EXPRESSION OF NADPH OXIDASE IS INDUCED BY ALL-TRANS-RETINOIC ACID BUTNOT BY PHORBOL-MYRISTATE ACETATE AND 1,25-DIHYDROXYVITAMIN-D3 IN THE HUMAN PROMYELOCYTIC CELL-LINE NB4

Human promyelocytic cells, NB4, differentiate into neutrophils in resp onse to all-trans retinoic acid (ATRA), It has recently been proposed that NB4 cells have bilineage potential because these cells are also a ble to differentiate into monocyte/macrophages when exposed to a combi nation of 1,25-dihydroxyvitamin D3 (VD3) and phorbol myristate acetate (PMA). Differentiation of myeloid cells into neutrophils or monocytes is associated with the acquisition of the O-2(-) producing enzyme, NA DPH oxidase, which plays a critical role in microbial killing. In this study, the expression of the components of the NADPH oxidase complex during the differentiation of NB4 cells into neutrophils or macrophage s has been investigated. Whereas cells exposed to ATRA were able to pr oduce O-2(-) after 2 days of differentiation, they remain unable to ge nerate O-2(-) when exposed to PMA or PMA + VD3, With the exception of p21rac, none of the other oxidase components was expressed in non-diff erentiated cells, Addition of ATRA induced the progressive expression and accumulation of p22phox, p91phox, p47phox and p67phox, Compared to the other components, p67phox was expressed late and its expression a ppeared to correlate most closely with the generation of O-2(-) in the differentiation process, In PMA or PMA + VD3-differentiaied NB4 cells , expression of the NADPH oxidase components was incomplete. Therefore , ATRA induced the expression of a functional NADPH oxidase complex in neutrophil-like NB4 cells, In contrast, when NB4 cells are exposed to monocytic differentiating agents, they acquire only part of the pheno typic characteristics of monocytes and lack one of the major phagocyti c functionalities, the respiratory burst oxidase.