PAK4 and breast cancer: Although there are no studies on the ability of VIP or secretin to activate PAK4, some studies reported that the activation of some G-protein-coupled receptors, such as those for ß-adrenergic agents, prostaglandins and alpha-MSH, can stimulate PAK4 activation via cAMP in HEK293 cells (human embryonic kidney 293 cells), B16 melanoma cells and MCF7 (breast cancer cells) [94,95,96].