Internal tandem duplication of Flt3 modulates chemotaxis and survival of hematopoietic cells by SDF1α but negatively regulates marrow homing in vivo

Objective. We have previously shown that Flt3 ligand (FL)/Flt3 signaling regulates hematopoietic cell migration by modulating the SDF1 alpha/CXCR4 signaling pathway. Herein, we evaluated whether a functional interaction between SDF1 alpha/CXCR4 signaling and internal tandem duplication (ITD) of F1t3 regulates aberrant hematopoietic survival. We also investigated molecular mechanisms responsible for enhanced migration to SDF1 alpha as a result of ITD-Flt3 expression and whether ITD-Flt3 regulates hematopoietic cell trafficking. Methods. Hematopoietic progenitor cell survival was determined using marrow cells retrovirally expressing ITD-Flt3 and stimulated with SDF1 alpha. Migration, to SDF1 alpha adhesion to vascular cell adhesion molecule-1, and in vivo homing were determined using Ba/F3 cells expressing ITD-Flt3 and transfected with dominant negative (DN) H-Ras. Results. Addition of SDF1 alpha significantly increased growth factor-independent proliferation of colony-forming unit granulocyte-macrophage induced by ITD-Flt3. Although a negative gradient of SDF1a inhibited migration regardless of the stimulation, a positive gradient of FL or ITD-Flt3 significantly increased cell migration even in the presence of a negative SDF1 alpha gradient. Enhanced migration induced by ITD-Flt3 was inhibited by DN-H-Ras, whereas overexpression of a constitutive active form of H-Ras in wild-type Flt3-Ba/F3 cells significantly elevated migration to SI)Floc. Despite enhanced migration to SDF1 alpha, preincubation with FL or ITD-Flt3 overexpression significantly reduced homing of primary mouse bone marrow cells or Ba/F3 cells to bone marrow that was associated with significant reduction in adhesion to vascular cell adhesion molecule-1 and VLA4 expression. Conclusion. Our results suggest that functional interactions between Flt3 and SDF1 alpha/CXCR4 regulate oncogenic proliferation and migration of hematopoietic cells, which is mediated by Ras, and that Flt3 signaling regulates hematopoietic cell trafficking in vivo. (c) 2006 International Society for Experimental Hematology. Published by Elsevier Inc.