Biomedical subjects

Dong-chul Kang

Publications and source records attributed to Dong-chul Kang.

5 recordsLinked to original sources

PubMed2003

Expression regulation and genomic organization of human polynucleotide phosphorylase, hPNPase(old-35), a Type I interferon inducible early response gene.

An overlapping pathway screening (OPS) approach designed to identify and clone genes displaying parallel expression profiles as a function of induction of terminal differentiation and cellular senescence in human cells identified a novel gene old-35. Sequence and functional analysis indicates that old-35 encodes human polynucleotide phosphorylase, hPNPase(old-35). Polynucleotide phosphorylases comprise a family of phosphate dependent 3'-5' RNA exonucleases implicated in RNA regulation. Treatment of HO-1 human melanoma and additional diverse normal and tumor-derived human cell types with Type I interferon (IFN), IFN-beta or IFN-alpha, induces hPNPase(old-35) expression. To provide insights into the regulation of hPNPase(old-35), we cloned and analyzed the promoter region of this gene. These studies demonstrate that IFN-beta controls hPNPase(old-35) expression by transcriptional modulation rather than by altering mRNA stability. Transcriptional activation of hPNPase(old-35) by IFN-beta is primarily mediated by the interferon stimulatory response element (ISRE) present in its promoter. Analysis of hPNPase(old-35) expression in cell lines defective in various IFN signaling molecules confirms that hPNPase(old-35) expression is dependent upon the Janus activated kinase (JAK)/signal transducers and activators of transcription (STAT) pathway. Furthermore, gel shift analyses document that hPNPase(old-35) is a direct target of the interferon stimulated gene factor 3 (ISGF3) complex. The hPNPase(old-35) gene spans approximately 54 kb of genomic DNA and is distributed on 28 exons and 27 introns. hPNPase(old-35) maps to 2p15-2p16.1, a region implicated in hereditary nonpolyposis colorectal cancer, Carney complex, Doyne's honeycomb retinal dystrophy and several other diseases. To provide insights into PNPase function in vivo, we have also cloned the mouse PNPase(old-35) cDNA, mPNPase(old-35). Induction of hPNPase(old-35) by IFN treatment as well as during differentiation and senescence suggest that this gene may play a significant role in regulating cellular growth and that overlapping gene expression changes, also induced by IFN, may contribute to these important physiological processes.

5' Untranslated Regions↗

PubMed2003

Down-regulation of Myc as a potential target for growth arrest induced by human polynucleotide phosphorylase (hPNPaseold-35) in human melanoma cells.

Terminal differentiation and senescence share several common properties, including irreversible cessation of growth and changes in gene expression profiles. To identify molecules that converge in both processes, an overlapping pathway screening was employed that identified old-35, which is human polynucleotide phosphorylase (hPNPaseold-35), a 3',5'-exoribonuclease. We previously demonstrated that hPNPaseold-35 is a type I interferon-inducible gene that is also induced in senescent fibroblasts. In vitro RNA degradation assays confirmed its exoribonuclease properties, and overexpression of hPNPaseold-35 resulted in growth suppression in HO-1 human melanoma cells. The present study examined the molecular mechanism of the growth-arresting property of hPNPaseold-35. When overexpressed by means of a replication-incompetent adenoviral vector (Ad.hPNPaseold-35), hPNPaseold-35 inhibited cell growth in all cell lines tested. Analysis of cell cycle revealed that infection of HO-1 cells with Ad.hPNPaseold-35 resulted in arrest in the G1 phase and eventually apoptosis accompanied by marked reduction in the S phase. Infection with Ad.hPNPaseold-35 resulted in reduction in expression of the c-myc mRNA and Myc protein and modulated the expression of proteins regulating G1 checkpoint and apoptosis. In vitro mRNA degradation assays revealed that hPNPaseOLD-35 degraded c-myc mRNA. Overexpression of Myc partially but significantly protected HO-1 cells from Ad.hPNPaseold-35-induced growth arrest, indicating that Myc down-regulation might directly mediate the growth-inhibitory properties of Ad.hPNPaseold-35. Inhibition of hPNPaseold-35 by an antisense approach provided partial but significant protection against interferon-beta-mediated growth inhibition, thus demonstrating the biological significance of hPNPaseold-35 in interferon action.

Antineoplastic Agents↗

PubMed2003

Customized rapid subtraction hybridization (RaSH) gene microarrays identify overlapping expression changes in human fetal astrocytes resulting from human immunodeficiency virus-1 infection or tumor necrosis factor-alpha treatment.

Genes displaying altered expression as a function of human immunodeficiency virus (HIV)-1 infection of cultured primary human fetal astrocytes (PHFA) were previously identified using a rapid subtraction hybridization (RaSH) method. This scheme identified both known and novel genes displaying elevated expression, astrocyte elevated genes (AEG), and decreased expression, astrocyte suppressed genes (ASG), in PHFA as a consequence of infection with HIV-1 or treatment with HIV-1 envelope glycoprotein (gp120). RaSH also identified both known and novel genes displaying enhanced (HR) or reduced (HS) expression in HIV-1 resistant versus HIV-1 susceptible human T-cell clones. In the present study, a customized microarray approach employing these RaSH-derived genes was used to distinguish overlapping gene expression changes occurring in PHFA as a function of treatment with HIV-1 and the neurotoxic agent tumor necrosis factor (TNF)-alpha. RaSH cDNAs were spotted (microarrayed) on nylon membranes and probed with temporally isolated reverse transcribed cDNAs from HIV-1-infected and TNF-alpha-treated PHFA. This strategy identified genes displaying parallel changes after TNF-alpha treatment as observed following HIV-1 infection. Confirmation of genuine differential expression was achieved by Northern blotting. These studies document that TNF-alpha can induce a set of corresponding changes in specific AEGs and ASGs as does HIV-1 infection in PHFA. Furthermore, this customized microarray approach with RaSH-derived clones represents an efficient and sensitive methodology for elucidating molecular changes in PHFA occurring as a consequence of treatment with pharmacological agents affecting astrocyte physiology.

Astrocytes↗

PubMed2003

Insights into glutamate transport regulation in human astrocytes: cloning of the promoter for excitatory amino acid transporter 2 (EAAT2).

Glutamate transport is central to neurotransmitter functions in the brain. Impaired glutamate transport induces neurotoxicity associated with numerous pathological processes, including stroke/ischemia, temporal lobe epilepsy, Alzheimer's disease, amyotrophic lateral sclerosis, Huntington's disease, HIV-1-associated dementia, and growth of malignant gliomas. Excitatory amino acid transporter-2 (EAAT2) is a major glutamate transporter in the brain expressed primarily in astrocytes. We presently describe the cloning and characterization of the human EAAT2 promoter, demonstrating elevated expression in astrocytes. Regulators of EAAT2 transport, both positive and negative, alter EAAT2 transcription, promoter activity, mRNA, and protein. These findings imply that transcriptional processes can regulate EAAT2 expression. Moreover, they raise the intriguing possibility that the EAAT2 promoter may be useful for targeting gene expression in the brain and for identifying molecules capable of modulating glutamate transport that could potentially inhibit, ameliorate, or prevent various neurodegenerative diseases.

Astrocytes↗

PubMed2002

mda-5: An interferon-inducible putative RNA helicase with double-stranded RNA-dependent ATPase activity and melanoma growth-suppressive properties.

Human melanoma cells can be reprogrammed to terminally differentiate and irreversibly lose proliferative capacity by appropriate pharmacological manipulation. Subtraction hybridization identified melanoma differentiation-associated gene-5 (mda-5) as a gene induced during differentiation, cancer reversion, and programmed cell death (apoptosis). This gene contains both a caspase recruitment domain and putative DExH group RNA helicase domains. Atypical helicase motifs of MDA-5 deviate from consensus sequences but are well conserved in a potentially new group of cloned and hypothetical proteins. mda-5 is an early response gene inducible by IFN and tumor necrosis factor-alpha, responding predominantly to IFN-beta. Protein kinase C activation by mezerein further augments mda-5 expression induced by IFN-beta. Expression of mda-5 is controlled transcriptionally by IFN-beta, and the MDA-5 protein localizes in the cytoplasm. mda-5 displays RNA-dependent ATPase activity, and ectopic expression of mda-5 in human melanoma cells inhibits colony formation. In these contexts, mda-5 may function as a mediator of IFN-induced growth inhibition and/or apoptosis. MDA-5 is a double-stranded RNA-dependent ATPase that contains both a caspase recruitment domain and RNA helicase motifs, with a confirmed association with growth and differentiation in human melanoma cells.

Adenosine Triphosphatases↗