A TUMOR-SUPPRESSOR GENE, CX26, ALSO MEDIATES THE BYSTANDER EFFECT IN HELA-CELLS

The connexin 26 (Cx26) gene suppresses the growth of HeLa cells in vit ro and in vivo. We explored the possibility that the Cx26 gene not onl y suppresses growth but can also mediate the bystander effect that is observed in some gene therapy. In gene therapy mediated by the herpes simplex virus thymidine kinase, the toxicity of ganciclovir affects no t only the cells transduced with the gene but also affects neighboring tumor cells; it has been suggested that gap junctional intercellular communication (GJIC) may play a role in such a bystander effect. HeLa cells expressing the Cx26 gene (Cx26(+)) or not expressing the Cx26 ge ne were transfected with the herpes simplex virus thymidine kinase (tk (+)) gene, producing Cx26(-)-tk(-) Cx26(-)-tk(+), Cx26(+)-tk(-), and C x26(+)-tk(+) cells. By making different kinds of cocultures of these c ells, we observed a clear bystander killing effect, assessed by the ne utral red toxicity test, in the coculture of Cx26(+)-tk(-)/Cx26(+)-tk( +) cells. The bystander effect was markedly prevented by a long-term i nhibitor of GJIC, 18-alpha-glycyrrhetinic acid, demonstrating that a m ajor part of the bystander effect seen occurred through Cx-mediated GJ IC. These data suggest the possibility of using of Cxs as both tumor s uppressor genes and as diffusers of ganciclovir toxicity in therapeuti c approaches.