Constitutive and functional expression of YB-1 in microglial cells

Neuroscience. 2015 Aug 20;301:439-53. doi: 10.1016/j.neuroscience.2015.06.023. Epub 2015 Jun 20.

Abstract

Y-box-binding protein (YB-1) is a member of the cold-shock protein family and participates in a wide variety of DNA/RNA-dependent cellular processes including DNA repair, transcription, mRNA splicing, packaging, and translation. At the cellular level, YB-1 is involved in cell proliferation and differentiation, stress responses, and malignant cell transformation. A general role for YB-1 during inflammation has also been well described; however, there are minimal data concerning YB-1 expression in microglia, which are the immune cells of the brain. Therefore, we studied the expression of YB-1 in a clinically relevant global ischemia model for neurological injury following cardiac arrest. This model is characterized by massive neurodegeneration of the hippocampal CA1 region and the subsequent long-lasting activation of microglia. In addition, we studied YB-1 expression in BV-2 cells, which are an accepted microglia culture model. BV-2 cells were stressed by oxygen/glucose deprivation (OGD), OGD-relevant mediators, lipopolysaccharide (LPS), and phagocytosis-inducing cell debris and nanoparticles. Using quantitative polymerase chain reaction (PCR), we show constitutive expression of YB-1 transcripts in unstressed BV-2 cells. The functional upregulation of the YB-1 protein was demonstrated in microglia in vivo and in BV-2 cells in vitro. All stressors except for LPS were potent enhancers of the level of YB-1 protein, which appears to be regulated primarily by proteasomal degradation and, to a lesser extent, by the activation (phosphorylation) of the translation initiation factor eIF4E. The proteasome of BV-2 cells is impaired by OGD, which results in decreased protein degradation and therefore increased levels of YB-1 protein. LPS induces proteasome activity, which enables the level of YB-1 protein to remain at control levels despite enhanced protein ubiquitination. The proteasome inhibitor MG-132 was able to increase YB-1 protein levels in control and LPS-treated cultures. YB-1 upregulation was not accompanied by its translocation from the cytoplasm to the nucleus. YB-1 induction appeared to be related to microglial proliferation because it was partially co-regulated with Ki67. In addition, YB-1 protein levels correlated with microglia phagocytic activity because its upregulation could also be induced by inert NPs.

Keywords: BV-2 cells; YB-1; hippocampus; microglia; neurodegeneration; rat cardiac arrest model.

MeSH terms

  • Animals
  • Asphyxia / complications
  • Calcium-Binding Proteins / genetics
  • Calcium-Binding Proteins / metabolism
  • Cell Line, Transformed
  • Disease Models, Animal
  • Eukaryotic Initiation Factor-4E / genetics
  • Eukaryotic Initiation Factor-4E / metabolism
  • Gene Expression Regulation / drug effects
  • Gene Expression Regulation / physiology*
  • Glial Fibrillary Acidic Protein / genetics
  • Glial Fibrillary Acidic Protein / metabolism
  • Glucose / deficiency
  • Green Fluorescent Proteins / genetics
  • Green Fluorescent Proteins / metabolism
  • Heart Arrest / etiology
  • Heart Arrest / pathology*
  • Ki-67 Antigen / metabolism
  • Lipopolysaccharides / pharmacology
  • Male
  • Microfilament Proteins / genetics
  • Microfilament Proteins / metabolism
  • Microglia / drug effects
  • Microglia / metabolism*
  • Nerve Tissue Proteins / metabolism
  • Oxygen / metabolism
  • Proteasome Endopeptidase Complex / metabolism
  • RNA, Messenger / metabolism
  • Rats
  • Rats, Wistar
  • Y-Box-Binding Protein 1 / genetics
  • Y-Box-Binding Protein 1 / metabolism*

Substances

  • Aif1 protein, rat
  • Calcium-Binding Proteins
  • Eukaryotic Initiation Factor-4E
  • Glial Fibrillary Acidic Protein
  • Ki-67 Antigen
  • Lipopolysaccharides
  • Microfilament Proteins
  • Nerve Tissue Proteins
  • RNA, Messenger
  • Y-Box-Binding Protein 1
  • Green Fluorescent Proteins
  • Proteasome Endopeptidase Complex
  • Glucose
  • Oxygen