The interaction between the import carrier Hikeshi and HSP70 is modulated by heat, facilitating the nuclear import of HSP70 under heat stress conditions.

Heat stress strongly triggers the nuclear localization of the molecular chaperone HSP70. Hikeshi functions as a unique nuclear import carrier of HSP70. However, how the nuclear import of HSP70 is activated in response to heat stress remains unclear. Here, we investigated the effects of heat on the nuclear import of HSP70. In vitro transport assays revealed that pretreatment of the test samples with heat facilitated the nuclear import of HSP70. Furthermore, binding of Hikeshi to HSP70 increased when temperatures rose. These results indicated that heat is one of the factors that activates the nuclear import of HSP70. Previous studies showed that the F97A mutation in Hikeshi in an extended loop induced an opening in the hydrophobic pocket and facilitated the translocation of Hikeshi through the nuclear pore complex. We found that nuclear accumulation of HSP70 occurred at a lower temperature in cells expressing the Hikeshi-F97A mutant than in cells expressing wild-type Hikeshi. Collectively, our results show that the movement of the extended loop may play an important role in the interaction of Hikeshi with both FG (phenylalanine-glycine)-nucleoporins and HSP70 in a temperature-dependent manner, resulting in the activation of nuclear import of HSP70 in response to heat stress.

A novel missense variant in HIKESHI: Clinical phenotype, in vitro functional testing, and potential for gene therapy.

A 7-month-old boy presented to our clinic with developmental delay, Magnetic Resonance Imaging (MRI) features of delayed myelination and diffusion restriction, and a homozygous variant of uncertain significance (c.4T>G, p.Phe2Val) in HIKESHI, a gene associated with autosomal-recessive hypomyelinating leukodystrophy 13. We hypothesized that the variant is disease-causing and aimed to rescue the cellular phenotype with vector-mediated gene replacement. HIKESHI mediates heat-induced nuclear accumulation of heat-shock proteins, including HSP70, to protect cells from stress. We generated skin fibroblasts from the proband and proband's mother (heterozygous) to compare protein expression and subcellular localization of HSP70 under heat stress conditions, and the effect of vector-mediated overexpression of HIKESHI in the proband's cells under the same heat stress conditions. Western blot analysis revealed absent HIKESHI protein from proband fibroblasts, contrasted with ample expression in parental cells. Under heat stress conditions, while the mother's cells displayed appropriate nuclear localization of HSP70, the proband's cells displayed impaired nuclear translocalization. When patient fibroblasts were provided exogenous HIKESHI, the transfected proband's cells showed restored heat-induced nuclear translocalization of HSP70 under conditions of heat stress. These functional data establish that the patient's variant is a pathogenic loss-of-function mutation, thus confirming a diagnosis of hypomyelinating leukodystrophy 13 and that vector-mediated gene replacement may be an effective treatment approach for patients with this disorder.

Thermal Stress and Nuclear Transport.

Nuclear transport is the basis for the biological reaction of eukaryotic cells, as it is essential to coordinate nuclear and cytoplasmic events separated by nuclear envelope. Although we currently understand the basic molecular mechanisms of nuclear transport in detail, many unexplored areas remain. For example, it is believed that the regulations and biological functions of the nuclear transport receptors (NTRs) highlights the significance of the transport pathways in physiological contexts. However, physiological significance of multiple parallel transport pathways consisting of more than 20 NTRs is still poorly understood, because our knowledge of each pathway, regarding their substrate information or how they are differently regulated, is still limited. In this report, we describe studies showing how nuclear transport systems in general are affected by temperature rises, namely, thermal stress or heat stress. We will then focus on Importin α family members and unique transport factor Hikeshi, because these two NTRs are affected in heat stress. Our present review will provide an additional view to point out the importance of diversity of the nuclear transport pathways in eukaryotic cells.

Alterations of Brain Quantitative Proteomics Profiling Revealed the Molecular Mechanisms of Diosgenin against Cerebral Ischemia Reperfusion Effects.

Diosgenin (DIO), the starting material for the synthesis of steroidal anti-inflammatory drugs in the pharmaceutical industry, has been previously demonstrated to display pharmaceutical effects against cerebral ischemic reperfusion (I/R). However, the alterations of brain proteome profiles underlying this treatment remain elusive. In the present study, the proteomics analysis of the brain tissues from I/R rats after DIO treatment was performed using an integrated TMT-based quantitative proteomic approach coupled with the liquid chromatography with tandem mass spectrometry technology. A total of 5043 proteins (ProteomeXchange identifier: PXD016303) were identified, of which 58 common differentially expressed proteins were significantly dysregulated in comparison between sham versus I/R and I/R versus DIO. The eight validated proteins including EPG5, STAT2, CPT1A, EIF2AK2, GGCT, HIKESHI, TNFAIP8, and EMC6 by quantitative polymerase chain reaction and western blotting consistently supported the TMT-based proteomic results, which were mainly associated with autophagy and inflammation response. Considering the anti-inflammatory characters of DIO, the biological functions of STAT2 and HIKESHI that are the probable direct anti-inflammatory targets were further investigated during the course of I/R treated with DIO. In addition, the combination of verified STAT2 and HIKESHI in peripheral blood samples from stroke patients resulted in the area under the curve value of 0.765 with P < 0.004 to distinguish stroke patients from healthy controls. Taken together, the current findings first mapped comprehensive proteomic changes after I/R was treated with DIO to better decipher the molecular mechanisms mainly based on the anti-inflammatory aspect underlying this therapeutic effect, providing a foundation for developing potentially therapeutic targets of anti-I/R of DIO and clinically prognostic biomarkers of stroke.

Nucleocytoplasmic transport under stress conditions and its role in HSP70 chaperone systems.

BACKGROUND: In eukaryotic cells, molecular trafficking between the nucleus and cytoplasm is a highly regulated process related to cellular homeostasis and cellular signaling. However, various cellular stresses induce the perturbation of conventional nucleocytoplasmic transport pathways, resulting in the nucleocytoplasmic redistribution of many functional proteins. SCOPE OF REVIEW: We describe the recent insights into the mechanism and functions of nuclear import of cytosolic chaperone HSP70 under stress conditions and the cellular distribution and functions of its co-chaperones. MAJOR CONCLUSIONS: Hikeshi mediates the nuclear import of the molecular chaperone HSP70. A few of the regulators of the HSP70 chaperone system also accumulate in the nucleus under heat stress conditions. These proteins function collaboratively to protect cells from stress-induced damage and aid in the recovery of cells from stress. GENERAL SIGNIFICANCE: Studies on the regulation of nucleocytoplasmic transport under several cellular stresses should provide new insights into the fundamental principles of protein homeostasis (proteostasis) in both compartments, the nucleus and cytoplasm.

Structural and functional analysis of Hikeshi, a new nuclear transport receptor of Hsp70s.

Hikeshi is a nuclear transport receptor required for cell survival after stress. It mediates heat-shock-induced nuclear import of 70 kDa heat-shock proteins (Hsp70s) through interactions with FG-nucleoporins (FG-Nups), which are proteins in nuclear pore complexes (NPCs). Here, the crystal structure of human Hikeshi is presented at 1.8 Šresolution. Hikeshi forms an asymmetric homodimer that is responsible for the interaction with Hsp70s. The asymmetry of Hikeshi arises from the distinct conformation of the C-terminal domain (CTD) and the flexibility of the linker regions of each monomer. Structure-guided mutational analyses showed that both the flexible linker region and the CTD are important for nuclear import of Hsp70. Pull-down assays revealed that only full-length Hsp70s can interact with Hikeshi. The N-terminal domain (NTD) consists of a jelly-roll/ß-sandwich fold structure which contains hydrophobic pockets involved in FG-Nup recognition. A unique extended loop (E-loop) in the NTD is likely to regulate the interactions of Hikeshi with FG-Nups. The crystal structure of Hikeshi explains how Hikeshi participates in the regulation of nuclear import through the recognition of FG-Nups and which part of Hikeshi affects its binding to Hsp70. This study is the first to yield structural insight into this highly unique import receptor.

Role of HIKESHI on Hyperthermia for Castration-Resistant Prostate Cancer and Application of a Novel Magnetic Nanoparticle with Carbon Nanohorn for Magnetic Hyperthermia.

The prognosis of castration-resistant prostate cancer (CRPC) is technically scarce; therefore, a novel treatment for CRPC remains warranted. To this end, hyperthermia (HT) was investigated as an alternative therapy. In this study, the analysis focused on the association between CRPC and heat shock protein nuclear import factor "hikeshi (HIKESHI)", a factor of heat tolerance. Silencing the HIKESHI expression of 22Rv1 cells (human CRPC cell line) treated with siRNAs inhibited the translocation of heat shock protein 70 from the cytoplasm to the nucleus under heat shock and enhanced the effect of hyperthermia. Moreover, a novel magnetic nanoparticle was developed via binding carbon nanohorn (CNH) and iron oxide nanoparticle (IONP) with 3-aminopropylsilyl (APS). Tumor-bearing model mice implanted with 22 Rv1 cells were examined to determine the effect of magnetic HT (mHT). We locally injected CNH-APS-IONP into the tumor, which was set under an alternative magnetic field and showed that tumor growth in the treatment group was significantly suppressed compared with other groups. This study suggests that HIKESHI silencing enhances the sensitivity of 22Rv1 cells to HT, and CNH-APTES-IONP deserves consideration for mHT.

Diosgenin revealed potential effect against cerebral ischemia reperfusion through HIKESHI/HSP70/NF-κB anti-inflammatory axis.

BACKGROUND: It is a research hotspot to use natural compounds in treatment of cerebral ischemia reperfusion (I/R) for a refractory disease throughout the worldwide without available drugs or treatments at present. Our previous study has demonstrated that diosgenin (DIO), a starting material to synthesize various steroid anti-inflammatory drugs in medical industry, showed medicinal effect against I/R via inhibiting aberrant inflammatory reaction induced by I/R. However, the detailed anti-inflammatory network of DIO in treatment of I/R still remains to be further explored. PURPOSE: HIKESHI was firstly identified as a novel target of DIO used for I/R by rat brain proteomic analysis, and mechanistic efforts were focused based on this gene. Hopefully, extensive detailed molecular mechanisms of DIO against I/R was established and confirmed. METHODS: The effect of DIO against I/R was examined in vitro and in vivo, which cells (SH-SY5Y and PC12) and rats were experienced to ORD/RP and MCAO exposures, respectively, to establish I/R modes. Staining was used to evaluate the pathological procedure of DIO used for I/R. Protein changes including expression, interaction, and activity during DIO's anti-I/R effect were assessed with real time PCR, western blot, Co-IP, luciferase reporter assay. RESULTS: In the current study, HIKESHI and HSP70 were both upregulated, when I/R cells and rats were treated with DIO in vitro and in vivo. Mechanistically, DIO stimulated the binding of HIKESHI to HSP70 and facilitated the translocation of HSP70 into nucleus. Subsequently, HSP70 blunted the transcription activity of NF-κB after physical interaction with this transcription factor, and therefore led to the suppression of its downstream pro-inflammatory cytokine (TNF-α, IL-1ß, and IL-6) release into surrounding I/R lesion area. Conversely, HIKESHI or HSP70 knockdowns attenuated the nuclear translocation and restraint on NF-κB-mediated inflammation, finally resulting in the abolishment of DIO-induced anti-I/R effect. NF-κB activation also relieved the inhibitory inflammation and reversed DIO's effect against I/R, suggesting that NF-κB was the downstream target of HIKESHI and HSP70 in I/R treatment with DIO. CONCLUSIONS: These findings established a novel HIKESHI/HSP70/NF-κB signaling pathway associated with DIO-treated I/R, which might be as therapeutic targets or drugs with potential implications for the therapeutic use of I/R in clinic.

Further Delineation of the Clinical and Pathologic Features of HIKESHI-Related Hypomyelinating Leukodystrophy.

BACKGROUND: A recurrent homozygous missense variant, c.160G>C;p.(Val54Leu) in HIKESHI, was found to cause a hypomyelinating leukodystrophy with high frequency in the Ashkenazi Jewish population. We provide extended phenotypic classification of this disorder based on clinical history of a further seven affected individuals, assess carrier frequency in the Ashkenazi Jewish population, and provide a neuropathological study. METHODS: Clinical information, neuroimaging, and biosamples were collected. Brain autopsy was performed for one case. RESULTS: Individuals with HIKESHI-related disease share common clinical features: early axial hypotonia evolving to dystonia or with progressive spasticity, hyperreflexia and clonus, feeding difficulties with poor growth, and nystagmus. Severe morbidity or death during febrile illness occurred in five of the nine affected individuals. Magnetic resonance images of seven patients were analyzed and demonstrated diffuse hypomyelination and thin corpus callosum. Genotyping data of more than 125,000 Ashkenazi Jewish individuals revealed a carrier frequency of 1 in 216. Gross pathology examination in one case revealed abnormal white matter. Microscopically, there was a near-total absence of myelin with a relative preservation of axons. The cerebral white matter showed several reactive astrocytes and microglia. CONCLUSIONS: We provide pathologic evidence for a primary disorder of the myelin in HIKESHI-related leukodystrophy. These findings are consistent with the hypomyelination seen in brain magnetic resonance imaging and with the clinical features of early-onset spastic/dystonic quadriplegia and nystagmus. The high carrier rate of the recurrent variant seen in the Ashkenazi Jewish population requires increased attention to screening and diagnosis of this condition, particularly in this population.

Nuclear Accumulation of HSP70 in Mouse Skeletal Muscles in Response to Heat Stress, Aging, and Unloading With or Without Reloading.

The purpose of this study was to investigate the nuclear accumulation of heat shock protein 70 (HSP70), a molecular chaperonin in mouse skeletal muscle in response to aging, heat stress, and hindlimb unloading with or without reloading. Profiles of HSP70-specific nuclear transporter Hikeshi in skeletal muscles were also evaluated. Heat stress-associated nuclear accumulation of HSP70 was observed in slow soleus (SOL) and fast plantaris (PLA) muscles of young (10-week-old) mice. Mean nuclear expression level of HSP70 in slow medial gastrocnemius (MGAS) and PLA muscles of aged (100-week-old) mice increased ~4.8 and ~1.7 times, compared to that of young (10-week-old) mice. Reloading following 2-week hindlimb unloading caused accumulation of HSP70 in myonuclei in MGAS and PLA of young mice ( p < 0.05). However, reloading-associated nuclear accumulation of HSP70 was not observed in both types of muscles of aged mice. On the other hand, 2-week hindlimb unloading had no impact on the nuclear accumulation of HSP70 in both muscles of young and aged mice. Nuclear expression level of Hikeshi in both MGAS and PLA in mice was suppressed by aging. No significant changes in the nuclear Hikeshi in both muscles were induced by unloading with or without reloading. Results of this study indicate that the nuclear accumulation of HSP70 might show a protective response against cellular stresses in skeletal muscle and that the protective response may be suppressed by aging. Protective response to aging might depend on muscle fiber types.

The Schizosaccharomyces pombe Hikeshi/Opi10 protein has similar biochemical functions to its human homolog but acts in different physiological contexts.

Human Hikeshi (HsHikeshi) is a nuclear import carrier for Hsp70s and is required for cell survival after heat shock. The Hikeshi homolog in Schizosaccharomyces pombe (SpHikeshi/Opi10) localizes to the nuclear rim, interacts with the Hsp70 homolog Ssa2, and mediates its nuclear import in a reconstituted mammalian nuclear transport system. However, SpHikeshi/Opi10 is not required for heat stress response and survival after heat stress. Instead, SpHikeshi/Opi10 is required for the normal expression of stress response genes under optimal conditions and for cell growth during glucose deprivation. Here, the functions of SpHikeshi/Opi10 are discussed and compared to the functions of HsHikeshi.

Crystallization and preliminary X-ray crystallographic study of human Hikeshi, a new nuclear transport receptor for Hsp70.

Hikeshi is a new nuclear transport receptor that plays an important role in the nuclear import of Hsp70 heat-shock proteins under thermal stress. Wild-type human Hikeshi and its Phe97Ala mutant were overproduced and purified using an Escherichia coli expression system. The purified proteins were crystallized using the hanging-drop vapour-diffusion technique. Wild-type crystals grew in space group C2221, with unit-cell parameters a = 61.1, b = 137.8, c = 97.9 Å, α = 90.0, ß = 90.0, γ = 90.0°. Phe97Ala mutant crystals were obtained in space group P32, with unit-cell parameters a = 85.7, b = 85.7, c = 69.1 Å, α = 90.0, ß = 90.0, γ = 120.0°. These crystals diffracted to 1.8 and 2.5 Šresolution, respectively. This study is the first to yield structural insight into this highly unusual fourth import receptor after importins, NTF2 and TAP.