NF-YA enters cells through cell penetrating peptides.

Cell Penetrating Peptides -CPPs- are short aminoacidic stretches present in proteins that have the ability to translocate the plasma membrane and facilitate delivery of various molecules. They are usually rich in basic residues, and organized as alpha helices. NF-Y is a transcription factor heterotrimer formed by two Histone Fold Domain -HFD- subunits and the sequence-specific NF-YA. NF-YA possesses two α-helices rich in basic residues. We show that it efficiently enters cells at nanomolar concentrations in the absence of carrier peptides. Mutagenesis identified at least two separate CPPs in the A1 and A2, which overlap with previously identified nuclear localization signals (NLS). The half-life of the transduced protein is short in human cancer cells, longer in mouse C2C12 myoblasts. The internalized NF-YA is capable of trimerization with the HFD subunits and binding to the target CCAAT box. Functionality is further suggested by protein transfection in C2C12 cells, leading to inhibition of differentiation to myotubes. In conclusion, NF-YA contains CPPs, hinting at novel -and unexpected- properties of this subunit.

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