Widdrol blocks 3T3-L1 preadipocytes growth and differentiation due to inhibition of mitotic clonal expansion.
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Adipocyte differentiation is strongly associated with obesity, which causes metabolic disorders. In this study, we investigated the inhibitory effects of widdrol on 3T3- L1 preadipocyte growth and differentiation. Widdrol decreased lipid droplet accumulation and down-regulated adipogenic transcription factors such as C/EBPalpha, C/EBPbeta, and PPARgamma. Widdrol blocked preadipocyte proliferation and differentiation through the inhibition of mitotic clonal expansion, which was accompanied by the failure of degradation of p21, a cyclin-dependent kinase inhibitor. Cell-cycle analysis clearly indicated that widdrol actively induces cell-cycle arrest at the G1-S phage transition, causing cells to remain in the preadipocyte state. Moreover, widdrol increased p21 expression and inhibited Rb phosphorylation in preadipocyte incubated in a hormone medium. Therefore, these findings clearly suggest that widdrol blocks preadipocyte growth and differentiation through the inhibition of mitotic clonal expansion by p21- and Rb-dependent G1 arrest and can be developed as a potent anti-adipogenic agent for reducing obesity. (+info)
alpha4betadelta GABA(A) receptors are high-affinity targets for gamma-hydroxybutyric acid (GHB).
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Kinetics and inhibition studies of catechol O-methyltransferase from the yeast Candida tropicalis.
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The Kms for esculetin and S-adenosyl-L-methionine for catechol O-methyltransferase from the yeast Candida tropicalis were 6.2 and 40 microM, respectively. S-Adenosyl-L-homocysteine was a very potent competitive inhibitor with respect to S-adenosyl-L-methionine, with a Ki of 6.9 microM. Of the catechol-related inhibitors, purpurogallin, with a Ki of 0.07 microM, showed the greatest inhibitory effect. Sulfhydryl group-blocking reagents, such as thiol-oxidizing 2-iodosobenzoic acid and mercaptide-forming p-chloromercuribenzoic acid, provided evidence for sulfhydryl groups in the active site of the enzyme. Yeast catechol O-methyltransferase is a metal-dependent enzyme and requires Mg2+ for full activity. Zn2+ and Mn2+ but not Ca2+ were able to substitute for Mg2+. Mn2+ showed optimal enzyme activation at concentrations 50- to 100-fold lower than those of Mg2+. (+info)
Possible role of microtubules in thyroid secretion.
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Colchicine and other microtubule-active agents have been found to block the release, stimulated by either thyroid-stimulating hormone or by dibutyryl cyclic adenosine 3':5'-monophosphate, of (131)I from previously (131)I-labeled mouse thyroid glands in vitro. The time and concentration characteristics of these inhibitors are consistent with their actions on microtubules in other systems. [(3)H]colchicine was also shown to be bound to a soluble 6S protein of bovine thyroid slices similar to the protein identified in other systems as a microtubular subunit. The demonstrated inhibition of colloid droplet formation and absence of an effect on thyroidal adenyl cyclase or cyclic 3':5'-phosphodiesterase suggests a colchicine-sensitive role for microtubules in colloid endocytosis in the thyroid gland. (+info)
The appearance and disappearance of the post-transcriptional repressor of tyrosine aminotransferase synthesis during the HTC cell cycle.
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The synthesis of the enzyme tyrosine aminotransferase in HTC cells (an established line of rat hepatoma cells) is inducible by glucocorticoid hormones only during the latter part of G1 phase and throughout S phase in the cell generation cycle. We have earlier shown that during the first few hours of G1 phase when the enzyme cannot be induced, its synthesis is constitutive, presumably using as template, preexisting messenger RNA. Our model for tyrosine aminotransferase gene regulation in eukaryotic cells entails a specific post-transcriptional repressor which is formed only during the periods in the cell cycle when tyrosine aminotransferase is inducible. This model predicts that during the noninducible period, G2, the tyrosine aminotransferase repressor would not be present and thus tyrosine aminotransferase synthesis would be constitutive. Data are presented which confirm this prediction in further support of the model. (+info)
Ultraviolet light-induced division delayed in synchronized Chinese hamster cells.
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The age-dependent, ultraviolet light (UVL) (254 nm)-induced division delay of surviving and nonsurviving Chinese hamster cells was studied. The response was examined after UVL exposures adjusted to yield approximately the same survival levels at different stages of the cell cycle, 60% or 30% survival. Cells irradiated in the middle of S suffered the longest division delay, and cells exposed in mitosis or in G(1) had about the same smaller delay in division. Cells irradiated in G(2), however, were not delayed at either survival level. It was further established, after exposures that yielded about 30% survivors at various stages of the cycle, that surviving cells had shorter delays than nonsurvivors. This difference was not observed for cells in G(2) at the time of exposure; i.e., neither surviving nor nonsurviving G(2) cells were delayed in division. The examination of mitotic index vs. time revealed that most cells reach mitosis, but all of the increase in the number of cells in the population can be accounted for by the increase of the viable cell fraction. These observations suggest strongly that nonsurviving cells, although present during most of the experiment, are stopped at mitosis and do not divide. Cells in mitosis at the time of irradiation complete their division, and in the same length of time as unirradiated controls. Division and mitotic delays after UVL are relatively much larger than after X-ray doses that reduce survival to about the same level. (+info)
Expression of H-2 and Moloney leukemia virus-determined cell-surface antigens in synchronized cultures of a mouse cell line.
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A mouse cell line derived from bone marrow (JLS-V9) was infected in vitro with Moloney leukemia virus. After the cell-surface antigens specified by this virus appeared, cells were synchronized in mitosis by a short treatment with colcemid. The expression of H-2- and virus-determined surface antigens was monitored during one cell cycle by an indirect membrane-immunofluorescence test. The highest proportion of antigen-positive cells was found during the G1 period; the proportion dropped as the cells entered the S period, and remained low until they entered the G1 period of the next cycle. The H-2- and virus-determined surface antigens were temporally coexpressed. (+info)