GJA1 and neoplasm: To determine whether HBL100 cells engineered to exogenously express Cx43 formed gap junctions and established GJIC with HMVEC cells, we co-cultured HBL100Cx43 with HMVEC monolayers, localized Cx43 in these cultures (Fig. 3a–c), and assayed for dye transfer between tumor and endothelial cells (Fig. 3d–j).