The high-affinity folate receptor of normal and malignant human colonic mucosa.
The hypothesis that folate depletion is a risk factor for development of colonic neoplasia prompted us to study the presence of a putative folate receptor in human colon mucosa. Binding of 3H-folate to normal and malignant mucosa studied by equilibrium dialysis was of high-affinity type (K = 10(10) L/mol) and displayed apparent positive cooperativity. Radioligand dissociation was slow at pH 7.4, but rapid at pH 3.5. As compared to methotrexate, 5-formyltetrahydrofolate was a potent inhibitor of binding. Gel filtration revealed a 25 kDa and a 100 kDa peak of folate-binding activity. Immunoreactivity studies were performed with rabbit antibodies against human 25 kDa milk folate-binding protein. Immunoblotting showed a single band at 65 kDa, and tissue sections exhibited immunostaining of mucosal areas. The present folate receptor with characteristics similar to those of other high-affinity folate-binding proteins may serve as a regulator of intracellular folate concentration in colon mucosa.
Department of Clinical Chemistry, Central Hospital Nykøbing Falster, Denmark.
J
J
Holm
S I
SI
Hansen
M
M
Høier-Madsen
K
K
Søndergaard
M
M
Bzorek
D002352:Carrier Proteins / Q000378:metabolism*; D003106:Colon / Q000378:metabolism*; D003110:Colonic Neoplasms / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D004797:Enzyme-Linked Immunosorbent Assay; D058973:Folate Receptors, GPI-Anchored; D005492:Folic Acid / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D007413:Intestinal Mucosa / Q000378:metabolism*; D011869:Radioligand Assay; D011956:Receptors, Cell Surface / Q000378:metabolism*
D002352:Carrier Proteins; D058973:Folate Receptors, GPI-Anchored; D011956:Receptors, Cell Surface; D005492:Folic Acid