sirolimus and 1-9-dideoxyforskolin

Neural cell development is regulated by membrane ion channel activity. We have previously demonstrated that cell membrane depolarization with veratridine or blockage of K+ channels with tetraethylammonium (TEA) inhibit oligodendrocyte progenitor (OP) proliferation and differentiation (); however the molecular events involved are largely unknown. Here we show that forskolin (FSK) and its derivative dideoxyforskolin (DFSK) block K+ channels in OPs and inhibit cell proliferation. The antiproliferative effects of TEA, FSK, DFSK, and veratridine were attributable to OP cell cycle arrest in G1 phase. In fact, (1) cyclin D accumulation in synchronized OP cells was not affected by K+ channel blockers or veratridine; (2) these agents prevented OP cell proliferation only if present during G1 phase; and (3) G1 blockers, such as rapamycin and deferoxamine, mimicked the anti-proliferative effects of K+ channel blockers. DFSK also prevented OP differentiation, whereas FSK had no effect. Blockage of K+ channels and membrane depolarization also caused accumulation of the cyclin-dependent kinase inhibitors p27(Kip1) and p21(CIP1) in OP cells. The antiproliferative effects of K+ channel blockers and veratridine were still present in OP cells isolated from INK4a-/- mice, lacking the cyclin-dependent kinase inhibitors p16(INK4a) and p19(ARF). Our results demonstrate that blockage of K+ channels and cell depolarization induce G1 arrest in the OP cell cycle through a mechanism that may involve p27(Kip1) and p21(CIP1) and further support the conclusion that OP cell cycle arrest and differentiation are two uncoupled events.

Topics: 8-Bromo Cyclic Adenosine Monophosphate; Animals; Cell Cycle Proteins; Cell Division; Cell Lineage; Cerebellum; Colforsin; Cyclin D; Cyclin-Dependent Kinase Inhibitor p21; Cyclin-Dependent Kinase Inhibitor p27; Cyclins; Deferoxamine; Ion Channel Gating; Isoproterenol; Membrane Potentials; Mice; Microtubule-Associated Proteins; Oligodendroglia; Potassium; Potassium Channel Blockers; Potassium Channels; Rats; Rats, Sprague-Dawley; Sirolimus; Stem Cells; Tetraethylammonium; Tumor Suppressor Proteins; Veratridine