Histone H1 Dephosphorylation Is Not a General Feature in Early Apoptosis

Abstract

Histone H1 is a family of nucleosomal proteins that exist in a number of subtypes. These subtypes can be modified after translation in various ways, above all by phosphorylation. Increasing levels of H1 phosphorylation has been correlated with cell cycle progression, while both phosphorylation and dephosphorylation of histone H1 have been linked to the apoptotic process. Such conflicting results may depend on which various apoptosis-inducing agents cause apoptosis via different apoptotic pathways and often interfere with cell proliferation. Therefore, we investigated the relation between apoptosis and H1 phosphorylation in Jurkat cells after apoptosis induction via both the extrinsic and intrinsic pathways and by taking cell cycle effects into account. After apoptosis induction by anti-Fas, no significant dephosphorylation, as measured by capillary electrophoresis, or cell cycle-specific effects were detected. In contrast, H1 subtypes were rapidly dephosphorylated when apoptosis was induced by camptothecin. We conclude that histone H1 dephosphorylation is not connected to apoptosis in general but may be coupled to apoptosis by the intrinsic pathway or to concomitant growth inhibitory signaling.

Histone H1 interphase phosphorylation becomes largely established in G1 or early S phase and differs in G1 between T-lymphoblastoid cells and normal T cells

“…The migration order coincided exactly with previously published data [27], and no other peaks were detected. The relative subtype compositions were then determined by measuring the height of the peaks containing H1.2, H1.3, H1.4 and H1.5 in the electropherograms, and normalizing these to the sum of these peak heights.…”

“…Exponentially growing Jurkat cells displayed a somewhat increased level of H1 phosphorylation (Figure 4B), compared with any T-cell sample. All migration orders coincided exactly with previously published data [27]. The differences between T cells and Jurkat cells were also shown by the H1.5 phosphorylation patterns obtained after RP-HPLC separation prior to HPCE (Figure 4, insets).…”

“…However, some caution should be taken in data interpretation from such T-cell cultures because these cells may be on the way to become apoptotic, even though only viable cells were sorted. We have recently shown that apoptosis may affect the H1 phosphorylation pattern [27]. …”

“…To determine the fraction of apoptotic PBLs in the cell cultures, apoptosis was assessed with Annexin V staining (Annexin V-PE Apoptosis Detection Kit I; BD Biosciences Pharmingen, San Diego, CA, USA) as described previously [27]. …”

“…All runs were performed at constant voltage (12 kV) and at a capillary temperature of 25°C. The peaks in the electropherograms were identified and designated as described previously in detail [27], using the same types of cells.…”