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 MDR transporter-a type of ATP-binding cassette transporter whose substrates include small hydrophobic molecules. RhT transports rhodamine 123 (Rh123) and is inhibited by low temperature, energy poisons, and several MDR transport inhibitors, such as verapamil. All vegetative cells have RhT activity, but during development prestalk cells lose RhT activity while prespore cells retain it. We also identified several RhT inhibitors. The most effective inhibitor is the stalk cell-inducing chlorinated alkyl phenone, DIF-1. The RhT 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 inhibitor 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 be required for the induction of stalk cells by the RhT inhibitors. Since DIF-1 is the most potent inhibitor of RhT activity, and thus a likely transport substrate itself, we propose that RhT inhibitors induce stalk cell differentiation by blocking DIF-1 export, causing DIF-1 to build up within cells. Our results provide evidence for a prespore-specific efflux pump that regulates cell fate determination, perhaps by regulating the cellular concentration of DIF-1.
Good
J R
JR
Department of Biochemistry and Molecular Biology, Program in Developmental Biology, Baylor College of Medicine, Houston, Texas 77030, USA.
Kuspa
A
A
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism; D018528:ATP-Binding Cassette Transporters / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002454:Cell Differentiation / Q000187:drug effects; D004023:Dictyostelium / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D005456:Fluorescent Dyes / Q000493:pharmacokinetics; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects; D017125:Genes, Protozoan; D015800:Protozoan Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D020112:Rhodamine 123 / Q000493:pharmacokinetics
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D018528:ATP-Binding Cassette Transporters; D005456:Fluorescent Dyes; D015800:Protozoan Proteins; D020112:Rhodamine 123