Figure 4.

(A) C/EBPɛ mRNA is preferentially expressed in granulocytic cells. Primary human CD34⁺ cells were enriched from peripheral blood of healthy donors and plated in medium supplemented with GM-CSF and M-CSF (GM + M; lanes 4–5), G-CSF (G; lanes 6–7), or erythropoietin (Epo, lanes 8–9). Northern blot was performed after 8 days (lanes 4, 6, 8) and 11 days (lanes 5, 7, 9) of culture. Lane 1, KG1a cells; lane 2, enriched CD34⁺ cells (83% CD34⁺); lane 3, primary CD34⁺ cells (CD34⁺) used for in vitro differentiation (lanes 4–9); lane 10, HL60 cells. (Upper) Hybridization to a C/EBPɛ-specific probe. (Lower) The blot was stripped and hybridized to a 28S RNA oligonucleotide control probe. (B) Mature human neutrophils express the long isoform of C/EBPɛ. Human monocytes and neutrophils were purified from peripheral blood of healthy donors. HeLa cells (lane 1), human monocytes (lane 2), human neutrophils (lane 3), and HL60 cells (lane 4) are shown. Migration of the 28S and 18S ribosomal RNA is shown to the left. (C) C/EBPɛ is up-regulated during granulocytic differentiation of human leukemic cell lines. K562 cells were cultured in medium supplemented with 1.5% DMSO (+DMSO) for 5 days to induce erythrocytic differentiation. U937 and HL60 cells were treated for 2 days with 1.3 × 10⁻⁷ M TPA (+TPA) for monocytic differentiation or with 10⁻⁶ M retinoic acid (+RA) for 4 days for granulocytic differentiation. Northern blot was performed at time points indicated above each lane, as described above with the exception that RNA was normalized to 18S ribosomal RNA (Lower).