The urokinase receptor in hematopoietic stem cells mobilization.

The receptor for urokinase plasminogen activator (uPAR) is required in hematopoietic stem/progenitor cells (HSC, HPC) mobilization in the mouse. Indeed, uPAR Ko mice are deficient both in retention and mobilization of HSC and HPC, because uPAR causes their retention in the BM through its interaction with the α4β1 integrin and at the same time its removal promotes their migration. Normally, the membrane signal is cleaved by plasmin which on one side releases the cells from their osteoblasts interaction and on the other produces a cleaved soluble uPAR product that stimulates mobilization. Available data suggest that a similar mechanism may take place in humans.