Biomedical subjects

M C Hung

Publications and source records attributed to M C Hung.

170 records · Page 10Linked to original sources

PubMed1981

The sequence of the Drosophila melanogaster gene for yolk protein 1.

We have determined the complete nucleotide sequence of the hormonally regulated yolk protein 1 (YP1) gene of Drosophila melanogaster. We have also determined the sequence location of the 5' and 3' ends of both the mature mRNA and the gene's only intron. The YP1 gene contains sequences similar to those found in many other eukaryotic genes. Among these sequences are the Hogness-Goldberg box, the capping site, the ribosome binding site and the polyadenylation signal sequence, all perhaps involved in transcriptional or translational control. Also among these sequences are the consensus splice sequences. They occur at each end of the 76 nucleotide intron. One distinctive secondary structure likely to occur in either the DNA or RNA and which might be involved in the regulation of transcription or translation was also found in the YP1 gene sequence. We show the protein sequence predicted by the DNA sequence and the RNA mapping results.

Animals↗

PubMed1978

The status of tyrosyl residues in a Formosan cobra cardiotoxin.

Spectrophotometric titration of Formosan cobra cardiotoxin showed that two of the three tyrosyl residues were titrated freely with a normal apparent pKa of 9.6 whereas the remaining one ionized at pH above 11.0. Nitration of cardiotoxin in Tris . HCl buffer with tetranitromethane resulted in the selective nitration of tyrosine 11 and tyrosine 22. It also revealed that tyrosine 51 was the abnormal one in the spectrophotometric titration. Complete nitration occurred in the presence of 6.0 M guanidine hydrochloride. Compared with the conformation of native cardiotoxin, the peptide conformation of the partially nitrated cardiotoxin did not change significantly but the conformation of the completely nitrated cardiotoxin changed remarkably. The biological activity of cardiotoxin was indeed affected by nitration, but the immunological activity was nearly intact even when all the tyrosine residues were nitrated.

Amino Acids↗

PubMed1978

Renaturation of a reduced Taiwan cobra cardiotoxin.

Refolding of a denatured protein obtained by reducing cardiotoxin from the Taiwan cobra with mercaptoethanol has been carried out in aqueous and non-aqueous solutions. Oxidation of the reduced protein in 0.05 M phosphate buffer (pH 7.2) resulted in isolating an active protein which showed, as compared to native cardiotoxin, identical conformation and biological activities such as lethality, antigenicity and muscle contracture inducing activity. On the other hand, the reduced protein was undergoing incorrect SS-pairing and several inactive products were formed in a mixture of 1,2-ethanediol and 1-propanol (1 : 1; v/v).

Animals↗

PubMed1977

Conformational stability of a snake cardiotoxin.

A snake cardiotoxin from the venom of the Formosan cobra, Naja naja atra, is a basic polypeptide. The protein can be denatured in 6.0 M guanidine hydrochloride or at elevated temperatures. Its conformation remains virtually the same in solvents of lower polarity than water such as 1, 2-ethanediol or 1-propanol and 1, 2-ethanediol (1:1 v/v). The circular dichroism spectrum is atypical in water in that the peptide chromophores show a small negative CD band at 214 nm and a large positive one at 195 nm. To some extent the CD pattern resembles that of the beta-form but differs in specific positions and magnitudes. Considering that the theoretical CD of the reverse beta-bend and the characteristics of model polypeptides in beta-form manifest a similar pattern, we suggest that cobra cardiotoxin is rich in beta structure including beta pleated-sheets and beta reverse-turns.

Animals↗

PubMedDate not supplied

The neu oncogene encodes an epidermal growth factor receptor-related protein.

The neu oncogene is repeatedly activated in neuro- and glioblastomas derived by transplacental mutagenesis of the BDIX strain of rat with ethylnitrosourea. Foci induced by the DNAs from such tumours on NIH 3T3 cells contain the neu oncogene and an associated phosphoprotein of relative molecular mass 185,000 (p185). Previous work has shown that the neu gene is related to, but distinct from, the gene encoding the EGF receptor (c-erb-B). Here we describe a neu complementary DNA clone isolated from a cell line transformed by this oncogene; the clone has biological activity in a focus-forming assay. The nucleotide sequence of this clone predicts a 1,260-amino-acid transmembrane protein product similar in overall structure to the EGF receptor. We found that 50% of the predicted amino acids of neu and the EGF receptor are identical; greater than 80% of the amino acids in the tyrosine kinase domain are identical. Our results suggest strongly that the neu gene encodes the receptor for an as yet unidentified growth factor.

Amino Acid Sequence↗

PubMedDate not supplied

Issues in the development of gene therapy: preclinical experiments in E1A gene delivery.

We recently completed a phase I trial of E1A gene therapy for patients with advanced breast or ovarian cancers. The trial's rationale was that E1A gene would downregulate HER-2/neu expression by repressing the gene's transcription, thus reversing the malignant phenotype. Our preclinical studies showed that i) transfection capabilities were not reduced in preparing E1A/cationic liposome complexes, ii) samples after ex vivo transfection, and iii) HER-2/neu gene expression could be quantified by quantitative imaging analysis. These results facilitated the translation of our basic research findings into a clinical trial and to obtain final approval from the National Institutes of Health Recombinant DNA Advisory Committee.

Adenovirus E1A Proteins↗

PubMedDate not supplied

Up-regulation of urokinase-type plasminogen activator expression by the HER2/neu proto-oncogene.

The HER2/neu (c-erbB2) protooncogene, which encodes a transmembrane receptor (p185neu), contributes to tumor cell invasion/metastasis through mechanism(s) which are, at present, poorly defined. Since basement membrane degradation is a prerequisite for tumor progression, we undertook a study to determine if the expression of urokinase, a key protease implicated in extracellular matrix proteolysis, was regulated by this oncogene. Stable overexpression of a cDNA encoding HER2/neu in H460 lung cancer cells led to elevated secretion of urokinase which was a consequence of a higher level of protease mRNA. Transfection of the HER2/neu-overexpressing B 104-1 cells with a CAT reporter construct driven by the urokinase promoter, gave rise to increased CAT activity when compared with parental NIH3T3 cells, which have low levels of HER2/neu, suggesting that the protooncogene can enhance urokinase promoter activity. Since the enhanced expression of HER2/neu results in increased tumor invasion/metastasis (1), these data suggest that, at least in vitro, HER2/neu-induced expression of urokinase may contribute to tumor progression in p185neu-positive cancers.

3T3 Cells↗

PubMedDate not supplied

Mutant SV40 large T antigen as a therapeutic agent for HER-2/neu-overexpressing ovarian cancer.

The HER-2/neu gene is frequently amplified and/or its protein product, p185, is overexpressed in a number of human cancers. Overexpression of p185 correlates with poor prognosis and low survival rates in ovarian cancer patients. We previously found that the K1 mutant of SV40 large T antigen inhibits rat neu promoter and suppresses mutation-activated rat neu transformation in mouse fibroblasts. We show here that K1 also inhibits human HER-2/neu promoter in human ovarian cancer cells. To investigate whether K1 can suppress HER-2/neu transformation and thus is a potential therapeutic agent, we used an orthotopic ovarian cancer model in which mice were injected intraperitoneally with HER-2/neu-overexpressing human ovarian cancer cells to induce tumor development. The tumor-bearing mice were then treated with K1-liposome complex weekly. We found that liposome-mediated K1 gene transfer decreased the p185 protein level by K1 expression in these cancer cells and significantly prolonged mice survival; about 40% of these treated mice were alive for more than 1 year without any tumor development. On the other hand, the animals from control groups that did not receive this gene therapy all developed tumors and died within 7 months. The results indicate that liposome-mediated K1 gene transfer is able to suppress tumor development from HER-2/neu-overexpressing ovarian cancer cells in mice.

Animals↗