DIRECT EVIDENCE THAT LACTOGENIC HORMONES INDUCE HOMODIMERIZATION OF MEMBRANE-ANCHORED PROLACTIN RECEPTOR IN INTACT NB-2-11C RAT LYMPHOMA-CELLS

The ability of full-size prolactin receptor (PRLR) from Nb-2 rat lymph oma cell line to undergo lactogenic hormone-induced dimerization in in tact cells or in a partially purified microsomal fraction was tested, The stoichiometry of ovine placental lactogen (oPL) binding to PRLR wa s documented by SDS-PAGE of the covalently cross-linked complexes betw een [I-125]oPL and intact Nb-2-11C cells. The molecular masses of the specific bands were 82 and 141 kDa, corresponding to PRLR:oPL and (PRL R)(2):oPL complexes. These results provide direct evidence for the occ urrence of hormone-induced receptor dimerization in intact cells, Gel- filtration studies revealed that under non-denaturing conditions, the purified receptor forms high-molecular-mass aggregates (190 and 540 kD a) composed of receptor dimers and oligomers. Since this aggregation w as not dependent on the presence of lactogenic hormone, it is possible that the receptor in the intact cells may already exist as a noncoval ent diner or oligomer and that hormone-induced dimerization stabilizes the complex or changes its conformation. (C) 1997 Federation of Europ ean Biochemical Societies.