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Biomedical subjects

I M Chiu

Publications and source records attributed to I M Chiu.

At least 73 records · Page 4Linked to original sources
PubMed1989

Growth factor genes as oncogenes.

The oncogenic retroviruses can be divided into two main categories: those that induce neoplasia after a long latent period (chronic leukemia viruses) and those that induce neoplasia relatively rapidly (acute transforming viruses). Chronic leukemia viruses do not transform cells in tissue culture and contain only the virally encoded genes. By nucleotide sequence comparison, it was possible to show that all retroviruses have a common evolutionary origin. In contrast, acute transforming viruses have substituted viral genes with genetic information specifically implicated in the oncogenic process. These genetic elements (oncogenes) were derived from uninfected host genomes. It was shown that one of the oncogenes, c-sis proto-oncogene, is the structural gene for the B-chain polypeptide of platelet-derived growth factor (PDGF). Furthermore, high level expression of human c-sis resulted in transformation of recipient cells. Similar results have been subsequently obtained for other growth factors, including granulocyte-macrophage colony stimulating factor, transforming growth factor alpha, epidermal growth factor, and basic fibroblast growth factor. It is possible that growth factor gene activation represents one of the steps leading toward malignancy in vivo.

Cell Transformation, Neoplastic↗
PubMed1989

Cloning of the gene coding for human class 1 heparin-binding growth factor and its expression in fetal tissues.

We have identified four overlapping genomic DNA clones coding for human class 1 heparin-binding growth factor (HBGF-1), also known as acidic fibroblast growth factor, by screening genomic DNA libraries with an HBGF-1 cDNA probe. The exon-intron structure of the HBGF-1 gene was determined by Southern hybridization and nucleotide sequence analysis. The complete amino acid sequence of human HBGF-1 was deduced from the nucleotide sequence of these genomic DNA clones. The predicted amino acid sequence is identical to the published amino acid sequence determined by protein sequencing. Southern blot analysis of human DNA suggested that there is a single-copy gene coding for HBGF-1. A 4.5-kilobase mRNA and two minor species (3.4 and 2.0 kilobases) homologous to the HBGF-1 gene were detected in cellular RNA isolated from human adult brain and kidney. The HBGF-1 mRNAs from brain and kidney had slightly different sizes. The mechanism for the synthesis of different sizes of mRNA was not determined. We also detected HBGF-1 transcript from glioblastoma cells, fetal brain, and kidney but not from placenta or fetal liver. Since HBGF-1 is an angiogenic factor, these data suggest that it may play a role in embryonic angiogenesis during fetal development.

Amino Acid Sequence↗
PubMed1986

Characterization of rodent epidermal growth factor receptor transcripts using a mouse genomic probe.

Two genomic DNA clones encoding part of the mouse epidermal growth factor (EGF) receptor were isolated: an 8.0 kb insert that hybridized with the human EGF receptor kinase domain; and a 2.4 kb insert that mapped between the kinase and 3' autophosphorylation domains of the human EGF receptor gene. The 2.4 kb insert was further digested to a 2.0 kb fragment and a 0.4 kb fragment containing 49 residues that were almost identical to the corresponding human EGF receptor sequence. Ribonuclease protection studies with mouse RNA identified three exons of 170 kb, 105 kb, and 50 kb in the 2.0 kb probe that were less homologous to the corresponding human or rat mRNAs. Northern blot hybridizations identified two EGF receptor transcripts of 10 kb and 6 kb in normal, but not EGF-nonresponsive, mouse cell lines, and a single 9.5 kb transcript in rat cells. An additional 6.5 kb transcript from rat NRK cells was identified that is related to but not transcribed from the EGF receptor gene.

Animals↗
PubMed1986

Molecular cloning and physical characterization of integrated equine infectious anemia virus: molecular and immunologic evidence of its close relationship to ovine and caprine lentiviruses.

Molecular clones of the integrated form of the genome of equine infectious anemia virus (EIAV), the etiologic agent of a naturally occurring, worldwide disease of horses, were obtained. The restriction map of a full-length genome was determined. Additional evidence for the close evolutionary relationship between EIAV and a prototype lentivirus (caprine arthritis encephalitis virus) was acquired by Southern blotting and immunological analyses. An interspecies radioimmunoassay was developed in which EIAV and ovine and caprine lentiviruses could be detected equally well. These studies make available precisely defined reagents to pursue the study of the mechanisms of pathogenesis of lentiviral induced diseases.

Animals↗
PubMed1986

Human endothelial cell growth factor: cloning, nucleotide sequence, and chromosome localization.

Several of the endothelial cell polypeptide mitogens that have been described probably play a role in blood vessel homeostasis. Two overlapping complementary DNA clones encoding human endothelial cell growth factor (ECGF) were isolated from a human brain stem complementary DNA library. Southern blot analysis suggested that there is a single copy of the ECGF gene and that it maps to human chromosome 5 at bands 5q31.3 to 33.2 A 4.8-kilobase messenger RNA was present in human brain stem messenger RNA. The complete amino acid sequence of human ECGF was deduced from the nucleic acid sequence of these clones; it encompasses all the well-characterized acidic endothelial cell polypeptide mitogens described by several laboratories. The ECGF-encoding open reading frame is flanked by translation stop codons and provides no signal peptide or internal hydrophobic domain for the secretion of ECGF. This property is shared by human interleukin-1, which is approximately 30 percent homologous to ECGF.

Base Sequence↗
PubMed1986

Structure and sequence of the human c-sis/platelet-derived growth factor 2 (SIS/PDGF2) transcriptional unit.

The structure of the normal human c-sis/platelet-derived growth factor 2 (SIS/PDGF2) transcript was determined by a combination of cDNA cloning, nuclease S1 mapping, and primer extension. Nucleotide sequence analysis revealed that the 3373-nucleotide SIS/PDGF2 mRNA contained only a 723-base-pair (bp) coding sequence for the PDGF2 precursor polypeptide. The coding sequence was flanked by long 5' (1022 bp) and 3' (1625 bp) untranslated regions. The 5' noncoding region, as well as upstream flanking genomic sequences, contained clusters of specific short repeat sequences. A consensus transcriptional promoter sequence, TATAAA, was identified 24 bp upstream of the mRNA start site and an enhancer-like "TG element" was detected about 180 bp downstream from the site of polyadenylylation. These findings identify putative regulatory elements of the SIS/PDGF2 gene.

Amino Acid Sequence↗
PubMed1986

Nucleotide sequence analysis of squirrel monkey retrovirus reveals a novel primer-binding site for tRNALys1,2.

Nucleotide sequences of a DNA fragment containing the long terminal repeat (LTR) of squirrel monkey retrovirus (SMRV) were determined. Sequence analysis showed that the SMRV LTR is 456 base pairs (bp) long and is bounded by 2-bp inverted repeats. Within the U3 region, there are two 43-bp repeats and two 42-bp repeats which are homologous to each other. These repeats are likely to provide enhancer activities commonly observed in other enhancer sequences. Following the repeats are transcriptional regulatory sequences including a CAT box, a Goldberg-Hogness box, and a polyadenylation signal, all positioned within the U3 region of SMRV LTR. A 22-nucleotide sequence immediately downstream from the LTR was found to be complementary to tRNALys1,2, suggesting that tRNALys1,2 serves as the primer for the reverse transcription of SMRV viral RNA.

Animals↗
PubMed1985

A new class of endogenous human retroviral genomes.

Human DNA contains multiple copies of a novel class of endogenous retroviral genomes. Analysis of a human recombinant DNA clone (HLM-2) containing one such proviral genome revealed that it is a mosaic of retroviral-related sequences with the organization and length of known endogenous retroviral genomes. The HLM-2 long terminal repeat hybridized with the long terminal repeat of the squirrel monkey virus, a type D retrovirus. The HLM-2 gag and pol genes share extensive nucleotide sequence homology with those of the M432 retrovirus (a type A-related retrovirus), mouse mammary tumor virus (a type B retrovirus), and the avian Rous sarcoma virus (a type C retrovirus). Nucleotide sequence analysis revealed regions in the HLM-2 pol gene that were as much as 70 percent identical to the mouse mammary tumor virus pol gene. A portion of the putative HLM-2 env gene hybridized with the corresponding region of the M432 viral genome.

Amino Acid Sequence↗
PubMed1985

Differential expression of two clusters of mouse histone genes.

The mouse histone mRNAs coded for by three different cloned DNA fragments have been characterized. Two of these cloned DNA fragments, MM221 and MM291, located on chromosome 13, code for H3, H2b and H2a histone mRNAs, which are expressed at low levels in cultured mouse cells and fetal mice. The other DNA fragment, MM614, located on chromosome 3, codes for an H3 and an H2a mRNA, which are expressed at high levels in these cells. The mRNAs for each histone protein share common coding region sequences, while the untranslated regions of all the genes have diverged significantly, as judged by S1 nuclease mapping. Amino acid substitutions in some H3, H2a and H2b proteins are detected as internal cleavages in the S1 nuclease maps. All of these genes code for replication variant histone mRNAs, which are regulated in parallel with DNA synthesis.

Amino Acid Sequence↗
PubMed1985

Molecular cloning of integrated caprine arthritis-encephalitis virus.

A full-length DNA clone of the exogenous retrovirus, caprine arthritis-encephalitis virus (CAEV), was isolated from high molecular weight DNA of CAEV-infected Himalayan tahr ovary cells. Although other restriction maps of CAEV have been published, this is the first time that the proviral DNA has been cloned. The restriction enzyme map of the clone was determined and found to be identical to that of unintegrated linear CAEV DNA except for the presence of cellular flanking sequences. These findings establish that lentiviruses are able to integrate within the infected host cellular genome. The cloned CAEV genome was shown to contain terminal repeats of approximately 450 base pairs in length, and its restriction enzyme map was oriented with respect to the direction of viral RNA transcription. When the cloned CAEV DNA was used as a molecular probe, it failed to detect related proviral sequences in the genomes of a variety of vertebrate species, including the goat, sheep, horse, mouse, and man. When CAEV DNA was hybridized under relaxed conditions to a variety of cloned DNAs, representing different oncoviral genera, homology to mouse mammary tumor virus (MMTV) was observed, while no homology to avian type C or mammalian type A, C, and D retroviruses was detected. This homology was localized to a region in MMTV corresponding to the 3' end of the gag gene and the 5' end of the pol gene.

Animals↗
PubMed1985

Genetic relatedness between intracisternal A particles and other major oncovirus genera.

Intracisternal A particles represent a major oncovirus genus. By reciprocal hybridization between molecularly cloned A particles and representatives of other oncovirus genera, we established pol gene homology with type B, type D and avian type C viruses. The most extensive homology was with mammalian type D viruses. The transcriptional orientation of the IAP genome was determined, as well as evidence indicating that its pol gene, which is apparently defective, contains coding regions for both reverse transcriptase and endonuclease proteins.

Base Sequence↗
PubMed1984

Major pol gene progenitors in the evolution of oncoviruses.

The genetic relationships among molecularly cloned prototype viruses representing all of the major oncovirus genera were investigated by molecular hybridization and nucleotide sequence analysis. One of the major progenitors of the pol genes of such viruses gives rise to mammalian type C viruses and another gives rise to type A, B, D, and avian type C oncoviruses. Evidence of unusual patterns of homology among the env genes of mammalian type C and D oncoviruses illustrates that genetic interactions between their progenitors contributed to the evolution of oncoviruses.

Amino Acid Sequence↗
PubMed1984

Expression of the normal human sis/PDGF-2 coding sequence induces cellular transformation.

The human sis proto-oncogene contains the coding sequence for one of two polypeptide chains present in preparations of biologically active human platelet-derived growth factor (PDGF). A human clone, c-sis clone 8, which contains all of the v-sis-related sequences present in human DNA, was transcriptionally inactive when transfected into NIH/3T3 cells. When placed under the control of a retrovirus LTR, the clone was transcribed at levels comparable to that observed in cells transformed by SSV DNA. However, c-sis clone 8 DNA did not express detectable sis/PDGF-2 proteins and lacked biologic activity. A putative upstream exon was identified by its ability to detect the 4.2 kb sis-related transcript in certain human cells. When this sequence was inserted in the proper orientation between the LTR and c-sis clone 8, the chimeric molecule acquired high titered transforming activity, comparable to that of SSV DNA. Transformants containing this construct expressed human sis/PDGF-2 translational products. Thus the normal coding sequence for a human growth factor has transforming activity when expressed in an appropriate assay cell.

Amino Acid Sequence↗
PubMed1984

Nucleotide sequence analysis identifies the human c-sis proto-oncogene as a structural gene for platelet-derived growth factor.

The simian sarcoma virus transforming gene, v-sis, encodes a protein, p28sis , that is closely related to human platelet-derived growth factor (PDGF). The human locus related to v-sis was cloned and shown to contain at least five exons corresponding to the v-sis coding region. Nucleotide sequence analysis of these exons revealed that the predicted amino acid sequence of human c-sis differed by 6% from that of the woolly monkey-derived v-sis. These findings imply that the sis proto-oncogene has been well conserved during primate evolution. By comparison of the known amino acid sequences of PDGF peptides with the predicted human c-sis protein, it was possible to demonstrate that this human proto-oncogene is the structural gene encoding one of the two major polypeptides of this potent mitogen for connective tissue cells.

Base Sequence↗
PubMed1984

Mechanism of activation of an N-ras oncogene of SW-1271 human lung carcinoma cells.

An N-ras-related transforming gene was detected in the human lung carcinoma cell line SW-1271 and molecularly cloned. The lesion responsible for its acquisition of transforming activity was localized to a single nucleotide transition from A to G in codon 61 of the predicted protein. This lesion in the second exon results in the substitution of arginine for glutamine at this position. These findings, together with previous studies, indicate that the activation of ras oncogenes in human tumors is most commonly due to point mutations at one of two major "hot spots" in the ras coding sequence.

Amino Acid Sequence↗
PubMed1983

Molecular cloning of the unintegrated squirrel monkey retrovirus genome: organization and distribution of related sequences in primate DNAs.

The closed circular form of the endogenous squirrel monkey type D retrovirus (SMRV) was molecularly cloned in a bacteriophage vector. The restriction map of the biologically active clone was determined and found to be identical to that of the parental SMRV linear DNA except for the deletion of one long terminal repeat. Restriction enzyme analysis and Southern blotting indicated that the SMRV long terminal repeat was approximately 300 base pairs long. The SMRV restriction map was oriented to the viral RNA by using a gene-specific probe from baboon endogenous virus. Restriction enzyme digests of a variety of vertebrate DNAs were analyzed for DNA sequence homology with SMRV by using the cloned SMRV genome as a probe. Consistent with earlier studies, multiple copies of SMRV were detected in squirrel monkey DNA. Related fragments were also detected in the DNAs from other primate species, including humans.

Animals↗
PubMed1982

Uncoordinate synthesis of histone H1 in cells arrested in the G1 phase.

It has been known for several years that DNA replication and histone synthesis occur concomitantly in cultured mammalian cells. Normally all five classes of histones are synthesized coordinately. However, mouse myeloma cells, synchronized by starvation for isoleucine, synthesize increased amounts of histone H1 relative to the four nucleosomal core histones. This unscheduled synthesis of histone H1 is reduced within 1 h after refeeding isoleucine, and is not a normal component of G1. The synthesis of H1 increases coordinately again with other histones during the S phase. The DNA synthesis inhibitors, cytosine arabinoside and hydroxyurea, block all histone synthesis in S-phase cells. The levels of histone H1 mRNA, relative to the other histone mRNAs, is increased in isoleucine-starved cells and decreases rapidly after refeeding isoleucine. The increased incorporation of histone H1 is at least partially due to the low isoleucine content of histone H1. Starvation of cells for lysine resulted in a decrease in H1 synthesis relative to core histones. Again the ratio was altered on refeeding the amino acid. 3T3 cells starved for serum also incorporated only H1 histones into chromatin. The ratio of different H1 proteins also changed. The synthesis of the H1(0) protein was predominant in G0 cells, and reduced in S-phase cells. These data indicate the metabolism of H1 is independent of the other histones when cell growth is arrested.

Animals↗