passages.id: split_4_validation_1395_passage
passages.type: progene_text
passages.text: Similarly to previously identified Rap GEFs , C3G and Smg GDS , each of the newly identified exchange factors promoted the activation of Elk-1 in the LNCaP prostate tumor cell line where B-Raf can couple Rap1 to the extracellular receptor - activated kinase cascade .