| Summary: | <p>Abstract</p> <p>Background</p> <p>Histone H1 is an important constituent of chromatin, and is involved in regulation of its structure. During the cell cycle, chromatin becomes locally decondensed in S phase, highly condensed during metaphase, and again decondensed before re-entry into G<sub>1</sub>. This has been connected to increasing phosphorylation of H1 histones through the cell cycle. However, many of these experiments have been performed using cell-synchronization techniques and cell cycle-arresting drugs. In this study, we investigated the H1 subtype composition and phosphorylation pattern in the cell cycle of normal human activated T cells and Jurkat T-lymphoblastoid cells by capillary electrophoresis after sorting of exponentially growing cells into G<sub>1</sub>, S and G<sub>2</sub>/M populations.</p> <p>Results</p> <p>We found that the relative amount of H1.5 protein increased significantly after T-cell activation. Serine phosphorylation of H1 subtypes occurred to a large extent in late G<sub>1 </sub>or early S phase in both activated T cells and Jurkat cells. Furthermore, our data confirm that the H1 molecules newly synthesized during S phase achieve a similar phosphorylation pattern to the previous ones. Jurkat cells had more extended H1.5 phosphorylation in G<sub>1 </sub>compared with T cells, a difference that can be explained by faster cell growth and/or the presence of enhanced H1 kinase activity in G<sub>1 </sub>in Jurkat cells.</p> <p>Conclusion</p> <p>Our data are consistent with a model in which a major part of interphase H1 phosphorylation takes place in G<sub>1 </sub>or early S phase. This implies that H1 serine phosphorylation may be coupled to changes in chromatin structure necessary for DNA replication. In addition, the increased H1 phosphorylation of malignant cells in G<sub>1 </sub>may be affecting the G<sub>1</sub>/S transition control and enabling facilitated S-phase entry as a result of relaxed chromatin condensation. Furthermore, increased H1.5 expression may be coupled to the proliferative capacity of growth-stimulated T cells.</p>
|
|---|
