PROLACTIN-LIKE PROTEIN-B - HETEROLOGOUS EXPRESSION AND CHARACTERIZATION OF PLACENTAL AND DECIDUAL SPECIES

Prolactin-like protein-B (PLP-B) is a member of a family of proteins e xpressed by the rat placenta and/or decidua with characteristics simil ar to prolactin (PRL). In this report, we present the heterologous exp ression and characterization of PLP-B. Recombinant PLP-B heterologousl y expressed in Chinese hamster ovary cells exhibited similar immunorea ctive and electrophoretic characteristics with PLP-B produced by rat p lacental and decidual tissues. N-terminal sequencing verified the iden tity and purity oi the recombinant PLP-B species and the site of cleav age of the signal peptide from the mature secreted PLP-B species. Poly clonal 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 co nditions. Treatment of recombinant and native PLP-B with N-glycanase a ccelerated their electrophoretic mobility, indicative of their glycopr otein nature. PLP-B was localized exclusively to decidual cells in the developing deciduum and spongiotrophoblast cells in the placental jun ctional zone. The level of PLP-B protein expression dramatically decli ned 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-depende nt Nb2 lymphoma cells. In conclusion, recombinant PLP-B possesses char acteristics similar to native decidual and placental PLP-B and may rep resent a hormone/cytokine that has important modulatory actions during the establishment of pregnancy and the initiation of parturition.