J. Biol. Chem., Vol. 260, Issue 21, 11422-11429, Sep, 1985
Monoclonal antibodies against rabbit mammary prolactin receptors. Specific antibodies to the hormone binding domain
M Katoh, J Djiane and PA Kelly
Three monoclonal antibodies (M110, A82, and A917) were obtained by fusing
myeloma cells and spleen cells from mice immunized with partially purified
rabbit mammary gland prolactin (PRL) receptors. All 3 antibodies were
capable of complete inhibition of 125I-ovine prolactin (oPRL) binding to
rabbit mammary PRL receptors in either particulate or soluble form. M110
showed slightly greater potency than oPRL in competing for 125I-oPRL
binding. These antibodies also inhibited PRL binding to microsomal
fractions from rabbit liver, kidney, adrenal, ovary, and pig mammary gland,
although A82 showed poor inhibition in pig mammary gland. There was no
cross-reaction of any of the 3 monoclonal antibodies (mAbs) for the other
species tested: human (T-47D breast cancer cells) and rat (liver, ovary).
In order to confirm that these antibodies are specific to the binding
domain, antibodies were purified, iodinated, and binding characteristics
were investigated. 125I-M110 and 125I-A82 binding was completely inhibited
by lactogenic hormones, whereas nonlactogenic hormones did not cross-
react. Competition of 125I-M110 by oPRL (ID50 = 0.44 nM) was comparable to
that of 125I-oPRL by unlabeled oPRL (ID50 = 0.35 nM), while 125I- A917
binding was only partially competed (30-60%) by lactogenic hormones. Tissue
and species specificity of labeled antibody binding paralleled results of
binding inhibition experiments using 125I-oPRL. In addition, A82 and A917
completely inhibited 125I-M110 binding. In contrast, 125I-A82 binding was
stimulated by A917 and 125I-A917 binding was stimulated by A82. These
findings indicate that monoclonal antibodies can be readily prepared from
partially purified PRL receptors from rabbit mammary gland; two antibodies
(M110 and A82) are hormone binding site specific while the other (A917)
binds a domain partially but not entirely distinct from the hormone binding
site, and that all three antibodies have strong species specificity.