Dynamic regulation of ERK2 nuclear translocation and mobility in living cells.
The extracellular signal-regulated protein kinase ERK1/2 is a crucial effector linking extracellular stimuli to cellular responses: upon phosphorylation ERK [also known as mitogen-activated protein kinase P42/P44 (MAPK)] concentrates in the nucleus where it activates specific programs of gene expression. Notwithstanding the importance of this process, little is known about the modalities, time course and regulation of ERK exchange between nucleus and cytoplasm in living cells. We visualized the dynamic of nuclear translocation by expressing low levels (<150 nM) of fluorescently tagged ERK2 in living fibroblasts. Time-lapse imaging demonstrated that nuclear concentration can change bidirectionally with a time constant of a few minutes. The increase of nuclear concentration requires continuous MEK (also known as MAPK kinase) activity upstream of ERK and is rapidly reduced by the operation of phosphatases. We measured quantitatively the speed of ERK2 shuttling between nucleus and cytoplasm and determined that shuttling accelerated after ERK activation, becoming fast enough not to be rate-limiting for translocation. Finally, we demonstrated that ERK2 did not diffuse freely in the nucleus and that diffusion was further impeded after phosphorylation, suggesting the formation of complexes of low mobility. These results show that nucleocytoplasmic trafficking of ERK2 and its mobility are dynamically regulated in living cells.
Costa
Mario
M
Institute of Neuroscience CNR, Via Moruzzi 1, 56100 Pisa, Italy.
Marchi
Matilde
M
Cardarelli
Francesco
F
Roy
Anusrhee
A
Beltram
Fabio
F
Maffei
Lamberto
L
Ratto
Gian Michele
GM
D021581:Active Transport, Cell Nucleus; D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism*; D004789:Enzyme Activation; D036681:Fluorescence Recovery After Photobleaching / Q000379:methods; D049452:Green Fluorescent Proteins / Q000378:metabolism; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D041681:NIH 3T3 Cells; D009685:Nuclear Envelope / Q000378:metabolism; D010766:Phosphorylation; D011994:Recombinant Proteins / Q000378:metabolism; D015398:Signal Transduction
D011994:Recombinant Proteins; D049452:Green Fluorescent Proteins; D019950:Mitogen-Activated Protein Kinase 1