The catalytic subunit of protein phosphatase 2A (PP2Ac) promotes DNA hypomethylation by suppressing the phosphorylated mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK) kinase (MEK)/phosphorylated ERK/DNMT1 protein pathway in T-cells from controls and systemic lupus erythematosus patients

J Biol Chem. 2013 Jul 26;288(30):21936-44. doi: 10.1074/jbc.M113.467266. Epub 2013 Jun 17.

Abstract

DNA hypomethylation is a characteristic feature of systemic lupus erythematosus (SLE) immune cells. Numerous reports have implicated the involvement of the MEK/ERK pathway in the reduction of DNA methyltransferase (DNMT) expression, hence inducing the transcription of methylation-sensitive genes in SLE patients. However, the molecular mechanisms involved remain unclear. Here, we investigated whether the catalytic subunit of protein phosphatase 2A (PP2Ac), which is overexpressed in SLE T-cells, contributes to reduced DNA methylation. We show that both chemical suppression and siRNA silencing of PP2Ac in T-cells resulted in sustained phosphorylation of MEK and ERK following stimulation with phorbol 12-myristate 13-acetate and ionomycin. Furthermore, PP2Ac suppression resulted in increased DNMT enzyme activity, DNA hypermethylation, and decreased expression of methylation-sensitive genes. Similarly, in SLE T-cells, suppression of PP2Ac resulted in increased MEK/ERK phosphorylation, enhanced DNMT1 expression and suppressed expression of the methylation-sensitive CD70 gene. Our results demonstrate that PP2A regulates DNA methylation by influencing the phosphorylation of MEK/ERK. We propose that enhanced PP2Ac in SLE T-cells may dephosphorylate and activate the signaling pathway upstream of DNMT1, thus disturbing the tight control of methylation-sensitive genes, which are involved in SLE pathogenesis.

Keywords: DNA Methylation; ERK; Epigenetics; Protein Phosphatase; SLE; T-cell.

MeSH terms

  • Adult
  • CD27 Ligand / genetics
  • CD27 Ligand / metabolism
  • Cells, Cultured
  • DNA (Cytosine-5-)-Methyltransferase 1
  • DNA (Cytosine-5-)-Methyltransferases / genetics
  • DNA (Cytosine-5-)-Methyltransferases / metabolism*
  • DNA Methylation
  • Extracellular Signal-Regulated MAP Kinases / metabolism*
  • Female
  • Gene Expression
  • Humans
  • Immunoblotting
  • Ionomycin / pharmacology
  • Lupus Erythematosus, Systemic / genetics
  • Lupus Erythematosus, Systemic / immunology
  • Lupus Erythematosus, Systemic / metabolism*
  • Middle Aged
  • Mitogen-Activated Protein Kinases / metabolism*
  • Phosphorylation
  • Protein Phosphatase 2 / genetics
  • Protein Phosphatase 2 / metabolism*
  • RNA Interference
  • Reverse Transcriptase Polymerase Chain Reaction
  • Signal Transduction / drug effects
  • T-Lymphocytes / drug effects
  • T-Lymphocytes / immunology
  • T-Lymphocytes / metabolism*
  • Tetradecanoylphorbol Acetate / pharmacology
  • Young Adult

Substances

  • CD27 Ligand
  • CD70 protein, human
  • Ionomycin
  • DNA (Cytosine-5-)-Methyltransferase 1
  • DNA (Cytosine-5-)-Methyltransferases
  • DNMT1 protein, human
  • Extracellular Signal-Regulated MAP Kinases
  • Mitogen-Activated Protein Kinases
  • PPP2CA protein, human
  • Protein Phosphatase 2
  • Tetradecanoylphorbol Acetate