An essential role for ClC-4 in transferrin receptor function revealed in studies of fibroblasts derived from
Raha Mohammad-Panah1, Leigh Wellhauser, Benjamin E Steinberg
1Programme in Molecular Structure and Function, Hospital for Sick Children, Toronto, Canada.
Abstract:
ClC-4 is closely related to ClC-5, a member of the ClC family of transporters and channels. Unlike ClC-5, for which a role in the regulation of endosomal function was well established, the cellular function of ClC-4 was uncertain. In the present study, we tested for a specific role for ClC-4 in recycling endosomes by comparing transferrin (Tfn) receptor function in primary cell lines generated from ClC-4-null mice and their wild-type siblings. We found that endosomal pH is relatively alkaline and receptor-mediated uptake of Tfn is reduced in ClC-4-null fibroblasts. Surprisingly, this reduction in Tfn uptake occurs, despite a minor increase in the total surface expression of the Tfn receptor in ClC-4-null fibroblasts. As impaired Tfn uptake by ClC-4-null fibroblasts could be rescued to wild-type levels by addition of the iron chelator: desoxiferramine, the primary defect in these cells is related to the failure of iron to dissociate from Tfn, a pH-dependent event in endosomes that precedes the dissociation of Tfn from its receptor at the cell surface. Interestingly, ClC-4 depletion had no effect on epidermal growth factor receptor (EGFR) trafficking to lysosomes for degradation pointing to its specific role in recycling endosomes. These observations provide direct evidence supporting an essential role for ClC-4 in the modulation of Tfn receptor accessibility at the cell surface through its role in endosomal acidification.
Insights
Chloride channel ClC-4 is essential for endosomal acidification, impacting iron-bound transferrin (Tfn) uptake. Loss of ClC-4 function impairs Tfn receptor recycling, highlighting its role in cellular iron homeostasis.
Area of Science:
- Cell Biology
- Molecular Physiology
- Ion Transport
Background:
- The cellular function of Chloride channel 4 (ClC-4) was previously uncertain, unlike its well-established role in endosomal function for ClC-5.
- ClC-4 is a member of the ClC family of transporters and channels, closely related to ClC-5.
Purpose of the Study:
- To investigate the specific role of ClC-4 in recycling endosomes.
- To compare transferrin (Tfn) receptor function in ClC-4-null mice and wild-type siblings.
Main Methods:
- Utilized primary cell lines from ClC-4-null mice and wild-type siblings.
- Assessed transferrin (Tfn) receptor-mediated uptake.
- Measured endosomal pH and Tfn receptor surface expression.
- Employed the iron chelator desoxiferramine to rescue Tfn uptake defects.
Main Results:
- ClC-4-null fibroblasts exhibited alkaline endosomal pH and reduced Tfn uptake.
- Impaired Tfn uptake was rescued by desoxiferramine, indicating a defect in iron dissociation from Tfn.
- ClC-4 depletion did not affect epidermal growth factor receptor (EGFR) trafficking to lysosomes.
- A minor increase in Tfn receptor surface expression was observed in ClC-4-null cells.
Conclusions:
- ClC-4 plays an essential role in endosomal acidification, crucial for recycling endosome function.
- ClC-4 modulates Tfn receptor accessibility at the cell surface via endosomal acidification.
- The findings elucidate a specific role for ClC-4 in cellular iron uptake and homeostasis.
