Regulation of plasma retinol binding protein secretion in human HepG2 cells

Francesca Tosetti, Nicoletta Ferrari, Ulrich Pfeffer, Claudio Brigati, Giorgio Vidali

Research output: Contribution to journalArticlepeer-review

Abstract

Retinol binding protein (RBP) is the plasma transport protein of retinol. Mobilization of RBP from the liver stores is stimulated by retinol. During vitamin A deficiency, RBP secretion is specifically inhibited while its rate of biosynthesis is unaffected. As a consequence, RBP, as apoprotein, accumulates inside the endoplasmic reticulum (ER) of the hepatocyte, and a new elevated steady-state concentration is reached. We have studied the role of degradation on the regulation of RBP metabolism in retinol deficient HepG2 cells and determined the intracellular site where RBP degradation takes place. Pulse-chase experiments show that RBP half-life is ca.9 h in retinol-depleted cells. RBP degradation is slow and is insensitive to the treatment with NH4Cl, which inactivates lysosomal proteases and to the drug brefeldin A, which prevents protein export from the ER. The data obtained suggest that RBP degradation occurs, at least in part, in a pre-Golgi compartment. 2-Mercaptoethanol, at millimolar concentration, induces RBP secretion, suggesting a possible role for sulfhydryl-mediated apo-RBP retention by resident ER proteins.

Original languageEnglish
Pages (from-to)467-472
Number of pages6
JournalExperimental Cell Research
Volume200
Issue number2
DOIs
Publication statusPublished - 1992

ASJC Scopus subject areas

  • Cell Biology

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