INTERLEUKIN-3 AND FLT3-LIGAND INDUCE ADHESION OF BAF3 FLT3 PRECURSOR B-LYMPHOID CELLS TO FIBRONECTIN VIA ACTIVATION OF VLA-4 AND VLA-5/

Adhesion of hematopoietic cells to extracellular matrix components is important for blood cell development. However, little is known regardi ng the potential influence of IL-3 on this process for precursor B cel ls and Flt3-ligand has not yet been implicated in induction of adhesio n of any blood cell types to extracellular matrix components, Therefor e, we examined the characteristics of cytokine-induced cell adhesion t o fibronectin (FN), using as a model the murine precursor B cell line, Baf3, a factor-dependent cell line requiring IL-3 for both growth and survival, Since factor-dependent hematopoietic cell lines expressing Flt3 receptor are extremely rare, we also studied Baf3/Flt3, a subline of Baf3 transduced with the Flt3 receptor gene. IL-3 induced adhesion of Baf3 and Baf3/Flt3 cells to FN, while Flt3-ligand induced adhesion of Baf3/Flt3 cells only. Whereas both :Baf3 and Baf3/Flt3 cells expre ssed VLA-4 and -5 integrins as FN receptors, expression levels of VLA- 4 and -5 were not affected by IL-3 or Flt3-ligand treatment, However, blocking experiments using anti-integrin antibodies showed that cytoki ne-induced adhesion of cells depended on both VLA-4 and -5 suggesting that IL-3 and Flt3-ligand activated these integrins. PI-3 kinase inhib itor wortmannin, PKC inhibitor H-7, or PKA inhibitor HA1004 did not su ppress adhesion induced by IL-3 or Flt3-ligand; in contrast, PLC inhib itor U-73122 did suppress adhesion, suggesting the possibility that PL C, but not PI-3 kinase, PKC, or PKA, may be involved in this process. Since it is known that IL-3 and Flt3-ligand receptors are expressed on precursor B cells, and these receptors are downregulated during B cel l maturation of primary cells, the induction of precursor B cell adhes ion to FN by IL-3 and Flt3-ligand may contribute a mechanism by which precursor B cells adhere to bone marrow stroma, thereby influencing th eir development. (C) 1998 Academic Press.