HeLa cells stably transfected with pLXSN-HER4 or -HER4db were serum-starved 16 h then treated +HRG (1h). HER4 IP's were analyzed for total HER4. B. Cells were serum-starved (16 h), treated +HRG (1h). Cells were analyzed for HER4 localization by immunocytofluorescence. DAPI staining is shown at bottom. N= nuclear localization of HER4. C= cytoplasmic localization of HER4. C. HeLa-HER4 and HeLa-HER4db cells were cultured in 10% serum +NOC (16 h), then in SF media +NOC (16 h), adding HRG for the final hour. Cells were released into SF media +HRG/+CHX at T=0 and cells were harvested at T=0, 15, 30, and 45 min. HER4 IPs were analyzed as described above.