RESOLUTION OF MULTIPLE AP-1 COMPLEXES IN HL-60 CELLS INDUCED TO DIFFERENTIATE BY 1,25-DIHYDROXYVITAMIN-D3

Activator protein-1 (AP-1) complex plays a central role in the regulation of both growth and differentiation in many cell types. Monocytic differentiation of HL-60 cells by TPA (12-0-tetradecanoyl phorbol-13-acetate) has been reported to be paralleled by increased AP-1 binding to DNA and by elevated c-jun expression, suggesting transcriptional level of control. We show that two forms of AP-1 complex, designated AP-1/1 and AP-1/2, can be demonstrated in logarithmically growing HL-60 cells, that the exposure of these cells to 10(-8) M 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) results in increased binding of these complexes to the AP-1 DNA element, and that the AP-1 complex can be resolved into at least three forms in differentiated cells. Binding to, or competition with, a mutated form of the AP-1 binding site shows that the most slowly migrating complex (AP-1/3) binds to DNA with greater specificity than do complexes AP-1/1 and AP-1/2, while antibody inhibition and binding studies performed at 37-degrees-C indicate that jun proteins predominate in AP-1/2 complexes. Exposure of extracts from differentiated, but not untreated, HL-60 cells to 2 mM ATP increases the prominence of AP-1/3 complexes, and reduces the DNA binding of AP-1/1 complexes. Treatment of the extracts with phosphatases abolishes the binding of AP-1/2 and AP-1/3 to DNA, and increases the binding intensity of AP-1/1. When extracts from differentiated cells are mixed with extracts from undifferentiated cells the AP-1/3 complexes become less prominent, suggesting than an inhibitory activity in undifferentiated cells prevents the formation of AP-1/3 complexes. These studies show the association of multiple forms of AP-1 complex with the mature monocytic phenotype, and suggest several levels of control of monocytic differentiation. (C) 1993 Wile -Liss, Inc.