Fibronectin increases the migration induced by stromal cell-derived factor-1 alpha (SDF-1 alpha) in pre-B acute lymphoblastic leukemia cells

The chemokine, stromal cell-derived factor-1 alpha (SDF-1 alpha) and its receptor CXCR-4 (fusin, LESTR) are thought to be involved in the trafficking of hematopoietic progenitors and stem cells, as suggested by the chemotactic effect of SDF-1 alpha on these cells. Gene inactivation studies have shown that both SDF-1 alpha and CXCR-4 are essential for B lymphopoiesis. Migration of leukemic cells may also be dependent on SDF-1 alpha and CXCR-4. Fibronectin (FN) is a component of the extracellular matrix (ECM), and one of the natural supports for cell movement in their bone hematopoietic environment. In the present study, we examined the influence of FN on the chemotactic effect of SDF-1 alpha and on the CXCR-4 expression and function on human precursor-B acute lymphoblastic leukemia (pre-B ALL) cells at sequential stages of development. Fourteen children with pre-B ALL were studied. Their immunophenotypes belonged to the first three stages of B cell differentiation. Despite relatively high levels of CXCR-4 expression at all stages, the responsiveness to SDF-1 alpha, measured as the percentage of migrating cells in the transwell culture system, varied with patients and seems to be less significant for pre-B3 (and pre-B1) than for pre-B2. There was no correlation (r = 0.2) between the SDF-1 alpha induced migration (range: 2.5-39%) and the cell surface density of CXCR-4 (range: 46.5-97.5%). The extracellular matrix protein FN, either coated on the filter (for more than 18 hours) or in soluble form, enhanced the SDF-1 alpha induced migration of pre-B ALL respectively (2 fold and 1.6 fold) without influencing CXCR-4 expression in short term cultures. Therefore, we analyzed the expression of the FN receptors, VLA-4 (CD49d) and VLA-5 (CD49e), by direct immunofluorescence, on these leukemic cells. VLA-4 was strongly expressed in all stages of pre-B ALL (range: 77-97%) while VLA-5 expression was more variable (range: 14-94%), but no correlation with the FN-dependent increased SDF-1 alpha chemotactic effect was noted. In conclusion, the migratory behavior of pre-B leukemic cells in response to SDF-1 alpha partly depends upon the stage of differentiation, and partly upon unexplained patient variability. Our results suggest that several molecules from the extracellular matrix, such as FN, may be implicated in this phenomenon.