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Biomedical subjects

Eigo Suyama

Publications and source records attributed to Eigo Suyama.

13 recordsLinked to original sources
PubMed2004

An RNA-dependent protein kinase is involved in tunicamycin-induced apoptosis and Alzheimer's disease.

Various types of stress, such as disruption of calcium homeostasis, inhibition of protein glycosylation and reduction of disulfide bonds, result in accumulation of misfolded proteins in the endoplasmic reticulum (ER). The initial cellular response involves removal of such proteins by the ER, but excessive and/or long-term stress results in apoptosis. In this study, we used a randomized ribozyme library and ER stress-mediated apoptosis (tunicamycin-induced apoptosis) in SK-N-SH human neuroblastoma cells as a selective phenotype to identify factors involved in this process. We identified a double-stranded RNA-dependent protein kinase (PKR) as one of the participants in this process. The level of nuclear PKR was elevated, but the level of cytoplasmic PKR barely changed in tunicamycin-treated SK-N-SH cells. Furthermore, tunicamycin also raised levels of phosphorylated PKR in the nucleus. We also detected the accumulation of phosphorylated PKR in the nuclei of autopsied brain tissues in Alzheimer's disease. Thus, PKR might play a role in ER stress-induced apoptosis and in Alzheimer's disease.

Aged↗
PubMed2003

Identification of genes involved in cell invasion by using a library of randomized hybrid ribozymes.

Libraries of RNA helicase-coupled randomized ribozymes are a powerful tool for the identification of functional genes. We have demonstrated the usefulness of this functional gene-discovery system by identifying genes involved in tumor invasion, a process that is an essential feature of tumor metastasis: the spread of cancer cells from the original tumor to other sites in the body that imposes serious problems in the prognosis and treatment of cancer. Using a filter-based invasion assay in vitro, we isolated ribozymes that enhanced the invasive properties of NIH 3T3 fibroblasts. Sequence analysis of selected clones and a database search revealed that genes such as the gene for Gem GTPase and uncharacterized genes that resemble genes for myosin phosphatase and protein-tyrosine-phosphatase are involved in cell invasion. Our system for gene identification by using ribozymes and the functional analysis of target genes should help to clarify the complex mechanisms of invasion and metastasis and might provide information that is relevant to cancer therapy.

3T3 Cells↗
PubMed2003

siRNAs generated by recombinant human Dicer induce specific and significant but target site-independent gene silencing in human cells.

RNA interference has emerged as a powerful tool for the silencing of gene expression in animals and plants. It was reported recently that 21 nt synthetic small interfering RNAs (siRNAs) specifically suppressed the expression of endogenous genes in several lines of mammalian cells. However, the efficacy of siRNAs is dependent on the presence of a specific target site within the target mRNA and it remains very difficult to predict the best or most effective target site. In this study, we demonstrate that siRNAs that have been generated in vitro by recombinant human Dicer (re-hDicer) significantly suppress not only the exogenous expression of a puromycin-resistance gene but also the endogenous expression of H-ras, c-jun and c-fos. In our system, selection of a target site is not necessary in the design of siRNAs. However, it is important to avoid homologous sequences within a target mRNA in a given protein family. Our diced siRNA system should be a powerful tool for the inactivation of genes in mammalian cells.

Cloning, Molecular↗
PubMed2003

Identification of genes responsible for cell migration by a library of randomized ribozymes.

Several genes appear to be associated with metastasis, but the underlying mechanisms of metastasis still remain unclear. In this study, we used a library of randomized ribozymes to identify, by inactivation of transcripts, genes involved in cell migration that is an essential aspect of metastasis. Using a chemotaxis assay, the ribozymes that inhibited cell migration were selected from the library. Among such ribozymes, we found two ribozymes that targeted and cleaved ROCK1 mRNA at independent sites. ROCK1 and ROCK2 are Rho kinases, and it has been demonstrated that they regulate the organization of the actin cytoskeleton and are responsible for cell motility and cytokinesis. The two ribozymes that specifically cleaved ROCK1 mRNA inhibited both the migration and invasion of invasive HT1080 fibrosarcoma, but neither had any effect on cell proliferation. Our analysis indicates that the ribozymes toward ROCK1 can block invasive activity but not the proliferation of HT1080 cells without having any effect on expression of ROCK2. Ribozymes identified in this study, including the ribozymes against ROCK1, might be useful in understanding the mechanisms of cell migration and metastasis.

Animals↗
PubMed2003

Cancer gene validation using ribozymes and macroarray.

Transcription factor AP-2 seems to play an important role in the malignancy of melanoma. In this study, we constructed ribozyme expression vectors to suppress the expression of AP-2 (AP-2-ribozymes) and then examined gene expression in human A375P melanoma cells that stably expressed ribozymes targeted to the AP-2 transcript. A comparison of the gene-expression profiles of A375P cells that expressed AP-2-ribozymes and those transfected with the empty vector revealed changes in levels of expression of several genes. Here we described that the combination of gene suppression by ribozymes and the analysis of gene expression using a macro-array provides a good approach for elucidating signal transduction pathways. These results provide further insight into the role of AP-2 in human melanoma cells.

DNA-Binding Proteins↗
PubMed2003

Use of a ribozyme library for validation of gene functions and cellular pathways.

An effective and simple technology is required to identify genes that function in a particular phenotype of interest. A system for identification of genes with libraries of randomized ribozymes has a great potential to investigate gene functions and cellular pathways. This system has been used to identify genes that are relevant to several phenotypes. In vivo application of the library of ribozymes in mice model was also performed to identify genes involved in metastasis. Libraries of ribozymes might be used in vitro and in vivo to study various aspects of basic cell biology and disease processes including metastasis.

Gene Library↗
PubMed2002

Identification of a caspase 3-independent role of pro-apoptotic factor Bak in TNF-alpha-induced apoptosis.

By using our recently developed gene discovery system, we have identified Bak, a member of the Bcl-2 family, as a pro-apoptotic factor in the tumor necrosis factor (TNF)-alpha-induced apoptotic pathway in caspase 3-deficient cells. Unlike Bcl-2, Bak stimulates several apoptotic pathways, however the molecular mechanism(s) of its action remains unclear. For example, it is unclear whether Bak induces apoptosis in caspase 3-deficient cells. In this study, we examined the effects of overexpression of Bak in MCF-7 cells that lack caspase 3. We found that despite the absence of caspase 3 in MCF-7 cells, they were more sensitive to the cell death effects of Bak as compared to caspase 3-expressing HeLa S3 cells. The targeting of Bak function by ribozymes suggests that Bak is required for the TNF-alpha-induced apoptotic pathway in caspase 3-deficient cells. This study demonstrates the caspase 3-independent function of Bak in the TNF-alpha-induced apoptotic pathway.

Apoptosis↗
PubMed2002

Identification of genes that function in the TNF-alpha-mediated apoptotic pathway using randomized hybrid ribozyme libraries.

Now that the sequences of many genomes are available, methods are required for the rapid identification of functional genes. We describe here a simple system for the isolation of genes that function in the tumor necrosis factor-alpha (TNF-alpha)-mediated pathway of apoptosis, using RNA helicase-associated ribozyme libraries with randomized substrate-binding arms. Because target-site accessibility considerably limits the effective use of intracellular ribozymes, the effectiveness of a conventional ribozyme library has been low. To overcome this obstacle, we attached to ribozymes an RNA motif (poly(A)-tail) able to interact with endogenous RNA helicase(s) so that the resulting helicase-attached, hybrid ribozymes can more easily attack target sites regardless of their secondary or tertiary structures. When the phenotype of cells changes upon introduction of a ribozyme library, genes responsible for these changes may be identified by sequencing the active ribozyme clones. In the case of TNF-alpha-mediated apoptosis, when a ribozyme library was introduced into MCF-7 cells, surviving clones were completely or partially resistant to TNF-alpha-induced apoptosis. We identified many pro-apoptotic genes and partial sequences of previously uncharacterized genes using this method. Our gene discovery system should be generally applicable to the identification of functional genes in various systems.

Apoptosis↗
PubMed2002

Identification of AP-2-regulated genes by macroarray profiling of gene expression in human A375P melanoma.

Transcription factor AP-2 is a negative regulator of metastasis. Its expression is down regulated with progression of melanoma cells to metastasis. In this study, we performed macroarray profiling of gene expression of human A375P melanoma cells and their derivatives with overexpression of AP-2 and dominant-negative AP-2. Such comprehensive analysis lead to an identification of genes such as MMP-2, E-cadherin, melanoma adhesion molecule, early growth response 1, fibroblast growth factor 3, ubiquitin C, histone deacetylase 3 and integrin alpha 5,7, beta 3,5 as regulated by AP-2. Whereas some of these are known as AP-2-regulated genes, the others are not so far. Thus the study reports for the first time identification of new genes regulated by AP-2 that may be involved in metastasis of melanoma.

DNA-Binding Proteins↗
PubMed2002

A functional gene discovery in cell differentiation by hybrid ribozyme and siRNA libraries.

Recently, we developed a gene discovery system that can identify functional genes using a randomized hybrid ribozyme library. In this system, inhibition of the expression of a particular gene by active ribozymes was reflected by a change in a particular phenotype, the method allowed the identification of functional genes. In the case of identification of functional genes for apoptosis pathways, we identified many pro-apoptotic genes in TNF-alpha and Fas-mediated apoptosis pathways. In this study, we tried to identify the functional genes that are necessary for the retinoic acid (RA)-induced cell differentiation using randomized ribozyme and siRNA libraries. We succeeded to identify the several differentiation factors. Therefore, our gene discovery system based on randomized ribozyme and siRNA libraries are high potential to identify the differentiation and undifferentiation factors in the post genome era.

Cell Differentiation↗