Cytokines direct the regulation of Bim mRNA stability by heat-shock cognate protein 70

Corelating the molecular structure of BAG3 to its oncogenic role

BAG3 is a multifaceted protein characterised by having WW domain, PXXP motif and BAG domain. This protein gets upregulated during malignant transformation of cells and has been associated with poorer survival of patients. Procancerous activity of BAG domain of BAG3 is well documented. BAG domain interacts with ATPase domain of Hsp-70 preventing protein delivery to proteasome. This impediment results in enhanced cell survival, proliferation, resistance to apoptosis and chemoresistance. Besides BAG domain other two domains/motifs of BAG3 are under research vigilance to explore its further oncogenic role. This review summarises the role of different structural determinants of BAG3 in elevating oncogenesis. Based on the already existing findings, more interacting partners of BAG3 are anticipated. The anticipated partners of BAG3 can shed a wealth of information into the mechanistic insights of its proproliferative role. Proper insights into the mechanistic details adopted by BAG3 to curtail/elaborate activity of anticipated interacting partners can serve as a potent target for development of therapeutic interventions.

HSPA8 regulates anti-bacterial autophagy through liquid-liquid phase separation

HSPA8 (heat shock protein family A (Hsp70) member 8) plays a significant role in the autophagic degradation of proteins, however, its effect on protein stabilization and anti-bacterial autophagy remains unknown. Here, it is discovered that HSPA8, as a binding partner of RHOB and BECN1, induce autophagy for intracellular bacteria clearance. Using its NBD and LID domains, HSPA8 physically binds to RHOB residues 1-42 and 89-118 as well as to BECN1 ECD domain, preventing RHOB and BECN1 degradation. Intriguingly, HSPA8 contains predicted intrinsically disordered regions (IDRs), and drives liquid-liquid phase separation (LLPS) to concentrate RHOB and BECN1 into HSPA8-formed liquid-phase droplets, resulting in improved RHOB and BECN1 interactions. Our study reveals a novel role and mechanism of HSPA8 in modulating anti-bacterial autophagy, and highlights the effect of LLPS-related HSPA8-RHOB-BECN1 complex on enhancing protein interaction and stabilization, which improves the understanding of autophagy-mediated defense against bacteria.

A Workflow Guide to RNA-Seq Analysis of Chaperone Function and Beyond

RNA sequencing (RNA-seq) is a powerful method of transcriptional analysis that allows for the sequence identification and quantification of cellular transcripts. RNA-seq can be used for differential gene expression (DGE) analysis, gene fusion detection, allele-specific expression, isoform and splice variant quantification, and identification of novel genes. These applications can be used for downstream systems biology analyses such as gene ontology or pathway analysis to provide insight into processes altered between biological conditions. Given the wide range of signaling pathways subject to chaperone activity as well as numerous chaperone functions in RNA metabolism, RNA-seq may provide a valuable tool for the study of chaperone proteins in biology and disease. This chapter outlines an example RNA-seq workflow to determine differentially expressed (DE) genes between two or more sample conditions and provides some considerations for RNA-seq experimental design.

Merkel cell polyomavirus T-antigens regulate DICER1 mRNA stability and translation through HSC70

Merkel cell carcinoma is an aggressive skin malignancy, mostly caused by Merkel cell polyomavirus (MCPyV). MCPyV T-antigens can induce mature microRNA expressions through the DnaJ domain, but its underlying mechanism is still unknown. Here, we report that the T-antigens induce protein expression and mRNA stability of DICER1, a key factor in microRNA biogenesis, through heat shock cognate 70 (HSC70). HSC70 directly interacts with the AU-rich elements (ARE) of DICER1 mRNA in both coding and 3′ untranslated region in the presence of MCPyV T-antigen. The T-antigen/HSC70 interaction could induce luciferase activity of synthetic ARE-containing reporter, as well as the stability of ARE-containing mRNAs, suggesting a broader role of MCPyV T-antigens in regulating multiple mRNAs via HSC70. These findings highlight a new role for the interaction of HSC70 and MCPyV T-antigens in mRNA regulation and an undescribed regulatory mechanism of DICER1 mRNA stability and translation through its direct interaction with HSC70.

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MCPyV T-antigen and HSC70 interaction regulates DICER1 expression

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HSC70 directly binds to ARE in the 3′UTR of DICER1 for expression regulation

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An unknown motif in DICER1 CDS is also required for its expression regulation by LT

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The LT-HSC70 interaction can regulate other ARE-containing mRNAs

Quantitative LC-MS/MS uncovers the regulatory role of autophagy in immune thrombocytopenia

BACKGROUND

Immune thrombocytopenia (ITP) is an autoimmune haemorrhagic disease whose pathogenesis is associated with bone marrow megakaryocyte maturation disorder and destruction of the haematopoietic stem cell microenvironment.

METHODS

In this study, we report the qualitative and quantitative profiles of the ITP proteome. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) was conducted to elucidate the protein profiles of clinical bone marrow mononuclear cell (BMMC) samples from ITP patients and healthy donors (controls). Gene Ontology (GO) and Kyoto Encyclopaedia Genes and Genome (KEGG) pathway analyses were performed to annotate the differentially expressed proteins. A protein-protein interaction (PPI) network was constructed with the BLAST online database. Target proteins associated with autophagy were quantitatively identified by parallel reaction monitoring (PRM) analysis.

RESULTS

Our approaches showed that the differentially expressed autophagy-related proteins, namely, HSPA8, PARK7, YWHAH, ITGB3 and CSF1R, were changed the most. The protein expression of CSF1R in ITP patients was higher than that in controls, while other autophagy-related proteins were expressed at lower levels in ITP patients than in controls.

CONCLUSION

Bioinformatics analysis indicated that disruption of the autophagy pathway is a potential pathological mechanism of ITP. These results can provide a new direction for exploring the molecular mechanism of ITP.

In Silico Analysis of HSP70 Gene Family in Bovine Genome

Heat shock proteins (HSPs), members of molecular chaperones families fulfill essential roles under normal conditions and provide protection and adaptation during and after stress. Among different HSPs, HSP70 kDa family of proteins is most abundant and well-studied in human and mouse but has not yet been characterized in bovines. In silico analysis was performed to characterize members of HSP70 gene family in bovine genome and a total of 17 genes of bovine HSP70 gene family were identified. The members of HSP70 family were distributed over 12 chromosomes with gene size ranging from 1911 (HSPA2) to 54,017 bp (HSPA4). Five genes were intronless, while rest of 12 genes were multiexonic. Phylogenetic analysis of HSP70 gene family distinguished them into eight major evolutionary groups wherein members of group 1 were most divergent and quite dissimilar than from rest of the HSP70 sequences. Domain structure of all bovine HSP70 genes was conserved and three signature patterns HSP70_1, HSP70_2, and HSP70_3 were identified. HSPA8, HSP9, and HSPA1A showed comparatively higher expression in majority of tissues. Like humans, bovine HSP70 family was characterized by remarkable evolutionary diversity. The analysis also suggested resemblance of bovine HSP70 family to that of human compared to mouse. Overall, the study indicates the presence of diversity for structure, function, localization, and expression in the bovine HSP70 family chaperons which could form the basis to understand thermotolerance/adaptive changes in the bovines.

Quiescence Entry, Maintenance, and Exit in Adult Stem Cells

Cells of unicellular and multicellular eukaryotes can respond to certain environmental cues by arresting the cell cycle and entering a reversible state of quiescence. Quiescent cells do not divide, but can re-enter the cell cycle and resume proliferation if exposed to some signals from the environment. Quiescent cells in mammals and humans include adult stem cells. These cells exhibit improved stress resistance and enhanced survival ability. In response to certain extrinsic signals, adult stem cells can self-renew by dividing asymmetrically. Such asymmetric divisions not only allow the maintenance of a population of quiescent cells, but also yield daughter progenitor cells. A multistep process of the controlled proliferation of these progenitor cells leads to the formation of one or more types of fully differentiated cells. An age-related decline in the ability of adult stem cells to balance quiescence maintenance and regulated proliferation has been implicated in many aging-associated diseases. In this review, we describe many traits shared by different types of quiescent adult stem cells. We discuss how these traits contribute to the quiescence, self-renewal, and proliferation of adult stem cells. We examine the cell-intrinsic mechanisms that allow establishing and sustaining the characteristic traits of adult stem cells, thereby regulating quiescence entry, maintenance, and exit.

Melatonin Promotes Ubiquitination of Phosphorylated Pro-Apoptotic Protein Bcl-2-Interacting Mediator of Cell Death-Extra Long (BimEL) in Porcine Granulosa Cells

Melatonin (N-acetyl-5-methoxytryptamine) is found in ovarian follicular fluid, and its concentration is closely related to follicular health status. Nevertheless, the molecular mechanisms underlying melatonin function in follicles are uncertain. In this study, melatonin concentration was measured in porcine follicular fluid at different stages of health. The melatonin concentration decreased as the follicles underwent atresia, suggesting that melatonin may participate in the maintenance of follicular health. The molecular pathway through which melatonin may regulate follicular development was further investigated. The pro-apoptotic protein Bim_EL (Bcl-2-interacting mediator of cell death-Extra Long), a key protein controlling granulosa cell apoptosis during follicular atresia, was selected as the target molecule. Bim_EL was downregulated when porcine granulosa cells were cultured in medium containing 10⁻⁹ M melatonin and isolated cumulus oocyte complexes (COCs) or follicle stimulating hormone (FSH). Interestingly, ERK-mediated phosphorylation was a prerequisite for the melatonin-induced decline in Bim_EL, and melatonin only promoted the ubiquitination of phosphorylated Bim_EL, and did not affect the activities of the lysosome or the proteasome. Moreover, the melatonin-induced downregulation of Bim_EL was independent of its receptor and its antioxidant properties. In conclusion, melatonin may maintain follicular health by inducing Bim_EL ubiquitination to inhibit the apoptosis of granulosa cells.

Epithelial Keratins Modulate cMet Expression and Signaling and Promote InlB-Mediated Listeria monocytogenes Infection of HeLa Cells

The host cytoskeleton is a major target for bacterial pathogens during infection. In particular, pathogens usurp the actin cytoskeleton function to strongly adhere to the host cell surface, to induce plasma membrane remodeling allowing invasion and to spread from cell to cell and disseminate to the whole organism. Keratins are cytoskeletal proteins that are the major components of intermediate filaments in epithelial cells however, their role in bacterial infection has been disregarded. Here we investigate the role of the major epithelial keratins, keratins 8 and 18 (K8 and K18), in the cellular infection by Listeria monocytogenes. We found that K8 and K18 are required for successful InlB/cMet-dependent L. monocytogenes infection, but are dispensable for InlA/E-cadherin-mediated invasion. Both K8 and K18 accumulate at InlB-mediated internalization sites following actin recruitment and modulate actin dynamics at those sites. We also reveal the key role of K8 and K18 in HGF-induced signaling which occurs downstream the activation of cMet. Strikingly, we show here that K18, and at a less extent K8, controls the expression of cMet and other surface receptors such TfR and integrin β1, by promoting the stability of their corresponding transcripts. Together, our results reveal novel functions for major epithelial keratins in the modulation of actin dynamics at the bacterial entry sites and in the control of surface receptors mRNA stability and expression.

Rabies viruses leader RNA interacts with host Hsc70 and inhibits virus replication

Viruses have been shown to be equipped with regulatory RNAs to evade host defense system. It has long been known that rabies virus (RABV) transcribes a small regulatory RNA, leader RNA (leRNA), which mediates the transition from viral RNA transcription to replication. However, the detailed molecular mechanism remains enigmatic. In the present study, we determined the genetic architecture of RABV leRNA and demonstrated its inhibitory effect on replication of wild-type rabies, DRV-AH08. The RNA immunoprecipitation results suggest that leRNA inhibits RABV replication via interfering the binding of RABV nucleoprotein with genomic RNA. Furthermore, we identified heat shock cognate 70 kDa protein (Hsc70) as a leRNA host cellular interacting protein, of which the expression level was dynamically regulated by RABV infection. Notably, our data suggest that Hsc70 was involved in suppressing RABV replication by leader RNA. Finally, our experiments imply that leRNA might be potentially useful as a novel drug in rabies post-exposure prophylaxis. Together, this study suggested leRNA in concert with its host interacting protein Hsc70, dynamically down-regulate RABV replication.

A Workflow Guide to RNA-seq Analysis of Chaperone Function and Beyond

RNA sequencing (RNA-seq) is a powerful method of transcript analysis that allows for the sequence identification and quantification of cellular transcripts. RNA-seq has many applications including differential gene expression (DE) analysis, gene fusion detection, allele-specific expression, isoform and splice variant quantification, and identification of novel genes. These applications can be used for downstream systems biology analyses such as gene ontology analysis to provide insights into cellular processes altered between biological conditions. Given the wide range of signaling pathways subject to chaperone activity as well as numerous chaperone functions in RNA metabolism, RNA-seq may provide a valuable tool for the study of chaperone proteins in biology and disease. This chapter outlines an example RNA-seq workflow to determine differentially expressed (DE) genes between two or more sample conditions and provides some considerations for RNA-seq experimental design.

HSPB1 facilitates ERK-mediated phosphorylation and degradation of BIM to attenuate endoplasmic reticulum stress-induced apoptosis

BIM, a pro-apoptotic BH3-only protein, is a key regulator of the intrinsic (or mitochondrial) apoptosis pathway. Here, we show that BIM induction by endoplasmic reticulum (ER) stress is suppressed in rat PC12 cells overexpressing heat shock protein B1 (HSPB1 or HSP27) and that this is due to enhanced proteasomal degradation of BIM. HSPB1 and BIM form a complex that immunoprecipitates with p-ERK1/2. We found that HSPB1-mediated proteasomal degradation of BIM is dependent on MEK-ERK signaling. Other studies have shown that several missense mutations in HSPB1 cause the peripheral neuropathy, Charcot-Marie-Tooth (CMT) disease, which is associated with nerve degeneration. Here we show that cells overexpressing CMT-related HSPB1 mutants exhibited increased susceptibility to ER stress-induced cell death and high levels of BIM. These findings identify a novel function for HSPB1 as a negative regulator of BIM protein stability leading to protection against ER stress-induced apoptosis, a function that is absent in CMT-associated HSPB1 mutants.

Tylophorine Analogs Allosterically Regulates Heat Shock Cognate Protein 70 And Inhibits Hepatitis C Virus Replication

Tylophorine analogs have been shown to exhibit diverse activities against cancer, inflammation, arthritis, and lupus in vivo. In this study, we demonstrated that two tylophorine analogs, DCB-3503 and rac-cryptopleurine, exhibit potent inhibitory activity against hepatitis C virus (HCV) replication in genotype 1b Con 1 isolate. The inhibition of HCV replication is at least partially mediated through cellular heat shock cognate protein 70 (Hsc70). Hsc70 associates with the HCV replication complex by primarily binding to the poly U/UC motifs in HCV RNA. The interaction of DCB-3503 and rac-cryptopleurine with Hsc70 promotes the ATP hydrolysis activity of Hsc70 in the presence of the 3' poly U/UC motif of HCV RNA. Regulating the ATPase activity of Hsc70 may be one of the mechanisms by which tylophorine analogs inhibit HCV replication. This study demonstrates the novel anti-HCV activity of tylophorine analogs. Our results also highlight the importance of Hsc70 in HCV replication.

Bim gene dosage is critical in modulating nephron progenitor survival in the absence of microRNAs during kidney development

Low nephron endowment at birth has been associated with an increased risk for developing hypertension and chronic kidney disease. We demonstrated in an earlier study that conditional deletion of the microRNA (miRNA)-processing enzyme Dicer from nephron progenitors results in premature depletion of the progenitors and increased expression of the proapoptotic protein Bim (also known as Bcl-2L11). In this study, we generated a compound mouse model with conditional deletion of both Dicer and Bim, to determine the biologic significance of increased Bim expression in Dicer-deficient nephron progenitors. The loss of Bim partially restored the number of nephron progenitors and improved nephron formation. The number of progenitors undergoing apoptosis was significantly reduced in kidneys with loss of a single allele, or both alleles, of Bim compared to mutant kidneys. Furthermore, 2 miRNAs expressed in nephron progenitors (miR-17 and miR-106b) regulated Bim levels in vitro and in vivo Together, these data suggest that miRNA-mediated regulation of Bim controls nephron progenitor survival during nephrogenesis, as one potential means of regulating nephron endowment.-Cerqueira, D. M., Bodnar, A. J., Phua, Y. L., Freer, R., Hemker, S. L., Walensky, L. D., Hukriede, N. A., Ho, J. Bim gene dosage is critical in modulating nephron progenitor survival in the absence of microRNAs during kidney development.

A small stem-loop structure of the Ebola virus trailer is essential for replication and interacts with heat-shock protein A8

Ebola virus (EBOV) is a single-stranded negative-sense RNA virus belonging to the Filoviridae family. The leader and trailer non-coding regions of the EBOV genome likely regulate its transcription, replication, and progeny genome packaging. We investigated the cis-acting RNA signals involved in RNA–RNA and RNA–protein interactions that regulate replication of eGFP-encoding EBOV minigenomic RNA and identified heat shock cognate protein family A (HSC70) member 8 (HSPA8) as an EBOV trailer-interacting host protein. Mutational analysis of the trailer HSPA8 binding motif revealed that this interaction is essential for EBOV minigenome replication. Selective 2′-hydroxyl acylation analyzed by primer extension analysis of the secondary structure of the EBOV minigenomic RNA indicates formation of a small stem-loop composed of the HSPA8 motif, a 3′ stem-loop (nucleotides 1868–1890) that is similar to a previously identified structure in the replicative intermediate (RI) RNA and a panhandle domain involving a trailer-to-leader interaction. Results of minigenome assays and an EBOV reverse genetic system rescue support a role for both the panhandle domain and HSPA8 motif 1 in virus replication.

Tylophorine Analog DCB-3503 Inhibited Cyclin D1 Translation through Allosteric Regulation of Heat Shock Cognate Protein 70

Tylophorine analog DCB-3503 is a potential anticancer and immunosuppressive agent that suppresses the translation of cellular regulatory proteins, including cyclin D1, at the elongation step. However, the molecular mechanism underlying this phenomenon remains unknown. This study demonstrates that DCB-3503 preferentially binds to heat shock cognate protein 70 (HSC70), which is a determinant for cyclin D1 translation by binding to the 3′-untranslated region (3′ UTR) of its mRNA. DCB-3503 allosterically regulates the ATPase and chaperone activities of HSC70 by promoting ATP hydrolysis in the presence of specific RNA binding motifs (AUUUA) of cyclin D1 mRNA. The suppression of cyclin D1 translation by DCB-3503 is not solely caused by perturbation of the homeostasis of microRNAs, although the microRNA processing complex is dissociated with DCB-3503 treatment. This study highlights a novel regulatory mechanism of protein translation with AUUUA motifs in the 3′ UTR of mRNA by HSC70, and its activity can be allosterically modulated by DCB-3503. DCB-3503 may be used to treat malignancies, such as hepatocellular carcinoma or breast cancer with elevated expression of cyclin D1.

Transcriptional regulation of the IL-7Rα gene by dexamethasone and IL-7 in primary human CD8 T cells

Interleukin-7 is essential for the development and maintenance of T cells, and the expression of the IL-7 receptor is tightly regulated at every stage of the T cell's lifespan. In mature CD8 T cells, IL-7 plays important roles in cell survival, peripheral homeostasis, and cytolytic function. The IL-7 receptor alpha-chain (CD127) is expressed at high levels on naïve and memory cells, but it is rapidly downregulated upon IL-7 stimulation. In this study, we illustrate the dynamicity of the CD127 promoter and show that it possesses positive as well as negative regulatory sites involved in upregulating and downregulating CD127 expression, respectively. We cloned the CD127 gene promoter and identified key cis-regulatory elements required for CD127 expression in mature resting primary CD8 T cells. The core promoter necessary for efficient basal transcription is contained within the first 262 bp upstream of the TATA box. Additional positive regulatory elements are located between -1200 and -2406 bp, conferring a further 2- to 4-fold enhancement in gene expression. While transcription of the CD127 gene is increased directly through a glucocorticoid response element located between -2255 and -2269 bp upstream of the TATA box, we identified a suppressive region that lies upstream of 1760 bp from the TATA box, which is likely involved in the IL-7-mediated suppression of CD127 transcription. Finally, we illustrated IL-7 does not bias alternative splicing of CD127 transcripts in primary human CD8 T cells.

Induction of apoptosis by HBI-8000 in adult T-cell leukemia/lymphoma is associated with activation of Bim and NLRP3

Adult T‐cell leukemia/lymphoma (ATL) is an aggressive T‐cell malignancy caused by human T‐cell lymphotropic virus 1. Treatment options for acute ATL patients include chemotherapy, stem cell transplantation, and recently the anti‐chemokine (C‐C motif) receptor 4 antibody, although most patients still have a poor prognosis and there is a clear need for additional options. HBI‐8000 is a novel oral histone deacetylase inhibitor with proven efficacy for treatment of T‐cell lymphomas that recently received approval in China. In the present study, we evaluated the effects of HBI‐8000 on ATL‐derived cell lines and primary cells obtained from Japanese ATL patients. In most cases HBI‐8000 induced apoptosis in both primary ATL cells and cell lines. In addition, findings obtained with DNA microarray suggested Bim activation and, interestingly, the contribution of the NLR family, pyrin domain containing 3 (NLRP3) inflammasome pathway in HBI‐8000‐induced ATL cell death. Further investigations using siRNAs confirmed that Bim contributes to HBI‐8000‐induced apoptosis. Our results provide a rationale for a clinical investigation of the efficacy of HBI‐8000 in patients with ATL. Although the role of NLRP3 inflammasome activation in ATL cell death remains to be verified, HBI‐8000 may be part of a novel therapeutic strategy for cancer based on the NLRP3 pathway.

Coupling of Ribostasis and Proteostasis: Hsp70 Proteins in mRNA Metabolism

A key aspect of the control of gene expression is the differential rates of mRNA translation and degradation, including alterations due to extracellular inputs. Surprisingly, multiple examples now argue that Hsp70 protein chaperones and their associated Hsp40 partners modulate both mRNA degradation and translation. Hsp70 proteins affect mRNA metabolism by various mechanisms including regulating nascent polypeptide chain folding, activating signal transduction pathways, promoting clearance of stress granules, and controlling mRNA degradation in an mRNA-specific manner. Taken together, these observations highlight the general principle that mRNA metabolism is coupled to the proteostatic state of the cell, often as assessed by the presence of unfolded or misfolded proteins.

Polymeric Gene Carriers Bearing Pendant β-Cyclodextrin: The Relevance of Glycoside Permethylation on the "In Vitro" Cell Response

The incorporation of cyclodextrins (CDs) to nonviral cationic polymer vectors is very attractive due to recent studies that report a clear improvement of their cytocompatibility and transfection efficiency. However, a systematic study on the influence of the CD derivatization is still lacking. In this work, the relevance of β-CD permethylation has been addressed by preparing and evaluating two series of copolymers of the cationic N-ethyl pyrrolidine methacrylamide (EPA) and styrenic units bearing pendant hydroxylated and permethylated β-CDs (HCDSt and MeCDSt, respectively). For both cell lines, CDs permethylation shows a strong influence on plasmid DNA complexation, "in vitro" cytocompatibility and transfection efficiency of the resulting copolymers over two murine cell lines. While the incorporation of the hydroxylated CD moiety increased the cytotoxicity of the copolymers in comparison with their homopolycationic counterpart, the permethylated copolymers have shown full cytocompatibility as well as superior transfection efficiency than the controls. This behavior has been related to the different chemical nature of both units and tentatively to a different distribution of units along the polymeric chains. Cellular internalization analysis with fluorescent copo-lymers supports this behavior.

Cell Death Signaling

In multicellular organisms, cell death is a critical and active process that maintains tissue homeostasis and eliminates potentially harmful cells. There are three major types of morphologically distinct cell death: apoptosis (type I cell death), autophagic cell death (type II), and necrosis (type III). All three can be executed through distinct, and sometimes overlapping, signaling pathways that are engaged in response to specific stimuli. Apoptosis is triggered when cell-surface death receptors such as Fas are bound by their ligands (the extrinsic pathway) or when Bcl2-family proapoptotic proteins cause the permeabilization of the mitochondrial outer membrane (the intrinsic pathway). Both pathways converge on the activation of the caspase protease family, which is ultimately responsible for the dismantling of the cell. Autophagy defines a catabolic process in which parts of the cytosol and specific organelles are engulfed by a double-membrane structure, known as the autophagosome, and eventually degraded. Autophagy is mostly a survival mechanism; nevertheless, there are a few examples of autophagic cell death in which components of the autophagic signaling pathway actively promote cell death. Necrotic cell death is characterized by the rapid loss of plasma membrane integrity. This form of cell death can result from active signaling pathways, the best characterized of which is dependent on the activity of the protein kinase RIP3.

Regulation of Bim in Health and Disease

The BH3-only Bim protein is a major determinant for initiating the intrinsic apoptotic pathway under both physiological and pathophysiological conditions. Tight regulation of its expression and activity at the transcriptional, translational and post-translational levels together with the induction of alternatively spliced isoforms with different pro-apoptotic potential, ensure timely activation of Bim. Under physiological conditions, Bim is essential for shaping immune responses where its absence promotes autoimmunity, while too early Bim induction eliminates cytotoxic T cells prematurely, resulting in chronic inflammation and tumor progression. Enhanced Bim induction in neurons causes neurodegenerative disorders including Alzheimer's, Parkinson's and Huntington's diseases. Moreover, type I diabetes is promoted by genetically predisposed elevation of Bim in β-cells. On the contrary, cancer cells have developed mechanisms that suppress Bim expression necessary for tumor progression and metastasis. This review focuses on the intricate network regulating Bim activity and its involvement in physiological and pathophysiological processes.

HCV upregulates Bim through the ROS/JNK signalling pathway, leading to Bax-mediated apoptosis

We previously reported that hepatitis C virus (HCV) infection induces Bax-triggered, mitochondrion-mediated apoptosis by using the HCV J6/JFH1 strain and Huh-7.5 cells. However, it was still unclear how HCV-induced Bax activation. In this study, we showed that the HCV-induced activation and mitochondrial accumulation of Bax were significantly attenuated by treatment with a general antioxidant, N-acetyl cysteine (NAC), or a specific c-Jun N-terminal kinase (JNK) inhibitor, SP600125, with the result suggesting that the reactive oxygen species (ROS)/JNK signalling pathway is upstream of Bax activation in HCV-induced apoptosis. We also demonstrated that HCV infection transcriptionally activated the gene for the pro-apoptotic protein Bim and the protein expression of three major splice variants of Bim (BimEL, BimL and BimS). The HCV-induced increase in the Bim mRNA and protein levels was significantly counteracted by treatment with NAC or SP600125, suggesting that the ROS/JNK signalling pathway is involved in Bim upregulation. Moreover, HCV infection led to a marked accumulation of Bim on the mitochondria to facilitate its interaction with Bax. On the other hand, downregulation of Bim by siRNA (small interfering RNA) significantly prevented HCV-mediated activation of Bax and caspase 3. Taken together, these observations suggest that HCV-induced ROS/JNK signalling transcriptionally activates Bim expression, which leads to Bax activation and apoptosis induction.

Reduced levels of Hspa9 attenuate Stat5 activation in mouse B cells

HSPA9 is located on chromosome 5q31.2 in humans, a region that is commonly deleted in patients with myeloid malignancies [del(5q)], including myelodysplastic syndrome (MDS). HSPA9 expression is reduced by 50% in patients with del(5q)-associated MDS, consistent with haploinsufficient levels. Zebrafish mutants and knockdown studies in human and mouse cells have implicated a role for HSPA9 in hematopoiesis. To comprehensively evaluate the effects of Hspa9 haploinsufficiency on hematopoiesis, we generated an Hspa9 knockout mouse model. Although homozygous knockout of Hspa9 is embryonically lethal, mice with heterozygous deletion of Hspa9 (Hspa9(+/-)) are viable and have a 50% reduction in Hspa9 expression. Hspa9(+/-) mice have normal basal hematopoiesis and do not develop MDS. However, Hspa9(+/-) mice have a cell-intrinsic reduction in bone marrow colony-forming unit-PreB colony formation without alterations in the number of B-cell progenitors in vivo, consistent with a functional defect in Hspa9(+/-) B-cell progenitors. We further reduced Hspa9 expression (<50%) using RNA interference and observed reduced B-cell progenitors in vivo, indicating that appropriate levels (≥50%) of Hspa9 are required for normal B lymphopoiesis in vivo. Knockdown of Hspa9 in an interleukin 7 (IL-7)-dependent mouse B-cell line reduced signal transducer and activator of transcription 5 (Stat5) phosphorylation following IL-7 receptor stimulation, supporting a role for Hspa9 in Stat5 signaling in B cells. Collectively, these data imply a role for Hspa9 in B lymphopoiesis and Stat5 activation downstream of IL-7 signaling.

Label-free quantitative mass spectrometry reveals a panel of differentially expressed proteins in colorectal cancer

To identify potential biomarkers involved in CRC, a shotgun proteomic method was applied to identify soluble proteins in three CRCs and matched normal mucosal tissues using high-performance liquid chromatography and mass spectrometry. Label-free protein profiling of three CRCs and matched normal mucosal tissues were then conducted to quantify and compare proteins. Results showed that 67 of the 784 identified proteins were linked to CRC (28 upregulated and 39 downregulated). Gene Ontology and DAVID databases were searched to identify the location and function of differential proteins that were related to the biological processes of binding, cell structure, signal transduction, cell adhesion, and so on. Among the differentially expressed proteins, tropomyosin-3 (TPM3), endoplasmic reticulum resident protein 29 (ERp29), 18 kDa cationic antimicrobial protein (CAMP), and heat shock 70 kDa protein 8 (HSPA8) were verified to be upregulated in CRC tissue and seven cell lines through western blot analysis. Furthermore, the upregulation of TPM3, ERp29, CAMP, and HSPA8 was validated in 69 CRCs byimmunohistochemistry (IHC) analysis. Combination of TPM3, ERp29, CAMP, and HSPA8 can identify CRC from matched normal mucosal achieving an accuracy of 73.2% using IHC score. These results suggest that TPM3, ERp29, CAMP, and HSPA8 are great potential IHC diagnostic biomarkers for CRC.

Hsp27 binding to the 3'UTR of bim mRNA prevents neuronal death during oxidative stress-induced injury: a novel cytoprotective mechanism

Neurons face a changeable microenvironment and therefore need mechanisms that allow rapid switch on/off of their cytoprotective and apoptosis-inducing signaling pathways. Cellular mechanisms that control apoptosis activation include the regulation of pro/antiapoptotic mRNAs through their 3'-untranslated region (UTR). This region holds binding elements for RNA-binding proteins, which can control mRNA translation. Here we demonstrate that heat shock protein 27 (Hsp27) prevents oxidative stress-induced cell death in cerebellar granule neurons by specific regulation of the mRNA for the proapoptotic BH3-only protein, Bim. Hsp27 depletion induced by oxidative stress using hydrogen peroxide (H2O2) correlated with bim gene activation and subsequent neuronal death, whereas enhanced Hsp27 expression prevented these. This effect could not be explained by proteasomal degradation of Bim or bim promoter inhibition; however, it was associated with a specific increase in the levels of bim mRNA and with its binding to Hsp27. Finally, we determined that enhanced Hsp27 expression in neurons exposed to H2O2 or glutamate prevented the translation of a reporter plasmid where bim-3'UTR mRNA sequence was cloned downstream of a luciferase gene. These results suggest that repression of bim mRNA translation through binding to the 3'UTR constitutes a novel cytoprotective mechanism of Hsp27 during stress in neurons.

Downregulation of proapoptotic Bim augments IL-2-independent T-cell transformation by human T-cell leukemia virus type-1 Tax

Human T-cell leukemia virus type 1 (HTLV-1), an etiological agent of adult T-cell leukemia, immortalizes and transforms primary human T cells in vitro in both an interleukin (IL)-2-dependent and IL-2-independent manner. Expression of the HTLV-1 oncoprotein Tax transforms the growth of the mouse T-cell line CTLL-2 from being IL-2-dependent to IL-2-independent. Withdrawal of IL-2 from normal activated T cells induces apoptosis, which is mediated through the inducible expression of several proapoptotic proteins, including Bim. In this study, we found that Tax protects IL-2-depleted T cells against Bim-induced apoptosis. Withdrawal of IL-2 from CTLL-2 cells induced a prominent increase in the level of Bim protein in CTLL-2 cells, but not in Tax-transformed CTLL-2 cells. This inhibition of Bim in Tax-transformed CTLL-2 cells was mediated by two mechanisms: downregulation of Bim mRNA and posttranscriptional reduction of Bim protein. Transient expression of Tax in CTLL-2 cells also inhibited IL-2 depletion–induced expression of Bim, however, this decrease in Bim protein expression was not due to downregulation of Bim mRNA, thus indicating that Bim mRNA downregulation in Tax-transformed CTLL-2 occurs only after long-term expression of Tax. Transient expression of Tax in CTLL-2 cells also induced Erk activation, however, this was not involved in the reduction of Bim protein. Knockdown of Bim expression in CTLL-2 cells augmented Tax-induced IL-2-independent transformation. HTLV-1 infection of human T cells also reduced their levels of Bim protein, and restoring Bim expression in HTLV-1-infected cells reduced their proliferation by inducing apoptosis. Taken together, these results indicate that Tax-induced downregulation of Bim in HTLV-1-infected T cells promotes their IL-2-independent growth, thereby supporting the persistence of HTLV-1 infection in vivo.

Transcriptional and post-translational regulation of Bim controls apoptosis in melatonin-treated human renal cancer Caki cells

Melatonin (N-acetyl-5-methoxytryptamine) has recently gained attention as an anticancer agent and for combined cancer therapy. In this study, we investigated the underlying molecular mechanisms of the effects of melatonin on cancer cell death. Treatment with melatonin induced apoptosis and upregulated the expression of the pro-apoptotic protein Bcl-2-interacting mediator of cell death (Bim) in renal cancer Caki cells. Furthermore, downregulation of Bim expression by siRNA markedly reduced melatonin-mediated apoptosis. Melatonin increased Bim mRNA expression through the induction of Sp1 and E2F1 expression and transcriptional activity. We found that melatonin also modulated Bim protein stability through the inhibition of proteasome activity. However, melatonin-induced Bim upregulation was independent of melatonin's antioxidant properties and the melatonin receptor. Taken together, our results suggest that melatonin induces apoptosis through the upregulation of Bim expression at the transcriptional level and at the post-translational level.

Novel role of HSP40/DNAJ in the regulation of HIV-1 replication

OBJECTIVES

DNAJ/HSP40 is an evolutionarily conserved family of proteins bearing various functions. Historically, it has been emphasized that HSP40/DNAJ family proteins play a positive role in infection of various viruses. We identified DNAJ/HSP40B6 as a potential negative regulator of HIV-1 replication in our genetic screens. In this study, we investigated the functional interactions between HIV-1 and HSP40 family members.

DESIGN

We took genetic and comparative virology approaches to expand the primary observation.

METHODS

Multiple HSP40/DNAJ proteins were tested for their ability to inhibit replication of adenovirus, herpes simplex virus type 1, HIV-1, and vaccinia virus. The mechanism of inhibition was investigated by using HSP40/DNAJ mutants and measuring the efficiencies of each viral replication steps.

RESULTS

HSP40A1, B1, B6, and C5, but not C3, were found to be able to limit HIV-1 production. This effect was specific to HIV-1 for such effects were not detected in adenovirus, herpes simplex virus type 1, and vaccinia virus. Genetic analyses suggested that the conserved DNAJ domain was responsible for the inhibition of HIV-1 production through which HSP40 regulates HSP70 ATPase activity. Interestingly, HSP40s lowered the levels of steady-state viral messenger RNA. This was not attributed to the inhibition of Tat/long terminal repeat-driven transcription but the downregulation of Rev expression.

CONCLUSIONS

This is the first report providing evidence that HSP70-HSP40 complex confers an innate resistance specific to HIV-1. For their interferon-inducible nature, HSP40 family members should account for the anti-HIV-1 function of interferon.

HSPA8/HSC70 chaperone protein: structure, function, and chemical targeting

HSPA8/HSC70 protein is a fascinating chaperone protein. It represents a constitutively expressed, cognate protein of the HSP70 family, which is central in many cellular processes. In particular, its regulatory role in autophagy is decisive. We focused this review on HSC70 structure-function considerations and based on this, we put a particular emphasis on HSC70 targeting by small molecules and peptides in order to develop intervention strategies that deviate some of HSC70 properties for therapeutic purposes. Generating active biomolecules regulating autophagy via its effect on HSC70 can effectively be designed only if we understand the fine relationships between HSC70 structure and functions.

Assembly of functional ribonucleoprotein complexes by AU-rich element RNA-binding protein 1 (AUF1) requires base-dependent and -independent RNA contacts

AU-rich element RNA-binding protein 1 (AUF1) regulates the stability and/or translational efficiency of diverse mRNA targets, including many encoding products controlling the cell cycle, apoptosis, and inflammation by associating with AU-rich elements residing in their 3'-untranslated regions. Previous biochemical studies showed that optimal AUF1 binding requires 33-34 nucleotides with a strong preference for U-rich RNA despite observations that few AUF1-associated cellular mRNAs contain such extended U-rich domains. Using the smallest AUF1 isoform (p37(AUF1)) as a model, we employed fluorescence anisotropy-based approaches to define thermodynamic parameters describing AUF1 ribonucleoprotein (RNP) complex formation across a panel of RNA substrates. These data demonstrated that 15 nucleotides of AU-rich sequence were sufficient to nucleate high affinity p37(AUF1) RNP complexes within a larger RNA context. In particular, p37(AUF1) binding to short AU-rich RNA targets was significantly stabilized by interactions with a 3'-purine residue and largely base-independent but non-ionic contacts 5' of the AU-rich site. RNP stabilization by the upstream RNA domain was associated with an enhanced negative change in heat capacity consistent with conformational changes in protein and/or RNA components, and fluorescence resonance energy transfer-based assays demonstrated that these contacts were required for p37(AUF1) to remodel local RNA structure. Finally, reporter mRNAs containing minimal high affinity p37(AUF1) target sequences associated with AUF1 and were destabilized in a p37(AUF1)-dependent manner in cells. These findings provide a mechanistic explanation for the diverse population of AUF1 target mRNAs but also suggest how AUF1 binding could regulate protein and/or microRNA binding events at adjacent sites.

BimEL is phosphorylated at mitosis by Aurora A and targeted for degradation by βTrCP1

Bcl-2-interacting mediator of cell death (Bim) is a pro-apoptotic B-cell lymphoma 2 family member implicated in numerous apoptotic stimuli. In particular, Bim is required for cell death mediated by antimitotic agents, however, mitotic regulation of Bim remains poorly understood. Here, we show that the major splice variant of Bim, BimEL, is regulated during mitosis by the Aurora A kinase and protein phosphatase 2A (PP2A). We observed that BimEL is phosphorylated by Aurora A early in mitosis and reversed by PP2A after mitotic exit. Aurora A phosphorylation stimulated binding of BimEL to the F-box protein beta-transducin repeat containing E3 ubiquitin protein ligase and promoted ubiquitination and degradation of BimEL. These findings describe a novel mechanism by which the oncogenic kinase Aurora A promotes cell survival during mitosis by downregulating proapoptotic signals. Notably, we observed that knockdown of Bim significantly increased resistance of cells to the Aurora A inhibitor MLN8054. Inhibitors of Aurora A are currently under investigation as cancer chemotherapeutics and our findings suggest that efficacy of this class of drugs may function in part by enhancing apoptotic activity of BimEL.

Epigenetic silencing of Bim transcription by Spi-1/PU.1 promotes apoptosis resistance in leukaemia

Deregulation of transcriptional networks contributes to haematopoietic malignancies. The transcription factor Spi-1/PU.1 is a master regulator of haematopoiesis and its alteration leads to leukaemia. Spi-1 overexpression inhibits differentiation and promotes resistance to apoptosis in erythroleukaemia. Here, we show that Spi-1 inhibits mitochondrial apoptosis in vitro and in vivo through the transcriptional repression of Bim, a proapoptotic factor. BIM interacts with MCL-1 that behaves as a major player in the survival of the preleukaemic cells. The repression of BIM expression reduces the amount of BIM-MCL-1 complexes, thus increasing the fraction of potentially active antiapoptotic MCL-1. We then demonstrate that Spi-1 represses Bim transcription by binding to the Bim promoter and by promoting the trimethylation of histone 3 on lysine 27 (H3K27me3, a repressive histone mark) on the Bim promoter. The PRC2 repressive complex of Polycomb is directly responsible for the deposit of H3K27me3 mark at the Bim promoter. SUZ12 and the histone methyltransferase EZH2, two PRC2 subunits bind to the Bim promoter at the same location than H3K27me3, distinct of the Spi-1 DNA binding site. As Spi-1 interacts with SUZ12 and EZH2, these results indicate that Spi-1 modulates the activity of PRC2 without directly recruiting the complex to the site of its activity on the chromatin. Our results identify a new mechanism whereby Spi-1 represses transcription and provide mechanistic insights on the antiapoptotic function of a transcription factor mediated by the epigenetic control of gene expression.

PKCι counteracts oxidative stress by regulating Hsc70 in an esophageal cancer cell line

Using a glutathione S-transferase pull-down liquid chromatography-coupled tandem mass spectrometry approach and immunoprecipitation/immunoblot analysis, we found that heat shock cognate protein 70 (Hsc70) was involved in the complex formed by atypical protein kinase Cι (PKCι) and LC3 in the esophageal cancer cell line KYSE30. Further study indicated that Hsc70 was targeted by autophagic degradation, and knockdown of PKCι down-regulated Hsc70 by promoting autophagy. PKCι knockdown sensitized cells to oxidative stress-induced apoptosis, whereas forced PKCι expression counteracted the oxidative stress-induced apoptosis via Hsc70.

Post-transcriptional regulation of connexin43 in H-Ras-transformed cells

Connexin43 (Cx43) expression is lost in cancer cells and many studies have reported that Cx43 is a tumor suppressor gene. Paradoxically, in a cellular NIH3T3 model, we have previously shown that Ha-Ras-mediated oncogenic transformation results in increased Cx43 expression. Although the examination of transcriptional regulation revealed essential regulatory elements, it could not solve this paradox. Here we studied post-transcriptional regulation of Cx43 expression in cancer using the same model in search of novel gene regulatory elements. Upon Ras transformation, both Cx43 mRNA stability and translation efficiency were increased. We investigated the role of Cx43 mRNA 3′ and 5′Untranslated regions (UTRs) and found an opposing effect; a 5′UTR-driven positive regulation is observed in Ras-transformed cells (NIH-3T3^Ras), while the 3′UTR is active only in normal NIH-3T3^Neo cells and completely silenced in NIH-3T3^Ras cells. Most importantly, we identified a previously unknown regulatory element within the 3′UTR, named S1516, which accounts for this 3′UTR-mediated regulation. We also examined the effect of other oncogenes and found that Ras- and Src-transformed cells show a different Cx43 UTRs post-transcriptional regulation than ErbB2-transformed cells, suggesting distinct regulatory pathways. Next, we detected different patterns of S1516 RNA-protein complexes in NIH-3T3^Neo compared to NIH-3T3^Ras cells. A proteomic approach identified most of the S1516-binding proteins as factors involved in post-transcriptional regulation. Building on our new findings, we propose a model to explain the discrepancy between the Cx43 expression in Ras-transformed NIH3T3 cells and the data in clinical specimens.

Targeting the regulatory machinery of BIM for cancer therapy

BIM represents a BH3-only proapoptotic member of the BCL-2 family of apoptotic regulatory proteins. Recent evidence suggests that in addition to its involvement in normal homeostasis, BIM plays a critical role in tumor cell biology, including the regulation of tumorigenesis through activities as a tumor suppressor, tumor metastasis, and tumor cell survival. Consequently, BIM has become the focus of intense interest as a potential target for cancer chemotherapy. The control of BIM expression is complex, and involves multiple factors, including epigenetic events (i.e., promoter acetylation or methylation, miRNA), transcription factors, posttranscriptional regulation, and posttranslational modifications, most notably phosphorylation. Significantly, the expression of BIM by tumor cells has been shown to play an important role in determining the response of transformed cells to not only conventional cytotoxic agents, but also to a broad array of targeted agents that interrupt cell signaling and survival pathways. Furthermore, modifications in BIM expression may be exploited to improve the therapeutic activity and potentially the selectivity of such agents. It is likely that evolving insights into the factors that regulate BIM expression will ultimately lead to novel BIM-based therapeutic strategies in the future.

Identification in the rat brain of a set of nuclear proteins interacting with H1° mRNA

Synthesis of H1° histone, in the developing rat brain, is also regulated at post-transcriptional level. Regulation of RNA metabolism depends on a series of RNA-binding proteins (RBPs); therefore, we searched for H1° mRNA-interacting proteins. With this aim, we used in vitro transcribed, biotinylated H1° RNA as bait to isolate, by a chromatographic approach, proteins which interact with this mRNA, in the nuclei of brain cells. Abundant RBPs, such as heterogeneous nuclear ribonucleoprotein (hnRNP) K and hnRNP A1, and molecular chaperones (heat shock cognate 70, Hsc70) were identified by mass spectrometry. Western blot analysis also revealed the presence of cold shock domain-containing protein 2 (CSD-C2, also known as PIPPin), a brain-enriched RBP previously described in our laboratory. Co-immunoprecipitation assays were performed to investigate the possibility that identified proteins interact with each other and with other nuclear proteins. We found that hnRNP K interacts with both hnRNP A1 and Hsc70 whereas there is no interaction between hnRNP A1 and Hsc70. Moreover, CSD-C2 interacts with hnRNP A1, Y box-binding protein 1 (YB-1), and hnRNP K. We also have indications that CSD-C2 interacts with Hsc70. Overall, we have contributed to the molecular characterization of a ribonucleoprotein particle possibly controlling H1° histone expression in the brain.

Hsp70 is a novel posttranscriptional regulator of gene expression that binds and stabilizes selected mRNAs containing AU-rich elements

The AU-rich elements (AREs) encoded within many mRNA 3' untranslated regions (3'UTRs) are targets for factors that control transcript longevity and translational efficiency. Hsp70, best known as a protein chaperone with well-defined peptide-refolding properties, is known to interact with ARE-like RNA substrates in vitro. Here, we show that cofactor-free preparations of Hsp70 form direct, high-affinity complexes with ARE substrates based on specific recognition of U-rich sequences by both the ATP- and peptide-binding domains. Suppressing Hsp70 in HeLa cells destabilized an ARE reporter mRNA, indicating a novel ARE-directed mRNA-stabilizing role for this protein. Hsp70 also bound and stabilized endogenous ARE-containing mRNAs encoding vascular endothelial growth factor (VEGF) and Cox-2, which involved a mechanism that was unaffected by an inhibitor of its protein chaperone function. Hsp70 recognition and stabilization of VEGF mRNA was mediated by an ARE-like sequence in the proximal 3'UTR. Finally, stabilization of VEGF mRNA coincided with the accumulation of Hsp70 protein in HL60 promyelocytic leukemia cells recovering from acute thermal stress. We propose that the binding and stabilization of selected ARE-containing mRNAs may contribute to the cytoprotective effects of Hsp70 following cellular stress but may also provide a novel mechanism linking constitutively elevated Hsp70 expression to the development of aggressive neoplastic phenotypes.

Comprehensive review on the HSC70 functions, interactions with related molecules and involvement in clinical diseases and therapeutic potential

Heat shock cognate protein 70 (HSC70) is a constitutively expressed molecular chaperone which belongs to the heat shock protein 70 (HSP70) family. HSC70 shares some of the structural and functional similarity with HSP70. HSC70 also has different properties compared with HSP70 and other heat shock family members. HSC70 performs its full functions by the cooperation of co-chaperones. It interacts with many other molecules as well and regulates various cellular functions. It is also involved in various diseases and may become a biomarker for diagnosis and potential therapeutic targets for design, discovery, and development of novel drugs to treat various diseases. In this article, we provide a comprehensive review on HSC70 from the literatures including the basic general information such as classification, structure and cellular location, genetics and function, as well as its protein association and interaction with other proteins. In addition, we also discussed the relationship of HSC70 and related clinical diseases such as cancer, cardiovascular, neurological, hepatic and many other diseases and possible therapeutic potential and highlight the progress and prospects of research in this field. Understanding the functions of HSC70 and its interaction with other molecules will help us to reveal other novel properties of this protein. Scientists may be able to utilize this protein as a biomarker and therapeutic target to make significant advancement in scientific research and clinical setting in the future.

Glucocorticoid-mediated BIM induction and apoptosis are regulated by Runx2 and c-Jun in leukemia cells

Glucocorticoids (GCs) are common components of many chemotherapeutic regimens for lymphoid malignancies. GC-induced apoptosis involves an intrinsic mitochondria-dependent pathway. BIM (BCL-2-interacting mediator of cell death), a BCL-2 homology 3-only pro-apoptotic protein, is upregulated by dexamethasone (Dex) treatment in acute lymphoblastic leukemia cells and has an essential role in Dex-induced apoptosis. It has been indicated that Dex-induced BIM is regulated mainly by transcription, however, the molecular mechanisms including responsible transcription factors are unclear. In this study, we found that Dex treatment induced transcription factor Runx2 and c-Jun in parallel with BIM induction. Dex-induced BIM and apoptosis were decreased in cells harboring dominant-negative c-Jun and were increased in cells with c-Jun overexpression. Cells harboring short hairpin RNA for Runx2 also decreased BIM induction and apoptosis. On the Bim promoter, c-Jun bound to and activated the AP-1-binding site at about −2.7 kb from the transcription start site. Treatment with RU486, a GC receptor antagonist, blocked Dex-induced Runx2, c-Jun and BIM induction, as well as apoptosis. Furthermore, pretreatment with SB203580, a p38-mitogen-activated protein kinase (MAPK) inhibitor, decreased Dex-induced Runx2, c-Jun and BIM, suggesting that p38-MAPK activation is upstream of the induction of these molecules. In conclusion, we identified the critical signaling pathway for GC-induced apoptosis, and targeting these molecules may be an alternative approach to overcome GC-resistance in leukemia treatment.

The absence of heat shock protein HSP101 affects the proteome of mature and germinating maize embryos

Maize heat shock protein HSP101 accumulates during embryo maturation and desiccation and persists at high levels during the first 24 h following kernel imbibition in the absence of heat stress. This protein has a known function in disaggregation of high molecular weight complexes and has been proposed to be a translational regulator of specific mRNAs. Here, a global proteomic approach was used to identify changes in the maize proteome due to the absence of HSP101 in embryos from mature-dry or 24 h-imbibed kernels. A total of 26 protein spots from the mature dry embryo exhibited statistically significant expression changes in the L10 inbred hsp101 mutant (hsp101-m5::Mu1/hsp101-m5::Mu1) line as compared to the corresponding wild type (Hsp101/Hsp101). Additional six spots reproducibly showed qualitative changes between the mutant and wild-type mature and germinating embryos. Several chaperones, translation-related proteins, actin, and enzymes participating in cytokinin metabolism were identified in these spots by tandem mass-spectrometry (MS). The proteomic changes partially explain the altered root growth and architecture observed in young hsp101 mutant seedlings. In addition, specific protein de novo synthesis was altered in the 24 h-imbibed mutant embryos indicating that maize HSP101 functions as both chaperone and translational regulator during germination. Supporting this, HSP101 was found as part of Cap-binding and translation initiation complexes during early kernel imbibition. Overall, these findings expose the relevance of maize HSP101 for protein synthesis and balance mechanisms during germination.

Role of heat shock proteins in stem cell behavior

Stress response is well appreciated to induce the expression of heat shock proteins (Hsps) in the cell. Numerous studies have demonstrated that Hsps function as molecular chaperones in the stabilization of intracellular proteins, repairing damaged proteins, and assisting in protein translocation. Various kinds of stem cells (embryonic stem cells, adult stem cells, or induced pluripotent stem cells) have to maintain their stemness and, under certain circumstances, undergo stress. Therefore, Hsps should have an important influence on stem cells. Actually, numerous studies have indicated that some Hsps physically interact with a number of transcription factors as well as intrinsic and extrinsic signaling pathways. Importantly, alterations in Hsp expression have been demonstrated to affect stem cell behavior including self-renewal, differentiation, sensitivity to environmental stress, and aging. This chapter summarizes recent findings related to (1) the roles of Hsps in maintenance of stem cell dormancy, proliferation, and differentiation; (2) the expression signature of Hsps in embryonic/adult stem cells and differentiated stem cells; (3) the protective roles of Hsps in transplanted stem cells; and (4) the possible roles of Hsps in stem cell aging.

p57(Kip2) and p27(Kip1) cooperate to maintain hematopoietic stem cell quiescence through interactions with Hsc70

Cell cycle regulators play critical roles in the balance between hematopoietic stem cell (HSC) dormancy and proliferation. In this study, we report that cell cycle entry proceeded normally in HSCs null for cyclin-dependent kinase (CDK) inhibitor p57 due to compensatory upregulation of p27. HSCs null for both p57 and p27, however, were more proliferative and had reduced capacity to engraft in transplantation. We found that heat shock cognate protein 70 (Hsc70) interacts with both p57 and p27 and that the subcellular localization of Hsc70 was critical to maintain HSC cell cycle kinetics. Combined deficiency of p57 and p27 in HSCs resulted in nuclear import of an Hsc70/cyclin D1 complex, concomitant with Rb phosphorylation, and elicited severe defects in maintaining HSC quiescence. Taken together, these data suggest that regulation of cytoplasmic localization of Hsc70/cyclin D1 complex by p57 and p27 is a key intracellular mechanism in controlling HSC dormancy.