Fig. 7. MEK5 is retained in the nucleus of resting but not of stimulated cells. HeLa (A) or Rat-1 (B) cells were grown on coverslips as described above, serum-starved and either stimulated with EGF (50 ng/ml, 15 minutes) or left unstimulated (NS). Then the cells were subjected to an in situ extraction with NP-40 (0.2% for HeLa and 0.5% for Rat-1, 5 minutes), after which the cells were fixed and stained with anti-MEK5 antibody and DAPI.