ERK phosphorylation and nuclear accumulation: insights from single-cell imaging

Area of Science:

• Cellular signaling
• Molecular biology
• Signal transduction

Background:

• Extracellular-signal-regulated kinase (ERK) activation and nuclear translocation are crucial for cellular responses.
• Mechanisms governing ERK nuclear targeting remain incompletely understood.
• Previous studies focused on population-level responses, neglecting single-cell variations.

Purpose of the Study:

• To investigate the relationship between ERK phosphorylation and nuclear localization in single cells.
• To elucidate the factors influencing ERK nuclear targeting in response to stimuli.

Main Methods:

• Utilized automated microscopy for single-cell analysis of ERK regulation.
• Employed inhibitors for tyrosine phosphatase, protein synthesis, and MEK (mitogen-activated protein kinase/ERK kinase).
• Investigated catalytically inactive ERK2-green fluorescent protein (GFP) mutants and mutants affecting docking interactions.

Main Results:

• Nuclear localization responses of ERK correlated with stimulus level, independent of TEY phosphorylation levels.
• A 'phosphorylation-unattributable' nuclear localization component was observed.
• This component persisted with inhibitors and certain ERK mutants but was reduced by MEK inhibition and mutations affecting ERK's common docking region.

Conclusions:

• ERK's TEY phosphorylation is necessary but not sufficient for full nuclear accumulation.
• Stimulus-mediated ERK nuclear localization involves a phosphorylation-independent component.
• This component relies on ERK's association with partner proteins via its common docking motif.