Characterization of antisera to a partially purified prolactin receptor: effect on prolactin binding in different target tissues

Abstract

Prolactin (PRL) receptors have been purified by affinity chromatography using a lactogenic hormone (human growth hormone, hGH) coupled to Affigel-10. The mean binding capacity of 3 separate purifications was 1.18 ± 0.26 moles prolactin per mg protein, representing a 836-fold purification over crude microsomes and 4000−5000-fold over mammary gland homogenates and 16% purity. The receptor was characterized by HPLC using a TSK-SW-4000 and 3000 column connected in series and eluted in 0.1 M borate buffer containing 0.2 M NaCl and 0.1% Triton. A single peak of [ 125I]hGH binding activity with a retention time of 45.2 min (22.6 ml), representing an apparent molecular weight of 133000, was observed. A single peak of activity was also observed following polyacrylamide gel electrophoresis of the purified receptor in 0.1% Triton coincident with the Coomassie-stained protein band. Antibodies to the partially purified receptor preparations were prepared in sheep, goats and guinea pigs. Antisera to the prolactin receptor prepared in all three species were capable of inhibiting the binding of 125I-labeled ovine prolactin to receptors from rabbit mammary glands. Significant inhibition of binding was observed at antisera dilution of 1:10 000 with the sheep antiserum being the most potent (half-maximal inhibition (IM 50) = 1:5700). All three antisera were able to inhibit PRL binding completely, but failed to affect labeled insulin or hCG binding and had very little effect on bGH binding. The specificity of the sheep antiserum was tested in rabbit mammary glands, ovary, adrenal, pig mammary glands and 8 rat tissues which contain PRL receptors. The antiserum was able to inhibit the binding of labeled PRL in all tissues, with the inhibition curves for the rat tissues being non-parallel when compared to rabbit mammary gland, suggesting a homology but not a complete identity between PR1 receptors in various tissues and animal species. These studies demonstrate that prolactin receptors can be purified from rabbit mammary tissue and that antisera can be produced in several species. In addition, the binding studies suggest that in the various tissues the receptor molecule is more or less exposed to interaction with the antisera, or that the receptor protein differs somewhat between species.