Reciprocal epigenetic modification of histone H2B occurs in chromatin during apoptosis in vitro and in vivo.

Histone H2B phosphorylation at Serine 14 (phosS14) has been proposed as an epigenetic marker of apoptotic cells, whereas acetylation at the adjacent Lysine 15 (acK15) is a property of non-dying cells. We investigated the relationship and the potential regulatory mechanisms between these two epigenetic histone modifications and internucleosomal DNA degradation during apoptosis. Using rat primary thymocytes induced to undergo apoptosis with glucocorticoids we found that H2B phosphorylated at Ser14 was associated with soluble, cleaved DNA in apoptotic nuclei.

An endogenous calcium-dependent, caspase-independent intranuclear degradation pathway in thymocyte nuclei: antagonism by physiological concentrations of K(+) ions.

Calcium ions have been implicated in apoptosis for many years, however the precise role of this ion in the cell death process remains incomplete. We have extensively examined the role of Ca(2+) on nuclear degradation in vitro using highly purified nuclei isolated from non-apoptotic rat thymocytes. We show that these nuclei are devoid of CAD (caspase-activated DNase), and DNA degradation occurs independent of caspase activity.

Isolation and characterization of mammalian cells that are undergoing apoptosis by a bovine serum albumin density gradient.

When cells are treated with cytotoxic agents, they enter apoptosis asynchronously to yield cells at various stages of cellular deterioration. This mixture makes it difficult to study the biochemical pathways leading to cell death. We have fractionated apoptotic mammalian cells in a simple discontinuous bovine serum albumin (BSA) density gradient centrifugation into five layers, each containing cells at different stages of apoptosis, (1) nonapoptotic, (2) undergoing apoptosis, and (3) mature apoptotic cells, as judged by light and electron microscopy of chromatin condensation and by the extent of DNA fragmentation.

Apoptotic phosphorylation of histone H2B is mediated by mammalian sterile twenty kinase.

DNA in eukaryotic cells is associated with histone proteins; hence, hallmark properties of apoptosis, such as chromatin condensation, may be regulated by posttranslational histone modifications. Here we report that phosphorylation of histone H2B at serine 14 (S14) correlates with cells undergoing programmed cell death in vertebrates. We identify a 34 kDa apoptosis-induced H2B kinase as caspase-cleaved Mst1 (mammalian sterile twenty) kinase.