he induction of PCC. Lasonolide A is a more potent PF-562271 inducer of premature chromosome condensation than okadaic acid in cells, but a weaker phosphatase inhibitor in biochemical assays. Next, we compared LSA to the classical PCC inducer, okadaic acid.21 Under conditions where 100 nM LSA induced PCC in 99.5% of CA46 www.landesbioscience.com Cell Cycle 4425 cells, 1 M OA induced PCC in only 31% of the cells. Therefore, LSA is a markedly more potent PCC inducer than OA. As OA is a known phosphatase inhibitor,21 we tested the effects of LSA on phosphatases in vitro. Purified phosphatase type 1 and phosphatase type 2A were incubated with LSA, and phosphatase activities were determined. As shown in 4426 Cell Cycle Volume 11 Issue 23 a much weaker phosphatase inhibitor but a more potent PCC inducer than OA. Lasonolide A induces premature chromosome condensation independently of MPF. During normal cell cycle progression, chromosome condensation is triggered as cells enter mitosis by the dephosphorylated mitosis-promoting 
factor.22 To investigate whether LSAinduced PCC is mediated through MPF signaling, Cdk1 and cyclin B1 were measured in LSA-treated cells. Ser10 was more persistent. Histones H125 and H2B 26 were also hyperphosphorylated in LSA-treated cells. On the other hand, LSA did not induce -H2AX . These data demonstrate that LSA induces rapid histone hyperphosphorylation in association with PCC. We also determined histone H3 acetylation in response to LSA. www.landesbioscience.com Cell Cycle 4427 phospho-epitope.28 To investigate whether Top2 is involved in the induction of PCC by LSA, we measured the overall Ser/Thr phosphorylation patterns by using MPM-2 antibodies, which recognize phospho-antigens of Top2 and other proteins that are phosphorylated specifically in mitosis.28,29 MPM-2 signals with the molecular size of Top2 were markedly enhanced within minutes of LSA treatment. MPM-2 induction was detectable within 15 min after LSA addition and was 16-fold above control at 1 h. The LSA-induced Top2 hyperphosphorylation reversed within minutes after removal of LSA. These results indicate that LSA induces rapid and reversible Top2 hyperphosphorylation. To investigate the modulation of Top2 activity by LSA, the decatenation activity of Top2 was determined.30 Nuclear extracts were prepared from LSA-treated CA46 cells and incubated with kinetoplast DNA. Decatenation was enhanced in the samples from LSA-treated cells, demonstrating Top2 activation by LSA. To further study the involvement of Top2, the effect of the Top2 inhibitors ICRF 187 and etoposide 30 were determined on LSA-induced PCC. The nuclear shape change PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19822626 and chromosome condensation could still be observed in cells co-treated with Top2 inhibitors. However, the pattern of chromosome condensation was significantly changed. Instead of the well-defined and organized pattern of chromosome condensation induced by LSA, PI staining of nuclei co-treated with LSA and Top2 inhibitors showed only partial condensation. Taken together, these data demonstrate that LSA induces Top2 hyperphosphorylation and activation and suggest that Top2 is a determinant of LSA-induced PCC. Aurora A is activated with the induction of PCC by Lasonolide A. Aurora kinase is a key player in mitosis.10-12 To investigate the involvement of Aurora A in LSA-induced chromosome condensation, we used specific antibodies to detect the phosphorylation of Aurora A at Thr288. Aurora A was quickly activated by Lasonolide A, without c