HSP90 has neurite-promoting activity in vitro for telencephalic and spinal neurons of chick embryos

Opposing effects of an F-box protein and the HSP90 chaperone network on microtubule stability and neurite growth in Caenorhabditis elegans

Molecular chaperones often work collaboratively with the ubiquitylation-proteasome system (UPS) to facilitate the degradation of misfolded proteins, which typically safeguards cellular differentiation and protects cells from stress. In this study, however, we report that the Hsp70/Hsp90 chaperone machinery and an F-box protein, MEC-15, have opposing effects on neuronal differentiation, and that the chaperones negatively regulate neuronal morphogenesis and functions. Using the touch receptor neurons (TRNs) of Caenorhabditis elegans, we find that mec-15(-) mutants display defects in microtubule formation, neurite growth, synaptic development and neuronal functions, and that these defects can be rescued by the loss of Hsp70/Hsp90 chaperones and co-chaperones. MEC-15 probably functions in a Skp-, Cullin- and F-box- containing complex to degrade DLK-1, which is an Hsp90 client protein stabilized by the chaperones. The abundance of DLK-1, and likely other Hsp90 substrates, is fine-tuned by the antagonism between MEC-15 and the chaperones; this antagonism regulates TRN development, as well as synaptic functions of GABAergic motor neurons. Therefore, a balance between the UPS and the chaperones tightly controls neuronal differentiation.

Heat Shock Proteins Regulatory Role in Neurodevelopment

Heat shock proteins (Hsps) are a large family of molecular chaperones that are well-known for their roles in protein maturation, re-folding and degradation. While some Hsps are constitutively expressed in certain regions, others are rapidly upregulated in the presence of stressful stimuli. Numerous stressors, including hyperthermia and hypoxia, can induce the expression of Hsps, which, in turn, interact with client proteins and co-chaperones to regulate cell growth and survival. Such interactions must be tightly regulated, especially at critical points during embryonic and postnatal development. Hsps exhibit specific patterns of expression consistent with a spatio-temporally regulated role in neurodevelopment. There is also growing evidence that Hsps may promote or inhibit neurodevelopment through specific pathways regulating cell differentiation, neurite outgrowth, cell migration, or angiogenesis. This review will examine the regulatory role that these individual chaperones may play in neurodevelopment, and will focus specifically on the signaling pathways involved in the maturation of neuronal and glial cells as well as the underlying vascular network.

Matrine Directly Activates Extracellular Heat Shock Protein 90, Resulting in Axonal Growth and Functional Recovery in Spinal Cord Injured-Mice

After spinal cord injury (SCI), reconstruction of neuronal tracts is very difficult because an inhibitory scar is formed at the lesion site, in which several axonal growth inhibitors, such as chondroitin sulfate proteoglycans (CSPG), accumulate. We previously found that matrine, a major alkaloid in Sophora flavescens, enhanced axonal growth in neurons seeded on CSPG coating. The aims of this study were to investigate therapeutic effects of matrine in SCI mice and to clarify the underlying mechanism. Matrine was orally administered to contusion SCI mice. In the matrine-treated mice, motor dysfunction of the hindlimbs was improved, and the density of 5-HT-positive tracts was increased in the injured spinal cord. We explored putative direct binding proteins of matrine in cultured neurons using drug affinity responsive target stability (DARTS). As a result, heat shock protein 90 (HSP90) was identified, and matrine enhanced HSP90 chaperon activity. We then presumed that extracellular HSP90 is a matrine-targeting signaling molecule, and found that specific blocking of extracellular HSP90 by a neutralizing antibody completely diminished matrine-induced axonal growth and SCI amelioration. Our results suggest that matrine enhances axonal growth and functional recovery in SCI mice by direct activation of extracellular HSP90. Matrine could be a significant candidate for therapeutic drugs for SCI with a novel mechanism.

Cell surface heparan sulfate proteoglycans are involved in the binding of Hsp90α and Hsp90β to the cell plasma membrane

Extracellular membrane-bound and secreted heat shock protein 90 (Hsp90) is known to be involved in cell motility and invasion. The mechanism of Hsp90 anchoring to the plasma membrane remains obscure. We showed that treatment of human glioblastoma A-172 and fibrosarcoma HT1080 cells with sodium chlorate, heparinase, and heparin causes a prominent loss of 2 Hsp90 cytosolic isoforms, Hsp90α and Hsp90β, from the cell surface and strongly inhibits the binding of exogenous Hsp90 to cells. We revealed that Hsp90α and Hsp90β are partly colocalized with heparan sulfate proteoglycans (HSPGs) on the cell surface and that this colocalization was sensitive to heparin. The results demonstrate that cell surface HSPGs are involved in the binding/anchoring of Hsp90α and Hsp90β to the plasma membrane.

The double-edged sword: conserved functions of extracellular hsp90 in wound healing and cancer

Heat shock proteins (Hsps) represent a diverse group of chaperones that play a vital role in the protection of cells against numerous environmental stresses. Although our understanding of chaperone biology has deepened over the last decade, the “atypical” extracellular functions of Hsps have remained somewhat enigmatic and comparatively understudied. The heat shock protein 90 (Hsp90) chaperone is a prototypic model for an Hsp family member exhibiting a duality of intracellular and extracellular functions. Intracellular Hsp90 is best known as a master regulator of protein folding. Cancers are particularly adept at exploiting this function of Hsp90, providing the impetus for the robust clinical development of small molecule Hsp90 inhibitors. However, in addition to its maintenance of protein homeostasis, Hsp90 has also been identified as an extracellular protein. Although early reports ascribed immunoregulatory functions to extracellular Hsp90 (eHsp90), recent studies have illuminated expanded functions for eHsp90 in wound healing and cancer. While the intended physiological role of eHsp90 remains enigmatic, its evolutionarily conserved functions in wound healing are easily co-opted during malignancy, a pathology sharing many properties of wounded tissue. This review will highlight the emerging functions of eHsp90 and shed light on its seemingly dichotomous roles as a benevolent facilitator of wound healing and as a sinister effector of tumor progression.

Neurite outgrowth mediated by the heat shock protein Hsp90α: a novel target for the antipsychotic drug aripiprazole

Aripiprazole is an atypical antipsychotic drug approved for the treatment of psychiatric disorders such as schizophrenia, bipolar disorder, major depressive disorder and autism. The drug shows partial agonistic activity at dopamine D(2) receptors and 5-hydroxytryptamine (5-HT) 5-HT(1A) receptors, and antagonistic activity at 5-HT(2A) receptors. However, the precise mechanistic pathways remain unclear. In this study, we examined the effects of aripiprazole on neurite outgrowth. Aripiprazole significantly potentiated nerve growth factor (NGF)-induced neurite outgrowth in PC12 cells, in a concentration-dependent manner. The 5-HT(1A) receptor antagonist WAY-100635, but not the dopamine D(2) receptor antagonist sulpiride, blocked the effects of aripiprazole, although, only partially. Specific inhibitors of inositol 1,4,5-triphosphate (IP(3)) receptors and BAPTA-AM, a chelator of intracellular Ca(2+), blocked the effects of aripiprazole. Moreover, specific inhibitors of several common signaling pathways phospholipase C-γ (PLC-γ), phosphatidylinositol-3 kinase (PI3K), mammalian target of rapamycin, p38 MAPK, c-Jun N-terminal kinase, Akt, Ras, Raf, ERK, MAPK) also blocked the effects of aripiprazole. Using proteomic analysis, we found that aripiprazole significantly increased levels of the heat shock protein Hsp90α in cultured cells. The effects of aripiprazole on NGF-induced neurite outgrowth were significantly attenuated by treatment with Hsp90α RNA interference, but not by the negative control of Hsp90α. These findings suggest that both 5-HT(1A) receptor activation and Ca(2+) signaling via IP(3) receptors, as well as their downstream cellular signaling pathways play a role in the promotion of aripiprazole-induced neurite outgrowth. Furthermore, aripiprazole-induced increases in Hsp90α protein expression may form part of the therapeutic mechanism for this drug.

Short-term memory formation and long-term memory consolidation are enhanced by cellular prion association to stress-inducible protein 1

Cellular prion protein (PrP(C)) is a cell surface glycoprotein that interacts with several ligands such as laminin, NCAM (Neural-Cell Adhesion Molecule) and the stress-inducible protein 1 (STI1). PrP(C) association with these proteins in neurons mediates adhesion, differentiation and protection against programmed cell death. Herein, we used an aversively motivated learning paradigm in rats to investigate whether STI1 interaction with PrP(C) affects short-term memory (STM) formation and long-term memory (LTM) consolidation. Blockage of PrP(C)-STI1 interaction with intra-hippocampal infusion of antibodies against PrP(C) or STI1 immediately after training impaired both STM and LTM. Furthermore, infusion of PrP(C) peptide 106-126, which competes for PrP(C)-STI1 interaction, also inhibited both forms of memory. Remarkably, STI1 peptide 230-245, which includes the PrP(C) binding site, had a potent enhancing effect on memory performance, which could be blocked by co-treatment with the competitive PrP(C) peptide 106-126. Taken together, these results demonstrate that PrP(C)-STI1 interaction modulates both STM and LTM and suggests a potential use of ST11 peptide 230-245 as a pharmacological agent.

The immunosuppressant FK506 elicits a neuronal heat shock response and protects against acrylamide neuropathy

Acrylamide (AC) is a known industrial neurotoxic chemical that has been recently found in carbohydrate-rich foods cooked at high temperatures. Repeated AC administration produces a pronounced neuropathy characterized by flaccid paralysis and ataxia and represents a well-established animal model of progressive axonal loss. AC also elicits prominent morphologic alterations (e.g., eccentrically placed nuclei, infolding of the nuclear membrane, accumulations of dense bodies, and clusters of smooth endoplasmic reticulum (SER) associated with numerous microtubules) in cerebellar Purkinje cells that may contribute to the pronounced ataxia in these animals. Here, we examined the neuroprotective action of FK506 (tacrolimus) in male and female rats given daily intraperitoneal injections of AC (30 mg/kg) for 4 weeks. Daily subcutaneous injections of FK506 (2 mg/kg/day) dramatically reduced the behavioral signs of neuropathy (i.e., paralysis and ataxia), markedly protected against axonal loss (by 82% and 73% in the tibial nerves of male and female rats, respectively), and reduced the pathologic changes in Purkinje cells. In a separate study, subcutaneous injections of FK506 (2 or 10 mg/kg) for 2 weeks markedly increased heat shock protein-70 (Hsp-70) immunostaining in sensory neurons, motor neurons, Purkinje cells, and other regions of the brain (in particular, the amygdala) from nonintoxicated and AC-intoxicated rats compared to controls. In contrast, AC-intoxicated animals not given FK506 demonstrated reduced Hsp-70 staining. Thus, the ability of FK506 to increase Hsp-70 expression may underlie its neuroprotective action. We suggest that compounds capable of eliciting a heat shock response may be useful for the treatment of human neuropathies.

Upregulation of heat shock proteins rescues motoneurones from axotomy-induced cell death in neonatal rats

Heat shock proteins (hsps) are induced in a variety of cells following periods of stress, where they promote cell survival. In this study, we examined the effect of upregulating hsp expression by treatment with BRX-220, a co-inducer of hsps, on the survival of injured motoneurones. Following sciatic nerve crush at birth, rat pups were treated daily with BRX-220. The expression of hsp70 and hsp90, motoneurone survival, and muscle function was examined at various intervals later and the number of functional motor units was assessed by in vivo isometric tension recordings. Fourteen days after injury, significantly more motoneurones survived in the BRX-220-treated group (39 +/- 2.8%) compared to the saline-treated group (21 +/- 1.7%). Moreover, in the BRX-220-treated group no further loss of motoneurones occurred, so that at 10 weeks 42 +/- 2.1% of motoneurones survived compared to 15 +/- 0.6% in the untreated group. There were also more functional motor units in the hindlimb muscles of BRX-220-treated animals. In addition, treatment with BRX-220 resulted in a significant increase in the expression of hsp70 and hsp90 in glia and neurones. Thus, treatment with BRX-220, a co-inducer of hsps, protects motoneurones from axotomy-induced cell death.

Odorants as cell-type specific activators of a heat shock response in the rat olfactory mucosa

Heat shock, or stress, proteins (HSPs) are induced in response to conditions that cause protein denaturation. Activation of cellular stress responses as a protective and survival mechanism is often associated with chemical exposure. One interface between the body and the external environment and chemical or biological agents therein is the olfactory epithelium (OE). To determine whether environmental odorants affect OE HSP expression, rats were exposed to a variety of odorants added to the cage bedding. Odorant exposure led to transient, selective induction of HSP70, HSC70, HSP25, and ubiquitin immunoreactivities (IRs) in supporting cells and subepithelial Bowman's gland acinar cells, two OE non-neuronal cell populations involved with inhalant biotransformation, detoxification, and maintenance of overall OE integrity. Responses exhibited odor specificity and dose dependency. HSP70 and HSC70 IRs occurred throughout the apical region of supporting cells; ubiquitin IR was confined to a supranuclear cone-shaped region. Electron microscopic examination confirmed these observations and, additionally, revealed odor-induced formation of dense vesicular arrays in the cone-like regions. HSP25 IR occurred throughout the entire supporting cell cytoplasm. In contrast to classical stress responses, in which the entire array of stress proteins is induced, no increases in HSP40 and HSP90 IRs were observed. Extended exposure to higher odorant doses caused prolonged activation of the same HSP subset in the non-neuronal cells and severe morphological damage in both supporting cells and olfactory receptor neurons (ORNs), suggesting that non-neuronal cytoprotective stress response mechanisms had been overwhelmed and could no longer adequately maintain OE integrity. Significantly, ORNs showed no stress responses in any of our studies. These findings suggest a novel role for these HSPs in olfaction and, in turn, possible involvement in other normal neurophysiological processes.

Identification of active regions for neurite outgrowth activity of neurocrescin

We previously identified and cloned a neurite outgrowth promoting protein, Neurocrescin (NC), from the extract of the chick denervated leg muscles. In this study, we explored the active region of NC for neurite outgrowth. Using the deletion mutants of NC, we tested their neurite outgrowth activity in the cultured telencephalic neurons of E5 chick embryos. We found three regions which independently had significant neurite outgrowth activity comparable with that of the extract of the chick denervated leg muscles. These regions were not homologous to any well-known active sites such as the laminin active region, IKVAV. In parallel, searching the endogenous deletion mutants of NC in the rat brain, we cloned a mutant in which the region including the larger part of one of the three active regions was deleted. The neurite outgrowth activity of the mutant was significantly lower than that of normal NC. These results suggest the physiological significance of these active regions.

Effect of rabies virus infection on gene expression in mouse brain

A variety of molecular genetic approaches were used to study the effect of rabies virus (RV) infection on host gene expression in mouse brain. The down-regulation of gene expression was found to be a major effect of RV infection by using subtraction hybridization. However, a combination of techniques identified approximately 39 genes activated by infection. These included genes involved in regulation of cell metabolism, protein synthesis, synaptic activity, and cell growth and differentiation. Northern blot analysis to monitor temporal activation of several of these genes following infection revealed essentially two patterns of activation: (i) an early response with up-regulation beginning within 3 days after infection and correlating with transcription of RV nuclear protein; and (ii) a late response with enhanced expression occurring at days 6-7 after infection and associated with peak RV replication. The gene activation patterns and the known functions of their products suggest that a number of host genes may be involved in the replication and spread of RV in the brain.

MDP77: A novel neurite-outgrowth-promoting protein predominantly expressed in chick muscles

A 4.7 kb chick cDNA clone that coded for the novel muscle-derived protein, MDP77, was isolated from a cDNA library of the denervated crus muscles using an antibody which inhibited the neurite outgrowth activity. MDP77 consisted of 676 aa with a calculated molecular mass of 77 k. The deduced amino acid sequence exhibited an extended coiled-coil domain and a leucine zipper motif. A recombinant protein promoted the neurite-outgrowth from the cultured chick neurons of the spinal cord in a dose-dependent manner. Northern blotting and in situ hybridization revealed that MDP77 was predominantly expressed in the cardiac and the skeletal muscles. In the COS-7 cells transfected with the cDNA of the epitope-tagged MDP77, the expressed protein was detected in the culture medium, suggesting that the MDP77 was secreted.