MAPK3 and pheochromocytoma: For example, in the rat PC12 phaeochromocytoma cell line seminal studies have shown that epidermal growth factor (EGF)-induced proliferation relies on a transient activation of the extracellular signal-regulated kinases 1 and 2 (ERK1/2) in the cytosol, whereas nerve growth factor (NGF)-induced differentiation requires a sustained ERK1/2 activation and translocation to the nucleus [2,3].