PMID: 16525719Mar 10, 2006Paper

Evidence for a specific cell membrane retinol-binding protein transport mechanism in a human keratinocyte line

International Journal of Molecular Medicine
Janet Huang, Amandio Vieira

Abstract

The epidermis is highly sensitive to retinoids, and vitamin A (retinol) is a critical factor in the regulation of skin cell differentiation and proliferation. Despite extensive knowledge of retinoid-mediated gene transcription effects on epidermal cells and evidence for retinoid-mediated suppression of carcinogenesis in skin, basic transport events, especially cellular uptake, of this vitamin remain poorly understood and controversial. Herein, evidence is presented for receptor-mediated uptake of retinol-binding protein, RBP, the specific circulatory vitamin A carrier, in the A431 human epidermal cell line. Cellular RBP uptake was significantly inhibited by anti-RBP IgG. Addition of transthyretin (TTR), a circulatory protein that can interact with RBP, to the internalization assay also significantly reduced RBP uptake to 49.4+/-4.6% (+/- SEM) of control values (p<0.01). RBP uptake was impaired by sucrose, a known inhibitor of early endocytosis, but not significantly affected by a disruptor of later trafficking events, chlorpromazine. Binding analysis indicated saturable RBP binding to the cell surface and a total of about 94,000 binding sites/cell. Based on dissociation constants, two RBP binding sites were detected with a 50-f...Continue Reading

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