Insulin-activated, K+-channel-sensitive Akt pathway is primary mediator of ML-1 cell proliferation

Voltage-gated K(+) channel activities are involved in regulating growth factor-stimulated cell proliferation in a variety of cell types. Here we report that suppression of a voltage-gated K(+) channel with 4-aminopyridine (4-AP), barium, and tetraethylammonium inhibited both EGF- and insulin-stimulated myeloblastic leukemia ML-1 cell proliferation in a concentration-dependent manner. Both MAPK/ERK and Akt pathways are known to mediate cell proliferative signals of a variety of growth factors including insulin. In serum-starved ML-1 cells, insulin rapidly stimulated phosphorylation of ERK1/2 and Akt, and the phosphorylation levels peaked approximately 30 min after treatment. Pretreatment of ML-1 cells with 4-AP potently and dose-dependently prevented phosphorylation of ERK1/2 and Akt. However, insulin-induced activation of the Akt pathway also played a role in promoting ML-1 cell proliferation. Flow cytometry analysis revealed that although ML-1 cells were primarily arrested at G(1) phase by serum starvation for 36 h, they reentered the cell cycle after treatment with serum or insulin for 24 h. However, concomitant 4-AP treatment was able to attenuate cell cycle progression in synchronized ML-1 cells stimulated with growth factors. Our results strongly suggest that a 4-AP-sensitive K(+) channel activity plays an important role in controlling proliferation of ML-1 cells by affecting the activation of multiple signal transduction processes induced by insulin.