Lnk negatively regulates self-renewal of hematopoietic stem cells by modifying thrombopoietin-mediated signal transduction

Proc Natl Acad Sci U S A. 2007 Feb 13;104(7):2349-54. doi: 10.1073/pnas.0606238104. Epub 2007 Feb 6.

Abstract

One of the central tasks of stem cell biology is to understand the molecular mechanisms that control self-renewal in stem cells. Several cytokines are implicated as crucial regulators of hematopoietic stem cells (HSCs), but little is known about intracellular signaling for HSC self-renewal. To address this issue, we attempted to clarify how self-renewal potential is enhanced in HSCs without the adaptor molecule Lnk, as in Lnk-deficient mice HSCs are expanded in number >10-fold because of their increased self-renewal potential. We show that Lnk negatively regulates self-renewal of HSCs by modifying thrombopoietin (TPO)-mediated signal transduction. Single-cell cultures showed that Lnk-deficient HSCs are hypersensitive to TPO. Competitive repopulation revealed that long-term repopulating activity increases in Lnk-deficient HSCs, but not in WT HSCs, when these cells are cultured in the presence of TPO with or without stem cell factor. Single-cell transplantation of each of the paired daughter cells indicated that a combination of stem cell factor and TPO efficiently induces symmetrical self-renewal division in Lnk-deficient HSCs but not in WT HSCs. Newly developed single-cell immunostaining demonstrated significant enhancement of both p38 MAPK inactivation and STAT5 and Akt activation in Lnk-deficient HSCs after stimulation with TPO. Our results suggest that a balance in positive and negative signals downstream from the TPO signal plays a role in the regulation of the probability of self-renewal in HSCs. In general, likewise, the fate of stem cells may be determined by combinational changes in multiple signal transduction pathways.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cell Division / drug effects*
  • Cells, Cultured
  • Cytokines
  • Hematopoietic Stem Cells / cytology*
  • Intracellular Signaling Peptides and Proteins / metabolism
  • Membrane Proteins
  • Mice
  • Mice, Knockout
  • Phosphorylation
  • Protein Kinases / metabolism
  • Proteins / genetics
  • Proteins / physiology*
  • Signal Transduction*
  • Thrombopoietin / pharmacology*

Substances

  • Cytokines
  • Intracellular Signaling Peptides and Proteins
  • Lnk protein, mouse
  • Membrane Proteins
  • Proteins
  • Thrombopoietin
  • Protein Kinases