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Histone H1 interphase phosphorylation pattern becomes largely established during G1/S transition in proliferating cells
Linköping University, Department of Clinical and Experimental Medicine. Linköping University, Faculty of Health Sciences.
Division of Clinical Biochemistry, Biocenter, Innsbruck Medical University, Fritz-Pregl-Strasse 3, A-6020 Innsbruck, Austria.
Linköping University, Faculty of Health Sciences. Linköping University, Department of Medicine and Health Sciences, Clinical Pharmacology .
Linköping University, Faculty of Health Sciences. Linköping University, Department of Clinical and Experimental Medicine, Cellbiology.
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(English)Manuscript (Other academic)
Abstract [en]

Histone H1 is an important constituent of chromatin, and is believed to be involved in regulation of chromatin structure. During the cell cycle, chromatin becomes locally decondensed in S phase, highly condensed during metaphase and again decondensed before re-entry into G1. This has been connected to increasing phosphorylation of H1 histones during the cell cycle. However, many of these experiments have been performed in non-human and human cancer   cell lines, and by the use of cell synchronization techniques and cell cycle-arresting drugs. In this study, we have investigated the H1 subtype composition and phosphorylation pattern in the cell cycle. Exponentially growing normal human activated T cells and Jurkat lymphoblastoid cells were sorted by fluorescence activated cell sorting into G1, S and G2/M populations, without the use of cell cycle arresting drugs. We found that the H1.5 protein level increased after T-cell activation. Our data indicate that serine phosphorylation of H1 subtypes occurred to a large extent in late G1 phase or early S, while some additional serine phosphorylation took place during S, G2 and M phases. Furthermore, our data suggest that the newly synthesized H1 molecules during S phase also achieve a similar phosphorylation pattern as the previous ones. Jurkat cells showed more extended H1.5 phosphorylation in G1 compared with T cells, a difference that can be explained by faster cell growth and/or the presence of enhanced H1 kinase activity in G1 in Jurkat cells. In conclusion, our data is consistent with a model where a major part of interphase H1 serine phosphorylation takes place within a narrow time window during the G1/Stransition. This implies that H1 serine phosphorylation may be coupled to changes in chromatin structure necessary for DNA replication.

National Category
Medical and Health Sciences
URN: urn:nbn:se:liu:diva-16384OAI: diva2:134392
Available from: 2009-01-20 Created: 2009-01-20 Last updated: 2010-01-14Bibliographically approved
In thesis
1. Histone H1: Subtypes and phosphorylation in cell life and death
Open this publication in new window or tab >>Histone H1: Subtypes and phosphorylation in cell life and death
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The genetic information of a human diploid cell is contained within approximately 2 metres of linear DNA. The DNA molecules are compacted and organized in various ways to fit inside the cell nucleus. Various kinds of histones are involved in this compaction. One of these histones, histone H1 is the topic of the present thesis. In addition to its structural role, H1 histones have been implicated in various processes, for example gene regulation and inhibition of chromatin replication.

H1 histones, also termed linker histones, are relatively conserved proteins, and the various subtypes seem to have different and important functions even though redundancy between the subtypes has been demonstrated. Despite the sequence conservation of H1 subtypes, two sequence variations were detected within the H1.2 and H1.4 subtypes using hydrophilic interaction liquid chromatographic separation of H1 proteins from K562 and Raji cell lines in Paper I in the present thesis. The variations were confirmed by genetic analysis, and the H1.2 sequence variation was also found in genomic DNA of normal blood donors, in an allele frequency of 6.8%. The H1.4 sequence variation was concluded to be Raji specific. The significance of H1 microsequence variants is unclear, since the physiological function of H1 histones remains to be established.

H1 histones can be phosphorylated at multiple sites. Changes in H1 phosphorylation has been detected in apoptosis, the cell cycle, gene regulation, mitotic chromatin condensation and malignant transformation. Contradictory data have been obtained on H1 phosphorylation in apoptosis, and many results indicate that H1 dephosphorylation occurs during apoptosis. We and others hypothesized that cell cycle effects by the apoptosis inducers may have affected previous studies. In Paper II, the H1 phosphorylation pattern was investigated in early apoptosis in Jurkat cells, taking cell cycle effects into account. In receptor-mediated apoptosis, apoptosis occurs with a mainly preserved phosphorylation pattern, while Camptothecin induced apoptosis results in rapid dephosphorylation of H1 subtypes, demonstrating that H1 dephosphorylation is not a general event in apoptosis, but may occur upon apoptosis induction via the mitochondrial pathway. The dephosphorylation may also be a result of early cell cycle effects or signalling.Therefore, the H1 phosphorylation pattern in the cell cycle of normal activated T cells was investigated in Paper IV in this thesis. Some studies, which have been made using cancer cell lines from various species and cell synchronization, have indicated a sequential addition of phosphate groupsacross the cell cycle. Normal T cells and cell sorting by flow cytometry were used to circumvent side-effects from cell synchronization. The data demonstrate that a pattern with phosphorylated serines is established in late G1/early S phase, with some additional phosphorylation occurring during S, and further up-phosphorylation seems to occur during mitosis. Malignant transformation may lead to an altered G1 H1 phosphorylation pattern, as was demonstrated using sorted Jurkat T lymphoblastoid cells.

During mitosis, certain H1 subtypes may be relocated to the cytoplasm. In Paper III, the location of histones H1.2, H1.3 and H1.5 during mitosis was investigated. Histone H1.3 was detected in cell nuclei in all mitotic stages, while H1.2 was detected in the nucleus during prophase and telophase, and primarily in the cytoplasm during metaphase and early anaphase. H1.5 was located mostly to chromatin during prophase and telophase, and to both chromatin and cytoplasm during metaphase and anaphase. Phosphorylated H1 was located in chromatin in prophase, and in both chromatin and cytoplasm during metaphase, anaphase and telophase, indicating that the mechanism for a possible H1 subtype relocation to the cytoplasm is phosphorylation.

In conclusion, data obtained during this thesis work suggest that H1 histones and their phosphorylation may participate in the regulation of events in the cell cycle, such as S-phase progression and mitosis, possibly through altered interactions with chromatin, and/or by partial or complete removal of subtypes or phosphorylated variants from chromatin.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2009. 97 p.
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1086
National Category
Cell Biology
urn:nbn:se:liu:diva-15925 (URN)978-91-7393-757-3 (ISBN)
Public defence
2009-01-16, Berzeliussalen, Hälsouniversitetet, Linköpings Universitet, Linköping, 09:00 (English)
Available from: 2009-01-20 Created: 2008-12-16 Last updated: 2009-06-24Bibliographically approved

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Gréen, Anna Gréen, Henrik Lönn, AnitaRundquist, Ingemar
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