Decidual/trophoblast prolactin-related protein: characterization of gene structure and cell-specific expression.

Abstract

Decidual/trophoblast PRL-related protein (d/tPRP) is a member of the PRL gene family and is dually expressed in uterine and placental tissues in a highly coordinated pattern during pregnancy. In the present study, we describe the isolation and characterization of the d/tPRP gene. A lambda DASH II Wistar-Kyoto rat genomic library was screened with a labeled d/tPRP complementary DNA, resulting in the isolation of two phage clones, RGLd-41 [17.7 kilobases (kb)] and RGLd-42 (15.8 kb). RGLd-41 alone was found to contain the full-length d/tPRP gene and was used for subsequent analyses. The d/tPRP gene possesses a six-exon, five-intron organization. Relative to other highly conserved members of the PRL gene family, d/tPRP contains a single small additional exon (exon 3) situated between exons 2 and 3 of the prototypical PRL gene. The region corresponding to exon 3 of d/tPRP encodes for a unique amino acid region found in a subset of PRL family members. A reverse transcription-PCR (RT-PCR) tissue survey for d/tPRP messenger RNA revealed that d/tPRP expression was restricted to decidual and trophoblast tissues. A single transcription start site 65 bp upstream of the initiation codon was identified in decidual tissue, whereas multiple transcription start sites ranging from 61-66 bp upstream of the initiation codon were detected in placental tissue. Various tissue culture systems (primary cultures and cell lines) were evaluated for d/tPRP expression and activation of a 3.96-kb d/tPRP promoter-luciferase reporter construct. Decidual, spongiotrophoblast, and trophoblast giant cell populations expressed d/tPRP and were capable of activating the d/tPRP promoter-reporter construct, whereas other cell types were ineffective. Limited d/tPRP promoter activation was noted in uterine stromal cell lines. In summary, d/tPRP possesses a unique six-exon, five-intron gene structure and exhibits cell-specific expression that is regulated at least in part by a 3.96-kb 5'-flanking region.