Prolactin-like protein-B (
PLP-B) is a member of a family of
proteins expressed by the rat placenta and/or decidua with characteristics similar to
prolactin (PRL). In this report, we present the heterologous expression and characterization of
PLP-B. Recombinant
PLP-B heterologously expressed in Chinese hamster ovary cells exhibited similar immunoreactive and electrophoretic characteristics with
PLP-B produced by rat placental and decidual tissues. N-terminal sequencing verified the identity and purity of the recombinant
PLP-B species and the site of cleavage of the
signal peptide from the mature secreted
PLP-B species. Polyclonal
antibodies were generated to the recombinant
PLP-B and used for Western blot and immunocytochemical analyses. Recombinant and native
PLP-B migrated as a doublet at 30-31 kDa in SDS-PAGE under reducing conditions. Treatment of recombinant and native
PLP-B with
N-glycanase accelerated their electrophoretic mobility, indicative of their
glycoprotein nature.
PLP-B was localized exclusively to decidual cells in the developing deciduum and spongiotrophoblast cells in the placental junctional zone. The level of
PLP-B protein expression dramatically declined prior to parturition. Potential PRL-like
biological actions of
PLP-B were also investigated.
PLP-B bound weakly to ovarian and liver
PRL receptors and did not stimulate the proliferation of lactogen-dependent Nb2
lymphoma cells. In conclusion, recombinant
PLP-B possesses characteristics similar to native decidual and placental
PLP-B and may represent a
hormone/
cytokine that has important modulatory actions during the establishment of pregnancy and the initiation of parturition.