The gap-junction-mediated intercellular communication (GJIC) is required for embryonic development, cell growth and tissue homeostasis. It has been repeatedly emphasized that GJIC is defective in most human malignancies. However, the potential role of GJIC in the carcinogenesis and tumor progression of several endocrine-related cancers, including prostate and liver, remains unclear. In this work, we inspected GJIC activity in both nontumoral (Chang Liver, CL) and malignant (HepG2, Huh7) human liver cell lines, as well as in nontumorigenic (RWPE1) and malignant (RWPE2, LNCaP, DU145) human prostate epithelial cells. The GJIC activity was assessed using the Scrape-Loading/Dye Transfer (SL/DT) and/or the Fluorescence Recovery After Photobleaching (FRAP) methods. Using the SL/DT assay, only Huh7 and RWPE1 cells exhibited a moderate degree of junctional activity in basic conditions, while all the remaining cell lines had defective GJIC. We observed that both estrogen (either estradiol or estrone) and forskolin (FK), which elevate intracellular cAMP levels, induce a significant increase of GJIC in Huh7 and RWPE1 cells, and only a limited rise of junctional activity HepG2 cells. Equivalent results were obtained using the FRAP method. Western blot analysis revealed that E1 induced a 3.5-fold increase of expression of the gap junction protein connexin (Cx) Cx43, while both E1 and FK caused a marked reduction of Cx32 expression, suggesting that these agents may restore GJIC activity by increasing the Cx43:Cx32 ratio. Estrogen also induced a marked reduction of the proliferative activity of both Huh7 and RWPE1 cells. While the above evidence suggests that estrogens are primarily implicated in growth regulation and communication of both prostate and liver epithelial cells, it also implies that compounds able to restore GJIC in junctionally-deficient cells or prevent its disruption in junctionally-proficient cells may be used for development of new strategies in the prevention and/or treatment of these malignancies. Preliminary results from studies of DNA microarray-based gene expression profiles (GEP) in both human liver and prostate indicate that, based on a list of ∼8,500 genes, a set of estrogen-regulated genes can be differentially expressed in nontumoral and malignant liver and prostate tissues and cells. They include: a) RODH (oxidative 3αHSD, R35197) and the P450 enzyme CYP2C9 (R89491), that show higher expression in normal than in cancer tissues and cells; b) Liv-1 (H05907), that is highly expressed in nontumoral tissues and cells only; c) the steroid-associated heat shock proteins, HSPB1 (AA404298) and HSPB2 (R50673), that are reciprocally expressed in liver and prostate tissue: HSBP1 expression is higher, while HSPB2 is reduced in cancer relative to other tissues or cells. Studies partly supported by Italian AIRC and CNR.
[Proc Amer Assoc Cancer Res, Volume 46, 2005]