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MT1-MMP and RECK are involved in human CD34+ progenitor cell retention, egress, and mobilization.

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Abstract
The mechanisms governing hematopoietic progenitor cell mobilization are not fully understood. We report higher membrane type 1–MMP (MT1-MMP) and lower expression of the MT1-MMP inhibitor, reversion-inducing cysteine-rich protein with Kazal motifs (RECK), on isolated circulating human CD34+ progenitor cells compared with immature BM cells. The expression of MT1-MMP correlated with clinical mobilization of CD34+ cells in healthy donors and patients with lymphoid malignancies. Treatment with G-CSF further increased MT1-MMP and decreased RECK expression in human and murine hematopoietic cells in a PI3K/Akt-dependent manner, resulting in elevated MT1-MMP activity. Blocking MT1-MMP function by Abs or siRNAs impaired chemotaxis and homing of G-CSF–mobilized human CD34+ progenitors. The mobilization of immature and maturing human progenitors in chimeric NOD/SCID mice by G-CSF was inhibited by anti–MT1-MMP treatment, while RECK neutralization promoted motility and egress of BM CD34+ cells. BM c-kit+ cells from MT1-MMP–deficient mice also exhibited inferior chemotaxis, reduced homing and engraftment capacities, and impaired G-CSF–induced mobilization in murine chimeras. Membranal CD44 cleavage by MT1-MMP was enhanced following G-CSF treatment, reducing CD34+ cell adhesion. Accordingly, CD44-deficient mice had a higher frequency of circulating progenitors. Our results reveal that the motility, adhesion, homing, and mobilization of human hematopoietic progenitor cells are regulated in a cell-autonomous manner by dynamic and opposite changes in MT1-MMP and RECK expression.
 
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