Evidence for multiple sites of regulation of heme synthesis in murine erythroleukemia cells

Friend murine erythroleukemia (MEL) cells can be induced to differentiate along the erythroid pathway by such dissimilar agents as dimethyl sulfoxide (DMSO), butyrate, inhibitors of DNA synthesis, and certain highly polar agents. This study showed differential biochemical effects of the potent inducers DMSO and butyrate on the heme biosynthetic pathway in three clones of Friend MEL cells. When the cells were incubated with combinations of DMSO and butyrate, hemoglobin production was less than that amount produced when each inducer was incubated singly with the cells. Procaine, a local anesthetic that competes with Ca2+ and thus affects membrane permeability, slightly inhibited DMSO-mediated hemoglobin production but almost tripled the level stimulated by butyrate alone. Similarly, EDTA, which also can bind Ca2+ and which can modify the activity of heme biosynthetic enzymes, also inhibited hemoglobin production mediated by DMSO, whereas it stimulated hemoglobin production in cells exposed to butyrate. Total porphyrin accumulation was greater in DMSO-treated cells than in butyrate-treated cells, which suggests that butyrate induces the enzymes of the heme pathway more efficiently than does DMSO. DMSO and butyrate may affect the heme biosynthetic pathway by multiple mechanisms or, alternatively, they may affect the multistep pathway at various points, producing partial blocks or incomplete enzyme induction.