RAPGEF3 and neuroblastoma: In addition, using an EPAC1 FRET sensor, where EPAC1 was sandwiched between two different fluorescent proteins, active EPAC1 was observed to co-localize to membranes and the cytosol, but particularly at the nuclear envelope and perinuclear region in four different cell lines tested, including HEK293 and NIE-115 neuroblastoma cell lines [39].