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Updated: May 1, 2026
Real-time Analyses of Retinol Transport by the Membrane Receptor of Plasma Retinol Binding Protein
Published on: January 28, 2013
Commentary: Cellular functions of vitamin D-binding protein.
David R Fraser1, Rebecca S Mason2
1Sydney School of Veterinary Science, Faculty of Science, The University of Sydney, Sydney, NSW 2006, Australia.
Plasma vitamin D-binding protein (DBP) transports vitamin D and clears circulating actin. Its cellular uptake and interaction with actin retain 25-hydroxyvitamin D, crucial for vitamin D hormone production and maintaining blood levels.
Area of Science:
- Biochemistry
- Cell Biology
- Endocrinology
Background:
- Plasma vitamin D-binding protein (DBP) traditionally transports vitamin D and its metabolites.
- DBP also binds actin, clearing it from circulation during cell damage.
- Emerging roles of DBP involve lymphoid cells and cellular uptake via megalin/cubilin.
Purpose of the Study:
- To elucidate the non-classical functions of DBP, particularly its role in vitamin D metabolism within cells.
- To investigate the mechanism of DBP internalization and its interaction with intracellular actin.
- To understand how DBP contributes to the regulation of circulating 25-hydroxyvitamin D levels.
Main Methods:
- Investigated DBP's interaction with actin filaments within cells.
- Examined the endocytosis of DBP by megalin and cubilin in kidney and skeletal muscle cells.
- Analyzed the retention and release of 25-hydroxyvitamin D (25(OH)D) mediated by DBP-actin complexes.
Main Results:
- DBP internalizes into kidney and skeletal muscle cells via megalin and cubilin.
- Intracellular DBP binds to actin, forming a complex that retains free 25(OH)D.
- Proteolysis of DBP releases 25(OH)D, supporting 1,25-dihydroxyvitamin D synthesis in the kidney and maintaining circulating 25(OH)D levels via skeletal muscle.
Conclusions:
- DBP plays a critical intracellular role in vitamin D homeostasis beyond transport.
- The DBP-actin complex acts as a cellular reservoir for 25(OH)D, influencing its circulating half-life.
- This mechanism is vital for vitamin D hormone production and maintaining overall vitamin D status.
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