Haploidentical Stem Cell Transplantation Using Post-Transplant Cyclophosphamide for T-Cell Prolymphocytic Leukemia after Alemtuzumab Induction Therapy: A Case Report

T-cell prolymphocytic leukemia (T-PLL) is a rare aggressive disease with a poor prognosis. Allogeneic stem cell transplantation (allo-SCT) followed by alemtuzumab administration is the most promising treatment for T-PLL but is associated with a high risk of infections as alemtuzumab strongly suppresses cellular immunity, leading to high transplant-related mortality and unsatisfactory survival rates. In addition, for patients without human leukocyte antigen-matched donors, haploidentical stem cell transplantation (haplo-SCT) using post-transplant cyclophosphamide (PTCy) has been used because of the ready availability of donors and achievement of results comparable to those of transplantation with human leukocyte antigen-matched donors. However, there are no reports on the efficacy and safety, including infectious complications, of haplo-SCT with PTCy after alemtuzumab therapy in patients with. Here, we describe a 66-year-old Japanese male patient with T-PLL treated successfully with haplo-SCT after induction therapy of alemtuzumab for T-PLL. Approximately 3 months after the achievement of complete remission with alemtuzumab for T-PLL, haplo-SCT with reduced-intensity conditioning and PTCy was performed. Infectious complications were improved by early therapeutic interventions, and peripheral T cell counts gradually recovered. The patient was alive for more than 16 months after allo-SCT with no signs of relapse. Thus, haplo-SCT using PTCy should be considered as an option after alemtuzumab treatment for T-PLL.

Respiratory alkalosis does not alter NOx concentrations in human plasma and erythrocytes

To test the hypothesis that NOx (NO and NO, metabolites of NO) accumulates in red blood cells (RBC) in response to changes in PCO(2) and bicarbonate (HCO) concentration in blood, we examined the effect of changes in PCO(2) and HCO induced by hyperventilation in healthy adults on partitioning of NOx in whole blood. NOx in hemolysate was measured by a high-performance liquid chromatography-Griess system equipped with a C(18) reverse phase column to trap hemoglobin, which enables determination of whole blood NOx concentration and calculation of NOx concentration in RBC with high accuracy and reproducibility. NOx concentration in RBC was lower than that in plasma, and equilibrium between plasma and RBC was achieved rapidly after addition of NO. Changes in PCO(2) and HCO by hyperventilation failed to influence NOx concentrations in both plasma and RBC. Plasma NOx concentrations correlated with whole blood NOx and RBC NOx concentrations. Our results indicate that changes in PCO(2) or HCO induced by hyperventilation do not influence NOx compartmentalization in plasma and RBC.

Evidence for distinct membrane traffic pathways to melanosomes and lysosomes in melanocytes

We report here morphologic and biochemical evidence that melanosomes are distinct from lysosomes. Immunofluorescence analysis revealed that TRP-1, a melanosomal membrane protein, did not colocalize with lysosomal membrane proteins LAMP1 and LGP85 in melan-a cells. Wortmannin treatment of melanocytes enhanced the distinct compartmentalization of these melanosomal/lysosomal membrane proteins by the swelling of the endosomal-lysosomal systems. The heavily melanized melanosomes did not have an altered shape, which suggests a lesser degree of membrane dynamics of stage IV melanosomes. Terminal lysosomes loaded with TR-dextran are also distinct from melanosomes, thus indicating that melanosomes are isolated from the endocytic pathway that is a representative route to lysosomes. Because AP-3 mutation leads to mistargeting of both melanosome and lysosome membrane proteins, we propose that there is a late sorting step for melanosomes and lysosomes in melanocytes after AP-3 sorting.

Overexpression of Cbfa1 in osteoblasts inhibits osteoblast maturation and causes osteopenia with multiple fractures

Targeted disruption of core binding factor alpha1 (Cbfa1) showed that Cbfa1 is an essential transcription factor in osteoblast differentiation and bone formation. Furthermore, both in vitro and in vivo studies showed that Cbfa1 plays important roles in matrix production and mineralization. However, it remains to be clarified how Cbfa1 controls osteoblast differentiation, bone formation, and bone remodelling. To understand fully the physiological functions of Cbfa1, we generated transgenic mice that overexpressed Cbfa1 in osteoblasts using type I collagen promoter. Unexpectedly, Cbfa1 transgenic mice showed osteopenia with multiple fractures. Cortical bone, which was thin, porous, and enriched with osteopontin, was invaded by osteoclasts, despite the absence of acceleration of osteoclastogenesis. Although the number of neonatal osteoblasts was increased, their function was impaired in matrix production and mineralization. Furthermore, terminally differentiated osteoblasts, which strongly express osteocalcin, and osteocytes were diminished greatly, whereas less mature osteoblasts expressing osteopontin accumulated in adult bone. These data indicate that immature organization of cortical bone, which was caused by the maturational blockage of osteoblasts, led to osteopenia and fragility in transgenic mice, demonstrating that Cbfa1 inhibits osteoblast differentiation at a late stage.

Increased basal levels of plasma nitric oxide in Type 2 diabetic subjects. Relationship to microvascular complications

To assess the underlying mechanisms of decreased endothelial function and advanced vascular complications in patients with Type 2 diabetes, we determined basal levels of plasma nitric oxide (NO(x): NO(2)(-) and NO(3)(-)) using a newly developed high-performance liquid chromatography (HPLC)-Griess method in hospitalized 129 diabetic and 76 nondiabetic subjects, and examined their clinical characteristics. Serum lipid peroxide and advanced glycation end products (AGEs) as markers of oxidative stress were also measured, and intima-media thickness (IMT) of the carotid artery was evaluated as a marker of atherosclerosis. In diabetic subjects, microvascular complications were newly evaluated during their admission. There were no differences in age or sex between the diabetic and nondiabetic subjects. Although there was no difference in basal plasma NO(2)(-) levels between the two groups, the basal levels of plasma NO(3)(-) in diabetic subjects were significantly higher than those in nondiabetic subjects. Plasma NO(x) levels in neither diabetic nor nondiabetic subjects correlated with serum lipids, HbA1c, or IMT. In diabetic subjects, plasma NO(3)(-) levels were related not only to the presence of hypertension but also to advanced microvascular complications. Moreover, plasma NO(3)(-) levels were positively correlated with both serum lipid peroxide and AGEs. Multiple regression analysis revealed that serum AGEs level was strongly associated with plasma NO(3)(-) level. Thus, the findings are consistent with the hypothesis that decreased endothelium-dependent vasodilation in diabetic subjects is associated with the impaired action of NO secondary to its inactivation resulting from increased oxidative stress, rather than decreased NO production from vascular endothelium, and that abnormal NO metabolism is related to advanced diabetic microvascular complications.

cDNA cloning of the Cry1Aa receptor variants from Bombyx mori and their expression in mammalian cells

We cloned cDNA of three variants of BtR175, a putative Bombyx mori receptor for Bacillus thuringiensis Cry1Aa delta-endotoxin by PCR. These variants were likely to be allelic to BtR175. cDNA of BtR175b, the most distant variant from BtR175, was introduced into mammalian cells. BtR175b protein was expressed in the plasma membrane of the cells and showed binding activity to Cry1Aa.

NO(x) contamination in laboratory ware and effect of countermeasures

Contamination of various types of laboratory wares with NO(x) (NO(-)(2) and NO(-)(3)) was assessed systematically and the effect of extensive washing as a countermeasure was evaluated. Mean NO(x) contamination arising from a model procedure for NO(x) determination in plasma was 0.93 microM (range, 0.35-1.49 microM). The major source of contamination included conical tubes (54.8%) and pipette tips used for transfer of solution (12.3-16.3%). Except for soft glassware, most NO(x) contamination could be washed out by pure water. Although NO(x) contamination in respective laboratory wares could be reduced below detection levels by extensive washing, summation of the contamination through the model procedure could not be completely abolished (but the effect of washing persisted at least 10 days). Heavy contamination was noted in glassware (especially soft glass) and ultrafiltration units, which was difficult to remove. Several types of vacuum blood sampling tubes contained various levels of NO(x). Our results indicated that a small but significant amount of contamination remained in laboratory ware even after extensive washing, and that it is advisable to avoid the use of glassware (soft glass), ultrafiltration units, and vacuum blood sampling tubes during the processing of clinical sampling for the measurement of NO(x).

Small guanosine triphosphatase Rho/Rho-associated kinase as a novel regulator of intracellular redistribution of lysosomes in invasive tumor cells

To investigate the role of RhoA on the intracellular membrane dynamics of lysosomes in rat hepatoma cells (MM1), we analyzed the localization of lysosomal aspartic proteinase cathepsin D by confocal immunofluorescence microscopy in the dominant active RhoA-transfected cells. Here we show that the transfection of the dominant active form of human small guanosine triphosphatase (GTPase) RhoA in MMI cells, a highly invasive cell line, causes the redistribution and spreading of small punctate structures stained for cathepsin D throughout the cytoplasm. We found that the microtubule organization was markedly different in the two cell lines: uniformly developed and polymerized microtubule filaments were seen in the mock transfectants; however, the dynamic organization of microtubules was less pronounced in the active RhoA transfectants. Furthermore, we found for the first time that a selective inhibitor of Rho-associated kinase (p160ROCK), Y-27632, impeded the subcellular spreading of cathepsin D staining and promoted reclustering of cathepsin D toward the perinuclear region in the active RhoA-transfected cells. To our knowledge, this is the first indication that the RhoA/ROCK-mediated signaling pathway is involved in the intracellular membrane dynamics of lysosomes by regulating the cytoskeletal microtubule organization as well as the actin cytoskeletons.

Centromere/kinetochore localization of human centromere protein A (CENP-A) exogenously expressed as a fusion to green fluorescent protein

Three human centromere proteins, CENP-A, CENP-B and CENP-C, are a set of autoantigens specifically recognized by anticentromere antibodies often produced by patients with scleroderma. Microscopic observation has indicated that CENP-A and CENP-C localize to the inner plate of metaphase kinetochore, while CENP-B localizes to the centromere heterochromatin beneath the kinetochore. The antigenic structure, called "prekinetochore", is also present in interphase nuclei, but little is known about its molecular organization and the relative position of these antigens. Here, to visualize prekinetochore in living cells, we first obtained a stable human cell line, MDA-AF8-A2, in which human CENP-A is exogenously expressed as a fusion to a green fluorescent protein of Aequorea victoria. Simultaneous staining with anti-CENP-B and anti-CENP-C antibodies showed that the recombinant CENP-A colocalized with the endogenous CENP-C and constituted small discrete dots attaching to larger amorphous mass of CENP-B heterochromatin. When the cell growth was arrested in G1/ S phase with hydroxyurea, CENP-B heterochromatin was sometimes highly extended, while the relative location between GFP-fused CENP-A and the endogenous CENP-C was not affected. These results indicated that the fluorescent CENP-A faithfully localizes to the centromere/kinetochore throughout the cell cycle. We then obtained several mammalian cell lines where the same GFP-fused human CENP-A construct was stably expressed and their centromere/kinetochore is fluorescent throughout the cell cycle. These cell lines will further be used for visualizing the prekinetochore locus in interphase nuclei as well as analyzing kinetochore dynamics in the living cells.

Lysosomal cysteine protease, cathepsin H, is targeted to lysosomes by the mannose 6-phosphate-independent system in rat hepatocytes

The contribution of mannose 6-phosphate (Man 6-P)-dependent and -independent systems to lysosomal targeting of cathepsin H, a lysosomal cysteine protease, was investigated by metabolic labeling with [32P]phosphate and [35S]methionine/cysteine in primary cultures of rat hepatocytes. Metabolic labeling experiments with [32]phosphate revealed that only the proform of cathepsin H acquired Man 6-P residues on its high mannose type oligosaccharide, and that most of the phosphorylated procathepsin H was secreted into the medium without having undergone significant intracellular dephosphorylation. Thus, acquisition of Man 6-P residues did not correlate with targeting of cathepsin H to lysosomes. Pulse-chase experiments with [35S]methionine/cysteine showed that only about 10% of the newly synthesized cathepsin H was secreted as a proform while the remainder was retained intracellularly in processed mature form. These results indicate that the majority of newly synthesized cathepsin H is targeted to lysosomes by a Man 6-P-independent mechanism, at least in rat hepatocytes.

Lysosomal cysteine protease, cathepsin B, is targeted to lysosomes by the mannose 6-phosphate-independent pathway in rat hepatocytes: site-specific phosphorylation in oligosaccharides of the proregion

Cathepsin B, a lysosomal cysteine protease, is synthesized as a glycoprotein with two N-linked oligosaccharide chains, one of which is in the propeptide region while the other is in the mature region. When cultured rat hepatocytes were labeled with [(32)P]phosphate, (32)P-labeled cathepsin B was immunoprecipitated only in the proform from cell lysates and medium. Either Endo H or alkaline phosphatase treatment of (32)P-labeled procathepsin B demonstrated the acquisition of a mannose 6-phosphate (Man 6-P) residue on high mannose type oligosaccharides. To identify the site of phosphorylation, immunoisolated (35)S- or (32)P-labeled procathepsin B was incubated with purified lysosomal cathepsin D, since cathepsin D cleaves 48 amino acid residues from the N-terminus of procathepsin B, in which one N-linked oligosaccharide chain was also included [Kawabata, T. et al. (1993) J. Biochem. 113, 389-394]. Treatment of intracellular (35)S-labeled procathepsin B with a molecular mass of 39-kDa with cathepsin D resulted in the production of the 31-kDa intermediate form, but the (32)P-label incorporated into procathepsin B disappeared after treatment with cathepsin D. These results indicate that the phosphorylation of procathepsin B is restricted to an oligosaccharide chain present in the propeptide region. Interestingly, cathepsin B sorting to lysosomes was not inhibited by NH(4)Cl treatment and about 90% of the intracellular procathepsin B initially phosphorylated was secreted into the medium without being dephosphorylated intracellularly, and did not bind significantly to cation-independent-Man 6-P receptor, suggesting the failure of Man 6-P-dependent transport of procathepsin B to lysosomes. Additionally, about 50% of the newly synthesized (35)S-labeled cathepsin B was retained in the cells in mature forms consisting of a 29-kDa single chain form and a 24-kDa two chain form, while part of the procathepsin B was associated with membranes in a Man 6-P-independent manner. Taken together, these results show that in rat hepatocytes, cathepsin B is targeted to lysosomes by an alternative mechanism(s) other than the Man 6-P-dependent pathway.

Cbfa1 is a positive regulatory factor in chondrocyte maturation

Cbfa1 is a transcription factor that belongs to the runt domain gene family. Cbfa1-deficient mice showed a complete lack of bone formation due to the maturational arrest of osteoblasts, demonstrating that Cbfa1 is an essential factor for osteoblast differentiation. Further, chondrocyte maturation was severely disturbed in Cbfa1-deficient mice. In this study, we examined the possibility that Cbfa1 is also involved in the regulation of chondrocyte differentiation. mRNAs for both Cbfa1 isotypes, type I Cbfa1 (Pebp2alphaA/Cbfa1) and type II Cbfa1 (Osf2/Cbfa1 or til-1), which are different in N-terminal domain, were expressed in terminal hypertrophic chondrocytes as well as osteoblasts. In addition, mRNA for type I Cbfa1 was expressed in other hypertrophic chondrocytes and prehypertrophic chondropcytes. In a chondrogenic cell line, ATDC5, the expression of type I Cbfa1 was elevated prior to differentiation to the hypertrophic phenotype, which is characterized by type X collagen expression. Treatment with antisense oligonucleotides for type I Cbfa1 severely reduced type X collagen expression in ATDC5 cells. Retrovirally forced expression of either type I or type II Cbfa1 in chick immature chondrocytes induced type X collagen and MMP13 expression, alkaline phosphatase activity, and extensive cartilage-matrix mineralization. These results indicate that Cbfa1 is an important regulatory factor in chondrocyte maturation.

Functional domain structure of human heterochromatin protein HP1(Hsalpha): involvement of internal DNA-binding and C-terminal self-association domains in the formation of discrete dots in interphase nuclei

Human heterochromatin protein HP1(Hsalpha) possesses two evolutionarily conserved regions in the N- and C-terminal halves, so-called chromo and chromo-shadow domains, and DNA-binding domain in the internal non-conserved region. Here, to examine its in vivo properties, we expressed HP1(Hsalpha) as a fusion product with green fluorescent protein in human cells. HP1(Hsalpha) was observed to form discrete dots in interphase nuclei and to localize in the centromeric region of metaphase chromosomes by fluorescence microscopy. Interestingly, this dot-forming activity was also found in the N-terminal half retaining the chromo and DNA-binding domains and in the C-terminal chromo-shadow domain. However, the chromo domain alone stained nuclei homogeneously. To correlate this dot-forming activity with self-associating activity in vitro, the chromo and chromo-shadow domain peptides were independently expressed in Escherichia coli, affinity purified, and chemically cross-linked with glutaraldehyde. In a SDS-polyacrylamide gel, the former mainly produced a dimer, while the latter produced a ladder of bands up to a tetramer. When passed through a gel filtration column in a native state, these peptides were exclusively separated as a dimer and a tetramer, respectively. These results suggested that the internal DNA-binding and C-terminal chromo-shadow domains are both involved in heterochromatin formation in vivo.

Oncogenic Ras triggers cell suicide through the activation of a caspase-independent cell death program in human cancer cells

To prevent neoplasia, cells of multicellular organisms activate cellular disposal programs such as apoptosis in response to deregulated oncogene expression, making the suppression of such programs an essential step for potentially neoplastic cells to become established as clinically relevant tumors. Since the mutation of ras proto-oncogenes, the most frequently mutated proto-oncogenes in human tumors, is very rare in some tumor types such as glioblastomas and gastric cancers, we hypothesized that mutated ras genes might activate a cell death program that cannot be overcome by these tumor types. Here we show that the expression of oncogenically mutated ras gene induces cellular degeneration accompanied by cytoplasmic vacuoles in human glioma and gastric cancer cell lines. Cells dying as a result of oncogenic Ras expression had relatively well-preserved nuclei that were negative for TUNEL staining. An immunocytochemical analysis demonstrated that the cytoplasmic vacuoles are derived mainly from lysosomes. This oncogenic Ras-induced cell death occurred in the absence of caspase activation, and was not inhibited by the overexpression of anti-apoptotic Bcl-2 protein. These observations suggested that oncogenic Ras-induced cell death is most consistent with a type of programmed cell death designated 'type 2 physiological cell death' or 'autophagic degeneration', and that this cell death is regulated by a molecular mechanism distinct from that of apoptosis. Our findings suggest a possible role for this non-apoptotic cell death in the prevention of neoplasia, and the activation of the non-apoptotic cell death program may become a potential cancer therapy complementing apoptosis-based therapies. In addition, the approach used in this study may be a valuable way to find genetically-regulated cell suicide programs that cannot be overcome by particular tumor types.

A 60 kDa plasma membrane protein changes its localization to autophagosome and autolysosome membranes during induction of autophagy in rat hepatoma cell line, H-4-II-E cells

We previously reported the preparation and characterization of an antibody against membrane fraction of autolysosomes from rat liver (J. Histochem. Cytochem. 38, 1571-1581, 1990). Immunoblot analyses of total membrane fraction of a rat hepatoma cell line, H-4-II-E cells by this antibody suggested that H-4-II-E cells expressed several autolysosomal proteins, including a protein with apparent molecular weight of 60 kDa. It was suggested that this 60 kDa protein was a peripheral membrane protein, because it was eluted from the membrane by sodium carbonate treatment. We prepared an antibody against this 60 kDa protein by affinity purification method, and examined its behavior during induction of autophagy. Autophagy was induced by transferring the cells from Dulbecco's modified Eagle medium (DMEM) containing 12% fetal calf serum into Hanks' balance salt solution. In DMEM, the 60 kDa protein showed diffused immunofluorescence pattern, and immunoelectron microscopy suggested that this protein was located on the extracellular side of the plasma membrane. After inducing autophagy, the immunofluorescence configuration of the 60 kDa protein changed from the diffused pattern to a granulous one. Immunoelectron microscopy showed that the 60 kDa protein was localized on the luminal side of the limiting membrane of autolysosomes and endosomes. In the presence of bafilomycin A1 which prevents fusion between autophagosomes and lysosomes, the 60 kDa protein was localized on the limiting membrane of the autophagosomes and endosomes. These results suggest that the 60 kDa protein is transported from the plasma membrane to the autophagosome membrane through the endosomes.

Maturational disturbance of chondrocytes in Cbfa1-deficient mice

Cbfa1, a transcription factor that belongs to the runt-domain gene family, plays an essential role in osteogenesis. Cbfa1-deficient mice completely lacked both intramembranous and endochondral ossification, owing to the maturational arrest of osteoblasts, indicating that Cbfa1 has a fundamental role in osteoblast differentiation. However, Cbfa1 was also expressed in chondrocytes, and its expression was increased according to the maturation of chondrocytes. Terminal hypertrophic chondrocytes expressed Cbfa1 extensively. The significant expression of Cbfa1 in hypertrophic chondrocytes was first detected at embryonic day 13.5 (E13.5), and its expression in hypertrophic chondrocytes was most prominent at E14.5-16.5. In Cbfa1-deficient mice, whose entire skeleton was composed of cartilage, the chondrocyte differentiation was disturbed. Calcification of cartilage occurred in the restricted parts of skeletons, including tibia, fibula, radius, and ulna. Type X collagen, BMP6, and Indian hedgehog were expressed in their hypertrophic chondrocytes. However, osteopontin, bone sialoprotein, and collagenase 3 were not expressed at all, indicating that they are directly regulated by Cbfa1 in the terminal hypertrophic chondrocytes. Chondrocyte differentiation was severely disturbed in the rest of the skeleton. The expression of PTH/PTHrP receptor, Indian hedgehog, type X collagen, and BMP6 was not detected in humerus and femur, indicating that chondrocyte differentiation was blocked before prehypertrophic chondrocytes. These findings demonstrate that Cbfa1 is an important factor for chondrocyte differentiation.

In vitro binding study of adaptor protein complex (AP-1) to lysosomal targeting motif (LI-motif)

Lysosomal membrane glycoproteins carry targeting information in cytoplasmic regions. Two distinct targeting motifs in these regions, GY (glycine-tyrosine) and LI (leucine-isoleucine), have been identified and characterized. Accumulating evidence suggests that the adaptor complexes (AP-1, AP-2, and AP-3) recognize this information in cytoplasmic tails of transmembrane proteins. Here we report two different in vitro analyses (affinity beads and surface plasmon resonance) which revealed specific interaction between the cytoplasmic tail of LGP85 and AP-1 but not so with AP-2. We also noted requirement of the LI motif of the LGP85 tail in binding to the AP-1 complex. Our data and others which indicated the binding of AP-3 to the LIMP II (synonym of LGP85) tail suggest that the cytoplasmic tail of LGP85 interacts with AP-1 at the trans-Golgi network (TGN) and AP-3 at late endosomes, respectively. We propose that this sequential interaction between the lysosomal targeting signal and distinct APs along its transport pathway is responsible for the critical sorting of lysosomal membrane proteins and/or the potential proofreading system of mistargeted molecules.

ADP-ribosylation factor-1 is sensitive to N-ethylmaleimide

The treatment of normal rat kidney cells with N-ethylmaleimide caused the release of beta-COP, a component of coatomer, from the Golgi apparatus without causing disassembly of the organelle. The release of beta-COP, which was not due to depolymerization of microtubules, was markedly blocked by the activation of GTP-binding proteins by aluminum fluoride or a nonhydrolyzable analogue of GTP. To determine which component is N-ethylmaleimide-sensitive, we reconstituted the recruitment of coatomer from the bovine brain cytosol onto the Golgi apparatus in digitonin-permeabilized cells. In cells treated with N-ethylmaleimide before permeabilization, beta-COP was still recruited onto the Golgi apparatus. In contrast, beta-COP was not recruited when N-ethylmaleimide-treated bovine brain cytosol was used. These results suggest that the N-ethylmaleimide-sensitive factor(s) are present in the cytosol. It is known that coatomer and ADP-ribosylation factor-1 (ARF1) are the only cytoplasmic proteins needed for the assembly of Golgi-derived coated vesicles. N-Ethylmaleimide treatment of a coatomer-rich fraction did not affect the binding of beta-COP to the Golgi apparatus, whereas the same treatment of an ARF-rich fraction abolished beta-COP binding. Similar results were obtained using purified recombinant ARF1. Concomitant with inactivation, 0.85 mol of N-ethylmaleimide was incorporated into 1 mol of ARF1. ARF1 contains only one cysteine residue (Cys-159), which is located near the base moiety of the bound guanine nucleotide.

Purification and partial amino acid sequences of the binding protein from Bombyx mori for CryIAa delta-endotoxin of Bacillus thuringiensis

The binding protein for Bacillus thuringiensis delta-endotoxin, CryIAa, from the brush border membrane of the midgut of Bombyx mori was purified by the dot blot method and delta-endotoxin affinity chromatography. The binding protein was purified to 235-fold enrichment from cholic acid extracts of brush border membranes from B. mori midgut by activated CryIAa-affinity chromatography and DEAE ion-exchange chromatography. The purified binding protein showed a single band of 180 kDa by sodium dodecyl sulfate polyacrylamide gel electrophoresis and this band specifically reacted to 125I-labeled CryIAa on Immobilon membrane. The affinity of the binding protein for CryIAa was equivalent to that of the brush border membrane vesicles and solubilized membrane proteins. Partial amino acid sequences of the binding protein showed sequence similarity to the cadherin-like binding protein for CryIAb from Manduca sexta, but not for CryIAc binding protein from M. sexta and Heliothis virescens.

Epitope mapping of human centromere autoantigen centromere protein C (CENP-C); heterogeneity of anti-CENP-C response in rheumatic diseases

OBJECTIVE

To analyze the autoantigenic epitopes of centromere protein C (CENP-C) recognized by anti-centromere antibodies (ACA).

METHODS

A series of truncated peptides of human CENP-C were expressed in Escherichia coli and immunoblotting analysis was performed with 45 ACA positive sera obtained from patients with different types of autoimmune diseases.

RESULTS

Although 9 epitopes were scattered over the entire molecule, the N terminus was immunodominant for IgG and IgM classes and the C terminus was dominant for IgG class. Both epitopes were separately located within the instability and centromere targeting domains in vivo, or the oligomerization-accessible and homodimerization domains in vitro, respectively. In contrast, minor epitopes were clustered at the internal DNA binding domain. A number of patterns of immunoreactivities against 3 representative antigenic sites by IgG or IgM class antibodies were found.

CONCLUSION

The results indicated the existence of different anti-CENP-C responses in rheumatic diseases and a possible correlation between antigenic regions and functional sites in the CENP-C antigen.

Nucleotide specificity at the boundary and size requirement of the target sites recognized by human centromere protein B (CENP-B) in vitro

Human centromere protein B (CENP-B) has a sequence-specific DNA binding activity. We previously reported several CENP-B binding motifs by analysing synthetic oligonucleotides as well as alphoid DNA isolated from the human genomic library. Here, we examined the size requirement and nucleotide specificity of human CENP-B binding sequences in vitro. We synthesized three sets of mixed oligonucleotides containing diverged authentic binding sites (CTTCGTTGGAAACGGGA) in which certain pairs of nucleotides (underlined) were degenerated. Each oligonucleotide with a defined sequence was separately introduced into a plasmid and mixed with GST-fused recombinant CENP-B. The DNA-protein complex formed was affinity purified with glutathione Sepharose. Any nucleotide substitutions at the positions 1, 2 and 17 did not significantly influence the recovery, while the substitutions at positions 3, 4 and 16 did, suggesting that the internal 14-bp motif (TCGTTGGAAACGGG) constituted the minimum requirement. However, it showed a lower affinity to CENP-B, compared with the authentic motif. The inclusion of T at the 5' end greatly increased the affinity, and the further addition of A or T at the 3' end (TTCGTTGGAAACGGGA/T) offered affinity similar to the authentic motif. The first nucleotide of the 17-bp authentic binding motif may not be essential for CENP-B binding.

cDNA cloning of a novel autoantigen targeted by a minor subset of anti-centromere antibodies

Using autoimmune serum from a patient with anti-centromere antibodies, we have identified and partially characterized a novel protein with a mol. wt of approximately 27 kD (hereafter referred to as p27). A cDNA expression library was screened with this serum, and two overlapping inserts were isolated among three positive clones other than clones corresponding to centromere protein (CENP)-B and CENP-C. Analysis of the sequence showed an open reading frame of approximately 0.6 kb encoding 199 amino acids with a predicted mol. wt of 21.5 kD. Immunoblotting analysis with bacterial recombinant p27 showed that approximately 2% of anti-centromere antibody-positive patients had autoantibodies to p27, whereas only one of 215 autoimmune patients without anti-centromere antibodies reacted with the recombinant. All five cases with anti-p27 antibodies, who were diagnosed as having scleroderma and/or Sjögren's syndrome, showed internal organ involvement. Although affinity-purified anti-p27 human or mouse polyclonal antibodies failed to stain any cellular structures in an immunofluorescence study, the potential association of anti-p27 with anti-centromere antibodies suggests that this novel autoantigen might play a role in mitosis.

The effects of a newly developed nonsteroidal anti-inflammatory drug (M-5011) on arachidonic acid metabolism in rheumatoid synovial fibroblasts

M-5011 (d-2-[4-(3-methyl-2-thienyl)phenyl]propionic acid) is a newly developed nonsteroidal anti-inflammatory drug (NSAID) that displays potent anti-inflammatory and analgesic properties with low ulcerogenic activities in animal models. In this study, the effects of M-5011 on arachidonic acid (AA) metabolism in synovial fibroblasts from patients with rheumatoid arthritis were evaluated and compared with those of other NSAIDs in vitro. Either M-5011 or ketoprofen potently inhibited prostaglandin (PG) E2 production by cyclooxygenase (COX)-2 from exogenous AA in interleukin-1beta (IL-1beta)-stimulated cells. The IC50 values of M-5011 and ketoprofen were 4.4 x 10(-7) and 5.9 x 10(-7) M, respectively. However, diclofenac and indomethacin were one order less potent. Although the latter two drugs exhibited time-dependent and irreversible inhibition on COX-2 in IL-1beta-stimulated cells, the inhibitory effects of M-5011 and ketoprofen were reversible. PGE2 production by COX-1 from exogenous AA in non-stimulated cells was also inhibited by M-5011 with a potency less than that of ketoprofen. In addition, M-5011 inhibited [14C]AA release from prelabeled synovial cells stimulated with bradykinin. However, ketoprofen hardly affected the [14C]AA release. It is likely that the effects of M-5011 on AA metabolism are, in part, responsible for its in vivo efficacy and safety profile.

A fluid-phase endocytotic capacity and intracellular degradation of a foreign protein (horseradish peroxidase) by lysosomal cysteine proteinases in the rat junctional epithelium

We investigated the co-localization of lysosomal cathepsins B, H and L, and horseradish peroxidase (HRP) in junctional epithelial (JE) cells both as a fluid-phase endocytotic marker to demonstrate the fluid-phase endocytotic capacity of JE cells, and to understand the morphological relationships of the endocytosed foreign substances to lysosomal cathepsins in these cells. The diaminobenzidine (DAB) histochemical and cytochemical methods and immunohistochemical avidin-biotin-peroxidase complex and immunocytochemical post-embedding colloidal gold methods were used. Under light microscopy, DAB reaction products based on HRP were found in JE but were rare or absent in the oral sulcular epithelium and oral epithelium. Immunolabeling for cathepsins B and H was found in the granular structures of the cells, but no cathepsin L was identified. With electron microscopy, DAB reaction products, which indicated both HRP and the azurophil granules of neutrophils, were endocytosed into JE cells. Using a post-embedding technique, gold particles indicating HRP were present on the plasma membrane of JE cells, at the periphery of electronlucent vacuoles, and in the electrondense granules. Gold particles indicating cathepsin B or H were found in the electrondense granules. With different sizes of colloidal golds, the co-localization of cathepsin B or H with HRP was indicated only in the electrondense portion of the larger vacuoles consisting of electronlucent and -dense parts. This study provided the first morphological data which indicate that JE has a fluid phase endocytotic capacity, and which suggest that the lysosomal cathepsins B and H are involved in the intracellular degradation of foreign substances invading through the gingival sulcus in JE cells.

Possible involvement of heterotrimeric G proteins in the organization of the Golgi apparatus

Nordihydroguaiaretic acid (NDGA) caused disassembly of the Golgi apparatus of NRK cells in a dose-, time-, and energy-dependent manner but not in a microtubule-dependent manner. In contrast to brefeldin A, NDGA did not cause release of beta-COP, a component of Golgi-derived vesicles. However, NDGA-induced disassembly was blocked by AlF4-, an activator of the heterotrimeric but not the small GTP-binding proteins. In digitonin-permeabilized cells, guanosine 5'-3-O-(thio)triphosphate (GTPgammaS) as well as AlF4- blocked the NDGA-promoted disassembly of the Golgi apparatus, and Gbetagamma (betagamma subunits of heterotrimeric G proteins) reversed this effect. Our present results suggest the possible involvement of heterotrimeric G proteins in the organization of the Golgi apparatus.

The distribution of binding sites for centromere protein B (CENP-B) is partly conserved among diverged higher order repeating units of human chromosome 6-specific alphoid DNA

We previously reported the isolation of alphoid satellite clones from a human genomic library using a DNA immunoprecipitation with centromere protein B (CENP-B). Here, we have characterized the distribution of CENP-B-binding sites on the 3-kb BamHI repeats of the cos2 clone. Using in situ hybridization, this alphoid satellite was located primarily at the centromeric region of chromosome 6. The functional binding sites were mapped by precipitating the restriction fragments with recombinant CENP-B in vitro. One repeat (2B3-11) consisted of 19 copies of alphoid monomer, eight of which possessed the binding sites, while another (2B3-9) consisted of 18 copies of the monomer, seven of which possessed the binding sites. The distribution of the sites was well conserved between them, except for the terminus. A similar analysis with the remaining 6-kb region suggested the presence of a continuous 1-kb region with regular spacing of EcoRI sites and the CENP-B-binding sites. When the nucleotide sequence of 2B3-11 was compared with that of another chromosome 6-specific alphoid repeat (p308) that had been described previously, this 1-kb region was highly conserved between them. The distribution of the CENP-B binding sites and the order of alphoid monomers might define the folding of alphoid repeats in the centromeric region.

Characterization of internal DNA-binding and C-terminal dimerization domains of human centromere/kinetochore autoantigen CENP-C in vitro: role of DNA-binding and self-associating activities in kinetochore organization

Human centromere protein C (CENP-C), a chromosomal component of the inner plate of kinetochores, was originally identified as one of the centromere autoantigens. In a previous study, we showed that it possesses DNA-binding activity in vitro. Recently, centromere-binding activity was suggested at the C-terminal region in vivo. However, little is known about the role of CENP-C in kinetochore organization. Here, to characterize its biochemical properties, three separate antigenic regions of human CENP-C were expressed in Escherichia coli, affinity purified and used in South-western blotting and chemical cross-linking analyses. We found that the internal DNA-binding domain was composed of two kinds of elements: the 'core' and two flanking 'stabilizing' elements that support the activity. When cross-linked with disuccinimidyl suberate (DSS), the N-terminal region produced the ladder bands of dimer and tetramer: the C-terminal region exclusively produced the dimer band, whereas the internal region was not affected at all. Dimer formation at the C-terminus in the native state was also indicated by gel filtration and the presence of conformation-specific autoantibodies in the patient's sera. These results suggest that human CENP-C consists of three functional units required for 'kinetochore assembly': a putative N-terminal oligomerization domain, an internal DNA-binding domain and a C-terminal dimerization domain.

Immunocytochemical study of cathepsin L and rat salivary cystatin-3 in rat osteoclasts treated with E-64 in vivo

The localization of cathepsin L and rat salivary cystatin-3 (RSC-3) in rat osteoclasts (rat femoral and alveolar bones) treated with or without E-64 (control) was examined immunocytochemically. In osteoclasts pretreated with E-64, immunoreactivity for cathepsin L was very weak extracellularly compared to that in the control osteoclasts. However, it was strong intracellularly. The localization of RSC-3 was unclear in the control osteoclasts, while in E-64 treated osteoclasts, both the clear zone and ruffled border areas showed a very strong immunoreaction. At the electron-microscopic level, in normal osteoclasts, numerous immunoreaction products for cathepsin L were found extracellularly in the bone matrix under the ruffled border, while few intracellular products were observed. In contrast, in the E-64-treated osteoclasts, only a few immunoreaction products were found extracellularly, while intracellularly cathepsin L was found in numerous endosome-lysosomal vacuoles. In the immunoreaction for RSC-3, the cytoplasm of the ruffled border was positive, and the tips of the RSC-3-positive ruffled border appeared to enter deeply into the bone matrix. Intracellularly, the granular reaction products of RSC-3 were found in the vacuoles (probably autophagolysosomes). Thus, in E-64-treated osteoclasts, inhibition of the extracellular release of cathepsin L was demonstrated. In addition, intralysosomal accumulation of RSC-3 and deep penetration of the RSC-3-positive ruffled border into the bone matrix were found. These findings suggest that RSC-3 is associated with the inhibition of cathepsin L in both the lysosomes (in the osteoclasts) and bone matrix.

Human homolog of Drosophila heterochromatin-associated protein 1 (HP1) is a DNA-binding protein which possesses a DNA-binding motif with weak similarity to that of human centromere protein C (CENP-C)

Heterochromatin-associated protein 1 (HP1) is a nonhistone chromosomal component tightly associated with the pericentromeric heterochromatic region of fruit fly, mouse, and human throughout the cell cycle. Drosophila HP1 has been shown to be involved in position effect variegation and to be required for the correct chromosome segregation in vivo, while the biological activity of human homolog (HP1Hsa) has not yet been characterized. We previously reported that human CENP-B and CENP-C, two major centromere heterochromatin autoantigens often recognized by autosera in scleroderma patients, possess DNA-binding activity in vitro. Here, we show that human HP1, which is also an autoantigen targeted by some types of anticentromere autosera, is a DNA-binding protein. Human HP1 was expressed as a GST-fusion in Escherichia coli and purified with glutathione-Sepharose. The DNA-binding activity of the recombinant HP1 was demonstrated by gel mobility shift assay and South-Western-type blotting. The minimum DNA-binding region was further limited to the internal 64-amino acid stretch that is less-conserved between human and fruit fly but retains a helix-enriched motif with weak similarity to CENP-C. This suggests that HP1 is involved in the pericentromeric heterochromatin formation by directly associating with genomic DNA.

[Lysosomal hydrolases have specific conformational domains for acquisition of mannose-6-phosphate]

In many mammalian cells, the transport of newly synthesized or externally added lysosomal enzymes to lysosomes is depend on their specific recognition by receptors for mannose 6-phosphate (Man-6-P). The physiological importance of this pathway was confirmed by the finding that fibroblasts from patients with mucolipidosis type II (ML-II ; I - cell disease) fail to phosphorylate mannose residues on their newly synthesized lysosomal enzymes, which results in the secretion of a large percentage of their acid hydrolases into the culture medium. However, lysosomal enzymes themselves do not contain the any consensus amino acid sequences for acquiring the Man-6-P recognition marker. Kornfeld et al revealed using cathepsin D-pepsinogen chimera proteins that UDP-N-acetylglucosamine: lysosomal enzyme N-acetylglucosamine-1-phosphotransferase recognizes not only oligosaccharides but also the three-dimensional structure of the lysosomal enzymes when transfers N-acetylglucosamine-1-phosphate to lysosomal acid hydrolases.

[Biosynthesis, processing, and lysosome targeting of acid phosphatase]

The biosyntheses, processing, and intracellular transport of lysosomal APase were studied using pulse-chase experiments with primary cultured rat hepatocytes and subcellular fractionation techniques of rat liver after pulse-labeling with [35S] methionine in vivo. Apase was transported as a membrane-bound enzyme from the site of synthesis in the ER through the Golgi complex to lysosomes. Unlike many lysosomal enzymes which are translocated into lysosomes through the mediation of the Man-6-P receptors, transport of APase to lysosomes was independent of the Man-6-P receptor system. The transport of APase to lysosomes is dependent on the GY-motif which is located in its cytoplasmic domain. Kinetic experiments combined with subcellular fractionation of rat liver showed that after reaching the lysosomes, the membrane-bound APase (67 kDa) is subsequently released into the lysosomal matrix in the 64 kDa form, which is further processed via the 55 kDa form to the 48 kDa one, the major form of APase in rat liver lysosomal content. Our data from the in vitro experiments further showed that APase is released from lysosomal membranes into the lysosomal matrix by cathepsin D in the 65 kDa form, with release of a 1 kDa peptide, following which the released enzyme is further processed to the 64 kDa form, probably by lysosomal cysteine protease.

Cathepsin D associates with lysosomal membranous protein

The membrane-association of early biosynthetic form of cathepsin D has been demonstrated in hepatoma cells, and this membrane-association is not mediated by mannose 6-phosphate residues, implying that a mannose 6-phosphate receptor-independent mechanism operates in the sorting of cathepsin D. In this paper, to demonstrate whether cathepsin D is associated with the lysosomal membranes, an in vitro binding experiment was carried out employing lysosomal cathepsin D or microsomal procathepsin D isolated from rat liver. Immunoblotting analysis revealed that an intermediate form of cathepsin D was associated with the lysosomal membranes; this lysosomal membrane-associated cathepsin D was released from the membranes by washing with Na2CO3 (pH 10.6) but not with solutions containing mannose 6-phosphate. This suggested that cathepsin D associates with the membranes by ionic-interaction, and that the membrane-associated cathepsin D resides as a peripheral membrane protein in the lysosomal membrane fraction. To confirm that the intermediate form of cathepsin D specifically interacts with the lysosomal integral membrane proteins, the lysosomal membrane fraction was treated with trypsin and the binding experiment was conducted. The result showed that the binding capacity of cathepsin D to the lysosomal membranes was apparently abolished and cathepsin D did not rebind to the membranes. These data suggest that the intermediate form of cathepsin D is preferentially recognized by the lysosomal membranous protein which complements the mannose 6-phosphate receptor-dependent intracellular sorting mechanism.

Expression of rat cathepsin D cDNA in Saccharomyces cerevisiae: implications for intracellular targeting of cathepsin D to vacuoles

To investigate the intracellular transport mechanisms of lysosomal cathepsin D in yeast cells, we produced cathepsin D in Saccharomyces cerevisiae by placing the coding region under the control of the promoter of the yeast glyceraldehyde-3-phosphate dehydrogenase (GAPDH) gene. Immunoblotting analysis by the use of an antibody specific for rat cathepsin D coding sequence produced an intermediate species which had a slightly higher molecular weight than that of the mature cathepsin D. Cell fractionation experiments demonstrated that the cathepsin D polypeptide was colocalized to the yeast vacuoles with the marker enzyme carboxypeptidase Y in a Ficoll step gradient. A biosynthesis study with pulse-chase kinetic analysis revealed that the precursor polypeptide was accurately sorted to the yeast vacuoles as determined by cell fractionation, and that N-linked carbohydrate modifications were not required for vacuolar sorting of this protein. To elucidate the role of the propeptide region of cathepsin D, which might function in the intracellular targeting to the vacuole, a deletion mutant of cathepsin D lacking the propeptide was prepared and its intracellular targeting was examined after transfection into yeast cells. Immunoblotting analysis demonstrated that the propeptide-deleted mutant protein was recovered in a low quantity as compared with that in the case of yeast cells expressing the wild-type protein in the isolated vacuolar fraction. Immunofluorescence analysis revealed that the deletion mutant protein appeared to be accumulated within the intracellular small vesicles but not in the carboxypeptidase Y-positive vacuoles. Overall, these results indicate that the rat cathepsin D precursor polypeptide is recognized by mechanisms similar to those involved in the intracellular sorting of vacuolar proteins through the ER/Golgi/vacuolar sorting pathway in yeast cells, and that the propeptide has an important function in translocation of the cathepsin D polypeptide to the vacuole.

Biochemical characterization of liver microsomal, Golgi, lysosomal, and serum beta-glucuronidases in dibutyl phosphate-treated rats

Organophosphate compounds are known to cause the selective release of rat liver microsomal beta-glucuronidase into plasma. To investigate the alterations of molecular forms and oligosaccharide moieties of liver beta-glucuronidase in organophosphate compound-administered rats, beta-glucuronidase was isolated from microsomal, Golgi, lysosomal, and serum fractions. In SDS-polyacrylamide gel electrophoresis, a single polypeptide band was observed on gels in Golgi and serum beta-glucuronidases. This result indicated that Golgi and serum beta-glucuronidases of treated rats did not undergo post-translational proteolytic processing, in contrast to those in control rat livers. Biochemical characterization of the isolated beta-glucuronidases by employing lectin affinity chromatography revealed that interaction of serum and Golgi enzymes with Ricinus communis agglutinin- and wheat germ agglutinin-Sepharose was fairly strong, and that microsomal and lysosomal enzymes were poorly retained on those columns. These results suggested that the serum and Golgi beta-glucuronidases are sialoglycoproteins. A clearance study also showed that infused serum beta-glucuronidase was slowly cleared from plasma with a half-life of about 60 min, but the asialo-serum enzyme was rapidly cleared with a half-life of about 5 min. These results imply that microsomal beta-glucuronidase undergoes extensive modification of the oligosaccharide moieties by terminal glycosyltransferases at the trans Golgi when it is destined for secretion into serum in response to treatment with an organophosphate compound.

Inhibitory effect of ethanol and colchicine on the intracellular processing of beta-glucuronidase which occurs in the Golgi complex

To investigate the effect of ethanol or colchicine on the intracellular proteolytic processing of lysosomal beta-glucuronidase, which is considered to occur in the Golgi complex in the intracellular sorting pathway, three rat liver Golgi subfractions, GF-1, GF-2, and GF-3, were isolated from ethanol- or colchicine-treated rats, and the electrophoretic patterns of the extracted Golgi beta-glucuronidase on polyacrylamide gel were examined. The isolated Golgi subfractions from the drug-treated rats gave a better yield of fraction than that from the control rats. The enzymatic characterization of these three subfractions showed no significant contamination by other subcellular structures such as plasma membranes, microsomes, or lysosomes, and no inhibitory effect of the drugs was observed. On the other hand, suppressed galactosyltransferase activity, a marker enzyme of the Golgi complex, was detected in the colchicine-treated rats. The electrophoretic pattern of Golgi beta-glucuronidase on polyacrylamide gel revealed one major band which moved to the same position as the lysosomal enzyme type in the control rats. In contrast, in the ethanol- and colchicine-treated rats, Golgi beta-glucuronidase was found to have two major bands stained for enzyme activity resulting from a mixture of microsomal- and lysosomal-type enzymes. These results suggested that the post-translational modification step, during conversion from a microsomal-type enzyme to a lysosomal-type enzyme, was apparently inhibited. Taken together, these findings indicated that ethanol or colchicine administration to rats caused an inhibitory effect on the intracellular post-translational modification of Golgi beta-glucuronidase destined for targeting to the lysosomes.

Inhibitory effect of leupeptin on the intracellular maturation of lysosomal cathepsin L in primary cultures of rat hepatocytes

To investigate the intracellular processing event for lysosomal cathespin L, we examined the effect of leupeptin, a non-covalent cysteine proteinase inhibitor, on the intracellular processing kinetics of cathepsin L as analyzed by pulse-chase experiments in vivo with [35S]methionine in primary cultures of rat hepatocytes. This revealed that cathepsin L was initially synthesized as proenzyme of molecular weight 39 kDa and the proenzyme was subsequently processed to the mature form of the enzyme, 30 and 25 kDa. In the leupeptin-treated cells, the proteolytic conversion of cellular procathepsin L, of molecular weight 39 kDa, to the mature enzyme was significantly inhibited and considerable amounts of proenzyme were found in the cell after 8 h chase periods. Furthermore, the subcellular fractionation experiment demonstrated that the intracellular processing of procathepsin L in the high density lysosomal fraction was significantly inhibited and that considerable amounts of the procathepsin L form were still observed in the dense lysosomal fraction after a 2 h chase period. These results suggest that leupeptin treatment caused significant inhibition of the intracellular maturation of cathepsin L. These findings show that cysteine proteinase plays an important role in the intracellular proteolytic processing and activation of lysosomal cathepsin L in vivo and that this processing event occurs within the lysosomes.

Intracellular sorting of lysosomal beta-glucuronidase is altered due to administration of dibutyl phosphate

Organophosphate compounds are known to cause a selective increase of beta-glucuronidase activity in rat serum. Previous data suggested that increase of serum beta-glucuronidase activity was well correlated with decrease of that activity in rat liver microsomal fraction, thereby, suggesting a role of the microsomal enzyme in mediating the organophosphate effect. To investigate further the intracellular sorting pathway of beta-glucuronidase in dibutyl phosphate-treated rats, liver subcellular fractions were prepared at 12 or 48 h after in vivo administration of [3H]leucine and it was established that microsomal beta-glucuronidase was the origin of the increased serum enzyme. To characterize the intracellular secretory pathway of beta-glucuronidase in dibutyl phosphate-treated rats, Golgi subfractions were isolated and a time course study was carried out. At 30 min after administration of dibutyl phosphate, specific activity of beta-glucuronidase in GF-2 (Golgi intermediate fraction) and GF-3 (Golgi heavy fraction) was significantly increased to the maximum. Furthermore, colchicine pretreatment of rats caused a delay of the peak of specific activity for 30 min in GF-2 and GF-3, and accumulation of enzyme activity in Golgi subfractions was observed. Colchicine pretreatment also had an inhibitory effect on release of beta-glucuronidase into serum until 30 min after dibutyl phosphate injection. The electrophoretic pattern of microsomal beta-glucuronidase on polyacrylamide gel was found to show two major bands of microsomal enzyme type and lysosomal enzyme type in dibutyl phosphate-treated rats. Taken together, these findings indicate that microsomal beta-glucuronidase follows the intracellular secretory pathway and is secreted into serum via Golgi complex in response to dibutyl phosphate.

Biosynthesis and processing of lysosomal cathepsin D in primary cultures of rat hepatocytes

To investigate the intracellular transport and maturation of lysosomal cathepsin D, we carried out an in vivo pulse-chase analysis with [35S]methionine in the primary cultures of rat hepatocytes. Cathepsin D was initially synthesized as a proenzyme of 45 kDa. The proenzyme was subsequently processed, becoming a mature enzyme of 43 kDa. The proenzyme and mature enzyme showed complete susceptibility to endoglycosidase H treatment, suggesting the presence of high-mannose type oligosaccharide chains. The effects of tunicamycin and chloroquine were also investigated. In the presence of tunicamycin, the 42.5-kDa unglycosylated precursor polypeptide appeared in the cell, and this protein was exclusively secreted from the cells without undergoing proteolytic processing. These results support the notion that the oligosaccharide moieties are of importance in addressing the lysosomal hydrolases to the lysosomes. However, in the presence of chloroquine, proteolytic processing of the proenzyme was prevented, and the enhanced release of proenzyme from the cells was observed. These results indicate that the processing of proenzyme to mature enzyme would take place in the lysosomes.

Biochemical properties and intracellular processing of lysosomal cathepsins B and H

Lysosomal cysteine proteinases of cathepsins B and H were isolated to a homogeneous state from rat liver by employing Sephadex G-75, DEAE-Sephacel, CM-Sephadex, and Mono S column chromatography. Each of the purified cathepsins B and H was demonstrated to be composed of a mixture of a single-chain form and the processed two-chain form upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). To investigate the proteolytic maturation of lysosomal cathepsins B and H, turnover kinetics of these enzymes were studied by comparing the specific radioactivities of the incorporated [3H]leucine into either the single-chain form or two-chain form in vivo. The specific radioactivity derived from each protein band of lysosomal cathepsin H in SDS-PAGE at 1, 3, 6, 12, 24 and 48 h after the injection of a radiolabel showed that the peak of specific radioactivity of the single-chain form of cathepsin H appeared at 6 h and that after 6 h, the radiolabel was sequentially incorporated into the two-chain form, while the radiolabel in the single-chain form started to gradually decrease, suggesting that the single-chain form was processed to generate the mature enzyme after the enzyme was incorporated into the lysosomes. In contrast, in the case of cathepsin B, the appearance of a radiolabel in the single-chain form or in the two-chain form was observed almost concomitantly without time lag, indicating that the processing of cathepsin B occurred very rapidly in the lysosomes.

Biochemical and immunohistochemical analysis of cathepsins B, H, L and D in human melanocytic tumours

We carried out biochemical and immunohistochemical analyses of cathepsins B, H, L and D in human melanocytic tumours using monospecific antibodies against rat cathepsins. In Western blot analysis, anti-rat cathepsin antibodies reacted with the cathepsins from normal human tissues and human malignant melanoma. However, the molecular profiles of the cathepsins from human melanoma were slightly different from those of the rat cathepsins, suggesting a distinct intracellular processing mechanism for cathepsins in human melanoma. Although cathepsins B, H, L and D were expressed in primary and metastatic melanomas and pigmented naevi immunohistochemically, the intensity of staining in metastatic melanomas was stronger than in primary melanomas and pigmented naevi. These findings suggest that anti-rat cathepsin antibodies may be useful in biochemical and/or immunohistochemical analysis of human melanocytic tumours.

Formation of autophagosomes during degradation of excess peroxisomes induced by di-(2-ethylhexyl)-phthalate treatment. III. Fusion of early autophagosomes with lysosomal compartments

Fusion of early autophagosomes containing peroxisomes with endosomal and lysosomal structures in rat liver cells was investigated. Male Wistar rats were administered di-(2-ethylhexyl)phthalate (DEHP) for 14 days to induce proliferation of peroxisomes, and then the animals were injected intravenously with horseradish peroxidase (HRP)-conjugated asialofetuin to label the lysosomal compartment. Either 30 min or 60 min after the injection, the animals were treated with leupeptin for 20, 40 and 60 min, respectively. Most of autophagic vacuoles containing peroxisomes were stained with diaminobenzidine (DAB) endocytosed HRP-asialofetuin 60 min after leupeptin injection, whereas many of them were negative for DAB reaction 20 min after leupeptin injection. Between 20 to 40 min after leupeptin treatment many autophagic vacuoles fused with DAB-positive lysosomal compartments, including late endosomes. Percoll gradient centrifugation showed that particles containing HRP activity migrated from a density of 1.09 g/ml to that of 1.14 g/ml as the time after leupeptin injection passed. Acid phosphatase activity migrated in the same manner. These results clearly show that early autophagosomes obtain the lysosomal proteinases by fusion with lysosomal compartments, including the late endosomes and that peroxisomes trapped in autophagosomes are degraded by these proteinases.

Immunocytochemical localization of cathepsin L in the synovial lining cells of the rat temporomandibular joint

Localization of cathepsin L in the synovial lining cells of the normal rat temporomandibular joint was investigated by the avidin-biotin-peroxidase complex method for semithin (1 microns) cryosections and the colloidal gold-labelled IgG method for ultrathin sections of LR gold resin. At the light-microscopic level, type A (macrophage-like) and B (fibroblast-like) cells formed the synovial lining layer. Extensive immunoreactivity for cathepsin L was observed in many granules and vacuoles of type A cells, while in the type B cells, immunoreactivity was found in very few granules. In the sublining layer, macrophages and a few fibroblasts were positive for cathepsin L. By electron microscopy, at the peripheral cytoplasm of the type A cells close to the lateral intercellular spaces and joint cavity, numerous coated vesicles and vacuoles (probably early endosomes) indicating endocytotic function were found. Gold particles indicating cathepsin L were localized in the vesicles (primary lysosomes) in the perinuclear cytoplasm and in the larger amorphous vacuoles (1 microns dia) as phagolysosomes. In type B cells, gold particles were limited to the vesicles only (primary lysosomes). The cathepsin L-positive primary lysosomes were numerous in a few fibroblasts in the sublining layer. These results indicate that type A cells contain a large amount of cathepsin L, and suggest that these cells endocytose surplus substances such as collagen and proteoglycan fragments in normal rat TMJ, effecting their digestion and degradation by the action of this proteolytic cathepsin.

Microtubule reorganization and lysosome redistribution by a viral v-src oncogene, in mouse Balb/3T3 cells expressing human EGF receptor

The epidermal growth factor (EGF)-induced endocytosis of its receptor is an obligatory pathway for the cellular regulation of the EGF-specific receptor (EGF-R). BNER4 is a mouse Balb/3T3 cell line transfected with human EGF-R complementary DNA (cDNA). B4/src-13 and B4/src-24 are BNER4 cells transfected with a viral oncogene v-src. Indirect immunofluorescence study demonstrated that EGF-R was mostly localized at the perinuclear region in BNER4 cells at 60 min after EGF addition, whereas it was diffusely distributed throughout the cytoplasm in its v-src transfectants. Double indirect immunofluorescence study further confirmed that EGF-R was localized in lysosomes in BNER4 and B4/src-13 cells at 60 min after EGF addition. Intracellular distribution of the Golgi apparatus, clathrin-coated vesicles and early endosomes were similar in all cell lines. However, the lysosomes detected by anti-lysosomal membrane protein (LGP85) antibodies were diffusely distributed throughout the cytoplasm in the v-src transfectacts. By contrast, in the parental BNER4 cells, the lysosomes were mostly localized in the perinuclear region. The organization of microtubules, but not of actin, was markedly different between BNER4 cells and its v-src transfectants. Nocodazole, which depolymerizes microtubules, altered the distribution of the lysosomes and EGF-R in BNER4 cells. Both intracellular lysosome distribution and microtubule organization in nocodazole-treated BNER4 cells were found to be similar to those in its v-src transfectants without nocodazole treatment. These findings support the notion that changes in lysosome distribution may be correlated with microtubule reorganization by v-src in mouse Balb/3T3 cells.

Functional cloning of centromere protein B (CENP-B) box-enriched alphoid DNA repeats utilizing the sequence-specific DNA binding activity of human CENP-B in vitro

The centromere is a distinctive portion of the chromosome consisting of 'centromere DNA' and 'centromere proteins'. Recently, a direct molecular interaction was discovered between human centromere protein B (CENP-B) and human centromeric alphoid repeats. This enabled us to isolate the CENP-B-targeted centromeric DNA sequences by positively utilizing the biologic activity of CENP-B in vitro. In the previous model experiment, we found that oligonucleotides covering the CENP-B binding sequences were enriched by the DNA immunoprecipitation procedure. Here we apply the same technique to the direct isolation of a functional part of human centromeric DNA from a genomic DNA library. Restriction digestion of two isolated clones showed the typical repeating pattern of an alphoid family that is known to localize at the centromeric region of all human chromosomes. Sequence analysis showed that these two clones frequently contain the authentic CENP-B binding motif, CTTCGTTGGAAACGGGA, or a new one with one base replaced, CTTCGTTGGAAACGGGT. The frequent distribution of these motifs suggests that the isolated sequences are directly involved in the organization of centromeric heterochromatin at the primary constriction in conjunction with CENP-B.

Human centromere protein C (CENP-C) is a DNA-binding protein which possesses a novel DNA-binding motif

Mammalian centromere proteins (CENPs) can be divided into those that translocate from centromere to midzone in the progress of mitosis, and those that remain at the centromere throughout the cell cycle. The latter including CENP-A, CENP-B, and CENP-C is the candidate for DNA-binding protein. CENP-B has been shown previously to possess the specific DNA-binding activity to 17-base pair sequences dispersed on human centromeric alphoid repeats. In this study, we examined DNA-binding property of CENP-C that is localized to inner kinetochore plate of the metaphase chromosome. We independently isolated a full-length cDNA encoding human CENP-C and expressed it as the polypeptide tagged with histidine oligomer in Escherichia coli. After affinity purification with Ni(2+)-chelated resin, DNA-binding activity of the recombinant CENP-C renatured on the membrane was demonstrated by using human genomic DNA and an alphoid subfamily in South-Western-type blotting analysis. By constructing a series of truncated products, the DNA-binding domain was located at an internal 101-amino-acid stretch with no apparent homology to any other DNA-binding proteins. This may suggest that CENP-C is directly involved in formation of kinetochore chromatin fibers.

Functional domain structure of human centromere protein B. Implication of the internal and C-terminal self-association domains in centromeric heterochromatin condensation

Centromere protein B (CENP-B) is a common centromere DNA-binding protein among mammalian centromeres. CENP-B possesses the specific DNA binding activity to the 17-base pair sequence dispersed in centromeric repetitive DNA sequences. In the previous study, we have shown that its DNA-binding domain exists within the N-terminal 134 amino acid residues. Here, to clarify the whole domain structure, another functional unit required for CENP-B self-association was examined. Recombinant CENP-B was expressed in Escherichia coli. First, a chemical cross-linking reagent, disuccinimidyl suberate, was used to fix the physical association without losing the DNA-binding activity. The complexes with the same molecular weight as homodimer and trimer were identified after a separation by SDS-polyacrylamide gel electrophoresis. With a series of CENP-B deletion constructs, the area responsible for this oligomer formation was located at the internal region. Second, an electrophoretic mobility shift assay was also used to survey the minimum regions required for the CENP-B self-association. Three separate elements were identified by assaying the capacity to form the additional slow-migrating complex, two in the internal region and one in the C terminus. These results suggest that CENP-B molecules interact with each other at the multiple sites to fold the centromeric DNA repeats into a heterochromatin structure.