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Biomedical subjects

M Suganuma

Publications and source records attributed to M Suganuma.

At least 73 records · Page 4Linked to original sources
PubMed1993

Absence of synergistic effects on tumor promotion in CD-1 mouse skin by simultaneous applications of two different types of tumor promoters, okadaic acid and teleocidin.

Okadaic acid, a specific inhibitor of protein phosphatases 1 and 2A, and teleocidin, an activator of protein kinase C, are both potent tumor promoters on mouse skin. The effects of simultaneous treatment of the two different types of tumor promoters on tumor promotion as well as on their biochemical activities were studied. Three independent experiments with different doses of tumor promoters revealed that simultaneous repeated applications of okadaic acid and teleocidin did not induce any synergistic or additive effects on tumor promotion in mouse skin initiated with 7,12-dimethylbenz(a)anthracene (DMBA). In Experiment 1, the group treated with a single application of DMBA, followed by repeated applications of 1.0 micrograms (1.2 nmol) okadaic acid and 2.5 micrograms (5.7 nmol) teleocidin, resulted in 64.3% tumor-bearing mice at week 20. But the groups treated with DMBA plus okadaic acid or DMBA plus teleocidin gave 73.3% and 71.4%, respectively. The biochemical activities were studied by means of induction of ornithine decarboxylase in mouse skin and protein phosphorylation in the cells. Simultaneous application of okadaic acid at three different doses with teleocidin did not induce ornithine decarboxylase activity synergistically or additively. Phosphorylation of proteins, cytokeratins, or heat shock protein 27 was not synergistically increased in human keratinocytes treated with okadaic acid and teleocidin, although the cotreatment in a cell-free system synergistically increased protein phosphorylation. Thus, the absence of synergistic effects on tumor promotion in mouse skin was also confirmed in two systems, induction of ornithine decarboxylase in mouse skin and protein phosphorylation in human keratinocytes. The effect of cotreatment of okadaic acid and teleocidin is discussed at the molecular level.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1993

Hyperphosphorylation of retinoblastoma protein and p53 by okadaic acid, a tumor promoter.

A potent tumor promoter, okadaic acid, induced hyperphosphorylation of tumor suppressor proteins, retinoblastoma protein and p53, by in vitro incubation with nuclei isolated from rat regenerating liver as well as by incubation with primary human fibroblasts. Most of the retinoblastoma protein migrated to a hyperphosphorylated position in electrophoresis. The phosphorylation of p53 was increased at a rate 8 times that in non-treated primary human fibroblasts. Hyperphosphorylation of tumor suppressor proteins, mediated through inhibition of protein phosphatases 1 and 2A, is involved in tumor promotion by okadaic acid. The significance of hyperphosphorylation of the retinoblastoma protein and p53 is discussed in relation to the regulation of the cell cycle.

Animals↗
PubMed1993

Anticarcinogenic activity of green tea polyphenols.

The main physiologically active polyphenol in green tea extract is (-)-epigallocatechin gallate (EGCG). Green tea extract has an advantage over EGCG as a cancer chemopreventive agent for humans, as is apparent from the Japanese custom of injesting green tea on a daily basis. Green tea extract similarly inhibited protein kinase C activation by teleocidin, a tumor promoter, as did EGCG. In addition, EGCG and green tea extract showed inhibitory effects on the growth of lung and mammary cancer cell lines with similar potencies. An experiment using the estrogen-dependent MCF-7 cell line showed the mechanisms of action of these compounds to be inhibiting the interaction of estrogen with its receptors. Considering our previous results of a single application of EGCG to mouse skin inhibiting the specific binding of 3H-12-0-tetradecanoylphorbol-13-acetate (3H-TPA) and 3H-okadaic acid, we postulated that EGCG and compounds in green tea extracts would block the interaction of tumor promoters, hormones and growth factors with their receptors: a kind of sealing effect. The sealing effect would account for reversible growth arrest, and may be induced by various kinds of compound.

Animals↗
PubMed1992

Liver tumor promotion by the cyanobacterial cyclic peptide toxin microcystin-LR.

Certain waterblooms of toxic cyanobacteria (blue-green algae) are a health threat because of their production of toxic peptides, termed microcystins, which cause liver damage in wild and domesticated animals. The most widely studied microcystin is microcystin-LR, a heptapeptide containing the two L-amino acids, leucine and arginine. The inhibition of protein phosphatase type 1 and type 2A activities by microcystin-LR is similar to that of the known protein phosphatase inhibitor and tumor promoter okadaic acid. We show in this report that microcystin-LR, applied below the acute toxicity level, dose-dependently increases the number and percentage area of positive foci for the placental form of glutathione S-transferase in rat liver, which was initiated with diethylnitrosamine. The result was obtained independently through two animal experiments. This observation indicates that microcystin-LR is a new liver tumor promoter mediated through inhibition of protein phosphatase type 1 and type 2A activities. This provides further evidence that the okadaic acid pathway is a general mechanism of tumor promotion in various organs, such as mouse skin, rat glandular stomach and rat liver.

Alanine Transaminase↗
PubMed1992

Structurally different members of the okadaic acid class selectively inhibit protein serine/threonine but not tyrosine phosphatase activity.

The relative potencies of four main types of okadaic acid class compounds as inhibitors of the catalytic subunits of protein serine/threonine phosphatases 1 and 2A and the protein tyrosine phosphatase 1 were determined. These four types of compounds are okadaic acid, calyculin A, microcystin-LR, and tautomycin, which are isolated from different natural sources, a black sponge Halichondria okadai, a marine sponge Discodermia calyx, a blue-green alga Microcystis aeruginosa, and Streptomyces spirover ticillatus, respectively. While okadaic acid was a more effective inhibitor of protein phosphatase 2A (IC50, 0.07 nM) than protein phosphatase 1 (IC50, 3.4 nM), other compounds of the okadaic acid class were equally effective against the two protein serine/threonine phosphatases. The order of potency was microcystin greater than calyculin A greater than tautomycin, and the IC50S ranged from 0.1 to 0.7 nM. None of the okadaic acid class compounds inhibited protein tyrosine phosphatase 1 activity at concentrations up to 0.01 mM. These results indicate that the compounds of the okadaic acid class are selective inhibitors of protein serine/threonine but not tyrosine phosphatases.

Animals↗
PubMed1992

Anticarcinogenic effects of (-)-epigallocatechin gallate.

BACKGROUND: Our research objective is to develop nontoxic cancer chemopreventive agents and to apply these agents in treating humans. We are identifying agents that inhibit the process of tumor promotion in two-stage carcinogenesis experiments on mouse skin. METHODS: We review (a) the inhibitory effect of penta-O-galloyl-beta-D-glucose (5GG) on tumor promotion by teleocidin, one of the 12-O-tetradecanoylphorbol-13-acetate (TPA)-type tumor promoters (5GG is structurally similar to (-)-epigallocatechin gallate (EGCG) and is isolated from hydrolyzed tannic acid); (b) the inhibitory effects of EGCG, the main constituent of Japanese green tea, on tumor promotion with two tumor promoters, teleocidin and okadaic acid, a non-TPA-type tumor promoter; (c) the mechanisms of action of EGCG, a single application of which reduced the specific binding of [3H]TPA and [3H]okadaic acid to a particulate fraction of mouse skin; and (d) the anticarcinogenic effects of EGCG on duodenal carcinogenesis induced by N-ethyl-N'-nitro-N-nitrosoguanidine in male C57BL/6 mice. EGCG is a nontoxic compound. CONCLUSION: We believe that the main constituent of Japanese green tea, EGCG, is a practical cancer chemopreventive agent available in everyday life.

Animals↗
PubMed1992

An alternative theory of tissue specificity by tumor promotion of okadaic acid in glandular stomach of SD rats.

To challenge the theory of tissue specificity of tumor promoters, the biochemical and tumor promoting effects of okadaic acid (OA), a potent tumor promoter on mouse skin, were studied in the mucosa of rat glandular stomach. OA strongly inhibited protein phosphatases 1 and 2A, and increased 4-fold the phosphorylation of elongation factor 2 in vitro in the mucosa. Intubation of 10 micrograms (12.4 nmol) OA induced ornithine decarboxylase in the mucosa. Tumor promotion of OA was studied in the glandular stomach initiated with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) in a two-stage carcinogenesis experiment. OA in drinking water, 10 micrograms (12.4 nmol) per rat per day from weeks 9-55 of the experiment, and 20 micrograms (24.8 nmol) from weeks 56-72, significantly enhanced development of the neoplastic changes in the glandular stomach (P < 0.05). The neoplastic changes included adenomatous hyperplasias and adenocarcinomas, both of which correspond to papillomas and carcinomas in a two-stage mouse skin carcinogenesis experiment. The percentages of neoplastic change-bearing rats of the groups treated with MNNG plus OA, MNNG alone or OA alone were 75.0, 46.4 and 0% respectively. OA enhanced tumorigenesis in the MNNG-initiated glandular stomach of rats through the same mechanisms of action as in mouse skin. The OA pathway mediated through inhibition of protein phosphatases 1 and 2A is applicable to various organs as a general mechanism of tumor promotion.

Animals↗
PubMed1992

Hyperphosphorylation of cytokeratins 8 and 18 by microcystin-LR, a new liver tumor promoter, in primary cultured rat hepatocytes.

Microcystin-LR (MC-LR), an inhibitor of protein phosphatases 1 and 2A, is a potent tumor promoter in rat liver initiated with diethylnitrosamine. To understand its biochemical process in hepatocytes, primary cultured rat hepatocytes were treated with MC-LR. MC-LR (1 microM) induced phosphorylation of various proteins. Two 55 and 49 kDa proteins were phosphorylated at a 3-fold higher rate than other proteins, and these proteins were identified to be cytokeratins 8 and 18 respectively, by immunoprecipitation and Western blot analysis using monoclonal anti-cytokeratin 8 and 18 antibodies. The basic cytokeratins 8 and 18 showed pI 6.4 and 5.4 respectively, in two-dimensional gel electrophoresis. MC-LR dose dependently increased phosphorylation of cytokeratins 8 and 18 in a cell-free system by incubation with a cytosolic fraction of rat liver containing both protein kinases and protein phosphatases 1 and 2A, and with [gamma-32P]ATP. Cytokeratins 8 and 18 were target proteins for phosphorylation induced by inhibition of protein phosphatases 1 and 2A, in vitro and in rat hepatocytes. Thus, the treatment of rat hepatocytes with MC-LR induced hyperphosphorylation of cytokeratins 8 and 18 associated with morphological changes, indicating that intermediate filament networks were rearranged in the cytoplasm. The hyperphosphorylation of cytokeratins is a significant biochemical process associated with liver tumor promotion.

Animals↗
PubMed1992

Okadaic acid is a potent angiogenesis inducer.

Okadaic acid, which is a non-12-O-tetradecanoylphorbol-13-acetate (TPA)-type tumor promoter and an inhibitor of protein phosphatases 1 and 2A, induced angiogenesis in the chorioallantoic membrane of the chick embryo. Its potent angiogenic activity was dose-dependent. The minimum effective dose was 5 fmol/egg and the effective dose for 50% induction was 90 fmol/egg. These results indicated that okadaic acid exhibits angiogenic activity one order of magnitude stronger than that of TPA (reported previously). Moreover, the time-course of angiogenesis induction by okadaic acid was much slower than that by TPA. The difference is consistent with the time-courses of other biochemical and biological activities and also various gene expressions induced by okadaic acid and TPA, indicating that the difference in the time-course is associated with their mechanisms of action. We conclude that okadaic acid induces angiogenesis through a different pathway than does TPA, indicating the existence of a new mechanism of angiogenesis induction.

Animals↗
PubMed1992

Marine natural products against tumor development.

This review article deals with significant effects of marine natural products in carcinogenesis, namely as chemical probes to understand the process of carcinogenesis and as possible cancer preventive agents in humans.

Amphibian Proteins↗
PubMed1991

Vimentin is hyperphosphorylated in primary human fibroblasts treated with okadaic acid.

Okadaic acid and dinophysistoxin-1 (35-methylokadaic acid) induced hyperphosphorylation of a 58 kDa protein in primary human fibroblasts, due to inhibition of protein phosphatase 1 and 2A activities. The protein was present in the nuclear and cytosolic fractions. Its pI was 5.3. The hyperphosphorylated protein reacted with monoclonal and polyclonal anti-vimentin antibodies, but not with anti-nucleolin antibody. Phosphorylation of vimentin was stimulated in vitro by dinophysistoxin-1 dose-dependently in the presence of protein phosphatase 2A and protein kinases.

Blotting, Western↗
PubMed1991

Rapid purification of protein phosphatase 2A from mouse brain by microcystin-affinity chromatography.

Microcystin LR, which is a monocyclic heptapeptide containing two L-amino acids, leucine and arginine, is a new inhibitor of protein phosphatases 1 and 2A. Microcystin LR-affinity chromatography was used to purify protein phosphatase 2A as a holoenzyme. Five mg of microcystin LR were immobilized to ECH Sepharose 4B by the carbodiimide coupling reaction. Following DEAE-cellulose column chromatography, microcystin-affinity chromatography, as the second step in the procedure, resulted in purification of protein phosphatase 2A in a pure form. The enzyme isolated from mouse brain consisted of two regulatory subunits of 67 kDa and 58 kDa and a catalytic subunit of 41 kDa. Microcystin-affinity chromatography is useful for isolation of protein phosphatase 2A.

Animals↗
PubMed1991

Binding competition of okadaic acid derivatives to anti-okadaic acid antibody.

The serologic activities of structurally related okadaic acid derivatives have been determined. Binding of [3H]okadaic acid to rabbit anti-okadaic acid is inhibited with equal effectiveness by okadaic acid, dinophysistoxin-1, acanthifolicin, okadaic acid tetramethyl ether, and okadaic acid spiroketal II. Okadaic acid spiroketal I, which lacks the F- and G-rings of okadaic acid, inhibits serologic binding about 60 times less effectively. The F- and G-rings of okadaic acid may comprise part of the epitopes recognized by some of the polyclonal antibodies.

Animals↗