High-affinity folate receptor in human ovary, serous ovarian adenocarcinoma, and ascites: radioligand binding mechanism, molecular size, ionic properties, hydrophobic domain, and immunoreactivity.

Autor: Holm J; Department of Clinical Chemistry, Central Hospital, Herning, Denmark., Hansen SI, Høier-Madsen M, Birn H, Helkjaer PE
Jazyk: angličtina
Zdroj: Archives of biochemistry and biophysics [Arch Biochem Biophys] 1999 Jun 15; Vol. 366 (2), pp. 183-91.
DOI: 10.1006/abbi.1999.1188
Abstrakt: High-affinity folate receptors are expressed in normal ovaries and ovarian carcinomas. Binding of [3H]folate in human ovary, serous ovarian carcinoma tissue, and ascites is a complex process that has not been well characterized. This study shows changes in binding affinity and mechanism of binding with decreasing receptor concentration, inhibition by folate derivatives, and a slow radioligand dissociation at pH 7.4 becoming rapid and complete at pH 3.5. The receptor seems to be positively charged since it elutes in the front effluent of a DEAE-Sepharose CL-6B ion-exchange column at pH 6.3. The gel filtration profile of Triton X-100-solubilized tissue and ascites contained two peaks of radioligand-bound receptor (25 and 100 kDa). Exposure of ascites to cleavage by phosphatidylinositol-specific phospholipase C resulted in a partial conversion of the 100-kDa peak to a 25-kDa peak. This suggests that the receptor may be anchored to the membrane by a glycosylphosphatidyl residue that inserts into Triton X-100 micelles, resulting in a large molecular size on gel filtration. The receptor in ovarian carcinoma tissue immunoreacts with antibodies against purified human milk folate receptor protein as shown by enzyme-linked immunosorbent assay, immunoprecipitation, sodium dodecyl sulfate-polyacrylamide gel electrophoresis immunoblotting (a single band of 45 kDa), and immunohistochemistry. In only three of seven ovarian carcinomas did expression of radioligand-bound receptors exceed levels found in five normal ovaries. However, only receptors in ovarian carcinoma specimens showed a high degree of immunoreactivity. Hence, even without elevations of the total receptor level, a folate receptor isoform homologous to human milk folate receptor protein seemed to prevail in serous ovarian carcinomas.
(Copyright 1999 Academic Press.)
Databáze: MEDLINE
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