HL-60 cell growth-conditioned medium is an effective inducer of myeloperoxidase expression in K-562 human leukemia cells

K-562 cells were cultured in HL-60 cell growth-conditioned medium (GCM) for up to 96 h. Myeloperoxidase (MPO) mRNA was transiently detected by reverse transcription-polymerase chain reaction (RT-PCR) techniques at 12, 24, and 48 h. The de novo expression of MPO protein was subsequently detectable by intracellular flow cytometry at 24, 48, 72 and 96 h. Immunogold staining and cytochemical analysis demonstrated granularly-sequestered MPO in approximately 40% of HL-60 GCM-cultured cells after 48 h of culture. The sequential detection of MPO mRNA and MPO biosynthesis is considered an indicator of serial maturation evocative of myeloblastic cells, and suggest that K-562 cells maintain the ability to differentiate along this lineage.