Fig. 4. Model for the involvement of Rap1 in cell-cell junction formation. At initial cell-cell contacts, C3G bound to E-cadherin is activated, resulting in Rap1 activation. Upon maturation, C3G is displaced by ß-catenin, which interacts with PDZ-GEF to further activate Rap1. Also, extracellular stimuli, including those that stimulate production of cAMP which activates Epac, induce Rap1 activation.