Biomedical subjects

Byungkook Lee

Publications and source records attributed to Byungkook Lee.

At least 19 recordsLinked to original sources

PubMed2006

Characterization of the B cell epitopes associated with a truncated form of Pseudomonas exotoxin (PE38) used to make immunotoxins for the treatment of cancer patients.

Recombinant immunotoxins composed of an Ab Fv fragment joined to a truncated portion of Pseudomonas exotoxin A (termed PE38) have been evaluated in clinical trials for the treatment of various human cancers. Immunotoxin therapy is very effective in hairy cell leukemia and also has activity in other hemological malignancies; however, a neutralizing Ab response to PE38 in patients with solid tumors prevents repeated treatments to maximize the benefit. In this study, we analyze the murine Ab response as a model to study the B cell epitopes associated with PE38. Sixty distinct mAbs to PE38 were characterized. Mutual competitive binding of the mAbs indicated the presence of 7 major epitope groups and 13 subgroups. The competition pattern indicated that the epitopes are discrete and could not be reproduced using a computer simulation program that created epitopes out of random surface residues on PE38. Using sera from immunotoxin-treated patients, the formation of human Abs to each of the topographical epitopes was demonstrated. One epitope subgroup, E1a, was identified as the principal neutralizing epitope. The location of each epitope on PE38 was determined by preparing 41 mutants of PE38 in which bulky surface residues were mutated to either alanine or glycine. All 7 major epitope groups and 9 of 13 epitope subgroups were identified by 14 different mutants and these retained high cytotoxic activity. Our results indicate that a relatively small number of discrete immunogenic sites are associated with PE38, most of which can be eliminated by point mutations.

ADP Ribose Transferases↗

PubMed2006

Evolution and expression of chimeric POTE-actin genes in the human genome.

We previously described a primate-specific gene family, POTE, that is expressed in many cancers but in a limited number of normal organs. The 13 POTE genes are dispersed among eight different chromosomes and evolved by duplications and remodeling of the human genome from an ancestral gene, ANKRD26. Based on sequence similarity, the POTE gene family members can be divided into three groups. By genome database searches, we identified an actin retroposon insertion at the carboxyl terminus of one of the ancestral POTE paralogs. By Northern blot analysis, we identified the expected 7.5-kb POTE-actin chimeric transcript in a breast cancer cell line. The protein encoded by the POTE-actin transcript is predicted to be 120 kDa in size. Using anti-POTE mAbs that recognize the amino-terminal portion of the POTE protein, we detected the 120-kDa POTE-actin fusion protein in breast cancer cell lines known to express the fusion transcript. These data demonstrate that insertion of a retroposon produced an altered functional POTE gene. This example indicates that new functional human genes can evolve by insertion of retroposons.

Actins↗

PubMed2006

Mesothelin-MUC16 binding is a high affinity, N-glycan dependent interaction that facilitates peritoneal metastasis of ovarian tumors.

BACKGROUND: The mucin MUC16 and the glycosylphosphatidylinositol anchored glycoprotein mesothelin likely facilitate the peritoneal metastasis of ovarian tumors. The biochemical basis and the kinetics of the binding between these two glycoproteins are not clearly understood. Here we have addressed this deficit and provide further evidence supporting the role of the MUC16-mesothelin interaction in facilitating cell-cell binding under conditions that mimic the peritoneal environment. RESULTS: In this study we utilize recombinant-Fc tagged human mesothelin to measure the binding kinetics of this glycoprotein to MUC16 expressed on the ovarian tumor cell line OVCAR-3. OVCAR-3 derived sublines that did not express MUC16 showed no affinity for mesothelin. In a flow cytometry-based assay mesothelin binds with very high affinity to the MUC16 on the OVCAR-3 cells with an apparent Kd of 5-10 nM. Maximum interaction occurs within 5 mins of incubation of the recombinant mesothelin with the OVCAR-3 cells and significant binding is observed even after 10 sec. A five-fold molar excess of soluble MUC16 was unable to completely inhibit the binding of mesothelin to the OVCAR-3 cells. Oxidation of the MUC16 glycans, removal of its N-linked oligosaccharides, and treatment of the mucin with wheat germ agglutinin and erythroagglutinating phytohemagglutinin abrogates its binding to mesothelin. These observations suggest that at least a subset of the MUC16-asscociated N-glycans is required for binding to mesothelin. We also demonstrate that MUC16 positive ovarian tumor cells exhibit increased adherence to A431 cells transfected with mesothelin (A431-Meso+). Only minimal adhesion is observed between MUC16 knockdown cells and A431-Meso+ cells. The binding between the MUC16 expressing ovarian tumor cells and the A431-Meso+ cells occurs even in the presence of ascites from patients with ovarian cancer. CONCLUSION: The strong binding kinetics of the mesothelin-MUC16 interaction and the cell adhesion between ovarian tumor cells and A431-Meso+ even in the presence of peritoneal fluid strongly support the importance of these two glycoproteins in the peritoneal metastasis of ovarian tumors. The demonstration that N-linked glycans are essential for mediating mesothlein-MUC16 binding may lead to novel therapeutic targets to control the spread of ovarian carcinoma.

Binding, Competitive↗

PubMed2006

Exon-based mapping of microarray probes: recovering differential gene expression signal in underpowered hypoxia experiment.

There is an immense collection of underpowered Affymetrix gene array experiments. Although a majority of these experiments generated biologically feasible results, the considerable fraction of assays failed to identify expected transcriptional changes. There is an unused potential of Affymetrix probe-set redundancy for common exonic and UTR regions. We hypothesized that group analysis of multiple probe-sets which hybridize to the same exon or UTR will increase array discriminating power of transcriptional changes. To test this hypothesis, we analyzed Affymetrix mouse probe-sets that share the same exon using blocking feature of the Significance Analysis of Microarrays (SAM). Two-thousand two-hundred one exon-sharing probe-sets targeting 1011 transcripts were identified by mapping 36701 MG-U74v2 probe-sets to genomic alignments of 3,971,086 known mouse transcripts. Using the blocking feature of SAM with an underpowered (two microarrays per experimental condition) mouse hypoxia-induced pulmonary hypertension model, we identified 24 genes that were significantly (FDR<5%) affected by hypoxia but were not detected by regular SAM. The relevance of the four newly identified genes (Mig6, F3, Bmp6, and Ndrg1) to known hypoxia-associated responses was confirmed by PubMatrix; and hypoxia-induced up-regulation of Mig6 expression was validated by real-time RT-PCR. We demonstrated that analysis of exon-sharing probe-sets allowed discovery of additional hypoxia-affected genes in an underpowered array experiment. This method will facilitate re-evaluation of existing underpowered Affymetrix gene expression profiles.

5' Untranslated Regions↗

PubMed2006

ROC and confusion analysis of structure comparison methods identify the main causes of divergence from manual protein classification.

BACKGROUND: Current classification of protein folds are based, ultimately, on visual inspection of similarities. Previous attempts to use computerized structure comparison methods show only partial agreement with curated databases, but have failed to provide detailed statistical and structural analysis of the causes of these divergences. RESULTS: We construct a map of similarities/dissimilarities among manually defined protein folds, using a score cutoff value determined by means of the Receiver Operating Characteristics curve. It identifies folds which appear to overlap or to be "confused" with each other by two distinct similarity measures. It also identifies folds which appear inhomogeneous in that they contain apparently dissimilar domains, as measured by both similarity measures. At a low (1%) false positive rate, 25 to 38% of domain pairs in the same SCOP folds do not appear similar. Our results suggest either that some of these folds are defined using criteria other than purely structural consideration or that the similarity measures used do not recognize some relevant aspects of structural similarity in certain cases. Specifically, variations of the "common core" of some folds are severe enough to defeat attempts to automatically detect structural similarity and/or to lead to false detection of similarity between domains in distinct folds. Structures in some folds vary greatly in size because they contain varying numbers of a repeating unit, while similarity scores are quite sensitive to size differences. Structures in different folds may contain similar substructures, which produce false positives. Finally, the common core within a structure may be too small relative to the entire structure, to be recognized as the basis of similarity to another. CONCLUSION: A detailed analysis of the entire available protein fold space by two automated similarity methods reveals the extent and the nature of the divergence between the automatically determined similarity/dissimilarity and the manual fold type classifications. Some of the observed divergences can probably be addressed with better structure comparison methods and better automatic, intelligent classification procedures. Others may be intrinsic to the problem, suggesting a continuous rather than discrete protein fold space.

Algorithms↗

PubMed2006

High expression of a cytokeratin-associated protein in many cancers.

We have described previously a cDNA library made from membrane-bound polysomal mRNA prepared from breast and prostate cancer cell lines. The library is highly enriched for cDNAs encoding membrane proteins, secreted proteins, and cytokeratins. To characterize this library, 25,277 cDNA clones were sequenced and aligned with various databases; 1,439 clones did not align with known genes. From this set of clones we identified a previously uncharacterized gene encoding a 334-aa protein. Although protein structural motif prediction programs indicate that the gene encodes a membrane protein comprising a signal sequence, a series of leucine-rich repeats, and a single transmembrane domain with a cytoplasmic tail, confocal microscopy of MCF7 breast cancer cells demonstrates that the protein is not directly associated with the plasma membrane or intracellular membranes but instead colocalizes with intermediate filaments and cytokeratins within the cell. Immunofluorescence studies also show that protein expression is increased greatly in mitotic MCF7 cells, and immunohistochemistry demonstrates its expression in human breast cancer cells. Analysis of mRNA levels in 25 different normal tissues by RT-PCR shows that this gene is expressed highly in normal prostate and salivary gland, very weakly in colon, pancreas, and intestine, and not at all in other tissues. RT-PCR studies on human cancer samples show that the RNA is expressed highly in many cancer cell lines and cancer specimens, including 26 of 33 human breast cancers, 3 of 3 prostate cancers, 3 of 3 colon cancers, and 3 of 3 pancreatic cancers. We name the protein CAPC, cytokeratin-associated protein in cancer.

Amino Acid Sequence↗

PubMed2006

Human-specific nonsense mutations identified by genome sequence comparisons.

The comparative study of the human and chimpanzee genomes may shed light on the genetic ingredients for the evolution of the unique traits of humans. Here, we present a simple procedure to identify human-specific nonsense mutations that might have arisen since the human-chimpanzee divergence. The procedure involves collecting orthologous sequences in which a stop codon of the human sequence is aligned to a non-stop codon in the chimpanzee sequence and verifying that the latter is ancestral by finding homologs in other species without a stop codon. Using this procedure, we identify nine genes (CML2, FLJ14640, MT1L, NPPA, PDE3B, SERPINA13, TAP2, UIP1, and ZNF277) that would produce human-specific truncated proteins resulting in a loss or modification of the function. The premature terminations of CML2, MT1L, and SERPINA13 genes appear to abolish the original function of the encoded protein because the mutation removes a major part of the known active site in each case. The other six mutated genes are either known or presumed to produce functionally modified proteins. The mutations of five genes (CML2, FLJ14640, MT1L, NPPA, TAP2) are known or predicted to be polymorphic in humans. In these cases, the stop codon alleles are more prevalent than the ancestral allele, suggesting that the mutant alleles are approaching fixation since their emergence during the human evolution. The findings support the notion that functional modification or inactivation of genes by nonsense mutation is a part of the process of adaptive evolution and acquisition of species-specific features.

Animals↗

PubMed2006

POTE paralogs are induced and differentially expressed in many cancers.

To identify new antigens that are targets for the immunotherapy of prostate and breast cancer, we used expressed sequence tag and genomic databases and discovered POTE, a new primate-specific gene family. Each POTE gene encodes a protein that contains three domains, although the proteins vary greatly in size. The NH2-terminal domain is novel and has properties of an extracellular domain but does not contain a signal sequence. The second and third domains are rich in ankyrin repeats and spectrin-like helices, respectively. The protein encoded by POTE-21, the first family member discovered, is localized on the plasma membrane of the cell. In humans, 13 highly homologous paralogs are dispersed among eight chromosomes. The expression of POTE genes in normal tissues is restricted to prostate, ovary, testis, and placenta. A survey of several cancer samples showed that POTE was expressed in 6 of 6 prostate, 12 of 13 breast, 5 of 5 colon, 5 of 6 lung, and 4 of 5 ovarian cancers. To determine the relative expression of each POTE paralog in cancer and normal samples, we employed a PCR-based cloning and analysis method. We found that POTE-2alpha, POTE-2beta, POTE-2gamma, and POTE-22 are predominantly expressed in cancers whereas POTE expression in normal tissues is somewhat more diverse. Because POTE is primate specific and is expressed in testis and many cancers but only in a few normal tissues, we conclude POTE is a new primate-specific member of the cancer-testis antigen family. It is likely that POTE has a unique role in primate biology.

Base Sequence↗

PubMed2005

Duplication and extensive remodeling shaped POTE family genes encoding proteins containing ankyrin repeat and coiled coil domains.

The POTE family genes encode a highly homologous group of primate-specific proteins that contain ankyrin repeats and coiled coil domains. At least 13 paralogous POTE family genes are found on 8 human chromosomes (2, 8, 13, 14, 15, 18, 21 and 22), which can be sorted into 3 groups based on sequence similarity. We identified by a database search a group of additional human ankyrin repeat domain proteins, of which ANKRD26 and ANKRD30A are the best characterized; these are more distant homologs of POTE family proteins. A comprehensive comparison of the genomic organization indicates that ANKRD26 has the genomic structure of the possible ancestor of ANKRD30A and all POTE family genes. Extensive remodeling involving segmental loss and internal duplication appears to have reshaped the ANKRD30A and POTE family genes after the primal duplication of the ancestor gene. We also identified a mouse homolog of human ANKRD26, but failed to find a mouse homolog that bears the structural characteristics of any of the POTE family of proteins. The mouse Ankrd26 may serve as a useful model for the study of the function of human ANKRD26, ANKRD30A and POTE family proteins.

Animals↗

PubMed2005

On the intactness of hydrogen bonds around nonpolar solutes dissolved in water.

Angell developed a simple two-state model of hydrogen bonds with the aim to describe some properties of pure water. Muller extended the two-state model description to treat the unusual thermodynamics of hydrophobic hydration. We show here that, to correctly reproduce a qualitative feature of the temperature dependence of the hydration heat capacity change of nonpolar solutes by means of the two-state Muller's model, the hydrogen bonds in the hydration shell have to be more broken than those in bulk water. This contrasts with the suggestion in the literature that more hydrogen bonds form around a nonpolar solute in water.

Hydrogen Bonding↗

PubMed2005

Domain definition and target classification for CASP6.

Assessment of structure predictions in CASP6 was based on single domains isolated from experimentally determined structures, which were categorized into comparative modeling, fold recognition, and new fold targets. Domain definitions were defined upon visual examination of the structures with the aid of automated domain-parsing programs. Domain categorization was determined by comparison of the target structures with those in the Protein Data Bank at the time each target expired and a variety of sequence and structure-based methods to determine potential homologous relationships.

Amino Acid Sequence↗

PubMed2005

Assessment of CASP6 predictions for new and nearly new fold targets.

This is a report of the assessment of the predictions made for the CASP6 protein structure prediction experiment conducted in 2004 in the New Fold (NF) category. There were nine protein domains that were judged to have new folds (NF) and 16 for which a similar structure was known but the sequence similarity was judged to be too low for them to be easily recognized (FR/A). We selected all NF targets and eight of the 16 FR/A targets judged to be at the borderline between NF and FR/A for evaluation in the NF category. A total of 165 prediction groups submitted over 7400 structural models for these targets. The quality of these models was evaluated using the GDT_TS scores of the structural similarity detection program LGA and by visual inspection of the top-scoring models. The best models submitted bore an overall similarity to the target structure for three or four of the nine NF targets and for all but one of the FR/A targets. High-scoring models for the NF targets were submitted by several different groups. When both the NF and FR/A targets were considered, Baker group dominated by submitting best models for seven of the 17 targets, but 14 other groups also managed to submit best models for one or more targets.

Algorithms↗

PubMed2005

Evaluation of domain prediction in CASP6.

We present an analysis of the domain boundary prediction, a new category, in the sixth community-wide experiment on the Critical Assessment of Techniques for Protein Structure Prediction (CASP6). There were 1011 predictions submitted for 63 targets. Each prediction was compared to the set of domains defined manually by visual inspection of the experimental structure. The comparison was scored using a new domain prediction scoring scheme. As the definition of a domain is subjective, many targets were assigned alternate definitions. For such targets, each prediction was compared with all different definitions and the best score was chosen. The predictors found it difficult to accurately predict domain boundaries when the target protein contained many domains or domains made of multiple sequence segments. The CBRC-DR (P0536) and Sternberg (P0237) groups were the most successful among human experts, while Baker-Rossettadom (P0353) and Baker-Robetta-Ginzu (P0421) did well among servers.

Algorithms↗

PubMed2005

Identification of nine human-specific frameshift mutations by comparative analysis of the human and the chimpanzee genome sequences.

MOTIVATION: The recent release of the draft sequence of the chimpanzee genome is an invaluable resource for finding genome-wide genetic differences that might explain phenotypic differences between humans and chimpanzees. AVAILABILITY: In this paper, we describe a simple procedure to identify potential human-specific frameshift mutations that occurred after the divergence of human and chimpanzee. The procedure involves collecting human coding exons bearing insertions or deletions compared with the chimpanzee genome and identification of homologs from other species, in support of the mutations being human-specific. Using this procedure, we identified nine genes, BASE, DNAJB3, FLJ33674, HEJ1, NTSR2, RPL13AP, SCGB1D4, WBSCR27 and ZCCHC13, that show human-specific alterations including truncations of the C-terminus. In some cases, the frameshift mutation results in gene inactivation or decay. In other cases, the altered protein seems to be functional. This study demonstrates that even the unfinished chimpanzee genome sequence can be useful in identifying modification of genes that are specific to the human lineage and, therefore, could potentially be relevant to the study of the acquisition of human-specific traits.

Amino Acid Sequence↗

PubMed2004

Finding fusion genes resulting from chromosome rearrangement by analyzing the expressed sequence databases.

Chromosomal rearrangements resulting in gene fusions are frequently involved in carcinogenesis. Here, we describe a semiautomatic procedure for identifying fusion gene transcripts by using publicly available mRNA and EST databases. With this procedure, we have identified 96 transcript sequences that are derived from 60 known fusion genes. Also, 47 or more additional sequences appear to be derived from 20 or more previously unknown putative fusion genes. We have experimentally verified the presence of a previously unknown IRA1/RGS17 fusion in the breast cancer cell line MCF7. The fusion gene encodes the full-length RGS17 protein, a regulator of G protein-coupled signaling, under the control of the IRA1 gene promoter. This study demonstrates that databases of ESTs can be used to discover fusion genes resulting from structural rearrangement of chromosomes.

Cell Line, Tumor↗

PubMed2004

Five POTE paralogs and their splice variants are expressed in human prostate and encode proteins of different lengths.

POTE is a new gene that contains ankyrin and spectrin domains and is expressed in prostate, testis, ovary, and placenta. In humans, 10 highly homologous variants of the gene are dispersed among eight chromosomes. POTE paralogs are detected in primates but not in other species. Using prostate RNA, we characterized cDNAs from five paralogs and their splice variants. The proteins encoded by the POTE paralogs and their variants range from 80 to 32 kDa. Transfection of POTE constructs into 293T cells shows that the POTE protein, like spectrin, is localized on the inner aspect of the plasma membrane. We also detect a noncoding transcript expressed on the opposite strand from POTE on chromosome 14 or 22. We speculate that POTE has an important signaling function in the reproductive system.

Alternative Splicing↗

PubMed2004

Frequency of gaps observed in a structurally aligned protein pair database suggests a simple gap penalty function.

Gap penalty is an important component of the scoring scheme that is needed when searching for homologous proteins and for accurate alignment of protein sequences. Most homology search and sequence alignment algorithms employ a heuristic 'affine gap penalty' scheme q + r x n, in which q is the penalty for opening a gap, r the penalty for extending it and n the gap length. In order to devise a more rational scoring scheme, we examined the pattern of gaps that occur in a database of structurally aligned protein domain pairs. We find that the logarithm of the frequency of gaps varies linearly with the length of the gap, but with a break at a gap of length 3, and is well approximated by two linear regression lines with R2 values of 1.0 and 0.99. The bilinear behavior is retained when gaps are categorized by secondary structures of the two residues flanking the gap. Similar results were obtained when another, totally independent, structurally aligned protein pair database was used. These results suggest a modification of the affine gap penalty function.

Computational Biology↗

PubMed2004

NGEP, a gene encoding a membrane protein detected only in prostate cancer and normal prostate.

We identified a gene (NGEP) that is expressed only in prostate cancer and normal prostate. The two NGEP transcripts are 0.9 kb and 3.5 kb in size and are generated by a differential splicing event. The short variant (NGEP-S) is derived from four exons and encodes a 20-kDa intracellular protein. The long form (NGEP-L) is derived from 18 exons and encodes a 95-kDa protein that is predicted to contain seven-membrane-spanning regions. In situ hybridization shows that NGEP mRNA is localized in epithelial cells of normal prostate and prostate cancers. Immunocytochemical analysis of cells transfected with NGEP cDNAs containing a Myc epitope tag at the carboxyl terminus shows that the protein encoded by the short transcript is localized in the cytoplasm, whereas the protein encoded by the long transcript is present on the plasma membrane. Because of its selective expression in prostate cancer and its presence on the cell surface, NGEP-L is a promising target for the antibody-based therapies of prostate cancer.

Animals↗