Induction of monocytic cell adherence to matrix-bound fibronectin by phorbol ester

The inflammatory response requires the localization of monocytic cells to sites of tissue injury through adherence to extracellular matrix molecules such as fibronectin (Fn), a nonimmune opsonin, which binds to collagen, fibrin, heparin and cell surfaces. Adherence to this molecule of two myeloid cell lines differing in their stage of differentiation, was studied. In the baseline state, U937 monocytic cells bound specifically to matrix-bound Fn, while HL-60 promyelocytic cells bound minimally. Exposure to Phorbol myristate acetate (PMA) dramatically increased binding of both U937 and HL-60 cells to Fn with plateau effects at 10 ng/ml for both cell lines and at 30 and 60 minutes for U937 and HL-60, respectively. Treatment with metabolic inhibitors suggests that PMA stimulation depends at least in part on intact energy metabolism, protein synthesis and cytoskeletal components. This system should help elucidate the early molecular and biochemical events involved in monocyte adherence to the extracellular matrix.