Interaction between alpha(5)beta(1) integrin and secreted fibronectin is involved in macrophage differentiation of human HL-60 myeloid leukemia cells

We examined the role of fibronectin (FN) and FN-binding integrins in macrop hage differentiation. Increased FN and alpha(5)beta(1) integrin gene expres sion was observed in phorbol 12-myristate 13-acetate PMA-treated HL-60 cell s and PMA- or macrophage-CSF-treated blood monocytes before the manifestati on of macrophage markers. After treatment of HL-60 cells and monocytes, new ly synthesized FN was released and deposited on the dishes. An HL-60 cell v ariant, HL-525, which is deficient in the protein kinase Cp (PKC-beta) and resistant to PMA-induced differentiation, failed to express FN after PMA tr eatment. Transfecting HL-525 cells with a PKC-beta expression plasmid resto red PMA-induced FN gene expression and macrophage differentiation. Untreate d HL-525 cells (which have a high level of the alpha(5)beta(1) integrin) in cubated on FN differentiated into macrophages. The percentage of cells havi ng a macrophage phenotype induced by PMA in HL-60 cells, by FN in HL-525 ce lls, or by either PMA or macrophage-CSF in monocytes was reduced in the pre sence of mAbs to FN and alpha(5)beta(1) integrin. The integrin-signaling no nreceptor tyrosine kinase, p72(Syk), was activated in PMA-treated HL-60 and FN-treated HL-525 cells. We suggest that macrophage differentiation involv es the activation of PKC-beta and expression of extracellular matrix protei ns such as FN and the corresponding integrins, alpha(5)beta(1) integrin in particular. The stimulated cells, through the integrins, attach to substrat es by binding to the deposited FN. This attachment, in turn, may through in tegrin signaling activate nonreceptor tyrosine kinases, including p72(Syk), and later lead to expression of other genes involved in evoking the macrop hage phenotype.