Vanadate Triggers the Transition from Chromosome Condensation to Decondensation in a Mitotic Mutant (tsTM13)

Abstract

At the nonpermissive temperature (39 "C), chromosomes remain condensed in a temperature-sensitive cell mutant (tsTM13) arrested in the late stage of mitosis. Highly increased activity of histone H1 kinase, hyperphosphorylation of histone H1, and mitosis-specific histone H3 phosphorylation are maintained, even in telophase. In the present study, the defect of chromosome decondensation in tsTM13 cells was found to be partially normalized by a tyrosine phosphatase inhibitor, vanadate, with induction of chromosome decondensation and the formation of multinucleated cells. In the presence of vanadate, the H1 kinase activity dropped to near normal levels and the amount of the inactive form of p3QdcZ protein phosphorylated at a tyrosine residue was increased. H1 and H3 were also extensively de-phosphorylated, the latter being tightly associated with chromosome decondensation. Serinehhreonine-protein phosphatase in late mitosis of the mutant works normally at 39°C. The results indicate that (a) the genetic defect in the mutant may be involved in the control mechanism of the ~34"~'*/Hl kinase activity in the late M phase rather than the phosphatase, (b) normalization of the defect of the mutant by vanadate results from inactivation of H1 kinase, and (c) late mitosis-specific events (p34"d"Z/H1 kinase inactivation, mitosisspecific dephosphorylation of histone H1 and H3) are closely operating with chromosome decondensation.Keywords: vanadate; chromosome decondensation ; cdc2/H1 kinase; histone H3 ; mitosis.The dynamics of the initiation of chromatin condensation at the transition from G2 to M phases and the M to G I phase decondensation during the eukaryotic cell cycle are not fully understood. Analysis of the reversibility of chromosome condensation is crucial for the study of cell cycle regulation and proliferation. It is highly probable that these reversible processes are controlled by a protein phosphorylation-dependent mechanism due to the balance of protein kinase and protein phosphatase activities [I 3. p34"d"2/H1 kinase activation correlates with the initiation and maintenance of M phase [2-41. However, we still do not have much downstream information after enzyme activation, for example, regarding how this is involved in chromatin condensation. For a complete understanding of chromosome condensation, it is necessary to examine critically the phosphorylation of possible substrates related to chromosome condensation together with p34'd'2/H1 kinase activity.Histone HI is a major chromosomal structural protein known to be phosphorylated in a cell-cycle-dependent manner at serine or threonine residues in the SeriThr-Pro-Xaa-Lys and analogous amino acid sequences [11] level of H3 phosphorylation occurring at the 10th serine residue [16, 171 is evident only in M phase [18, 191 or during premature chromosome condensation [20, 211. We earlier indicated that H3 phosphorylation is specific to premature chromosome condensation since (a) H3 is dephosphorylated when the condensation is reversed without dephosphorylation of H1 [...

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