(A) Stat3 downregulation eliminates gap junctional permeability in human lung carcinoma QU-DB cells. LY was electroporated into QU-DB cells following treatment with the DMSO carrier alone (a–c), or the Stat3 inhibitor CPA7 (d–f). Cells from the same field were photographed under fluorescence (b,e) or phase contrast (a,d) illumination. Cells at the edge of the conductive area which were loaded with LY through electroporation were marked with a star, and cells at the non-electroporated area which received LY through gap junctions were marked with a dot [53]. Arrows point to the edge of the electroporated area. (c,f) Overlay of phase-contrast and fluorescence. Magnification: 240×. Note the extensive gap junctional communication in (b). (From ref. [4], reproduced with permission). (B) Stat3 downregulation does not increase gap junctional permeability in human lung carcinoma A549 cells. Same as above, A549 cells. Note the absence of GJIC, even after Stat3 downregulation (e). (From ref. [4], reproduced with permission). (C) Stat3C increases GJIC. LY was electroporated into SK-LuCi6, lung carcinoma cells before (top panel) or after (bottom panel) expression of Stat3C with a pBabe-puro-Stat3C retroviral vector. Note the increase in dye transfer following Stat3C expression. Arrows point to the edge of the electroporated area (Figure not previously published).