Two monoclonal antibodies against prolactin-receptor are internalized in epithelial mammary cells without mimetic prolactin effect on casein secretion.
Prolactin exerts an early stimulatory effect on casein secretion which was qualified as a secretagogue effect. After binding to its receptor, the hormone transits intracellularly through the mammary epithelial cell. When this transit is slowed down the secretagogue effect does not occur. Different monoclonal antibodies which bind to the rabbit prolactin receptor have been previously developed. One of them (A917) mimics prolactin effect on casein gene expression. Another (M110) blocks this prolactin effect. In order to study the respective role of the hormone and its receptor, we have examined the binding of the two monoclonal antibodies (M110 and A917), labeled with biotin or colloidal gold, to the receptor of lactating rabbit mammary epithelial cells in incubation. Subsequently, the intracellular movement of these antibodies and the secretory response have been measured. Irrespective of the labeling (biotin or colloidal gold) or the preparation of tissues (fragments or enzymatically dissociated cells), M110 and A917 bound to the basal membrane of mammary epithelial cells. However, only M110 bound to apical membrane of dissociated cell when this membrane was in direct contact with the incubation medium, showing that the two antibodies discriminate the receptor located on the apical membrane. Following internalization, each antibody was carried via a peculiar pathway. M110 remained associated with the cells during a 1-h incubation, mainly in endosomes, multivesicular bodies and lysosomes like vesicles. In contrast, A917 was very quickly detectable in endosomes, multivesicular bodies and vesicles of the Golgi region and was carried throughout the cell to the lumen of the acini. M110 and A917 were extremely rare in secretory vesicles containing casein micelles.(ABSTRACT TRUNCATED AT 250 WORDS)
Seddiki
T
T
Laboratoire de Biologie Cellulaire et Moléculaire, Institut National de la Recherche Agronomique, Jouy-en-Josas, France.
Delpal
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S
Aubourg
A
A
Ollivier-Bousquet
M
M
D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology*; D001666:Binding Sites, Antibody; D002364:Caseins / Q000378:metabolism*; D046508:Culture Techniques; D004705:Endocytosis; D005260:Female; D006651:Histocytochemistry; D007774:Lactation; D008321:Mammary Glands, Animal / Q000378:metabolism*; D011388:Prolactin / Q000378:metabolism*; D011817:Rabbits; D011981:Receptors, Prolactin / Q000276:immunology* / Q000378:metabolism
D000911:Antibodies, Monoclonal; D002364:Caseins; D011981:Receptors, Prolactin; D011388:Prolactin