The Combinatorial PP1-Binding Consensus Motif (R/K)x (0,1)V/IxFxx(R/K)x(R/K) Is a New Apoptotic Signature

Background

Previous studies established that PP1 is a target for Bcl-2 proteins and an important regulator of apoptosis. The two distinct functional PP1 consensus docking motifs, R/Kx_(0,1)V/IxF and FxxR/KxR/K, involved in PP1 binding and cell death were previously characterized in the BH1 and BH3 domains of some Bcl-2 proteins.

Principal Findings

In this study, we demonstrate that DPT-AIF₁, a peptide containing the AIF_562–571 sequence located in a c-terminal domain of AIF, is a new PP1 interacting and cell penetrating molecule. We also showed that DPT-AIF₁ provoked apoptosis in several human cell lines. Furthermore, DPT-APAF₁ a bi-partite cell penetrating peptide containing APAF-1_122–131, a non penetrating sequence from APAF-1 protein, linked to our previously described DPT-sh1 peptide shuttle, is also a PP1-interacting death molecule. Both AIF_562–571 and APAF-1_122–131 sequences contain a common R/Kx_(0,1)V/IxFxxR/KxR/K motif, shared by several proteins involved in control of cell survival pathways. This motif combines the two distinct PP1c consensus docking motifs initially identified in some Bcl-2 proteins. Interestingly DPT-AIF₂ and DPT-APAF₂ that carry a F to A mutation within this combinatorial motif, no longer exhibited any PP1c binding or apoptotic effects. Moreover the F to A mutation in DPT-AIF₂ also suppressed cell penetration.

Conclusion

These results indicate that the combinatorial PP1c docking motif R/Kx_(0,1)V/IxFxxR/KxR/K, deduced from AIF_562–571 and APAF-1_122–131 sequences, is a new PP1c-dependent Apoptotic Signature. This motif is also a new tool for drug design that could be used to characterize potential anti-tumour molecules.