MT1-MMP association with membrane lipid rafts facilitates G-CSF-induced hematopoietic stem/progenitor cell mobilization

Objective. Soluble matrix metalloproteinases (MMI's) facilitate the egress of hematopoietic stem/progenitor cells (HSPC) from the hone marrow (BM) during granulocyte colony-stimulating factor (G-CSF) induced mobilization. Because membrane-type (MT)I-MMP, which is localized on the leading edge of migrating cells, activates the latent forms of soluble MMPs. we investigated its role in HSPC mobilization. Materials and Methods. We examined the effect of G-CSF on the expression of MTI-MMP and its activities (proMMP-2 activation and migration) in hematopoietic cells. We also investigated the subcellular localization of MTI-MMP and the signaling pathways that regulate its expression and function in hematopoietic cells after exposure to G-CSF. Results. We found that G-CSF increases MTI-MMP transcription and protein synthesis in hematopoietic cells; proMMP-2 activation in cocultures of HSPC with BM fibroblasts; chemoinvasion across reconstituted basement membrane Matrigel toward a stromal cell derived factor-1 gradient, which is reduced by small interfering RNA silencing of MTI-MMP; and localization of MTI-MMP to membrane lipid rafts through a mechanism that is regulated by the phosphatidylinositol 3-kinase signaling pathway. Disruption of ran formation (by the cholesterol-sequestering agent methyl-beta-cyclodextrin) abrogated phosphatidylinositol 3-kinase phosphorylation and MTI-MMP incorporation into lipid rafts resulting in reduced proMMP-2 activation and HSPC migration. Conclusion. G-CSF induced upregulation of MTI-MMP in hematopoietic cells and its enhanced incorporation into membrane lipid rafts contributes to proMMP-2 activation, which facilitates mobilization of HSPC. (C) 2010 ISEH - Society for Hematology and Stem Cells. Published by Elsevier Inc.