Use of a penetratin-linked peptide in Dictyostelium.

The plasma membrane is an effective barrier to most macromolecules and hydrophilic molecules. Remarkably, a class of positively charged cell-penetrating peptides (CPPs) has been discovered that can translocate themselves and associated cargoes into the cytoplasm. These have been used to carry oligopeptide- and oligonucleotide-based inhibitors into mammalian cells. A recent report indicates that the same CPPs are internalized by plant protoplasts, suggesting that this may be a universal phenomenon. We report here that the prototypical CPP, penetratin, enters cells of the free-living amoebae Dictyostelium discoideum. To investigate the functionality of this technology, we fused the penetratin sequence to PKI, a peptide inhibitor of the cAMP-dependent protein kinase (PKA). Consistent with its PKA inhibitory action, Penetratin-PKI blocked aggregation in wild-type cells and, at appropriate concentrations, rescued the phenotype of a Dictyostelium mutant that has constitutively high PKA activity. This technology offers an effective method for delivery of oligopeptides and oligonucleotides into Dictyostelium.