Growth inhibition in G(1) and altered expression of cyclin D1 and p27(kip-1) after forced connexin expression in lung and liver carcinoma cells

Gap junctional intercellular communication (GJIC) and connexin expression a re frequently decreased in neoplasia and may contribute to defective growth control and loss of differentiated functions. GJIC, in E9 mouse lung carci noma cells and WB-aB1 neoplastic rat liver epithelial cells, was elevated b y forced expression of the gap junction proteins, connexin43 (Cx43) and con nexin32 (Cx32), respectively. Transfection of Cx43 into E9 cells increased fluorescent dye-coupling in the transfected clones, E9-2 and E9-3, to level s comparable to the nontransformed sibling cell line, E10, from which E9 ce lls originated. Transduction of Cx32 into WB-aB1 cells also increased dye-c oupling in the clone, WB-a/32-10, to a level that was comparable to the non transformed sibling cell line, WB-F344. The cell cycle distribution was als o affected as a result of forced connexin expression. The percentage of cel ls in G(1)-phase increased and the percentage in S-phase decreased in E9-2 and WB-a/32-10 cells as compared to E9 and WB-aB1 cells. Concomitantly, the se cells exhibited changes in G(1)-phase cell cycle regulators. E9-2 and WB -a/32-10 cells expressed significantly less cyclin D1 and more p27(kip-1) p rotein than E9 and WB-aB1 cells. Other growth-related properties (expressio n of platelet-derived growth factor receptor-beta, epidermal growth factor receptor, protein kinase C-alpha, protein kinase A regulatory subunit-1 alp ha, and production of nitric oxide in response to a cocktail of pro-inflamm atory cytokines) were minimally altered or unaffected. Thus, enhancement of connexin expression and GJIC in neoplastic mouse lung and rat liver epithe lial cells restored G(1) growth control. This was associated with decreased expression of cyclin in D1 and increased expression of p27(kip-1), but not with changes in other growth-related functions. (C) 2000 Wiley-Liss, Inc.