BIOCHEMICAL DIFFERENCES BETWEEN STAUROSPORINE-INDUCED APOPTOSIS AND PREMATURE MITOSIS

Apoptosis is morphologically related to premature mitosis, an aberrant form of mitosis. Staurosporine, a potent protein kinase inhibitor, in duces not only apoptotic cell death in a wide variety of mammalian cel ls but also premature initiation of mitosis in hamster cells that are arrested in S phase by DNA synthesis inhibitors. Here we report on the biochemical differences between the two phenomena commonly caused by staurosporine. Rat 3Y1 fibroblasts that had been arrested in S phase w ith hydroxyurea underwent apoptosis by treatment with staurosporine, w hereas S-phase-arrested CHO cells initiated mitosis prematurely when s imilarly treated with a low concentration of staurosporine. Chromosome condensation occurred in both apoptosis (3Y1) and premature mitosis ( CHO). However, neither formation of mitotic spindles nor mitosis-speci fic phosphorylation of MPM-2 antigens was observed in apoptosis of 3Y1 cells, unlike premature mitosis of CHO cells. The p34(cdc2) kinase ac tivated in normal and prematurely mitotic cells remained inactive in t he apoptotic cells, probably because the active cyclin B/p34(cdc2) com plex was almost absent in the S-phase-arrested 3Y1 cells. The absence of intracellular activation of p34(cdc2) in apoptosis was confirmed by immunohistochemical analyses using a specific antibody raised against Ser(55)-phosphorylated vimentin which is specifically phosphorylated by p34(cdc2) during M phase. Furthermore, phosphorylation of histones H1 and H3, which is associated with mitotic chromosome condensation, d id not occur in the apoptotic cells. These results indicate that the t wo phenomena, staurosporine-induced apoptosis and premature mitosis, a re different in their requirement for p34(cdc2) kinase activation and histone phosphorylation. (C) 1997 Academic Press.