Changes in isoenzyme profiles during induction of differentiation in human myelomonocytic leukemia cell lines

The human leukemia cell lines HL-60, KG-1, KLM-2, ML-3, THP-1, and U-937 were treated with the phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA). TPA partially or completely inhibited the proliferative activity of the cell cultures. The number of cells with the ability to reduce nitroblue tetrazolium increased in the TPA-treated cell lines HL-60, ML-3, THP-1, and U-937, whereas the cell lines KG-1 and KLM-2 remained nitroblue tetrazolium negative. Except for KG-1 and KLM-2, all TPA-treated cell lines showed varying degrees of strong adherence to plastic surface. The carboxylic esterase, acid phosphatase, hexosaminidase, and lactate dehydrogenase isoenzyme profiles from these cell lines were analyzed by isoelectric focusing on horizontal polyacrylamide gels. The new or stronger expression of an esterase isoenzyme which is specific for monocytes-macrophages was induced in HL-60, ML-3, THP-1, and U-937 but not in KG-1 or KLM-2. The new expression of the tartrate-resistant acid phosphatase isoenzyme was induced in ML-3, THP-1, and U-937. The number of esterase and acid phosphatase isoenzymes and the staining intensity of isoenzymes characteristic for myeloid cells were increased by TPA in all cell lines. The loss of the hexosaminidase I isoenzyme which is a marker of immature hematopoietic cells was noted in KG-1, ML-3, THP-1, and U-937. TPA triggered an increase in number and staining intensity of the lactate dehydrogenase isoenzymes in all cell lines. Some isoenzymatic changes (e.g., monocyte-specific esterase, tartrate-resistant acid phosphatase, hexosaminidase I) appear to correlate with TPA-induced differentiation while other alterations in the isoenzyme patterns do not (e.g., lactate dehydrogenase, other esterase and acid phosphatase isoenzymes). Differentiation of nonmonocytoid cells appears, at the isoenzyme level, to be quite different from that of the monocytoid cell lines.