Protein phosphatase 2A controls the activity of histone deacetylase 7 during T cell apoptosis and angiogenesis

Abstract

Class IIa histone deacetylases (HDACs) act as key transcriptional regulators in several important developmental programs. Their activities are controlled via phosphorylation-dependent nucleocytoplasmic shuttling. Phosphorylation of conserved serine residues triggers association with 14-3-3 proteins and cytoplasmic relocalization of class IIa HDACs, which leads to the derepression of their target genes. Although a lot of effort has been made toward the identification of the inactivating kinases that phosphorylate class IIa HDAC 14-3-3 motifs, the existence of an antagonistic protein phosphatase remains elusive. Here we identify PP2A as a phosphatase responsible for dephosphorylating the 14-3-3 binding sites in class IIa HDACs. Interestingly, dephosphorylation of class IIa HDACs by PP2A is prevented by competitive association of 14-3-3 proteins. Using both okadaic acid treatment and RNA interference, we demonstrate that PP2A constitutively dephosphorylates the class IIa member HDAC7 to control its biological functions as a regulator of T cell apoptosis and endothelial cell functions. This study unravels a dynamic interplay among 14-3-3s, protein kinases, and PP2A and provides a model for the regulation of class IIa HDACs.chromatin ͉ shuttling ͉ endothelial cells ͉ thymocytes ͉ 14-3-3 D eacetylation of histones by histone deacetylases (HDACs) results in a compact chromatin structure that imposes specific restrictions on the transcriptional machinery. Based on structural and biochemical characteristics, the 18 human HDACs fall into four distinct classes, with members of the class II further divided into two subclasses, IIa and IIb (1). Class IIa HDACs (HDAC4, -5, -7, and -9) are regulated by phosphorylation-dependent nuclear export. Several canonical binding motifs for 14-3-3 proteins are found in the N-terminal adapter domain of all class IIa HDAC members. When phosphorylated on specific serine residues, these consensus motifs recruit 14-3-3 proteins. Association with 14-3-3 overcomes the repressor activity of class IIa HDACs by eliciting their sequestration in the cytoplasm and making them unavailable for their cognate transcription factors and corepressors.Class IIa HDACs act as transcriptional modulators of specific genetic programs associated with several important developmental processes (1). In humans, HDAC7 is transiently and predominantly expressed in CD4/CD8 double positive thymocytes, where it represses the expression of nur77, a proapoptotic gene involved in negative selection (2). Recently, in situ hybridization unraveled expression of HDAC7 in the vascular endothelium of the developing mouse embryo. Consistent with this, inactivation of the HDAC7 gene led to embryonic lethality resulting from blood vessel dilatations, rupture, and hemorrhages. The vascular defects associated with HDAC7 deficiency were attributed to the up-regulation of matrix metalloproteinase 10 (MMP-10), a secreted proteinase that degrades the extracellular matrix (3).Modulation of class IIa HDAC subcellular distribution by phosphory...

LB100, a small molecule inhibitor of PP2A with potent chemo- and radio-sensitizing potential

“…[120][121][122][123] These results were recently corroborated in a pancreatic cancer model, in which increased intratumoral doxorubicin levels was found in tumors with LB100 pre-treatment. 124 Notably, this study also demonstrated that LB100 induced upregulation of hypoxia-inducible factor-1a (HIF-1a) expression, which correlated with elevated VEGF levels.…”

Dephosphorylation at a Conserved SP Motif Governs cAMP Sensitivity and Nuclear Localization of Class IIa Histone Deacetylases*

“…As for phosphatases, PP2A forms stable complexes with class IIa HDACs and inhibits their phosphorylation at 14-3-3 binding sites (10,35,36,79). Okadaic acid, an inhibitor of PP2A, did not have any effect on Ser-266 phosphorylation in response to cAMP treatment (supplemental Fig.…”

“…an increase in intracellular [Ca 2ϩ ] (32,33) and VEGF treatment (11,34)) induce class IIa HDAC phosphorylation and nuclear export, leading to derepression of MEF2-dependent transcription. In contrast, dephosphorylation of these serine residues by phosphatases, such as protein phosphatase 2A (PP2A) and myosin phosphatase (PP1␤/MYPT1), promotes nuclear localization of class IIa HDACs and repression of MEF2-dependent transcription (10,(35)(36)(37). An important issue is how various cellular stimuli act through these kinases and phosphatases to link class IIa HDAC regulation to cellular signaling networks.…”

Post-translational Modifications Regulate Class IIa Histone Deacetylase (HDAC) Function in Health and Disease

“…Furthermore, the ability of a diverse set of kinases to regulate the same sites may reflect an evolutionary flexibility that allows differential modulation of critical functional sites. Interestingly, dephosphorylation of the four 14 -3-3 binding sites in HDAC7 is mediated by PP2A, which shows no preference for one site over the others (85). Although the precise sites of action remain unknown, protein phosphatase 1␤ and myosin phosphatase targeting subunit 1 promote nuclear accumulation of HDAC7 (86).…”