Antigenic protein specific for C3H strain mouse is a mitochondrial stress-70 protein

Mortalin: a protein associated with progression of Parkinson disease?

Parkinson disease (PD) is a progressive neurodegenerative disorder that is considered to affect the brainstem at its early stages and other brain regions, including the limbic system and isocortex, in advanced stages. It has been suggested that PD progression is characterized pathologically by the spreading of Lewy body deposition. To identify novel proteins involved in PD progression, we prepared subcellular fractions from the frontal cortex of pathologically verified PD patients at different stages of disease and Lewy body deposition and from age-matched controls. Protein expression profiles were compared using a robust quantitative proteomic technique called isobaric tagging for relative and absolute quantification in conjunction with mass spectrometry. Approximately 200 proteins were found to display significant differences in their relative abundance between PD patients at various stages and controls. Gene ontology analysis indicated that these altered proteins belonged to many categories (e.g. mitochondrial function and neurotransmission) that were likely critically involved in the pathogenesis of PD. Of those, mortalin, a mitochondrial protein, was decreased in the advanced PD cases and was further validated to be decreased using independent techniques. These results suggest a role for mortalin in PD progression.

Susceptibility to colon carcinogenesis in C3H<-->C57BL/6 chimeric mice reflects both tissue microenvironment and genotype

Considerable rodent strain differences have been documented with regard to susceptibility to colon carcinogens. To clarify mechanisms, chimeras of susceptible strain C3H and relatively resistant strain C57BL/6N (B6) mice were exposed to a colonotropic carcinogen, 1,2-dimethylhydrazine (DMH) and tumor incidence and multiplicity were assessed. In the chimeras, incidence was as high as the C3H level. Multiplicity of lesions of B6 cells was also increased (P<0.001), but maintenance of the strain difference. When tumor localization was analyzed, tumors of B6 genotype in chimeras demonstrated a greater spread of distribution than in the parental case. The chimeric environment may thus stimulate tumor initiation but cell autonomous suppressive factors may be retained.

Mouse strain susceptibility to diethylnitrosamine induced hepatocarcinogenesis is cell autonomous whereas sex-susceptibility Is due to the micro-environment: analysis with C3H <--> BALB / c sexually chimeric mice

In man, liver cancer is on the increase, especially in males. Sex differences also exist in rodent models. To elucidate the mechanisms, chimeric mice were produced by amalgamation of early embryos from high and low hepatocarcinogen-susceptible strains, C3H and BALB / c. Tumor formation was initiated with 10 mg / kg of diethylnitrosamine at the ages of 7 and 14 days and mice were sacrificed at 30 and 45 weeks. The chimeras were classified into XY <--> XY, XY <--> XX, XX <--> XY, and XX <--> XX in terms of sex chromosomes by means of polymerase chain reaction-simple sequence length polymorphism analysis (SSLP) using Y chromosome-specific Sry primers in combination with the D3Mit21 marker. Liver lesions were analyzed histopathologically, by immunostaining using a C3H strain-specific antibody and by DNA in situ hybridization with the Y chromosome-specific digoxigenin-labeled Y353 / B probe. Sex and strain genotyping by SSLP analysis matched histological observations, confirming the reliability of our system. The strain differences in liver tumor numbers of each strain type in XY <--> XY and XX <--> XX subtypes of C3H <--> BALB / c chimeras were retained well (P < 0. 0001 and P < 0.001, respectively), indicating a minimum influence of the C3H or BALB / c surrounding milieu on development of individual lesions. On the other hand, significant promotion of XX cell tumors was evident in phenotypically male sexually chimeric XY <--> XX and XX <--> XY chimeras for both C3H (P < 0.02) and BALB / c (P < 0.01) lesions compared to the XX <--> XX case. The results suggest the presence of hormonal or micro-environmental factors specific for males, which are not caused cell-autonomously. Basic strain differences, however, are determined by intrinsic genetic factors rather than the strain-dependent micro-environment.

MPTP selectively induces haem oxygenase-1 expression in striatal astrocytes

Parkinson's disease (PD) is characterized by the loss of dopaminergic neurons in the substantia nigra pars compacta with accompanying evidence of increased oxidative damage, deficits in mitochondrial function and iron deposition. Recently, haem oxygenase-1 levels were reported to be elevated in PD brains. Because this enzyme is involved in the response to oxidative stress and is critical for cellular haem and iron homeostasis, it could play a role in the pathogenesis of PD. Therefore, we investigated the expression of haem oxygenase isoform 1 (HO-1) in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD. MPTP triggered a relatively rapid and persistent increase in HO-1 mRNA exclusively in the mouse striatum. In situ hybridization and immunohistochemistry showed HO-1 to be localized to striatal astrocytes. The induction of HO-1 by MPTP was blocked by selegiline and GBR-12909, indicating the protoxin had to be metabolized by monoamine oxidase B and taken up by dopaminergic neurons to exert its action in astrocytes. MPTP did not alter the expression of other enzymes of haem synthesis or degradation nor were the levels of mRNA for haem or iron-binding proteins changed. Thus, expression of HO-1 was not part of a cellular program involving haem biosynthesis or homeostasis. In addition, heat shock proteins were not induced by MPTP. Thus, MPTP elicited a selective transcriptional response in striatal astrocytes. This response appears to be mediated by molecules released from affected dopaminergic nerve terminals in the striatum acting upon neighbouring astrocytes. This signalling pathway and its potential relevance to PD are discussed.

Induction of novel Grp75 isoforms by 2-deoxyglucose in human and murine fibroblasts

Grp75 is a stress-inducible mitochondrial chaperone which has a high homology to senescence-related protein, p66mot mortalin. In human cells the mortalin gene assigns to the locus of a putative tumor suppressor gene for myeloid malignancies. In order to study expression and localization of Grp75 and p66mot in human and murine fibroblast lines, polyclonal antibodies were raised to conserved portions of each sequence. HT1080 and C3H10T1/2 cells were treated with various Grp-inducing agents. A single 75 kDa band was detected by Western blot of cytoplasmic proteins which was not greatly altered after thermal stress or treatment with L-azetidine-2-carboxylic acid or nonactin. However, glucose deprivation by 2-deoxyglucose treatment induced five novel isoforms at 74-75 kDa mass. Mortalin at 66 kDa could not be detected under these treatment conditions.

Cloning and some novel characteristics of mitochondrial Hsp70 from Chinese hamster cells

The cDNA for Chinese hamster mitochondrial Hsp70 (mHsp70) was cloned and sequenced using a polymerase chain reaction probe based on conserved regions in the Hsp70 family of proteins. The encoded protein consists of 679 amino acids which includes a N-terminal mitochondrial targeting sequence of 46 amino acids. The mHsp70 protein contains several sequence signatures that are characteristics of prokaryotic and eukaryotic organellar Hsp70 homologs. In a phylogenetic tree based on Hsp70 sequences, it branches with the gram-negative proteobacteria, supporting the endosymbiotic origin of mitochondria from this group of prokaryotes. The mHsp70 cDNA was transcribed and translated in vitro and its import into isolated rat heart mitochondria was examined. The precursor mHsp70 was converted into a mature form of lower molecular mass (approximately 71 kDa) which became resistant to trypsin digestion. The import of mHsp70 into mitochondria was not observed in the presence of an uncoupler of energy metabolism or when the N-terminal presequence was lacking. The cDNA for mHsp70 was expressed in Escherichia coli and a polyclonal antibody to the purified recombinant protein was raised. The antibody shows no cross-reactivity to recombinant cytosolic Hsp70 protein and in 2-D gel blots it reacted specifically with the mHsp70 protein only. In immunofluorescence experiments, the antibody predominantly labeled mitochondria, and the observed labeling pattern was identical to that seen with a monoclonal antibody to the mitochondrial Hsp60 chaperonin. The affinity-purified antibody to mHsp70 was also employed to examine the subcellular distribution of the protein by cryoelectron microscopy and the immunogold-labeling technique. In these experiments, in addition to mitochondria, labeling with mitochondrial Hsp70 antibody was also observed on the plasma membrane and in unidentified cytoplasmic vesicles and granules. These studies raise the possibility that similar to the Hsp60 chaperonin and a number of other mitochondrial proteins, mHsp70 may have an extramitochondrial role.

Isolation of a germline-transmissible embryonic stem (ES) cell line from C3H/He mice

We have isolated three embryonic stem (ES) cell lines from C3H/He mice using mouse STO cells as a feeder layer. One ES cell line (H-1) was male, and two (H-2 and H-3) were female, as determined by polymerase chain reaction, in situ hybridization, and karyotype analyses. All were immunocytochemically reactive with a C3H strain-specific antibody. Injection of cells from the female ES H-3 line into C57BL/6 blastocysts yielded four chimeras with slight coat color chimerism. All chimeras were male, and as expected, no germline-transmission was observed. By contrast, when male ES H-1 cells were injected into the perivitelline space of 8-cell C57BL/6 embryos, one male mouse with overt coat color chimerism was recovered, and it produced ES H-1-derived offspring exclusively. This germline-transmissible C3H/He cell line represents a novel addition to those ES lines currently employed for gene manipulation studies of development.

Primary monoclonal and secondary polyclonal growth of colon neoplastic lesions in C3H/HeN<-->BALB/c chimeric mice treated with 1,2-dimethylhydrazine immunohistochemical detection of C3H strain-specific antigen and simple sequence length polymorphism analysis of DNA

To determine the clonality and cellular origin of colon pre-neoplastic and neoplastic lesions, C3H/HeN<-->BALB/c chimeric mice treated with 1,2-dimethylhydrazine (DMH) were investigated immunohistochemically using a specific antibody to C3H strain-specific antigen (CSA) enabling immunohistochemical discrimination of C3H cells in histological sections of chimeric mouse tissues. To confirm the results of immunostaining, simple sequence length polymorphism (SSLP) analysis was performed on DNA samples extracted from histological sections of adenocarcinomas. C3H/HeN<-->BALB/c chimeric mice were produced by an aggregation procedure and together with BALB/c and C3H/HeN animals were given weekly s.c. injections of 20 mg/kg body weight DMH for up to 20 weeks. At weeks 20 and 35 animals were killed and autopsied. In normal colonic mucosa of the chimeras, each gland was composed entirely of either CSA-positive or -negative cells and no mixed glands were found. Cells of all focal atypias in chimeric mice were, in each case, homogeneous for one or another of the parental types. Of 91 adenomas in chimeric mice, only one comprised both types of cell. Among 119 adenocarcinomas, 12 contained cells of both parental types. In these tumors, however, the 2 phenotypes were not mixed together at random but arranged in discrete areas, with intermingling limited to the junctions. SSLP analysis demonstrated DNAs extracted from CSA-positive and -negative tumors to exhibit the polymorphic patterns of C3H and BALB/c, respectively, while mixed CSA-positive and -negative tumors showed mixtures of both polymorphic DNA types.

Cloning of rat grp75, an hsp70-family member, and its expression in normal and ischemic brain

Following metabolic stress a variety of gene products are induced in cells in the brain, some of which may protect the tissue from subsequent stresses. The heat shock proteins (hsps), in particular hsp70, have been widely studied in this context, but evidence for the involvement of known hsps in protection of the CNS is inconclusive. We have therefore undertaken the search for other stress-induced proteins which may mitigate ischemic injury. Beginning with degenerate RT-PCR, we have isolated a rat-brain cDNA encoding a protein highly similar to human grp75, a mitochondrial member of the hsp70-family of stress proteins. It is also highly similar to two non-mitochondrial proteins; mortalin, a senescence-related gene product, and pbp74, a protein implicated in B-cell peptide processing. Sequence structure and phylogenetic analyses predict mitochondrial localization and induction by a calcium ionophore and glucose deprivation in PC12 cells support its identification as rat grp75. In situ analysis of normal brain reveals an unusual distribution, with very high expression in neurons of the basal forebrain, reticular and subthalamic nuclei, globus pallidus, amygdala and elsewhere. grp75-mRNA is upregulated following focal brain ischemia in a distinctive fashion. When the degree of injury is small, induction occurs in the area of injury, similar to the pattern observed for hsp70. However, when the injury is extensive, hsr is upregulated in neurons outside the ischemic area. The induction of grp75 may represent a sensitive marker of metabolically compromised tissue.

Mouse and human chromosomal assignments of mortalin, a novel member of the murine hsp70 family of proteins

Mortalin has been shown to exhibit differential distributions in cells with mortal and immortal phenotypes. In the present study, we report mot-2 cDNA cloning from RS-4 cells--an immortal clone from CD1-ICR mouse embryonic fibroblasts--and the chromosomal assignments of mortalin related genes to mouse chromosomes 18 and X by fluorescence in situ hybridization. Similar analysis assigned the gene to chromosome 5q31.1 in human.

Cloning and subcellular localization of human mitochondrial hsp70

We report the cloning, nucleotide sequence, and localization of mitochondrial hsp70, a member of the human hsp70 multi-gene family. The human mthsp75 gene was cloned by screening an expression library with monoclonal antibody 3A3 that recognizes three members of the human hsp70 family (hsp70, hsc70, and a 75-kDa protein with characteristics identical to that previously established for mitochondrial hsp70). The identity of the 75-kDa protein was confirmed by subcellular fraction of HeLa cells and the demonstration that the 3A3-reactive 75-kDa protein co-fractionates with mitochondrial localized proteins. The nucleotide sequence of the respective cDNA clone revealed an open reading frame of 679 amino acids with extensive sequence identity with members of the human hsp70 family. The derived amino-terminal pre-sequence shares features common to other mitochondrial targeting sequences. The identity of the cDNA was unequivocally established by introduction of an epitope-tag at the carboxyl terminus of the cloned gene, transfection and analysis by immunofluorescence. The tagged 75-kDa protein localizes to mitochondria, thus providing conclusive evidence that it corresponds to the human mitochondrial hsp70, referred to here as mthsp75.

cDNA cloning and efficient mitochondrial import of pre-mtHSP70 from rat liver

Members of the 70-kD heat shock protein family have been found in all free-living organisms investigated and in major compartments of eukaryotic cells where they are essential to a wide range of functions, including protein folding and targeting. We have isolated a mitochondrial homolog (mtHSP70) from rat liver using ATP agarose affinity chromatography. Its identity was confirmed on the basis of immunological analysis and Ca(2+)-dependent autophosphorylation. Using protein sequence obtained from the amino termius and nine endo Lys-C peptide fragments, we have employed oligonucleotides to isolate a full-length cDNA clone. The open reading frame encodes a protein of 679 amino acids and calculated M(r) 73,913 daltons. The sequence has a high degree of identity with other members of the HSP70 family, including Escherichia coli DnaK (51%), Saccharomyces cerevisiae SSC1p (65%), the constitutive cytosolic HSP70 from rat, HSC70 (46%), and the rat endoplasmic reticulum isoform, BiP, (49%). The cDNA encodes a precursor protein with a 46-amino-acid signal peptide that is absent from the protein isolated from rat liver. The protein also shows a high degree of identity (98%) with a protein isolated from mouse and human tissues (PBP74, Domanico et al., 1993; mortalin, Wadhwa et al., 1993a; CSA, Michikawa et al., 1993a); however, the intracellular localization of these proteins is uncertain. We show that the precursor of mtHSP70 is efficiently imported into isolated mitochondria from rat liver and processed from 74 kD to the mature 69-kD protein.

PBP74, a new member of the mammalian 70-kDa heat shock protein family, is a mitochondrial protein

The cloning of a cDNA encoding a new member of the highly conserved mammalian 70-kDa heat shock protein (hsp 70) family termed PBP74 was recently reported. Critical to an understanding of the function of this new hsp 70 is delineating its subcellular localization. Here we use a variety of immunological and biochemical approaches both in vitro and in vivo to demonstrate that PBP74 is imported into and resides in mitochondria. By confocal immunofluorescence microscopy PBP74 is detected in mitochondria, colocalizing with the mitochondrial 60-kDa heat shock protein. To address the inherent problem of serological cross-reactivity among the hsp70 family members, an influenza virus hemagglutinin epitope tag was introduced into the PBP74 cDNA. The epitope-tagged PBP74 protein transiently expressed in L cells localized to mitochondria. Moreover, deletion of the N-terminal 46-amino acid presequence results in a cytosolic localization of the epitope-tagged protein. Cell fractionation studies demonstrated PBP74 in purified mitochondria in a protease-protected location. After coupled transcription-translation the precursor of PBP74 is imported into isolated yeast mitochondria, where it becomes processed to the mature protein. According to a subfractionation of the mitochondria, the imported protein was found to be localized in the matrix space. Import in vitro is time- and temperature-dependent, requires matrix ATP, and is abolished upon depletion of the membrane potential across the mitochondrial inner membrane. Similarly, in mammalian cells PBP74 is synthesized as a pre-protein that requires membrane potential-dependent import into mitochondria for its maturation. Taken together, our data demonstrate that PBP74 is a mammalian mitochondrial hsp70.

Separation and sequencing of familiar and novel murine proteins using preparative two-dimensional gel electrophoresis

Strategies are needed for rapid protein isolation in order to identify disease-related proteins and facilitate the design of oligonucleotides for further molecular inquiry. In our laboratory, C3H10T1/2 murine fibroblasts have been found to express a variety of proteins in various subcellular fractions which are relevant to experimental transformation and carcinogenesis. Preparative two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) procedures were developed to identify major cytoplasmic proteins by electroblotting and microsequencing. Isoelectric focusing tube gels were enlarged to 6 mm ID to accommodate larger protein loads at 0.5 to 2 mg protein. Separated proteins were electrotransferred from 6 mm thick slab gels onto 0.22 mu polyvinylidene difluoride membranes. Nearly 100 prominent blotted proteins were stained with Coomassie Brilliant Blue between pI 4.5-7.0 and 18-106 kDa and, of these, 27 prominent and well-resolved proteins were selected for sequencing. Sequences of 14 to 24 amino acid residues in length were obtained from 11 proteins which were identified from computerized databases. Some of these identified proteins had structural or enzymatic functions while others had only recently been discovered, including a newly reported Hsp 70 class member and a novel calcium-binding protein, reticulocalbin. The new heat shock protein has a molecular mass of 75 kDa and has been designated as Grp75, PBP74, CSA or p66mot-1 in mice and humans with purported roles in transformation and antigen processing. Reticulocalbin is an endoplasmic reticular protein which contains six domains of the EF-hand motif associated with high-affinity calcium-binding proteins. It may be involved in protein transport and luminal protein processing. In addition, sequences of 5 to 11 residues in length were also obtained from six other unidentified proteins. Thus, we have found that preparative 2-D PAGE serves as a powerful one-step purification method for protein isolation and characterization from an important in vitro murine model for the study of carcinogenesis.