Paracrine stimulation of polarized secretion from monolayers of a neoplastic prostatic epithelial cell line by prostatic stromal cell proteins.

The paracrine influence of prostatic stromal cell proteins on a neoplastic prostate cell line (PA-III) was investigated. We have utilized an in vitro experimental model whereby confluent epithelial sheets of PA-III cells are grown on Matrigel-coated filters in bicameral chambers (Millicell-HA). Confluence of the epithelial sheet was confirmed morphologically by electrical resistance measurements and by impedence of [3H]inulin permeability across paracellular channels. Stromal cells were isolated from the ventral prostate of 50-day-old rats by isopyknic Percoll centrifugation. Purity (92%) of the isolated stromal cells was confirmed by indirect immunofluorescence of vimentin intermediate filaments. Prostatic epithelial cells were negative for vimentin immunofluorescence. Prostatic stromal cell secretory proteins with molecular weights greater than 10,000 were placed in the basal reservoir of the bicameral chambers underneath the confluent epithelial sheets of PA-III in a manner that mimics the relationship between stroma and epithelia in vivo. After 24 h incubation the stromal cell proteins increased the [35S]methionine-labeled protein secretion from the epithelial sheet of cells. Trypsinization of the stromal cell secretory proteins eliminated the stimulatory effect on epithelial protein secretion. In addition, conditioned media from Swiss 3T3 fibroblasts, A431 cells, or bovine serum albumin did not stimulate epithelial protein secretion. Two-dimensional gel electrophoresis of the [35S]methionine-labeled epithelial protein secretion showed that the stromal cell proteins induced the secretion of a novel peptide (SE-1) from the basal domain of the epithelial sheet of cells within the first hour of metabolic labeling. These results indicate that stromal cell secretory proteins contain a stimulatory protein that can induce overall protein secretion as well as the vectorial secretion of a novel peptide from the basal domain of PA-III epithelial cells. These results are consistent with a paracrine interaction between epithelial and stromal cells in the regulation of prostatic secretion.