Characterization of a High-Affinity Folate Receptor in Normal and Malignant Human Testicular Tissue |
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Authors: | Jan Holm Steen Ingemann Hansen Mimi Høier-Madsen Thomas Broe Christensen Carl W Nichols |
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Institution: | (1) Department of Clinical Chemistry, Central Hospital Herning, Herning, DK-, 7400, Denmark;(2) Department of Clinical Chemistry, Central Hospital, Hillerød, DK-, 3400, Denmark;(3) Laboratory for Autoimmune Serology, State Serum Institute, Copenhagen, DK, 2300 S, Denmark;(4) Department of Oncology, Århus Kommunehospital Århus, DK, 8000, Denmark;(5) Department of Pathology, West Paces Medical Center, 3200 Howell Mill Rd. NW, Atlanta, GA, 30327, U.S.A |
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Abstract: | We have characterized the folate receptor in normal and malignant tissue from male gonads. Radioligand binding displayed characteristics typical of other folate receptors. Those included a high-affinity type of binding (K = 1010 M–1), apparent positive cooperativity changing into non-cooperativity at low receptor concentrations, a tendency to increased binding affinity with decreasing receptor concentrations, a slow dissociation at pH 7.4 becoming rapid at pH 3.5 and inhibition by folates, in particular oxidized forms. The gel filtration profile of Triton X-100 solubilized tissue contained a 25 and 100 kDa peak of radioligand-receptor. The latter peak could represent receptor equipped with a hydrophobic membrane anchor that inserts into Triton X-100 micelles. The concentration of radiolabelled receptor ranged from 0.41 nmol/g protein to 1.68 nmol/g protein in specimens of normal testicular tissue from patients with prostatic carcinomas and from 1.54 nmol/g protein to 3.82 nmol/g protein in testicular tissue from young individuals. Compared to normal testicular tissue the concentration of receptor in seminoma tissue was low (0.38–1.27 nmol/g protein) but showed a higher degree of immunoreactivity in the presence of antibodies against human milk folate binding protein as evidenced by ELISA and immunohistochemistry data. Hence a folate receptor isoform homologous to human milk folate binding protein is apparently expressed in seminomas where the total expression of receptor, however, seems to be lower than in normal testicles. |
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Keywords: | High-affinity folate binding folate receptor in seminoma folate receptor in human testis |
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