Co-immunoprecipitation of Hsp101 with cytosolic Hsc70

Effect of terminal heat stress on osmolyte accumulation and gene expression during grain filling in bread wheat (Triticum aestivum L.)

The grain-filling stage in Triticum aestivum (wheat) is highly vulnerable to increasing temperature as terminal heat stress diminishes grain quality and yield. To examine the mechanism of terminal heat tolerance, we performed the biochemical and gene expression analyses using two heat-tolerant (WH730 and WH1218) and two heat-sensitive (WH711 and WH157) wheat genotypes. We observed a significant increase in total soluble sugar (25%-47%), proline (7%-15%), and glycine betaine (GB) (22%-34%) contents in flag leaf, whereas a decrease in grain-filling duration, 1000-kernel weight (8%-25%), and grain yield per plant (11%-23%) was observed under the late-sown compared to the timely sown. The maximum content of osmolytes, including total soluble sugar, proline, and GB, was observed in heat-tolerant genotypes compared to heat-sensitive genotypes. The expression of 10 heat-responsive genes associated with heat shock proteins (sHsp-1, Hsp17, and HsfA4), flavonoid biosynthesis (F3'-1 and PAL), β-glucan synthesis (CslF6 and CslH), and xyloglucan metabolism (XTH1, XTH2, and XTH5) was studied in flag leaf exposed to different heat treatments (34, 36, 38, and 40°C) at 15 days after anthesis by quantitative real-time polymerase chain reaction. A significant increase in the relative fold expression of these genes with increasing temperature indicated their involvement in providing heat-stress tolerance. The high differential expression of most of the genes in heat-tolerant genotype "WH730" followed by "WH1218" indicates the high adaptability of these genotypes to heat stress compared to heat-sensitive wheat genotypes. Based on the previous results, "WH730" performed better in terms of maximum osmolyte accumulation, grain yield, and gene expression under heat stress.

Overexpression of Seagrass Nucleotide Exchange Factor Gene ZjFes1 Enhances Heat Tolerance in Transgenic Arabidopsis

Nucleotide exchange factors (NEFs) play an important role in plant abiotic stress response, but their characteristics and functions in seagrass have not been studied. Zostera japonica (Z. japonica) is one of the most widely distributed seagrass species in China and are distributed in subtropical and temperate coastal areas. Z. japonica is intertidal seagrass, which often undergoes heat stress during summer when the tide ebbs. Overexpression of ZjFes1 in Arabidopsis results in an increase in heat tolerance. We found that ZjFes1 associates with ZjHsp70 in vivo by yeast two-hybrid and bimolecular fluorescence complementarity (BiFC). Overexpression of ZjFes1 leads to selective reduction of Hsp70 transcription and an increase in Hsp101. In conclusion, our results suggest that ZjFes1 may be an active regulator of heat tolerance.

Interplay between heat shock proteins HSP101 and HSA32 prolongs heat acclimation memory posttranscriptionally in Arabidopsis

Heat acclimation improves the tolerance of organisms to severe heat stress. Our previous work showed that in Arabidopsis (Arabidopsis thaliana), the "memory" of heat acclimation treatment decayed faster in the absence of the heat-stress-associated 32-kD protein HSA32, a heat-induced protein predominantly found in plants. The HSA32 null mutant attains normal short-term acquired thermotolerance but is defective in long-term acquired thermotolerance. To further explore this phenomenon, we isolated Arabidopsis defective in long-term acquired thermotolerance (dlt) mutants using a forward genetic screen. Two recessive missense alleles, dlt1-1 and dlt1-2, encode the molecular chaperone heat shock protein101 (HSP101). Results of immunoblot analyses suggest that HSP101 enhances the translation of HSA32 during recovery after heat treatment, and in turn, HSA32 retards the decay of HSP101. The dlt1-1 mutation has little effect on HSP101 chaperone activity and thermotolerance function but compromises the regulation of HSA32. In contrast, dlt1-2 impairs the chaperone activity and thermotolerance function of HSP101 but not the regulation of HSA32. These results suggest that HSP101 has a dual function, which could be decoupled by the mutations. Pulse-chase analysis showed that HSP101 degraded faster in the absence of HSA32. The autophagic proteolysis inhibitor E-64d, but not the proteasome inhibitor MG132, inhibited the degradation of HSP101. Ectopic expression of HSA32 confirmed its effect on the decay of HSP101 at the posttranscriptional level and showed that HSA32 was not sufficient to confer long-term acquired thermotolerance when the HSP101 level was low. Taken together, we propose that a positive feedback loop between HSP101 and HSA32 at the protein level is a novel mechanism for prolonging the memory of heat acclimation.

Expression, purification of recombinant human mitochondrial transcription termination factor 3 (hMTERF3) and preparation of polyclonal antibody against hMTERF3

In mammalian cells, a family of mitochondrial transcription termination factors (MTERFs) regulates mitochondrial gene expression. Mitochondrial transcription termination factor 3 (MTERF3) is the most conserved member of the MTERF family and a negative regulator of mammalian mitochondrial DNA transcription. To create a specific polyclonal antibody against human MTERF3 (hMTERF3), we first cloned hMTERF3 into prokaryotic expression vector pGEX-4T-1, and GST-hMTERF3 was efficiently expressed in Escherichia coli after induction by IPTG. The expressed GST-tagged hMTERF3 fusion protein was purified by passive electro-elution process and then used to immunize BALB/c mice, we obtained anti-GST-hMTERF3 polyclonal antibody purified by protein A column and determined the sensitivity and specificity of the antibody against human MTERF3 by enzyme-linked immunosorbent assay and Western blot assay. Furthermore, the full-length hMTERF3 protein expressed in human embryonic kidney 293T cells was detected by anti-GST-hMTERF3 in western blot analysis and immunofluorescence staining. Taken together, our results demonstrate the functionality of the mouse anti-GST-hMTERF3 polyclonal antibody which will provide a useful tool for further characterization of hMTERF3.

Production, purification and characterization of mouse monoclonal antibodies against human mitochondrial transcription termination factor 2 (MTERF2)

Human mitochondrial transcription termination factor 2 (MTERF2) is a member of the mitochondrial transcription termination factors (MTERFs) family and a cell growth inhibitor. To create a specific mouse monoclonal antibody against human MTERF2, the full-length His-tag MTERF2 protein (1-385 aa) was expressed in Escherichia coli, and purified recombinant protein was injected into three BALB/c mice to perform an immunization procedure. Eight stable positive monoclonal cell lines were screened and established. ELISA results demonstrated that all antibody light chains were kappa, while the heavy chains displayed three subtypes IgG1, IgG2a, and IgG2b respectively. The sensitivity and specificity of the monoclonal antibodies against human MTERF2 were determined using immunoblotting, immunoprecipitation and immunofluorescence analyses. Furthermore, serum regulation of human MTERF2 protein expression levels in human glioma U251 cells was examined with these monoclonal antibodies and the results demonstrated that the expression level of MTERF2 protein was dramatically inhibited by the addition of serum to serum-starved cells. Taken together, our results demonstrate the functionality of these mouse anti-human MTERF2 monoclonal antibodies, which may provide a useful tool to elucidate the role of MTERF2 in human mitochondrial transcription as well as other potential activities. To our knowledge, this is the first report on the preparation and characterization of mouse monoclonal antibodies against human MTERF2.

Species-specific collaboration of heat shock proteins (Hsp) 70 and 100 in thermotolerance and protein disaggregation

Yeast Hsp104 and its bacterial homolog, ClpB, are Clp/Hsp100 molecular chaperones and AAA+ ATPases. Hsp104 and ClpB collaborate with the Hsp70 and DnaK chaperone systems, respectively, to retrieve and reactivate stress-denatured proteins from aggregates. The action of Hsp104 and ClpB in promoting cell survival following heat stress is species-specific: Hsp104 cannot function in bacteria and ClpB cannot act in yeast. To determine the regions of Hsp104 and ClpB necessary for this specificity, we tested chimeras of Hsp104 and ClpB in vivo and in vitro. We show that the Hsp104 and ClpB middle domains dictate the species-specificity of Hsp104 and ClpB for cell survival at high temperature. In protein reactivation assays in vitro, chimeras containing the Hsp104 middle domain collaborate with Hsp70 and those with the ClpB middle domain function with DnaK. The region responsible for the specificity is within helix 2 and helix 3 of the middle domain. Additionally, several mutants containing amino acid substitutions in helix 2 of the ClpB middle domain are defective in protein disaggregation in collaboration with DnaK. In a bacterial two-hybrid assay, DnaK interacts with ClpB and with chimeras that have the ClpB middle domain, implying that species-specificity is due to an interaction between DnaK and the middle domain of ClpB. Our results suggest that the interaction between Hsp70/DnaK and helix 2 of the middle domain of Hsp104/ClpB determines the specificity required for protein disaggregation both in vivo and in vitro, as well as for cellular thermotolerance.

Hsp90 and Hsp40/Erdj3 are required for the expression and anti-apoptotic function of KSHV K1

Kaposi sarcoma-associated herpesvirus (KSHV) is a member of the gammaherpesvirus family. It is the etiological agent of three different human cancers, Kaposi sarcoma (KS), primary effusion lymphoma (PEL) and multicentric Castleman disease. The far left end of the KSHV genome encodes a unique transmembrane glycoprotein called K1. K1 possesses the ability to transform rodent fibroblasts and block apoptosis. K1 has also been shown to activate the PI3K/Akt/mTOR pathway in different cells. Using tandem affinity purification, we identified heat shock protein 90beta (Hsp90beta) and endoplasmic reticulum-associated Hsp40 (Erdj3/DnaJB11), as cellular binding partners of K1. Interactions of K1 with Hsp90beta and Hsp40 were confirmed by co-immunoprecipitation in both directions. Furthermore, K1 also interacted with the Hsp90alpha isoform. We report that small-interfering RNAs directed against Hsp90 and Hsp40/Erdj3, as well as pharmacological inhibitors of Hsp90, dramatically reduced K1 expression, suggesting that K1 is a client protein of these chaperones. In addition, both Hsp90 and Hsp40/Erdj3 were essential for K1's anti-apoptotic function. Finally, we report that the Hsp90 inhibitors, 17-AAG and 17-DMAG, can suppress the proliferation of KSHV-positive PEL cell lines and exhibited IC(50) values of 50 nM and below.

The role of Arabidopsis AtFes1A in cytosolic Hsp70 stability and abiotic stress tolerance

AtFes1A is induced by high temperatures, and encodes a protein containing the armadillo repeat motif. Little is known about its biological function, however. In this study, we observed an increased heat-sensitive phenotype in atfes1a mutants, suggesting the involvement of AtFes1A in acquired thermotolerance. We found that AtFes1A is cytosolic and associates with cytosolic Hsp70. Loss of AtFes1A leads to a selective reduction of cytosolic Hsp70 and a global increase in heat shock transcription. Thus, AtFes1A appears to prevent cytosolic Hsp70 degradation, and acts as a negative regulator of heat-shock transcription. We also found increased ubiquitination of total protein in atfes1a mutants after severe heat stress. These findings suggest that AtFes1A plays an important role in heat response signalling pathways, in addition to its role in thermotolerance.

Methodological framework for functional characterization of plant microRNAs

Since the beginning of this century, microRNAs (miRNAs), which are tiny RNA molecules, have become one of the major research topics on gene expression regulation in both animals and plants. The major task of miRNA study is to elucidate how the miRNAs are expressed in vivo, how they exert regulatory effects on their targets, and how they can be qualitatively or quantitatively cloned. For these purposes, the methodology of miRNA study has been developed and significantly improved in recent years. The focus here is on a number of powerful methods for plant miRNA research including bioinformatics tools and experimental approaches being used for upstream or downstream analysis of miRNAs or miRNA cloning. Some discrepancies exist in the miRNA research methodology between plants and animals, for example, 5' modified RACE (Rapid Amplification of cDNA Ends) can be used for cleavage target validation only in plants. However, numerous common methods are shared by these two miRNA research areas. Thus, this review will enhance our understanding of miRNA research methodology in organisms.

WPP-domain proteins mimic the activity of the HSC70-1 chaperone in preventing mistargeting of RanGAP1-anchoring protein WIT1

Arabidopsis (Arabidopsis thaliana) tryptophan-proline-proline (WPP)-domain proteins, WPP1 and WPP2, are plant-unique, nuclear envelope-associated proteins of unknown function. They have sequence similarity to the nuclear envelope-targeting domain of plant RanGAP1, the GTPase activating protein of the small GTPase Ran. WPP domain-interacting tail-anchored protein 1 (WIT1) and WIT2 are two Arabidopsis proteins containing a coiled-coil domain and a C-terminal predicted transmembrane domain. They are required for RanGAP1 association with the nuclear envelope in root tips. Here, we show that WIT1 also binds WPP1 and WPP2 in planta, we identify the chaperone heat shock cognate protein 70-1 (HSC70-1) as in vivo interaction partner of WPP1 and WPP2, and we show that HSC70-1 interacts in planta with WIT1. WIT1 and green fluorescent protein (GFP)-WIT1 are targeted to the nuclear envelope in Arabidopsis. In contrast, GFP-WIT1 forms large cytoplasmic aggregates when overexpressed transiently in Nicotiana benthamiana leaf epidermis cells. Coexpression of HSC70-1 significantly reduces GFP-WIT1 aggregation and permits association of most GFP-WIT1 with the nuclear envelope. Significantly, WPP1 and WPP2 show the same activity. A WPP1 mutant with reduced affinity for GFP-WIT1 fails to decrease its aggregation. While the WPP-domain proteins act on a region of WIT1 containing the coiled-coil domain, HSC70-1 additionally acts on the C-terminal transmembrane domain. Taken together, our data suggest that both HSC70-1 and the WPP-domain proteins play a role in facilitating WIT1 nuclear envelope targeting, which is, to our knowledge, the first described in planta activity for the WPP-domain proteins.

Genetic engineering for heat tolerance in plants

High temperature tolerance has been genetically engineered in plants mainly by over-expressing the heat shock protein genes or indirectly by altering levels of heat shock transcription factor proteins. Apart from heat shock proteins, thermotolerance has also been altered by elevating levels of osmolytes, increasing levels of cell detoxification enzymes and through altering membrane fluidity. It is suggested that Hsps may be directly implicated in thermotolerance as agents that minimize damage to cell proteins. The other three above approaches leading to thermotolerance in transgenic experiments though operate in their own specific ways but indirectly might be aiding in creation of more reductive and energy-rich cellular environment, thereby minimizing the accumulation of damaged proteins. Intervention in protein metabolism such that accumulation of damaged proteins is minimized thus appears to be the main target for genetically-engineering crops against high temperature stress.

Four members of the HSP101 gene family are differently regulated in Triticum durum Desf

Heat shock proteins play an essential role in preventing deleterious effects of high temperatures. In many plants, HSP101 has a central role in heat stress survival. We report the isolation and characterization of four cDNAs corresponding to different members of the durum wheat HSP101 gene family. Expression analysis revealed differences in their induction. Accordingly, durum wheat HSP101 genes are differently regulated, therefore having distinct roles in stress response and thermotolerance acquisition. These findings are important for further dissection of the molecular mechanisms underlying the stress response and for understanding the functions of the HSP101 family members. This information could be important for the exploitation of specific alleles in marker assisted selection for abiotic stress resistance.

Transactivation of protein expression by rice HSP101 in planta and using Hsp101 as a selection marker for transformation

Plant HSP101 has dual activities, first, in conferring thermotolerance, and secondly, in serving as a translational activator. In this study, we introduced Oryza sativa Hsp101 (osHsp101) cDNA into tobacco by Agrobacterium-mediated transformation. Stable integration and expression of the transgene into the tobacco genome was demonstrated by Southern and Western blot analysis. Overexpression of osHSP101 had no noticeable effect on growth or development of the transgenic plants. Homozygous T(2) transgenic plants with overexpressed osHSP101 survived heat treatment better than untransformed control plants. In addition, taking advantage of conferring basal thermotolerance by plant HSP101, we were able to demonstrate the feasibility of using osHsp101 as a selection marker and select the transformants under high temperature in tobacco leaf disc transformation mediated by Agrobacterium. Furthermore, transgenic tobacco plants with overexpressed osHSP101 were able to enhance luciferase expression up to 2.9-fold more than untransformed plants in the progeny of reciprocally crossed with omega-luciferase reporter lines.

Molecular chaperones of the Hsp110 family act as nucleotide exchange factors of Hsp70s

Hsp70 molecular chaperones function in protein folding in a manner dependent on regulation by co-chaperones. Hsp40s increase the low intrinsic ATPase activity of Hsp70, and nucleotide exchange factors (NEFs) remove ADP after ATP hydrolysis, enabling a new Hsp70 interaction cycle with non-native protein substrate. Here, we show that members of the Hsp70-related Hsp110 family cooperate with Hsp70 in protein folding in the eukaryotic cytosol. Mammalian Hsp110 and the yeast homologues Sse1p/2p catalyze efficient nucleotide exchange on Hsp70 and its orthologue in Saccharomyces cerevisiae, Ssa1p, respectively. Moreover, Sse1p has the same effect on Ssb1p, a ribosome-associated isoform of Hsp70 in yeast. Mutational analysis revealed that the N-terminal ATPase domain and the ultimate C-terminus of Sse1p are required for nucleotide exchange activity. The Hsp110 homologues significantly increase the rate and yield of Hsp70-mediated re-folding of thermally denatured firefly luciferase in vitro. Similarly, deletion of SSE1 causes a firefly luciferase folding defect in yeast cells under heat stress in vivo. Our data indicate that Hsp110 proteins are important components of the eukaryotic Hsp70 machinery of protein folding.

The molecular chaperone Hsp104--a molecular machine for protein disaggregation

At the Cold Spring Harbor Meeting on 'Molecular Chaperones and the Heat Shock Response' in May 1996, Susan Lindquist presented evidence that a chaperone of yeast termed Hsp104, which her group had been investigating for several years, is able to dissolve protein aggregates (Glover, J.R., Lindquist, S., 1998. Hsp104, Hsp70, and Hsp40: a novel chaperone system that rescues previously aggregated proteins. Cell 94, 73-82). Among many of the participants this news stimulated reactions reaching from decided skepticism to utter disbelief because protein aggregation was widely considered to be an irreversible process. Several years and publications later, it is undeniable that Susan had been right. Hsp104 is an ATP dependent molecular machine that-in cooperation with Hsp70 and Hsp40-extracts polypeptide chains from protein aggregates and facilitates their refolding, although the molecular details of this process are still poorly understood. Meanwhile, close homologues of Hsp104 have been identified in bacteria (ClpB), in mitochondria (Hsp78), and in the cytosol of plants (Hsp101), but intriguingly not in the cytosol of animal cells (Mosser, D.D., Ho, S., Glover, J.R., 2004. Saccharomyces cerevisiae Hsp104 enhances the chaperone capacity of human cells and inhibits heat stress-induced proapoptotic signaling. Biochemistry 43, 8107-8115). Observations that Hsp104 plays an essential role in the maintenance of yeast prions (see review by James Shorter in this issue) have attracted even more attention to the molecular mechanism of this ATP dependent chaperone (Chernoff, Y.O., Lindquist, S.L., Ono, B., Inge-Vechtomov, S.G., Liebman, S.W., 1995. Role of the chaperone protein Hsp104 in propagation of the yeast prion-like factor [PSI+]. Science 268, 880-884).