Biomedical subjects

R N Wong

Publications and source records attributed to R N Wong.

31 records · Page 2Linked to original sources

PubMed1995

Induction of metallothionein in the Reuber H-35 rat hepatoma cell.

The feasibility of using the Reuber H-35 rat hepatoma cell (RH-35 cells) as model for studying metallothionein induction was examined. The RH-35 cells were treated with Cd, a toxic metal which is known to induce metallothionein. The LC50 after a 3-h treatment was 70 microM. The value was significantly higher (P < 0.05) if the cells were pre-treated with a sublethal dose of CdCl2 (5 microM) for 2 days, indicating that pre-treatment with a low dose of Cd can protect against a subsequent higher dose of the same metal. Both the mRNA and the gene product metallothionein can be identified in the cells 2 days after treatment with 5 microM Cd. In addition to Cd, Zn and Cu were also able to induce the expression of metallothionein to various degrees. The results indicate that the MT gene is present in RH-35 cells and is responsive to treatment with various metals. Thus, this cell line can be used as a model to study metallothionein induction.

Animals↗

PubMed1995

Cellular origin, complementary deoxyribonucleic acid and N-terminal amino acid sequences of human seminal progastricsin.

The aspartic protease progastricsin (EC 3.4.23.3) is found in all parts of the mammalian stomach and has also been found extragastrically. In humans and monkeys, seminal fluid usually contains high concentrations of progastricsin. Using immunohistochemistry and in situ hybridization, we determined in this investigation the origin of seminal progastricsin to be the epithelia of both the prostatic gland and the seminal vesicles. In addition, Northern (RNA) blotting showed the presence of a 1.8-kb transcript in both tissues. Seminal progastricsin clones from two human prostatic gland cDNA libraries were isolated and sequenced. The combined sequence manifested only six nucleotide differences from the published genomic and gastric cDNA sequence. One conservative base substitution was present in both libraries. N-Terminal amino acid sequencing of all 43 residues of the seminal proenzyme and the first 34 residues of the mature enzyme yielded sequences identical to those deduced from cDNAs derived from both gastric and prostatic origin. The results obtained indicate that gastric and seminal progastricsin are products of the same gene and that the observed molecular differences between the zymogen from the two sources are probably due to posttranslational modifications.

Blotting, Northern↗

PubMed1994

Isolation and characterization of a novel ribosome-inactivating protein, beta-kirilowin, from the seeds of Trichosanthes kirilowii.

A novel ribosome-inactivating protein designated beta-kirilowin was isolated from the seeds of Trichosanthes kirilowii. The proteins exhibited strong abortifacient activity in pregnant mice and produced a single band after SDS-polyacrylamide gel electrophoresis with an apparent mol. wt. of 27,500 daltons. It was active in inhibiting the cell-free translation system with an ID50 of about 1.8 ng/ml. No cross-reactivity with trichosanthin could be detected by immunodiffusion. Sequence comparison of the first 10 residues of beta-kirilowin with ribosome-inactivating proteins isolated from T. kirilowii such as trichosanthin, trichokirin and karasurin indicated 70%, 60% and 70% identity, respectively.

Abortifacient Agents↗

PubMed1992

Characterization of Mirabilis antiviral protein--a ribosome inactivating protein from Mirabilis jalapa L.

A protein was purified from root tubers of Mirabilis jalapa to homogeneity by ion-exchange chromatography on CM-Sepharose CL-6B and FPLC on Mono-S column. The purified protein was confirmed to be Mirabilis antiviral protein (MAP). However, in addition to its antiviral property, the MAP was demonstrated to possess abortifacient activity in pregnant mice, inhibitory effect on cell-free protein synthesis and antiproliferative effect on tumor cells. As judged from its biological and physiochemical properties, MAP is a type I ribosome-inactivating protein.

Abortifacient Agents↗

PubMed1992

Two proteins with ribosome-inactivating, cytotoxic and abortifacient activities from seeds of Luffa cylindrica roem (Cucurbitaceae).

Two immunologically distinct glycoproteins, with a molecular weight of 28,000 and 28,500 respectively, were isolated from seeds of Luffa cylindrica using a procedure that involved acetone precipitation, gel filtration on Sephadex G-75 and ion exchange chromatography on CM-Sepharose CL-6B. The proteins differed in the content of aspartic acid, threonine, proline and alanine but were otherwise similar in amino acid composition. The proteins were capable of inducing mid-term abortion in mice, inhibiting protein synthesis in a cell-free system and suppressing thymidine uptake by human choriocarcinoma cells.

Abortifacient Agents, Nonsteroidal↗

PubMed1991

Minireview: enzymatic properties of ribosome-inactivating proteins (RIPs) and related toxins.

Ribosome-inactivating proteins (RIPs) are a group of proteins that inhibit protein synthesis in eucaryotic cells. While the biological effects have been well characterized, the underlying enzymatic mechanisms have not been elucidated until recently. Two different mechanisms have been identified. Plant and bacterial RIPs act as N-glycosidases. They cleave a single N-glycosidic bond between adenine and ribose at a specific nucleotide A-4324 of the 28S rRNA of the 60S ribosomal subunit. On the other hand, the fungal RIPs act as ribonucleases and cleave a single phosphodiester bond between G-4325 and A-4326 of the same rRNA, just one nucleotide away from the site of action of plant/bacterial RIPs. Other protein synthesis inhibitory proteins act by their ADP-ribosyltransferase activity which modify and thus inactivate elongation factor-2. Recently, some toxins have been shown to possess deoxyribonuclease activity which may also account for their toxicity.

Amino Acid Sequence↗

PubMed1991

Methylation and expression of human pepsinogen genes in normal tissues and their alteration in stomach cancer.

In normal human tissues, pepsinogen A mRNA was expressed only in the fundic mucosa of the stomach, whereas pepsinogen C mRNA was expressed in all regions of the stomach mucosa and also in the proximal duodenal mucosa. The distributions of these mRNAs were consistent with those of pepsinogens A and C in the gastroduodenal mucosa. Methylation analysis of DNAs from normal tissues with methylation-sensitive restriction enzymes, HpaII and HhaI, revealed that pepsinogen A and C genes are hypomethylated in tissues producing pepsinogens A and C, suggesting a role of DNA methylation in the regulation of the differential expression of the genes for the two human pepsinogens during normal differentiation. In stomach cancer tissues and cancer cell lines, the expressions of the pepsinogen genes were decreased or lost, in good accordance with their pepsinogen productions. No gross structural changes of the pepsinogen genes were observed in these cancers, but the methylation patterns of the pepsinogen genes were found to be altered in different ways in different cancers. The functional significance of the altered methylation is unknown; however, these results suggest that considerable heterogeneity of the methylation patterns occurs in human stomach cancers.

Blotting, Northern↗

PubMed1989

Synthesis, purification, and active site mutagenesis of recombinant porcine pepsinogen.

In order to carry out studies on structure and function relationships of porcine pepsinogen using site-directed mutagenesis approaches, the cDNA of this zymogen was cloned, sequenced, expressed in Escherichia coli, and the protein refolded, and purified to homogeneity. Porcine pepsinogen cDNA, obtained from a lambda gt10 cDNA library of porcine stomach contains 1364 base pairs. It contains leader, pro, and pepsin regions of 14, 44, and 326 residues, respectively. In addition, it also contains 5'- and 3'-untranslated regions. Four differences are present between the sequence deduced from the cDNA and the pepsinogen sequence determined previously by protein chemistry methods. Residues P19 (in the pro region) and 263 are asparagines in the cDNA sequence instead of aspartic acids. Isoleucine 230 is not present in the cDNA sequence and residue 242 is a tyrosine in the cDNA instead of an aspartic acid. Porcine pepsinogen cDNA was placed under the control of a tac promoter in a plasmid and expressed in E. coli. The synthesis of pepsinogen was optimized to about 50 mg/liter of culture. The recombinant (r-) pepsinogen, which was insoluble, was recovered by centrifugation, washed, dissolved in 6 M urea in Tris-HCl, pH 8, and refolded by rapid dilution. r-pepsinogen was purified to homogeneity after chromatography on Sephacryl S-300 and fast protein liquid chromatography on a monoQ column. r-pepsinogen contains an additional methionine residue at the NH2 terminus as compared to native (n-) pepsinogen. However, r- and n-pepsinogens are indistinguishable in their intramolecular activation constants. After activation, r- and n-pepsins have the same NH2-terminal sequences as well as Km values. Based on these data, r-pepsinogen was judged suitable for mutagenesis studies. A mutant pepsinogen (D32A) with the active site aspartic acid changed to an alanine was produced and purified. D32A-pepsinogen did not convert to pepsin in acid solution but it bound to pepstatin with an apparent KD of about 5 x 10(-10) M. D32A-pepsinogen possesses no detectable proteolytic activity. These results indicate that (i) intramolecular pepsinogen activation is accomplished by the pepsin active site, and (ii) unlike subtilisin (Carter, P., and Wells, J. A. (1988) Nature 332, 564-568), the active site mutant of pepsin is not enzymically active.

Amino Acid Sequence↗

PubMed1989

In situ localization of pepsinogens I and II mRNA in human gastric mucosa.

Localization of pepsinogens I and II mRNA in the human gastric mucosa was investigated by an in situ hybridization method using digoxigenin-labeled cDNA probes. Gastric fundic mucosa from healthy volunteers, which was stained with digoxigenin-labeled pepsinogens I and II cDNA probes, showed positive staining in the cytoplasm of both chief cells and mucous neck cells. In contrast, gastric antral mucosa stained with the pepsinogen I cDNA probe showed no positive reaction in the surface mucous cells or pyloric glands. On the other hand, the pyloric glands were stained positively with the pepsinogen II cDNA probe and the staining appeared to be identical to that obtained with the antipepsinogens I and II monoclonal antibodies using the avidin-biotin-peroxidase complex technique. These results are consistent with those of previous studies that have employed immunochemical and immunohistochemical techniques.

DNA↗

PubMed1988

Structures at the proteolytic processing region of cathepsin D.

The amino acid sequences at the "proteolytic processing regions" of cathepsin Ds have been determined for the enzymes from cows, pigs, and rats in order to deduce the sites of cleavage as well as the function of the proteolytic processing of cathepsin D. For bovine cathepsin D, the "processing region" sequence was determined from a peptide isolated from the single-chain enzyme. The COOH-terminal sequence of the light chain and the NH2-terminal sequence of the heavy chain were also determined. The processing region sequence of porcine cathepsin D was determined from its cDNA structure, and the same structure from rat cathepsin D was determined from the peptide sequence of the single-chain rat enzyme. From sequence homology to other aspartic proteases whose x-ray crystallographic structures are known, such as pepsinogen and penicillopepsin, it is clear that the processing regions are insertions to form an extended beta-hairpin loop between residues 91 and 92 (porcine pepsin numbers). However, the sizes of the processing regions of cathepsin Ds from different species are considerably different. For the enzymes from rats, cows, pigs, and human, the sizes of the processing regions are 6, 9, 9, and 11 amino acid residues, respectively. The amino acid sequences within the processing regions are considerably different. In addition, the proteolytic processing sites were found to be completely different in the bovine and porcine cathepsin Ds. While in the porcine enzyme, an Asn-Ser bond and a Gly-Val bond are cleaved to release 5 residues as a consequence of the processing; in the bovine enzyme, two Ser-Ser bonds are cleaved to release 2 serine residues. These findings would argue that the in vivo proteolytic processing of the cathepsin D single chain is probably not carried out by a specific "processing protease." Model building of the cathepsin D processing region conformation was conducted utilizing the homology between procathepsin D and porcine pepsinogen. The beta-hairpin structure of the processing region was found to (i) interact with the activation peptide of the procathepsin D in a beta-structure and (ii) place the Cys residue in the processing region within disulfide linkage distance to Cys-27 of cathepsin D light chain. These observations support the view that the processing region of cathepsin D may function to stabilize the conformation of procathepsin D and may play a role in its activation.

Amino Acid Sequence↗

PubMed1987

Amino acid sequence of rhizopuspepsin isozyme pI 5.

The complete amino acid sequence of an aspartic protease from Rhizopus chinensis, rhizopuspepsin isozyme pI 5, has been determined. Partial sequences were first obtained from the isolated isozyme by a combination of chemical and proteolytic enzyme cleavages, peptide purifications, and Edman degradations. About one-half of the sequence was revealed by this approach. To complete the amino acid sequence, a cDNA library of R. chinensis in pBR322 was constructed. An oligonucleotide probe was synthesized based on the sequence Trp-Trp-Gly-Ile-Thr, and about 40 positive clones were identified by colony hybridization. A clone, 33E2, which had an insert size of about 1.1 kilobase pairs, was found to contain the entire coding region of rhizopuspepsin isozyme pI 5. The sequence of rhizopuspepsin contains 325 amino acid residues. The alignment of the rhizopuspepsin sequence against other aspartic proteases revealed expected homology, with the closest similarity to penicillopepsin which shares 39% identical residues. Porcine pepsin shares about 36% identical residues with rhizopuspepsin.

Amino Acid Sequence↗

PubMed1987

Evolution in the structure and function of aspartic proteases.

Aspartic proteases (EC3.4.23) are a group of proteolytic enzymes of the pepsin family that share the same catalytic apparatus and usually function in acid solutions. This latter aspect limits the function of aspartic proteases to some specific locations in different organisms; thus the occurrence of aspartic proteases is less abundant than other groups of proteases, such as serine proteases. The best known sources of aspartic proteases are stomach (for pepsin, gastricsin, and chymosin), lysosomes (for cathepsins D and E), kidney (for renin), yeast granules, and fungi (for secreted proteases such as rhizopuspepsin, penicillopepsin, and endothiapepsin). These aspartic proteases have been extensively studied for their structure and function relationships and have been the topics of several reviews or monographs (Tang: Acid Proteases, Structure, Function and Biology. New York: Plenum Press, 1977; Tang: J Mol Cell Biochem 26:93-109, 1979; Kostka: Aspartic Proteinases and Their Inhibitors. Berlin: Walter de Gruyter, 1985). All mammalian aspartic proteases are synthesized as zymogens and are subsequently activated to active proteases. Although a zymogen for a fungal aspartic protease has not been found, the cDNA structure of rhizopuspepsin suggests the presence of a "pro" enzyme (Wong et al: Fed Proc 44:2725, 1985). It is probable that other fungal aspartic proteases are also synthesized as zymogens. It is the aim of this article to summarize the major models of structure-function relationships of aspartic proteases and their zymogens with emphasis on more recent findings. Attempts will also be made to relate these models to other aspartic proteases.

Amino Acid Sequence↗

PubMedDate not supplied

alpha-Kirilowin, a novel ribosome-inactivating protein from seeds of Trichosanthes kirilowii (family Cucurbitaceae): a comparison with beta-kirilowin and other related proteins.

A novel ribosome-inactivating protein (RIP) designated alpha-kirilowin was isolated from the seeds of Trichosanthes kirilowii. The molecular weight of alpha-kirilowin was estimated by SDS-polyacrylamide gel electrophoresis to be 28 800 Da, which is slightly larger than another previously characterized ribosome-inactivating protein, beta-kirilowin. The amino-acid composition of alpha-kirilowin grossly resembled beta-kirilowin and other ribosome-inactivating proteins isolated from T. kirilowii tissues, including trichokirin, trichosanthin and karasurin. Intense immunological cross-reactivity between the two kirilowins was detected by immunodiffusion. The N-terminal sequence of alpha-kirilowin was identical to that of beta-kirilowin, at least in the first ten residues. Peptide fingerprinting indicated both kirilowins were closely related. Biological activities as determined by inhibition of protein synthesis in a cell-free system, suppression of [3H]-thymidine incorporation into mouse melanoma cells and induction of abortion in mice were very similar for both kirilowins. We propose that the size difference between alpha- and beta-kirilowin is either due to a C-terminal extension in alpha-kirilowin or differences in glycosylation, or a combination of both.

Abortifacient Agents↗