Lithium inhibits stress-induced changes in tau phosphorylation in the mouse hippocampus.

It has been pointed out that hyperphosphorylation of microtubule-associated protein tau caused by stress might participate in the early stages of Alzheimer's disease pathogenesis. In the present study, we investigated the effects of cold water stress (CWS) on tau phosphorylation in the mouse hippocampus and the effects of GSK-3beta inhibitor, LiCl, on CWS-induced changes in tau phosphorylation levels by immunoblot analyses. CWS exposure caused an increase in tau phosphorylation at the Tau-1 (Ser199/202), AT8 (Ser202/Thr205) and Ser396 sites. CWS-induced changes in tau phosphorylation at the Ser199/202 and Ser396, but not at Ser202/Thr205, were significantly attenuated by LiCl pretreatment. Total tau levels also showed a decided tendency to increase after CWS, which tendency was also countered by LiCl. Finally, we showed that CWS increased the active form of GSK-3beta that was phosphorylated at Tyr216. These results suggest that a CWS-induced increase in phosphorylated tau in the hippocampus is mediated, at least partly, by the activation of GSK-3beta.

Mechanism of action of aragusterol a (YTA0040), a potent anti-tumor marine steroid targeting the G(1) phase of the cell cycle.

Aragusterol A (YTA0040), isolated from the Okinawan marine sponge of the genus Xestospongia, is a potent anti-tumor marine steroid that possesses a unique structural component. This compound showed broad-spectrum anti-proliferative activity against a panel of 14 human cancer cell lines (IC(50) = 0.01-1.6 microM). P-glycoprotein-mediated, multidrug-resistant cells showed cross-resistance to YTA0040 cells, whereas cisplatin-resistant non-small-cell lung-cancer (NSCLC) sublines showed a collateral sensitivity to YTA0040. In transplantable murine tumor models, YTA0040 displayed a broad spectrum and high degree of anti-tumor activity when administered i.p. or p.o. (life span T/C = 135-234%). In P388 murine leukemia cells, YTA0040 caused dose- and time-dependent suppression of nucleic acid and protein synthesis, with protein synthesis being more potently and rapidly inhibited than nucleic acid synthesis. Flow-cytometric analysis revealed that YTA0040 blocked the entry of human NSCLC-derived A549 cells into S phase, leading to arrest in the G(1) phase of the cell cycle. Western blot analysis demonstrated that YTA0040 caused a dose-dependent decrease in the levels of expression of hyperphosphorylated pRb and cyclin A in A549 cells. The level of p53 protein expression was decreased by YTA0040 treatment. A higher concentration of YTA0040 down-regulated the levels of expression of CDK2, CDK4, cyclin D1 and cyclin E. These findings indicated that YTA0040 arrested human NSCLC cells in late G(1) phase of the cell cycle through inhibition of pRb phosphorylation. Inhibition of pRb phosphorylation by YTA0040 resulted from down-regulation of levels of expression of the CDKs and cyclins involved in the G(1)/S transition and not from induction of p53 and/or the CDK inhibitor p21.

A novel antitumor compound, NC-190, induces topoisomerase II-dependent DNA cleavage and DNA fragmentation.

A novel benzophenazine derivative, NC-190, is a potent antitumor compound. NC-190 has been shown to inhibit the DNA strand-passing activity of DNA topoisomerase II. We investigated further the mode of action of NC-190 against DNA topoisomerase II and DNA fragmentation. NC-190 inhibited the decatenation activity of purified topoisomerase II, but had only a weak inhibitory effect against topoisomerase I. A topoisomerase II-dependent DNA cleavage assay showed that NC-190 inhibited the enzyme activity by stabilizing a topoisomerase II-DNA cleavable complex. NC-190 induced growth inhibition, protein-linked DNA breaks, and DNA fragmentation in cultured HL-60 cells in a dose-dependent manner. These activities of NC-190 in HL-60 cells were comparable to those of etoposide (VP-16). These results demonstrate a good correlation among growth inhibition, topoisomerase II-dependent DNA cleavage, and DNA fragmentation induced by NC-190. A DNA unwinding assay showed that NC-190 had intercalating activity, but its activity appeared to be weaker than those of ethidium bromide and adriamycin. These results indicate that the mechanism by which NC-190 exhibits antitumor activity may be the inhibition of topoisomerase II.

Fc epsilon RI-stimulated Ca(2+)-dependent secretion from rat basophilic leukemia (RBL-2H3) cells permeabilized with Staphylococcal alpha-toxin: Fc epsilon RI-operated signals are not mimicked by the actions of GTP gamma S.

1. RBL-2H3 cells permeabilized with alpha-toxin responded to dinitrophenol (30-40 mol/mol)-conjugated human serum albumin, as antigen, to secrete [14C]serotonin in the micromolar range of free Ca2+. 2. Calcium ion alone did not cause substantial secretion. 3. Guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) (100 microM) in combination with Ca2+ produced only negligible [14C]serotonin secretion. 4. GTP gamma S, in the presence of cytochalasin D, caused optimal secretion of [14C]serotonin in a Ca(2+)-dependent manner.

Hyaluronate depolymerization activity induced by progesterone in cultured fibroblasts derived from human uterine cervix.

High-molecular-weight [14C]hyaluronate was incubated with cultured fibroblasts from human uterine cervix and skin, and then the depolymerization of the hyaluronate was investigated. [14C]Hyaluronate in the medium of skin fibroblasts was depolymerized into a constant molecular weight (M(r) about 40,000), whereas that of cervix fibroblasts was not depolymerized, irrespective of incubation period. However, when progesterone was added to the medium of cervix fibroblasts, hyaluronate was depolymerized to the same extent as that in skin fibroblasts. The reducing terminal sugar of the depolymerized hyaluronate was N-acetylglucosamine. These results suggest that a hyaluronate-depolymerizing enzyme, endo-beta-N-acetylglucosaminidase, was induced by progesterone in cultured fibroblasts derived from human uterine cervix.