Detection of partially phosphorylated forms of ERK by monoclonal antibodies reveals spatial regulation of ERK activity by phosphatases

When cells are stimulated by mitogens, extracellular signal-regulated kinas e (ERK) is activated by phosphorylation of its regulatory threonine (Thr) a nd tyrosine (Tyr) residues, The inactivation of ERK may occur by phosphatas e-mediated removal of the phosphates from these Tyr, Thr or both residues t ogether. In this study, antibodies that selectively recognize all combinati ons of phosphorylation of the regulator; Thr and Tyr residues of ERK were d eveloped, and used to study the inactivation of ERK upon mitogenic stimulat ion. We found that inactivation of ERK in the early stages of mitogenic sti mulation involves separate Thr and Tyr phosphatases which operate different ly in the nucleus and in the cytoplasm, Thus, ERK is differentially regulat ed in various subcellular compartments to secure proper length and strength of activation, which eventually determine the physiological outcome of man y external signals. (C) 2000 Federation of European Biochemical Societies.