Evidence that a cell-type-specific efflux pump regulates cell differentiation in Dictyostelium

We have identified a cellular efflux pump, RhT, with the properties of an M DR transporter-a type of ATP-binding cassette transporter whose substrates include small hydrophobic molecules. RhT transports rhodamine 123 (Rh123) a nd is inhibited by low temperature, energy poisons, and several MDR transpo rt inhibitors, such as verapamil. All vegetative cells have RhT activity, b ut during development prestalk cells lose RhT activity while prespore cells retain it. We also identified several RhT inhibitors. The most effective i nhibitor is the stalk cell-inducing chlorinated alkyl phenone, DIF-1. The R hT inhibitors disrupted development, to varying degrees, and induced stalk cell formation in submerged culture. The inhibitors displayed the same rank order of pharmacological efficacy for stalk cell induction as they did for Rh123 transport inhibition. We also found that cerulenin, a specific inhib itor of DIF-1 biosynthesis (R. R. Kay, 1998, J. Biol. Chem. 273, 2669-2675) , abolished the induction of stalk cells by each of the RhT inhibitors, and this effect could be reversed by DIF-1. Thus, DIF-1 synthesis appears to b e required for the induction of stalk cells by the RhT inhibitors. Since DI F-1 is the most potent inhibitor of RhT activity, and thus a likely transpo rt substrate itself, we propose that RhT inhibitors induce stalk cell diffe rentiation by blocking DIF-1 export, causing DIF-1 to build up within cells . Our results provide evidence for a prespore-specific efflux pump that reg ulates cell fate determination, perhaps by regulating the cellular concentr ation of DIF-1. (C) 2000 Academic Press.