Analysis of signaling events leading to activation of egr-1 and c-fos promoters. (A) Effects of dn Ras on hGM-CSF=ninduced activation of egr-1 and c-fos promoters. The egr600CAT (3 ;gmg) and c-fos-luciferase (2 ;gmg) plasmids were transfected to BA/FGMR cells either alone or in combination with 5 ;gmg of SR;ga-Ras17N, MMTV-Ras12V, or vector. Cells were divided to 6 samples and resuspended in mIL-3 free media with or without dexamethasone (final, 2 ;gmmol/L) after transfection. Cells were cultured for 5 hours and then stimulated with 5 ng/mL of hGM-CSF. CAT (▨) and luciferase (;bb) activities were analyzed as described in the Materials and Methods. (B) Effects of ;gDJAK1 or ;gDJAK2 on activation of egr-1 and c-fos promoters by hGM-CSF. Either alone or in combination with ;gDJAK1, ;gDJAK2, or wild-type JAK2, plasmids were transfected with egr600CAT and c-fos-luciferase plasmids. After depletion of mIL-3 for 5 hours, cells were stimulated for 5 hours with hGM-CSF (5 ng/mL) and were harvested. CAT (▨) and luciferase (;bb) activities were analyzed as described.