No abstract

Ring-shaped cohesin keeps sister chromatids paired until cleavage of its Scc1/Rad21 subunit by separase triggers chromosome segregation in anaphase. Vertebrate separase is held inactive by mutually exclusive binding to securin or Cdk1-cyclin B1 and becomes unleashed only upon ubiquitin-dependent degradation of these regulators. Although most separase is usually found in association with securin, this anaphase inhibitor is dispensable for murine life while Cdk1-cyclin B1-dependent control of separase is essential. Here, we show that securin-independent inhibition of separase by Cdk1-cyclin B1 in early mitosis requires the phosphorylation-specific peptidyl-prolyl cis/trans isomerase Pin1. Furthermore, isomerization of previously securin-bound separase at the metaphase-to-anaphase transition renders it resistant to re-inhibition by residual securin. At the same time, isomerization also limits the half-life of separase's proteolytic activity, explaining how cohesin can be reloaded onto telophase chromatin in the absence of securin and cyclin B1 without being cleaved.

Whether aged hematopoietic stem and progenitor cells (HSPCs) have impaired DNA damage repair is controversial. Using a combination of DNA mutation indicator assays, we observe a 2-3 fold increase in the number of DNA mutations in the hematopoietic system upon aging. Young and aged HSCs and HPCs do not show an increase in mutation upon irradiation-induced DNA damage repair, and young and aged HSPCs respond very similarly to DNA damage with respect to cell cycle checkpoint activation and apoptosis. Both, young and aged HSPCs show impaired activation of the DNA-damage induced G1-S checkpoint. Induction of chronic DNA double strand breaks by zinc-finger nucleases suggest that HSPCs undergo apoptosis rather than faulty repair. These data reveal a protective mechanism in both the young and aged hematopoietic system against accumulation of mutations in response to DNA damage.

Background: Separase, the trigger protease of eukaryotic anaphase, remains regulated in the absence of its inhibitor, securin. Results: Cdk1-cyclin B1 triggers precipitation of separase by phosphorylation but stabilizes it by inhibitory binding. Conclusion: Only separase that is first complexed by Cdk1-cyclin B1 can later be activated by cyclin B1 degradation. Significance: These minimal requirements of separase regulation could explain the faithful execution of anaphase in the absence of securin.

Effects of a combretastatin A4 analogous chalcone and its Pt-complex on cancer cells: a comparative study of uptake, cell cycle and damage to cellular compartments. Biochemical Pharmacology, Elsevier, 2010, 80 (10) Please cite this article as: Zoldakova M, Kornyei Z, Brown A, Biersack B, Madarász E, Schobert R, Effects of a combretastatin A4 analogous chalcone and its Pt-complex on cancer cells: a comparative study of uptake, cell cycle and damage to cellular compartments, Biochemical Pharmacology (2008Pharmacology ( ), doi:10.1016Pharmacology ( /j.bcp.2010 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Page 1 of 48A c c e p t e d M a n u s c r i p t 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 Effects of a combretastatin A4 analogous chalcone and its Pt ((classification: antibiotics and chemotherapeutics))Page 2 of 48 A c c e p t e d M a n u s c r i p t 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 2 ((Abstract))The combretastatin A4 analogous chalcone (2E)-3-(3-hydroxy-4-methoxyphenyl)-1-(3,4,5-trimethoxyphenyl)prop-2-en-1-one 1 and its dichloridoplatinum(II) (6-aminomethylnicotinate) complex 2 were previously found to be highly active against a variety of cancer cell lines while differing in their apoptosis induction and long-term regrowth retardation (Schobert R et al. J Med Chem 2009;52:241-6) [1]. Further differences were identified now.The cellular uptake of complex 2, like that of oxaliplatin, occurred mainly via organic cation transporters (OCT-1/2; ~32%) and copper transporter related proteins (Ctr1; ~24%), whereas that of chalcone 1 was dependent on endocytosis (~80%). Complex 2 was more tumourspecific than 1 concerning neural cells. This was apparent from the ratios of IC 50 (48 h) values against primary astrocytes versus human astroglioma cells U87 ( > 7000 for complex 2; 55 for compound 1). In tubulin-rich neurons and 518A2 melanoma cells complex 2 disrupted microtubules and actin filaments. Cancer cells treated with 2 could repair the cytoskeletal damage but ceased to proliferate and perished. Complex 2 was particularly cytotoxic against P-gp-rich cells. It acted as a substrate for ABC-transporters of types BCRP, MRP3, and MRP1 and so was less active against the corresponding can...