title: Wortmannin alters the transferrin receptor endocytic pathway in vivo and in vitro.
abstract: Treatment with the phosphatidylinositol 3-kinase inhibitor wortmannin promotes approximately 30% decrease in the steady-state number of cell-surface transferrin receptors. This effect is rapid and dose dependent, with maximal down-regulation elicited with 30 min of treatment and with an IC50 approximately 25 nM wortmannin. Wortmannin-treated cells display an increased endocytic rate constant for transferrin internalization and decreased exocytic rate constants for transferrin recycling. In addition to these effects in vivo, wortmannin is a potent inhibitor (IC50 approximately 15 nM) of a cell-free assay that detects the delivery of endocytosed probes into a common compartment. Inhibition of the in vitro assay involves the inactivation of a membrane-associated factor that can be recruited onto the surface of vesicles from the cytosol. Its effects on the cell-free assay suggest that wortmannin inhibits receptor sorting and/or vesicle budding required for delivery of endocytosed material to "mixing" endosomes. This idea is consistent with morphological changes induced by wortmannin, which include the formation of enlarged transferrin-containing structures and the disruption of the perinuclear endosomal compartment. However, the differential effects of wortmannin, specifically increased transferrin receptor internalization and inhibition of receptor recycling, implicate a role for phosphatidylinositol 3-kinase activity in multiple sorting events in the transferrin receptor's membrane traffic pathway.
authors.affiliation: Program in Biological and Biomedical Sciences, Harvard Medical School, Boston, Massachusetts 02115, USA.
authors.forename: D J
authors.initials: DJ
authors.lastname: Spiro
authors.forename: W
authors.initials: W
authors.lastname: Boll
authors.forename: T
authors.initials: T
authors.lastname: Kirchhausen
authors.forename: M
authors.initials: M
authors.lastname: Wessling-Resnick
mesh_terms: D000730:Androstadienes / Q000494:pharmacology*; D015536:Down-Regulation; D004705:Endocytosis; D011992:Endosomes; D006367:HeLa Cells; D006801:Humans; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000037:antagonists & inhibitors*; D011990:Receptors, Transferrin / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D000077191:Wortmannin
chemical_list: D000730:Androstadienes; D011990:Receptors, Transferrin; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); D000077191:Wortmannin