The taming of the cell penetrating domain of the HIV Tat: Myths and realities

Abstract

Protein transduction with cell penetrating peptides over the past several years has been shown to be an effective way of delivering proteins in vitro and now several reports have also shown valuable in vivo applications in correcting disease states. An impressive bioinspired phenomenon of crossing biological barriers came from HIV transactivator Tat protein. Specifically, the protein transduction domain of HIV-Tat has been shown to be a potent pleiotropic peptide in protein delivery. Various approaches such as molecular modeling, arginine guanidinium head group structural strategy, multimerization of PTD sequence and phage display system have been applied for taming of the PTD. This has resulted in identification of PTD variants which are efficient in cell membrane penetration and cytoplasmic delivery. Inspite of these state of the art technologies, the dilemma of low protein transduction efficiency and target specific delivery of PTD fusion proteins remains unsolved. Moreover, some misconceptions about PTD of Tat in the literature require considerations. We have assembled critical information on secretory, plasma membrane penetration and transcellular properties of Tat and PTD using molecular analysis and available experimental evidences.

Tapasin modification on the intracellular epitope HBcAg18–27 enhances HBV-specific CTL immune response and inhibits hepatitis B virus replication in vivo

“…However, the majority of PTD and PTD-conjugated molecules translocates to the nucleus rather than to the cytoplasm after transduction, owing to the functional nuclear localization sequence (NLS). 38,39 A new approach that appears to be the safest is to produce recombinant proteins exogenously and then deliver them systemically or by localized injections into the target cells or tissues. In comparison with PTD, CTP and its fusion partners exhibited a clear preference for cytoplasmic localization, and also markedly enhanced membrane transduction potential.…”

“…In comparison with PTD, CTP and its fusion partners exhibited a clear preference for cytoplasmic localization, and also markedly enhanced membrane transduction potential. 39,40 By constructing recombinant protein and cell-penetrating peptide, different proteins and polypeptides were delivered into a variety of cells in vivo and in vitro. 41,42 HBcAg 18-27 epitope has been shown to be able to induce HBV-specific CTL response and thus is a potential for the therapeutic design of chronic HBV infection.…”

Characterization of HIV-1 TAT peptide as an enhancer of HSV-TK/GCV cancer gene therapy

“…Although the exogenous full-length TAT protein is cytotoxic to certain cell types, 21 less has been reported about the cytotoxicity concerning TAT PTD. 22 Jones et al 23 have demonstrated that 11-mer TAT PTD exhibits cytotoxicity at higher concentrations (4100 mM) in different cell types, including A549, HeLa and CHO cells. However, in our study, due to the use of FACSanalysis, the exact concentration of expressed fusion proteins was not determined.…”

“…Consequently, the intercellular transport property of TAT fusion proteins is suggested to be dependent on secretion signal of the proteins attached to TAT peptide. 22 Because in TAT-TK-GFP triple fusion protein neither GFP nor TK contains any secretion sequence, we have previously suggested the following hypothesis for TAT-mediated enhancement of GCV-cytotoxicity: shortly after GCV exposure, TAT fusion proteins are released from the GCV-treated dead cells and can diffuse into the neighboring, non-transduced cells, thus enhancing cell killing. The cytotoxic mechanism of HSV-TK/GCV therapy is shown to be mediated mainly via apoptosis, and necrotic cell death has been shown to play a minor role.…”

A novel concept in antiangiogenic and antitumoral therapy: multitarget destabilization of short-lived mRNAs by the zinc finger protein ZFP36L1

“…The HIV-1 transactivator TAT is capable of crossing the plasma membrane and thereby mediating the intracellular delivery of heterologous proteins (Chauhan et al, 2007). Most of the recent studies indicate that PTDs use various forms of endocytosis (Richard et al, 2003;Snyder and Dowdy, 2004;Asoh and Ohta, 2008).…”