Molecular chaperones and the centrosome. A role for TCP-1 in microtubule nucleation

Identification and subcellular localization analysis of CCTα in microsporidian Nosema bombycis

CCT is a chaperonin which is widely present in eukaryotic cells and mainly involves in the folding and assembly of cytoskeletal proteins β-tubulin and actin. The alpha subunit of CCT(CCTα) plays a pivotal role in the folding and assembly of cytoskeletal protein(s) as an individuals or complexes. In this study, we report cloning, characterization and expression of the CCTα of Nosema bombycis (NbCCTα) for the first time. The NbCCTα gene contains a complete ORF of 1629 bp in length that encodes a 542-amino acid polypeptide. The NbCCTα is 59.662 kDa molecular weight in size with an isoelectric point (pI) of 5.81, no signal peptide or transmembrane domain. The IFA results showed that the NbCCTα was co-localized with actin and β-tubulin in the cytoplasm, nucleus, nuclear membrane and plasma membrane of N. bombycis in the process of proliferation. qPCR analysis showed that the relative expression level of NbCCTα increased from 24 h to 96 h post-infection (hp.i) of N. bombycis, and reached the highest at 96 hp.i. The relative expression level of NbCCTα gene after RNAi was restrained at a low level from 48 hp.i to 96 hp.i. Knockdown of NbCCTα gene down-regulated the expression of Nbβ-tubulin and Nbactin genes. These results imply that NbCCTα may play an important role in the lifecycle of N. bombycis.

DNA damage as indicator of the environmental vulnerability of bats in Brazil's Caatinga drylands

Brazil's Caatinga drylands is under extensive environmental deterioration, with 38% of its natural cover already lost. There is a need for a better understanding of the effects of such degradation on Caatinga's rich and singular biota. Bats form a large part of this biota, and are pointed as good bioindicators. Here, we used the micronucleus test -an easy-to-use, accessible and cost-effective in vivo approach- to detect DNA damage in cells from bats of different species and feeding habits in three protected areas in the Caatinga, comparing them with samples from an industrial sugarcane plantation. We hypothesized that environmental disturbance would reflect in DNA damage, with lower levels of damage in the less disturbed protected areas. The frequency of micronucleated cells differed significantly between sites and feeding habits (carnivores > insectivores > frugivores > nectarivores > hematophagous) but did not differ between sexes. Alarmingly, the highest levels of DNA damage were in two strictly protected areas (Seridó and Raso da Catarina Ecological Stations). Glossophaga and Anoura were the genera with more damaged cells, and had, respectively, 1.48 and 3.53 times more micronucleated cells (average of 19.33 and 22.67 cells, respectively) than individuals from the same genera from the area with least damaged cells (average of 7.80 and 5.00 cells, respectively). Our analysis is a warning call for an in-depth investigation on the effects of both genotoxic contamination and environmental stressors on bats and other species in Brazil's Caatinga, including the role that historical human-induced processes -like the intense use of agrochemicals- may have had in the region.

Principal Postulates of Centrosomal Biology. Version 2020

The centrosome, which consists of two centrioles surrounded by pericentriolar material, is a unique structure that has retained its main features in organisms of various taxonomic groups from unicellular algae to mammals over one billion years of evolution. In addition to the most noticeable function of organizing the microtubule system in mitosis and interphase, the centrosome performs many other cell functions. In particular, centrioles are the basis for the formation of sensitive primary cilia and motile cilia and flagella. Another principal function of centrosomes is the concentration in one place of regulatory proteins responsible for the cell's progression along the cell cycle. Despite the existing exceptions, the functioning of the centrosome is subject to general principles, which are discussed in this review.

Proteomic identification and expression of oral apparatus constituents in cell regeneration of giant ciliate Stentor coeruleus (strain WHEL)

The giant ciliate Stentor coeruleus (S. coeruleus) is a suitable model organism for studying morphogenesis and regeneration at the single-cell level. It contains a prominent structure on the anterior end of the cell, known as the oral apparatus (OA). OA can be induced to shed by urea treatment and then new OA regenerates via a series of defined morphological events and the cell resumes normal feeding activity. We identified OA constituents in S. coeruleus by mass spectrometry. A total of 882 OA-associated proteins were identified; the homologs of 181 of these are known OA constituents in other organisms. The expression pattern of OA-associated genes during regeneration was investigated using single-cell transcriptome sequencing. The expression of most OA-associated genes was high during regeneration, indicating their stable expression after OA shedding. We also identified OA-associated differentially expressed genes that may be involved in regulating OA reconstruction. In summary, this study gives preliminary insight into the molecular basis of OA in S. coeruleus.

An iTRAQ Based Comparative Proteomic Profiling of Thermotolerant Saccharomyces cerevisiae JRC6 in Response to High Temperature Fermentation

Background:

Bioethanol derived from lignocellulosic biomass can supplement the ethanol supplies in a sustainable manner. However, the bioethanol production process is still not cost effective and researchers are looking for novel strategies like simultaneous saccharification fermentation to cut down the production cost. Thermotolerant yeast Saccharomyces cerevisiae JRC6 is reported to improve the fermentation efficiency under SSF. However, the mechanism of thermotolerance of the strain is unknown which is important for developing more robust yeast strains for simultaneous saccharification and fermentation.

Objective:

To identify proteomic changes responsible for imparting thermotolerance by iTRAQ based profiling of Saccharomyces cerevisiae JRC6 by growing at optimum (30°C) and high temperature (40°C). Methods: iTRAQ labeling followed by electrospray ionization based tandem mass spectrometry using SCIEX 5600 Triple-TOF Mass Spectrometer (MS).

Methods:

iTRAQ labeling followed by electrospray ionization based tandem mass spectrometry using SCIEX 5600 Triple-TOF Mass Spectrometer (MS).

Results:

A total of 582 proteins involved in heat shock, metabolism, biosynthesis, transport of biomolecules, cell division, etc. were identified. Cells grown at 40°C showed many-fold increase in the expression for many proteins involved in different functions specially biosynthesis, heat stress and metabolism. At 40°C heat shock proteins (78), prefoldin subunit (6), DNA binding protein SNT1, J type co-chaperone JAC1, elongation factor 1-β, glutathione synthase, malate synthase (2), purine biosynthesis protein ADE17, SSD1 protein, alcohol dehydrogenase 1, 3, 60S ribosomal protein L35-B, mitochondrial import protein MAS5 and many other proteins were significantly upregulated.

Conclusion:

The iTRAQ analysis revealed many heat shock proteins and heat stable alcohol dehydrogenases which can be exploited to develop a more robust yeast strain suitable for simultaneous saccharification and fermentation or consolidated bioprocessing.

Changes of hippocampus proteomic profiles after blueberry extracts supplementation in APP/PS1 transgenic mice

Objective: To examine protein changes in the hippocampus of APP/PS1 transgenic mice after blueberry extracts (BB) intervention.Methods: Eight APP/PS1 transgenic mice were randomly assigned to Alzheimer's disease (AD)+BB group (n=4) and AD+control group (n=4). After a 16-week treatment, 2-DE and MALDI-TOF-MS were used to compare the proteomic profiles of the hippocampus in the two groups and Western blot was used to confirm the important differentially expressed proteins.Results: Twelve proteins were differentially expressed between the two groups. Nine of them were identified. Cytochrome b-c1 complex subunit 6, beta-actin, dynamin 1, and heat shock cognate 71 were up-regulated in AD+BB group, while a-enolase, stress-induced-phosphoprotein 1, malate dehydrogenase (MDH), MDH 1, and T-complex protein 1 subunit beta were down-regulated, respectively. Importantly, some of the identified proteins (e.g. dynamin 1) are known to be involved in cognitive impairment. Western blot analysis of hippocampus dynamin 1 expression confirmed the proteomic findings.Conclusions: The consumption of BB modulates the expression of proteins that are linked to the improvements of cognitive dysfunction in hippocampus of APP/PS1 transgenic mice.

The Centrosome, a Multitalented Renaissance Organelle

The centrosome acts as a microtubule-organizing center (MTOC) from the G₁ to G₂ phases of the cell cycle; it can mature into a spindle pole during mitosis and/or transition into a cilium by elongating microtubules (MTs) from the basal body on cell differentiation or cell cycle arrest. New studies hint that the centrosome functions in more than MT organization. For instance, it has recently been shown that a specific substructure of the centrosome-the mother centriole appendages-are required for the recycling of endosomes back to the plasma membrane. This alone could have important implications for a renaissance in our understanding of the development of primary cilia, endosome recycling, and the immune response. Here, we review newly identified roles for the centrosome in directing membrane traffic, the immunological synapse, and the stress response.

Revisiting the tubulin folding pathway: new roles in centrosomes and cilia

Centrosomes and cilia are critical eukaryotic organelles which have been in the spotlight in recent years given their implication in a myriad of cellular and developmental processes. Despite their recognized importance and intense study, there are still many open questions about their biogenesis and function. In the present article, we review the existing data concerning members of the tubulin folding pathway and related proteins, which have been identified at centrosomes and cilia and were shown to have unexpected roles in these structures.

Direct evidence for intracellular anterograde co-transport of M-PMV Gag and Env on microtubules

The intracellular transport of Mason-Pfizer monkey virus (M-PMV) assembled capsids from the pericentriolar region to the plasma membrane (PM) requires trafficking of envelope glycoprotein (Env) to the assembly site via the recycling endosome. However, it is unclear if Env-containing vesicles play a direct role in trafficking capsids to the PM. Using live cell microscopy, we demonstrate, for the first time, anterograde co-transport of Gag and Env. Nocodazole disruption of microtubules had differential effects on Gag and Env trafficking, with pulse-chase assays showing a delayed release of Env-deficient virions. Particle tracking demonstrated an initial loss of linear movement of GFP-tagged capsids and mCherry-tagged Env, followed by renewed movement of Gag but not Env at 4h post-treatment. Thus, while delayed capsid trafficking can occur in the absence of microtubules, efficient anterograde transport of capsids appears to be mediated by microtubule-associated Env-containing vesicles.

Genes involved in centrosome-independent mitotic spindle assembly in Drosophila S2 cells

Animal mitotic spindle assembly relies on centrosome-dependent and centrosome-independent mechanisms, but their relative contributions remain unknown. Here, we investigated the molecular basis of the centrosome-independent spindle assembly pathway by performing a whole-genome RNAi screen in Drosophila S2 cells lacking functional centrosomes. This screen identified 197 genes involved in acentrosomal spindle assembly, eight of which had no previously described mitotic phenotypes and produced defective and/or short spindles. All 197 genes also produced RNAi phenotypes when centrosomes were present, indicating that none were entirely selective for the acentrosomal pathway. However, a subset of genes produced a selective defect in pole focusing when centrosomes were absent, suggesting that centrosomes compensate for this shape defect. Another subset of genes was specifically associated with the formation of multipolar spindles only when centrosomes were present. We further show that the chromosomal passenger complex orchestrates multiple centrosome-independent processes required for mitotic spindle assembly/maintenance. On the other hand, despite the formation of a chromosome-enriched RanGTP gradient, S2 cells depleted of RCC1, the guanine-nucleotide exchange factor for Ran on chromosomes, established functional bipolar spindles. Finally, we show that cells without functional centrosomes have a delay in chromosome congression and anaphase onset, which can be explained by the lack of polar ejection forces. Overall, these findings establish the constitutive nature of a centrosome-independent spindle assembly program and how this program is adapted to the presence/absence of centrosomes in animal somatic cells.

Proteomic analysis of Fusarium oxysporum f. sp. cubense tropical race 4-inoculated response to Fusarium wilts in the banana root cells

BACKGROUND

Fusarium wilt of banana is one of the most destructive diseases in the world. This disease has caused heavy losses in major banana production areas. Except for molecular breeding methods based on plant defense mechanisms, effective methods to control the disease are still lacking. Dynamic changes in defense mechanisms between susceptible, moderately resistant, and highly resistant banana and Fusarium oxysporum f. sp. cubense tropical race 4 (Foc4) at the protein level remain unknown. This research reports the proteomic profile of three banana cultivars in response to Foc4 and transcriptional levels correlated with their sequences for the design of disease control strategies by molecular breeding.

RESULTS

Thirty-eight differentially expressed proteins were identified to function in cell metabolism. Most of these proteins were positively regulated after Foc4 inoculation. These differentially regulated proteins were found to have important functions in banana defense response. Functional categories implicated that these proteins were associated with pathogenesis-related (PR) response; isoflavonoid, flavonoid, and anthocyanin syntheses; cell wall strengthening; cell polarization; reactive oxygen species production and scavenging; jasmonic acid-, abscisic acid-, and auxin-mediated signaling conduction; molecular chaperones; energy; and primary metabolism. By comparing the protein profiles of resistant and susceptible banana cultivars, many proteins showed obvious distinction in their defense mechanism functions. PR proteins in susceptible 'Brazil' were mainly involved in defense. The proteins related to PR response, cell wall strengthening and antifungal compound synthesis in moderately resistant 'Nongke No.1' were mainly involved in defense. The proteins related to PR response, cell wall strengthening, and antifungal compound synthesis in highly resistant 'Yueyoukang I' were mainly involved in defense. 12 differentially regulated genes were selected to validate through quantitative real time PCR method. Quantitative RT-PCR analyses of these selected genes corroborate with their respective protein abundance after pathogen infection.

CONCLUSIONS

This report is the first to use proteomic profiling to study the molecular mechanism of banana roots infected with Foc4. The differentially regulated proteins involved in different defense pathways are likely associated with different resistant levels of the three banana cultivars.

Regulation of nuclear factor κB (NF-κB) transcriptional activity via p65 acetylation by the chaperonin containing TCP1 (CCT)

The NF-κB family member p65 is central to inflammation and immunity. The purpose of this study was to identify and characterize evolutionary conserved genes modulating p65 transcriptional activity. Using an RNAi screening approach, we identified chaperonin containing TCP1 subunit η (CCTη) as a regulator of Drosophila NF-κB proteins, Dorsal and Dorsal-related immunity factor (Dif). CCTη was also found to regulate NF-κB-driven transcription in mammalian cells, acting in a promoter-specific context, downstream of IκB kinase (IKK). CCTη knockdown repressed IκBα and CXCL2/MIP2 transcription during the early phase of NF-κB activation while impairing the termination of CCL5/RANTES and CXCL10/IP10 transcription. The latter effect was associated with increased DNA binding and reduced p65 acetylation, presumably by altering the activity of histone acetyltransferase CREB-binding protein (CBP). We identified p65 lysines (K) 122 and 123 as target residues mediating the CCTη-driven termination of NF-κB-dependent transcription. We propose that CCTη regulates NF-κB activity in a manner that resolves inflammation.

Proteomics reveals a switch in CDK1-associated proteins upon M-phase exit during the Xenopus laevis oocyte to embryo transition

Cyclin-dependent kinase 1 (CDK1) is a major M-phase kinase which requires the binding to a regulatory protein, Cyclin B, to be active. CDK1/Cyclin B complex is called M-phase promoting factor (MPF) for its key role in controlling both meiotic and mitotic M-phase of the cell cycle. CDK1 inactivation is necessary for oocyte activation and initiation of embryo development. This complex process requires both Cyclin B polyubiquitination and proteosomal degradation via the ubiquitin-conjugation pathway, followed by the dephosphorylation of the monomeric CDK1 on Thr161. Previous proteomic analyses revealed a number of CDK1-associated proteins in human HeLa cells. It is, however, unknown whether specific partners are involved in CDK1 inactivation upon M-phase exit. To better understand CDK1 regulation during MII-arrest and oocyte activation, we immunoprecipitated (IPed) CDK1 together with its associated proteins from M-phase-arrested and M-phase-exiting Xenopus laevis oocytes. A mass spectrometry (MS) analysis revealed a number of new putative CDK1 partners. Most importantly, the composition of the CDK1-associated complex changed rapidly during M-phase exit. Additionally, an analysis of CDK1 complexes precipitated with beads covered with p9 protein, a fission yeast suc1 homologue well known for its high affinity for CDKs, was performed to identify the most abundant proteins associated with CDK1. The screen was auto-validated by identification of: (i) two forms of CDK1: Cdc2A and B, (ii) a set of Cyclins B with clearly diminishing number of peptides identified upon M-phase exit, (iii) a number of known CDK1 substrates (e.g. peroxiredoxine) and partners (e.g. HSPA8, a member of the HSP70 family) both in IP and in p9 precipitated pellets. In IP samples we also identified chaperones, which can modulate CDK1 three-dimensional structure, as well as calcineurin, a protein necessary for successful oocyte activation. These results shed a new light on CDK1 regulation via a dynamic change in the composition of the protein complex upon M-phase exit and the oocyte to embryo transition.

Proteomic analysis of phosphotyrosyl proteins in human embryonic stem cell-derived neural stem cells

Phosphorylation can reveal essential cell functions, such as cell differentiation, signal transduction, metabolic maintenance and cell division. The aim of this study was to investigate phosphorylated protein expression changes during neuronal lineage differentiation from hESCs. To measure the phosphorylated protein expression change during neuronal differentiation, we performed a comparative phosphoproteome analysis using 2-DE after MALDI-TOF MS and an MS/MS protein identification method, making a comparison between neural lineage differentiating cells and normal embryoid bodies (EBs) differentiated from human embryonic stem cells (hESCs) and profiling constituent phosphorylated proteins. Of 36 differentially expressed protein spots, 12 spots were shown to be up-regulated in differentiating neural cells. Specifically, the 7 up-regulated proteins of the 12 have potential roles in neuronal differentiation or neuronal damage recovery, including ACTB, heterogeneous nuclear ribonucleoprotein A2B1 (hnRNP A2B1), heterogeneous nuclear ribonucleoprotein L (hnRNP L), SET, chaperonin-containing TCP-1, vimentin and voltage-dependent anion channel protein 1 (VDAC1). These proteins are discussed further below.

Differential expression and redox proteomics analyses of an Alzheimer disease transgenic mouse model: effects of the amyloid-β peptide of amyloid precursor protein

Among the pathological factors known to be associated with Alzheimer disease (AD), oxidative stress induced by the amyloid-β peptide (Aβ) has been demonstrated to play a key role in human brain and animal models of AD. Recently, we reported elevated levels of oxidative damage in the brain of a transgenic (Tg) AD mouse model with Swedish and Indiana familial AD mutations in human amyloid precursor protein (APP) [PDAPP mice, line J20], as evidenced by increased levels of protein carbonyls, 3-nitrotyrosine, and protein-bound 4-hydroxy-2-nonenal. This oxidative damage was dependent on the methionine 35 residue within the Aβ peptide. Further insight into the molecular pathways affected in this Tg model of AD may be gained with discovery-based proteomics studies; therefore, two-dimensional gel-based expression proteomics was performed to compare differences in brain protein levels of J20 Tg mice with non-transgenic (NTg) littermate controls. Based on our studies, we identified six proteins that had significantly increased levels in J20 Tg relative to NTg mice: calcineurin subunit B type 1, ρ GDP-dissociation inhibitor 1, T-complex protein 1 subunit α A, α-enolase, peptidyl-prolyl cis-trans isomerase (Pin-1), and ATP synthase subunit α mitochondrial. Several of these proteins have previously been implicated in in vitro and in vivo models and subjects with AD. Additionally, using redox proteomics analyses we identified two oxidatively-modified proteins: phosphatidylethanolamine-binding protein 1 and Pin-1 with decreased levels of protein 3-nitrotyrosine in J20 Tg mice relative to NTg. Western blotting and immunoprecipitation analyses were used to validate proteomics results. Overall, these studies provide information about changes in the brain proteome as a result of Aβ deposition and clues with which to further direct studies on elucidating AD pathogenesis.

BBS6, BBS10, and BBS12 form a complex with CCT/TRiC family chaperonins and mediate BBSome assembly

Bardet-Biedl syndrome (BBS) is a human genetic disorder resulting in obesity, retinal degeneration, polydactyly, and nephropathy. Recent studies indicate that trafficking defects to the ciliary membrane are involved in this syndrome. Here, we show that a novel complex composed of three chaperonin-like BBS proteins (BBS6, BBS10, and BBS12) and CCT/TRiC family chaperonins mediates BBSome assembly, which transports vesicles to the cilia. Chaperonin-like BBS proteins interact with a subset of BBSome subunits and promote their association with CCT chaperonins. CCT activity is essential for BBSome assembly, and knockdown of CCT chaperonins in zebrafish results in BBS phenotypes. Many disease-causing mutations found in BBS6, BBS10, and BBS12 disrupt interactions among these BBS proteins. Our data demonstrate that BBS6, BBS10, and BBS12 are necessary for BBSome assembly, and that impaired BBSome assembly contributes to the etiology of BBS phenotypes associated with the loss of function of these three BBS genes.

Activities of the chaperonin containing TCP-1 (CCT): implications for cell cycle progression and cytoskeletal organisation

The chaperonin containing TCP-1 (CCT) is required for the production of native actin and tubulin and numerous other proteins, several of which are involved in cell cycle progression. The mechanistic details of how CCT acts upon its folding substrates are intriguing: whilst actin and tubulin bind in a sequence-specific manner, it is possible that some proteins could use CCT as a more general binding interface. Therefore, how CCT accommodates the folding requirements of its substrates, some of which are produced in a cell cycle-specific manner, is of great interest. The reliance of folding substrates upon CCT for the adoption of their native structures results in CCT activity having far-reaching implications for a vast array of cellular processes. For example, the dependency of the major cytoskeletal proteins actin and tubulin upon CCT results in CCT activity being linked to any cellular process that depends on the integrity of the microfilament and microtubule-based cytoskeletal systems.

Heat shock proteins in animal neoplasms and human tumours--a comparison

Heat shock proteins (HSPs) are implicated in all phases of cancer from proliferation, impaired apoptosis and sustained angiogenesis to invasion and metastasis. The presence of abnormal HSP levels in several human tumours suggests that these proteins could be used as diagnostic and/or prognostic markers, whilst the direct correlation between HSP expression and drug resistance in neoplastic tissues means they could also be used to predict cancer response to specific treatment. HSPs have also been successfully targeted in clinical trials modifying their expression or chaperone activity. Preliminary studies in veterinary medicine have also demonstrated the presence of altered HSP expression in neoplasms, and the study of carcinogenesis and the role of HSPs in animal models will surely be an additional source of information for clinical cancer research.

Centrosome and retroviruses: the dangerous liaisons

Centrosomes are the major microtubule organizing structures in vertebrate cells. They localize in close proximity to the nucleus for the duration of interphase and play major roles in numerous cell functions. Consequently, any deficiency in centrosome function or number may lead to genetic instability. Several viruses including retroviruses such as, Foamy Virus, HIV-1, JSRV, M-PMV and HTLV-1 have been shown to hamper centrosome functions for their own profit, but the outcomes are very different. Foamy viruses, HIV-1, JSRV, M-PMV and HTLV-1 use the cellular machinery to traffic towards the centrosome during early and/or late stages of the infection. In addition HIV-1 Vpr protein alters the cell-cycle regulation by hijacking centrosome functions. Enthrallingly, HTLV-1 Tax expression also targets the functions of the centrosome, and this event is correlated with centrosome amplification, aneuploidy and transformation.

Down-regulation of glutaminase C in human hepatocarcinoma cell by diphenylarsinic acid, a degradation product of chemical warfare agents

In a poisonous incident in Kamisu, Japan, it is understood that diphenylarsinic acid (DPAA) was a critical contaminant of ground water. Most patients showed dysfunction of the central nervous system. To understand the overall mechanism of DPAA toxicity and to gain some insight into the application of a remedy specific for intoxication, the molecular target must be clarified. As an approach, a high throughput analysis of cell proteins in cultured human hepatocarcinoma HpG2 exposed to DPAA was performed by two-dimensional electrophoresis (2-DE). Four proteins, which were up- and down-regulated by exposure of cultured HepG2 cells to DPAA, were identified. They were chaperonin containing TCP-1 (CCT) beta subunit, aldehyde dehydrogenase 1 (ALDH1), ribosomal protein P0 and glutaminase C (GAC). Of these, GAC was the only protein that was down-regulated by DPAA exposure, and cellular expression levels were reduced by DPAA in a concentration- and time-dependent manner. Decrease in cellular GAC levels was accompanied by decreased activity of the enzyme, phosphate-activated glutaminase (PAG). Decreased expression of GAC by DPAA was also observed in human cervical carcinoma HeLa and neuroblastoma SH-SY5Y cells. By contrast, no significant changes in GAC protein expression were observed when cells were incubated with arsenite [iAs (III)] and trivalent dimethylarsinous acid [DMA (III)]. In the central nervous system, GAC plays a role in the production of the neurotransmitter glutamic acid. Selective inhibition of GAC expression by DPAA may be a cause of dysfunction of glutamatergic neuronal transmission and the resultant neurological impairments.

Chaperone-mediated inhibition of tubulin self-assembly

Molecular chaperones are known to play an important role in facilitating the proper folding of many newly synthesized proteins. Here, we have shown that chaperone proteins exhibit another unique property to inhibit tubulin self-assembly efficiently. Chaperones tested include alpha-crystallin from bovine eye lenses, HSP16.3, HSP70 from Mycobacterium tuberculosis and alpha (s)-casein from milk. All of them inhibit polymerization in a dose-dependent manner independent of assembly inducers used. The critical concentration of MTP polymerization increases with increasing concentration of HSP16.3. Increase in chaperone concentration lowers the extent of polymerization and increases the lag time of self-assembly reaction. Although the addition of a chaperone at the early stage of elongation phase shows no effect on polymerization, the same concentration of chaperone inhibits polymerization completely when added before the initiation of polymerization. Bindings of HSP16.3 and alpha (s)-casein to tubulin have been confirmed using isothermal titration calorimetry. Affinity constants of tubulin are 5.3 xx 10(4) and 9.8 xx 10(5) M(-1) for HSP16.3 and alpha (s)-casein, respectively. Thermodynamic parameters indicate favourable entropy and enthalpy changes for both chaperones-tubulin interactions. Positive entropy change suggests that the interaction is hydrophobic in nature and desolvation occurring during formation of tubulin-chaperone complex. On the basis of thermodynamic data and observations made upon addition of chaperone at early elongation phase or before the initiation of polymerization, we hypothesize that chaperones bind tubulin at the protein-protein interaction site involved in the nucleation phase of self-assembly.

UXT is a novel centrosomal protein essential for cell viability

Ubiquitously expressed transcript (UXT) is a prefoldinlike protein that has been suggested to be involved in human tumorigenesis. Here, we have found that UXT is overexpressed in a number of human tumor tissues but not in the matching normal tissues. We demonstrate that UXT is located in human centrosomes and is associated with gamma-tubulin. In addition, overexpression of UXT disrupts centrosome structure. Furthermore, abrogation of UXT protein expression by small interfering RNA knockdown leads to cell death. Together, our findings suggest that UXT is a component of centrosome and is essential for cell viability. We propose that UXT may facilitate transformation by corrupting regulated centrosome functions.

Hsp70 protects mitotic cells against heat-induced centrosome damage and division abnormalities

The effect of heat shock on centrosomes has been mainly studied in interphase cells. Centrosomes play a key role in proper segregation of DNA during mitosis. However, the direct effect and consequences of heat shock on mitotic cells and a possible cellular defense system against proteotoxic stress during mitosis have not been described in detail. Here, we show that mild heat shock, applied during mitosis, causes loss of dynamitin/p50 antibody staining from centrosomes and kinetochores. In addition, it induces division errors in most cells and in the remaining cells progression through mitosis is delayed. Expression of heat shock protein (Hsp)70 protects against most heat-induced division abnormalities. On heat shock, Hsp70 is rapidly recruited to mitotic centrosomes and normal progression through mitosis is observed immediately after release of Hsp70 from centrosomes. In addition, Hsp70 expression coincides with restoration of dynamitin/p50 antibody staining at centrosomes but not at kinetochores. Our data show that during mitosis, centrosomes are particularly affected resulting in abnormal mitosis. Hsp70 is sufficient to protect against most division abnormalities, demonstrating the involvement of Hsp70 in a repair mechanism of heat-damaged mitotic centrosomes.

A comparative analysis of αA- and αB-crystallin expression during the cell cycle in primary mouse lens epithelial cultures

AlphaA- and alphaB-crystallins are small heat shock proteins and molecular chaperones that prevent non-specific aggregation of denaturing proteins. Previous work in our laboratory has shown that lens epithelial cells derived from alphaA-/- mice exhibit slower growth, whereas alphaB-/- lens epithelial cells hyperproliferate at a higher rate in culture [Andley et al., J. Biol. Chem. 273 (1998) 31252; FASEB J. 15 (2001) 221]. Although both have been implicated in apoptosis and cell proliferation, direct analysis of their expression during the cell cycle has not been investigated. This study was undertaken to define the expression levels of alphaA and alphaB-crystallins during the cell cycle. Primary lens epithelial cell cultures derived from wild type mice were synchronized by serum starvation, and pulsed with bromodeoxyuridine (BrdU) at different times after re-stimulation with serum. Dual parameter flow cytometric studies with BrdU and propidium iodide (PI)-labeled cells were performed. Cells entered S phase 14 hr after serum re-stimulation. The duration of the S phase was 6 hr, and the total cell cycle transit time was between 24-27 hr. Enhanced expression of cyclin A, a protein essential for DNA synthesis was used as an additional marker to define the initiation of the S phase. Immunoblotting analysis demonstrated that the expression of alphaA and alphaB-crystallin was up to 10-fold higher in cells synchronized in G0 phase than in G1 phase. The levels of the proteins increased three-fold again as the cells entered the S phase and progressed to mitosis, but did not rise to the levels observed in G0 phase. This increase in expression of alphaA-crystallin resulted in part from enhanced synthesis during the S phase, as shown by an increase in [35S]methionine-labeling and immunoprecipitation of the radiolabeled alphaA-crystallin. The results were further confirmed by flow cytometric analysis using DNA content and alphaA-crystallin expression. The increase in alphaB-crystallin in S phase was paralleled by an increase in gene expression as shown by real-time RT-PCR analysis. These results demonstrate for the first time that in lens epithelial cells, alphaA and alphaB-crystallin levels are modulated during the cell cycle. Since the absence of alphaA and alphaB- crystallin in lens epithelial cells has been associated with disturbance of the tubulin cytoskeleton during mitosis, and with increased cell death or genomic instability, our results indicating that the alphaA- and alphaB-crystallin expression increases prior to mitosis are significant. The differential expression of these crystallins in the cell cycle may be important for optimal lens epithelial growth and lens transparency.

Large-scale identification of tubulin-binding proteins provides insight on subcellular trafficking, metabolic channeling, and signaling in plant cells

Microtubules play an essential role in the growth and development of plants and are known to be involved in regulating many cellular processes ranging from translation to signaling. In this article, we describe the proteomic characterization of Arabidopsis tubulin-binding proteins that were purified using tubulin affinity chromatography. Microtubule co-sedimentation assays indicated that most, if not all, of the proteins in the tubulin-binding protein fraction possessed microtubule-binding activity. Two-dimensional gel electrophoresis of the tubulin-binding protein fraction was performed, and 86 protein spots were excised and analyzed for protein identification. A total of 122 proteins were identified with high confidence using LC-MS/MS. These proteins were grouped into six categories based on their predicted functions: microtubule-associated proteins, translation factors, RNA-binding proteins, signaling proteins, metabolic enzymes, and proteins with other functions. Almost one-half of the proteins identified in this fraction were related to proteins that have previously been reported to interact with microtubules. This study represents the first large-scale proteomic identification of eukaryotic cytoskeleton-binding proteins, and provides insight on subcellular trafficking, metabolic channeling, and signaling in plant cells.

A subclass of myosin XI is associated with mitochondria, plastids, and the molecular chaperone subunit TCP-1? in maize

The role and regulation of specific plant myosins in cyclosis is not well understood. In the present report, an affinity-purified antibody generated against a conserved tail region of some class XI plant myosin isoforms was used for biochemical and immunofluorescence studies of Zea mays. Myosin XI co-localized with plastids and mitochondria but not with nuclei, the Golgi apparatus, endoplasmic reticulum, or peroxisomes. This suggests that myosin XI is involved in the motility of specific organelles. Myosin XI was more than 50% co-localized with tailless complex polypeptide-1alpha (TCP-1alpha) in tissue sections of mature tissues located more than 1.0 mm from the apex, and the two proteins co-eluted from gel filtration and ion exchange columns. On Western blots, TCP-1alpha isoforms showed a developmental shift from the youngest 5.0 mm of the root to more mature regions that were more than 10.0 mm from the apex. This developmental shift coincided with a higher percentage of myosin XI /TCP-1alpha co-localization, and faster degradation of myosin XI by serine protease. Our results suggest that class XI plant myosin requires TCP-1alpha for regulating folding or providing protection against denaturation.

Proteomic characterization of the human centrosome by protein correlation profiling

The centrosome is the major microtubule-organizing centre of animal cells and through its influence on the cytoskeleton is involved in cell shape, polarity and motility. It also has a crucial function in cell division because it determines the poles of the mitotic spindle that segregates duplicated chromosomes between dividing cells. Despite the importance of this organelle to cell biology and more than 100 years of study, many aspects of its function remain enigmatic and its structure and composition are still largely unknown. We performed a mass-spectrometry-based proteomic analysis of human centrosomes in the interphase of the cell cycle by quantitatively profiling hundreds of proteins across several centrifugation fractions. True centrosomal proteins were revealed by both correlation with already known centrosomal proteins and in vivo localization. We identified and validated 23 novel components and identified 41 likely candidates as well as the vast majority of the known centrosomal proteins in a large background of nonspecific proteins. Protein correlation profiling permits the analysis of any multiprotein complex that can be enriched by fractionation but not purified to homogeneity.

Subunits of the chaperonin CCT are associated with Tetrahymena microtubule structures and are involved in cilia biogenesis

The cytosolic chaperonin CCT is a heterooligomeric complex of about 900 kDa that mediates the folding of cytoskeletal proteins. We observed by indirect immunofluorescence that the Tetrahymena TpCCTalpha, TpCCTdelta, TpCCTepsilon, and TpCCTeta-subunits colocalize with tubulin in cilia, basal bodies, oral apparatus, and contractile vacuole pores. TpCCT-subunits localization was affected during reciliation. These findings combined with atomic force microscopy measurements in reciliating cells indicate that these proteins play a role during cilia biogenesis related to microtubule nucleation, tubulin transport, and/or axoneme assembly. The TpCCT-subunits were also found to be associated with cortex and cytoplasmic microtubules suggesting that they can act as microtubule-associated proteins. The TpCCTdelta being the only subunit found associated with the macronuclear envelope indicates that it has functions outside of the 900 kDa complex. Tetrahymena cytoplasm contains granular/globular-structures of TpCCT-subunits in close association with microtubule arrays. Studies of reciliation and with cycloheximide suggest that these structures may be sites of translation and folding. Combined biochemical techniques revealed that reciliation affects the oligomeric state of TpCCT-subunits being tubulin preferentially associated with smaller CCT oligomeric species in early stages of reciliation. Collectively, these findings indicate that the oligomeric state of CCT-subunits reflects the translation capacity of the cell and microtubules integrity.

The M-PMV cytoplasmic targeting-retention signal directs nascent Gag polypeptides to a pericentriolar region of the cell

Intracytoplasmic protein targeting in mammalian cells is critical for organelle function as well as virus assembly, but the signals that mediate it are poorly defined. We show here that Mason-Pfizer monkey virus specifically targets Gag precursor proteins to the pericentriolar region of the cytoplasm in a microtubule dependent process through interactions between a short peptide signal, known as the cytoplasmic targeting-retention signal, and the dynein/dynactin motor complex. The Gag molecules are concentrated in pericentriolar microdomains, where they assemble to form immature capsids. Depletion of Gag from this region by cycloheximide treatment, coupled with the presence of ribosomal clusters that are in close vicinity to the assembling capsids, suggests that the dominant N-terminal cytoplasmic targeting-retention signal functions in a cotranslational manner. Transport of the capsids out of the pericentriolar assembly site requires the env-gene product, and a functional vesicular transport system. A single point mutation that renders the cytoplasmic targeting-retention signal defective abrogates pericentriolar targeting of Gag molecules. Thus the previously defined cytoplasmic targeting-retention signal appears to act as a cotranslational intracellular targeting signal that concentrates Gag proteins at the centriole for assembly of capsids.

Hyperproliferation and p53 status of lens epithelial cells derived from alphaB-crystallin knockout mice

alphaB-Crystallin, a major protein of lens fiber cells, is a stress-induced chaperone expressed at low levels in the lens epithelium and numerous other tissues, and its expression is enhanced in certain pathological conditions. However, the function of alphaB in these tissues is not known. Lenses of alphaB-/- mice develop degeneration of specific skeletal muscles but do not develop cataracts. Recent work in our laboratory indicates that primary cultures of alphaB-/- lens epithelial cells demonstrate genomic instability and undergo hyperproliferation at a frequency 4 orders of magnitude greater than that predicted by spontaneous immortalization of rodent cells. We now demonstrate that the hyperproliferative alphaB-/- lens epithelial cells undergo phenotypic changes that include the appearance of the p53 protein as shown by immunoblot analysis. Sequence analysis showed a lack of mutations in the p53 coding region of hyperproliferative alphaB-/- cells. However, the reentry of hyperproliferative alphaB-/- cells into S phase and mitosis after DNA damage by gamma-irradiation were consistent with impaired p53 checkpoint function in these cells. The results demonstrate that expression of functionally impaired p53 is one of the factors that promote immortalization of lens epithelial cells derived from alphaB-/- mice. Fluorescence in situ hybridization using probes prepared from centromere-specific mouse P1 clones of chromosomes 1 and 9 demonstrated that the hyperproliferative alphaB-/- cells were 30% diploid and 70% tetraploid, whereas wild type cells were 83% diploid. Further evidence of genomic instability was obtained when the hyperproliferative alphaB-/- cells were labeled with anti-beta-tubulin antibodies. Examination of the hyperproliferative alphaB-/- mitotic profiles revealed the presence of cells that failed to round up for mitosis, or arrested in cytokinesis, and binucleated cells in which nuclear division had occurred without cell division. These results suggest that the stress protein and molecular chaperone alphaB-crystallin protects cells from acquiring impaired p53 protein and genomic instability.

Eukaryotic chaperonin containing T-complex polypeptide 1 interacts with filamentous actin and reduces the initial rate of actin polymerization in vitro

We have previously observed that subunits of the chaperonin required for actin production (type-II chaperonin containing T-complex polypeptide 1 [CCT]) localize at sites of microfilament assembly. In this article we extend this observation by showing that substantially substoichiometric CCT reduces the initial rate of pyrene-labeled actin polymerization in vitro where eubacterial chaperonin GroEL had no such effect. CCT subunits bound selectively to F-actin in cosedimentation assays, and CCT reduced elongation rates from both purified actin filament "seeds" and the short and stabilized, minus-end blocked filaments in erythrocyte membrane cytoskeletons. These observations suggest CCT might remain involved in biogenesis of the actin cytoskeleton, by acting at filament (+) ends, beyond its already well-established role in producing new actin monomers.

Slow axonal transport of the cytosolic chaperonin CCT with Hsc73 and actin in motor neurons

Molecular chaperones are well known for their role in facilitating the folding of nascent and newly synthesized proteins, but have other roles, including the assembly, translocation and renaturation of intracellular proteins. Axons are convenient tissues for the study of some of these other roles because they lack the capacity for significant protein synthesis. We examine the axonal transport of the cytosolic chaperonin containing T- complex polypeptide 1 (CCT) by labeling lumbar motor neurons with [35S]methionine and examining sciatic nerve proteins by 2-D gel electrophoresis and immunoblotting. All CCT subunits identifiable with specific antibodies, namely CCTalpha, CCTbeta, CCTgamma and CCTepsilon/CCTtheta; (the latter two subunits colocalized in analyses of rat nerve samples), appeared to be labeled in "slow component b" of axonal transport along with the molecular chaperone Hsc73 and actin, a major folding substrate for CCT. Our results are consistent with molecular chaperones having a post-translational role in maintaining the native form of actin during its slow transport to the axon terminal and ensuring its correct assembly into microfilaments.

HSP70 overexpression increases resistance of V79 cells to cytotoxicity of airborne pollutants, but does not protect the mitotic spindle against damage caused by airborne toxins

Exposure of Chinese hamster V79 cells to extracts of airborne pollutants induced formation of multipolar or incomplete mitotic spindles. To find out whether overexpression of the HSP70 chaperone protein could protect spindles against airborne toxins we constructed V79 cells stably transfected with an expression vector containing rat heat-inducible hsp70.1 gene under the control of a constitutive CMV promoter. When cells were incubated with extracts of airborne pollutants (5-20 microg/ml) no protective effect of the HSP70 protein against mitotic spindle damage was observed. Moreover, at 20 microg/ml of extracts of airborne toxins the frequency of mitotic malformations was even higher in HSP70-overexpressing cells than in control ones. Extracts of airborne pollutants of 50 microg/ml blocked the formation of mitotic figures both in control and HSP70-overexpressing cells and led to destruction of cell nuclei. However, the HSP70-overproducing cells exhibited higher survival rates when exposed to heat shock and airborne toxins than the control ones, as determined by MTT assay. This suggests that HSP70 overexpression-a frequent feature of cancer cells-should be considered as a factor facilitating survival of cells with damaged mitotic spindles and aberrantly segregated chromosomes.

Tektin B1 demonstrates flagellar localization in human sperm

The human flagellar protein tektin B1 (h-tekB1) in human sperm was cloned, and its sequence and subcellular location were determined. Human sperm proteins were separated by 2-dimensional electrophoresis, and a resolved protein spot of 54 kDa with an isoelectric point (pI) of 5.3 was removed from the gel, trypsinized, and microsequenced by tandem mass spectrometry. The resulting peptides did not match any protein in the (then current) protein databases. Degenerate oligonucleotides based on the microsequences were used with a polymerase chain reaction to amplify a partial cDNA clone from human testis poly(A)(+) mRNA, and subsequently a full-length 1.5-kilobase (kb) clone (GenBank AF054910) was obtained from a testis cDNA library. The open reading frame encoded a 430-amino acid protein with 47% homology to the sea urchin tektin B1. Hybridization of labeled h-tekB1 cDNA to a multiple-tissue Northern blot demonstrated a transcript of 1.7 kb in human testis, and a multiple tissue dot-blot demonstrated high levels of expression in testis, trachea, and lung, intermediate levels in fetal brain and appendix, and low levels in ovary, pituitary, and fetal kidney. Rat polyclonal serum generated against a recombinant h-tekB1 demonstrated 3 h-tekB1 isoforms of pI 5.25, 5.5, and 5.35 at 53.5 kDa on a 2-dimensional Western blot of human sperm proteins. Immunofluorescent studies localized h-tekB1 to the principal piece of human sperm, but the endpiece was unstained.

Differential expression of molecular chaperones in brain of patients with Down syndrome

Heat shock proteins (HSPs) in their molecular capacity as chaperones have been reported to regulate the apoptotic pathway and also play a critical role in protein conformational diseases such as Alzheimer's disease (AD). As all Down syndrome (DS) brains display AD-like neuropathology, neuronal loss in DS was shown to be mediated by apoptosis. We decided to investigate the expression patterns of HSPs in seven brain regions of adults with DS using two-dimensional polyacrylamide gel electrophoresis (2-DE). Following 2-DE, approximately 120 protein spots were successfully identified by matrix-assisted laser desorption/ionization--mass spectrometry (MALDI-MS) followed by quantification of the identified proteins. We unambiguously identified and quantified nine different chaperone proteins. Accordingly, all but three chaperone proteins did exhibit a significant change in expression. HSP 70 RY, heat shock cognate (HSC) 71 and glucose-regulated protein (GRP) 75 showed a significant decrease (P < 0.05) in DS temporal cortex whereas HSP 70.1 and GRP 78 were significantly increased (P<0.05) in cerebellum. Whilst T-complex 1 (TCP-1) epsilon subunit showed a significant decrease (P< 0.05) in parietal cortex, a similar extent of increase (P<0.05) as that observed in cerebellum was obtained in parietal levels of GRP 78. Alpha-crystallin B, HSP 60 and GRP 94 did not show any detectable changes in expression patterns. This report presents the first approach to quantify nine different chaperones simultaneously at the protein level in different brain regions and provides evidence for aberrant chaperone expression patterns in DS. The relevance of this aberrant expression patterns are discussed in relation to the biochemical and neuropathological abnormalities in DS brain.

A constitutive 70 kDa heat-shock protein is localized on the fibres of spindles and asters at metaphase in an ATP-dependent manner: a new chaperone role is proposed

In the present study, double immunofluorescence and immunoblot analysis have been used to show that centrosomes, isolated from Paracentrotus lividus sea urchin embryos at the first mitotic metaphase, contain the constitutive chaperone, heat-shock protein (HSP) 70. More specifically, we demonstrate that centrosomes contain only the HSP70-d isoform, which is one of the four isoforms identified in P. lividus. We also provide evidence that p34(cell division control kinase-2) and t complex polypeptide-1 (TCP-1) alpha, a subunit of the TCP-1 complex, are localized on the centrosomes. Furthermore, inhibition of TCP-1 in vivo, via microinjecting an anti-(TCP-1 alpha) antibody into P. lividus eggs before fertilization, either impaired mitosis or induced severe malformations in more than 50% of embryos. In addition, we have isolated the whole mitotic apparatus and shown that HSP70 localizes on the fibres of spindles and asters, and binds them in an ATP-dependent manner. These observations suggest that HSP70 has a chaperone role in assisting the TCP-1 complex in tubulin folding, when localized on centrosomes, and during the assembling and disassembling of the mitotic apparatus, when localized on the fibres of spindles and asters.

AlphaB-crystallin phosphorylated at Ser-59 is localized in centrosomes and midbodies during mitosis

We have reported that the three serine residues in alphaB-crystallin are phosphorylated under various stress conditions. We prepared affinity-purified antibodies recognizing each of the phosphorylated serine residues (Ser-19, Ser-45, and Ser-59, respectively) in alphaB-crystallin with peptides (p19S, p45S, or p59S) that contained the corresponding phosphorylated serine residue. Immunocytochemically anti-p45S antibodies stained the cytoplasm of mitotic cells (J. Biol. Chem. 273, 28,346-28,354). We have now found that the anti-p59S antibodies recognize centrosomes and midbodies of dividing cells. alphaB-Crystallin was the only protein recognized by the anti-p59S antibodies in Western blot analyses of isolated centrosome fractions. alphaB-Crystallin phosphorylated at Ser-59 was localized at the microtubule organizing centers by means of double staining with anti-beta-tubulin antibody in aster formation analysis and was co-localized with gamma-tubulin in centrosomes. Gamma-Tubulin was co-immunoprecipitated with alphaB-crystallin in U373 glioma cell extracts. On the other hand, the location of the phosphorylated alphaB-crystallin deviated from that of alpha-tubulin or gamma-tubulin in the midbody region. Taken together with the evidences that several chaperones are distributed to centrosomes, these results suggest that alphaB-crystallin as a chaperone might be also involved in the quality control of proteins.

Identification of Tetrahymena hsp60 as a 14-nm filament protein/citrate synthase-binding protein and its possible involvement in the oral apparatus formation

BACKGROUND

Tetrahymena 14-nm filament protein (14FP) is bifunctional, with roles as a citrate synthase in mitochondria and as a cytoskeletal protein in nuclear events during fertilization and in oral morphogenesis. In this study, to further our understanding of the bifunctional property of 14FP, we attempted to screen 14FP-binding proteins using affinity column chromatography.

RESULTS

Through the screening of 14FP-binding proteins using 14FP-affinity chromatography, we detected 65 kDa and 70 kDa proteins that bound to 14FP in an ATP dependent manner. From the N-terminal amino acid sequence, these proteins were identified as the Tetrahymena mitochondrial chaperones, hsp60 and mthsp70, respectively. Tetrahymena hsp60 was recognized with a monoclonal antibody raised against human hsp60. Immunofluorescence and immunoelectron microscopy using the monoclonal antibody showed that Tetrahymena hsp60 was localized to mitochondria. Moreover, Tetrahymena hsp60 was also present at extramitochondrial sites including basal bodies of cilia and oral apparatus, and particularly at the developing oral apparatus during cell division.

CONCLUSION

These results suggest that Tetrahymena hsp60 is localized in basal bodies and is involved in cortical patterning such as the formation of the oral apparatus as well as having a role in the folding of mitochondrial proteins in mitochondria.

Deranged expression of molecular chaperones in brains of patients with Alzheimer's disease

Alzheimer's disease (AD) is one of the disorders caused by protein conformational changes and recent studies have shown that several chaperone proteins are involved in this process. As information of chaperone expression in AD brain is limited, we aimed to study the expressional pattern of chaperones in several brain regions, as this may be essential to understand how folding defects can lead to disease. We studied the concomitant expressional patterns of molecular chaperones in seven brain regions of adults with AD using two-dimensional polyacrylamide gel electrophoresis (2-DE) and matrix-associated laser desorption ionization mass spectroscopy (MALDI-MS). We unambiguously identified and quantified nine different chaperone proteins. Six chaperone proteins, heat shock protein 60 (HSP 60), HSP 70 RY, heat shock cognate (HSC) 71, alpha crystallin B chain, glucose regulated protein (GRP) 75, and GRP 94 showed aberrant expressional patterns depending on brain region. HSP 70.1, GRP 78 and T-complex 1 (TCP-1) epsilon subunit did not show any significant expressional change. These findings are compatible with neuropathological and biochemical abnormalities in AD brain and this report presents the first approach to quantify nine different chaperones simultaneously at the protein level in individual AD brain regions providing evidence for the relevance of aberrant chaperone expression to AD neuropathology.

LIS1 regulates CNS lamination by interacting with mNudE, a central component of the centrosome

LIS1, a microtubule-associated protein, is required for neuronal migration, but the precise mechanism of LIS1 function is unknown. We identified a LIS1 interacting protein encoded by a mouse homolog of NUDE, a nuclear distribution gene in A. nidulans and a multicopy suppressor of the LIS1 homolog, NUDF. mNudE is located in the centrosome or microtubule organizing center (MTOC), and interacts with six different centrosomal proteins. Overexpression of mNudE dissociates gamma-tubulin from the centrosome and disrupts microtubule organization. Missense mutations that disrupt LIS1 function block LIS1-mNudE binding. Moreover, misexpression of the LIS1 binding domain of mNudE in Xenopus embryos disrupts the architecture and lamination of the CNS. Thus, LIS1-mNudE interactions may regulate neuronal migration through dynamic reorganization of the MTOC.

Characterization of protein and transcript levels of the chaperonin containing tailless complex protein-1 and tubulin during light-regulated growth of oat seedlings

In grass seedlings the network of cortical microtubules is reorganized during light-dependent growth of coleoptiles and mesocotyls. We investigated the effects of light-dependent growth on the relative steady-state levels of the mRNAs and protein levels of alpha-tubulin and the epsilon-subunit of the chaperonin containing tailless complex protein-1 in oat (Avena sativa) coleoptiles, which were grown in different light conditions to establish different growth responses. The soluble pools of the epsilon-subunit of the chaperonin containing tailless complex protein-1 and alpha-tubulin decreased in nonelongating coleoptiles, suggesting that the dynamics of the light-regulated soluble pool reflect the processes occurring during reorganization of cortical microtubules. The shifts in pool sizes are discussed in relation to the machinery that controls the dynamic structure of cortical microtubules in plant cells.

Type I muscle atrophy caused by microgravity-induced decrease of myocyte enhancer factor 2C (MEF2C) protein expression

To investigate the molecular mechanisms of muscle atrophy under microgravity, the paraspinal muscles of rats after 14 days spaceflight and those of ground-based controls were examined. In the microgravitational environment, expressions of 42 genes changed, and the expressions of heat shock protein 70 and t complex polypeptide 1 increased. In Northern blotting, myocyte-specific enhancer binding factor 2C (MEF2C) and MEF2C-related genes including aldolase A and muscle ankyrin decreased. After 9 days ground recovery, expression of MEF2C increased and it was located mainly on the satellite cells in the muscle regeneration state. MEF2C could be a key transcriptional factor for skeletal muscle atrophy and regeneration under microgravity.

Integrating centrosome structure with protein composition and function in animal cells

The centrosome found in animal cells is a complex and dynamic organelle that functions as the major microtubule organizing center. Structural studies over the past several decades have defined the primary structural features of the centrosome but recent studies are now beginning to reveal structural detail previously unknown. Concurrent with these studies has been an explosion in the identification of the proteins that reside within the centrosome. Our growing understanding of how protein composition integrates with centrosome structure and hence with function is the focus of this review.

Hsp90 is a core centrosomal component and is required at different stages of the centrosome cycle in Drosophila and vertebrates

To determine the molecular composition of the centrosome of a higher eukaryote, we carried out a systematic nano-electrospray tandem or MALDI mass spectrometry analysis of the polypeptides present in highly enriched preparations of immunoisolated Drosophila centrosomes. One of the proteins identified is Hsp83, a member of the highly conserved Hsp90 family including chaperones known to maintain the activity of many proteins but suspected to have other essential, unidentified functions. We have found that a fraction of the total Hsp90 pool is localized at the centrosome throughout the cell cycle at different stages of development in Drosophila and vertebrates. This association between Hsp90 and the centrosome can be observed in purified centrosomes and after treatment with microtubule depolymerizing drugs, two criteria normally used to define core centrosomal components. Disruption of Hsp90 function by mutations in the Drosophila gene or treatment of mammalian cells with the Hsp90 inhibitor geldanamycin, results in abnormal centrosome separation and maturation, aberrant spindles and impaired chromosome segregation. This suggests that another role of Hsp90 might be to ensure proper centrosome function.

Molecular chaperones in cilia and flagella: implications for protein turnover

The mechanisms of protein incorporation and turnover in 9+2 ciliary axonemes are not known. Previous reports of an HSP70-related protein, first in Chlamydomonas flagella and then in sea urchin embryonic cilia, suggested a potential role in protein transport or incorporation. The present study further explores this and other chaperones in axonemes from a representative range of organisms. Two-dimensional gel electrophoresis proved identity between the sea urchin ciliary 78 kDa HSP and a constitutive cytoplasmic HSP70 cognate (pI = 5.71). When isolated flagella from mature sea urchin sperm were analyzed, the same total amount and distribution of 78 kDa protein as in cilia were found. Antigens of similar size were detected in ctenophore comb plate, molluscan gill, and rabbit tracheal cilia. Absent from sea urchin sperm flagella, TCP-1alpha was detected in sea urchin embryonic and rabbit tracheal cilia; the latter also contained HSP90, detected by two distinct antibodies. Tracheal cilia were shown to undergo axonemal protein turnover while tracheal cells mainly synthesized ciliary proteins. TCP-1alpha progressively appeared in regenerating embryonic cilia only as their growth slowed, suggesting a regulatory role in incorporation or turnover. These results demonstrate that chaperones are widely distributed ciliary and flagellar components, potentially related to axonemal protein dynamics.

Direct interaction of pericentrin with cytoplasmic dynein light intermediate chain contributes to mitotic spindle organization

Pericentrin is a conserved protein of the centrosome involved in microtubule organization. To better understand pericentrin function, we overexpressed the protein in somatic cells and assayed for changes in the composition and function of mitotic spindles and spindle poles. Spindles in pericentrin-overexpressing cells were disorganized and mispositioned, and chromosomes were misaligned and missegregated during cell division, giving rise to aneuploid cells. We unexpectedly found that levels of the molecular motor cytoplasmic dynein were dramatically reduced at spindle poles. Cytoplasmic dynein was diminished at kinetochores also, and the dynein-mediated organization of the Golgi complex was disrupted. Dynein coimmunoprecipitated with overexpressed pericentrin, suggesting that the motor was sequestered in the cytoplasm and was prevented from associating with its cellular targets. Immunoprecipitation of endogenous pericentrin also pulled down cytoplasmic dynein in untransfected cells. To define the basis for this interaction, pericentrin was coexpressed with cytoplasmic dynein heavy (DHCs), intermediate (DICs), and light intermediate (LICs) chains, and the dynamitin and p150(Glued) subunits of dynactin. Only the LICs coimmunoprecipitated with pericentrin. These results provide the first physiological role for LIC, and they suggest that a pericentrin-dynein interaction in vivo contributes to the assembly, organization, and function of centrosomes and mitotic spindles.

Constitutive hsp70 is essential to mitosis during early cleavage of Paracentrotus lividus embryos: the blockage of constitutive hsp70 impairs mitosis

Localization of constitutive hsp70 in eggs and early embryos of sea urchin Paracentrotus lividus is shown by means of in situ immunostaining. An accumulation of this protein is shown in the mitotic structures (asters, spindles and centrosomes). Microinjection of anti-hsp70 antibodies into eggs causes impairment of formation of mitotic structures and of cell division. This impairment goes from a complete mitotic block, to irregular mitotic apparatus formation with irregular cleavage, depending upon the antibody concentration. The localization of hsp70 after antibody microinjection is also described. Blockage of mitotic apparatus formation by nocodazole also blocks the concentration of hsp70 molecules observed in nontreated eggs. That the constitutive hsp70 plays a role in sea urchin mitosis is indicated.

Molecular characteristics of the centrosome

As an organizer of the microtubule cytoskeleton in animals, the centrosome has an important function. From the early light microscopic observation of the centrosome to examination by electron microscopy, the centrosome field is now in an era of molecular identification and precise functional analyses. Tables compiling centrosomal proteins and reviews on the centrosome are presented here and demonstrate how active the field is. However, despite this intense research activity, many classical questions are still unanswered. These include those regarding the precise function of centrioles, the mechanism of centrosome duplication and assembly, the origin of the centrosome, and the regulation and mechanism of the centrosomal microtubule nucleation activity. Fortunately, these questions are becoming elucidated based on experimental data discussed here. Given the fact that the centrosome is primarily a site of microtubule nucleation, special focus is placed on the process of microtubule nucleation and on the regulation of centrosomal microtubule nucleation capacity during the cell cycle and in some tissues.