Phosphoproteomic Identification of a PDX-1/14-3-3ε Interaction in Pancreatic Beta Cells

Glucose-dependent activation of the homeo-domain transcription factor PDX-1 leads to its phosphorylation, to an increase in DNA binding capacity, and to NLS dependent translocation into the nucleus. To uncover unknown mediators of PDX-1 activation, PDX-1 interacting proteins were analysed by pull-down from 32 P-labelled, glucose-stimulated MIN6 cells. Recovered proteins were analysed by 2D gel electrophoresis and mass spectrometry. We identified 14-3-3e as a novel PDX-1 binding protein and confirmed the interaction in vivo by Fluorescence Resonance Energy Transfer (FRET) analysis. We propose that 14-3-3e interacts directly with PDX-1 to regulate its cellular distribution in pancreatic beta cells.