Hydroxyl Radicals as an Early Signal Involved in Phorbol Ester-Induced Monocytic Differentiation of HL60 Cells

A useful model for the study of monocytic differentiation has been the induction of myeloid leukemic cell differentiation. Employing human HL60 leukemic cells, we sought to clarify whether reactive oxygen intermediates (ROI) are involved in phorbol myristate acetate (PMA)-induced monocytic differentiation. We found that hydroxyl radical (OH·) scavenger pyrrolinodimethylthiocarbamate (PDTC), but not O₂—, H₂O₂ or ¹O₂ scavenger, suppressed PMA-mediated HL60 cell differentiation in a dose dependent fashion (0.1 to 1.0 μM). PDTC suppressed OH· but not O₂— or H₂O₂ production by HL60 cells stimulated with PMA (32 nM). Addition of PDTC before and right after, but not 16 hours after, PMA stimulation inhibited PMA-induced HL60 cell differentiation. Taken together, these findings indicate that OH·, but not O₂—, H₂O₂, or ¹O₂, is a critical early signal involved in the PMA-induced monocytic differentiation of HL60 cells.