Interactions between normal human fibroblasts and human prostate cancer cells in a co-culture system

Stroma affects the development and the structure of many organs and plays an important role in regulating epithelial malignancies, including those derived from the prostate. Fibroblasts represent the major cell type of the stromal compartment. Aiming at clarifying the relationships between normal fibroblasts and epithelial cancer cells, we utilized a co-culture system, which included both androgen-sensitive (LNCaP) and -insensitive (PC-3, DU-145) prostate cancer cell lines and a human gingival fibroblast cell line (FG).

The morphological aspects of the cultures were analyzed under an inverted phase-contrast microscope; the proliferation in conditioned media (CM) was assessed by cell counts, and the E-cadherin expression was evaluated by immunocytochemistry.

In co-culture, androgen-sensitive LNCaP cells grew in a network on the top of the monolayer formed by FG, while colonies of androgen-insensitive PC-3 and DU-145 cells were surrounded by FG cells. After six days, the LNCaP cell number was apparently lower in the co-cultures than in the plates where they grew alone. Both LNCaP and FG cells underwent morphological changes. After the same period of time, the growth of PC-3 and DU-145 cells overcame the growth of FG cells, which were almost abolished. The CM of FG inhibited the proliferation of LNCaP cells, after three days by 33% (p<0.01) and after six days by up to 82% (p<0.01), but had no effect on the PC-3 and DU-145 cell growth. The CM of all three prostate cancer cell lines reduced the growth of FG. Growth reduction in DU-145 cells was the most effective (50% inhibition after three days, p<0.01, and 55% after six days, p<0.01). FG did not express E-cadherin, while strong E-cadherin staining was detected in LNCaP cells. PC-3 cells exhibited E-cadherin nuclear staining, while sporadic membrane expression of the specific protein was observed in DU-145 cells. In co-culture, there seemed to be a reduction in the nuclear E-cadherin reactivity of PC-3 cells.

Our data confirm the existence of a dialogue between normal fibroblasts and prostate cancer cells, which results in both a peculiar modality of growth and a regulation of proliferation, probably due to factors secreted in the culture medium. The variation in E-cadherin expression found in PC-3 cells co-cultured with FG merits further investigation.