Constitutive DNA binding of the low mobility forms of the AP-1 and SP-1 transcription factors in HL60 cells resistant to 1-beta-D-arabinofuranosylcytosine.

DNA binding of the AP-1 transcription factor, a dimer of jun-fos or jun-jun proteins, is regulated during monocytic differentiation of HL60 cells. The abundance of AP-1 complexes capable of binding to DNA increases and complexes with slow electrophoretic mobility appear after exposure of HL60 cells to 1,25-dihydroxyvitamin D3. Similar changes are seen in the SP-1 transcription factor. In contrast, variants of HL60 cells that are resistant to both 1,25-dihydroxyvitamin D3 and 1-beta-D-arabinofuranosylcytosine constitutively express the slowly migrating AP-1 and SP-1 complexes which are found only in the differentiated parental HL60 cells. Because this form of AP-1 complex is highly phosphorylated, the data show that altered phosphorylation of at least two transcription factors is associated with resistance to 1-beta-D-arabinofuranosylcytosine.