Heat shock protein 90beta: a novel mediator of vitamin D action

Cytosolic Hsp90 Isoform-Specific Functions and Clinical Significance

The heat shock protein 90 (Hsp90) is a molecular chaperone and a key regulator of proteostasis under both physiological and stress conditions. In mammals, there are two cytosolic Hsp90 isoforms: Hsp90α and Hsp90β. These two isoforms are 85% identical and encoded by two different genes. Hsp90β is constitutively expressed and essential for early mouse development, while Hsp90α is stress-inducible and not necessary for survivability. These two isoforms are known to have largely overlapping functions and to interact with a large fraction of the proteome. To what extent there are isoform-specific functions at the protein level has only relatively recently begun to emerge. There are studies indicating that one isoform is more involved in the functionality of a specific tissue or cell type. Moreover, in many diseases, functionally altered cells appear to be more dependent on one particular isoform. This leaves space for designing therapeutic strategies in an isoform-specific way, which may overcome the unfavorable outcome of pan-Hsp90 inhibition encountered in previous clinical trials. For this to succeed, isoform-specific functions must be understood in more detail. In this review, we summarize the available information on isoform-specific functions of mammalian Hsp90 and connect it to possible clinical applications.

Glycocholic acid and butyrate synergistically increase vitamin D-induced calcium uptake in Caco-2 intestinal epithelial cell monolayers

Background

Roux-en-Y gastric bypass (RYGB) substantially decreases intestinal calcium absorption and may eventually lead to bone resorption. This is likely a consequence of bile diversion from the alimentary limb, as the presence of bile seems necessary for vitamin D-mediated calcium uptake. We recently suggested that the mediating mechanism may be a down-regulation of the vitamin D co-activator heat-shock protein (Hsp)90β. Recent evidence suggests that vitamin D may have effects on both active and passive calcium absorption.

Aim

To identify mechanisms in vitro that may be responsible for the decreased calcium absorption after RYGB. We hypothesized that bile, alone or in concert with nutritional compounds, could be of importance.

Material & methods

Caco-2 cells were grown confluent on semi-permeable membranes in a double-chamber setup to mimic small intestinal mucosa. The effect of bile acids chenodeoxycholic, lithocholic, glycocholic and taurocholic acid, with and without the addition of the fatty-acid butyrate, were tested for their effects on Hsp90β expression and active and passive calcium-flux monitored using radioactive ⁴⁵Ca.

Results

We initially found that whole human bile, but only together with the fatty acid butyrate, potently induced Hsp90β expression. In line with this, a single bile acid, e.g. glycocholic acid (GCA), in combination with butyrate, increased Hsp90β expression (40 ± 13% vs. GCA, butyrate or vehicle alone; p < 0,001; n = 14–25). Further, this combination together with vitamin D increased the passive gradient-driven flux of calcium, compared to stimulation with vitamin D alone or in combination with either GCA or butyrate (880 ± 217% vs. vitamin D and GCA or butyrate, or vitamin D only; p = 0,01–0.006; n = 5–11). Surprisingly, this combination had no effect on active calcium transport in the absence of calcium gradient.

Conclusion

The combination of GCA and butyrate increased gradient-driven calcium uptake up to 9-fold in Caco-2 intestinal epithelial cells, but had no effect on active calcium absorption. This effect was mediated via the vitamin D receptor co-activator Hsp90β.

Effect of vitamin D3 on the immunomodulation of head kidney after Edwardsiella ictaluri challenge in yellow catfish (Pelteobagrus fulvidraco)

Edwardsiella ictaluri (E. ictaluri) causes severe infections in yellow catfish (Pelteobagrus fulvidraco), which leads to a massive loss in the aquaculture industry especially in catfish commercial production. Previous studies have confirmed that vitamin D₃ is essential in immune regulation in mammals. Based on next-generation sequencing, this study explored the immunomodulatory effects of dietary vitamin D₃ on the head kidney of yellow catfish after E. ictaluri challenge. Current results showed that increasing the content of dietary vitamin D₃ within the experimental concentration range (1120IU/kg-16600IU/kg) could reduce the mortality of the yellow catfish after E. ictaluri challenge. Results of the next-generation sequencing showed that dietary vitamin D₃ regulates the immune mechanism of the head kidney mainly through three pathways i.e. negative regulation of interferon-β production, negative regulation of interleukin-6 production and neutrophil chemotaxis. Proteins HSPA8, MAP4K4 and MRC1 may be involved in vitamin D₃-mediated immunoregulation in the head kidney. qPCR results showed that increasing the content of dietary vitamin D₃ can improve the immune function of the yellow catfish by down-regulating ifn-β and pro-inflammatory factors tnf-α, il1-β, il-6, il-8 and up-regulating the anti-inflammatory factor il-10. The above results indicated that dietary addition of vitamin D₃ regulated the immune response in head kidney of yellow catfish and helped the fish to resist the negative effects of infection by E. ictaluri in a dose-dependent manner.

Downregulation of the Vitamin D Receptor Regulated Gene Set in the Hippocampus After MDMA Treatment

The active ingredient of ecstasy, ±3,4-methylenedioxymethamphetamine (MDMA), in addition to its initial reinforcing effects, induces selective and non-selective brain damage. Evidences suggest that the hippocampus (HC), a central region for cognition, may be especially vulnerable to impairments on the long-run, nevertheless, transcription factors that may precede and regulate such chronic changes remained uninvestigated in this region. In the current study, we used gene-set enrichment analysis (GSEA) to reveal possible transcription factor candidates responsible for enhanced vulnerability of HC after MDMA administration. Dark Agouti rats were intraperitoneally injected with saline or 15 mg/kg MDMA. Three weeks later HC gene expression was measured by Illumina whole-genome beadarrays and GSEA was performed with MSigDB transcription factor sets. The number of significantly altered genes on the genome level (significance < 0.001) in up/downregulated sets was also counted. MDMA upregulated one, and downregulated 13 gene sets in the HC of rats, compared to controls, including Pax4, Pitx2, FoxJ2, FoxO1, Oct1, Sp3, AP3, FoxO4, and vitamin D receptor (VDR)-regulated sets (q-value <0.05). VDR-regulated set contained the second highest number of significantly altered genes, including among others, Camk2n2, Gria3, and Grin2a. Most identified transcription factors are implicated in the response to ischemia confirming that serious hypoxia/ischemia occurs in the HC after MDMA administration, which may contribute to the selective vulnerability of this brain region. Moreover, our results also raise the possibility that vitamin D supplementation, in addition to the commonly used antioxidants, could be a potential alternative method to attenuate MDMA-induced chronic hippocampal impairments.

Methyl donor deficiency impairs bone development via peroxisome proliferator-activated receptor-γ coactivator-1α-dependent vitamin D receptor pathway

Deficiency in methyl donor (folate and vitamin B12) and in vitamin D is independently associated with altered bone development. Previously, methyl donor deficiency (MDD) was shown to weaken the activity of nuclear receptor coactivator, peroxisome proliferator-activated receptor-γ coactivator-1α (PGC1α), for nuclear signaling in rat pups, including estrogen receptor-α and estrogen-related receptor-α; its effect on vitamin D receptor (VDR) signaling, however, is unknown. We studied bone development under MDD in rat pups and used human MG-63 preosteoblast cells to better understand the associated molecular mechanism. In young rats, MDD decreased total body bone mineral density, reduced tibia length, and impaired growth plate maturation, and in preosteoblasts, MDD slowed cellular proliferation. Mechanistic studies revealed decreased expression of VDR, estrogen receptor-α, PGC1α, arginine methyltransferase 1, and sirtuin 1 in both rat proximal diaphysis of femur and in MG-63, as well as decreased nuclear VDR-PGC1α interaction in MG-63 cells. The weaker VDR-PGC1α interaction could be attributed to the reduced protein expression, imbalanced PGC1α methylation/acetylation, and nuclear VDR sequestration by heat shock protein 90 (HSP90). These together compromised bone development, which is reflected by lowered bone alkaline phosphatase and increased proadipogenic peroxisome proliferator-activated receptor-γ, adiponectin, and estrogen-related receptor-α expression. Of interest, under MDD, the bone development effects of 1,25-dihydroxyvitamin D3 were ineffectual and these could be rescued by the addition of S-adenosylmethionine, which restored expression of arginine methyltransferase 1, PGC1α, adiponectin, and HSP90. In conclusion, MDD inactivates vitamin D signaling via both disruption of VDR-PGC1α interaction and sequestration of nuclear VDR attributable to HSP90 overexpression. These data suggest that vitamin D treatment may be ineffective under MDD.-Feigerlova, E., Demarquet, L., Melhem, H., Ghemrawi, R., Battaglia-Hsu, S.-F., Ewu, E., Alberto, J.-M., Helle, D., Weryha, G., Guéant, J.-L. Methyl donor deficiency impairs bone development via peroxisome proliferator-activated receptor-γ coactivator-1α-dependent vitamin D receptor pathway.

Vitamin D and/or calcium deficient diets may differentially affect muscle fiber neuromuscular junction innervation

INTRODUCTION

There is evidence that supports a role for Vitamin D (Vit. D) in muscle. The exact mechanism by which Vit. D deficiency impairs muscle strength and function is not clear.

METHODS

Three-week-old mice were fed diets with varied combinations of Vit. D and Ca²⁺ deficiency. Behavioral testing, genomic and protein analysis, and muscle histology were performed with a focus on neuromuscular junction (NMJ) -related genes.

RESULTS

Vit. D and Ca²⁺ deficient mice performed more poorly on given behavioral tasks than animals with Vit. D deficiency alone. Genomic and protein analysis of the soleus and tibialis anterior muscles revealed changes in several Vit. D metabolic, NMJ-related, and protein chaperoning and refolding genes.

CONCLUSIONS

These data suggest that detrimental effects of a Vit. D deficient or a Vit. D and Ca²⁺ deficient diet may be a result of differential alterations in the structure and function of the NMJ and a lack of a sustained stress response in muscles. Muscle Nerve 54: 1120-1132, 2016.

Middle domain of human Hsp90 isoforms differentially binds Aha1 in human cells and alters Hsp90 activity in yeast

Hsp90 is an essential chaperone for more than 200 client proteins in eukaryotic cells. The human genome encodes two highly similar cytosolic Hsp90 proteins called Hsp90α and Hsp90β. Most of the client proteins can interact with either Hsp90 protein; however, only a handful client proteins and one co-chaperone that interact specifically with one of the Hsp90 isoforms were identified. Structural differences underlying these isoform-specific interactions were not studied. Here we report for the first time that the Hsp90 co-chaperone Aha1 interacts preferentially with Hsp90α. The distinction depends on the middle domain of Hsp90. The middle domain of Hsp90α is also responsible for the slow growth phenotype of yeasts that express this isoform as a sole source of Hsp90. These results suggest that differences in the middle domain of Hsp90α and Hsp90β may be responsible for the isoform-specific interactions with selected proteins. Also shown here within, we determine that preferential chaperoning of cIAP1 by Hsp90β is mediated by the N-terminal domain of this isoform.

Bone mineral density and expression of vitamin D receptor-dependent calcium uptake mechanisms in the proximal small intestine after bariatric surgery

BACKGROUND

Roux-en-Y gastric bypass may lead to impaired calcium uptake. Therefore, operation-specific effects of gastric bypass and vertical banded gastroplasty on bone mineral density (BMD) were examined in a randomized clinical trial. Bone resorption markers and mechanisms of decreased calcium uptake after gastric bypass were investigated using blood and endoscopic samples from two additional patient cohorts.

METHODS

Total BMD and non-weight-bearing skull BMD were measured by dual-energy X-ray absorptiometry at baseline, and 1 and 6 years after gastric bypass or vertical banded gastroplasty in patients who were not receiving calcium supplements. Bone resorption markers in serum and calcium uptake mechanisms in jejunal mucosa biopsies were analysed after gastric bypass by proteomics including radioimmunoassay, gel electrophoresis and mass spectrometry.

RESULTS

One year after surgery, weight loss was similar after gastric bypass and vertical banded gastroplasty. There was a moderate decrease in skull BMD after gastric bypass, but not after vertical banded gastroplasty (P < 0·001). Between 1 and 6 years after gastric bypass, skull BMD and total BMD continued to decrease (P = 0·001). C-terminal telopeptide levels in serum had increased twofold by 18 months after gastric bypass. Proteomic analysis of the jejunal mucosa revealed decreased levels of heat-shock protein 90β, a co-activator of the vitamin D receptor, after gastric bypass. Despite increased vitamin D receptor levels, expression of the vitamin D receptor-regulated calcium transporter protein TRPV6 decreased.

CONCLUSION

BMD decreases independently of weight after gastric bypass. Bone loss might be attributed to impaired calcium absorption caused by decreased activation of vitamin D-dependent calcium absorption mechanisms mediated by heat-shock protein 90β and TRPV6.

Combined protein- and nucleic acid-level effects of rs1143679 (R77H), a lupus-predisposing variant within ITGAM

Integrin alpha M (ITGAM; CD11b) is a component of the macrophage-1 antigen complex, which mediates leukocyte adhesion, migration and phagocytosis as part of the immune system. We previously identified a missense polymorphism, rs1143679 (R77H), strongly associated with systemic lupus erythematosus (SLE). However, the molecular mechanisms of this variant are incompletely understood. A meta-analysis of published and novel data on 28 439 individuals with European, African, Hispanic and Asian ancestries reinforces genetic association between rs1143679 and SLE [Pmeta = 3.60 × 10(-90), odds ratio (OR) = 1.76]. Since rs1143679 is in the most active region of chromatin regulation and transcription factor binding in ITGAM, we quantitated ITGAM RNA and surface protein levels in monocytes from patients with each rs1143679 genotype. We observed that transcript levels significantly decreased for the risk allele ('A') relative to the non-risk allele ('G'), in a dose-dependent fashion: ('AA' < 'AG' < 'GG'). CD11b protein levels in patients' monocytes were directly correlated with RNA levels. Strikingly, heterozygous individuals express much lower (average 10- to 15-fold reduction) amounts of the 'A' transcript than 'G' transcript. We found that the non-risk sequence surrounding rs1143679 exhibits transcriptional enhancer activity in vivo and binds to Ku70/80, NFKB1 and EBF1 in vitro, functions that are significantly reduced with the risk allele. Mutant CD11b protein shows significantly reduced binding to fibrinogen and vitronectin, relative to non-risk, both in purified protein and in cellular models. This two-pronged contribution (nucleic acid- and protein-level) of the rs1143679 risk allele to decreasing ITGAM activity provides insight into the molecular mechanisms of its potent association with SLE.

Hsp90: structure and function

Hsp90 is a highly abundant and ubiquitous molecular chaperone which plays an essential role in many cellular processes including cell cycle control, cell survival, hormone and other signalling pathways. It is important for the cell's response to stress and is a key player in maintaining cellular homeostasis. In the last ten years, it has become a major therapeutic target for cancer, and there has also been increasing interest in it as a therapeutic target in neurodegenerative disorders, and in the development of anti-virals and anti-protozoan infections. The focus of this review is the structural and mechanistic studies which have been performed in order to understand how this important chaperone acts on a wide variety of different proteins (its client proteins) and cellular processes. As with many of the other classes of molecular chaperone, Hsp90 has a critical ATPase activity, and ATP binding and hydrolysis known to modulate the conformational dynamics of the protein. It also uses a host of cochaperones which not only regulate the ATPase activity and conformational dynamics but which also mediate interactions with Hsp90 client proteins. The system is also regulated by post-translational modifications including phosphorylation and acetylation. This review discusses all these aspects of Hsp90 structure and function.

Chaperoning steroidal physiology: lessons from mouse genetic models of Hsp90 and its cochaperones

The molecular chaperone Hsp90 is abundant, ubiquitous, and catholic to biological processes in eukaryotes, controlling phosphorylation cascades, protein stability and turnover, client localization and trafficking, and ligand-receptor interactions. Not surprisingly, Hsp90 does not accomplish these activities alone. Instead, an ever-growing number of cochaperones have been identified, leading to an explosion of reports on their molecular and cellular effects on Hsp90 chaperoning of client substrates. Notable among these clients are many members of the steroid receptor family, such as glucocorticoid, androgen, estrogen and progesterone receptors. Cochaperones typically associated with the mature, hormone-competent states of these receptors include p23, the FK506-binding protein 52 (FKBP52), FKBP51, protein phosphatase 5 (PP5) and cyclophilin 40 (Cyp40). The ultimate relevance of these cochaperones to steroid receptor action depends on their physiological effects. In recent years, the first mouse genetic models of these cochaperones have been developed. This work will review the complex and intriguing phenotypes so far obtained in genetically-altered mice and compare them to the known molecular and cellular impacts of cochaperones on steroid receptors. This article is part of a Special Issue entitled: Heat Shock Protein 90 (HSP90).

Heat shock protein 90 interacts with vitamin D receptor in human leukemia cells

The active form of vitamin D, 1alpha,25-dihydroxyvitamin D3 (1,25D), has a broad range of effects which are mediated by nuclear vitamin D receptor (VDR). Many experiments that investigate the role of VDR can be done in human acute myeloid leukemia (AML) cells, since these cells are responsive to 1,25D and express VDR in a 1,25D-regulated manner. In this paper we show that in HL60 and in THP-1 cells VDR protein interacts with heat shock protein 90 (Hsp90) and that Hsp90 is important for differentiation of AML cells. Geldanamycin (GA), an Hsp90 inhibitor, is able to suppress 1,25-induced differentiation of HL60 cells.

Severity of experimental autoimmune encephalomyelitis is unexpectedly reduced in mice born to vitamin D-deficient mothers

Accumulating data indicate that vitamin D, a sun-induced hormone, plays a key role in multiple sclerosis (MS) etiology. Notably, it has been shown that there is a remarkable season of birth effect in MS. We surmised that gestational vitamin D deficiency is a risk factor for MS. To test this hypothesis, a vitamin D deficiency was induced in C57BL/6 female mice 6 weeks prior to conception and prolonged until offspring birth. Contrary to our prediction, we show here that adult offspring exposed to developmental vitamin D deficiency (DVD) developed a striking milder and delayed experimental autoimmune encephalomyelitis (EAE), when compared to control offspring. Using reverse transcription and quantitative real-time PCR, we measured the expression level of 22 candidate transcripts in the spleen, the cerebrum and the spinal cord, at Day0 and Day30 post-immunization. We report here that, at Day30 post-immunization, TNF, osteopontin, H2-Eb were over-expressed and IFN was under-expressed in the spinal cord of control mice and not in DVD mice. Another discrepancy between nervous and immune systems was observed: expression of IL4 was dysregulated exclusively in the spleen. Reduced symptom severity in DVD mice can partially be explained by a nervous system-restricted over-expression of vitamin D receptor (VDR), two heat shock proteins (HSP90, HSPa8) and FK506 binding protein 1a (FKBP1a), at Day0. Our clinical test and molecular findings converge to indicate that maternal hypovitaminosis D imprints the foetus and alters the susceptibility of the offspring to EAE. We propose a new hypothesis to explain our unexpected observations.

The impact of methylmercury on 1,25-dihydroxyvitamin D3-induced transcriptomic responses in dolphin skin cells

The Atlantic bottlenose dolphin has been the focus of much attention owing to the considerable impact of environmental stress on its health and the associated implications for human health. Here, we used skin cells from the dolphin to investigate the protective role of the vitamin D pathway against environmental stressors. We previously reported that dolphin skin cells respond to 1,25-dihydroxyvitamin D3 (1,25D3), the bioactive metabolite of vitamin D3, by upregulation of the vitamin D receptor (VDR) and expression of several genes. Methylmercury is a highly bioaccumulative environmental stressor of relevance to the dolphin. We currently report that in dolphin cells sublethal concentrations of methylmercury compromise the ability of 1,25D3 to upregulate VDR, to transactivate a vitamin D-sensitive promoter, and to express specific target genes. These results help elucidate the effects of vitamin D and methylmercury on innate immunity in dolphin skin and potentially in human skin as well, considering similarities in the vitamin D pathway between the two species.

Vitamin D metabolites as clinical markers in autoimmune and chronic disease

Recent research has implicated vitamin D deficiency (serum levels of 25-hydroxyvitamin D <50 nmol/L) with a number of chronic conditions, including autoimmune conditions such as multiple sclerosis, lupus, and psoriasis, and chronic conditions such as osteoporosis, osteoarthritis, metabolic syndrome, fibromyalgia and chronic fatigue syndrome. It has been assumed that low levels of 25-hydroxyvitamin D (25-D) accurately indicate vitamin D storage and vitamin D receptor (VDR)-mediated control of calcium metabolism and innate immunity. To evaluate this assumption, 25-D and 1,25-dihydroxyvitamin D3 (1,25-D) levels were measured in 100 Canadian patients with these conditions. Additionally, other inflammatory markers (CK, CRP) were measured. Results showed a strong positive association between these autoimmune conditions and levels of 1,25-D >110 pmol/L. However, there was little association with vitamin D deficiency or the other inflammatory markers, meaning that the results challenge the assumption that serum levels of 25-D are a sensitive measure of the autoimmune disease state. Rather, these findings support the use of 1,25-D as a clinical marker in autoimmune conditions. High levels of 1,25-D may result when dysregulation of the VDR by bacterial ligands prevents the receptor from expressing enzymes necessary to keep 1,25-D in a normal range.

The effect of differentiation on 1,25 dihydroxyvitamin D-mediated gene expression in the enterocyte-like cell line, Caco-2

We examined 1,25 dihydroxyvitamin D (1,25(OH)(2)D(3))-induced expression of 25-hydroxyvitamin D(3) 24-hydroxylase (CYP24) and apical calcium channel (TRPV6) mRNA levels in 2-, 9-, and 15-day cultures Caco-2 cells that model proliferating, post-proliferative, and differentiated enterocytes. 1,25(OH)(2)D(3)-induced (10 nM, 8 h) CYP24 and TRPV6 mRNA levels were significantly greater in differentiated and post-proliferative than proliferating Caco-2 cells (>16X and >3X, respectively). Neither CYP24 mRNA half-life nor induction of a -298 bp rat CYP24 promoter-luciferase reporter construct (10 nM 1,25(OH)(2)D(3), 24 h) were different between proliferating and post-proliferating Caco-2 cells. We next tested whether the blunted response of natural genes to 1,25(OH)(2)D(3) in proliferating Caco-2 cells is due to altered chromatin remodeling. VDR and coactivator protein levels do not increase with differentiation but the level of the co-repressor Alien falls by 50% with differentiation. Over-expression of Alien reduced 1,25(OH)(2)D(3)-induced activity of a minimal VDRE containing promoter-luciferase construct by more than 60% in differentiated Caco-2 cells while siRNA knockdown of Alien in proliferating Caco-2 cells increased 1,25(OH)(2)D(3)-induced CYP24 mRNA level by 40%. These observations suggest that Alien is a regulator of VDR-mediated gene transcription in Caco-2 cells. In addition, we found that 1,25(OH)(2)D(3)-induced association of VDR with chromatin and with the CYP24 promoter was lower in proliferating cells. This suggests that decreased recruitment of VDR to vitamin D response elements also contributes to the blunted transcriptional responsiveness to 1,25(OH)(2)D(3) in proliferating Caco-2 cells.

Minireview: the intersection of steroid receptors with molecular chaperones: observations and questions

An involvement of molecular chaperones in the action and well-being of steroid receptors was recognized early in the molecular era of hormone research. However, this has continued to be a topic of much enquiry and some confusion. All steroid receptors associate with heat shock protein 90, the main character of a series of multiprotein chaperone complexes generally referred to as the "heat shock protein 90 chaperoning machine." Receptor association with chaperones occurs in an ordered, step-wise fashion and is necessary for the maintenance of unliganded receptor in a state ready to bind and respond to hormone. Chaperones additionally modulate how receptors respond to hormone and activate target genes. Although much is known about the participants in this chaperoning process and the consequences of chaperoning, many key questions remain unanswered, particularly those concerning molecular mechanisms, cellular dynamics, and the functions of an array of cochaperone proteins. Here, we point out several areas in need of investigation to encourage new ideas and participants in this burgeoning field.