ACTIVATION-INDEPENDENT NUCLEAR TRANSLOCATION OF MITOGEN-ACTIVATED PROTEIN-KINASE ERK1 MEDIATED BY THIOL-MODIFYING CHEMICALS

The extracellular signal-regulated kinases ERK1 and ERK2 are key media tors of mitogenic signals in most cell types, In fibroblasts, sustaine d activation and nuclear translocation are mandatory for S-phase induc tion, The events leading to activation of these kinases are well under stood, whereas little is known about the mechanism of their translocat ion, Using indirect immunofluorescence and biochemical analysis we sho w that ERK1 can translocate to the nucleus in the absence of activatio n and phosphorylation by upstream kinases when cells are treated with thiol-modifying chemicals. We propose that these chemicals inactivate a protein contributing to the cytoplasmic localization of ERK1.