Induction of macrophage colony-stimulating factor receptor up-regulation in THP-1 human leukemia cells is dependent on the activation of c-fyn protein tyrosine kinase

Abstract

We investigated the role of fyn kinase on the expression of macrophage colonystimulating factor (M-CSF) receptors (M-CSFR) and macrophage differentiation using a human myelomonocytic leukemic cell line THP-1. Treatment of THP-1 cells with Bryostatin 1 (bryo1), a potent protein kinase C (PKC) activator, caused a major fraction of them to become adherent (AD) with distinct monocyte/macrophage characteristics. The differentiation was associated with an enhanced expression of M-CSFR and fyn tyrosine kinase activity, occurring primarily on cells in the AD fraction. Scatchard plot analysis showed that the enhanced expression of M-CSFR binding activity was due to an increase in total receptor number per AD cell, rather than an increase in the binding affinity. Fyn antisense (AS) phosphorothioate oligonucleotides (soligos) inhibited the up-regulation of both M-CSFR and c-fms transcripts in bryo1-treated THP-1 cells. In contrast, fyn sense s-oligos did not affect the up-regulation of either M-CSFR or c-fms mRNA in bryo1-treated cells. In addition, fyn AS s-oligos blocked the expression of AD capacity in bryo1-treated THP-1 cells. The efficacy of fyn AS s-oligos as macromolecular inhibitors was verified by their ability to lower fyn-associated tyrosine kinase and in vitro autophosphorylation activity in bryo1-treated THP-1 cells. Taken together, our results show a strong correlation between M-CSFR expression and monocytic differentiation in THP-1 cells, and suggest a possible role of c-fyn tyrosine kinase in mediating these processes.