Development of a site-directed polyclonal antibody against the pituitary growth hormone-releasing hormone receptor and its use to estimate GHRH receptor concentration in normal and hypothyroid rats.
A site-directed polyclonal antipeptide antibody was generated in rabbits against segment 392-404 of the rat pituitary growth hormone-releasing hormone receptor (GHRH-R), using a multiple antigenic peptide system strategy of immunization. This C-terminal intracellular region of the rat GHRH-R exhibits 85% sequence identity with the human GHRH-R. The purified anti-GHRH-R(392-404) IgGs were characterized in cell lines expressing the human GHRH-R and in rat and human anterior pituitary, using immunoblotting. The polyclonal antibody recognized a 45-kD protein in human GHRH-R-transfected BHK 570 cell membrane preparations but not in wild-type cells. A 45-kD N(alpha)-tagged human GHRH-R was immunodetected with both antitag and anti-GHRH-R antibodies in human GHRH-R-transfected HEK 293 cells. Cross-linking of [(125)I-Tyr(10)]hGHRH(1-44)NH(2) to GHRH-R-transfected BHK cells led to the detection of a major and specific 45-kD radioactive complex. Its probing with the anti-GHRH-R(392-404) IgGs led also to the detection of a 45-kD entity. In rat anterior pituitary homogenates or membrane preparations, immunoblotting led to the detection of 44-, 47- and 65-kD proteins. In human anterior pituitary membrane preparations, immunoblotting led to the detection of 52- and 55-kD proteins. No immunoreactive signal was observed in the rat liver. Cross-linking of [(125)I-Tyr(10)]hGHRH(1-44)NH(2) to rat anterior pituitary homogenates revealed the presence of specific 28-, 47- and 65-kD radioactive complexes. Probing of these radioactive complexes with the anti-GHRH-R(392-404) IgGs resulted in the visualization of 28-, 47- and 65-kD entities and of an additional immunoreactive 44-kD protein. To assess the usefulness of this GHRH-R antibody, estimation of changes in the concentration of rat anterior pituitary GHRH-R was performed by immunoblotting and compared to binding data after a 3-week antithyroid treatment. The treatment known to depress the 2.5- and 4-kb GHRH-R mRNA transcripts by at least 1.7-fold decreased the apparent maximal concentration of high (B(max1)) and low (B(max2)) affinity binding sites by 4.6- and 15.2-fold, respectively, and the 47- and 65-kD GHRH-R proteins by 3.5- and 1. 25-fold, respectively. Altogether, the characteristics of the anti-GHRH-R(392-404) polyclonal antibody indicate that it specifically recognizes the human and rat GHRH-R. It also represents an additional valuable tool to estimate variations of GHRH-Rs in physiopathological conditions known to affect GHRH-R mRNA and/or GHRH binding site concentrations.
Boulanger
L
L
Laboratory of Neuroendocrinology of Aging, Notre-Dame Hospital Research Center, Department of Medicine, University of Montreal, Quebec, Canada.
Andersen
P H
PH
Gaudreau
P
P
D000818:Animals; D019138:Antibodies, Blocking / Q000276:immunology / Q000302:isolation & purification / Q000494:pharmacology*; D000918:Antibody Specificity; D001345:Autoradiography; D015153:Blotting, Western; D006224:Cricetinae; D003432:Cross-Linking Reagents; D006801:Humans; D007037:Hypothyroidism / Q000378:metabolism*; D007668:Kidney / Q000187:drug effects / Q000378:metabolism; D008297:Male; D010903:Pituitary Gland, Anterior / Q000187:drug effects / Q000378:metabolism; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D011817:Rabbits; D011863:Radioimmunoassay; D051381:Rats; D017207:Rats, Sprague-Dawley; D018013:Receptors, Neuropeptide / Q000037:antagonists & inhibitors / Q000276:immunology*; D018017:Receptors, Pituitary Hormone-Regulating Hormone / Q000037:antagonists & inhibitors / Q000276:immunology*; D013974:Thyroxine / Q000097:blood
D019138:Antibodies, Blocking; D003432:Cross-Linking Reagents; D012333:RNA, Messenger; D018013:Receptors, Neuropeptide; D018017:Receptors, Pituitary Hormone-Regulating Hormone; C048250:somatotropin releasing hormone receptor; D013974:Thyroxine