Loss of mismatch repair activity in simian virus 40 large T antigen-immortalized BPH-1 human prostatic epithelial cell line

Snail1 is over-expressed in prostate cancer

Transcription factor Snail1 is a mediator of cell migration and survival, and expression is elevated in several cancer types. The Snail1 gene is reportedly amplified in prostate cancer (PC), and we investigated Snail1 expression in PC. Immunohistochemical Snail1 staining was determined on a tissue microarray which includes 327 specimens of PC, 30 specimens from patients with benign prostatic hyperplasia (BPH), benign tissue from 30 PC patients and 15 high-grade prostate intraepithelial neoplasia (high-grade PIN) specimens. Clinicopathological and follow-up data were available for all patients. No BPH specimen and only 21% of benign tissue from PC patients showed high expression of Snail1. Only 7% of high-grade PIN patients expressed a high level of Snail1. In contrast, approximately 50% of PC tissue from patients with PC showed marked nuclear immunostaining. Snail1 immunostaining was significantly associated with Gleason score (p<0.05). Snail1 expression was not correlated to T stage, metastasis at time of diagnosis, risk of or time to recurrence. Snail1 expression was significantly increased in PC with a positive correlation to dedifferentiation, but not to cancer progression or prognosis. The presented data indicate that Snail1 expression is upregulated from the early stages of PC.

Basal prostate epithelial cells stimulate the migration of prostate cancer cells

Carcinoma cells in PIN are situated above a layer of basal epithelial cells, which shield the tumor cells from stimulation by factors from the prostate stroma. During progression to invasive carcinoma, the basal cell layer becomes disrupted and tumor cells adhere to the basement membrane. The close proximity of basal epithelial cells to tumor cells in the early stages of prostate oncogenesis raises the possibility that basal epithelial cells participate in tumor cell invasion. Here, we investigated the migration-promoting activity of secreted factors from basal epithelial cells on BPH-1 cells, which we used as an in vitro model of preinvasive prostate cancer cells. We showed that the conditioned medium of basal epithelial cells (PEC-CM) contains adhesion proteins and chemotactic factors that stimulate adhesion, planar polarization, migration, and phosphorylation of Akt and that LY294002 and Wortmannin partially inhibit PEC-CM-triggered migration. We identified laminin-5 as a major migration-stimulating protein for BPH-1 cells in PEC-CM. Laminin-5 induced migration is completely inhibited by LY294002 or Wortmannin. In addition, antibody-depletion of laminin-5 from PEC-CM significantly diminishes the migration of BPH-1 cells. These results demonstrated, that laminin-5 is secreted by basal prostate epithelial cells in vivo and in vitro and stimulates migration of BPH-1 cells through a PI3-kinase dependent mechanism. Altogether, the possibility that basal epithelial cells assist in the invasion of in situ carcinoma cells is supported by the results from our in vitro system.