Biomedical subjects

Hyo Jin Kang

Publications and source records attributed to Hyo Jin Kang.

8 recordsLinked to original sources

PubMed2006

Isolation of 151 mutants that have developmental defects from T-DNA tagging.

In order to understand the mechanisms underlying plant development, a necessary first step involves the elucidation of the functions of the genes, via the analysis of mutants that exhibit developmental defects. In this study, an activation tagging mutant library harboring 80,650 independent Arabidopsis transformants was generated in order to screen for developmental mutants. A total of 129 mutants manifesting dominant developmental abnormalities were isolated, and their T-DNA insertion loci were mapped. The activation of one or more genes adjacent to a T-DNA insertion locus was confirmed in eight dominant mutants. A gene adjacent to the right border was usually activated by the 35S enhancers. Interestingly, the transcriptional activation of multiple genes within a broad range was observed in one of the mutants, which raises the possibility that activation by the 35S enhancers was not limited strictly to a single gene. In order to gain a better understanding of sexual reproduction in higher plants, we isolated 22 mutants exhibiting defects in female gametophyte development, and determined their T-DNA insertion loci. We propose that this mutant population may prove useful in the further determination of the functions of genes that play important roles in plant development.

Base Sequence↗

PubMed2006

SNP@Domain: a web resource of single nucleotide polymorphisms (SNPs) within protein domain structures and sequences.

The single nucleotide polymorphisms (SNPs) in conserved protein regions have been thought to be strong candidates that alter protein functions. Thus, we have developed SNP@Domain, a web resource, to identify SNPs within human protein domains. We annotated SNPs from dbSNP with protein structure-based as well as sequence-based domains: (i) structure-based using SCOP and (ii) sequence-based using Pfam to avoid conflicts from two domain assignment methodologies. Users can investigate SNPs within protein domains with 2D and 3D maps. We expect this visual annotation of SNPs within protein domains will help scientists select and interpret SNPs associated with diseases. A web interface for the SNP@Domain is freely available at http://snpnavigator.net/ and from http://bioportal.net/.

Computer Graphics↗

PubMed2006

BRCA1 modulates xenobiotic stress-inducible gene expression by interacting with ARNT in human breast cancer cells.

Previously, we have reported that BRCA1 regulates the expression of various classes of genes, including genes involved in xenobiotic stress responses (Bae, I., Fan, S., Meng, Q., Rih, J. K., Kim, H. J., Kang, H. J., Xu, J., Goldberg, I. D., Jaiswal, A. K., and Rosen, E. M. (2004) Cancer Res. 64, 7893-7909). In the present study, we have investigated the effects of BRCA1 on xenobiotic stress-inducible gene expression. In response to aryl hydrocarbon receptor (AhR) ligands, cytoplasmic AhR becomes activated and then translocates to the nucleus where it forms a complex with the aryl hydrocarbon receptor nuclear translocator (ARNT). Subsequently, the AhR.ARNT complex binds to the enhancer or promoter of genes containing a xenobiotic stress-responsive element and regulates the expression of multiple target genes including cytochrome P450 subfamily polypeptide 1 (CYP1A1). In this study, we have found that endogenous and overexpressed exogenous wild-type BRCA1 affect xenobiotic stress-induced CYP1A1 gene expression. Using a standard chromatin immunoprecipitation assay, we have demonstrated that BRCA1 is recruited to the promoter regions of CYP1A1 and CYP1B1 along with ARNT and/or AhR following xenobiotic exposure. Our findings suggest that BRCA1 may be physiologically important for mounting a normal response to xenobiotic insults and that it may function as a coactivator for ARNT activity. Using immunoprecipitation, Western blotting, and glutathione S-transferase capture assays, a xenobiotic-independent interaction between BRCA1 and ARNT has been identified, although it is not yet known whether this is a direct or indirect interaction. We have also found that the inducibility of CYP1A1 and CYP1B1 transcripts following xenobiotic stress was significantly attenuated in BRCA1 knockdown cells. This reduced inducibility is associated with an altered stability of ARNT and was almost completely reversed in cells transfected with an ARNT expression vector. Finally, we have found that xenobiotic (TCDD) treatments of breast cancer cells containing reduced levels of BRCA1 cause the transcription factor ARNT to become unstable.

Aryl Hydrocarbon Receptor Nuclear Translocator↗

PubMed2006

BRCA1 plays a role in the hypoxic response by regulating HIF-1alpha stability and by modulating vascular endothelial growth factor expression.

A recent study of breast cancer patients with and without BRCA1 gene mutations found significantly lower levels of VEGF in serum from patients with BRCA1 mutations (Tarnowski, B., Chudecka-Glaz, A., Gorski, B., and Rzepka-Gorska, I. (2004) Breast Cancer Res. Treat. 88, 287-288). Here, we describe a possible mechanistic explanation for this correlation. Because hypoxia in tumors stimulates VEGF expression and secretion we hypothesized that altered BRCA1 protein levels in breast tumors could affect hypoxia-stimulated VEGF promoter activity. This possibility was tested in cells transfected with various combinations of expression plasmids for BRCA1, BRCA1 specific inhibitory RNAs (BRCA1-siRNAs), HIF-1alpha, and a VEGF promoter-reporter and then incubated in normoxia (21%, O2) or hypoxia (0.1%, O2). As predicted, increased BRCA1 levels enhanced both hypoxia-stimulated VEGF promoter activity and the amounts of VEGF mRNA, as determined by semiquantitative RT-PCR and quantitative real time PCR. Using the ChIP assay, we discovered that BRCA1 could be recruited to the endogenous human VEGF promoter along with HIF-1alpha following hypoxia. An interaction between BRCA1 and HIF-1alpha was found in human breast cancer cells. We also found that hypoxia-stimulated VEGF promoter activity and secretion was reduced in cells containing reduced amounts of endogenous BRCA1 protein (obtained by transfecting with BRCA1 siRNAs). A mechanistic explanation for these effects is provided by our finding a reduced half-life and reduced accumulation of HIF-1alpha in hypoxic cells transfected with BRCA1-siRNAs and that proteasome inhibitors blocked these effects of BRCA1-siRNAs. Thus, our results suggest that normal amounts of BRCA1 function in hypoxia to regulate HIF-1alpha stability, probably by interacting with HIF-1alpha.

BRCA1 Protein↗

PubMed2005

BRCA1 regulates gene expression for orderly mitotic progression.

Germline mutations of the BRCA1 gene confer an increased risk for breast cancer and ovarian cancer. To study the contribution of BRCA1 to sporadic cancers, which often exhibit reduced BRCA1 expression, we tested the effect of knocking down BRCA1 on gene expression in human prostate (DU-145) and breast (MCF-7) cancer cells. DNA microarray and confirmatory RNA analyses revealed that BRCA1 small interfering (si) RNA caused down-regulation of multiple genes implicated in the mitotic spindle checkpoint (eg., BUB1B, HEC, and STK6), chromosome segregation (eg., ESPL1, NEK2, and PTTG1), centrosome function (eg., ASPM), cytokinesis (eg., PRC1, PLK, and KNSL2), and the progression into and through mitosis (eg., CDC2, and CDC20). Cells treated with BRCA1-siRNA showed attenuation of the mitotic spindle checkpoint; but not several G2 checkpoints. Finally, BRCA1 knockdown caused the accumulation of multinucleated cells, suggesting a defect in cytokinesis. We conclude that BRCA1 regulates gene expression for orderly mitotic progression.

BRCA1 Protein↗

PubMed2005

FESD: a Functional Element SNPs Database in human.

We have created the Functional Element SNPs Database (FESD) that categorizes functional elements in human genic regions and provides a set of single nucleotide polymorphisms (SNPs) located within each area. In the FESD, the human genic regions were divided into 10 different functional elements, such as promoter regions, CpG islands, 5'-untranslated regions (5'-UTRs), translation start sites, splice sites, coding exons, introns, translation stop sites, polyadenylation signals and 3'-UTRs, and subsequently, all the known SNPs were assigned to each functional element at their respective position. With the FESD web interface, users can select a set of SNPs in the specific functional elements and get their flanking sequences for genotyping experiments, which will help in finding mutations that contribute to the common and polygenic diseases. A web interface for the FESD is freely available at http://combio.kribb.re.kr/ksnp/resd/.

Databases, Nucleic Acid↗

PubMed2004

BRCA1 induces antioxidant gene expression and resistance to oxidative stress.

Mutations of the breast cancer susceptibility gene 1 (BRCA1), a tumor suppressor, confer an increased risk for breast, ovarian, and prostate cancers. To investigate the function of the BRCA1 gene, we performed DNA microarray and confirmatory reverse transcription-PCR analyses to identify BRCA1-regulated gene expression changes. We found that BRCA1 up-regulates the expression of multiple genes involved in the cytoprotective antioxidant response, including glutathione S-transferases, oxidoreductases, and other antioxidant genes. Consistent with these findings, BRCA1 overexpression conferred resistance while BRCA1 deficiency conferred sensitivity to several different oxidizing agents (hydrogen peroxide and paraquat). In addition, in the setting of oxidative stress (due to hydrogen peroxide), BRCA1 shifted the cellular redox balance to a higher ratio of reduced to oxidized glutathione. Finally, BRCA1 stimulated antioxidant response element-driven transcriptional activity and enhanced the activity of the antioxidant response transcription factor nuclear factor erythroid-derived 2 like 2 [also called NRF2 (NFE2L2)]. The ability of BRCA1 to stimulate antioxidant response element-dependent transcription and to protect cells against oxidative stress was attenuated by inhibition of nuclear factor erythroid-derived 2 like 2. These findings suggest a novel function for BRCA1, i.e., to protect cells against oxidative stress. This function would be consistent with the postulated role of BRCA1 as a caretaker gene in preserving genomic integrity.

Antioxidants↗

PubMed2002

Radicicol represses the transcriptional function of the estrogen receptor by suppressing the stabilization of the receptor by heat shock protein 90.

The estrogen receptor (ER) is a hormone-dependent transcription factor that belongs to the steroid/thyroid hormone receptor superfamily. Since the ER contributes to development and progression in human breast cancer, a number of studies have explored ways to inactivate this receptor. Previous studies have suggested that the 90-kDa heat shock protein (Hsp90) interacts with the ER, thus stabilizing the receptor in an inactive state. Here, we report that radicicol, an Hsp90-specific inhibitor, repressed estrogen-dependent transactivation of the ER as measured by pS2 gene transcription and a reporter gene encoding an estrogen-responsive element. Furthermore, we showed that radicicol induced rapid degradation of ERalpha, while the amount of ubiquitinated ERalpha was increased. A proteasome inhibitor, LLnL, almost completely abrogated the radicicol-induced decrease in expression level, as well as in transcriptional activity of ERalpha. These results suggest that radicicol disrupts the ER-Hsp90 heterodimeric complex, thereby generating ERalpha that is susceptible to ubiquitin/proteasome-induced degradation.

Animals↗