Membrane folate-binding proteins are responsible for folate-protein conjugate endocytosis into cultured cells

C. P. Leamon, P. S. Low

Research output: Contribution to journalArticle

125 Scopus citations

Abstract

Folate-protein conjugates have been shown to bind to and enter HeLa and KB cells by receptor-mediated endocytosis. Although these cells contain a membrane folate-binding protein (FBP) involved in the uptake of free folate, no studies have been conducted to evaluate whether the folate-protein conjugates enter cells via the same protein. To address this issue, HeLa cell monolayers were treated with folate-labelled 125I-RNAase under various conditions characteristic of FBP-mediated folate uptake. Folate-labelled 125I-RNAase was found to bind to cells with high affinity (K(d) = 24 nM), and like the free vitamin, its binding could be competitively blocked by excess free folate. Furthermore, binding could be reversed by either washing the cells with acid/saline, pH 3.0, or by treating the cells with phosphatidylinositol-specific phospholipase C, an enzyme known to release FBP from cell surfaces. Because cells pretreated with anti-FBP serum were unable to bind folate conjugates, and since the same antiserum identified a single 65 kDa band reminiscent of FBPs found in many other tissues, we conclude that a classical FBP is responsible for the uptake of folate-protein conjugates by receptor-bearing cells.

Original languageEnglish (US)
Pages (from-to)855-860
Number of pages6
JournalBiochemical Journal
Volume291
Issue number3
DOIs
StatePublished - 1993

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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