Studies on the cellular uptake of retinol binding protein and retinol

Francesca Tosetti, Francesco Campelli, Giovanni Levi

Research output: Contribution to journalArticle

Abstract

The uptake and release of 125I-RBP and of holoRBP labeled with [3H]retinol (3H-ROH) were studied in two cell lines which synthesize and secrete RBP, the HepG2 hepatocarcinoma cell line and the Caki-1 kidney adenocarcinoma cell line, and in HeLa cells that do not express the endogenous RBP gene. In all three cell lines a part of endocytosed 125I- RBP is recycled to the extracellular medium and part is degraded. Nonspecific endocytosis of 125I-RBP was estimated to be approximately 10% of total endocytosed 125I-RBP. In HepG2 cells the 3H-ROH from the [3H]retinol-RBP complex (3H-ROH-RBP) is recycled bound to RBP into serum-free chase medium. This 3H-ROH recycling is blocked in HepG2 cells by cyclohexymide and by brefeldin A, an inhibitor of protein export from the main secretory route, and is absent in HeLa cells, which do not synthesize RBP. These data suggest that at least part of retinol taken up from exogenous holoRBP is delivered to newly synthesized RBP. 3H-ROH recycled by HeLa cells is bound to serum albumin, as is a portion of that recycled by HepG2 cells. Transfer of 3H-ROH from RBP to serum albumin does not occur in the absence of cells. We conclude that RBP is endocytosed through a specific pathway and that the RBP- associated retinol is transferred to newly synthesized RBP or to serum albumin.

Original languageEnglish
Pages (from-to)423-433
Number of pages11
JournalExperimental Cell Research
Volume250
Issue number2
DOIs
Publication statusPublished - Aug 1 1999

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Keywords

  • Caki-1
  • Endocytosis
  • Hela
  • HepG2
  • Retinol recycling
  • Serum albumin

ASJC Scopus subject areas

  • Cell Biology

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