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E H Chang

Publications and source records attributed to E H Chang.

At least 55 records · Page 3Linked to original sources
PubMed1989

Modulation of ras expression by anti-sense, nonionic deoxyoligonucleotide analogs.

Anti-ras oligodeoxyribonucleoside methylphosphonates (ONMP's) complementary to the initiation codon region have been synthesized to explore their efficacy and specificity on ras-p21 translation. ONMP (IC-0) precisely complementing the first initial 11 nucleotides of the Balb-ras initiation codon region acts in a dose-dependent manner to inhibit p21 translation by a rabbit reticulocyte lysate. At 100 microM, IC-0 inhibits the cell-free translation of p21 close to completion. The two control oligomers containing one or two nucleotide mismatches were significantly less effective than IC-0 at the equivalent concentration. In living cells, a perfectly matched ONMP directed against the initiation codon region inhibited Ha-ras p21 expression by 90% at a concentration of 50 microM.

Animals↗
PubMed1989

Comparative inhibition of ras p21 protein synthesis with phosphorus-modified antisense oligonucleotides.

A rabbit reticulocyte lysate translation assay was used to quantitatively compare a series of antisense oligodeoxyribonucleotides (11-mers) having different internucleoside linkages and various degrees of complementarity (100-80%) with the start codon and downstream 8 bases of Balb-ras p21 mRNA. The oligomers had either contiguous phosphodiester, or alternating methylphosphonate-phosphodiester, or contiguous methylphosphonate, or contiguous phosphorothioate linkages. Under the conditions used for the assay, all of the test compounds when present in about 10(3)-10(4) excess over mRNA (15 nM mRNA) inhibited protein synthesis to a degree which was dependent on both the concentration and sequence of the oligomer. At low concentrations (12.5-25 microM), the phosphorothioate analogs were the most potent inhibitors of p21 protein synthesis; however, a sequence non-specific effect for these oligomers was dominant at higher concentrations of oligomer (100-200 microM). The methylphosphonate oligomers appeared to be slightly more discriminant. Relative hybridization strengths were assessed by melting (Tm) studies using a DNA oligomer target to mimic the mRNA.

Animals↗
PubMed1987

Oncogenes in radioresistant, noncancerous skin fibroblasts from a cancer-prone family.

Li-Fraumeni syndrome is manifested in a variety of neoplasms that are transmitted in a dominantly inherited pattern. The noncancerous skin fibroblasts of family members exhibit a unique characteristic of being resistant to the killing effect of ionizing radiation. A three- to eightfold elevation in expression of c-myc and an apparent activation of c-raf-1 gene have been observed in these noncancerous skin fibroblasts. These results may provide insight into the heritable defect underlying the familial predisposition to a variety of cancers.

Animals↗
PubMed1987

Interferon-gamma induces altered oncogene expression and terminal differentiation in A431 cells.

In tumor cell lines in which oncogene expression is abnormal, modulation of the expression of the oncogene (myc, src, or ras) by interferons (IFNs) has been observed concurrently with cell growth inhibition or phenotypic reversion. Oncogene expression has also been reported to vary during the differentiation of several neoplastic cell lines. Treatment of monolayer cultures of A431, a human epidermoid carcinoma cell line, with IFN-gamma resulted in rapid morphological alterations and cell death not seen with either IFN-alpha or IFN-beta. These changes were accompanied by elevated expression of mRNA's for p21 (the c-ras gene product) and the epidermal growth factor receptor as well as increases in the biosynthetic rate of their respective proteins. These effects likewise appeared to be specific for IFN-gamma. Growth inhibition by IFN-gamma was also observed when A431 cells were grown in a three dimensional in vitro culture system. Immunohistochemical staining of these "tumoroids" with a differentiation specific, anti-keratin antibody indicated that IFN-gamma enhanced expression of this keratin. This observation suggests that the killing by IFN-gamma of A431 cells may result from an acceleration of terminal differentiation.

Animals↗
PubMed1986

Assignment of RAS proto-oncogenes in Chinese hamsters: implications for mammalian gene linkage conservation and neoplasia.

HRAS and KRAS are the cellular homologs of the oncogenic transforming genes found in the Harvey strain of murine sarcoma virus and the Kirsten murine sarcoma virus, respectively. Phyla as diverse as insects, birds, and mammals possess distinct HRAS and KRAS sequences, suggesting that these genes are essential to metazoa. In this report, we used a clone panel of Chinese hamster X mouse C11D somatic cell hybrids segregating hamster chromosomes to map those genes. Southern filter hybridization analyses of the hybrids revealed that hamster HRAS and KRAS gene sequences are on chromosomes 3 and 8, respectively. These gene assignments are consistent with the conservation of autosomal gene linkage groups observed among hamsters, humans, and mice and may provide insight into specific chromosomal alterations that have been observed during the spontaneous neoplastic transformation of Chinese hamster fibroblasts in vitro.

Animals↗
PubMed1985

Development of transformed phenotype induced by a human ras oncogene is inhibited by interferon.

Mouse IFN inhibited the development of transformed foci in NIH 3T3 cultures transfected with the viral Ha-MuSV(ras) and Mo-MuSV(mos) oncogenes, or with the human bladder carcinoma ras EJ/T24 DNA. IFN treatment five or seven days after transfection was still effective in inhibiting the oncogenic transformation, but did not inhibit significantly the biochemical transformation induced by pSV2-neo or Ecogpt DNA, so that inhibition of ras-induced transformation was not a result of a general effect on the transfection process. Treatment with IFN did not alter the expression of ras EJ/T24 DNA after the transformed phenotype had been established.

Animals↗
PubMed1985

Interferon-induced modulation of human ras oncogene expression.

Treatment of NIH 3T3 cells with interferon (IFN) after transfection with human bladder carcinoma EJ/T24 c-Ha-ras1 oncogene DNA caused inhibition of ras-induced cell transformation. Furthermore, the effect of IFN on oncogene expression in an established tumor line was studied. A tumor line of NIH 3T3 (RS485) was transformed by human c-Ha-ras1 activated by a viral long terminal repeat. Treatment of the tumor cells with IFN was associated with a progressive appearance of reverted, flat colonies which exhibited a normal phenotype with respect to morphology and growth. The revertants were well spread, contact inhibited cells; they did not grow in soft agar and were not tumorigenic in nude mice. Revertants retained their normal phenotype, although they contained transfecting human c-Ha-ras1 DNA; but, they produced significantly decreased levels of the onc-encoded protein p21 and c-Ha-ras1 mRNA as compared to RS485 cells.

Animals↗
PubMed1985

Biological and morphological characteristics of phenotypic revertants appearing in interferon-treated mouse cells transformed by a human oncogene.

Phenotypic revertants appearing in interferon-treated mouse cells that had been transformed by an activated human c-Ha-ras1 oncogene (cell line RS485) were tested for several biological properties. The cloned revertants regained the growth characteristics of the untransformed parental NIH 3T3 cell line; unlike RS485 cells the revertants failed to form colonies in soft agar or to form rapidly growing tumors in nude mice. Animals inoculated with RS485 cells developed tumors within one week. In contrast, revertant clonal line 4C3 failed to form tumors four months after transplantation. Revertant 4C8 cells were tumorigenic; however, the developing tumors had increased latency, slower growth rate, and remained smaller than tumors of RS485 cells. Histopathological analysis revealed that revertant-associated fibrosarcomas were less anaplastic, less cellular and had relatively infrequent mitotic figures as compared to fibrosarcomas of RS485 cells. The result suggest the IFN-induced revertants exhibit a significantly less malignant phenotype than their parental transformed cells and that the biological differences are maintained after IFN treatment is discontinued.

Animals↗
PubMed1985

Pathogenicity of retroviruses containing either the normal human c-Ha-ras1 gene or its mutated form derived from the bladder carcinoma EJ/T24 cell line.

Cellular ras oncogenes transduced by retroviruses carry mutations in amino acids 12, 59 and 122. Similar mutations have been observed in ras oncogenes activated during induction of neoplasia in both humans and experimental animals. The unmutated normal rat or human c-Ha-ras-1 genes have the ability to transform NIH 3T3 cells in culture when activated by a RNA synthesis promoter. These findings raise the question of whether the mutations are necessary for the ras oncogenes to induce the neoplastic phenotype in vivo. To address this question, we inserted the normal human c-Ha-ras-1 or its mutated counterpart EJ/T24 bladder carcinoma oncogene independently into a retrovirus vector derived from the M1 strain of Moloney murine sarcoma virus (MoMuSV). Both recombinant clones induced foci of transformed cells in an NIH 3T3 cell transfection assay. Infectious virus particles were rescued from cloned transformants carrying a single copy of the integrated provirus using the nonpathogenic amphotrophic wild mouse leukemia virus (WMLV) as helper. The pseudotypes rescued from the EJ/T24-containing transformants had higher titers than the normal c-Ha-ras-1 pseudotypes as determined by a focus assay and gave rise to larger and earlier detected foci upon infection of NIH 3T3 cells. The two pseudotypes were tested for in vivo pathogenicity by inoculation into newborn NFS mice and were compared to the pseudotype WMLV/Harvey murine sarcoma virus (HaMuSV) (positive control) and WMLV (negative control). While the WMLV/EJ/T24 and the WMLV/HaMuSV pseudotypes induced erythroleukemias and sarcomas with a latency period of 6-9 weeks, the WMLV/c-Ha-ras-1 pseudotype induced only mild splenomegaly. As expected the WMLV negative control induced no pathology. Tumor-bearing animals that were not euthanized at 6-9 weeks died within 2-3 months following virus inoculation.

Animals↗
PubMed1984

Biochemical correlates of phenotypic reversion in interferon-treated mouse cells transformed by a human oncogene.

Mouse interferon (IFN) induced a phenotypic reversion in RS 485, a clonal line of NIH 3T3 oncogenically transformed by a human c-Ha-rasl gene activated by Ha-MuSV long terminal repeats (LTRs). Transfected c-Ha-ras DNA, unchanged in quantity and distribution, as compared to the parental RS 485 transformed cells, was still present in these revertants; however, there was a significant reduction in the amount of c-Ha-ras specific mRNA and of c-Ha-ras specified p21 protein.

Animals↗
PubMed1983

Characterization of a human colon/lung carcinoma oncogene.

DNA sequences capable of inducing oncogenic transformation of NIH3T3 mouse cells are found in a number of human tumour cell lines. When DNAs of these cell lines are applied to monolayer cultures of the mouse fibroblasts, foci of transformed cells are observed 2-3 weeks later. DNA from cells of such primary foci can be used in turn to induce foci in a second cycle of gene transfer. The human DNA sequences responsible for transformation have been called oncogenes, the best characterized of which is closely related to the Harvey murine sarcoma virus oncogene. Here we present a characterization of an oncogene which we found originally to be present in DNA of the SW480 colon carcinoma cell line. We indicate its structural outlines and demonstrate, in extension of reported results, its presence in an activated form in the genome of several types of human tumour cell lines as well as in biopsy tissue from an adenocarcinoma of the large bowel. We identify this tumour oncogene with c-Ki-ras2, one of two known members of the Kirsten ras family of human proto-oncogenes, extending a series of recent reports which have demonstrated homologies between human oncogenes and those of Harvey and Kirsten murine sarcoma viruses. The c-Ki-ras2 oncogene of several tumour cell lines is shown to be amplified.

Colonic Neoplasms↗
PubMed1983

Prediction of the three-dimensional structure of the transforming region of the EJ/T24 human bladder oncogene product and its normal cellular homologue.

The three-dimensional structures of the transforming region of the product of the EJ/T24 human bladder oncogene and of the c-Ha ras-1 gene product have been calculated by using conformational energy calculations. These two genes, representing a transforming oncogene and its normal cellular homologue, encode 21,000-dalton peptides that differ by one amino acid at position 12. We therefore examined the energetically allowed conformations of the hydrophobic decapeptide surrounding this substitution site. The calculations show that the most favorable form of the c-Ha ras-1 gene product exists when glycine-12 is in a left-handed bend conformation. No other amino acid can adopt this conformation and thus the bladder oncogene peptide containing valine at position 12 has a markedly different three-dimensional structure. A simple model is proposed to account for the consequences of a position 12 mutation.

Amino Acid Sequence↗
PubMed1982

Mechanism of activation of a human oncogene.

The oncogene of the human EJ bladder carcinoma cell lines arose via alteration of a cellular proto-oncogene. Experiments are presented that localize the genetic lesion that led to activation of the oncogene. The lesion has no affect on levels of expression of the oncogene. Instead, it affects the structure of the oncogene-encoded protein.

Base Sequence↗
PubMed1982

Tumorigenic transformation of mammalian cells induced by a normal human gene homologous to the oncogene of Harvey murine sarcoma virus.

A normal human gene homologous to the p21 ras oncogene of Harvey murine sarcoma virus induced oncogenic transformation and high p21 ras levels in murine fibroblasts when this gene was ligated to a control element (the long terminal repeat) from a murine or feline retrovirus. These results indicate that high levels of a gene product encoded by a normal human oncogene can induce tumorigenic transformation.

Animals↗