Gap-junctional communication and expression of gap junction-forming proteins were investigated in normal human prostate epithelial cells and in several malignant prostate cell lines. In comparison with normal cells, gap-junctional communication in malignant cells, as assayed by the transfer of 443-Da fluorescent tracer Lucifer yellow, was either reduced or not detected. Malignant cells expressed mRNA transcripts for connexin (Cx) 43, whereas normal cells expressed mRNA transcripts for Cx32 and Cx40. In both normal and malignant cells, gap-junctional communication was enhanced twofold to fivefold by treatment with forskolin, an agent known to increase intracellular levels of cAMP. Immunocytochemical staining with a Cx43-specific antibody revealed that in malignant cells this enhancement correlated with the number of gap junctions and occurred without any qualitative or quantitative alteration in Cx43 mRNA or protein. Moreover, western blot analyses showed that both control and forskolin-treated malignant cells expressed only one form of Cx43. Our data suggest that gap-junctional communication in both normal and malignant prostate cells may be regulated by hormones that work via a cAMP-dependent signal transduction pathway. Thus, both normal and malignant cells offer a new experimental model system in which interactions between a hormonal form of cellular communication and intercellular communication mediated via gap junctions can be studied.