title: De novo synthesis and secretion of prolactin-like protein-B by rat placental explants.
abstract: Mid- to late-gestation rat placenta expresses three PRL-related mRNAs, rat placental lactogen-II (rPL-II), rat PRL-like protein-A (rPLP-A), and rat PRL-like protein-B (rPLP-B). The protein product of rPL-II mRNA has been characterized, and the protein products of the rPLP-A mRNA were recently identified. The mol wt of a nonsecreted nonglycosylated rPLP-B protein would be 27,145 based on the mRNA sequence. The present study is the first to report the identification of the rPLP-B protein. Antiserum was generated against a chemically synthesized oligopeptide inferred from a specific region of the rPLP-B cDNA. Three or four distinct proteins synthesized and secreted by rat basal zone explants (day 15 gestation) showed cross-reactivity with the rPLP-B antiserum. The relative mol wt of these immunoreactive proteins is approximately 30,000, with a pI varying from 6.1-6.6. De novo synthesized rPLP-B proteins were not secreted by the explant tissue in the presence of tunicamycin, suggesting that the proteins are glycosylated. These data are consistent with the presence of one potential N-glycosylation site derived from the rPLP-B mRNA sequence. The rPLP-B antiserum showed no cross-reactivity with proteins identified using antisera against rPLP-A, rPL-II, or human pregnancy-specific beta 1-glycoprotein. Immunocytochemical studies were carried out using paraffin sections from placentas of day 14 and 17 pregnant rats which were treated with anti-rPLP-B, followed by avidin-biotin-peroxidase complex. These experiments show perinuclear staining, which was localized in basophilic cytotrophoblast cells, confirming previous in situ mRNA hybridization studies. Although no physiological role has been established for rPLP-B, the synthesis and secretion of this protein by cells in contact only with maternal circulation suggest a hormonal role.
authors.affiliation: Department of Pharmacology and Therapeutics, University of Florida, Gainesville 32610.
authors.forename: S
authors.initials: S
authors.lastname: Ogilvie
authors.forename: M L
authors.initials: ML
authors.lastname: Duckworth
authors.forename: L H
authors.initials: LH
authors.lastname: Larkin
authors.forename: W C
authors.initials: WC
authors.lastname: Buhi
authors.forename: K T
authors.initials: KT
authors.lastname: Shiverick
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000918:Antibody Specificity; D015153:Blotting, Western; D046508:Culture Techniques; D005260:Female; D006031:Glycosylation; D007106:Immune Sera / Q000276:immunology; D007150:Immunohistochemistry; D007526:Isoelectric Point; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010452:Peptide Biosynthesis; D010446:Peptide Fragments / Q000276:immunology; D010455:Peptides / Q000276:immunology / Q000378:metabolism; D010920:Placenta / Q000187:drug effects / Q000378:metabolism*; D011247:Pregnancy; D051381:Rats; D014415:Tunicamycin / Q000494:pharmacology
chemical_list: D007106:Immune Sera; D010446:Peptide Fragments; D010455:Peptides; D014415:Tunicamycin