The TAT-RasGAP317-326 anti-cancer peptide can kill in a caspase-, apoptosis-, and necroptosis-independent manner

Plasma membrane depolarization reveals endosomal escape incapacity of cell-penetrating peptides

Cell-penetrating peptides (CPPs) are short (<30 amino acids), generally cationic, peptides that deliver diverse cargos into cells. CPPs access the cytosol either by direct translocation through the plasma membrane or via endocytosis followed by endosomal escape. Both direct translocation and endosomal escape can occur simultaneously, making it non-trivial to specifically study endosomal escape alone. Here we depolarize the plasma membrane and showed that it inhibits the direct translocation of several CPPs but does not affect their uptake into endosomes. Despite good endocytic uptake many CPPs previously considered to access the cytosol via endosomal escape, failed to access the cytosol once direct translocation was abrogated. Even CPPs designed for enhanced endosomal escape actually showed negligible endosomal escape into the cytosol. Our data reveal that cytosolic localization of CPPs occurs mainly by direct translocation across the plasma membrane. Cell depolarization represents a simple manipulation to stringently test the endosomal escape capacity of CPPs.

Ras superfamily GTPase activating proteins in cancer: Potential therapeutic targets?

To search more therapeutic strategies for Ras-mutant tumors, regulators of the Ras superfamily involved in the GTP/GDP (guanosine triphosphate/guanosine diphosphate) cycle have been well concerned for their anti-tumor potentials. GTPase activating proteins (GAPs) provide the catalytic group necessary for the hydrolysis of GTPs, which accelerate the switch by cycling between GTP-bound active and GDP-bound inactive forms. Inactivated GAPs lose their function in activating GTPase, leading to the continuous activation of downstream signaling pathways, uncontrolled cell proliferation, and eventually carcinogenesis. A growing number of evidence has shown the close link between GAPs and human tumors, and as a result, GAPs are believed as potential anti-tumor targets. The present review mainly summarizes the critically important role of GAPs in human tumors by introducing the classification, function and regulatory mechanism. Moreover, we comprehensively describe the relationship between dysregulated GAPs and the certain type of tumor. Finally, the current status, research progress, and clinical value of GAPs as therapeutic targets are also discussed, as well as the challenges and future direction in the cancer therapy.

In vitro synergistic action of TAT-RasGAP317-326 peptide with antibiotics against Gram-negative pathogens

OBJECTIVES

Multidrug-resistant (MDR) bacteria are a continuously increasing threat for medicine, causing infections recalcitrant to antibiotics. Antimicrobial peptides (AMPs) were identified as alternatives to antibiotics, being naturally occurring short peptides and part of the innate immune system of a vast majority of organisms. However, the clinical application of AMPs is limited by suboptimal pharmacokinetic properties and relatively high toxicity. Combinatorial treatments using AMPs and classical antibiotics may decrease the concentrations of AMPs required for bacterial eradication, thus lowering the side effects of these peptides.

METHODS

Here, we investigate the in vitro efficiency of combinations of the recently described antimicrobial peptide TAT-RasGAP_317-326 with a panel of commonly used antimicrobial agents against three Gram-negative bacteria, Escherichia coli, Pseudomonas aeruginosa and Acinetobacter baumannii, using checkerboard and time-kill assays.

RESULTS

We identified synergistic combinations towards all three bacteria and demonstrated that these combinations had an increased bactericidal effect compared to individual drugs. Moreover, combinations were also effective against clinical isolates of A. baumannii. Finally, combination of TAT-RasGAP_317-326 and meropenem had a promising antibiofilm effect towards A. baumannii.

CONCLUSIONS

Taken together, our results indicate that combinations of TAT-RasGAP_317-326 with commonly used antimicrobial agents may lead to the development of new treatment protocols against infections caused by MDR bacteria.

The EnvZ/OmpR Two-Component System Regulates the Antimicrobial Activity of TAT-RasGAP317-326 and the Collateral Sensitivity to Other Antibacterial Agents

The rapid emergence of antibiotic-resistant bacteria poses a serious threat to public health worldwide. Antimicrobial peptides (AMPs) are promising antibiotic alternatives; however, little is known about bacterial mechanisms of AMP resistance and the interplay between AMP resistance and the bacterial response to other antimicrobials. In this study, we identified Escherichia coli mutants resistant to the TAT-RasGAP_317-326 antimicrobial peptide and found that resistant bacteria show collateral sensitivity to other AMPs and antibacterial agents. We determined that resistance to TAT-RasGAP_317-326 peptide arises through mutations in the histidine kinase EnvZ, a member of the EnvZ/OmpR two-component system responsible for osmoregulation in E. coli. In particular, we found that TAT-RasGAP_317-326 binding and entry is compromised in E. coli peptide-resistant mutants. We showed that peptide resistance is associated with transcriptional regulation of a number of pathways and EnvZ-mediated resistance is dependent on the OmpR response regulator but is independent of the OmpC and OmpF outer membrane porins. Our findings provide insight into the bacterial mechanisms of TAT-RasGAP_317-326 resistance and demonstrate that resistance to this AMP is associated with collateral sensitivity to other antibacterial agents. IMPORTANCE Antimicrobial peptides (AMP) are promising alternatives to classical antibiotics in the fight against antibiotic resistance. Resistance toward antimicrobial peptides can occur, but little is known about the mechanisms driving this phenomenon. Moreover, there is limited knowledge on how AMP resistance relates to the bacterial response to other antimicrobial agents. Here, we address these questions in the context of the antimicrobial peptide TAT-RasGAP_317-326. We show that resistant Escherichia coli strains can be selected and do not show resistance to other antimicrobial agents. Resistance is caused by a mutation in a regulatory pathway, which lowers binding and entry of the peptide in E. coli. Our results highlight a mechanism of resistance that is specific to TAT-RasGAP_317-326. Further research is required to characterize these mechanisms and to evaluate the potential of antimicrobial combinations to curb the development of antimicrobial resistance.

Cell membrane breakage and triggering T cell infiltration are involved in human telomerase reverse transcriptase (hTERT) promoter-driven novel peptide KK-64 for liver cancer gene therapy

Liver cancer is an aggressive malignancy with exhibits both high mortality and morbidity. The current treatment options are associated with several limitations, novel specific anti-cancer drugs are urgently needed to improve liver cancer treatment. In this study, a new peptide KK-64 was designed, and it showed strong cytotoxicity against liver cancer cells. To obtain the tumor targeting property, a plasmid that contains KK-64 DNA fragment and driven by human telomerase reverse transcriptase (hTERT) promoter was constructed. pcTERT-kk-64 plasmid was found to specifically inhibit the viability of liver cancer cells HepG2, induce substantial apoptosis as well as damage to the cell membranes, but had minimal effects toward normal liver HL-7702 cells. Furthermore, pcTERT-kk-64 plasmids was also noted to significantly attenuate migration and invasion of HepG2 cells. The anti-tumor effect of pcTERT-kk-64 plasmid was also observed in H22 cell-bearing mice, and it appeared to cause significant tumor regression, trigger tumor cell apoptosis, and infiltrate cytotoxicity T cells to the tumor tissues after plasmids injection. Thus, pcTERT-kk-64 plasmids showed both strong cytotoxicity and tumor selectivity in vitro and in tumor-bearing mice in liver cancer models.

The endocytic pathway taken by cationic substances requires Rab14 but not Rab5 and Rab7

Endocytosis and endosome dynamics are controlled by proteins of the small GTPase Rab family. Besides possible recycling routes to the plasma membrane and various organelles, previously described endocytic pathways (e.g., clathrin-mediated endocytosis, macropinocytosis, CLIC/GEEC pathway) all appear to funnel the endocytosed material to Rab5-positive early endosomes that then mature into Rab7-positive late endosomes/lysosomes. By studying the uptake of a series of cell-penetrating peptides (CPPs), we identify an endocytic pathway that moves material to nonacidic Lamp1-positive late endosomes. Trafficking via this endocytic route is fully independent of Rab5 and Rab7 but requires the Rab14 protein. The pathway taken by CPPs differs from the conventional Rab5-dependent endocytosis at the stage of vesicle formation already, as it is not affected by a series of compounds that inhibit macropinocytosis or clathrin-mediated endocytosis. The Rab14-dependent pathway is also used by physiological cationic molecules such as polyamines and homeodomains found in homeoproteins.

Genetic, cellular, and structural characterization of the membrane potential-dependent cell-penetrating peptide translocation pore

Cell-penetrating peptides (CPPs) allow intracellular delivery of bioactive cargo molecules. The mechanisms allowing CPPs to enter cells are ill-defined. Using a CRISPR/Cas9-based screening, we discovered that KCNQ5, KCNN4, and KCNK5 potassium channels positively modulate cationic CPP direct translocation into cells by decreasing the transmembrane potential (V_m). These findings provide the first unbiased genetic validation of the role of V_m in CPP translocation in cells. In silico modeling and live cell experiments indicate that CPPs, by bringing positive charges on the outer surface of the plasma membrane, decrease the V_m to very low values (–150 mV or less), a situation we have coined megapolarization that then triggers formation of water pores used by CPPs to enter cells. Megapolarization lowers the free energy barrier associated with CPP membrane translocation. Using dyes of varying dimensions in CPP co-entry experiments, the diameter of the water pores in living cells was estimated to be 2 (–5) nm, in accordance with the structural characteristics of the pores predicted by in silico modeling. Pharmacological manipulation to lower transmembrane potential boosted CPP cellular internalization in zebrafish and mouse models. Besides identifying the first proteins that regulate CPP translocation, this work characterized key mechanistic steps used by CPPs to cross cellular membranes. This opens the ground for strategies aimed at improving the ability of cells to capture CPP-linked cargos in vitro and in vivo.

Before a drug can have its desired effect, it must reach its target tissue or organ, and enter its cells. This is not easy because cells are surrounded by the plasma membrane, a fat-based barrier that separates the cell from its external environment. The plasma membrane contains proteins that act as channels, shuttling specific molecules in and out of the cell, and it also holds charge, with its inside surface being more negatively charged than its outside surface.

Cell-penetrating peptides are short sequences of amino acids (the building blocks that form proteins) that carry positive charges. These positive charges allow them to cross the membrane easily, but it is not well understood how.

To find out how cell-penetrating peptides cross the membrane, Trofimenko et al. attached them to dyes of different sizes. This revealed that the cell-penetrating peptides enter the cell through temporary holes called water pores, which measure about two nanometres across. The water pores form when the membrane becomes ‘megapolarized’, this is, when the difference in charge between the inside and the outside of the membrane becomes greater than normal. This can happen when the negative charge on the inside surface or the positive charge on the outer surface of the membrane increase. Megapolarization depends on potassium channels, which transport positive potassium ions outside the cell, making the outside of the membrane positive. When cell-penetrating peptides arrive at the outer surface of the cell near potassium channels, they make it even more positive. This increases the charge difference between the inside and the outside of the cell, allowing water pores to form. Once the peptides pass through the pores, the charge difference between the inside and the outside of the cell membrane dissipates, and the pores collapse.

Drug developers are experimenting with attaching cell-penetrating peptides to drugs to help them get inside their target cells. Currently there are several experimental medications of this kind in clinical trials. Understanding how these peptides gain entry, and what size of molecule they could carry with them, provides solid ground for further drug development.

APOBEC3C, a nucleolar protein induced by genotoxins, is excluded from DNA damage sites

The human genome contains 11 APOBEC (apolipoprotein B mRNA editing catalytic polypeptide‐like) cytidine deaminases classified into four families. These proteins function mainly in innate antiviral immunity and can also restrict endogenous retrotransposable element multiplication. The present study focuses on APOBEC3C (A3C), a member of the APOBEC3 subfamily. Some APOBEC3 proteins use their enzymatic activity on genomic DNA, inducing mutations and DNA damage, while other members facilitate DNA repair. Our results show that A3C is highly expressed in cells treated with DNA‐damaging agents. Its expression is regulated by p53. Depletion of A3C slightly decreases proliferation and does not affect DNA repair via homologous recombination or nonhomologous end joining. The A3C interactomes obtained from control cells and cells exposed to the genotoxin etoposide indicated that A3C is a nucleolar protein. This was confirmed by the detection of either endogenous or ectopic A3C in nucleoli. Interestingly, we show that A3C is excluded from areas of DNA breaks in live cells. Our data also indicate that the C‐terminal part of A3C is responsible for its nucleolar localization and exclusion from DNA damage sites.

Bacterial surface properties influence the activity of the TAT-RasGAP317-326 antimicrobial peptide

Antibiotic resistance is an increasing threat for public health, underscoring the need for new antibacterial agents. Antimicrobial peptides (AMPs) represent an alternative to classical antibiotics. TAT-RasGAP_317-326 is a recently described AMP effective against a broad range of bacteria, but little is known about the conditions that may influence its activity. Using RNA-sequencing and screening of mutant libraries, we show that Escherichia coli and Pseudomonas aeruginosa respond to TAT-RasGAP_317-326 by regulating metabolic and stress response pathways, possibly implicating two-component systems. Our results also indicate that bacterial surface properties, in particular integrity of the lipopolysaccharide layer, influence peptide binding and entry. Finally, we found differences between bacterial species with respect to their rate of resistance emergence against this peptide. Our findings provide the basis for future investigation on the mode of action of TAT-RasGAP_317-326, which may help developing antimicrobial treatments based on this peptide.

The proteolytic landscape of cells exposed to non-lethal stresses is shaped by executioner caspases

Cells are in constant adaptation to environmental changes to insure their proper functioning. When exposed to stresses, cells activate specific pathways to elicit adaptive modifications. Those changes can be mediated by selective modulation of gene and protein expression as well as by post-translational modifications, such as phosphorylation and proteolytic processing. Protein cleavage, as a controlled and limited post-translational modification, is involved in diverse physiological processes such as the maintenance of protein homeostasis, activation of repair pathways, apoptosis and the regulation of proliferation. Here we assessed by quantitative proteomics the proteolytic landscape in two cell lines subjected to low cisplatin concentrations used as a mild non-lethal stress paradigm. This landscape was compared to the one obtained in the same cells stimulated with cisplatin concentrations inducing apoptosis. These analyses were performed in wild-type cells and in cells lacking the two main executioner caspases: caspase-3 and caspase-7. Ninety-two proteins were found to be cleaved at one or a few sites (discrete cleavage) in low stress conditions compared to four hundred and fifty-three in apoptotic cells. Many of the cleaved proteins in stressed cells were also found to be cleaved in apoptotic conditions. As expected, ~90% of the cleavage events were dependent on caspase-3/caspase-7 in apoptotic cells. Strikingly, upon exposure to non-lethal stresses, no discrete cleavage was detected in cells lacking caspase-3 and caspase-7. This indicates that the proteolytic landscape in stressed viable cells fully depends on the activity of executioner caspases. These results suggest that the so-called executioner caspases fulfill important stress adaptive responses distinct from their role in apoptosis. Mass spectrometry data are available via ProteomeXchange with identifier PXD023488.

The antimicrobial peptide TAT-RasGAP317-326 inhibits the formation and expansion of bacterial biofilms in vitro

OBJECTIVES

Biofilms are structured aggregates of bacteria embedded in a self-produced matrix that develop in diverse ecological niches. Pathogenic bacteria can form biofilms on surfaces and in tissues, causing nosocomial and chronic infections that are difficult to treat. While antibiotics are largely inefficient in limiting biofilm formation and expansion, antimicrobial peptides (AMPs) are emerging as alternative antibiofilm treatments. In this study, we explore the effect of the newly described AMP TAT-RasGAP_317-326 on Acinetobacter baumannii, Pseudomonas aeruginosa and Staphylococcus aureus biofilms.

METHODS

Efficiency of TAT-RasGAP_317-326 on biofilms was tested in vitro. Both viability of bacteria contained in the biofilm as well as biomass of the biofilm were quantified using resazurin and crystal violet staining, respectively. The antibiofilm effect of TAT-RasGAP_317-326 was compared with a selection of classical antibiotics and AMPs.

RESULTS

We observe that TAT-RasGAP_317-326 inhibits biofilm formation at concentrations equivalent or two times greater than the minimum inhibitory concentration (MIC) of planktonic bacteria. Moreover, TAT-RasGAP_317-326 limits the expansion of A. baumannii and P. aeruginosa established biofilms at twice the concentration inhibiting biofilm formation.

CONCLUSION

These results underscore the potential use of TAT-RasGAP_317-326 against biofilms and encourage further studies in the development of AMPs to treat biofilm-related infections.

TAT-RasGAP317-326 kills cells by targeting inner-leaflet-enriched phospholipids

TAT-RasGAP_317-326 is a cell-penetrating peptide-based construct with anticancer and antimicrobial activities. This peptide kills a subset of cancer cells in a manner that does not involve known programmed cell death pathways. Here we have elucidated the mode of action allowing TAT-RasGAP_317-326 to kill cells. This peptide binds and disrupts artificial membranes containing lipids typically enriched in the inner leaflet of the plasma membrane, such as phosphatidylinositol-bisphosphate (PIP₂) and phosphatidylserine (PS). Decreasing the amounts of PIP₂ in cells renders them more resistant to TAT-RasGAP_317-326, while reducing the ability of cells to repair their plasma membrane makes them more sensitive to the peptide. The W317A TAT-RasGAP_317-326 point mutant, known to have impaired killing activities, has reduced abilities to bind and permeabilize PIP₂- and PS-containing membranes and to translocate through biomembranes, presumably because of a higher propensity to adopt an α-helical state. This work shows that TAT-RasGAP_317-326 kills cells via a form of necrosis that relies on the physical disruption of the plasma membrane once the peptide targets specific phospholipids found on the cytosolic side of the plasma membrane.

CRISPR/Cas9 genome-wide screening identifies KEAP1 as a sorafenib, lenvatinib, and regorafenib sensitivity gene in hepatocellular carcinoma

Sorafenib is the first-line drug used for patients with advanced hepatocellular carcinoma (HCC). However, acquired sorafenib resistance in cancer patients limits its efficacy. Here, we performed the first genome-wide CRISPR/Cas9-based screening on sorafenib-treated HCC cells to identify essential genes for non-mutational mechanisms related to acquired sorafenib resistance and/or sensitivity in HCC cells. KEAP1 was identified as the top candidate gene by Model-based Analysis of Genome-wide CRISPR/Cas9 Knockout (MAGeCK). KEAP1 disrupted HCC cells were less sensitive than wild-type cells in short- and long-term sorafenib treatments. Compared to wild-type cells, KEAP1-disrupted cells showed lower basal and sorafenib-induced reactive oxygen species (ROS) levels and were more resistant to oxidative stress-induced cell death. The absence of KEAP1 led to increased activity of Nrf2, a key transcription factor controlling antioxidant responses, as further evidenced by increased expression of Nrf2-controlled genes including NQO1, GPX2 and TXNRD1, which were positively associated with chemoresistance. In addition, KEAP1 disruption counteracted the reduction of cell viability and the elevation of ROS caused by lenvatinib, a drug that recently showed clinical efficacy as a first-line treatment for unresectable HCC. Finally, Keap1 disruption also increased the resistance of cells to regorafenib, a recently approved drug to treat HCC as a second line therapy. Taken together, our data indicate that deregulation of the KEAP1/Nrf2 pathway following KEAP1 inactivation contributes to sorafenib, lenvatinib, and regorafenib resistance in human HCC cells through up-regulation of Nrf2 downstream genes and decreased ROS levels.

Transdermal Delivery of 5-Aminolevulinic Acid by Nanoethosome Gels for Photodynamic Therapy of Hypertrophic Scars

5-Aminolevulinic acid (ALA)-loaded nanoethosome (ALA-ES) gels are successfully prepared to realize a transdermal delivery of ALA, and they provide a feasible approach for the photodynamic therapy (PDT) of hypertrophic scars (HS). Herein, the morphological and physicochemical features indicate that ALA-ES is stable in gel matrix. In vitro transdermal penetration studies suggest ALA-ES gels can overcome the compact dermal barrier and deliver more ALA into human HS tissue. In vivo delivery studies further reveal that ALA-ES gels can penetrate into rabbit HS tissue to facilitate ALA accumulating in hypertrophic scar fibroblast (HSF) and converting into protoporphyrin IX in the cytoplasm. Utilizing transmission electron microscopy, the visual in vivo penetration process indicates ALA-ES penetrate into HS tissue utilizing its deformable membrane, enters HSF by a pinocytotic-like mechanism, and then releases ALA in the cytoplasm. Subsequently, PDT efficacy is assessed using rabbit HS models. The morphological and histological analysis reveal that ALA-ES gels can improve HS by promoting HSF apoptosis, remodelling collagen fibers and increasing MMP3 expression. The results demonstrate that ALA-ES gels are suitable in clinical treatment of HS and make a substantial progress within the field.

Triggering of cancer cell cycle arrest by a novel scorpion venom-derived peptide-Gonearrestide

In this study, a novel scorpion venom-derived peptide named Gonearrestide was identified in an in-house constructed scorpion venom library through a combination of high-throughput NGS transcriptome and MS/MS proteome platform. In total, 238 novel peptides were discovered from two scorpion species; and 22 peptides were selected for further study after a battery of functional prediction analysis. Following a series of bioinformatics analysis alongside with in vitro biological functional screenings, Gonearrestide was found to be a highly potent anticancer peptide which acts on a broad spectrum of human cancer cells while causing few if any observed cytotoxic effects on epithelial cells and erythrocytes. We further investigated the precise anticancer mechanism of Gonearrestide by focusing on its effects on the colorectal cancer cell line, HCT116. NGS RNA sequencing was employed to obtain full gene expression profiles in HCT116 cells, cultured in the presence and absence of Gonearrestide, to dissect signalling pathway differences. Taken together the in vitro, in vivo and ex vivo validation studies, it was proven that Gonearrestide could inhibit the growth of primary colon cancer cells and solid tumours by triggering cell cycle arrest in G1 phase through inhibition of cyclin-dependent kinases 4 (CDK4) and up-regulate the expression of cell cycle regulators/inhibitors-cyclin D3, p27, and p21. Furthermore, prediction of signalling pathways and potential binding sites used by Gonearrestide are also presented in this study.

The Anticancer Peptide TAT-RasGAP317-326 Exerts Broad Antimicrobial Activity

Antibiotic resistance has become a major health issue. Nosocomial infections and the prevalence of resistant pathogenic bacterial strains are rising steadily. Therefore, there is an urgent need to develop new classes of antibiotics effective on multi-resistant nosocomial pathogenic bacteria. We have previously shown that a cell-permeable peptide derived from the p120 Ras GTPase-activating protein (RasGAP), called TAT-RasGAP_317-326, induces cancer cell death, inhibits metastatic progression, and sensitizes tumor cells to various anti-cancer treatments in vitro and in vivo. We here report that TAT-RasGAP_317-326 also possesses antimicrobial activity. In vitro, TAT-RasGAP_317-326, but not mutated or truncated forms of the peptide, efficiently killed a series of bacteria including Escherichia coli, Acinetobacter baumannii, Staphylococcus aureus, and Pseudomonas aeruginosa. In vivo experiments revealed that TAT-RasGAP_317-326 protects mice from lethal E. coli-induced peritonitis if administrated locally at the onset of infection. However, the protective effect was lost when treatment was delayed, likely due to rapid clearance and inadequate biodistribution of the peptide. Peptide modifications might overcome these shortcomings to increase the in vivo efficacy of the compound in the context of the currently limited antimicrobial options.