphatidylinositol 3-kinase inhibitor LY-294001 or the MAP kinase inhibitor PD-98059 abolished the NO response to [E.sub.2], but not that to ATP. Finally, the NO response evoked by a combined stimulus of [E.sub.2] plus ATP was similar to that of ATP alone. In conclusion, our data directly demonstrate that an individual human EA.hy926 cell contains at least two distinct mechanisms for stimulated NO synthesis that depend on either calcium or protein kinase signaling events. nitric oxide; endothelial function; calcium; signal transduction

Cysteine string protein (CSPα) is a presynaptic J protein co-chaperone that opposes neurodegeneration. Mutations in CSPα (i.e., Leu115 to Arg substitution or deletion (Δ) of Leu116) cause adult neuronal ceroid lipofuscinosis (ANCL), a dominantly inherited neurodegenerative disease. We have previously demonstrated that CSPα limits the expression of large conductance, calcium-activated K+ (BK) channels in neurons, which may impact synaptic excitability and neurotransmission. Here we show by western blot analysis that expression of the pore-forming BKα subunit is elevated ~2.5 fold in the post-mortem cortex of a 36-year-old patient with the Leu116∆ CSPα mutation. Moreover, we find that the increase in BKα subunit level is selective for ANCL and not a general feature of neurodegenerative conditions. While reduced levels of CSPα are found in some postmortem cortex specimens from Alzheimer’s disease patients, we find no concomitant increase in BKα subunit expression in Alzheimer’s specimens. Both CSPα monomer and oligomer expression are reduced in synaptosomes prepared from ANCL cortex compared with control. In a cultured neuronal cell model, CSPα oligomers are short lived. The results of this study indicate that the Leu116∆ mutation leads to elevated BKα subunit levels in human cortex and extend our initial work in rodent models demonstrating the modulation of BKα subunit levels by the same CSPα mutation. While the precise sequence of pathogenic events still remains to be elucidated, our findings suggest that dysregulation of BK channels may contribute to neurodegeneration in ANCL. [ABSTRACT FROM AUTHOR]

The article discusses the synaptic protein complexes and ion channels under the influence of cysteine string protein (CSPα), a molecular chaperone and presynaptic vesicle protein. Topics discussed include the central role of CSPα in synaptic loss and neurodegeneration prevention, the disease onset of adult onset neuronal ceroid lipofusinosis (ANCL), and the neurodegeneration in CSPα knockout (KO) mice.

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. Here we show by Western blot analysis of transfected neuroblastoma cells that when BK channels are present at elevated levels, CSPα acts to reduce expression. Moreover, we demonstrate that the accessory subunits, BKβ4 and BKβ1 do not alter CSPα-mediated reduction of expressed BKα subunits. Structure-function analysis reveals that the N-terminal J-domain of CSPα is critical for the observed regulation of BK channels levels. Finally, we demonstrate that CSPα limits BK current amplitude, while the loss-of-function homologue CSPαHPD-AAA increases BK current. Our observations indicate that CSPα has a role in regulating synaptic excitability and neurotransmission by limiting expression of BK channels. [ABSTRACT FROM AUTHOR]

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). CSPα null mice show 2.5 fold higher BK channel expression compared to wild type mice, which is not seen with other neuronal channels (i.e. Cav2.2, Kv1.1 and Kv1.2). Furthermore, mutations in either CSPα's J domain or cysteine string region markedly increase BK expression and current amplitude. We conclude that CSPα acts to regulate BK channel expression, and consequently CSPα-associated changes in BK activity may contribute to the pathogenesis of neurodegenerative disorders, such as ANCL. [ABSTRACT FROM AUTHOR]

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 Aβ42, the amyloid peptide involved in the pathological sequence of Alzheimer's disease (AD). Extracellular Aβ42 associates with neuronal cells and is a major constituent of senile plaques, one of the hallmarks of AD. Although Hsps are generally thought to prevent accumulation of misfolded proteins, there is a lack of mechanistic evidence that heat shock chaperones directly modulate Aβ42 toxicity. In this study we show that neither extracellular Aβ42 nor Aβ42/PrPC trigger the heat shock response in neurons. To address the influence of the neuroprotective heat shock response on cellular Aβ42, Western analysis of Aβ42 was performed following external Aβ42 application. Five hours after a conditioning heat shock, Aβ42 association with CAD cells was increased compared to control neurons. However, at forty-eight hours following heat shock Aβ42 levels were reduced compared to that found for control cells. Moreover, transient transfection of the stress induced Hsp40, decreased CAD levels of Aβ42. In contrast to CAD cells, hippocampal neurons transfected with Hsp40 retained Aβ42 indicating that Hsp40 modulation of Aβ42 proteostasis is cell specific. Mutation of the conserved HPD motif within Hsp40 significantly reduced the Hsp40-mediated Aβ42 increase in hippocampal cultures indicating the importance of this motif in regulating cellular Aβ42. Our data reveal a biochemical link between Hsp40 expression and Aβ42 proteostasis that is cell specific. Therefore, increasing Hsp40 therapeutically with the intention of interfering with the pathogenic cascade leading to neurodegeneration in AD should be pursued with caution. [ABSTRACT FROM AUTHOR]

Background: Cysteine string protein (CSPα) is a synaptic vesicle protein that displays unique anti-neurodegenerative properties. CSPα 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 CSPα 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. How CSPα prevents neurodegeneration is currently not known. As a neuroprotective synaptic vesicle protein, CSPα represents a promising therapeutic target for the prevention of neurodegenerative disorders. Methodology/Principal Findings: Here, we demonstrate that the flavonoid quercetin promotes formation of stable CSPα- CSPα dimers and that quercetin-induced dimerization is dependent on the unique cysteine string region. Furthermore, in primary cultures of Lymnaea neurons, quercetin induction of CSPα dimers correlates with an inhibition of synapse formation and synaptic transmission suggesting that quercetin interfers with CSPα function. Quercetin's action on CSPα is concentration dependent and does not promote dimerization of other synaptic proteins or other J protein family members and reduces the assembly of CSPα:Hsc70 units (70kDa heat shock cognate protein). Conclusions/Significance: Quercetin is a plant derived flavonoid and popular nutritional supplement proposed to prevent memory loss and altitude sickness among other ailments, although its precise mechanism(s) of action has been unclear. In view of the therapeutic promise of upregulation of CSPα and the undesired consequences of CSPα dysfunction, our data establish an essential proof of principle that pharmaceutical agents can selectively target the neuroprotective J protein CSPα. [ABSTRACT FROM AUTHOR]

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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-α) is a zymogen granule (ZG) membrane protein characterized by an NH2-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. A role for CSP-α in regulating digestive enzyme exocytosis from pancreas was investigated by introducing CSP-α truncations into isolated following their permeabilization with Perfringolysin O. Incubation of acini with CSP-α1-82, containing the J domain, significantly augmented Ca2+-stimulated amylase secretion. Effects of CSP-α1-82 were concentration dependent, with a maximum 80% increase occurring at 200 μg/ml of protein. Although CSP-α1-82 had no effects on basal secretion measured in the presence of ≤ 10 nM free Ca2+, it did significantly augment GTP-γS-induced secretion under basal Ca2+ conditions by -25%. Mutation of the J domain to abolish its cochaperone activity failed to augment Ca2+-stimulated secretion, implicating the CSP-α/Hsc70 cochaperone system as a regulatory component of the secretory pathway. CSP-α physically associates with vesicle-associated membrane protein 8 (VAMP 8) on ZGs, and the CSP-α- VAMP 8 interaction was dependent on amino acids 83-112 of CSP-α. Immunofluorescence analysis of acinar lobules or purified ZGs confirmed the CSP-α colocalization with VAMP 8. These data establish a role for CSP-α in regulating digestive enzyme secretion and suggest that CSP-α and Hsc70 modulate specific soluble N-ethylmaleimide- sensitive attachment receptor interactions necessary for exocytosis. [ABSTRACT FROM AUTHOR]

In this study, we have systematically evaluated the signaling mechanisms underlying stimulated nitric oxide (NO) synthesis by estrogen (E2) and other vasoactive agents at the level of a single endothelium-derived cell. To do so, we have characterized and contrasted rapid E2-evoked NO synthesis with that of ATP using single-cell microfluorimetry and patch-clamp recordings to monitor stimulated changes in cellular NO synthesis (via 4-amino-5-methylamino-2′,7′-difluorofluorescein), Ca2+ transients (via Fluo-3), and membrane hyperpolarization in cultured human EA.hy926 cells. E2-evoked NO synthesis in single cells (EC50 ∼0.3 nM) was blocked by the E2 receptor antagonist ICI 182,780 and the NO synthase inhibitor Nω-nitro-L-arginine methyl ester. Although both E2 and ATP stimulated comparable Ca2+ transients, E2-induced NO synthesis was insensitive to intracellular BAPTA-AM or removal of external Ca2+. In contrast, ATP-evoked NO production was abolished by either one of these treatments. ATP-evoked hyperpolarizations (∼20 mV) and NO production were both inhibited by the respective small-conductance and intermediate-conductance calcium-activated K+ channel blockers apamin and charybdotoxin. E2 minimally affected membrane potential, and stimulated NO synthesis was insensitive to calcium-activated K+ channel blockers. Exposure to either the phosphatidylinositol 3-kinase inhibitor LY-294001 or the MAP kinase inhibitor PD-98059 abolished the NO response to E2, but not that to ATP. Finally, the NO response evoked by a combined stimulus of E2 plus ATP was similar to that of ATP alone. In conclusion, our data directly demonstrate that an individual human EA.hy926 cell contains at least two distinct mechanisms for stimulated NO synthesis that depend on either calcium or protein kinase signaling events. [ABSTRACT FROM AUTHOR]

Large conductance, calcium-activated potassium channels (BK[subCa] channels) are regulated by several distinct mechanisms, including phosphorylation/dephosphorylation events and protein-protein interactions. In this study, we have examined the interaction between BK[subCa] channels and syntaxin 1A, a soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) that is reported to modulate the activity and/or localization of different classes of ion channels. Using a reciprocal co-immunoprecipitation strategy, we observed that native BK[subCa] channels in rat hippocampus co-associate with syntaxin 1A, but not the closely related homologue syntaxin 3. This BK[subCa] channel-syntaxin 1A interaction could be further demonstrated in a non-neuronal cell line (human embryonic kidney (HEK) 293 cells) following co-expression of rat syntaxin 1A and BK[subCa], channels cloned from either mouse brain or bovine aorta. However, co-expression of these same channels with syntaxin 3 did not lead to a detectable protein-protein interaction. Immunofluorescent co-staining of HEK 293 cells expressing BK[subCa], channels and syntaxin 1A demonstrated overlapping distribution of these two proteins in situ. Functionally, co-expression of BK[subCa], channels with syntaxin 1A, but not syntaxin 3, was observed to enhance channel gating and kinetics at low concentrations (1-4 µm) of free cytosolic calcium, but not at higher concentrations (≤ 10 µm), as judged by macroscopic current recordings in excised membrane patches. Interactions between BK[subCa], channels and neighbouring membrane proteins may thus play important roles in regulating the activity and/or distribution of these channels within specialized cellular compartments. [ABSTRACT FROM AUTHOR]