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K Kokura

Publications and source records attributed to K Kokura.

12 recordsLinked to original sources
PubMed2001

The Ski protein family is required for MeCP2-mediated transcriptional repression.

DNA methylation is essential for development in the mouse and plays an important role in inactivation of the X chromosome and genomic imprinting. MeCP2 is the founder member of a family of methyl-CpG-binding proteins. MeCP2 directly binds to the co-repressor mSin3, which interacts with class I histone deacetylase, recruiting them to methyl-CpG regions to suppress transcription. Here, we report that MeCP2 directly binds to two co-repressors, c-Ski and N-CoR, in addition to mSin3A, and that the c-Ski, which is encoded by the c-ski proto-onocogene, is required for MeCP2-mediated transcriptional repression. The two regions of c-Ski, including the C-terminal coiled-coil region, interact with the transcriptional repression domain in the center of the MeCP2 molecule. The immunostaining signals for c-Ski and MeCP2 overlap in the nuclear heterochromatin region, suggesting the co-localization of the two proteins. The degree of transcriptional repression mediated by a Gal4-MeCP2 fusion protein was abrogated by overexpression of the putative dominant negative form of c-Ski. Furthermore, injection of antibodies against c-Ski and Sno almost completely abolished the transcriptional repression mediated by the Gal4-MeCP2 fusion protein. These results suggest that the ski gene family is involved in methyl CpG-mediated transcriptional repression.

Blotting, Western↗
PubMed2001

Molecular cloning and characterization of neural activity-related RING finger protein (NARF): a new member of the RBCC family is a candidate for the partner of myosin V.

Activity-dependent synaptic plasticity has been thought to be a cellular basis of memory and learning. The late phase of long-term potentiation (L-LTP), distinct from the early phase, lasts for up to 6 h and requires de novo synthesis of mRNA and protein. Many LTP-related genes are enhanced in the hippocampus during pentyrenetetrazol (PTZ)- and kainate (KA)-mediated neural activation. In this study, mice were administered intraperitoneal injections of PTZ 10 times, once every 48 h, and showed an increase in seizure indexes. Genes related to plasticity were efficiently induced in the mouse hippocampus. We used a PCR-based cDNA subtraction method to isolate genes that are expressed in the hippocampus of repeatedly PTZ-treated mice. One of these genes, neural activity-related RING finger protein (NARF), encodes a new protein containing a RING finger, B-box zinc finger, coiled-coil (RBCC domain) and beta-propeller (NHL) domain, and is predominantly expressed in the brain, especially in the hippocampus. In addition, KA up-regulated the expression of NARF mRNA in the hippocampus. This increase correlated with the activity of the NMDA receptor. By analysis using GFP-fused NARF, the protein was found to localize in the cytoplasm. Enhanced green fluorescent protein-fused NARF was also localized in the neurites and growth cones in neuronal differentiated P19 cells. The C-terminal beta-propeller domain of NARF interacts with myosin V, which is one of the most abundant myosin isoforms in neurons. The NARF protein increases in hippocampal and cerebellar neurons after PTZ-induced seizure. These observations indicated that NARF expression is enhanced by seizure-related neural activities, and NARF may contribute to the alteration of neural cellular mechanisms along with myosin V.

Amino Acid Sequence↗
PubMed2000

Identity between rat htf and human xbp-1 genes: determination of gene structure, target sequence, and transcription promotion function for HTF.

Hepatocarcinogenesis-related transcription factor (HTF) was originally isolated from rats in which the expression was enhanced in hepatocellular carcinomas. Rat HTF (rHTF) is structurally similar to human X-box-binding protein-1 (hXBP-1), and both factors are unique in respective genomes. A previous study showed that hXBP-1 mRNA is detectable ubiquitously but is enriched in the human liver as rHTF. In this study, we demonstrated the analogous exon-intron organization and significant sequence homology for rhtf and hxbp-1 genes. Alignment of amino acid sequences of rHTF and hXBP-1 revealed that all the characteristic motifs in rHTF were conserved in hXBP-1. Moreover, Southern blotting patterns provided with the rHTF and hXBP-1 probes were basically the same. These two genes were thus thought to belong to the same evolutional lineage. We determined the consensus binding sequence (CRCGTCA) for rHTF by CASTing, and it was found to be nearly the same as that for hXBP-1. Transactivation ability of rHTF was also demonstrated. The rhtf gene generates two types of mRNAs (2.0 kb and 2.5 kb), both of which encode identical rHTF protein. These transcripts had distinct transcription initiation sites. The 2.0 kb promoter, that was revealed by the transient luciferase assay, contained GC-box and CAAT-box. Sequences around the transcription initiation site for the 2.0 kb transcript were similar in rhtf and hxbp-1 genes. Our observations suggest that HTF is a rat homolog of hXBP-1.

Animals↗
PubMed1999

Heterogeneous nuclear RNA-ribonucleoprotein F binds to DNA via an oligo(dG)-motif and is associated with RNA polymerase II.

BACKGROUND: The heterogeneous nuclear ribonucleoprotein F (hnRNP-F) is one of the constituents of the splicing-related hnRNP complex. Recent studies suggest that pre-mRNA modification and splicing factors are associated with transcriptional initiation factors and RNA polymerase II (RNA pol II) at a promoter, implying that pre-mRNA-engaged factors might be associated with a promoter. RESULTS: We isolated a cDNA of rat hnRNP-F and expressed the recombinant protein. HnRNP-F selectively bound to oligo(dG) in constructions with other oligohomonucleotides. The ssDNA of an SV40 promoter sequence having the GC-boxes was bound to hnRNP-F, while hnRNP-F bound to the (G/C)-stretch as dsDNA. Consequently, hnRNP-F was designated as an oligo(dG)-binding protein. None of the RNA-binding domains (RBDs) in hnRNP-F were critical for the oligo(dG)-binding. In contrast, the GY-rich region that exists between RBD-II and -III exhibited an oligo(dG)-binding ability. We suggest that the GY-rich region is a novel DNA-binding motif. HnRNP-F was shown to contain two types of binding motifs for RNA and DNA. Additionally, we found that hnRNP-F was co-precipitated with RNA pol II. Interestingly, the RNA pol II holoenzyme also contained hnRNP-F. The tissue distribution profile of hnRNP-F was similar to that of both RNA pol II and TBP. CONCLUSION: The above results suggest that hnRNP-F is associated with a transcriptional initiation apparatus that includes RNA pol II. The DNA-binding ability of hnRNP-F might facilitate the entry of pre-mRNA modification/splicing factors at a promoter.

Amino Acid Sequence↗
PubMed1998

Cloning of a novel rat gene, DB83, that encodes a putative membrane protein.

Using a partial cDNA sequence and a 5'-RACE technique, we isolated a novel cDNA from rat liver referred to as DB83. DB83 had four hydrophobic trans-membrane domains and one N-myristoylation site as well as multiple possible phosphorylation sites. The db83 gene was highly expressed in the liver and significantly in brain, lungs and kidneys. We suggest that DB83 is a tissue-specific putative membrane protein. p6

Amino Acid Sequence↗
PubMed1998

Enhanced expression of a new class of liver-enriched b-Zip transcription factors, hepatocarcinogenesis-related transcription factor, in hepatocellular carcinomas of rats and humans.

Rat hepatocarcinogenesis-related transcription factor (HTF) was earlier identified as a b-Zip transcription factor in chemically induced rat hepatocellular carcinoma (HCC) by cDNA subtraction, and its structure was found to be different from that of the conventional b-Zip proteins. We investigated htf gene expression in rat tissues by Northern analysis and found that HTF expression was ubiquitous but was enriched in the liver. HTF expression increased concomitantly with HCC development in rat liver, and the HTF-containing DNA-binding factor also increased. Stimulated HTF gene expression also was observed in rat regenerating livers. From the results of various assays, X-box-binding protein 1/Tax-response element binding factor 5 was suggested to be a human homologue of rat HTF. In humans, HTF gene expression was also abundant in the liver and was revealed to be specifically stimulated in HCCs, but not in other types of cancers. To our knowledge, HTF is the first example of a liver-enriched transcription factor that exhibits HCC-associated gene expression. Injection of anti-HTF antibody decreased the growth rate of cultured HCC cells. Consequently, HTF is thought to participate in hepatocyte growth as well as in hepatocarcinogenesis.

Animals↗
PubMed1998

Gene expression in hepatomas.

Gene expression changes in accordance with cell growth, differentiation and carcinogenesis. To elucidate the molecular mechanisms for hepatocarcinogenesis as well as maintenance of normal hepatocytes, it is important to identify the genes that have altered expression with carcinogenesis. We established a new and efficient cDNA subtraction method via two cDNA populations. By using this method along with rat hepatomas made by the Solt-Farber protocol, we identified a number of genes, some of which are activated in hepatocellular carcinoma (HCC). These genes include ones which code for a transcription factor and a metabolic enzyme. One particular gene can be used as a tumour marker. Our method is beneficial for the isolation of a wide range of HCC-related genes in rats which, in turn, enables easy identification of their human counterparts. In this review, we describe details of our method and the isolated genes. We also briefly describe transcription factors in the liver.

Animals↗
PubMed1996

Overexpression of cysteine sulfinic acid decarboxylase stimulated by hepatocarcinogenesis results in autoantibody production in rats.

We developed a novel and efficient cDNA subtraction method to isolate rat hepatocellular carcinoma (HCC)-related genes. cDNAs from Solt-Farber procedure-driven HCCs were synthesized on Latex beads. The subtraction was accomplished by a simple centrifugation, PCR amplification, and dot blot screening. Among 2000 clones from the subtracted cDNA library, one clone with a full-length HCC-related cDNA was eventually obtained. Sequence analysis of this clone showed it to exhibit 90 and 60% similarity with the rat cysteine sulfinic acid decarboxylase (CSAD) and mammalian glutamic acid decarboxylases (GAD), respectively. Differences between our sequence data on CSAD and those reported previously were observed at two positions, which arose from a single amino acid substitution and frame shift mutation. The CSAD expression was restricted to the liver and kidney of rats. During hepatocarcinogenesis, expression of the CSAD mRNA and its protein was stimulated in the precancerous liver and maintained its high expression afterward. Interestingly, a high level of anti-CSAD autoantibody was detected in the HCC-bearing rats. The titer of anti-CSAD autoantibodies in these rats was 30-200 times higher than that in normal rats. The anti-CSAD autoantibody appeared in the precancerous state and was maintained afterward, and its pattern of appearance was similar to that of CSAD mRNAs and proteins. Thus, we propose that the high-titer CSAD autoantibody resulted from increased CSAD gene expression in the liver due to stimulation by the HCC. These results remind us of human autoimmune diseases including insulin-dependent diabetes mellitus and stiff-man syndrome, which are caused by autoantibodies against GAD.

Amino Acid Sequence↗
PubMed1996

HTF: A b-ZIP transcription factor that is closely related to the human XBP/TREB5 and is activated by hepatocellular carcinoma in rats.

We screened for rat hepatocellular carcinoma (HCC)-related genes by a novel cDNA subtraction method and obtained one gene. This gene was transcribed as 2.0- and 2.5-kb mRNAs, and its transcription was specifically enhanced in HCC. These cDNAs had the same open reading frame, but the 2.5 kb transcript had an extra 495 bases of 5'-UTR at the 5'-terminus. The deduced aa sequence revealed a basic-leucine zipper (b-ZIP) and proline/glutamine-rich structures, both of which are characteristic motifs for transcription factors. We designated the translation product of this gene HTF (Hepatocarcinogenesis-related Transcription Factor). Electrophoretic mobility shift assay demonstrated the DNA-binding ability of the recombinant HTF. It is most interesting that HTF had a considerable homology with human XBP/TREB5, which has been reported to be a binding factor for the X-box of the MHC class II gene and for the 21-bp enhancer of the HTLV-1 LTR. Genomic Southern analysis suggested that the 2.0- and 2.5-kb mRNAs are transcribed by a dual promoter of a single gene. Our results may suggest that HTF is a b-ZIP-type transcription factor involved in rat hepatocellular carcinoma.

Amino Acid Sequence↗
PubMed1992

[Prader-Willi syndrome associated with chromosomal aberration: report of a case].

A male case of Prader-Willi syndrome (2.8 years in age) with an interstitial deletion of a chromosome affecting 15q 11-12 region is reported. The chief complaints were hypoplastic scrotum and defect of bilateral scrotal content. The clinical features were short stature, obesity, delayed mental development, bilateral cryptorchidism, hypogenitalism, hypopigmentation, and bilateral moderate vesicoureteral reflux with a history of muscular hypotonia. Bilateral orchidopexy was done. Endocrinologically both base values of luteinizing hormone (LH) and follicle stimulating hormone (FSH) were normal although LH reserve function was impaired on gonadotropin releasing hormone (GnRH) test. Testosterone response was normal by the stimulation of human chorionic gonadotropin. An interstitial deletion of proximal 15q, and pituitary-gonadal axis in Prader-Willi syndrome are discussed in relation to the clinical features and therapy.

Child, Preschool↗