Molecular mechanisms in human leukemic cell (HL-60) differentiation

The human promyelocytic leukemic (HL-60) cell line can be induced to differentiate in vitro into mature granulocytes when retinoic acid (RA) is added to the culture medium. Tumor-promoting phorbol esters such as phorbol 12-myristate 13 acetate (PMA) induced HL-60 cells to differentiate into monocytes/macrophages. In this study, HL-60 cells as well as RA and PMA-treated cells were used in order to study the molecular events associated with human leukemic cell differentiation in vitro. First, the data suggest that a retinoic acid binding protein (RABP) may be responsible for mediating the binding of RA to chromatin in HL-60 cells. Second, HL-60 cells have an amplified c-myc proto-oncogene and its expression is dramatically reduced following treatment with RA or PMA. Their protein products have been identified as DNA binding proteins, perhaps as RABP. We analyzed the protein and DNA compositions of the chromatin at the c-myc and c-fos loci in HL-60 cell differentiation. Southern hybridization analysis of the nucleosomal DNA with a [32-P]-labelled human c-myc oncogene probe showed positive hybridization of the DNA from PMA-treated HL-60, but not for DNA of uninduced cells. Rehybridization of the filters with [32-P]-labelled human c-fos DNA showed that the nucleosomal DNA isolated from uninduced HL-60 cells contained c-fos sequences unlike the DNA of PMA-treated cells