Folate-protein conjugates have been shown to bind to and enter HeLa and KB cells by receptor-mediated endocytosis [Leamon and Low (1991) Proc. Natl. Acad. Sci. U.S.A. 88, 5572-5576]. 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 (Kd = 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 phosphatidyl-inositol-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.
Research Article| May 01 1993
Membrane folate-binding proteins are responsible for folate-protein conjugate endocytosis into cultured cells
C P Leamon;
Biochem J (1993) 291 (3): 855–860.
- Views Icon Views
- Share Icon Share
- Cite Icon Cite
C P Leamon, P S Low; Membrane folate-binding proteins are responsible for folate-protein conjugate endocytosis into cultured cells. Biochem J 1 May 1993; 291 (3): 855–860. doi: https://doi.org/10.1042/bj2910855
Download citation file: