We have previously shown that Cx37 is potently growth suppressive in EC and in cancer cells through regulation of cell cycle regulator p27,7,14,39 and that endothelial expression of this Cx suppresses developmental and postischemic angiogenesis.7,40,41 Cx40 is also coexpressed with Cx37 in the larger vessels of many vessel beds,2,3,7 where it promotes and stabilizes Cx37 expression.3,13 Thus, we hypothesized that Cx40 may regulate sprouting angiogenesis, in part, through effects on Cx37 levels. This evidence concerns the gene GJA5 and cancer.