Role of Cyclin B1/Cdc2 Up-Regulation in the Development of Mitotic Prometaphase Arrest in Human Breast Cancer Cells Treated with Nocodazole

Background: During a normal cell cycle, the transition from G 2 phase to mitotic phase is triggered by the activation of the cyclin B1-dependent Cdc2 kinase. Here we report our finding that treatment of MCF-7 human breast cancer cells with nocodazole, a prototypic microtubule inhibitor, results in strong up-regulation of cyclin B1 and Cdc2 levels, and their increases are required for the development of mitotic prometaphase arrest and characteristic phenotypes. Methodology/Principal Findings: It was observed that there was a time-dependent early increase in cyclin B1 and Cdc2 protein levels (peaking between 12 and 24 h post treatment), and their levels started to decline after the initial increase. This early up-regulation of cyclin B1 and Cdc2 closely matched in timing the nocodazole-induced mitotic prometaphase arrest. Selective knockdown of cyclin B1or Cdc2 each abrogated nocodazole-induced accumulation of prometaphase cells. The nocodazole-induced prometaphase arrest was also abrogated by pre-treatment of cells with roscovitine, an inhibitor of cyclin-dependent kinases, or with cycloheximide, a protein synthesis inhibitor that was found to suppress cyclin B1 and Cdc2 up-regulation. In addition, we found that MAD2 knockdown abrogated nocodazole-induced accumulation of cyclin B1 and Cdc2 proteins, which was accompanied by an attenuation of nocodazole-induced prometaphase arrest. Conclusions/Significance: These observations demonstrate that the strong early up-regulation of cyclin B1 and Cdc2 contributes critically to the rapid and selective accumulation of prometaphase-arrested cells, a phenomenon associate

Alpha-santalol, a chemopreventive agent against skin cancer, causes G2/M cell cycle arrest in both p53-mutated human epidermoid carcinoma A431 cells and p53 wild-type human melanoma UACC-62 cells

<p>Abstract</p> <p>Background</p> <p>α-Santalol, an active component of sandalwood oil, has shown chemopreventive effects on skin cancer in different murine models. However, effects of α-santalol on cell cycle have not been studied. Thus, the objective of this study was to investigate effects of α-santalol on cell cycle progression in both p53 mutated human epidermoid carcinoma A431 cells and p53 wild-type human melanoma UACC-62 cells to elucidate the mechanism(s) of action.</p> <p>Methods</p> <p>MTT assay was used to determine cell viability in A431 cells and UACC-62; fluorescence-activated cell sorting (FACS) analysis of propidium iodide staining was used for determining cell cycle distribution in A431 cells and UACC-62 cells; immunoblotting was used for determining the expression of various proteins and protein complexes involved in the cell cycle progression; siRNA were used to knockdown of p21 or p53 in A431 and UACC-62 cells and immunofluorescence microscopy was used to investigate microtubules in UACC-62 cells.</p> <p>Results</p> <p>α-Santalol at 50-100 μM decreased cell viability from 24 h treatment and α-santalol at 50 μM-75 μM induced G₂/M phase cell cycle arrest from 6 h treatment in both A431 and UACC-62 cells. α-Santalol altered expressions of cell cycle proteins such as cyclin A, cyclin B1, Cdc2, Cdc25c, p-Cdc25c and Cdk2. All of these proteins are critical for G₂/M transition. α-Santalol treatment up-regulated the expression of p21 and suppressed expressions of mutated p53 in A431 cells; whereas, α-santalol treatment increased expressions of wild-type p53 in UACC-62 cells. Knockdown of p21 in A431 cells, knockdown of p21 and p53 in UACC-62 cells did not affect cell cycle arrest caused by α-santalol. Furthermore, α-santalol caused depolymerization of microtubules similar to vinblastine in UACC-62 cells.</p> <p>Conclusions</p> <p>This study for the first time identifies effects of α-santalol in G₂/M phase arrest and describes detailed mechanisms of G₂/M phase arrest by this agent, which might be contributing to its overall cancer preventive efficacy in various mouse skin cancer models.</p

Self-assembly of a polyrotaxane containing a cyclic &apos;&apos;bead&apos;&apos; in every structural unit in the solid state: Cucurbituril molecules threaded on a one-dimensional coordination polymer

X11195sciescopu

Molecular container assembly capable of controlling binding and release of its guest molecules: Reversible encapsulation of organic molecules in sodium ion complexed cucurbituril

X11268sciescopu

A simple construction of a rotaxane and pseudorotaxane: Syntheses and X-ray crystal structures of cucurbituril threaded on substituted spermine

A simple, one-step, high-yield synthesis of a rotaxane and pseudorotaxane based on cucurbituril and spermine is presented. Various spectroscopic techniques and X-ray diffraction methods were used to characterize the supramolecular species.open1173sciescopu

Novel low-valent zirconium porphyrin complexes: syntheses, characterization and x-ray crystal structures of (eta(5)-cyclopentadienyl)zirconium tetraphenylporphyrin and (eta(2)-diphenylacetylene)zirconium octaethylporphyrin

Reactions of (por)ZrCl2 [por = octaethylporphyrinato (oep) or tetraphenylporphyrinato (tpp) dianion] with TlCp and diphenylacetylene in the presence of Na/Hg or Mg produce novel low-valent zirconium porphyrin complexes (por)Zr(eta(5)-Cp) 1 and (por)Zr(eta(2)-PhC=CPh) 2, respectively; spectroscopic and/or structural data for 1 and 2 are consistent with a formalism in which 1 is a resonance hybrid of a zirconium(III) metal-centered radical and a zirconium(IV) porphyrin radical anion while 2 is a zirconium(II) complex stabilized by a four-electron-donor alkyne ligand.open1113sciescopu

Novel eta(1)-alkynyl zirconium porphyrin complexes: synthesis and characterization of (por)Zr(eta(1)-C CR)(3)Li(THF) [por = octaethylporphyrinato (oep) or tetraphenylporphyrinato dianion (tpp); R = Ph, SiMe3]

Reaction of (por)ZrCl2 [por = 2,3,7,8,12,13,17,18-octa-ethylporphyrinato dianion (oep) or 5,10,15,20-tetraphenylporphyrinato dianion (tpp)] with 3 equiv, of LiC=CR (R = Ph and SiMe3) produces novel alkynyl zirconium(Iv) porphyrin complexes (por)Zr(eta(1)-C=CR)(3)Li(THF) in which three alkynyl ligands are coordinated to the zirconium center in a piano stool fashion and the Li+ ion is bound to the pocket formed by three alkynyl ligands; treatment of (por)Zr(eta(1)-CECPh)(3)Li(THF) with anhydrous HCl produces a C-C bond coupled product H2C=CPh(C=CPh) and HC=CPh quantitatively.open119sciescopu

Self-assembly of interlocked structures: Rotaxanes, polyrotaxanes and molecular necklaces

Our recent work on construction of interlocked structures such as rotaxanes, polyrotaxanes and molecular necklaces using the principles of self assembly and coordination chemistry is described. In the synthesis of these structures, the barrel-shape molecule cucurbituril is used as a molecular "bead" and metal ions or metal complexes are used as "glue" or "angle connectors". Judicious choice of metal ions, counter ions and "strings" is important in order to construct the desired supramolecular structures.X1122sciescopu