Dysregulation of Ack1 inhibits down-regulation of the EGF receptor.
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.
Grøvdal
Lene Melsaether
LM
University of Oslo, Institute of Pathology, Rikshospitalet HF, Oslo, Norway.
Johannessen
Lene E
LE
Rødland
Marianne Skeie
MS
Madshus
Inger Helene
IH
Stang
Espen
E
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
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