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

摘要: Folate-protein conjugates have been shown to bind and enter HeLa KB cells by receptor-mediated endocytosis [Leamon Low (1991) Proc. Natl. Acad. Sci. U.S.A. 88, 5572-5576]. Although these contain a membrane folate-binding protein (FBP) involved in the uptake of free folate, no studies conducted evaluate whether folate-protein via same protein. To address this issue, cell monolayers were treated with folate-labelled 125I-RNAase under various conditions characteristic FBP-mediated folate uptake. Folate-labelled was found high affinity (Kd = 24 nM), like vitamin, its binding could be competitively blocked excess folate. Furthermore, reversed either washing acid/saline, pH 3.0, or treating phosphatidyl-inositol-specific phospholipase C, an enzyme known release FBP from surfaces. Because pretreated anti-FBP serum unable conjugates, since antiserum identified single 65 kDa band reminiscent FBPs many other tissues, we conclude that classical is responsible for receptor-bearing cells.