Glycogen Synthase Kinase 3β Promotes the Endocytosis of Transferrin in the African Trypanosome.
Human parasite Trypanosoma brucei proliferates in the blood of its host, where it takes up iron via receptor-mediated endocytosis of transferrin (Tf). Mechanisms of Tf endocytosis in the trypanosome are not fully understood. Small molecule lapatinib inhibits Tf endocytosis in T. brucei and associates with protein kinase GSK3β (TbGSK3β). Therefore, we hypothesized that Tf endocytosis may be regulated by TbGSK3β, and we used three approaches (both genetic and small molecule) to test this possibility. First, the RNAi knock-down of TbGSK3β reduced Tf endocytosis selectively, without affecting the uptake of haptaglobin-hemoglobin (Hp-Hb) or bovine serum albumin (BSA). Second, the overexpression of TbGSK3β increased the Tf uptake. Third, small-molecule inhibitors of TbGSK3β, TWS119 (IC50 = 600 nM), and GW8510 (IC50 = 8 nM) reduced Tf endocytosis. Furthermore, TWS119, but not GW8510, selectively blocked Tf uptake. Thus, TWS119 phenocopies the selective endocytosis effects of a TbGSK3β knockdown. Two new inhibitors of TbGSK3β, LY2784544 (IC50 = 0.6 μM) and sorafenib (IC50 = 1.7 μM), were discovered in a focused screen: at low micromolar concentrations, they prevented Tf endocytosis as well as trypanosome proliferation (GI50's were 1.0 and 3.1 μM, respectively). These studies show that (a) TbGSK3β regulates Tf endocytosis, (b) TWS119 is a small-molecule tool for investigating the endocytosis of Tf,
Department of Cellular Biology, The Center for Tropical and Emerging Global Diseases, University of Georgia , 724 Biological Sciences Building, Athens, Georgia 30605, United States.
Paul J
PJ
Guyett
Institute for Rare and Neglected Disease Drug Discovery (IRND3) , 897 Independence Avenue #2C, Mountain View, California 94043, United States.
Shuangluo
S
Xia
Institute for Rare and Neglected Disease Drug Discovery (IRND3) , 897 Independence Avenue #2C, Mountain View, California 94043, United States.
David C
DC
Swinney
Department of Chemistry and Chemical Biology, Northeastern University , 417 Egan Building, 360 Huntington Avenue, Boston, Massachusetts 02115, United States.
Michael P
MP
Pollastri
Department of Cellular Biology, The Center for Tropical and Emerging Global Diseases, University of Georgia , 724 Biological Sciences Building, Athens, Georgia 30605, United States.
Kojo
K
Mensa-Wilmot
D004705:Endocytosis; D000071679:Glycogen Synthase Kinase 3 beta / Q000235:genetics / Q000378:metabolism*; D006790:Host-Parasite Interactions; D006801:Humans; D015800:Protozoan Proteins / Q000235:genetics / Q000378:metabolism*; D014168:Transferrin / Q000378:metabolism*; D014346:Trypanosoma brucei brucei / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D014353:Trypanosomiasis, African / Q000378:metabolism / Q000469:parasitology*
D015800:Protozoan Proteins; D014168:Transferrin; D000071679:Glycogen Synthase Kinase 3 beta
drug discovery; endocytosis; glycogen synthase kinase 3β; protein kinase; trypanosome