title: Characterization of placental prolactin-like protein-A in intracellular and extracellular compartments.
abstract: Prolactin-like protein-A (PLP-A) was purified from medium conditioned by junctional zone explants dissected from the rat chorioallantoic placenta via concanavalin A affinity chromatography, sodium dodecyl sulfate-gel electrophoresis and two-dimensional gel electrophoresis. Monomeric PLP-A was found to be heterogeneous and consisted of two major molecular sizes, 29 and 33 kDa. The charge and size heterogeneity attributed to monomeric PLP-A could be accounted for by the addition of N-linked carbohydrate moieties to the PLP-A structure. Monomeric PLP-A lacked lactogenic bioactivities and several attempts to sequence 29 and 33 kDa PLP-A monomers proved unsuccessful. Biochemical characterization of PLP-A species present in various intracellular and extracellular compartments indicated that PLP-A is normally secreted as high molecular weight complexes and that PLP-A species were also targeted to the nucleus. PLP-A species isolated from placental cytosol or from serum of pregnant rats predominantly circulated as disulfide-linked high molecular weight complexes. PLP-A antipeptide antisera showed limited but specific reactivity with the high molecular weight PLP-A species. We have specifically identified a 29 kDa protein species in placental cell nuclei with three antibodies directed to three different regions of the predicted amino acid sequence of PLP-A. The 29 kDa nuclear immunoreactive protein had an equivalent electrophoretic mobility to the 29 kDa PLP-A protein of junctional zone cytosol. The 33 kDa PLP-A protein was not identified in the nucleus. The biological significance of the circulating high molecular weight PLP-A species or the nuclear PLP-A species remains to be determined.
authors.affiliation: Department of Physiology, University of Kansas Medical Center, Kansas City 66103.
authors.forename: S
authors.initials: S
authors.lastname: Deb
authors.forename: M J
authors.initials: MJ
authors.lastname: Soares
mesh_terms: D000818:Animals; D000918:Antibody Specificity; D015153:Blotting, Western; D002467:Cell Nucleus / Q000737:chemistry; D002846:Chromatography, Affinity; D003600:Cytosol / Q000737:chemistry; D015180:Electrophoresis, Gel, Two-Dimensional; D005260:Female; D007526:Isoelectric Point; D008970:Molecular Weight; D010920:Placenta / Q000737:chemistry*; D011247:Pregnancy; D011257:Pregnancy Proteins / Q000737:chemistry* / Q000276:immunology / Q000302:isolation & purification; D011388:Prolactin / Q000737:chemistry* / Q000276:immunology / Q000302:isolation & purification; D051381:Rats
chemical_list: D011257:Pregnancy Proteins; D011388:Prolactin