Increases in intracellular calcium dephosphorylate histone H3 at serine 10 in human hepatoma cells: Potential role of protein phosphatase 2A–protein kinase CβII complex

Abstract

We present evidence that increases in intracellular calcium, induced by treatment with calcium ionophore A23187 or the endoplasmic reticulum calcium-ATPase inhibitor thapsigargin, dephosphorylated histone H3 at serine10 (histone H3-Ser10) in a dose-dependent manner in human hepatoma HepG2 cells. Inhibition of p42/44MAPK, pp90RSK, or p38MAPK did not affect the ability of A23187 to dephosphorylate histone H3-Ser10. This response is significantly blocked by okadaic acid, indicating a requirement for protein phosphatase 2A (PP2A). A23187 increased the activity of PP2A towards phosphorylated histone H3-Ser10. Furthermore, pretreatment with calphostin C, a selective protein kinase C (PKC) inhibitor, blocked A23187-dependent dephosphorylation of histone H3-Ser10, and coimmunoprecipitation analysis showed PP2A association with the PKCbetaII isoform. Unlike untreated cells, coimmunoprecipitated complex from A23187-treated cells showed greater dephosphorylation of histone H3-Ser10 in a PP2A-dependent manner. Inhibition of PP2A increased phosphorylation at Ser660 that determines calcium sensitivity and activity of PKCbetaII isoform, thus supporting a role for intracomplex regulation. Finally, chromatin immunoprecipitation assays following exposure to A23187 and okadaic acid revealed regulatory role of histone H3-Ser10 phosphorylation in selective gene induction. Altogether, our findings suggest a novel role for calcium in modulating histone H3-Ser10 phosphorylation level and led us to propose a model emphasizing PP2A activation, occurring downstream following perturbations in calcium homeostasis, as key event in dephosphorylating histone H3-Ser10 in mammalian cells.

Histone modifications induced by a family of bacterial toxins

“…However, the precise role of this modification in transcription is not fully understood. It has been suggested that, in a mechanism similar to histone acetylation, where both acetyltransferases and deacetyltransferases interact with components of the transcription machinery, specific protein kinases and phosphatases might link phosphoSer 10 H3 to transcriptional regulation (26,28). Our ChIP results indicate that a decrease in phospho-Ser 10 H3 correlates with a decrease in acH4 and down-regulation of basal transcription of specific genes, whereas an increase correlates with an increase in acetyated H4 and transcriptional activation.…”

The use of okadaic acid to elucidate the intracellular role(s) of protein phosphatase 2A: Lessons from the mast cell model system

“…OA-mediated inhibition of PP2A, one of the mammalian cell's most important serine/ threonine phosphatases, has provided new insights into the complex role(s) of this signaling molecule in mast cells, as well as other cell systems [72][73][74][75]. The mast cell, because of its ability to react with different responses, at different times, to different stimuli, has proven to be a useful model system in which to clarify the functions of PP2A in regulating both classical signal transduction cascades and granule exocytosis.…”

Histone H3 phosphorylation at serine 10 and serine 28 is mediated by p38 MAPK in rat hepatocytes exposed to ethanol and acetaldehyde⁎

“…The phosphorylation of histone H3 decreased at 4 h after ethanol treatment. This decrease in H3 phosphorylation may be due to transient activation of protein kinase C (PKC) since PKC activates H3 phosphatase in human hepatoma cells (Huang et al, 2005) and ethanol has been shown to activate PKC in rat hepatocytes (Domenicotti et al, 1998). The phosphorylation of p38 MAPK and phosphorylation of histone H3 by acetaldehyde were transient compared to persistent activation by ethanol.…”