A novel cell-penetrating peptide to facilitate intercellular transport of fused proteins

Abstract

Cell-based delivery of cell penetrating peptides (CPPs) could represent a new platform for intracellular peptide delivery to local tissues. Expressed CPPs, coupled to a secretory signal peptide (SP), can support intercellular transport. However, low secretion efficiency, which may correlate with the positive charge of most CPPs, has emerged as one of the main impediments for efficient intercellular transport. We have reported that a modified Tat-based CPP (Tatm) with reduced positive charge is secreted efficiently, but its transduction activity was greatly reduced. We now show that a triple repeat of Tatm (Tatm3x) with an elongated α-helical amphipathic structure enhances transduction activity and simultaneously retains its secretion efficacy, although passage through the secretory pathway reduces its cell-penetrating activity. SP-Tatm3x supports intercellular transport of fused fluorescent proteins, as well as cell entry and function of a pro-apoptotic peptide. In addition, SP-Tatm3x largely escapes RNA inhibition, which is identified as another potential impediment to CPP-mediated intercellular transport. Expression of SP-Tatm3x in heparan sulfate proteoglycan-negative cells further improves its transduction activity. These results demonstrate the feasibility of intercellular transport of proteins, but further work is needed to better understand the reduction of cell-penetrating activity associated with secretion of CPP-fusion proteins.