Heat shock-induced HIKESHI protects cell viability via nuclear translocation of heat shock protein 70

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.

Advances in nuclear proteostasis of metazoans

The proteostasis network and associated protein quality control (PQC) mechanisms ensure proteome functionality and are essential for cell survival. A distinctive feature of eukaryotic cells is their high degree of compartmentalization, requiring specific and adapted proteostasis networks for each compartment. The nucleus, essential for maintaining the integrity of genetic information and gene transcription, is one such compartment. While PQC mechanisms have been investigated for decades in the cytoplasm and the endoplasmic reticulum, our knowledge of nuclear PQC pathways is only emerging. Recent developments in the field have underscored the importance of spatially managing aberrant proteins within the nucleus. Upon proteotoxic stress, misfolded proteins and PQC effectors accumulate in various nuclear membrane-less organelles. Beyond bringing together effectors and substrates, the biophysical properties of these organelles allow novel PQC functions. In this review, we explore the specificity of the nuclear compartment, the effectors of the nuclear proteostasis network, and the PQC roles of nuclear membrane-less organelles in metazoans.

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.

Rare forms of hypomyelination and delayed myelination

Hypomyelination is defined by the evidence of an unchanged pattern of deficient myelination on two MRIs performed at least 6 months apart in a child older than 1 year. When the temporal criteria are not fulfilled, and the follow-up MRI shows a progression of the myelination even if still not adequate for age, hypomyelination is excluded and the pattern is instead consistent with delayed myelination. This can be mild and nonspecific in some cases, while in other cases there is a severe delay that in the first disease stages could be difficult to differentiate from hypomyelination. In hypomyelinating leukodystrophies, hypomyelination is due to a primary impairment of myelin deposition, such as in Pelizaeus Merzabcher disease. Conversely, myelin lack is secondary, often to primary neuronal disorders, in delayed myelination and some condition with hypomyelination. Overall, the group of inherited white matter disorders with abnormal myelination has expanded significantly during the past 20 years. Many of these disorders have only recently been described, for many of them only a few patients have been reported and this contributes to make challenging the diagnostic process and the interpretation of Next Generation Sequencing results. In this chapter, we review the clinical and radiologic features of rare and lesser known forms of hypomyelination and delayed myelination not mentioned in other chapters of this handbook.

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.

Lack of Hikeshi activates HSF1 activity under normal conditions and disturbs the heat-shock response

Hikeshi mediates the nuclear import of the molecular chaperone HSP70 under heat-shock (acute heat stress) conditions, which is crucial for recovery from cellular damage. The cytoplasmic function of HSP70 is well studied, but its nuclear roles, particularly under nonstressed conditions, remain obscure. Here, we show that Hikeshi regulates the nucleocytoplasmic distribution of HSP70 not only under heat-shock conditions but also under nonstressed conditions. Nuclear HSP70 affects the transcriptional activity of HSF1 and nuclear proteostasis under nonstressed conditions. Depletion of Hikeshi induces a reduction in nuclear HSP70 and up-regulation of the mRNA expression of genes regulated by HSF1 under nonstressed conditions. In addition, the heat-shock response is impaired in Hikeshi-knockout cells. Our results suggest that HSF1 transcriptional activity is tightly regulated by nuclear HSP70 because nuclear-localized Hsp70 effectively suppresses transcriptional activity in a dose-dependent manner. Furthermore, the cytotoxicity of nuclear pathologic polyglutamine proteins was increased by Hikeshi depletion. Thus, proper nucleocytoplasmic distribution of HSP70, mediated by Hikeshi, is required for nuclear proteostasis and adaptive response to heat shock.

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-1β, 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.

Ischaemic postconditioning reduces apoptosis in experimental jejunal ischaemia in horses

BACKGROUND

Ischaemic postconditioning (IPoC) refers to brief periods of reocclusion of blood supply following an ischaemic event. This has been shown to ameliorate ischaemia reperfusion injury in different tissues, and it may represent a feasible therapeutic strategy for ischaemia reperfusion injury following strangulating small intestinal lesions in horses. The objective of this study was to assess the degree cell death, inflammation, oxidative stress, and heat shock response in an equine experimental jejunal ischaemia model with and without IPoC.

METHODS

In this randomized, controlled, experimental in vivo study, 14 horses were evenly assigned to a control group and a group subjected to IPoC. Under general anaesthesia, segmental ischaemia with arterial and venous occlusion was induced in 1.5 m jejunum. Following ischaemia, the mesenteric vessels were repeatedly re-occluded in group IPoC only. Full thickness intestinal samples and blood samples were taken at the end of the pre-ischaemia period, after ischaemia, and after 120 min of reperfusion. Immunohistochemical staining or enzymatic assays were performed to determine the selected variables.

RESULTS

The mucosal cleaved-caspase-3 and TUNEL cell counts were significantly increased after reperfusion in the control group only. The cleaved-caspase-3 cell count was significantly lower in group IPoC after reperfusion compared to the control group. After reperfusion, the tissue myeloperoxidase activity and the calprotectin positive cell counts in the mucosa were increased in both groups, and only group IPoC showed a significant increase in the serosa. Tissue malondialdehyde and superoxide dismutase as well as blood lactate levels showed significant progression during ischaemia or reperfusion. The nuclear immunoreactivity of Heat shock protein-70 increased significantly during reperfusion. None of these variables differed between the groups. The neuronal cell counts in the myenteric plexus ganglia were not affected by the ischaemia model.

CONCLUSIONS

A reduced apoptotic cell count was found in the group subjected to IPoC. None of the other tested variables were significantly affected by IPoC. Therefore, the clinical relevance and possible protective mechanism of IPoC in equine intestinal ischaemia remains unclear. Further research on the mechanism of action and its effect in clinical cases of strangulating colic is needed.

HIKESHI silencing can enhance mild hyperthermia sensitivity in human oral squamous cell carcinoma HSC‑3 cells

Hyperthermia (HT) is considered to be of value as a treatment modality in various cancers. However, the acquisition of thermotolerance in cancer cells due to the induction of heat shock proteins (HSPs) makes HT less effective. Recent findings have indicated that heat shock protein nuclear import factor hikeshi (HIKESHI), also referred to as C11orf73, acts as a nuclear import carrier of Hsp70 under heat stress conditions. The aim of the present study was to determine whether knockdown (KD) of HIKESHI by small interfering RNA (siRNA) can potentiate mild HT (MHT) sensitivity in human oral squamous cell carcinoma (OSCC) HSC‑3 cells. The mRNA and protein expression of HIKESHI was found to be markedly suppressed in HSC‑3 cells treated with siRNA for HIKESHI (siHIKE). Silencing HIKESHI significantly decreased the cell viability under MHT conditions (42˚C for 90 min). Immunocytochemical and western blot analyses clearly demonstrated that Hsp70 protein translocated from the cytoplasm to the nucleus under MHT conditions, and this translocation was significantly inhibited in cells treated with siHIKE. Treatment of the cells with MHT transiently increased the phosphorylation level of extracellular signal‑regulated kinase (ERK)2. Furthermore, the phosphorylation was sustained in HIKESHI‑KD cells under MHT conditions, and this sustained phosphorylation was abolished by pretreatment with U0126, an inhibitor of mitogen‑activated protein kinase/ERK. In addition, U0126 significantly decreased the viability of cells treated with the combination of HIKESHI‑KD and MHT. The data of the present study suggest that HIKESHI silencing enhanced the sensitivity of human OSCC HSC‑3 cells to MHT.

Lamin A/C modulates spatial organization and function of the Hsp70 gene locus via nuclear myosin I

The structure-function relationship of the nucleus is tightly regulated, especially during heat shock. Typically, heat shock activates molecular chaperones that prevent protein misfolding and preserve genome integrity. However, the molecular mechanisms that regulate nuclear structure-function relationships during heat shock remain unclear. Here, we show that lamin A and C (hereafter lamin A/C; both lamin A and C are encoded by LMNA) are required for heat-shock-mediated transcriptional induction of the Hsp70 gene locus (HSPA genes). Interestingly, lamin A/C regulates redistribution of nuclear myosin I (NM1) into the nucleus upon heat shock, and depletion of either lamin A/C or NM1 abrogates heat-shock-induced repositioning of Hsp70 gene locus away from the nuclear envelope. Lamins and NM1 also regulate spatial positioning of the SC35 (also known as SRSF2) speckles - important nuclear landmarks that modulates Hsp70 gene locus expression upon heat shock. This suggests an intricate crosstalk between nuclear lamins, NM1 and SC35 organization in modulating transcriptional responses of the Hsp70 gene locus during heat shock. Taken together, this study unravels a novel role for lamin A/C in the regulation of the spatial dynamics and function of the Hsp70 gene locus upon heat shock, via the nuclear motor protein NM1.This article has an associated First Person interview with the first author of the paper.

Heat stress-induced nuclear transport mediated by Hikeshi confers nuclear function of Hsp70s

The prime feature of eukaryotic cells is the separation of the intracellular space into two compartments, the nucleus and the cytoplasm. Active nuclear transport is crucial for the maintenance of this separation. In this report, we focus on a nuclear transport receptor named Hikeshi, which mediates the heat stress-induced nuclear import of 70-kDa heat shock proteins (Hsp70s), and discuss how the same protein can function differently depending on the cellular compartment in which it is localized. Hsp70 is a molecular chaperone that is predominantly localized in the cytoplasm under normal conditions but is known to accumulate in the nucleus under conditions of heat stress. Although the reported function of Hsp70 is mostly attributed to its molecular function in the cytoplasm, the functions of Hsp70 may extend beyond molecular chaperone activity in the nucleus.