Interaction of recombinant rat placental lactogen-I with extracellular domains of prolactin receptors from three species.
Rat placental lactogen-I (rPL-I), expressed in rat uteri at midpregnancy, belongs to the GH/PRL/cytokine family of hormones (Wallis, 1992), all members of which exhibit a similar mechanism of receptor activation. Lactogenic activity of rPL-I as determined by Nb2 lymphoma cell bioassay was slightly higher than that of hGH. rPL-I was capable also of stimulating beta-casein production in mouse HC-11 cells. Competitive binding experiments using [125I]hGH or [125I]bPL and purified prolactin receptor extracellular domains (PRLR-ECDs) from rat (r), rabbit (rb), and bovine (b) showed rPL-I to be 12, 40, and 7-fold, respectively, less effective than hGH when competing with [125I]hGH. Displacement of [125I]bPL by rPL-I from rPRLR-ECD and rbPRLR-ECD was also 4-, and 30-fold less effective, respectively, than that by bPL. rPL-I did not compete at all with [125I]bPL for binding to bPRLR-ECD. In contrast, competitive binding experiments with [125I]hGH to a microsomal fraction of Nb2 cells showed rPL-I to be slightly more active than hGH. The stoichiometries of the complexes formed by rPL-I with rbPRLR-ECD, rPRLR-ECD, and bPRLR-ECD were studied by gel filtration. Whereas a 1:1 complex was formed between rPL-I and rPRLR-ECD and rbPRLR-ECD, no complex could be detected between rPL-I and bPRLR-ECD. The present results support the hypothesis that transient forms of a homodimer complex may be sufficient to initiate the biological signal, despite its short half-life.
Sakal
E
E
Institute of Biochemistry, Food Science and Nutrition, Faculty of Agriculture, Hebrew University of Jerusalem, Rehovot, Israel.
Robertson
M C
MC
Chapnik-Cohen
N
N
Tchelet
A
A
Gertler
A
A
D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D002364:Caseins / Q000096:biosynthesis; D002417:Cattle; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D005260:Female; D066298:In Vitro Techniques; D007457:Iodine Radioisotopes; D051379:Mice; D008934:Mitogens / Q000494:pharmacology; D010928:Placental Lactogen / Q000378:metabolism* / Q000494:pharmacology; D011247:Pregnancy; D011817:Rabbits; D051381:Rats; D011981:Receptors, Prolactin / Q000737:chemistry / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism / Q000494:pharmacology; D015398:Signal Transduction; D013045:Species Specificity
D002364:Caseins; D007457:Iodine Radioisotopes; D008934:Mitogens; D011981:Receptors, Prolactin; D011994:Recombinant Proteins; C085699:placental lactogen I, rat; D010928:Placental Lactogen