title: The Endocytic Fate of the Transferrin Receptor Is Regulated by c-Abl Kinase.
abstract: Clathrin-mediated endocytosis of transferrin (Tf) and its cognate receptor (TfR1) is a central pathway supporting the uptake of trophic iron. It has generally been assumed that this is a constitutive process. However, we have reported that the non-receptor tyrosine kinase, Src, is activated by Tf to facilitate the internalization of the Tf-TfR1 ligand-receptor complex. As an extension of these findings, we have tested whether subsequent trafficking steps might be regulated by additional kinase-dependent cascades, and we observed a significant endocytic block by inhibiting c-Abl kinase by a variety of methods. Importantly, Tf internalization was reduced significantly in all of these cell models and could be restored by re-expression of WT c-Abl. Surprisingly, this attenuated Tf-TfR1 endocytosis was due to a substantial drop in both the surface and total cellular receptor levels. Additional studies with the LDL receptor showed a similar effect. Surprisingly, immunofluorescence microscopy of imatinib-treated cells revealed a marked colocalization of internalized TfR1 with late endosomes/lysosomes, whereas attenuating the lysosome function with several inhibitors reduced this receptor loss. Importantly, inhibition of c-Abl resulted in a striking redistribution of the chaperone Hsc70 from a diffuse cytosolic localization to an association with the TfR1 at the late endosome-lysosome. Pharmacological inhibition of Hsc70 ATPase activity in cultured cells by the drug VER155008 prevents this chaperone-receptor interaction, resulting in an accumulation of the TfR1 in the early endosome. Thus, inhibition of c-Abl minimizes receptor recycling pathways and results in chaperone-dependent trafficking of the TfR1 to the lysosome for degradation. These findings implicate a novel role for c-Abl and Hsc70 as an unexpected regulator of Hsc70-mediated transport of trophic receptor cargo between the early and late endosomal compartments.
authors.affiliation: From the Department of Biochemistry and Molecular Biology, Center for Basic Research in Digestive Diseases, and.
authors.forename: Hong
authors.initials: H
authors.lastname: Cao
authors.affiliation: Department of Experimental Pathology and Laboratory Medicine, Mayo Clinic, Rochester, Minnesota 55905.
authors.forename: Barbara
authors.initials: B
authors.lastname: Schroeder
authors.affiliation: From the Department of Biochemistry and Molecular Biology, Center for Basic Research in Digestive Diseases, and.
authors.forename: Jing
authors.initials: J
authors.lastname: Chen
authors.affiliation: From the Department of Biochemistry and Molecular Biology, Center for Basic Research in Digestive Diseases, and.
authors.forename: Micah B
authors.initials: MB
authors.lastname: Schott
authors.affiliation: From the Department of Biochemistry and Molecular Biology, Center for Basic Research in Digestive Diseases, and mmcniven@mayo.edu.
authors.forename: Mark A
authors.initials: MA
authors.lastname: McNiven
mesh_terms: D000818:Animals; D015703:Antigens, CD / Q000235:genetics / Q000378:metabolism*; D004705:Endocytosis / Q000502:physiology*; D011992:Endosomes / Q000235:genetics / Q000378:metabolism; D050883:HSC70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D008247:Lysosomes / Q000235:genetics / Q000378:metabolism; D021381:Protein Transport / Q000502:physiology; D016315:Proto-Oncogene Proteins c-abl / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D011990:Receptors, Transferrin / Q000235:genetics / Q000378:metabolism*
chemical_list: D015703:Antigens, CD; C068126:CD71 antigen; D050883:HSC70 Heat-Shock Proteins; C494371:HSPA8 protein, human; C494373:Hspa8 protein, rat; D011990:Receptors, Transferrin; C545564:Tfrc protein, rat; D016315:Proto-Oncogene Proteins c-abl
keywords: ABL tyrosine kinase; heat shock protein (HSP); lysosome; trafficking; transferrin