The cytosolic protein G0S2 maintains quiescence in hematopoietic stem cells

PLoS One. 2012;7(5):e38280. doi: 10.1371/journal.pone.0038280. Epub 2012 May 31.

Abstract

Bone marrow hematopoietic stem cells (HSCs) balance proliferation and differentiation by integrating complex transcriptional and post-translational mechanisms regulated by cell intrinsic and extrinsic factors. We found that transcripts of G(0)/G(1) switch gene 2 (G0S2) are enriched in lineage(-) Sca-1(+) c-kit(+) (LSK) CD150(+) CD48(-) CD41(-) cells, a population highly enriched for quiescent HSCs, whereas G0S2 expression is suppressed in dividing LSK CD150(+) CD48(-) cells. Gain-of-function analyses using retroviral expression vectors in bone marrow cells showed that G0S2 localizes to the mitochondria, endoplasmic reticulum, and early endosomes in hematopoietic cells. Co-transplantation of bone marrow cells transduced with the control or G0S2 retrovirus led to increased chimerism of G0S2-overexpressing cells in femurs, although their contribution to the blood was reduced. This finding was correlated with increased quiescence in G0S2-overexpressing HSCs (LSK CD150(+) CD48(-)) and progenitor cells (LS(-)K). Conversely, silencing of endogenous G0S2 expression in bone marrow cells increased blood chimerism upon transplantation and promoted HSC cell division, supporting an inhibitory role for G0S2 in HSC proliferation. A proteomic study revealed that the hydrophobic domain of G0S2 interacts with a domain of nucleolin that is rich in arginine-glycine-glycine repeats, which results in the retention of nucleolin in the cytosol. We showed that this cytosolic retention of nucleolin occurs in resting, but not proliferating, wild-type LSK CD150(+) CD48(-) cells. Collectively, we propose a novel model of HSC quiescence in which elevated G0S2 expression can sequester nucleolin in the cytosol, precluding its pro-proliferation functions in the nucleolus.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Blood Cells / metabolism
  • Cell Cycle Proteins / chemistry
  • Cell Cycle Proteins / genetics
  • Cell Cycle Proteins / metabolism*
  • Cell Cycle*
  • Cytosol / metabolism*
  • Gene Expression Regulation
  • HEK293 Cells
  • Hematopoietic Stem Cells / cytology*
  • Hematopoietic Stem Cells / metabolism*
  • Humans
  • Hydrophobic and Hydrophilic Interactions
  • Mice
  • NIH 3T3 Cells
  • Phosphoproteins / metabolism
  • Protein Structure, Tertiary
  • RNA-Binding Proteins / metabolism
  • Ribonucleoproteins / metabolism

Substances

  • Cell Cycle Proteins
  • G0S2 protein, mouse
  • Phosphoproteins
  • RNA-Binding Proteins
  • Ribonucleoproteins
  • nucleolin