The role of the fgr tyrosine kinase in the control of the adhesive properties of U937 monoblastoid cells and their derivatives

In humans, expression of the cellular proto-oncogene c-fgr is normally restricted to mature cells of the myeloid lineage, mantle zone B cells and various myeloid and B-cell lines. Previous studies of the monoblastoid cell line, U937, showed that c-fgr expression increased following differentiation, but its role in monocytes and related cells has not been defined in functional terms. We therefore investigated the role of c-fgr in U937 cells transfected with the c-fgr gene such that its expression could be manipulated independent of differentiation. Induction of the transfected c-fgr gene by cadmium ions did not affect cell proliferation, responses to phorbol 12-myristate 13-acetate (PMA), dihydroxycholecalciferol (DHCC), tumour necrosis factor-alpha (TNF-alpha) or retinoic acid, or phagocytosis of antibody-coated sheep red blood cells. However, there was increased surface expression of CD54 (intracellular adhesion molecule-1; ICAM-1) and CD102 (ICAM-2) and decreased surface expression of CD50 (ICAM-3) compared with cells that had been transfected with plasmid only and treated in the same way. These findings suggest that the product of the c-fgr gene may be important in control of relative adhesive properties of mature monocytic cells.