Masuji Yamamoto

Bio: Masuji Yamamoto is an academic researcher from Wistar Institute. The author has contributed to research in topics: Cell cycle & Cyclin A. The author has an hindex of 2, co-authored 3 publications receiving 293 citations.

Quercetin Arrests Human Leukemic T-Cells in Late G1 Phase of the Cell Cycle

Abstract: The effect of quercetin, a flavonoid found in many plants, on the proliferation of human leukemic T-cells was analyzed. Quercetin reversibly blocked the cell cycle at a point 3-6 h before the start of DNA synthesis. Expression of the growth-related genes histone H4, cyclin A and B, and p34cdc2 was suppressed in cells blocked with quercetin. Comparison of the quercetin arrest points with those of the cell cycle inhibitors aphidicolin and mimosine revealed a temporal order of arrest points in G1 of quercetin, mimosine, and aphidicolin. Mimosine and aphidicolin did not inhibit the expression of cyclin A or p34cdc2, whereas all three reagents inhibited expression of cyclin B. Low concentrations of the protein inhibitor cycloheximide inhibited release of the quercetin but not the mimosine or aphidicolin block. A [35S]methionine-labeled M(r) 60,000 protein disappeared in quercetin-treated cells and was rapidly synthesized after removal of quercetin, suggesting the possibility that the M(r) 60,000 protein induces DNA synthesis after the cell is released from a quercetin block. These results suggest the usefulness of quercetin in studies of the regulation of late G1 phase.

Cell cycle regulation in normal versus leukemic t cells

Abstract: DNA replication is a central feature of the cell cycle, yet very little is known about the control of this process in eukaryotes. Genetic analysis of yeasts has defined proteins with potentially important roles in the control of DNA replication, e.g. CDC28 gene from Saccharomyces cerevisiae and its homolog cdc2 from S. pombe 1–4, for which human functional homologs exist5–8. A homolog of the cdc2 gene product, p34cdc2, has been identified in Xenopus eggs as a component of the mitotic inducer maturation-promoting factor (MPF)9, 10 Active MPF is a complex of p34cdc2 and cyclin B1114. Cyclins are rapidly degraded as cells exit from metaphase15 and therefore must be newly synthesized during interphase of each cell cycle so that cells can generate MPF and progress into mitosis 16, 17. in addition to its role at metaphase, p34cdc2 function is also required at the G1/S transition in yeast.

The Effects of Plant Flavonoids on Mammalian Cells:Implications for Inflammation, Heart Disease, and Cancer

Abstract: Flavonoids are nearly ubiquitous in plants and are recognized as the pigments responsible for the colors of leaves, especially in autumn. They are rich in seeds, citrus fruits, olive oil, tea, and red wine. They are low molecular weight compounds composed of a three-ring structure with various substitutions. This basic structure is shared by tocopherols (vitamin E). Flavonoids can be subdivided according to the presence of an oxy group at position 4, a double bond between carbon atoms 2 and 3, or a hydroxyl group in position 3 of the C (middle) ring. These characteristics appear to also be required for best activity, especially antioxidant and antiproliferative, in the systems studied. The particular hydroxylation pattern of the B ring of the flavonoles increases their activities, especially in inhibition of mast cell secretion. Certain plants and spices containing flavonoids have been used for thousands of years in traditional Eastern medicine. In spite of the voluminous literature available, however, Western medicine has not yet used flavonoids therapeutically, even though their safety record is exceptional. Suggestions are made where such possibilities may be worth pursuing.

The Cell Cycle

Abstract: 5 The activity of cyclin-dependent protein kinase p34cdc2 is regulated by phosphorylation. In this study, we show that the presence of phosphatase inhibitors can have major effects on the levels of phosphorylation and the activities of the kinase extracted from cells. The combination of okadaic acid and sodium vanadate was most effective in protecting p34cdc2 against cellular phosphatases. In the absence of these inhibitors, p34cdc2 was dephosphorylated with an altered activity, indicating that phosphatase activities remained high during extractions. In contrast to when both inhibitors were used, lower activity of the kinase was found when only sodium vanadate was used, whereas higher activity was found in the presence of okadaic acid. Other conventional phosphatase inhibitors such as NaP, NaRS03 and glycero12-phosphate, were not effective in preventing dephosphorylation from p34cdc2 in whole cell lysates.

Deregulated transcription factor E2F-1 expression leads to S-phase entry and p53-mediated apoptosis.

Abstract: E2F-1 is a transcription factor suspected of activating genes required for S phase and a known target for the action of RB, the retinoblastoma gene product. Its induction in quiescent fibroblasts led to S-phase entry followed by apoptosis. E2F-1-mediated apoptosis was suppressed by coexpression of wild-type RB or a transdominant negative mutant species of p53. In contrast, coexpression of a naturally occurring loss-of-function RB mutant or wild-type p53 did not suppress the induction of apoptosis under these conditions. Thus, deregulated E2F-1 activity gives rise to proliferative and apoptotic signals. p53 appears to participate in the execution of the latter.

Wine as a biological fluid: History, production, and role in disease prevention

Abstract: Wine has been part of human culture for 6,000 years, serving dietary and socio-religious functions. Its production takes place on every continent, and its chemical composition is profoundly influenced by enological techniques, the grape cultivar from which it originates, and climatic factors. In addition to ethanol, which in moderate consumption can reduce mortality from coronary heart disease by increasing high-density lipoprotein cholesterol and inhibiting platelet aggregation, wine (especially red wine) contains a range of polyphenols that have desirable biological properties. These include the phenolic acids (p-coumaric, cinnamic, caffeic, gentisic, ferulic, and vanillic acids), trihydroxy stilbenes (resveratrol and polydatin), and flavonoids (catechin, epicatechin, and quercetin). They are synthesized by a common pathway from phenylalanine involving polyketide condensation reactions. Metabolic regulation is provided by competition between resveratrol synthase and chalcone synthase for a common precursor pool of acyl-CoA derivatives. Polymeric aggregation gives rise, in turn to the viniferins (potent antifungal agents) and procyanidins (strong antioxidants that also inhibit platelet aggregation). The antioxidant effects of red wine and of its major polyphenols have been demonstrated in many experimental systems spanning the range from in vitro studies (human low-density lipoprotein, liposomes, macrophages, cultured cells) to investigations in healthy human subjects. Several of these compounds (notably catechin, quercetin, and resveratrol) promote nitric oxide production by vascular endothelium; inhibit the synthesis of thromboxane in platelets and leukotriene in neutrophils, modulate the synthesis and secretion of lipoproteins in whole animals and human cell lines, and arrest tumour growth as well as inhibit carcinogenesis in different experimental models. Target mechanisms to account for these effects include inhibition of phospholipase A2 and cyclo-oxygenase, inhibition of phosphodiesterase with increase in cyclic nucleotide concentrations, and inhibition of several protein kinases involved in cell signalling. Although their bioavailability remains to be fully established, red wine provides a more favourable milieu than fruits and vegetables, their other dietary source in humans.