Developmentally Regulated RNA-binding Protein 1 (Drb1)/RNA-binding Motif Protein 45 (RBM45), a Nuclear-Cytoplasmic Trafficking Protein, Forms TAR DNA-binding Protein 43 (TDP-43)-mediated Cytoplasmic Aggregates.

Cytoplasmic protein aggregates are one of the pathological hallmarks of neurodegenerative disorders, including amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD). Several RNA-binding proteins have been identified as components of inclusion bodies. Developmentally regulated RNA-binding protein 1 (Drb1)/RNA-binding motif protein 45 is an RNA-binding protein that was recently described as a component in ALS- and FTLD-related inclusion bodies. However, the molecular mechanism underlying cytoplasmic Drb1 aggregation remains unclear. Here, using an in vitro cellular model, we demonstrated that Drb1 co-localizes with cytoplasmic aggregates mediated by TAR DNA-binding protein 43, a major component of ALS and FTLD-related inclusion bodies. We also defined the domains involved in the subcellular localization of Drb1 to clarify the role of Drb1 in the formation of cytoplasmic aggregates in ALS and FTLD. Drb1 predominantly localized in the nucleus via a classical nuclear localization signal in its carboxyl terminus and is a shuttling protein between the nucleus and cytoplasm. Furthermore, we identify a double leucine motif serving as a nuclear export signal. The Drb1 mutant, presenting mutations in both nuclear localization signal and nuclear export signal, is prone to aggregate in the cytoplasm. The mutant Drb1-induced cytoplasmic aggregates not only recruit TAR DNA-binding protein 43 but also decrease the mitochondrial membrane potential. Taken together, these results indicate that perturbation of Drb1 nuclear-cytoplasmic trafficking induces toxic cytoplasmic aggregates, suggesting that mislocalization of Drb1 is involved in the cause of cytotoxicity in neuronal cells.

Paraneoplastic cerebellar degeneration associated with an onconeural antibody against creatine kinase, brain-type.

Onconeural immunity, a cancer-stimulated immune reaction that cross-reacts with neural tissues, is considered to be the principal pathological mechanism for paraneoplastic neurological syndromes (PNS). A common PNS is paraneoplastic cerebellar degeneration (PCD). We had encountered a PCD patient with urothelial carcinomas (UC) of the urinary bladder who was negative for the well-characterized PNS-related onconeural antibodies. In the present study, we aimed to identify a new PCD-related onconeural antibody, capable of recognizing both cerebellar neurons and cancer tissues from the patient, and applied a proteomic approach using mass spectrometry. We identified anti-creatine kinase, brain-type (CKB) antibody as a new autoantibody in the serum and cerebrospinal fluid from the patient. Immunohistochemistry indicated that anti-CKB antibody reacted with both cerebellar neurons and UC of the urinary bladder tissues. However, anti-CKB antibody was not detected in sera from over 30 donors, including bladder cancer patients without PCD, indicating that anti-CKB antibody is required for onset of PCD. We also detected anti-CKB antibody in sera from three other PCD patients. Our study demonstrated that anti-CKB antibody may be added to the list of PCD-related autoantibodies and may be useful for diagnosis of PCD.

Translational repression of the McKusick-Kaufman syndrome transcript by unique upstream open reading frames encoding mitochondrial proteins with alternative polyadenylation sites.

BACKGROUND: Upstream open reading frames (uORFs) are commonly found in the 5'-untranslated region (UTR) of many genes and function in translational control. However, little is known about the existence of the proteins encoded by uORFs, and the role of the proteins except translational control. There was no report about uORFs of the McKusick-Kaufman syndrome (MKKS) gene that causes a genetic disorder. METHODS: Northern blotting, 3'-RACE, and bioinformatics were used for determining the length of transcripts and their 3' ends. Luciferase assay and in vitro translation were used for evaluation of translational regulatory activity of uORFs. Immunoblotting and immunocytochemical analyses were used for detection of uORF-derived protein products and their subcellular localization. RESULTS: The MKKS gene generates two types of transcripts: a canonical long transcript that encodes both uORFs and MKKS, and a short transcript that encodes only uORFs by using alternative polyadenylation sites at the 5'-UTR. The simultaneous disruption of the uORF initiation codons increased the translation of the downstream ORF. Furthermore, both protein products from the two longest uORFs were detected in the mitochondrial membrane fraction of HeLa cells. Database searches indicated that such uORFs with active alternative polyadenylation sites at the 5'-UTR are atypical but surely exist in human transcripts. CONCLUSIONS: Multiple uORFs at the 5'-UTR of the MKKS long transcript function as translational repressor for MKKS. Two uORFs are translated in vivo and imported onto the mitochondrial membrane. GENERAL SIGNIFICANCE: Our findings provide unique insights into production of uORF-derived peptides and functions of uORFs.

Crystallization and preliminary crystallographic studies of the metalloglycoprotein esterase A4 using a baculovirus expression system.

Esterase A4 (EA4) is a timer protein found in diapause eggs of the silkworm Bombyx mori. The gene for this metalloglycoprotein was cloned from B. mori eggs and expressed using a baculovirus expression system in silkworm pupae. Crystals of the purified protein have been grown that diffract to beyond 2.1 A resolution at 100 K using synchrotron radiation. The protein crystals belong to space group P2(1), with unit-cell parameters a = 47.1, b = 73.9, c = 47.4 A, beta = 104.1 degrees. With one dimer per asymmetric unit, the crystal volume per unit protein weight (V(M)) is 2.3 A3 Da(-1) and the solvent content is 47%.

Damaged DNA-binding protein 2 accelerates UV-damaged DNA repair in human corneal endothelium.

PURPOSE: To determine damaged DNA-binding protein 2-gene expression levels in vitro and ex vivo, and the degree of DNA repair in damaged DNA-binding protein 2-overexpressing cultured human corneal endothelium after ultraviolet irradiation. METHODS: Constitutive damaged DNA-binding protein 2-gene expression levels in various human tissues were determined by semi-quantitative reverse transcription-polymerase chain reactions. The dynamics of nucleotide excision repair-related gene expression in cultured human corneal endothelium were investigated in a ribonuclease protection assay after ultraviolet-irradiation. The effect of damaged DNA-binding protein 2 on DNA repair was studied after ultraviolet-irradiation in cultured human corneal endothelium infected with adenovirus carrying damaged DNA-binding protein 2. RESULTS: Human corneal endothelium and epithelium in the donor cornea had the highest constitutive damaged DNA-binding protein 2-gene expression of the various human tissues studied. Gene expression level dynamics associated with nucleotide excision repair factors after ultraviolet-irradiation showed that the increase in the rate of damaged DNA-binding protein 2-gene expression in cultured human corneal endothelium was highest of the nucleotide excision repair-related genes studied. An in vivo DNA repair assay showed that DNA repair efficiency in damaged DNA-binding protein 2-overexpressing cultured human corneal endothelium after ultraviolet-irradiation was significantly improved as compared with that in the control human corneal endothelium. CONCLUSION: The human corneal endothelium abundantly expresses the damaged DNA-binding protein 2-gene that is produced efficiently on ultraviolet exposure. This overexpressed damaged DNA-binding protein 2 in the human corneal endothelium contributes to the protection system against DNA damage after ultraviolet-irradiation. Our findings show a critical role for damaged DNA-binding protein 2 in DNA repair to maintain the human corneal endothelium function.

Human DDB2 splicing variants are dominant negative inhibitors of UV-damaged DNA repair.

Damaged DNA-binding protein (DDB) is a heterodimer (DDB1 and DDB2), which is implicated in the repair of UV-irradiated DNA damage. Here we have identified four DDB2 variants from HeLa cells (D1-D4) that are generated by alternative splicing. Analysis of tissue distribution by RT-PCR indicates that D1 is the most highly expressed in human brain and heart. A DNA repair assay revealed that both D1 and D2 are dominant negative inhibitors. Electrophoresis mobility shift assays indicated that D1 and D2 are not part of the damaged DNA-protein complex. Co-immunoprecipitation studies show that DDB2-WT interacts with D1 and itself. Nuclear import of DDB1 was less induced by transfection with D1 than WT. Based on these results, D1 and D2 are dominant negative inhibitors of DNA repair, which is probably due to disruption of complex formation between DDB1 and DDB2-WT and of DDB1 nuclear import.

Mammalian D-aspartyl endopeptidase: a scavenger for noxious racemized proteins in aging.

The accumulation of D-isomers of aspartic acid (D-Asp) in proteins during aging has been implicated in the pathogenesis of Alzheimer's disease, cataracts, and arteriosclerosis. Here, we identified a specific lactacystin-sensitive endopeptidase that cleaves the D-Asp-containing protein and named it D-aspartyl endopeptidase (DAEP). DAEP has a multi-complex structure (MW: 600kDa) and is localized in the inner mitochondrial membrane of mouse and rabbit, but DAEP activity was not detected in Escherichia coli, Saccharomyces cerevisiae, and Caenorhabditis elegans. A specific inhibitor for DAEP was newly synthesized, and inhibited DAEP activity (IC(50), 3microM), a factor of 10 greater than lactacystin on DAEP. On the other hand, the inhibitor did not inhibit either the 20S or 26S proteasome.

Differential sublocalization of the dynamin-related protein OPA1 isoforms in mitochondria.

OPA1 is a cause gene for autosomal dominant optic atrophy and possesses eight alternative splicing variants. Here, we identified two isoforms of OPA1 proteins in HeLa cells and examined their submitochondrial localization and complex formations. RT-PCR shows that HeLa cells mainly express isoforms 7 and 1 of OPA1. Since the third cleavage site is mainly utilized in HeLa cells, the predicted molecular masses of their processed proteins are consistent with the 93- and 88-kDa proteins. Biochemical examinations indicate that both of the OPA1 isoforms are present in the intermembrane space. Submitochondrial fractionation by sucrose density-gradient centrifugation shows that the 88-kDa protein predominantly associates with the mitochondrial outer membrane, on the contrary, the 93-kDa protein associates with the inner membrane. Gel filtration analysis indicates that they compose the different molecular mass complexes in mitochondria. These differences between two isoforms of OPA1 would suggest their crucial role involved in the mitochondrial membrane formation.

cDNA cloning and characterization of Drb1, a new member of RRM-type neural RNA-binding protein.

Neural RNA recognition motif (RRM)-type RNA-binding proteins play essential roles in neural development. To search for a new member of neural RRM-type RNA-binding protein, we screened rat cerebral expression library with polyclonal antibody against consensus RRM sequences. We have cloned and characterized a rat cDNA that belongs to RRM-type RNA-binding protein family, which we designate as drb1. Orthologs of drb1 exist in human and mouse. The predicted amino acid sequence reveals an open reading frame of 476 residues with a corresponding molecular mass of 53kDa and consists of four RNA-binding domains. drb1 gene is specifically expressed in fetal (E12, E16) rat brain and gradually reduced during development. In situ hybridization demonstrated neuron-specific signals in fetal rat brain. RNA-binding assay indicated that human Drb1 protein possesses binding preference on poly(C)RNA. These results indicate that Drb1 is a new member of neural RNA-binding proteins, which expresses under spatiotemporal control.

Isoliquiritigenin suppresses pulmonary metastasis of mouse renal cell carcinoma.

Isoliquiritigenin is a chalcone isolated from licorice and shallots. The ability of isoliquiritigenin to suppress metastasis was examined in a pulmonary metastasis model of mouse renal cell carcinoma. Isoliquiritigenin significantly reduced pulmonary metastasis, without any weight loss or leukocytopenia. Isoliquiritigenin suppressed in vitro proliferation of carcinoma cells, potentiated nitric oxide production by lipopolysaccharide-stimulated macrophages, and facilitated cytotoxicity of splenic lymphocytes in vitro. These findings suggest activation of macrophages, activation of cytotoxicity of lymphocytes, and direct cytotoxicity as possible mechanisms of metastasis suppression by isoliquiritigenin. In addition, isoliquiritigenin prevented severe leukocytopenia caused by administration of 5-fluorouracil.

Muscle-specific exonic splicing silencer for exon exclusion in human ATP synthase gamma-subunit pre-mRNA.

Mitochondrial ATP synthase gamma-subunit (F(1)gamma) pre-mRNA undergoes alternative splicing in a tissue- or cell type-specific manner. Exon 9 of F(1)gamma pre-mRNA is specifically excluded in heart and skeletal muscle tissues and in acid-stimulated human fibrosarcoma HT1080 cells, rhabdomyosarcoma KYM-1 cells, and mouse myoblast C2C12 cells. Recently, we found a purine-rich exonic splicing enhancer (ESE) element on exon 9 via transgenic mice bearing F(1)gamma mutant minigenes and demonstrated that this ESE functions ubiquitously with exception of muscle tissue (Ichida, M., Hakamata, Y., Hayakawa, M., Ueno E., Ikeda, U., Shimada, K., Hamamoto, T., Kagawa, Y., Endo, H. (2000) J. Biol. Chem. 275, 15992-16001). Here, we identified an exonic negative regulatory element responsible for muscle-specific exclusion of exon 9 using both in vitro and in vivo splicing systems. A supplementation assay with nuclear extracts from HeLa cells and acid-stimulated HT1080 cells was performed for an in vitro reaction of muscle-specific alternative splicing of F(1)gamma minigene and revealed that the splicing reaction between exons 8 and 9 was the key step for regulation of muscle-specific exon exclusion. Polypyrimidine tract in intron 8 requires ESE on exon 9 for constitutive splice site selection. Mutation analyses on the F(1)gammaEx8-9 minigene using a supplementation assay demonstrated that the muscle-specific negative regulatory element is positioned in the middle region of exon 9, immediately downstream from ESE. Detailed mutation analyses identified seven nucleotides (5'-AGUUCCA-3') as a negative regulatory element responsible for muscle-specific exon exclusion. This element was shown to cause exon skipping in in vivo splicing systems using acid-stimulated HT1080 cells after transient transfection of several mutant F(1)gammaEx8-9-10 minigenes. These results demonstrated that the 5'-AGUUCCA-3' immediately downstream from ESE is a muscle-specific exonic splicing silencer (MS-ESS) responsible for exclusion of exon 9 in vivo and in vitro.