Size matters: of the small HSP27 and its large oligomers

Advances in the structures, mechanisms and targeting of molecular chaperones

Molecular chaperones, a class of complex client regulatory systems, play significant roles in the prevention of protein misfolding and abnormal aggregation, the modulation of protein homeostasis, and the protection of cells from damage under constantly changing environmental conditions. As the understanding of the biological mechanisms of molecular chaperones has increased, their link with the occurrence and progression of disease has suggested that these proteins are promising targets for therapeutic intervention, drawing intensive interest. Here, we review recent advances in determining the structures of molecular chaperones and heat shock protein 90 (HSP90) chaperone system complexes. We also describe the features of molecular chaperones and shed light on the complicated regulatory mechanism that operates through interactions with various co-chaperones in molecular chaperone cycles. In addition, how molecular chaperones affect diseases by regulating pathogenic proteins has been thoroughly analyzed. Furthermore, we focus on molecular chaperones to systematically discuss recent clinical advances and various drug design strategies in the preclinical stage. Recent studies have identified a variety of novel regulatory strategies targeting molecular chaperone systems with compounds that act through different mechanisms from those of traditional inhibitors. Therefore, as more novel design strategies are developed, targeting molecular chaperones will significantly contribute to the discovery of new potential drugs.

Mechanical activation and expression of HSP27 in epithelial ovarian cancer

Understanding the complex biomechanical tumor microenvironment (TME) is of critical importance in developing the next generation of anti-cancer treatment strategies. This is especially true in epithelial ovarian cancer (EOC), the deadliest of the gynecologic cancers due to recurrent disease or chemoresistance. However, current models of EOC progression provide little control or ability to monitor how changes in biomechanical parameters alter EOC cell behaviors. In this study, we present a microfluidic device designed to permit biomechanical investigations of the ovarian TME. Using this microtissue system, we describe how biomechanical stimulation in the form of tensile strains upregulate phosphorylation of HSP27, a heat shock protein implicated in ovarian cancer chemoresistance. Furthermore, EOC cells treated with strain demonstrate decreased response to paclitaxel in the in vitro vascularized TME model. The results provide a direct link to biomechanical regulation of HSP27 as a mediator of EOC chemoresistance, possibly explaining the failure of such therapies in some patients. The work presented here lays a foundation to elucidating mechanobiological regulation of EOC progression, including chemoresistance and could provide novel targets for anti-cancer therapeutics.

Heat shock proteins and exosomes in cancer theranostics

Heat shock proteins (HSPs) are a superfamily of molecular chaperones that were discovered through their ability to be induced by different stresses including heat shock. Other than their function as chaperones in proteins homeostasis, HSPs have been shown to inhibit different forms of cell death and to participate in cell proliferation and differentiation processes. Because cancer cells have to rewire their metabolism, they require a high amount of these stress-inducible chaperones for their survival. Therefore, HSPs are unusually abundant in cancer cells where they have oncogene-like functions. In cancer, HSPs have been involved in the regulation of apoptosis, immune responses, angiogenesis, metastasis and treatment resistance. Recently, HSPs have been shown to be secreted through exosomes by cancer cells. These tumor-derived exosomes can be used as circulating markers: HSP-exosomes have been reported as biomarkers of cancer dissemination, response to therapy and/or patient outcome. A new range of functions, mostly in modulation of anticancer immune responses, have been described for these extracellular HSPs. In this review, we will describe those recently reported functions of HSP-exosomes that makes them both targets for anticancer therapeutics and biomarkers for the monitoring of the disease. We will also discuss their emerging interest in cancer vaccines.

HSP27 role in cardioprotection by modulating chemotherapeutic doxorubicin-induced cell death

The common phenomenon expected from any anti-cancer drug in use is to kill the cancer cells without any side effects to non-malignant cells. Doxorubicin is an anthracycline derivative anti-cancer drug active over different types of cancers with anti-cancer activity but attributed to unintended cytotoxicity and genotoxicity triggering mitogenic signals inducing apoptosis. Administration of doxorubicin tends to both acute and chronic toxicity resulting in cardiomyopathy (left ventricular dysfunction) and congestive heart failure (CHF). Cardiotoxicity is prevented through administration of different cardioprotectants along with the drug. This review elaborates on mechanism of drug-mediated cardiotoxicity and attenuation principle by different cardioprotectants, with a focus on Hsp27 as cardioprotectant by prevention of drug-induced oxidative stress, cell survival pathways with suppression of intrinsic cell death. In conclusion, Hsp27 may offer an exciting/alternating cardioprotectant, with a wider study being need of the hour, specifically on primary cell line and animal models in conforming its cardioprotectant behaviour.

Flavonoids: Potential Candidates for the Treatment of Neurodegenerative Disorders

Neurodegenerative disorders, such as Parkinson's disease (PD), Alzheimer's disease (AD), Amyotrophic lateral sclerosis (ALS), and Huntington's disease (HD), are the most concerning disorders due to the lack of effective therapy and dramatic rise in affected cases. Although these disorders have diverse clinical manifestations, they all share a common cellular stress response. These cellular stress responses including neuroinflammation, oxidative stress, proteotoxicity, and endoplasmic reticulum (ER)-stress, which combats with stress conditions. Environmental stress/toxicity weakened the cellular stress response which results in cell damage. Small molecules, such as flavonoids, could reduce cellular stress and have gained much attention in recent years. Evidence has shown the potential use of flavonoids in several ways, such as antioxidants, anti-inflammatory, and anti-apoptotic, yet their mechanism is still elusive. This review provides an insight into the potential role of flavonoids against cellular stress response that prevent the pathogenesis of neurodegenerative disorders.

Functional Diversity of Non-Histone Chromosomal Protein HmgB1

The functioning of DNA in the cell nucleus is ensured by a multitude of proteins, whose interactions with DNA as well as with other proteins lead to the formation of a complicated, organized, and quite dynamic system known as chromatin. This review is devoted to the description of properties and structure of the progenitors of the most abundant non-histone protein of the HMGB family-the HmgB1 protein. The proteins of the HMGB family are also known as "architectural factors" of chromatin, which play an important role in gene expression, transcription, DNA replication, and repair. However, as soon as HmgB1 goes outside the nucleus, it acquires completely different functions, post-translational modifications, and change of its redox state. Despite a lot of evidence of the functional activity of HmgB1, there are still many issues to be solved related to the mechanisms of the influence of HmgB1 on the development and treatment of different diseases-from oncological and cardiovascular diseases to pathologies during pregnancy and childbirth. Here, we describe molecular structure of the HmgB1 protein and discuss general mechanisms of its interactions with other proteins and DNA in cell.

Nephroprotective Effect of Cilastatin against Gentamicin-Induced Renal Injury In Vitro and In Vivo without Altering Its Bactericidal Efficiency

Gentamicin is a used antibiotic that causes nephrotoxicity in 10-20% of treatment periods, which limits its use considerably. Our results have shown that cilastatin may be a promising therapeutic alternative in toxin-induced acute kidney injury (AKI). Here, we investigated its potential use as a nephroprotector against gentamicin-induced AKI in vitro and in vivo. Porcine renal cells and rats were treated with gentamicin and/or cilastatin. In vivo nephrotoxicity was analyzed by measuring biochemical markers and renal morphology. Different apoptotic, oxidative and inflammatory parameters were studied at cellular and systemic levels. Megalin, mainly responsible for the entry of gentamicin into the cells, was also analyzed. Results show that cilastatin protects cells from gentamicin-induced AKI. Cilastatin decreased creatinine, BUN, kidney injury molecule-1 (KIM-1) and severe morphological changes previously increased by gentamicin in rats. The interference of cilastatin with lipid rafts cycling leads to decreased expression of megalin, and therefore gentamicin uptake and myeloid bodies, resulting in a decrease of apoptotic, oxidative and inflammatory events. Moreover, cilastatin did not prevent bacterial death by gentamicin. Cilastatin reduced gentamicin-induced AKI by preventing key steps in the amplification of the damage, which is associated to the disruption of megalin-gentamicin endocytosis. Therefore, cilastatin might represent a novel therapeutic tool in the prevention and treatment of gentamicin-induced AKI in the clinical setting.

Loss of NF-E2 expression contributes to the induction of profibrotic signaling in diabetic kidneys

AIMS

This study aimed to examine the anti-fibrotic role of Nuclear Factor-Erythroid derived 2 (NF-E2) in human renal tubule (HK-11) cells and in type 1 and type 2 diabetic (T1D, T2D) mouse kidneys.

MAIN METHODS

Anti-fibrotic effects of NF-E2 were examined in transforming growth factor-β (TGF-β) treated HK-11 cells by over-expressing/silencing NF-E2 expression and determining its effects on profibrotic signaling. NF-E2 proteasomal degradation was confirmed by proteasome inhibition in HK-11 cells and diabetic mice. Clinical relevance of changes in NF-E2 expression to fibrotic changes in the kidney were assessed in T1D and T2D mouse kidneys.

KEY FINDINGS

NF-E2 expression was significantly decreased in TGF-β treated HK-11 cells and in kidneys of diabetic mice with concurrent increase in expression of fibrotic proteins. TGF-β treatment of HK-11 cells did not inhibit NF-E2 mRNA expression, suggesting that the post-translational changes may contribute to NF-E2 protein degradation. The down-regulation of NF-E2 expression was attributed to its proteasomal degradation, as TGF-β- and diabetes-induced NF-E2 down regulation was prevented by proteasome inhibitor treatment. In HK-11 cells TGF-β treatment decreased E-cadherin expression and induced pSer82Hsp27/NF-E2 association, likely to promote NF-E2 degradation, as Hsp27 can target proteins to the proteasome. A critical role for NF-E2 in regulation of renal fibrosis was demonstrated as over-expression of NF-E2 or silencing NF-E2 expression, decreased or increased profibrotic proteins in TGF-β-treated HK-11 cells, respectively.

SIGNIFICANCE

NF-E2, a novel anti-fibrotic protein, is down-regulated in diabetic kidneys. Preserving/inducing NF-E2 expression in diabetic kidneys may provide a therapeutic potential to combat DN.

Adapting to stress - chaperome networks in cancer

In this Opinion article, we aim to address how cells adapt to stress and the repercussions chronic stress has on cellular function. We consider acute and chronic stress-induced changes at the cellular level, with a focus on a regulator of cellular stress, the chaperome, which is a protein assembly that encompasses molecular chaperones, co-chaperones and other co-factors. We discuss how the chaperome takes on distinct functions under conditions of stress that are executed in ways that differ from the one-on-one cyclic, dynamic functions exhibited by distinct molecular chaperones. We argue that through the formation of multimeric stable chaperome complexes, a state of chaperome hyperconnectivity, or networking, is gained. The role of these chaperome networks is to act as multimolecular scaffolds, a particularly important function in cancer, where they increase the efficacy and functional diversity of several cellular processes. We predict that these concepts will change how we develop and implement drugs targeting the chaperome to treat cancer.

Noxa/HSP27 complex delays degradation of ubiquitylated IkBα in airway epithelial cells to reduce pulmonary inflammation

IFN-γ is known as a pro-inflammatory cytokine, but can also block inflammation in certain chronic diseases although the underlying mechanisms are poorly understood. We found that IFN-γ rapidly induced Noxa expression and that extent of inflammation by repeated house dust mite exposure was enhanced in noxa^-/- compared with noxa^+/+ mice. Noxa expression blocked transforming necrosis factor alpha (TNF-α)-induced nuclear translocation of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and the production of pro-inflammatory cytokines. Noxa did not affect TNF-α-induced IκBα phosphorylation but the degradation of 48-chain-ubiquitylated IκBα. The Cys25 of Noxa was cross-linked with Cys137 of phospho-HSP27 and both proteins were required for blocking the degradation of ubiquitylated IκBα. Because phospho-HSP27 is present in airway epithelial cells and not in fibroblasts or thymocytes, we generated transgenic mice that inducibly expressed Noxa in airway epithelia. These mice showed protection from allergen-induced inflammation and mucous cell metaplasia by blocking nuclear translocation of NF-κB. Further, we identified a Noxa-derived peptide that prolonged degradation of 48-chain-ubiquitylated IκBα, blocked nuclear translocation of NF-κB, and reduced allergen-induced inflammation in mice. These results suggest that the anti-inflammatory role of the Noxa protein may be restricted to airway epithelial cells and the use of Noxa for therapy of chronic lung diseases may be associated with reduced side effects.

Analysis of HspB1 (Hsp27) Oligomerization and Phosphorylation Patterns and Its Interaction with Specific Client Polypeptides

Human HspB1 (also denoted as Hsp27) belongs to the family of small (or stress) proteins (sHsps). The family, which contains ten members including αA,B-crystallin polypeptides, is characterized by a conserved C-terminal α-crystallin domain and molecular weights ranging from 20 to 40 kDa. Here, procedures are described for analyzing the dynamic oligomerization and phosphorylation patterns of HspB1 in cells exposed to different environments. Changes in the structural organization of HspB1 can reprogram its interaction with specific partner/client polypeptides. Methods are presented to analyze these interactions using tissue culture cells genetically modified to express different levels of this protein. In addition, the laboratory approaches presented here could be used to test the nine other human sHsp members as well as sHsps from other species.

Evaluating the Effect of Phosphorylation on the Structure and Dynamics of Hsp27 Dimers by Means of Ion Mobility Mass Spectrometry

The quaternary structure and dynamics of the human small heat-shock protein Hsp27 are linked to its molecular chaperone function and influenced by post-translational modifications, including phosphorylation. Phosphorylation of Hsp27 promotes oligomer dissociation and can enhance chaperone activity. This study explored the impact of phosphorylation on the quaternary structure and dynamics of Hsp27. Using mutations that mimic phosphorylation, and ion mobility mass spectrometry, we show that successive substitutions result in an increase in the conformational heterogeneity of Hsp27 dimers. In contrast, we did not detect any changes in the structure of an Hsp27 12-mer, representative of larger Hsp27 oligomers. Our data suggest that oligomer dissociation and increased flexibility of the dimer contribute to the enhanced chaperone activity of phosphorylated Hsp27. Thus, post-translational modifications such as phosphorylation play a crucial role in modulating both the tertiary and quaternary structure of Hsp27, which is pivotal to its function as a key component of the proteostasis network in cells. Our data demonstrate the utility of ion mobility mass spectrometry for probing the structure and dynamics of heterogeneous proteins.

The Conjugated Double Bond of Coniferyl Aldehyde Is Essential for Heat Shock Factor 1 Mediated Cytotoprotection

Coniferyl aldehyde (1) is previously reported as a potent inducer of heat shock factor 1 (HSF1). Here, we further examined the active pharmacophore of 1 for activation of HSF1 using the derivatives coniferyl alcohol (2), 4-hydroxy-3-methoxyphenylpropanal (3), and 4-hydroxy-3-methoxyphenylpropanol (4). Both 1 and 2 resulted in increased survival days after a lethal radiation (IR) dose. The decrease in bone marrow (BM) cellularity and Ki67-positive BM cells by IR was also significantly restored by 1 or 2 in mice. These results suggested that the vinyl moiety of 1 and 2 is necessary for inducing HSF1, which may be useful for developing small molecules for cytoprotection of normal cells against damage by cytotoxic drugs and radiation.

Targeting Hsp27/eIF4E interaction with phenazine compound: a promising alternative for castration-resistant prostate cancer treatment

The actual strategy to improve current therapies in advanced prostate cancer involves targeting genes activated by androgen withdrawal, either to delay or prevent the emergence of the castration-refractory phenotype. However, these genes are often implicated in several physiological processes, and long-term inhibition of survival proteins might be accompanied with cytotoxic effects. To avoid this problem, an alternative therapeutic strategy relies on the identification and use of compounds that disrupt specific protein-protein interactions involved in androgen withdrawal. Specifically, the interaction of the chaperone protein Hsp27 with the initiation factor eIF4E leads to the protection of protein synthesis initiation process and enhances cell survival during cell stress induced by castration or chemotherapy. Thus, in this work we aimed at i) identifying the interaction site of the Hsp27/eIF4E complex and ii) interfere with the relevant protein/protein association mechanism involved in castration-resistant progression of prostate cancer. By a combination of experimental and modeling techniques, we proved that eIF4E interacts with the C-terminal part of Hsp27, preferentially when Hsp27 is phosphorylated. We also observed that the loss of this interaction increased cell chemo-and hormone-sensitivity. In order to find a potential inhibitor of Hsp27/eIF4E interaction, BRET assays in combination with molecular simulations identified the phenazine derivative 14 as the compound able to efficiently interfere with this protein/protein interaction, thereby inhibiting cell viability and increasing cell death in chemo- and castration-resistant prostate cancer models in vitro and in vivo.

Mammalian HspB1 (Hsp27) is a molecular sensor linked to the physiology and environment of the cell

Constitutively expressed small heat shock protein HspB1 regulates many fundamental cellular processes and plays major roles in many human pathological diseases. In that regard, this chaperone has a huge number of apparently unrelated functions that appear linked to its ability to recognize many client polypeptides that are subsequently modified in their activity and/or half-life. A major parameter to understand how HspB1 is dedicated to interact with particular clients in defined cellular conditions relates to its complex oligomerization and phosphorylation properties. Indeed, HspB1 structural organization displays dynamic and complex rearrangements in response to changes in the cellular environment or when the cell physiology is modified. These structural modifications probably reflect the formation of structural platforms aimed at recognizing specific client polypeptides. Here, I have reviewed data from the literature and re-analyzed my own studies to describe and discuss these fascinating changes in HspB1 structural organization.

Heat Shock Proteins in Multiple Sclerosis

Multiple sclerosis (MS) is an immune-mediated and neurodegenerative central nervous system disease, mostly affect myelin sheaths. The MS pathogenesis is still under debate. It is influenced by genetic, environment factors. Heat shock proteins (HSPs) are highly conserved proteins seen in all organisms. Not only heat stress but also under many stress conditions they are overexpressed. Their roles in MS pathogenesis are highly correlated with their location (intracellular or extracellular). In this chapter, we will discuss the role of HSP in MS pathogenesis.

Heat Shock Protein Beta-1 Modifies Anterior to Posterior Purkinje Cell Vulnerability in a Mouse Model of Niemann-Pick Type C Disease

Selective neuronal vulnerability is characteristic of most degenerative disorders of the CNS, yet mechanisms underlying this phenomenon remain poorly characterized. Many forms of cerebellar degeneration exhibit an anterior-to-posterior gradient of Purkinje cell loss including Niemann-Pick type C1 (NPC) disease, a lysosomal storage disorder characterized by progressive neurological deficits that often begin in childhood. Here, we sought to identify candidate genes underlying vulnerability of Purkinje cells in anterior cerebellar lobules using data freely available in the Allen Brain Atlas. This approach led to the identification of 16 candidate neuroprotective or susceptibility genes. We demonstrate that one candidate gene, heat shock protein beta-1 (HSPB1), promoted neuronal survival in cellular models of NPC disease through a mechanism that involved inhibition of apoptosis. Additionally, we show that over-expression of wild type HSPB1 or a phosphomimetic mutant in NPC mice slowed the progression of motor impairment and diminished cerebellar Purkinje cell loss. We confirmed the modulatory effect of Hspb1 on Purkinje cell degeneration in vivo, as knockdown by Hspb1 shRNA significantly enhanced neuron loss. These results suggest that strategies to promote HSPB1 activity may slow the rate of cerebellar degeneration in NPC disease and highlight the use of bioinformatics tools to uncover pathways leading to neuronal protection in neurodegenerative disorders.

Niemann-Pick type C1 (NPC) disease is an autosomal recessive lipid storage disorder for which there is no effective treatment. Patients develop a clinically heterogeneous phenotype that typically includes childhood onset neurodegeneration and early death. Mice with loss of function mutations in the Npc1 gene model many aspects of the human disease, including cerebellar degeneration that results in marked ataxia. Cerebellar Purkinje cells in mutant mice exhibit striking selective vulnerability, with neuron loss in anterior lobules and preservation in posterior lobules. As this anterior to posterior gradient is reproduced following cell autonomous deletion of Npc1 and is also observed in other forms of cerebellar degeneration, we hypothesized that it is mediated by differential gene expression. To test this notion, we probed the Allen Brain Atlas to identify 16 candidate neuroprotective or susceptibility genes. We confirmed that one of these genes, encoding the small heat shock protein Hspb1, promotes survival in cell culture models of NPC disease. Moreover, we found that modulating Hspb1 expression in NPC mice promoted (following over-expression) or diminished (following knock-down) Purkinje cell survival, confirming its neuroprotective activity. We suggest that this approach may be similarly used in other diseases to uncover pathways that modify selective neuronal vulnerability.

Weight loss-induced stress in subcutaneous adipose tissue is related to weight regain

Initial successful weight loss is often followed by weight regain after the dietary intervention. Compared with lean people, cellular stress in adipose tissue is increased in obese subjects. However, the relation between cellular stress and the risk for weight regain after weight loss is unclear. Therefore, we determined the expression levels of stress proteins during weight loss and weight maintenance in relation to weight regain. In vivo findings were compared with results from in vitro cultured human Simpson-Golabi-Behmel syndrome (SGBS) adipocytes. In total, eighteen healthy subjects underwent an 8-week diet programme with a 10-month follow-up. Participants were categorised as weight maintainers or weight regainers (WR) depending on their weight changes during the intervention. Abdominal subcutaneous adipose tissue biopsies were obtained before and after the diet and after the follow-up. In vitro differentiated SGBS adipocytes were starved for 96 h with low (0·55 mm) glucose. Levels of stress proteins were determined by Western blotting. WR showed increased expressions of β-actin, calnexin, heat shock protein (HSP) 27, HSP60 and HSP70. Changes of β-actin, HSP27 and HSP70 are linked to HSP60, a proposed key factor in weight regain after weight loss. SGBS adipocytes showed increased levels of β-actin and HSP60 after 96 h of glucose restriction. The increased level of cellular stress proteins in the adipose tissue of WR probably resides in the adipocytes as shown by in vitro experiments. Cellular stress accumulated in adipose tissue during weight loss may be a risk factor for weight regain.

Proteomic Analysis Reveals PGAM1 Altering cis-9, trans-11 Conjugated Linoleic Acid Synthesis in Bovine Mammary Gland

cis-9, trans-11 Conjugated linoleic acid (CLA) is one of the most extensively studied CLA isomers due to its multiple isomer-specific effects. However, the molecular mechanisms of cis-9,trans-11 CLA synthesis in ruminant mammary gland are still not clearly understood. This process may be mediated, to a certain extent, by trans-11 C18:1 regulated by stearoyl-CoA desaturase-1 (SCD1) and/or its syntrophic proteins. This study aimed to investigate the effects of TVA on SCD1-mediated cis-9,trans-11 CLA synthesis in MAC-T cells and its potential molecular mechanism. Results showed that trans-11 C18:1 was continually taken up and converted into cis-9,trans-11 CLA in MAC-T cells during the 4-h incubation of 50 μM trans-11 C18:1. SCD1 protein expression increased more than twofold at 2 h (P < 0.01) and 2.5 h (P < 0.05) before decreasing to less than half of the normal level at 4 h (P < 0.05). One up-regulated (RAS guanyl releasing protein 4 isoform 1 [RASGRP4]) and six down-regulated proteins (glucosamine-6-phosphate deaminase 1 [GNPDA1], triosephosphate isomerase [TPI1], phosphoglycerate mutase 1 [PGAM1], heat shock protein beta-1 [HSPB1], annexin A3 [ANXA3], thiopurine S-methyltransferase [TPMT]) were found in MAC-T cells treated with trans-11 C18:1. Of these seven identified proteins, the presence of GNPDA1 and PGAM1 was verified in several models. More trans-11 C18:1 was taken up after PGAM1 knockdown by small interfering RNA (siRNA). In conclusion, our data suggested that PGAM1 may have a negative relationship with SCD1 and seemed to be involved in cis-9, trans-11 CLA synthesis by facilitating the absorption of trans-11 C18:1 in the bovine mammary gland.

Palytoxin induces dissociation of HSP 27 oligomers through a p38 protein kinase pathway

Palytoxin (PlTX) induces a stress response in MCF-7 cells that involves the phosphorylation of HSP 27 at serines 15, 78, and 82 by an as yet undetermined mechanism. We have studied the involvement of major groups of the mitogen-activated protein kinase (MAPK) family in this molecular response and focused our analyses on the ERK1/2, JNK, p38 protein kinase (p38K), and ERK5 pathways. The results show that PlTX induces the activation of JNK and p38 kinase but not ERK1/2 and 5 in MCF-7 cells. Through the use of protein kinase inhibitors, we established that blocking p38K, but not JNK, prevents the phosphorylation of HSP 27 induced by PlTX and that MAPKAPK2 participates in the response induced by the toxin under our experimental conditions. The cell death response induced by PlTX was inhibited by preventing JNK phosphorylation but not by blocking p38K/MAPKAPK2 and HSP 27 phosphorylation. Sucrose density gradient centrifugation revealed that MCF-7 cell extracts contain a heterodisperse population of HSP 27, including oligomers and smaller forms. Treating MCF-7 cells with PlTX caused the dissociation of HSP 27 oligomers, and using inhibitors of the JNK and p38K pathways showed that the dissociation of HSP 27 oligomers induced by PlTX involves a p38K-dependent process. We conclude that the changes induced by PlTX in the HSP 27 stress response protein system proceed through a molecular mechanism involving the activation of the p38 kinase pathway and its substrate, MAPKAK2, leading to dissociation of HSP 27 oligomers and the stabilization of a cellular pool of monomers phosphorylated at serines 15, 78 and 82, which could play a protective role against the death response induced by PlTX.

Heat shock protein 27 phosphorylation state is associated with cancer progression

Understanding the mechanisms that control stress-induced survival is critical to explain how tumors frequently resist to treatment and to improve current anti-cancer therapies. Cancer cells are able to cope with stress and escape drug toxicity by regulating heat shock proteins (Hsps) expression and function. Hsp27 (HSPB1), a member of the small Hsp family, represents one of the key players of many signaling pathways contributing to tumorigenicity, treatment resistance, and apoptosis inhibition. Hsp27 is overexpressed in many types of cancer and its functions are regulated by post-translational modifications, such as phosphorylation. Protein phosphorylation is the most widespread signaling mechanism in eukaryotic cells, and it is involved in all fundamental cellular processes. Aberrant phosphorylation of Hsp27 has been associated with cancer but the molecular mechanisms by which it is implicated in cancer development and progression remain undefined. This mini-review focuses on the role of phosphorylation in Hsp27 functions in cancer cells and its potential usefulness as therapeutic target in cancer.

HspB1, HspB5 and HspB4 in Human Cancers: Potent Oncogenic Role of Some of Their Client Proteins

Human small heat shock proteins are molecular chaperones that regulate fundamental cellular processes in normal unstressed cells as well as in many cancer cells where they are over-expressed. These proteins are characterized by cell physiology dependent changes in their oligomerization and phosphorylation status. These structural changes allow them to interact with many different client proteins that subsequently display modified activity and/or half-life. Nowdays, the protein interactomes of small Hsps are under intense investigations and will represent, when completed, key parameters to elaborate therapeutic strategies aimed at modulating the functions of these chaperones. Here, we have analyzed the potential pro-cancerous roles of several client proteins that have been described so far to interact with HspB1 (Hsp27) and its close members HspB5 (αB-crystallin) and HspB4 (αA-crystallin).

Transduced protein transduction domain linked HSP27 protected LECs against UVB radiation-induced damage

PTD-fusion protein technology was used to transduce heat shock protein 27 (HSP27), an anti-apoptotic protein, into human lens epithelial cells (HLECs) (SRA01/04). The protein transduction domain (PTD) of the 11-amino acid YGRKKRRQRRR was tagged at the N-terminus of HSP27. The fusion protein was purified from bacteria transformed with a pKYB-PTD-HSP27 construct. The HLECs were incubated with PTD-HSP27-FITC and the fluorescence inside HLECs was found by fluorescence microscopic examination. To test the ability of PTD-HSP27 to pass through the corneas, PTD-HSP27-FITC was dropped onto the conjunctival sacs of rabbits; fluorescent labeled PTD-HSP27 was then observed in the rabbit aqueous humor. After being incubated with the PTD-HSP27 protein and irradiated with ultraviolet-B (UVB) light, HLECs was analyzed by flow cytometry, Hoechst 33258 staining and measurement of the potential of the mitochondrial transmembrane. HLECs incubated with PTD-HSP27 had a lower apoptotic rate and a higher mitochondrial membrane potential than the control cells. PTD-HSP27 appears to be sufficient to protect HLECs against UVB-induced apoptosis.

The effect of heat shock protein 27 on extravillous trophoblast differentiation and on eukaryotic translation initiation factor 4E expression

Heat shock protein (HSP27) is expressed in human placentae. Previously, we showed that HSP27 is expressed in the villous cell column of first trimester placental explants and in extravillous trophoblast (EVT) cells. EVT differentiation is accompanied by increased motility, matrix metalloproteinase (MMP) activity, decreased proliferation and expression of specific markers such as HLAG and CD9. HSP27 regulates cell apoptosis, migration, protein stability and the availability of eukaryotic translation initiation factors, such as eukaryotic translation initiation factor 4E (eIF4E). eIF4E supports trophoblast cell proliferation and survival. We wanted to explore the effect of HSP27 silencing on trophoblast cell phenotype, EVT markers and eIF4E expression and regulators [4E-binding protein (4E-BP1) and MAP kinase-interacting kinase (MNK1)]. This study evaluated the effect of HSP27 siRNA on placental explant and HTR-8/SVneo migration, MMP activity/mRNA, cell death, cell cycle, HLAG/CD9 levels, and eIF4E and its regulators' total and phosphorylated levels. Furthermore, we evaluated HSP27 levels in placentae exposed to ribavirin, which triggers EVT differentiation. We found that HSP27 silencing increased cell death in HTR-8/SVneo and placental explants. Furthermore, it reduced HTR-8/SVneo migration and EVT outgrowth from the explants (P < 0.05), MMP2 activity and expression of EVT markers HLAG and CD9 (in placental explants and HTR-8/SVneo, respectively, P < 0.05). Induction of EVT differentiation by ribavirin elevated HSP27 levels. Finally, HSP27 silencing in both HTR-8/SVneo and placental explants reduced eIF4E levels (33 and 28%, respectively, P < 0.05) and the levels of its regulators 4E-BP1 and MNK1 (37 and 32%, respectively, done on HTR-8/SVneo only), but not their phosphorylated forms. Altogether, our results suggest that HSP27 contributes to EVT cell differentiation.

Expression of heat shock proteins in medulloblastoma

OBJECT

Medulloblastoma (MB) is the most common malignant brain tumor in children. Heat shock proteins (HSPs) comprise a superfamily of proteins that serve as molecular chaperones and are overexpressed in a wide range of human cancers. The purpose of the present study was to investigate the expression of HSP27 (pSer(82)), HSP27 (pSer(15)), HSP40, HSP60, HSP70, HSP90-α, Akt, and phospho-Akt by multiplex bead array assay of MBs. The results of HSP and Akt expression were correlated with MB subtype; immunohistochemical expression of Ki-67 index, bcl-2, and p53; and patients' prognosis.

METHODS

The authors retrospectively evaluated 25 children with MB who underwent surgery. Immunohistochemical analysis of Ki-67, p53, and bcl-2 expression was performed in all cases. By using multiplex bead array assay, a simultaneous detection of HSP27 (pSer(82)), HSP27 (pSer(15)), HSP40, HSP60, HSP70, HSP90-α, Akt, and phospho-Akt was performed.

RESULTS

Medulloblastoma with extensive nodularity had significantly lower HSP27 (pSer(15)) expression (p = 0.039) but significantly higher HSP60 expression (p = 0.021) than classic MB. Large-cell MB had significantly higher HSP70 expression (p = 0.028) than classic MB. No significant difference was found between HSP27 (pSer(82)), HSP40, HSP90-α, Akt, or phospho-Akt expression and MB subtype. Large-cell MBs had significantly higher Ki-67 index compared with classic MBs (p = 0.033). When analyzing all MBs, there was a significant negative correlation between HSP27 (pSer(15)) and Ki-67 index (r = -0.475, p = 0.016); a significant positive correlation between HSP70 expression and Ki-67 index (r = 0.407, p = 0.043); and a significant positive correlation between HSP70 expression and bcl-2 index (r = 0.491, p = 0.023). Patients with large-cell MB had a worse survival than those with classic MB, but the difference did not reach statistical significance (p = 0.076).

CONCLUSIONS

A substantial expression of several HSPs in MB was observed. Given that HSPs represent an attractive strategy for anticancer therapy, further studies, involving larger series of patients, are obviously necessary to clarify the relationship of HSPs with tumor aggressiveness and prognosis.

Synthesis and anticancer mechanism investigation of dual Hsp27 and tubulin inhibitors

Heat shock protein 27 (Hsp27) is a chaperone protein, and its expression is increased in response to various stress stimuli including anticancer chemotherapy, which allows the cells to survive and causes drug resistance. We previously identified lead compounds that bound to Hsp27 and tubulin via proteomic approaches. Systematic ligand based optimization in the current study significantly increased the cell growth inhibition and apoptosis inducing activities of the compounds. Compared to the lead compounds, one of the new derivatives exhibited much better potency to inhibit tubulin polymerization but a decreased activity to inhibit Hsp27 chaperone function, suggesting that the structural modification dissected the dual targeting effects of the compound. The most potent compounds 20 and 22 exhibited strong cell proliferation inhibitory activities at subnanomolar concentration against 60 human cancer cell lines conducted by Developmental Therapeutic Program at the National Cancer Institute and represented promising candidates for anticancer drug development.

Cilastatin protects against cisplatin-induced nephrotoxicity without compromising its anticancer efficiency in rats

Cisplatin is an anticancer agent marred by nephrotoxicity; however, limiting this adverse effect may allow the use of higher doses to improve its efficacy. Cilastatin, a small molecule inhibitor of renal dehydropeptidase I, prevents proximal tubular cells from undergoing cisplatin-induced apoptosis in vitro. Here, we explored the in vivo relevance of these findings and the specificity of protection for kidney cells in cisplatin-treated rats. Cisplatin increased serum blood urea nitrogen and creatinine levels, and the fractional excretion of sodium. Cisplatin decreased the glomerular filtration rate, promoted histological renal injury and the expression of many pro-apoptotic proteins in the renal cortex, increased the Bax/Bcl2 ratio, and oxidative stress in kidney tissue and urine. All these features were decreased by cilastatin, which preserved renal function but did not modify the pharmacokinetics of cisplatin area under the curve. The cisplatin-induced death of cervical, colon, breast, and bladder-derived cancer cell lines was not prevented by cilastatin. Thus, cilastatin has the potential to prevent cisplatin nephrotoxicity without compromising its anticancer efficacy.

Heat shock proteins in hematopoietic malignancies

Inducible heat shock proteins are molecular chaperones whose expression is increased after many different types of stress. They have a protective function helping the cell to cope with lethal conditions. Their basal expression is low in nonstressed, normal and nontransformed cells. However, in cancer cells and particularly in hematological malignancies, they are surprisingly abundant. Malignant cells have to rewire their metabolic requirements and therefore have a higher need for chaperones. This cancer cell addiction for HSPs is the basis for the use of HSP inhibitors in cancer therapy. HSPs have been shown to interact with different key apoptotic proteins. As a result, HSPs can essentially block the apoptotic pathways at several steps, most of them involving the activation of cystein proteases called caspases. Apoptosis and differentiation are physiological processes that share many common features, for instance, a controlled caspase activation and chromatin condensation are frequently observed. It is, therefore, not surprising that HSPs may be implicated in the differentiation process. HSPs may determine the fate of the cells by orchestrating the decision of apoptosis versus differentiation. This review will focus on the role of HSPs in hematological malignancies and the emerging therapeutic options that are being either proposed or used to target these protective proteins.

Small heat shock proteins HSP27 (HspB1), αB-crystallin (HspB5) and HSP22 (HspB8) as regulators of cell death

Hsp27, αB-crystallin and HSP22 are ubiquitous small heat shock proteins (sHsp) whose expression is induced in response to a wide variety of unfavorable physiological and environmental conditions. These sHsp protect cells from otherwise lethal conditions mainly by their involvement in cell death pathways such as necrosis, apoptosis or autophagy. At a molecular level, the mechanisms accounting for sHsp functions in cell death are (1) prevention of denatured proteins aggregation, (2) regulation of caspase activity, (3) regulation of the intracellular redox state, (4) function in actin polymerization and cytoskeleton integrity and (5) proteasome-mediated degradation of selected proteins. In cancer cells, these sHsp are often overexpressed and associated with increased tumorigenicity, cancer cells metastatic potential and resistance to chemotherapy. Altogether, these properties suggest that Hsp27, αB-crystallin and Hsp22 are appropriate targets for modulating cell death pathways. In the present, we briefly review recent reports showing molecular evidence of cell death regulation by these sHsp and co-chaperones. This article is part of a Directed Issue entitled: Small HSPs in physiology and pathology.

The heat shock proteins as targets for radiosensitization and chemosensitization in cancer

The heat shock proteins (HSPs) represent a class of proteins which are induced under physiologic stress to promote cell survival in the face of endogenous or exogenous injury. HSPs function predominantly as molecular chaperones, maintaining their "client" proteins in the correct conformational state in order to withstand a biologic stressor. Elevated HSP expression is also found in a range of pathologic conditions, notably malignancy. Cancer cells exploit the pro-survival phenotype endowed by HSPs to bolster their proliferative potential. Consequently, developing means of abrogating HSP expression may provide a way to render cancer cells more susceptible to radiation or chemotherapy. Here, we review the members of the HSP class and their roles in malignancy. We focus on attempts to target these proteins, particularly the small HSPs, in developing potent radiation and chemotherapy sensitizers, as well as proposed mechanisms for this sensitization effect.

Roles of the N- and C-terminal sequences in Hsp27 self-association and chaperone activity

The small heat shock protein 27 (Hsp27 or HSPB1) is an oligomeric molecular chaperone in vitro that is associated with several neuromuscular, neurological, and neoplastic diseases. Although aspects of Hsp27 biology are increasingly well known, understanding of the structural basis for these involvements or of the functional properties of the protein remains limited. As all 11 human small heat shock proteins (sHsps) possess an α-crystallin domain, their varied functional and physiological characteristics must arise from contributions of their nonconserved sequences. To evaluate the role of two such sequences in Hsp27, we have studied three Hsp27 truncation variants to assess the functional contributions of the nonconserved N- and C-terminal sequences. The N-terminal variants Δ1-14 and Δ1-24 exhibit little chaperone activity, somewhat slower but temperature-dependent subunit exchange kinetics, and temperature-independent self-association with formation of smaller oligomers than wild-type Hsp27. The C-terminal truncation variants exhibit chaperone activity at 40 °C but none at 20 °C, limited subunit exchange, and temperature-independent self-association with an oligomer distribution at 40 °C that is very similar to that of wild-type Hsp27. We conclude that more of the N-terminal sequence than simply the WPDF domain is essential in the formation of larger, native-like oligomers after binding of substrate and/or in binding of Hsp27 to unfolding peptides. On the other hand, the intrinsically flexible C-terminal region drives subunit exchange and thermally-induced unfolding, both of which are essential to chaperone activity at low temperature and are linked to the temperature dependence of Hsp27 self-association.

OGX-427 inhibits tumor progression and enhances gemcitabine chemotherapy in pancreatic cancer

Despite many advances in oncology, almost all patients with pancreatic cancer (PC) die of the disease. Molecularly targeted agents are offering hope for their potential role in helping translate the improved activity of combination chemotherapy into improved survival. Heat shock protein 27 (Hsp27) is a chaperone implicated in several pathological processes such as cancer. Further, Hsp27 expression becomes highly upregulated in cancer cells after chemotherapy. Recently, a modified antisense oligonucleotide that is complementary to Hsp27 (OGX-427) has been developed, which inhibits Hsp27 expression and enhances drug efficacy in cancer xenograft models. Phase II clinical trials using OGX-427 in different cancers like breast, ovarian, bladder, prostate and lung are in progress in the United States and Canada. In this study, we demonstrate using TMA of 181 patients that Hsp27 expression and phosphorylation levels increase in moderately differentiated tumors to become uniformly highly expressed in metastatic samples. Using MiaPaCa-2 cells grown both in vitro and xenografted in mice, we demonstrate that OGX-427 inhibits proliferation, induces apoptosis and also enhances gemcitabine chemosensitivity via a mechanism involving the eukaryotic translation initiation factor 4E. Collectively, these findings suggest that the combination of Hsp27 knockdown with OGX-427 and chemotherapeutic agents such as gemcitabine can be a novel strategy to inhibit the progression of pancreas cancer.

Alteration of protein folding and degradation in motor neuron diseases: Implications and protective functions of small heat shock proteins

Motor neuron diseases (MNDs) are neurodegenerative disorders that specifically affect the survival and function of upper and/or lower motor neurons. Since motor neurons are responsible for the control of voluntary muscular movement, MNDs are characterized by muscle spasticity, weakness and atrophy. Different susceptibility genes associated with an increased risk to develop MNDs have been reported and several mutated genes have been linked to hereditary forms of MNDs. However, most cases of MNDs occur in sporadic forms and very little is known on their causes. Interestingly, several molecular mechanisms seem to participate in the progression of both the inherited and sporadic forms of MNDs. These include cytoskeleton organization, mitochondrial functions, DNA repair and RNA synthesis/processing, vesicle trafficking, endolysosomal trafficking and fusion, as well as protein folding and protein degradation. In particular, accumulation of aggregate-prone proteins is a hallmark of MNDs, suggesting that the protein quality control system (molecular chaperones and the degradative systems: ubiquitin-proteasome-system and autophagy) are saturated or not sufficient to allow the clearance of these altered proteins. In this review we mainly focus on the MNDs associated with disturbances in protein folding and protein degradation and on the potential implication of a specific class of molecular chaperones, the small heat shock proteins (sHSPs/HSPBs), in motor neuron function and survival. How boosting of specific HSPBs may be a potential useful therapeutic approach in MNDs and how mutations in specific HSPBs can directly cause motor neuron degeneration is discussed.

Hsp-27 induction requires POU4F2/Brn-3b TF in doxorubicin-treated breast cancer cells, whereas phosphorylation alters its cellular localisation following drug treatment

POU4F2/Brn-3b transcription factor (referred to as Brn-3b) is elevated in >60% of breast cancers and profoundly alters growth and behaviour of cancer cells by regulating distinct subsets of target genes. Previous studies showed that Brn-3b was required to maximally transactivate small heat shock protein, HSPB1/Hsp-27 (referred to as Hsp-27), and consequently, Brn-3b expression correlated well with Hsp27 levels in human breast biopsies. In these studies, we showed that Brn-3b is increased in MCF7 breast cancer cells that survive following treatment with chemotherapeutic drug doxorubicin (Dox) with concomitant increases in Hsp-27 expression. Targeting of Brn-3b using short interfering RNA reduced Hsp-27 in Dox-treated cells, suggesting that Brn-3b regulates Hsp-27 expression under these conditions. Wound healing assays showed increased Brn-3b in Dox-treated migratory cells that also express Hsp-27. Interestingly, Hsp-27 phosphorylation and cellular localisation are also significantly altered at different times following Dox treatment. Thus, phospho-Hsp-27 (p-Hsp27) protein displayed widespread distribution after 24 hrs of Dox treatment but was restricted to the nucleus after 5 days. However, in drug-resistant cells (grown in Dox for > 1 month), p-Hsp-27 was excluded from nuclei and most of the cytoplasm and appeared to be associated with the cell membrane. Studies to determine how this protein promotes survival and migration in breast cancer cells showed that the protective effects were conferred by unphosphorylated Hsp-27 protein. Thus, complex and dynamic mechanisms underlie effects of Hsp-27 protein in breast cancer cells following treatment with chemotherapeutic drugs such as Dox, and this may contribute to invasiveness and drug resistance following chemotherapy.

High-mobility group box 1 is essential for mitochondrial quality control

Mitochondria are organelles centrally important for bioenergetics as well as regulation of apoptotic death in eukaryotic cells. High-mobility group box 1 (HMGB1), an evolutionarily conserved chromatin-associated protein which maintains nuclear homeostasis, is also a critical regulator of mitochondrial function and morphology. We show that heat shock protein beta-1 (HSPB1 or HSP27) is the downstream mediator of this effect. Disruption of the HSPB1 gene in embryonic fibroblasts with wild-type HMGB1 recapitulates the mitochondrial fragmentation, deficits in mitochondrial respiration, and adenosine triphosphate (ATP) synthesis observed with targeted deletion of HMGB1. Forced expression of HSPB1 reverses this phenotype in HMGB1 knockout cells. Mitochondrial effects mediated by HMGB1 regulation of HSPB1 expression serve as a defense against mitochondrial abnormality, enabling clearance and autophagy in the setting of cellular stress. Our findings reveal an essential role for HMGB1 in autophagic surveillance with important effects on mitochondrial quality control.

Heat shock proteins in oncology: diagnostic biomarkers or therapeutic targets?

Heat shock proteins (HSP) are a family of proteins induced in cells exposed to different insults. This induction of HSPs allows cells to survive stress conditions. Mammalian HSPs have been classified into six families according to their molecular size: HSP100, HSP90, HSP70, HSP60, HSP40 and small HSPs (15 to 30kDa) including HSP27. These proteins act as molecular chaperones either helping in the refolding of misfolded proteins or assisting in their elimination if they become irreversibly damaged. In recent years, proteomic studies have characterized several different HSPs in various tumor types which may be putative clinical biomarkers or molecular targets for cancer therapy. This has led to the development of a series of molecules capable of inhibiting HSPs. Numerous studies speculated that over-expression of HSP is in part responsible for resistance to many anti-tumor agents and chemotherapeutics. Hence, from a pharmacological point of view, the co-administration of HSP inhibitors together with other anti-tumor agents is of major importance in overcoming therapeutic resistance. In this review, we provide an overview of the current status of HSPs in autoimmune, cardiovascular, and neurodegenerative diseases with special emphasis on cancer.

Structure-functions of HspB1 (Hsp27)

Human HspB1 (also denoted Hsp27) is a well-known member, together with alphaB-crystallin, of the small heat-shock (or stress) proteins (sHsps) (20-40 kDa). In this chapter, I describe procedures for testing the oligomeric and phosphorylation patterns of HspB1 as well as its interaction with specific partner/client polypeptides using tissue culture cells genetically modified to express different levels of this protein. The procedures have been developed in my laboratory and could be used in any well-established cellular laboratory. In addition, the different procedures presented here could be extended to test the nine other human sHsp members as well as sHsps from other species.

Immunocompetent cells and cytokine expression in the rat periodontal ligament at the initial stage of orthodontic tooth movement

OBJECTIVE

The aim of the present study is to investigate the involvement of immunocompetent cells, pro-inflammatory cytokines and HSP, to evaluate a change of periodontal ligament during the initial stage of orthodontic tooth movement.

DESIGN

In the present study, we investigated the distributional density of immunocompetent cells, the localisation of cytokines, and the expression levels of their mRNA in the periodontal ligament during the initial stage of orthodontic tooth movement, using immunohistochemistry and real-time PCR.

RESULTS

Orthodontic tooth movement led to significant recruitment of OX6(+) cells and ED1(+) cells in the rat PDL. Double-immunofluorescence staining showed that some ED1(+) cells expressed pro-inflammatory factors of IL-1β and TNF-α in the PDL during orthodontic tooth movement. Real-time PCR analysis revealed that the expression levels of IL-1β (Il1b) and TNF-α (Tnf) mRNA gradually increased following its decrease after 1h of orthodontic tooth movement. These findings suggest that ED1(+) cells are involved in the expression of TNF-α and IL-1β and the subsequent regulation of bone resorption on pressure side. HSP27 (Hspb1) mRNA levels were significantly increased as compared with the control at 1h of the initial stage of treatment.

CONCLUSION

ED1(+) cells involved in the expression of TNF-α and IL-1β may play an important role in the initial reaction of the PDL and in the induction of the osteoclastic bone resorption during orthodontic tooth movement.

Hsp27 protects adenocarcinoma cells from UV-induced apoptosis by Akt and p21-dependent pathways of survival

Transcriptional activation of p53 target genes, due to DNA damage, causes either apoptosis or survival by cell cycle arrest and DNA repair. However, the regulators of the choice between cell death and survival signaling have not been completely elucidated. Here, we report that human adenocarcinoma cells (MCF-7) survive UV-induced DNA damage by heat shock protein 27 (Hsp27)-assisted Akt/p21 phosphorylation/translocation. Protein levels of the p53 target genes, such as p21, Bcl-2, p38MAPK, and Akt, showed a positive correlation to Hsp27 level during 48 hours postirradiation, whereas p53 expression increased initially but started decreasing after 12 hours. Hsp27 prevented the G(1)-S phase cell cycle arrest, observed after 8 hours of post-UV irradiation, and PARP-1 cleavage was inhibited. Conversely, silencing Hsp27 enhanced G(1)-S arrest and cell death. Moreover, use of either Hsp27 or Akt small interference RNA reduced p21 phosphorylation and enhanced its retention in nuclei even after 48 hours postirradiation, resulting in enhanced cell death. Our results showed that Hsp27 expression and its direct chaperoning interaction increases Akt stability, and p21 phosphorylation and nuclear-to-cytoplasm translocation, both essential effects for the survival of UV-induced DNA-damaged cells. We conclude that the role of Hsp27 in cancer is not only for enhanced p53 proteolysis per se, rather it is also a critical determinant in p21 phosphorylation and translocation.

Apigenin-induced apoptosis of leukemia cells is mediated by a bimodal and differentially regulated residue-specific phosphorylation of heat-shock protein-27

Apigenin, a natural plant flavonoid with antiproliferative activity, is emerging as a promising compound for cancer prevention and therapy, but its mechanism of action remains unclear. High expression of the small heat-shock protein-27 (Hsp27) in leukemia contributes to the resistance of these cells to cancer treatments. Changes in Hsp27 phosphorylation have been associated with heat and metabolic stress, but its role in flavonoid anticancer activity has not been investigated. In this study, we examined the effect of apigenin in the regulation of Hsp27 on leukemia. We showed that apigenin does not affect Hsp27 expression but induces a bimodal phosphorylation on Ser78 and Ser82. The phosphorylation at early times was regulated by p38. At later times, Hsp27 phosphorylation was dependent on p38 activity and for some residues on PKCδ. Silencing of p38 expression reduced apigenin-induced phosphorylation on Ser15, Ser78, and Ser82, whereas silencing of PKCδ expression reduced the phosphorylation on Ser15 and Ser82 without affecting Ser78. In addition, we found that apigenin-induced PKCδ activity is mediated by p38. We also showed that the phosphorylation of Hsp27 significantly increased the susceptibility of leukemia cells to apigenin-induced apoptosis. Together, these results identify a complex signaling network regulating the cytotoxic effect of apigenin through Hsp27 phosphorylation.

Examination of association with candidate genes for diabetic nephropathy in a Mexican American population

BACKGROUND AND OBJECTIVES

Diabetic nephropathy (DN) is a multifactorial complication characterized by persistent proteinuria in susceptible individuals with type 1 and type 2 diabetes. Disease burden in people of Mexican-American descent is particularly high, but there are only a few studies that characterize genes for DN in this ethnic group. Two genes, carnosine dipeptidase 1 (CNDP1) and engulfment and cell motility 1 (ELMO1) previously showed association with DN in other ethnic groups. CNDP1 and ELMO1 were examined along with eight other genes that are less well characterized for DN in a new study of Mexican-Americans.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

The target sample was patients of Mexican-American ancestry collected from three centers: 455 patients with DN and 437 controls with long-term diabetes but no incident nephropathy. Forty-two, 227, and 401 single nucleotide polymorphisms (SNPs) in CNDP1, ELMO1, and the other eight genes, respectively, were examined.

RESULTS

No region in CNDP1 or ELMO1 showed significant P values. Of the other eight candidate genes, an association of DN with a SNP pair, rs2146098 and rs6659783, was found in hemicentin 1 (HMCN1) (unadjusted P = 6.1 x 10(-5)). Association with a rare haplotype in this region was subsequently identified.

CONCLUSIONS

The associations in CNDP1 or ELMO1 were not replicable; however, an association of DN with HMCN1 was found. Additional work at this and other loci will enable refinement of the genetic hypotheses regarding DN in the Mexican-American population to find therapies for this debilitating disease.

Dynamic processes that reflect anti-apoptotic strategies set up by HspB1 (Hsp27)

Human HspB1 (also denoted Hsp27) is an oligomeric anti-apoptotic protein that has tumorigenic and metastatic roles. To approach the structural organizations of HspB1 that are active in response to apoptosis inducers acting through different pathways, we have analyzed the relative protective efficiency induced by this protein as well its localization, oligomerization and phosphorylation. HeLa cells, that constitutively express high levels of HspB1 were treated with either etoposide, Fas agonist antibody, staurosporine or cytochalasin D. Variability in HspB1 efficiency to interfere with the different apoptotic transduction pathways induced by these agents were detected. Moreover, inducer-specific dynamic changes in HspB1 localization, native size and phosphorylation were observed, that differed from those observed after heat shock. Etoposide and Fas treatments gradually shifted HspB1 towards large but differently phosphorylated oligomeric structures. In contrast, staurosporine and cytochalasin D induced the rapid but transient formation of small oligomers before large structures were formed. These events correlated with inducer-specific phosphorylations of HspB1. Of interest, the formation of small oligomers in response to staurosporine and cytochalasin D was time correlated with the rapid disruption of F-actin. The subsequent, or gradual in the case of etoposide and Fas, formation of large oligomeric structures was a later event concomitant with the early phase of caspase activation. These observations support the hypothesis that HspB1 has the ability, through specific changes in its structural organization, to adapt and interfere at several levels with challenges triggered by different signal transduction pathways upstream of the execution phase of apoptosis.

Cellular stress responses: cell survival and cell death

Cells can respond to stress in various ways ranging from the activation of survival pathways to the initiation of cell death that eventually eliminates damaged cells. Whether cells mount a protective or destructive stress response depends to a large extent on the nature and duration of the stress as well as the cell type. Also, there is often the interplay between these responses that ultimately determines the fate of the stressed cell. The mechanism by which a cell dies (i.e., apoptosis, necrosis, pyroptosis, or autophagic cell death) depends on various exogenous factors as well as the cell's ability to handle the stress to which it is exposed. The implications of cellular stress responses to human physiology and diseases are manifold and will be discussed in this review in the context of some major world health issues such as diabetes, Parkinson's disease, myocardial infarction, and cancer.