|Lasonolide A, a potent and reversible inducer of chromosome condensation.|
Zhang, YW; Ghosh, AK; Pommier, Y
Cell cycle (Georgetown, Tex.)
Lasonolide A (LSA) is a natural product with high and selective cytotoxicity against mesenchymal cancer cells, including leukemia, melanomas and glioblastomas. Here, we reveal that LSA induces rapid and reversible premature chromosome condensation (PCC) associated with cell detachment, plasma membrane smoothening and actin reorganization. PCC is induced at all phases of the cell cycle in proliferative cells as well as in circulating human lymphocytes in G 0. It is independent of Cdk1 signaling, associated with cyclin B downregulation and induced in cells at LSA concentrations that are three orders of magnitude lower than those required to block phosphatases 1 and 2A in vitro. At the epigenetic level, LSA-induced PCC is coupled with histone H3 and H1 hyperphosphorylation and deacetylation. Treatment with SAHA reduced LSA-induced PCC, implicating histone deacetylation as one of the PCC effector mechanisms. In addition, PCC is coupled with topoisomerase II (Top2) and Aurora A hyperphosphorylation and activation. Inhibition of Top2 or Aurora A partially blocked LSA-induced PCC. Our findings demonstrate the profound epigenetic alterations induced by LSA and the potential of LSA as a new cytogenetic tool. Based on the unique cellular effects of LSA, further studies are warranted to uncover the cellular target of lasonolide A ("TOL").
|Growth factors that repress myoblast differentiation sustain phosphorylation of a specific site on histone H1.|
Cole, F, et al.
J. Biol. Chem., 268: 1580-5 (1993)
A monoclonal antibody (12D11) is presented that binds an epitope on histone H1 only when it is phosphorylated. Skeletal myoblasts, which are cultured in high mitogen medium to induce proliferation and inhibit differentiation, contain histone H1 reactive with monoclonal antibody 12D11, whereas differentiated myocytes and adult skeletal muscle do not. Phosphorylation of H1 at the 12D11 epitope, as assessed by antibody binding, is also induced and maintained in myoblasts cultured in low mitogen medium supplemented with transforming growth factor beta, which blocks differentiation but allows the cells to withdraw from the cell cycle (Olson, E., Sternberg, E., Hu, J., Spizz, G., and Wilcox, C. (1986) J. Cell Biol. 103, 1799-1805; Massague, J., Cheipetz, S., Endo, T., and Nadal-Ginard, B. (1986) Proc. Natl. Acad. Sci. U.S.A. 83, 8206-8210). These observations suggest that phosphorylation of histone H1 at the 12D11 epitope is associated with the negative regulation of myoblast differentiation by growth factors.