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.

Leucine zipper transcription factor-like 1 binds adaptor protein complex-1 and 2 and participates in trafficking of transferrin receptor 1

“…As shown in Fig 5A, TfR1 colocalized with AP-1 in the PNR and the cytoplasm. This is consistent with the previously reported PNR of TfR1 [17][18][19][20][40][41][42]. Interestingly, TfR1 also colocalized with LZTFL1 in the PNR and the cytoplasm in a pattern similar to that of AP-1 (Fig 5B).…”

Enabling Tumor Growth and Progression: Recent Progress in Unraveling the Functions of ABL Kinases in Solid Tumor Cells

“…Moreover, cathepsin pro-invasive proteases, which are synthesized in the rough endoplasmic reticulum are transported to early endosomes, initially processed in late endosomes, and full activated in lysosomes, where they cleave intracellular and membrane-bound proteins, and old organelles/long lived proteins (autophagy) [93]. ABL proteins regulate multiple processes that are dependent on vesicle trafficking as they prevent EGFR endocytosis/degradation (in 293T and COS7 cells); induce transferrin (in rat hepatocytes) and B-cell receptor endocytosis; induce clustering of acetylcholine receptors at the neuromuscular junction (mouse muscle cells); and regulate phagocytosis [8, 94]. ABL kinases also promote autophagy in alveolar carcinoma cells by inducing lysosome/autophagasome fusion [95].…”

Molecular regulation of cellular iron balance

“… for review), but recent studies have shown that also ZRT/IRT‐like protein (ZIP)8 and ZIP14, members of the solute carrier family 39 that transport zinc and is involved in NTBI uptake at the plasma membrane , play a role in iron transport from endocytic vesicles . The process of TfR1‐mediated endocytosis is thought to be rather constitutive, but events like c‐Abl‐mediated phosphorylation may be involved in its regulation .…”