Myeloperoxidase is a primary response gene in HL60 cells, directly regulated during hematopoietic differentiation.

The expression of myeloperoxidase was studied in three human myeloid leukemic cell lines. The myeloperoxidase transcript was strongly expressed in promyelocytic HL 60 cells, whereas much lower levels were detected in immature monocytic U 937 cells. Phorbol-12-myristate-13-acetate induction resulted in inhibition of myeloperoxidase expression within 24 hrs. This regulatory event could not be blocked by cycloheximide. Furthermore, cycloheximide did not superinduce myeloperoxidase mRNA levels in KG 1, HL 60 and U 937 cells, arguing against the existence of a negative gene regulator for myeloperoxidase. Therefore, the myeloperoxidase gene can be classified as a primary response gene.