Subcorneal colocalization of the small heat shock protein, hsp27, with keratins and proteins of the cornified cell envelope

BACKGROUND

hsp27 is a member of the small heat shock protein family. Its expression in epidermal keratinocytes in situ and in tissue culture correlates with differentiation. Experimental evidence points to the fact that hsp27 is a molecular chaperone and is involved in the regulation of cell growth and differentiation.

OBJECTIVES

To investigate whether epidermal hsp27 through its chaperone function plays a role in the assembly of keratin filaments and the cornified cell envelope.

METHODS

We performed double staining immunofluorescence and immunogold microscopy on normal human skin (n = 15). We analysed the colocalization of hsp27 with actin, keratins and proteins of the cornified cell envelope (loricrin, filaggrin, transglutaminase 1).

RESULTS

Actin staining did not reveal detectable colocalization with hsp27. For keratins, transglutaminase, loricrin and filaggrin colocalization was found in more than 60% of the samples. Colocalization was confined to a narrow subcorneal layer with varying patterns of expression. Electron microscopy revealed that loricrin and filaggrin colocalize with hsp27 indirectly through binding to intermediate filaments.

CONCLUSIONS

These results provide morphological evidence that in normal human skin hsp27 might act as a chaperone of cornification. Investigations of the molecular hsp27 interactions with the proteins of the cornified cell envelope are necessary to gain further insight into terminal keratinocyte differentiation and disorders of keratinization.

Up-regulation of Hsp27 plays a role in the resistance of human colon carcinoma HT29 cells to photooxidative stress

The Photofrin-resistant cell line (HT29-P14) was used in the present study to investigate the mechanism(s) involved in Photofrin-mediated photodynamic therapy (PDT). We compared gene expression profiles between the resistant cell line and its parental cell line (HT29) using DNA microarray analysis. A significant up-regulation of small heat shock protein 27 (Hsp27) was found in HT29-P14 cells. The elevated Hsp27 level may play an important role in the resistance of HT29-P14 to Photofrin-PDT. To test this hypothesis, we stably transfected HT29 cells with human Hsp27 complementary DNA. The potential role of Hsp27 in the resistance to PDT was examined in Hsp27-overexpressing cells. Stable trasnfected cells (H13) showed an increased survival after Photofrin-PDT, suggesting that the up-regulation of Hsp27 is related to the induced resistance to Photofrin-PDT. Phosphorylation of Hsp27 has been suggested to play an important role in cytoprotection. We have examined the phosphorylation activity of Hsp27 among the parental and resistant cells, as well as the overexpression cells. An elevated level of Hsp27 resulted in an increased ability of phosphorylation in both resistant and overexpressing cells after PDT. The activation of the phosphorylation of Hsp27 induced by PDT was not mediated by the p38 mitogen-activated protein kinase. These data suggest that Hsp27 may play an important role in mediating the adaptive response to Photofrin-PDT-induced oxidative stress and that the pathways leading to Hsp27 phosphorylation may contribute to the resistance of the cells to photooxidative damage.

Heat shock protein-27 protects human bronchial epithelial cells against oxidative stress-mediated apoptosis: possible implication in asthma

Inflammation of the human bronchial epithelium, as observed in asthmatics, is characterized by the selective death of the columnar epithelial cells, which desquamate from the basal cells. Tissue repair initiates from basal cells that resist inflammation. Here, we have evaluated the extent of apoptosis as well as the Hsp27 level of expression in epithelial cells from bronchial biopsy samples taken from normal and asthmatic subjects. Hsp27 is a chaperone whose expression protects against oxidative stress. We report that in asthmatic subjects the basal epithelium cells express a high level of Hsp27 but no apoptotic morphology. In contrast, apoptotic columnar cells are devoid of Hsp27 expression. Moreover, we observed a decreased resistance to hydrogen peroxide-induced apoptosis in human bronchial epithelial 16-HBE cells when they were genetically modified to express reduced levels of Hsp27.

The clpP multigene family for the ATP-dependent Clp protease in the cyanobacterium Synechococcus

In the cyanobacterium Synechococcus sp. strain PCC 7942 a multigene family of three different isozymes encodes the proteolytic subunit ClpP of the ATP-dependent Clp protease. In contrast to the monocistronic clpPI gene, clpPII and clpPIII are part of two bicistronic operons with clpX and clpR, respectively. Unlike most bacterial Clp proteins, the Synechococcus ClpP2, ClpP3, ClpR and ClpX proteins were not highly inducible by high temperatures, or by other stresses such as cold, high light or oxidation, although slower gradual rises occurred for all four proteins during high light, and for ClpP3, ClpR and ClpX at low temperature. Attempts to inactivate the clpPII, clpIII, clpR or clpX genes were only successful for clpPII, suggesting the others are essential for Synechococcus cell viability. The DeltaclpPII mutant exhibited no significant phenotypic changes from the wild-type, including no change in ClpX content. Despite the apparent bicistronic arrangement of both clpPII-clpX and clpR-clpPIII, all four genes primarily produce monocistronic transcripts, although polycistronic transcripts were detected. Mapping of 5' ends for the clpX and clpPIII monocistronic transcripts revealed promoters situated within the 3' region of clpPII and clpR, respectively. Transcriptional and translational studies further showed differences in the expression and regulation between the clpP-clpR-clpX genes. Inactivation of clpPI caused a significant decrease in ClpP2 protein concomitant to small increases in both ClpP3 and ClpR. Inactivation of clpPII resulted in a large rise in clpPI transcripts but to a lesser extent in ClpP1 protein. Similar small increases in ClpP3, ClpR and ClpX proteins also occurred in DeltaclpPII. These results highlight the regulatory complexity of these multiple clp genes and their functional importance in cyanobacteria.

Deconstructing PML-induced premature senescence

In this study, we investigated the subcellular and molecular mechanisms underlying promyelocytic leukemia (PML)-induced premature senescence. We demonstrate that intact PML nuclear bodies are not required for the induction of senescence. We have determined further that of seven known PML isoforms, only PML IV is capable of causing premature senescence, providing the first evidence for functional differences among these isoforms. Of interest is the fact that in contrast to PML(+/+) fibroblasts, PML(-/-) cells are resistant to PML IV-induced senescence. This suggests that although PML IV is necessary for this process to occur, it is not sufficient and requires other components for activity. Finally, we provide evidence that PML IV-induced senescence involves stabilization and activation of p53 through phosphorylation at Ser46 and acetylation at Lys382, and that it occurs independently of telomerase and differs from that elicited by oncogenic Ras. Taken together, our data assign a specific pro-senescent activity to an individual PML isoform that involves p53 activation and is independent from PML nuclear bodies.

Global transcriptional analysis of clpP mutations of type 2 Streptococcus pneumoniae and their effects on physiology and virulence

Streptococcus pneumoniae is an important human pathogen that contains single copies of genes encoding the ClpP and FtsH ATP-dependent proteases but lacks the Lon and HslV proteases. We constructed and characterized the phenotypes of clpP, clpC, and clpX deletion replacement mutants, which lack the ClpP protease subunit or the putative ClpC or ClpX ATPase specificity factor. A DeltaclpP mutant, but not a DeltaclpC or DeltaclpX mutant, of the virulent D39 type 2 strain of S. pneumoniae grew poorly at 30 degrees C and failed to grow at 40 degrees C. Despite this temperature sensitivity, transcription of the heat shock regulon determined by microarray analysis was induced in a DeltaclpP mutant, which was also more sensitive to oxidative stress by H2O2 and to puromycin than its clpP+ parent strain. A DeltaclpP mutant, but not a DeltaclpC mutant, was strongly attenuated for virulence in the murine lung and sepsis infection models. All of these phenotypes were complemented in a DeltaclpP/clpP+ merodiploid strain. Consistent with these complementation patterns, clpP was found to be in a monocistronic operon, whose transcription was induced about fivefold by heat shock in S. pneumoniae as determined by Northern and real-time reverse transcription-PCR analyses. Besides clpP, transcription of clpC, clpE, and clpL, but not clpX or ftsH, was induced by heat shock or entry into late exponential growth phase. Microarray analysis of DeltaclpP mutants showed a limited change in transcription pattern (approximately 80 genes) consistent with these phenotypes, including repression of genes involved in oxidative stress, metal ion transport, and virulence. In addition, transcription of the early and late competence regulon was induced in the DeltaclpP mutant, and competence gene expression and DNA uptake seemed to be constitutively induced throughout growth. Together, these results indicate that ClpP-mediated proteolysis plays a complex and central role in numerous pneumococcal stress responses, development of competence, and virulence.

Differential expression of a novel gene in response to hsp27 and cell differentiation in human keratinocytes

The 27 kDa heat shock protein (hsp27) is expressed in keratinocytes in a differentiation-related pattern. Keratinocyte differentiation involves a coordinated program of expression and interaction of specific differentiation-related genes and proteins. To investigate the functional role of hsp27 in these processes we used a differential display approach to identify genes that might be regulated by the expression of hsp27 in human keratinocytes. mRNA was extracted from the human squamous carcinoma cell line A431 and a subclone stably transfected with human hsp27. Reverse transcriptase differential display polymerase chain reaction was performed using one base anchored oligo-dT and arbitrary primers. Differentially expressed genes were confirmed by northern blot analysis and further characterized by sequencing. Their expression in human skin and other tissues was investigated by northern blot and in situ hybridization. Out of five fragments detected with the initial reverse transcriptase differential display polymerase chain reaction screen one could be confirmed by northern blot to be downregulated in hsp27-overexpressing A431. This mRNA (G24) is not only downregulated by overexpression of hsp27 in A431 but also during differentiation in normal human keratinocytes in culture and in situ, situations where hsp27 is known to be induced. According to sequence analysis G24 represents a novel gene that does not code for a protein and thus might belong to the growing family of noncoding RNAs. These results not only demonstrate for the first time that overexpression of hsp27 by gene transfer is associated with regulation of gene expression but also reveal a novel differentiation-associated gene in human keratinocytes.

Stress protection by a fluorescent Hsp27 chimera that is independent of nuclear translocation or multimeric dissociation

A chimeric protein consisting of enhanced green fluorescent protein (EGFP) fused to the N-terminus of human Hsp27 conferred stress protection in human A549 lung carcinoma and murine L929 cells that were stably transfected to express the chimera constitutively. The resultant protection was comparable with that in the same cell lines when they were transfected to express corresponding levels of Hsp27. Unlike L929 cells, A549 cells exhibit endogenous Hsp27 expression, whose expression was inhibited in proportion to the amount of fluorescent chimera expressed, suggesting that the A549 cells recognized the latter as Hsp27. Upregulation of Hsp27 or chimeric Hsp27 in all transfected cell lines (stable or transient transfection) caused no measurable change in cellular glutathione levels, indicating that glutathione played no role in the stress protection associated with either protein. Chimeric Hsp27 had a monomeric molecular weight of 55 kDa (that of Hsp27 plus EGFP) in both cell types and formed a 16-mer complex twice as massive as that formed by Hsp27. Heat shock or sodium arsenite induced phosphorylation of both chimeric Hsp27 and Hsp27, which resulted in the disaggregation of Hsp27 multimers in both cell types and disaggregation of 20% of the chimeric multimers in L929 cells. But chimeric Hsp27 multimers did not disaggregate after stress in A549 cells. Epifluorescence and confocal microscopy demonstrated that chimeric Hsp27 was restricted to the cytoplasm under normal growth conditions and after heat shock in all cells. This study supports the conclusions that Hsp27 stress protection requires neither its translocation into the nucleus nor the dissociation of its multimeric complex. Furthermore, it demonstrates that fluorescent chimeras of heat shock proteins can be functional and used to observe the protein's distribution within living cells.

Regulatory interaction of phosducin-like protein with the cytosolic chaperonin complex

Phosducin and phosducin-like protein (PhLP) bind G protein betagamma subunits and regulate their activity. This report describes a previously uncharacterized binding partner unique to PhLP that was discovered by coimmunoprecipitation coupled with mass spectrometric identification. Chaperonin containing tailless complex polypeptide 1 (CCT), a cytosolic chaperone responsible for the folding of many cellular proteins, binds PhLP with a stoichiometry of one PhLP per CCT complex. Unlike protein-folding substrates of CCT, which interact only in their nonnative conformations, PhLP binds in its native state. Native PhLP competes directly for binding of protein substrates of CCT and thereby inhibits CCT activity. Overexpression of PhLP inhibited the ability of CCT to fold newly synthesized beta-actin by 80%. These results suggest that the interaction between PhLP and CCT may be a means to regulate CCT-dependent protein folding or alternatively, to control the availability of PhLP to modulate G protein signaling.

The SUMO E3 ligase RanBP2 promotes modification of the HDAC4 deacetylase

Transcriptional repression mediated through histone deacetylation is a critical component of eukaryotic gene regulation. Here we demonstrate that the class II histone deacetylase HDAC4 is covalently modified by the ubiquitin-related SUMO-1 modifier. A sumoylation-deficient point mutant (HDAC4-K559R) shows a slightly impaired ability to repress transcription as well as reduced histone deacetylase activity. The ability of HDAC4 to self-aggregate is a prerequisite for proper sumoylation in vivo. Calcium/calmodulin-dependent protein kinase (CaMK) signalling, which induces nuclear export, abrogates SUMO-1 modification of HDAC4. Moreover, the modification depends on the presence of an intact nuclear localization signal and is catalysed by the nuclear pore complex (NPC) RanBP2 protein, a factor newly identified as a SUMO E3 ligase. These findings suggest that sumoylation of HDAC4 takes place at the NPC and is coupled to its nuclear import. Finally, modification experiments indicate that the MEF2-interacting transcription repressor (MITR) as well as HDAC1 and -6 are similarly SUMO modified, indicating that sumoylation may be an important regulatory mechanism for the control of transcriptional repression mediated by both class I and II HDACs.

An autoantibody inhibitory to glutamic acid decarboxylase in the neurodegenerative disorder Batten disease

Mutations in the CLN3 gene are responsible for the neurodegenerative disorder Batten disease; however, the molecular basis of this disease remains unknown. In studying a mouse model for Batten disease, we report the presence of an autoantibody to glutamic acid decarboxylase (GAD65) in cln3-knockout mice serum that associates with brain tissue but is not present in sera or brain of normal mice. The autoantibody to GAD65 has the ability to inhibit the activity of glutamic acid decarboxylase. Furthermore, brains from cln3-knockout mice have decreased activity of glutamic acid decarboxylase as a result of the inhibition of this enzyme by the autoantibody, resulting in brain samples from cln3-knockout mice having elevated levels of glutamate as compared with normal. This elevated glutamate in the brain of cln3-knockout mice co-localizes with presynaptic markers. The decreased activity of GAD65 and increased levels of glutamate may have a causative role in astrocytic hypertrophy evident in cln3-knockout mice, and in altered expression of genes involved in the synthesis and utilization of glutamate that underlie a shift from synthesis to utilization of glutamate. An autoantibody to GAD65 is also present in sera of 20 out of 20 individuals tested who have Batten disease. Postmortem tissue shows decreased reactivity to an anti-GAD65 antibody that may be due to loss of GAD65-positive neurons or due to the reactive epitope being blocked by the presence of the autoantibody. We propose that an autoimmune response to GAD65 may contribute to a preferential loss of GABAergic neurons associated with Batten disease.

Implication of alpha4 phosphoprotein and the rapamycin-sensitive mammalian target-of-rapamycin pathway in prolactin receptor signalling

A prolactin (PRL)-responsive 3'-end cDNA encoding rat alpha4 phosphoprotein was previously isolated from a rat lymphoma cDNA library. Rat alpha4 is a homologue of yeast Tap42 and is a component of the mammalian target-of-rapamycin (mTOR) signalling pathway that stimulates translation initiation and G1 progression in response to nutrients and growth factors. In the present study, the full-length rat alpha4 cDNA was obtained by 5'-RACE and the 1023 bp open reading frame predicted a 340 amino acid protein of 39.1 kDa. The alpha4 mRNA was expressed in quiescent PRL-dependent Nb2 lymphoma cells deprived of PRL for up to 72 h but expression was downregulated within 4 h of PRL treatment. In contrast, PRL-independent Nb2-Sp cells showed constitutive expression of alpha4 that was not affected by PRL. Western analysis of Nb2 cell lysates or of V5-tagged-alpha4 expressed in COS-1 cells detected a single immunoreactive band of approximately 45 kDa. Enzymatic deglycosylation of affinity-purified 45 kDa alpha4 yielded the predicted 39 kDa protein. Phosphorylation of Nb2 alpha4 was induced by PRL or 2-O-tetradecanoyl-phorbol-13-acetate (TPA) and further enhanced by a combination of PRL and TPA. The Nb2 alpha4 associated with the catalytic subunit of protein phosphatase 2A and localized predominantly in Nb2 nuclear fractions with trace amounts in the cytosol. The immunosuppressant drug rapamycin inhibited proliferation of Nb2 cells in response to PRL or interleukin-2, but had no effect on Nb2-Sp cells. Furthermore, transient overexpression of alpha4 in COS-1 cells inhibited PRL stimulation of the immediate-early gene interferon regulatory factor-1 promoter activity. Therefore, PRL downregulation of alpha4 expression and/or PRL-inducible phosphorylation of alpha4 may be necessary for PRL receptor (PRLr) signalling to the interferon regulatory factor-1 promoter in the Nb2 cells and, furthermore, implicates cross-talk between the mTOR and PRLr signalling cascades during Nb2 cell mitogenesis.

Hsp25 regulates the expression of p21(Waf1/Cip1/Sdi1) through multiple mechanisms

Exposure of cells to external stresses leads to the induction or activation of certain proteins. Expression of heat shock proteins (Hsps) is induced in response to these stresses. Hsps are known to have molecular chaperone activities; but recent studies have shown that Hsps have a variety of functions such as the triggering of proliferation, differentiation, and apoptosis of cells. Previously, we found that overexpression of a 25 kDa Hsp (Hsp25) induced expression of cell cycle inhibitory protein p21 (Waf1/Cip1/Sdi1) in murine fibroblastoid L929 cells. However, the mechanisms underlying the induction of p21 by Hsp25 are unknown. In the present study, we investigated the mechanisms underlying the regulation of p21 expression by Hsp25 in these cells. The introduction of Hsp25 cDNA stimulated the accumulation of p21 transcripts through transcriptional but not posttranscriptional regulation in these cells. We also found that overexpression of Hsp25 markedly increased the translational rate of p21 and stabilized the protein. Studies involving proteasome inhibitors and Western blot analysis for ubiquitination of p21 demonstrated that the stabilization of p21 is regulated through a ubiquitin-independent pathway. However, no direct association of Hsp25 with p21 was observed. These findings suggest that Hsp25 induces p21 expression through multiple mechanisms, and that transcriptional, translational, and post-translational regulation are important in the regulation of p21.

Functional interaction between the pp71 protein of human cytomegalovirus and the PML-interacting protein human Daxx

The tegument protein pp71 (UL82) of human cytomegalovirus (HCMV) has previously been shown to transactivate the major immediate-early enhancer-promoter of HCMV. Furthermore, this protein is able to enhance the infectivity of viral DNA and to accelerate the infection cycle, suggesting an important regulatory function during viral replication. To gain insight into the underlying mechanisms that are used by pp71 to exert these pleiotropic effects, we sought for cellular factors interacting with pp71 in a yeast two-hybrid screen. Here, we report the isolation of the human Daxx (hDaxx) protein as a specific interaction partner of HCMV pp71. hDaxx, which was initially described as an adapter protein involved in apoptosis regulation, has recently been identified as a nuclear protein that interacts and colocalizes with PML in the nuclear domain ND10. In order to assess whether pp71 can also be detected in ND10 structures, a vector expressing pp71 in fusion with the green fluorescent protein was used for transfection of human fibroblasts. This revealed a colocalization of pp71 with the ND10 proteins PML and Sp100. In addition, cotransfection of a hDaxx expression vector resulted in an enhanced recruitment of pp71 to ND10. Targeting of pp71 to nuclear dots could also be observed in infected human fibroblasts in the absence of de novo viral protein synthesis. Moreover, cotransfection experiments revealed that pp71-mediated transactivation of the major immediate-early enhancer-promoter was synergistically enhanced in the presence of hDaxx. These results suggest an important role of hDaxx for pp71 protein function.

Glucocorticoid treatment induces expression of small heat shock proteins in human satellite cell populations: consequences for a desmin-related myopathy involving the R120G alpha B-crystallin mutation

A missense mutation (R120G) of the molecular chaperone alpha B-crystallin has recently been linked to a familial form of desmin-related myopathy characterized by intrasarcoplasmic aggregates of desmin. It was previously demonstrated that the mutant R120G had a defective chaperone-like function. However, the cellular and physiopathological consequences of R120G mutant expression in human muscle cells are as yet unclear. Thus, we developed a cellular model for the study of this R120G alpha B-crystallin-related desmin-related myopathy. We demonstrate that dexamethasone enhances alpha B-crystallin and HSP27 expression in normal and desmin-related myopathy-derived muscle cells. In the undifferentiated desmin-related myopathy satellite cell population no intracytoplasmic aggregates were observed. However, in differentiated satellite cells derived from a related myopathy patient, we observed an enhanced plasma membrane localization of alpha B-crystallin following glucocorticoid. We also observed that the protective effect against stress of alpha B-crystallin is altered upon glucocorticoid-induced small heat shock protein expression for the desmin-related myopathy-derived cells.

The insulin-sensitive glucose transporter, GLUT4, interacts physically with Daxx. Two proteins with capacity to bind Ubc9 and conjugated to SUMO1

In this study we have used the yeast two-hybrid system to identify proteins that interact with the carboxyl-cytoplasmic domain (residues 464-509) of the insulin-sensitive glucose transporter GLUT4 (C-GLUT4). Using as bait C-GLUT4, we have isolated the carboxyl domain of Daxx (C-Daxx), the adaptor protein associated with the Fas and the type II TGF-beta (TbetaRII) receptors (1,2 ). The two-hybrid interaction between C-GLUT4 and C-Daxx is validated by the ability of in vitro translated C-GLUT4 to interact with in vitro translated full-length Daxx and C-Daxx. C-Daxx does not interact with the C-cytoplasmic domain of GLUT1, the ubiquitous glucose transporter homologous to GLUT4. Replacement of alanine and serine for the dileucine pair (Leu(489)-Leu(490)) critical for targeting GLUT4 from the trans-Golgi network to the perinuclear intracellular store as well as for its surface internalization by endocytosis inhibits 2-fold the interaction of C-GLUT4 with Daxx. Daxx is pulled down with GLUT4 immunoprecipitated from lysates of 3T3-L1 fibroblasts stably transfected with GLUT4 and 3T3-L1 adipocytes expressing physiological levels of the two proteins. Similarly, GLUT4 is recovered with anti-Daxx immunoprecipitates. Using an established cell fractionation procedure we present evidence for the existence of two distinct intracellular Daxx pools in the nucleus and low density microsomes. Confocal immunofluorescence microscopy studies localize Daxx to promyelocytic leukemia nuclear bodies and punctate cytoplasmic structures, often organized in strings and underneath the plasma membrane. Daxx and GLUT4 are SUMOlated as shown by their reaction with an anti-SUMO1 antibody and by the ability of this antibody to pull down Daxx and GLUT4.

Molecular cloning and expression of rat torsinA in the normal and genetically dystonic (dt) rat

Deletions within the TOR1A gene cause early-onset (DYT1) torsion dystonia. We have cloned and sequenced the rat cDNA homologue of TOR1A and found a 91% identity with the human sequence. Northern blot analysis detects a single transcript of approximately 1.5 kb. In situ hybridization reveals a widespread distribution of torsinA mRNA within brain. No mutations were identified in the coding region of the gene in the genetically dystonic (dt) rat.

Elucidation of the function of lipoprotein-sorting signals that determine membrane localization

Escherichia coli lipoproteins are anchored to the inner or outer membrane depending on the residue at position 2. Aspartate at this position makes lipoproteins specific to the inner membrane, whereas other residues cause the release of lipoproteins from the inner membrane in a manner dependent on both ATP binding cassette (ABC) transporter LolCDE and molecular chaperone LolA, followed by LolB-dependent localization in the outer membrane. The function of lipoprotein-sorting signals was examined in proteoliposomes reconstituted from LolCDE and lipoproteins. The release of outer membrane-specific lipoproteins was inhibited on reconstitution with other outer membrane-specific, but not inner membrane-specific, lipoproteins. Outer membrane-specific lipoproteins stimulated ATP hydrolysis by LolCDE whereas inner membrane-specific ones did not. LolA was not required for the stimulation of ATP hydrolysis. These results revealed a previously undocumented function of aspartate at position 2, i.e., lipoproteins having this signal avoid being recognized by LolCDE, thereby remaining in the inner membrane.

Protein NMR structure determination with automated NOE assignment using the new software CANDID and the torsion angle dynamics algorithm DYANA

Combined automated NOE assignment and structure determination module (CANDID) is a new software for efficient NMR structure determination of proteins by automated assignment of the NOESY spectra. CANDID uses an iterative approach with multiple cycles of NOE cross-peak assignment and protein structure calculation using the fast DYANA torsion angle dynamics algorithm, so that the result from each CANDID cycle consists of exhaustive, possibly ambiguous NOE cross-peak assignments in all available spectra and a three-dimensional protein structure represented by a bundle of conformers. The input for the first CANDID cycle consists of the amino acid sequence, the chemical shift list from the sequence-specific resonance assignment, and listings of the cross-peak positions and volumes in one or several two, three or four-dimensional NOESY spectra. The input for the second and subsequent CANDID cycles contains the three-dimensional protein structure from the previous cycle, in addition to the complete input used for the first cycle. CANDID includes two new elements that make it robust with respect to the presence of artifacts in the input data, i.e. network-anchoring and constraint-combination, which have a key role in de novo protein structure determinations for the successful generation of the correct polypeptide fold by the first CANDID cycle. Network-anchoring makes use of the fact that any network of correct NOE cross-peak assignments forms a self-consistent set; the initial, chemical shift-based assignments for each individual NOE cross-peak are therefore weighted by the extent to which they can be embedded into the network formed by all other NOE cross-peak assignments. Constraint-combination reduces the deleterious impact of artifact NOE upper distance constraints in the input for a protein structure calculation by combining the assignments for two or several peaks into a single upper limit distance constraint, which lowers the probability that the presence of an artifact peak will influence the outcome of the structure calculation. CANDID test calculations were performed with NMR data sets of four proteins for which high-quality structures had previously been solved by interactive protocols, and they yielded comparable results to these reference structure determinations with regard to both the residual constraint violations, and the precision and accuracy of the atomic coordinates. The CANDID approach has further been validated by de novo NMR structure determinations of four additional proteins. The experience gained in these calculations shows that once nearly complete sequence-specific resonance assignments are available, the automated CANDID approach results in greatly enhanced efficiency of the NOESY spectral analysis. The fact that the correct fold is obtained in cycle 1 of a de novo structure calculation is the single most important advance achieved with CANDID, when compared with previously proposed automated NOESY assignment methods that do not use network-anchoring and constraint-combination.

Characterization of proteins associated with heat shock protein hsp27 in the squamous cell carcinoma cell line A431

Heat shock protein hsp27 is a molecular chaperone and identification of hsp27-binding proteins might help to elucidate its functional role in keratinocyte biology. In the present investigation we used a human epidermal cell carcinoma cell line (A431) transfected with hsp27 (A431/16) to study interference between hsp27 protein and other proteins. Immunoprecipitation experiments with anti-hsp27 antibody revealed a multicomponent complex when analysed by silver staining. By immunoblotting analysis we could demonstrate that hsp27 associates with actin, the mutant form of p53, hsp70 and hsp90. Immunofluorescence analysis showed a co-localization between hsp27 and p53, hsp70 and hsp90. To control for the specificity of the observed interactions, immuno-precipitations with antibodies to actin, p53, hsp70 and hsp90 respectively, were performed. All of the tested proteins demonstrated a coimmunoprecipitation with hsp27. We conclude that hsp27, like the other heat shock proteins, is part of a complex system of molecular chaperones in epidermal keratinocytes.

Copper transfer from the Cu(I) chaperone, CopZ, to the repressor, Zn(II)CopY: metal coordination environments and protein interactions

Extracellular copper regulates the DNA binding activity of the CopY repressor of Enterococcus hirae and thereby controls expression of the copper homeostatic genes encoded by the cop operon. CopY has a CxCxxxxCxC metal binding motif. CopZ, a copper chaperone belonging to a family of metallochaperones characterized by a MxCxxC metal binding motif, transfers copper to CopY. The copper binding stoichiometries of CopZ and CopY were determined by in vitro metal reconstitutions. The stoichiometries were found to be one copper(I) per CopZ and two copper(I) per CopY monomer. X-ray absorption studies suggested a mixture of two- and three-coordinate copper in Cu(I)CopZ, but a purely three-coordinate copper coordination with a Cu-Cu interaction for Cu(I)2CopY. The latter coordination is consistent with the formation of a compact binuclear Cu(I)-thiolate core in the CxCxxxxCxC binding motif of CopY. Displacement of zinc, by copper, from CopY was monitored with 2,4-pyridylazoresorcinol. Two copper(I) ions were required to release the single zinc(II) ion bound per CopY monomer. The specificity of copper transfer between CopZ and CopY was dependent on electrostatic interactions. Relative copper binding affinities of the proteins were investigated using the chelator, diethyldithiocarbamic acid (DDC). These data suggest that CopY has a higher affinity for copper than CopZ. However, this affinity difference is not the sole factor in the copper exchange; a charge-based interaction between the two proteins is required for the transfer reaction to proceed. Gain-of-function mutation of a CopZ homologue demonstrated the necessity of four lysine residues on the chaperone for the interaction with CopY. Taken together, these results suggest a mechanism for copper exchange between CopZ and CopY.

Estramustine phosphate enhances the effects of hyperthermia and induces the small heat shock protein HSP27 in the human prostate carcinoma cell line PC-3

The antimicrotubule drug estramustine phosphate (EMP) has been shown to sensitize prostate carcinoma cells to radiation via synchronization at the G2/M phase of the cell cycle. This synchronization may also render cells more sensitive to hyperthermia, providing a rationale for multimodal treatment approaches. We have investigated the effects of EMP and hyperthermia, as well as the regulation of heat shock proteins (HSP) in the PC-3 prostatic carcinoma cell line. Cells were incubated with four doses of EMP for 48 h followed by a 1-h hyperthermia treatment ranging from 41 degrees C to 44 degrees C. Cell cycle distribution at the end of the EMP incubation was investigated by flow cytometry. Cytotoxicity was assessed by colony formation assays. HSP accumulation was investigated by Western immunoblotting. Doses of 1, 5, 10 and 15 microM EMP synchronized 27, 28, 46, and 68% of PC-3 cells at G2/M. With 5, 10 and 15 microM, a sensitizing effect of EMP was assessed at hyperthermic temperatures of 42, 43 and 44 degrees C. EMP did not alter the expression of HSP72, but substantially induced the synthesis of HSP27 in PC-3 cells. Our data show that EMP sensitizes PC-3 cells to hyperthermia induced cytotoxicity. This observation supports the rationale for multimodal treatment approaches in locally advanced prostate cancer.

Subtle alterations of the native zinc finger structures have dramatic effects on the nucleic acid chaperone activity of human immunodeficiency virus type 1 nucleocapsid protein

The nucleocapsid protein (NC) of human immunodeficiency virus type 1 has two zinc fingers, each containing the invariant CCHC zinc-binding motif; however, the surrounding amino acid context is not identical in the two fingers. Recently, we demonstrated that zinc coordination is required when NC unfolds complex secondary structures in RNA and DNA minus- and plus-strand transfer intermediates; this property of NC reflects its nucleic acid chaperone activity. Here we have analyzed the chaperone activities of mutants having substitutions of alternative zinc-coordinating residues, i.e., CCHH or CCCC, for the wild-type CCHC motif. We also investigated the activities of mutants that retain the CCHC motifs but have mutations that exchange or duplicate the zinc fingers (mutants 1-1, 2-1, and 2-2); these changes affect amino acid context. Our results indicate that in general, for optimal activity in an assay that measures stimulation of minus-strand transfer and inhibition of nonspecific self-priming, the CCHC motif in the zinc fingers cannot be replaced by CCHH or CCCC and the amino acid context of the fingers must be conserved. Context changes also reduce the ability of NC to facilitate primer removal in plus-strand transfer. In addition, we found that the first finger is a more crucial determinant of nucleic acid chaperone activity than the second finger. Interestingly, comparison of the in vitro results with earlier in vivo replication data raises the possibility that NC may adopt multiple conformations that are responsible for different NC functions during virus replication.

ClpP-dependent degradation of PopR allows tightly regulated expression of the clpP3 clpP4 operon in Streptomyces lividans

Five clpP genes have been identified in Streptomyces coelicolor. The clpP1 and clpP2 genes form one operon, the clpP3 and clpP4 genes form another, and clpP5 is monocistronic. Previous studies in Streptomyces lividans have shown that the first operon (clpP1 clpP2) is required for a normal cell cycle. Expression of the second operon (clpP3 clpP4) is activated by PopR if the first operon is nonfunctional. We show here that PopR degradation is primarily dependent on ClpP1 and ClpP2, but can also be achieved by ClpP3 and ClpP4. The carboxy-terminus of PopR plays an essential part in the degradation process. Indeed, replacement of the last two alanine residues by aspartate residues greatly increased PopR stability. These substitutions did not impair PopR activity and, as expected, accumulation of the mutant form of PopR led to very strong expression of the clpP3 clpP4 operon. Increased PopR levels led to delayed sporulation. The results obtained in this study support the notion of cross-processing between ClpP1 and ClpP2.

Gene control in germinal differentiation: RNF6, a transcription regulatory protein in the mouse sertoli cell

In mouse Sertoli cells, transcription of the Inha gene encoding the alpha subunit of inhibin, which acts locally as a tumor suppressor, is down-regulated in tumors and in normal cells during aging. Previous studies suggested that regulation of Inha transcription involves the binding of a protein(s) to a repeat of the GGGGC motif in the promoter. Expression screening identified a cDNA encoding a protein that binds this sequence. Of the RING-H2 family, it is the mouse homologue of a human protein of unknown function, RNF6. The mouse gene, Rnf6, is predominantly expressed in two interacting cell types of the testis, Sertoli cells and pachytene spermatocytes. In Sertoli cells, it colocalizes with the PML and Daxx proteins in punctate nuclear bodies. In transient and stable transfectants, Rnf6 expression from a heterologous promoter increased the expression of reporter genes driven by the Inha promoter. In a Sertoli tumor cell line in which expression of both Inha and Rnf6 was reduced, reexpression of the latter restored the level of Inha while, concomitantly, the cells reverted to normal growth control in culture.