S1P1 overexpression stimulates S1P-dependent chemotaxis of human CD34+ hematopoietic progenitor cells but strongly inhibits SDF-1/CXCR4-dependent migration and in vivo homing

The CXC chemokine receptor 4 (CXCR4) and its ligand stromal derived factor 1 (SDF-1) regulate egress and homing of hematopoietic stem cells. Activation of sphingosine-1-phosphate (S1P) receptors (S1P1–5) modulates chemokine-induced migration of lymphocytes and hematopoietic stem cells. To analyze the influence of S1P1 on SDF-1-dependent chemotaxis and trafficking, we overexpressed S1P1 in CD34+ mobilized peripheral blood progenitor cells (PBPCs). Using a gamma-retroviral vector, transgene overexpression was achieved in more than 90% of target cells. S1P1 transgene positive PBPCs showed enhanced chemotaxis towards S1P. S1P1 overexpression resulted in reduced CXCR4 surface expression levels and strong inhibition of SDF-1-dependent ERK1/2 phosphorylation and Ca2+ flux. Furthermore, SDF-1-dependent migration of S1P1 overexpressing PBPCs or Jurkat cells was reduced up to 10-fold. Sublethally irradiated NOD/SCID mice were transplanted with 6-day cultured PBPCs overexpressing either S1P1-IRES-GFP or GFP alone. Screening for GFP positive human cells in the mouse bone marrow 20 h after transplantation revealed an eightfold reduction in bone marrow homing of S1P1 transgene expressing cells. Our data suggest that S1P1 acts as an inhibitor of CXCR4-dependent migration of hematopoietic cells to sites of SDF-1 production.