Murine erythroleukemia (MEL) cells provide a valuable model to study the molecular events leading to erythroid differentiation. Maturing erythroid cells synthesize large quantitities of hemoglobin, a process requiring the coordinated synthesis of heme and globin. Here, we investigated the role of the ERK and p38 mitogen-activated protein kinase (MAPK) signaling pathways in chemically induced differentiating MEL cells. We showed that treatment of DMSO- or HMBA-induced MEL cells with the MEK1/2 inhibitor UO126, blocking the ERK pathway, results in the increase of beta-globin and 5-aminolevulinate synthase-2 (ALAS-2) transcript levels. We found that addition of the p38 inhibitor SB203580 has the opposite effect, leading to decreased beta-globin and ALAS-2 mRNA levels. The regulation on the transcript level correlated with increased or decreased hemoglobin levels in the presence of MEK1/2 and p38 inhibitors, respectively. Our results suggest that the ERK and p38 pathways play antagonistic roles in DMSO- and HMBA induced erythroid differentiation in MEL cells. This data also provide a novel link between MAPK signaling and the regulation of intracellular heme levels, as ERK and p38 MAPK signaling cascades appear to differentially regulate one of the key enzymes of the heme biosynthesis pathway.

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