Increased binding and defective migration across fibronectin of cycling hematopoietic progenitor cells

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Abstract
Engraftment of hematopoietic progenitor cells has been shown to decrease during cell cycle transit. We studied cell cycle–associated changes in adhesion and migration of mitotically activated cord blood CD34+ cells. Migration toward medium conditioned by the stromal-derived factor-1–producing cell line MS-5 was studied in bovine serum albumin– and fibronectin (Fn)–coated transwells. Migration was reduced in cycling CD34+ cells and long-term culture-initiating cells (LTC-ICs) compared with their noncycling counterparts across Fn but not across bovine serum albumin. Conversely, Fn binding was higher in cycling CD34+ cells and LTC-ICs compared with noncycling progenitor cells, while adhesion of both subsets to bovine serum albumin was undetectable. The contribution of α4 and α5 integrins in mediating adhesion and migration of activated CD34+ cells onto Fn was analyzed by neutralization experiments. While α4-mediated Fn binding decreased during G2/M, α5 integrin–mediated adhesion increased during transit from G0/G1 to S and G2/M phases. As for migration, the contribution of α4 integrin was similar in all phases, whereas α5-directed migration was lower in G2/M compared with G0/G1and S phases. Defective migration of cycling CD34+ cells was not due to differences in α5 integrin expression. In conclusion, chemotaxis across Fn is less efficient in cycling progenitor cells in correlation with an increased Fn binding capacity. In addition, α4 and α5 integrin functions are independently modulated during cell cycle transit.