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Biomedical subjects

I M Chiu

Publications and source records attributed to I M Chiu.

At least 55 records · Page 3Linked to original sources
PubMed1993

Cloning of two novel forms of human acidic fibroblast growth factor (aFGF) mRNA.

We have previously isolated two different aFGF cDNA clones from kidney and brain. The two corresponding mRNA, designated aFGF 1.A and 1.B, are the predominant species in kidney and brain, respectively. During the characterization of aFGF mRNA in glioblastoma cells, we demonstrated that aFGF mRNA in U1242MG and D65MG glioblastoma cells contain 5'-untranslated sequences different from those of 1.A and 1.B. Through a strategy combining chromosome walking, identification and sequencing of evolutionarily conserved DNA regions, and a reverse transcription and polymerase chain reaction (RT-PCR)-based assay for RNA expression, we have isolated two novel aFGF cDNA clones. The cDNA clone representing aFGF mRNA 1.C was isolated from U1242MG cells; another aFGF cDNA, designated 1.D, was isolated from D65MG cells. Promoter 1C has extensive sequence homology to the hamster aFGF gene promoter that was shown to respond to testosterone stimulation by chloramphenicol acetyltransferase reporter gene assays. Using RT-PCR, we showed that normal, benign and cancerous prostate tissues do not express aFGF 1.C mRNA. In contrast, a prostate carcinoma cell line (PC-3) expresses 1.C mRNA. RT-PCR using 1.D-specific primers showed that kidney, brain and prostate do not express 1.D mRNA even though kidney and brain are the most abundant source for aFGF protein. RNase protection analysis further showed that 1.D mRNA is the predominant aFGF transcript in D65MG glioblastoma cells and in NFF-6 neonatal foreskin fibroblast cells. The genomic DNA corresponding to these two cDNA clones and the 5'-flanking regions were also isolated and their sequences determined. These DNA clones will provide important reagents for studying the regulatory elements of aFGF gene expression.

Animals↗
PubMed1993

Heterogeneity in the expression of fibroblast growth factor receptors during limb regeneration in newts (Notophthalmus viridescens).

Two closely related fibroblast growth factor receptors, FGFR1 and FGFR2, have been cloned from a newt (Notophthalmus viridescens) limb blastema cDNA library. Sequence analysis revealed that we have isolated both the bek and KGFR variants of FGFR2. These two variants differ only in the second half of the last of their three Ig-like domains. The expression patterns of FGFR1 and FGFR2 during limb regeneration have been determined by in situ hybridization. During the preblastema stages of regeneration, FGFR2 expression is observed in the basal layer of the wound epithelium and in the cells of the periosteum. As regeneration progresses to the blastema stages, FGFR2 expression continues to be observed in the basal layer of the wound epithelium with additional hybridization seen in the blastema mesenchyme closely associated with the bisected bones. From the early bud to the mid-bud blastema stage, FGFR1 expression is observed throughout the blastema mesenchyme but, unlike FGFR2, is distinctly absent from the wound epithelium. In the differentiation stages of regeneration, the mesenchymal expression of FGFR2 becomes restricted to the cells of the condensing cartilage and later to the perichondrium. During these later stages of regeneration, the wound epithelium hybridization to the FGFR2 probe is no longer observed. The expression patterns of these receptors suggest that FGFR1 and FGFR2 have distinct roles in limb regeneration, despite their sharing a number of the FGF ligands. Further investigation regarding the potential sources of the FGF ligands will help establish the role that FGFs and FGFRs play in limb regeneration.

Amino Acid Sequence↗
PubMed1993

Gene structure and differential expression of acidic fibroblast growth factor mRNA: identification and distribution of four different transcripts.

We have isolated four cDNA clones coding for human acidic fibroblast growth factor (aFGF) containing alternative 5' untranslated exons. Using RNAase protection analyses, we demonstrated the presence of at least four upstream, untranslated exons that are alternatively spliced to the first protein-coding exon. We designate these four untranslated exons, -1A, -1B, -1C and -1D. Splicing of these exons to the first coding exon will generate mRNA 1.A, 1.B, 1.C and 1.D respectively. Expression of these transcripts is regulated in a tissue-specific manner, as the major aFGF transcript in human brain frontal cortex differs from that in kidney. Furthermore, the pattern of aFGF transcripts in several glioblastoma cell lines tested is different from that in normal brain tissue. We isolated nine overlapping genomic clones containing these four upstream, untranslated exons. These four exons were localized on these clones by Southern hybridization and nucleotide sequence analysis. The overlapping clones are shown to be contiguous with our previously isolated genomic clones that contain the three aFGF-coding exons. The sizes of the four introns are 82.9, 71.1, 29.3 and 6.9 kbp. The transcriptional start sites of the two most upstream exons (-1A and -1B) have been mapped using RNAase protection and primer extension analyses. The sequences upstream of the start sites for aFGF 1.B mRNA do not contain a consensus TATA box. In contrast, the canonical CCAAT and TATA sequences are located at the proper distances from the transcription start site of aFGF 1.A mRNA.

Base Sequence↗
PubMed1992

Three genes for the human high affinity Fc receptor for IgG (Fc gamma RI) encode four distinct transcription products.

Three distinct but closely related classes of receptors that bind the Fc portion of immunoglobulin G (Fc gamma RI, -II, and -III) have been identified in humans. Only Fc gamma RI has high affinity for ligand and has a unique third extracellular domain (EC3). We have characterized three genes for human Fc gamma RI (A, B, and C). Each gene consists of six exons, spans 9.4 kilobase pairs, and localizes to chromosome 1. Although they are remarkably similar, genes B and C are notably different from A; in-frame stop codons are present in the EC3 domain of genes B and C, and deletions occur in a splice donor sequence of gene B. Four distinct Fc gamma RI transcripts were analyzed. One transcript, from gene A, would encode a transmembrane receptor with three external domains. A second transcript, an alternatively spliced product of gene B, would encode a two-external domain transmembrane receptor. Two transcripts, from genes B and C, have stop codons in EC3 and would be predicted to generate secreted receptors.

Amino Acid Sequence↗
PubMed1992

Detection of the PTC/retTPC oncogene in human thyroid cancers.

We have investigated the PTC/retTPC oncogene, an activated form of ret proto-oncogene with a specific rearrangement, in thyroid malignancies. Southern analysis was used to screen 36 thyroid papillary carcinomas (PC), 22 normal thyroid tissues from glands with PC elsewhere, three follicular carcinomas, eight follicular adenomas and 30 other non-malignant thyroids. Rearrangements were detected in four PCs (11%) using probes derived from the ret proto-oncogene. Genomic breakpoints from a PC and a PC cell line (TPC-1) were cloned and sequenced. The rearrangement points of ret proto-oncogene were found in the intron between the exon for the transmembrane domain and the first exon for the tyrosine kinase domain. Furthermore, the PTC/retTPC chimeric transcripts were detected in two PCs with the rearrangement by reverse transcription polymerase chain reaction. Distant metastases were present in 50% (2/4) of PCs with the rearrangement, but in only two out of 32 PCs without a detectable rearrangement (P = 0.05, Fisher exact test). Our study suggests that the rearrangement of the ret proto-oncogene may be involved in the development of distant metastases in patients with papillary thyroid carcinomas. However, a larger clinical study will be required to verify this observation.

Adolescent↗
PubMed1991

Characterization of the 5q- breakpoint in an acute nonlymphocytic leukemia patient using pulsed-field gel electrophoresis.

Multiple genes of hematopoietic importance have been localized to the long arm of chromosome 5 including granulocytemacrophage colony stimulating factor (GM-CSF) and interleukins (IL) 3, 4 and 5 to 5q23-31, colony stimulating factor 1 (CSF1) to 5q33.1 and its receptor (c-fms) to 5q33.3. The genes coding for platelet-derived growth factor receptor (PDGFR) and acidic fibroblast growth factor (FGFA) have been localized to 5q31-32 and 5q31.3-33.2, respectively. These genes fall in the region of chromosome 5 which is deleted in the 5q- refractory anemia syndrome (5q-RA) and acute nonlymphocytic leukemia (ANLL). We have characterized this region in a 5q- patient with therapy-related ANLL (t-ANLL) by pulsed-field gel electrophoresis and Southern blotting analysis utilizing DNA probes for PDGFR, c-fms, and FGFA. A single 300 kbp M1uI restriction fragment was detected in the patient using a PDGFR probe as compared to a 200 kbp fragment in normal controls. BssHII digestions also showed restriction fragment length difference. Similar data for both M1uI and BssHII digestions were also obtained when c-fms was used as a probe. Southern blotting analysis of EcoRI-digested DNA showed that each of the PDGFR, c-fms, and FGFA alleles were deleted. These results suggested that one chromosome 5 has a large deletion involving PDGFR, c-fms and FGFA, which is consistent with the cytogenetic analysis of the patient. In contrast, the other chromosome 5, which appeared normal cytogenetically, may have a smaller deletion (or alteration) in proximity to but not involving any of these 3 genes.

Adult↗
PubMed1991

Gene organization of the human high affinity receptor for IgG, Fc gamma RI (CD64). Characterization and evidence for a second gene.

We have isolated, characterized, and sequenced the gene coding for the 72-kDa human high affinity IgG FcR, hFc gamma RI. It consists of six exons and spans 9.4 kilobase pairs. The leader sequence is encoded by two exons, the second of which is 21 base pairs long and contains the predicted site of peptidase cleavage. The third, fourth, and fifth exons each encode homologous Ig-like extracellular domains. The hydrophobic transmembrane region and a highly charged cytoplasmic tail are encoded by a single final exon. The sequence of the 5'-flanking region was determined. Two major transcription initiation sites were identified by RNase protection. The first, more downstream site was confirmed by primer extension studies; canonical CAAT and TATA boxes are located in appropriate positions upstream from this site. The second transcription initiation site was utilized only in RNA from cells incubated with gamma-interferon. This site initiates transcription upstream from the first major site. These data are consistent with the finding of two species of mRNA for hFc gamma RI in myeloid cells that are upregulated when cultured with gamma-interferon. Southern analysis of genomic DNA confirms the restriction map generated from the cloned DNA. One additional HindIII fragment was observed in genomic DNA from 13 randomly selected individuals that was not present in the phage clone used to characterize the gene. This observation suggests the existence of a second hFc gamma RI gene which lacks one of the two internal HindIII sites rather than a restriction fragment length polymorphism.

Amino Acid Sequence↗
PubMed1991

Transformed phenotype conferred to NIH/3T3 cells by ectopic expression of heparin-binding growth factor 1/acidic fibroblast growth factor.

Heparin-binding growth factor 1 (HBGF-1), also known as acidic fibroblast growth factor, is a potent mitogen and angiogenic factor found in tissues such as brain, kidney and heart. The genomic and cDNA sequences indicate that HBGF-1 does not have a typical signal peptide sequence. HBGF-1 was shown to be localized to the extracellular matrix of cardiac myocytes, but the mechanism of secretion is not presently known. We have cloned the HBGF-1 cDNA which allowed us to directly test the biological activity, mechanism of secretion and transforming potential of the recombinant protein. A previous report showed that the truncated HBGF-1 confers partial transformed phenotype to the recipient fibroblasts. However, expression of full-length HBGF-1 has not been reported. The HBGF-1 coding sequence was cloned into the retroviral expression vector, SVX, and transfected into NIH/3T3 cells. Transfectants expressing full-length HBGF-1 protein at high levels form foci and grow to a higher cell density than the parental NIH/3T3 cells. Western blotting analysis showed that the recombinant HBGF-1 is a unique band of approximately 20 kDa and can be detected in the cell homogenate but not in the conditioned medium. NIH/3T3 cells were conferred anchorage independence when HBGF-1 was provided exogenously. We showed the transformed cells are capable of growing on soft agar even in the absence of exogenously-provided HBGF-1. Transfected cells expressing HBGF-1 also induced tumor formation when injected into nude mice. Thus NIH/3T3 cells acquired a full spectrum of transformed phenotype when full length HBGF-1 was expressed at high levels.

Animals↗
PubMed1991

Characterization of a newt tenascin cDNA and localization of tenascin mRNA during newt limb regeneration by in situ hybridization.

We previously showed that tenascin, a large, extracellular matrix glycoprotein, exhibits a temporally and spatially restricted distribution during urodele limb regeneration. To further investigate the role of tenascin in regeneration, we cloned a newt tenascin cDNA, NvTN.1, that has 70% homology to the chicken tenascin sequence. A deduced amino acid sequence of NvTN.1 showed a modular structure unique to tenascin characterized by epidermal growth factor-like and fibronectin type III repeats. To determine the cellular origin of tenascin protein during limb regeneration, we localized tenascin transcripts by in situ hybridization using a riboprobe synthesized from NvTN.1. Transcripts could not be detected in normal limb tissues but first became detectable in the wound epithelium at 2 days and in the distal mesoderm at 5 days after amputation. These wound epithelial cells are probably the source of tenascin protein found within and immediately underneath the wound epithelium. At preblastema stages, hybridization was seen in cells associated with most of the distal mesodermal tissues but not in dermis. At blastema stages, essentially every mesenchymal cell contained tenascin transcripts. Thus, regardless of origin, blastemal mesenchymal cells may share a common regulatory mechanism that results in tenascin gene transcription. Finally, during redifferentiation stages of regeneration, tenascin gene transcription was associated with both differentiation and growth. The results show that initiation of tenascin gene expression is an early event in regeneration and continued tenascin gene transcription is associated with some of the important processes of regeneration, namely wound epithelial-mesenchymal interactions, dedifferentiation, initiation of cell cycling, blastema outgrowth, and cellular differentiation.

Amino Acid Sequence↗
PubMed1991

Single primer-mediated polymerase chain reaction: application in cloning of two different 5'-untranslated sequences of acidic fibroblast growth factor mRNA.

Polymerase chain reactions (PCR) are used to generate specific DNA sequences from minute amounts of DNA templates using a pair of oligonucleotide primers. To amplify regions of unknown sequence, methods such as inverted PCR, Alu PCR, and rapid amplification of cDNA ends (RACE) have been developed. These methods require several enzymatic manipulations of DNA which are either tedious or only suitable for certain special conditions. We have explored the possibility of PCR using a single primer. This method takes advantage of the fact that partial complementarity provides sufficient affinity for the oligonucleotide primer to anneal to a secondary, imperfect binding site. Thus, no modification of DNA template was required for the single primer-mediated PCR. We have used this method to generate two different aFGF cDNA clones containing different 5'-untranslated sequences.

Base Sequence↗
PubMed1991

Cloning and sequence analysis of the human acidic fibroblast growth factor gene and its preservation in leukemia patients.

Acidic fibroblast growth factor (aFGF), also known as heparin-binding growth factor 1, is a mitogen for a variety of mesoderm- and neuroectoderm-derived cells. Several different aFGF mRNA species resulting from alternative splicing have been reported. These results suggest that the gene structure and regulatory mechanism for gene expression of aFGF are complex. As a first step toward understanding aFGF gene structure, we have isolated nine overlapping genomic DNA clones spanning 54 kbp and determined the complete DNA sequences of all three coding exons. Comparison of the nucleotide sequences between the human and bovine DNA showed that the sequence similarity extended 2400 bp downstream from the coding region. Cloning of the aFGF gene allowed us to characterize this locus in acute nonlymphocytic leukemia (ANLL) patients. A fraction of ANLL patients (10-20%) have a deletion in the long arm of chromosome 5, whose distal breakpoint overlaps the aFGF locus. Therefore, a prospective cohort of eight ANLL patients was screened using three different repetitive sequence-free probes derived from the aFGF locus. Using beta-globin gene as a normalization probe for hybridizing band intensities, we conclude that there is no allelic loss or gross rearrangement within the 40 kbp stretch of the aFGF gene locus in ANLL patients with or without 5q- deletion. Consistent with this observation, the aFGF mRNA was not detected in the mononuclear cells derived from either an ANLL patient or a normal individual as judged by the reverse transcription and polymerase chain reaction. We also identified a DNA fragment, 10.7 kbp upstream from the first coding exon of human aFGF, whose sequence is conserved in both the primate and rodent genomes. Further characterization of this fragment is likely to provide insight into the significance of this high degree of conservation.

Amino Acid Sequence↗
PubMed1990

Direct cloning of cDNA inserts from lambda gt11 phage DNA into a plasmid vector by a novel and simple method.

Bacteriophage lambda gt11 has been used quite extensively for producing cDNA libraries. The cDNA inserts are usually subcloned into a plasmid vector for large scale production and analysis. However, isolating the recombinant DNA of interest from the phage clones can be a tedious task. Since the E. coli strain Y1088 used for lambda gt11 phage infection carries a pBR322-derived plasmid endogenously, we reasoned that this endogenous plasmid could be used directly for cloning the cDNA phage insert. In this report, we describe a method in which cDNA inserts from lambda gt11 phage were cloned directly into the pBR322 plasmid vector, bypassing the time-consuming procedures of preparing plasmid DNA as a subcloning vector. This method is likely to be extended to the cloning of DNA inserts derived from other phage lambda vectors when bacteria containing endogenous pBR322 are used as host cells.

Bacteriophage lambda↗
PubMed1990

Alternative splicing generates two forms of mRNA coding for human heparin-binding growth factor 1.

Human class 1 heparin-binding growth factor (HBGF-1), also known as acidic fibroblast growth factor, is a mitogen for a variety of mesoderm- and neutroectoderm-derived cells in vitro as well as an angiogenic factor in vivo. Several oncogenes and growth factors have been shown to be homologous to HBGF-1. Four cDNA clones coding for HBGF-1 have been isolated from a human brain stem cDNA library. Nucleotide sequence analysis revealed that alternative splicing generated at least two different forms of HBGF-1 mRNA. Because the difference occurs in the 5'-untranslated regions, these transcripts may result from the usage of alternative promoters. One of the cDNA clones contains the polyadenylation signal, AATAAA, and a poly(A) tail, representing the 3'-end of an HBGF-1 mRNA. RNAase protection assays suggested this cDNA clone corresponds to a minor transcript, and the majority of the HBGF-1 mRNA terminates at 3.1 kbp downstream from the translation termination codon. The biological significance of this unusually long 3'-untranslated sequence is not known. To study the HBGF-1 gene structure, we have isolated 50 kbp of contiguous genomic DNA coding for the HBGF-1 protein. Both restriction enzyme mapping and nucleotide sequencing established that the distance between the first and second protein-coding exons is 13.6 kbp while that between the second and third is 5.3 kbp. By using the HBGF-1 cDNA as a probe, we showed that human fetal heart expresses high levels of HBGF-1 mRNA. Thus, HBGF-1 may be involved in mediating processes such as embryonic development and vascular growth in the heart.

Amino Acid Sequence↗