Effect of herbimycin A on hsp30 and hsp70 heat shock protein gene expression in Xenopus cultured cells

Glucose intolerance and diabetes mellitus are both prevalent in patients with chronic liver diseases. We examined the efficacy and systemic safety of therapy with an alpha-glucosidase inhibitor, acarbose, in diabetes mellitus associated with chronic liver diseases. Twenty patients with chronic hepatitis or liver cirrhosis and overt diabetes mellitus received acarbose (taken orally) for 8 weeks. The initial dosage of acarbose was 50 mg three times daily, taken before meals; this was increased to 100 mg three times daily after 2 weeks. The mean fasting plasma glucose level was 173.7 +/- 18.6 mg/dl (mean +/- SE) at entry, and was significantly decreased to 132.9 +/- 7.5 mg/dl (P < 0.05) after 8 weeks of acarbose treatment. The improved glycemic control was reflected by a significant decrease in glycosylated hemoglobin (HbA1c) from 7.2 +/- 0.3% at entry to 6.3 +/- 0.2% (P < 0.05) after 8 weeks. Serum levels of both aspartate and alanine aminotransferases fluctuated during acarbose treatment, probably due to the natural course of chronic liver diseases, but the mean values had decreased after 8 weeks of treatment. Plasma ammonia levels increased, from 61.3 +/- 10.7 micrograms/dl to 71.1 +/- 9.6 micrograms/dl after 8 weeks of acarbose treatment but the increase was not significant. Clinically significant elevation of plasma ammonia concentration was seen in 2 cirrhotic patients (121 and 124 micrograms/dl); this was asymptomatic and gradually returned to the normal range despite continuous acarbose treatment in one patient, and was reversed after the withdrawal of acarbose with the concomitant administration of lactulose in the other patient. No other blood tests results, including albumin, cholinesterase, and prothrombin time, or lipid profile and nutritional status, in terms of rapid turnover proteins, prealbumin, retinol binding protein, and transferin, were altered throughout the study period. These results indicate that diabetes mellitus associated with chronic liver diseases may be safely and effectively treated with acarbose. However, clinicians must be aware of the possibility of hyperammonemia when they prescribe acarbose for patients with diabetes mellitus and advanced liver cirrhosis.     

Aggregation of hsp70 and hsc70 in vivo is distinct and temperature-dependent and their chaperone function is directly related to non-aggregated forms

We used non-denaturing gradient analysis of cell extracts before and after heat treatment of the cells and showed that hsp70 and hsc70 aggregate in vivo in a temperature-dependent fashion. Their aggregation profiles were found to be clearly distinguishable and sensitive to ATP depletion. Pore exclusion limit electrophoresis showed that these two proteins are mainly found in autoaggregated forms including dimers, trimers and oligomers. The addition of denatured luciferase to the cell extracts reversed the aggregation of both proteins towards their non-aggregated forms. Immunoprecipitation and Western-blot analysis showed that the non-aggregated form is the only one bound to denatured luciferase. Our results suggest that aggregated hsp70 and hsc70 represent predominantly self-associated molecules unable to exert chaperone activity. The cochaperone hsp40 was also found to be aggregated and, on addition of denatured luciferase, its aggregation was reversed to a non-aggregated state. Immunoprecipitation analysis indicated that hsp40 forms a complex with the non-aggregated form of hsc70 and denatured luciferase. These results confirm previous in vitro studies and support the suggestion that in vivo cytosolic hsp70 and hsc70 exist mainly in an oligomer-monomer equilibrium which is dependent on the environmental temperature, the levels of ATP and the presence of denatured proteins.     

Cloning, expression and characterization of a gene which encodes a topoisomerase I with positive supercoiling activity in pea

We have isolated and sequenced the full length cDNA for topoisomerase I. Using degenerate primers, based on the conserved amino acid sequences of five eukaryotic topoisomerase I, a 386 bp fragment was PCR amplified using pea cDNA as template. This fragment was used as a probe to screen a pea cDNA library. Two partial cDNA clones were isolated which were truncated at the 5' end. RACE-PCR was employed to isolate the remaining portion of the gene. The total size of the gene was 3055 bp with an open reading frame of 2676 bp. The deduced structure of pea topoisomerase I contain 892 amino acids with a calculated molecular weight of 100 kDa and an estimated pI of 9.3. A comparison of the deduced amino acid sequences of the pea topo I with the other eukaryotic topoisomerases clearly suggested that they are all related. Pea topoisomerase I has been overexpressed in E. coli system and the recombinant topoisomerase purified to homogeneity. The purified protein relaxes both positive and negative supercoiled DNA in the absence of divalent cation Mg2+. In the presence of Mg2+ ions the purified enzyme introduces positive supercoils a unique property not reported in any other organism except in archaebacterial topoisomerase I. Polyclonal antibodies were raised against recombinant topoisomerase I and western blotting with sub-cellular fractions indicated the localization of this topoisomerase in pea nuclei.     

Different peptide binding specificities of hsp70 family members

A set of heptapeptides was used to compare the relative peptide affinities of three proteins of the hsp70 family: bacterial DnaK, mammalian cytosolic hsc70, and BiP from mammalian ER. Each hsp displays a characteristic pattern of relative affinities. DnaK and hsc70 are more similar to each other than to BiP. A difference in peptide binding specificity may be an important determinant in adjusting an hsp70 family member to its particular cellular function.     

Discontinuous occurrence of the hsp70 (dnaK) gene among Archaea and sequence features of HSP70 suggest a novel outlook on phylogenies inferred from this protein

Occurrence of the hsp70 (dnaK) gene was investigated in various members of the domain Archaea comprising both euryarchaeotes and crenarchaeotes and in the hyperthermophilic bacteria Aquifex pyrophilus and Thermotoga maritima representing the deepest offshoots in phylogenetic trees of bacterial 16S rRNA sequences. The gene was not detected in 8 of 10 archaea examined but was found in A. pyrophilus and T. maritima, from which it was cloned and sequenced. Comparative analyses of the HSP70 amino acid sequences encoded in these genes, and others in the databases, showed that (i) in accordance with the vicinities seen in rRNA-based trees, the proteins from A. pyrophilus and T. maritima form a thermophilic cluster with that from the green nonsulfur bacterium Thermomicrobium roseum and are unrelated to their counterparts from gram-positive bacteria, proteobacteria/mitochondria, chlamydiae/spirochetes, deinococci, and cyanobacteria/chloroplasts; (ii) the T. maritima HSP70 clusters with the homologues from the archaea Methanobacterium thermoautotrophicum and Thermoplasma acidophilum, in contrast to the postulated unique kinship between archaea and gram-positive bacteria; and (iii) there are exceptions to the reported association between an insert in HSP70 and gram negativity, or vice versa, absence of insert and gram positivity. Notably, the HSP70 from T. maritima lacks the insert, although T. maritima is phylogenetically unrelated to the gram-positive bacteria. These results, along with the absence of hsp70 (dnaK) in various archaea and its presence in others, suggest that (i) different taxa retained either one or the other of two hsp70 (dnaK) versions (with or without insert), regardless of phylogenetic position; and (ii) archaea are aboriginally devoid of hsp70 (dnaK), and those that have it must have received it from phylogenetically diverse bacteria via lateral gene transfer events that did not involve replacement of an endogenous hsp70 (dnaK) gene.     

Protein folding activity of Hsp70 is modified differentially by the hsp40 co-chaperones Sis1 and Ydj1

Specification of Hsp70 action in cellular protein metabolism may occur through the formation of specialized Hsp70:Hsp40 pairs. To test this model, we compared the ability of purified Sis1 and Ydj1 to regulate the ATPase and protein-folding activity of Hsp70 Ssa1 and Ssb1/2 proteins. Ydj1 and Sis1 could both functionally interact with Ssa1, but not the Ssb1/2 proteins, to refold luciferase. Interestingly, Ydj1:Ssa1 could promote up to four times more luciferase folding than Sis1:Ssa1. This functional difference was explored and could not be accounted for by differences in the ability of Sis1 and Ydj1 to regulate Ssa1 ATPase activity. Instead, differences in the chaperone function of Ydj1 and Sis1 were observed. Ydj1 was dramatically more effective than Sis1 at suppressing the thermally induced aggregation of luciferase. Paradoxically, Sis1 and Ydj1 could bind similar quantities of chemically denatured luciferase. The polypeptide binding domain of Sis1 was found to lie between residues 171-352 and correspond to its conserved carboxyl terminus. The conserved carboxyl terminus of Ydj1 is also known to participate in the binding of nonnative polypeptides. Thus, Ydj1 appears more efficient at assisting Ssa1 in folding luciferase because its contains a zinc finger-like region that is absent from Sis1. Ydj1 and Sis1 are structurally and functionally distinct Hsp40 proteins that can specify Ssa1 action by generating Hsp70:Hsp40 pairs that exhibit different chaperone activities.     

Production and characterization of bovine herpesvirus 1 glycoprotein B ectodomain derivatives in an hsp70A gene promoter-based expression system

Different derivatives of bovine herpesvirus 1 (BHV-1) glycoprotein B (gB) ectodomain were expressed in a novel heat-shock expression system. The putative ectodomain, gBt, and the N-terminal subunit, gBb, were of the expected molecular weight and were secreted. Their production were heat-inducible and the purified proteins were able to elicit antibody responses in mice of a comparable level as induced by authentic gB. The truncated C-terminal subunit, gBct, was retained in the endoplasmic reticulum. Our studies suggest that the gBb subunit may play a major role in constituting the overall configuration of gB and is required for the intracellular transport of gB.     

Folding of the glucocorticoid receptor by the heat shock protein (hsp) 90-based chaperone machinery. The role of p23 is to stabilize receptor.hsp90 heterocomplexes formed by hsp90.p60.hsp70

In cytosols from animal and plant cells, the abundant heat shock protein hsp90 is associated with several proteins that act together to assemble steroid receptors into receptor.hsp90 heterocomplexes. We have reconstituted a minimal receptor.hsp90 assembly system containing four required components, hsp90, hsp70, p60, and p23 (Dittmar, K. D., Hutchison, K. A., Owens-Grillo, J. K., and Pratt, W. B. (1996) J. Biol. Chem. 271, 12833-12839). We have shown that hsp90, p60, and hsp70 are sufficient for carrying out the folding change that converts the glucocorticoid receptor (GR) hormone binding domain (HBD) from a non-steroid binding to a steroid binding conformation, but to form stable GR.hsp90 heterocomplexes, p23 must also be present in the incubation mix (Dittmar, K. D., and Pratt, W. B. (1997) J. Biol. Chem. 272, 13047-13054). In this work, we show that addition of p23 to native GR.hsp90 heterocomplexes immunoadsorbed from L cell cytosol or to GR.hsp90 heterocomplexes prepared with the minimal (hsp90.p60.hsp70) assembly system inhibits both receptor heterocomplex disassembly and loss of steroid binding activity. p23 stabilizes the GR.hsp90 heterocomplex in a dynamic and ATP-independent manner. In contrast to hsp90 that is bound to the GR, free hsp90 binds p23 in an ATP-dependent manner, and hsp90 in the hsp90.p60.hsp70 heterocomplex is in a conformation that does not bind p23 at all. The effect of p23 in the minimal GR heterocomplex assembly system is to stabilize GR.hsp90 heterocomplexes once they are formed and it does not appear to affect the rate of heterocomplex assembly. Molybdate has the same ability as p23 to stabilize GR heterocomplexes with mammalian hsp90, but GR heterocomplexes with plant hsp90 are stabilized by p23 and not by molybdate. We propose that incubation of the GR with hsp90.p60.hsp70 forms a GR.hsp90 heterocomplex in which hsp90 is in an ATP-dependent conformation. The ATP-dependent conformation of hsp90 is required for the hormone binding domain to have a steroid binding site, and binding of p23 to that state of hsp90 stabilizes the GR.hsp90 heterocomplex to inactivation and disassembly.     

Parallin, a cerebellar granule cell protein the expression of which is developmentally regulated by Purkinje cells: evidence from mutant mice

In this paper we report on monoclonal antibody 3H6 with unique specificities for development of the cerebellum. Immunohistochemical studies on normal and mutant mice suggest that it is primarily located in or on granule cell parallel fibers in the cerebellum. The only other region showing immunoreactivity is a small region of the hippocampus. The antigen is detected immunohistochemically as early as postnatal day 11 in the molecular layer of the cerebellum. In adult wild-type mice parallin expression is seen in the molecular layer and to a lesser degree in the internal granular layer. In the cerebella of two neurological granule cell-deficient mutants, weaver (wv) and staggerer (sg), parallin is not detected. However, in two Purkinje cell-deficient mutants, Purkinje cell degeneration (pcd) and nervous (nr), a more complex and interesting pattern is observed. These two mutants do have granule cells and parallel fibers and 3H6 immunoreactivity is observed. However, in both of these Purkinje cell-deficient mutants the 3H6 immunoreactivity is drastically reduced in regions where Purkinje cells have degenerated. Furthermore, in nr mutants, the antigen appears to be concentrated in regions of the parallel fiber that are in close proximity to Purkinje cells, suggesting its possible association with synapses. Taken together these results suggest that parallin is a marker of granule cells and their parallel fibers, its onset correlates with the formation of granule cell synapses on developing Purkinje cells, and it requires Purkinje cells for the maintenance of expression.     

Inactivation of tumor suppressor p53 by mot-2, a hsp70 family member

The mortalin genes, mot-1 and mot-2, are hsp70 family members that were originally cloned from normal and immortal murine cells, respectively. Their proteins differ by only two amino acid residues but exhibit different subcellular localizations, arise from two distinct genes, and have contrasting biological activities. We report here that the two proteins also differ in their interactions with the tumor suppressor protein p53. The pancytosolic mot-1 protein in normal cells did not show colocalization with p53; in contrast, nonpancytosolic mot-2 and p53 overlapped significantly in immortal cells. Transfection of mot-2 but not mot-1 resulted in the repression of p53-mediated transactivation in p53-responsive reporter assays. Inactivation of p53 by mot-2 was supported by the down-regulation of p53-responsive genes p21(WAF-1) and mdm-2 in mot-2-transfected cells only. Furthermore, NIH 3T3 cells transfected with expression plasmid encoding green fluorescent protein-tagged mot-2 but not mot-1 showed an abrogation of nuclear translocation of wild-type p53. These results demonstrate a novel mechanism of p53 inactivation by mot-2 protein.