title: Dysregulation of Ack1 inhibits down-regulation of the EGF receptor.
abstract: The protein tyrosine kinase Ack1 has been linked to cancer when over-expressed. Ack1 has also been suggested to function in clathrin-mediated endocytosis and in down-regulation of the epidermal growth factor (EGF) receptor (EGFR). We have studied the intracellular localization of over-expressed Ack1 and found that Ack1 co-localizes with the EGFR upon EGF-induced endocytosis in cells with moderate over-expression of Ack. This co-localization is mainly observed in early endosomes. Furthermore, we found that over-expression of Ack1 retained the EGFR at the limiting membrane of early endosomes, inhibiting sorting to inner vesicles of multivesicular bodies. Down-regulation of Ack1 in HeLa cells resulted in reduced rate of (125)I-EGF internalization, whereas internalization of (125)I-transferrin was not affected. In cells where Ack1 had been knocked down by siRNA, recycling of internalized (125)I-EGF was increased, while degradation of (125)I-EGF was inhibited. Together, these data suggest that Ack1 is involved in an early step of EGFR desensitization.
authors.affiliation: University of Oslo, Institute of Pathology, Rikshospitalet HF, Oslo, Norway.
authors.forename: Lene Melsaether
authors.initials: LM
authors.lastname: Grøvdal
authors.forename: Lene E
authors.initials: LE
authors.lastname: Johannessen
authors.forename: Marianne Skeie
authors.initials: MS
authors.lastname: Rødland
authors.forename: Inger Helene
authors.initials: IH
authors.lastname: Madshus
authors.forename: Espen
authors.initials: E
authors.lastname: Stang
mesh_terms: D002451:Cell Compartmentation; D002966:Clathrin / Q000378:metabolism / Q000648:ultrastructure; D015536:Down-Regulation; D004705:Endocytosis; D011992:Endosomes / Q000378:metabolism / Q000648:ultrastructure; D004815:Epidermal Growth Factor / Q000378:metabolism; D066246:ErbB Receptors / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D007457:Iodine Radioisotopes; D008565:Membrane Proteins / Q000378:metabolism; D021381:Protein Transport; D011505:Protein-Tyrosine Kinases / Q000172:deficiency / Q000378:metabolism* / Q000648:ultrastructure; D034741:RNA, Small Interfering / Q000378:metabolism; D033921:Vesicular Transport Proteins / Q000378:metabolism
chemical_list: D002966:Clathrin; D007457:Iodine Radioisotopes; D008565:Membrane Proteins; D034741:RNA, Small Interfering; D033921:Vesicular Transport Proteins; C093846:early endosome antigen 1; D004815:Epidermal Growth Factor; D066246:ErbB Receptors; D011505:Protein-Tyrosine Kinases; C403262:TNK2 protein, human