lambda-Carrageenan-induced inhibition of gap-junctional intercellular communication in rat liver epithelial cells

lambda-Carrageenan, a food additive extracted from red seaweed, is widely u sed as an emulsifier, stabilizer, or thickener. Previously, it has been sho wn that carrageenan could play a role in carcinogenesis. However, the mecha nism by which it might influence the multimechanism, multistep process of c arcinogenesis is not known. Gap-junctional intercellular communication (GJI C) has been associated with maintaining homeostatic regulation of cell prol iferation and differentiation. Most cancer cells have dysfunctional GJIC, a nd many tumor-promoting chemicals, growth factors, and oncogenes can downre gulate GJIC. The experiments in this study were designed to test the hypoth esis that carrageenan might function as a tumor-promoting chemical by inhib iting GJIC. To test this hypothesis, nontumorigenic vat liver epithelial ce lls were exposed to carrageenan, and GJIC was measured. Western blot analys is and immunofluorescent staining were used to monitor the phosphorylation and localization of connexin 43. The data revealed inhibition of GJIC by ca rrageenan similar to that by the well-documented tumor promoter phorbol est er. However the phosphorylation and localization of connexin 43 were not al tered. Although the mechanism by which carrageenan inhibits GJIC is unknown , carrageenan's influence on the carcinogenic process might be via its abil ity to be a tumor promoter.