FOLATE RECEPTORS IN MALIGNANT AND BENIGN TISSUES OF HUMAN FEMALE GENITAL-TRACT

We have characterized the folate receptor in malignant and benign tiss ues of human female genital tract (Fallopian tube and benign and malig nant tissues of uterus). Radioligand binding displayed characteristics similar to those of other folate binding proteins. Those include a hi gh-affinity type of binding (K = 10(10)M(-1)), apparent positive coope rativity, a slow dissociation at pH 7.4 becoming rapid at pH 3.5, and inhibition of binding by folate analogues. The gel filtration profile of Triton X-100 solubilized tissue contained two large peaks of H-3-fo late labelled protein (> = 130 and 100 kDa) as well as a 25 kDa peak. Only a single band of 70 kDa was seen on SDS-PAGE immunoblotting. The large molecular size forms on gel filtration appear to represent folat e receptors having a hydrophobic membrane anchor inserted into Triton X-100 micelles. The folate receptor of female genital tract showed cro ss-reactivity in ELISA and positive immunostaining with rabbit antibod ies against human milk folate binding protein. Variations in the ratio of immunoresponse to total high affinity folic acid binding suggests the presence of multiple isoforms of the receptor in different types o f malignant and benign tissues.