ERK2 enters the nucleus by a carrier- independent mechanism

摘要

In stimulated cells, the mitogen-activated protein kinase ERK2 (extracellular signal-regulated kinase 2) concentrates in the nu- cleus. Evidence exists for CRM1-dependent, mitogen-activated protein kinase kinase-mediated nuclear export of ERK2, but its mechanism of nuclear entry is not understood. To determine requirements for nuclear transport, we tagged ERK2 with green fluorescent protein (GFP) and examined its nuclear uptake by using an in vitro import assay. GFP-ERK2 entered the nucleus in a saturable, time- and temperature-dependent manner. Entry of GFP-ERK2, like that of ERK2, required neither energy nor transport factors and was visible within minutes.