Membrane Depolarization was Required to Induce DNA Synthesis in Murine Macrophage Cell Line PU5-1.8

Abstract

The role of membrane potential (Em) on the initiation of DNA synthesis in murine macrophage cell line PU5–1.8 was investigated with fluorescent probes bis-oxonol and diS-C₃₋(5). Incubation of PU5–1.8 cells in high K⁺-HEPES buffer or with gramicidin at 37°C for lh that depolarized the membrane induced L3H]-thymidine incorporation and expression of early response gene such as c-myc and c-fos. When PU5–1.8 cells were treated with a number of agents including fetal calf serum (FCS), lipopolysaccharide (LPS), epidermal growth factor (EGF), N-formyl-methionyl-leucyl-phenylalanine (FMLP) and bradykinin (BK), only FCS caused DNA synthesis and membrane depolarization. Other agents had no effect on these events. the FCS-mediated DNA synthesis in PU5–1.8cells was inhibited by clamping the membrane potential with valinomycin. Moreover, intracellular alkalinization induced by nigericin at pH 7.9, which is believed to be a permissive signal for mitogenesis, caused membrane depolarization. On the other hand, challenge of cells with phorbol 12-myristate 13 acetate (PMA) suppressed the K⁺-mediated DNA synthesis. However, the treatment of cells with PMA did not change the membrane potential but suppressed the gramicidin-mediated membrane depolarization. These observations suggest that there is a correlation between membrane depolarization and initiation of DNA synthesis in PUS-1.8 cells. PKC may be acting as a modulator in this transducing pathway.