Expression of the mRNAs encoding the primary granule protein myeloperoxidase and secondary granule proteins lactoferrin and 24p3 lipocalin in 32D-derived cell lines after EPO stimulation. The cells were cultured in medium containing 2 units/mL of EPO for the indicated times. Ten ug of total cellular RNA was analyzed by Northern blot hybridization, using as probes 32P-labeled murine cDNAs encoding MPO (A), L F or 24p3 lipocalin (B), and β-actin as a control for the amount of sample. FE: 32DEPOR-FE cells, expressing a C-terminal truncated human EPOR; WT: 32DEPOR-WT cells, expressing wild-type human EPOR; wt18: 32Dwt18 cells, expressing a chimeric EPOR/G-CSFR (see Materials and methods).