Inhibition of regulated cell death by cell-penetrating peptides

TAT-RHIM: a more complex issue than expected

Murine cytomegalovirus protein M45 contains a RIP homotypic interaction motif (RHIM) that is sufficient to confer protection of infected cells against necroptotic cell death. Mechanistically, the N-terminal region of M45 drives rapid self-assembly into homo-oligomeric amyloid fibrils, and interacts with the endogenous RHIM domains of receptor-interacting protein kinases (RIPK) 1, RIPK3, Z-DNA binding protein 1, and TIR domain-containing adaptor-inducing interferon-β. Remarkably, all four mammalian proteins harbouring such a RHIM domain are key components of inflammatory signalling and regulated cell death processes. Immunogenic cell death by regulated necrosis causes extensive tissue damage in a wide range of diseases, including ischemia reperfusion injury, myocardial infarction, sepsis, stroke and organ transplantation. To harness the cell death suppression properties of M45 protein in a therapeutically usable manner, we developed a synthetic peptide encompassing only the RHIM domain of M45. To trigger delivery of RHIM into target cells, we fused the transactivator protein transduction domain of human immunodeficiency virus 1 to the N-terminus of the peptide. The fused peptide could efficiently penetrate eukaryotic cells, but unexpectedly it killed all tested cancer cell lines and primary cells irrespective of species without further stimulus through a necrosis-like cell death. Typical inhibitors of different forms of regulated cell death cannot impede this process, which appears to involve a direct disruption of biomembranes. Nevertheless, our finding has potential clinical relevance; reliable induction of a necrotic form of cell death distinct from all known forms of regulated cell death may offer a novel therapeutic approach to combat resistant tumour cells.

Non-apoptotic cell death such as pyroptosis, autophagy, necroptosis and ferroptosis acts as partners to induce testicular cell death after scrotal hyperthermia in mice

Cell death is a biologically uncontrollable and regulated process associated with human diseases which usually occur in response to oxidative stress that activates signalling pathways in multiple forms and can therefore contribute to human diseases. Thus, the current study aims to evaluate the signalling pathway involved in cell death after testicular hyperthermia. For this purpose, 32 mice were equally divided into four groups; I: Control; II, III and IV, Scrotal hyperthermia in which the testes are exposed to water at 43°C for 20 min every other day, respectively, 15, 10 and 5 times. Then, animals were euthanized and testicular tissue samples were isolated to evaluate protein expression as well as germ cell gene marker expression by Western blot and real-time PCR tests. Our data showed that the protein expression of Caspase-1, Beclin1, Atg7, Mlkl and Acsl4 together with the expression of Caspase-1, Beclin1, Atg7, Mlkl and Acsl4 genes was significantly up-regulated in scrotal hyperthermia-induced mice. In conclusion, the present study showed that heat stress disrupts spermatogenesis by activating several non-apoptotic signalling pathways in testicular tissue.

ERK and mTORC1 Inhibitors Enhance the Anti-Cancer Capacity of the Octpep-1 Venom-Derived Peptide in Melanoma BRAF(V600E) Mutations

Melanoma is the main cause of skin cancer deaths, with special emphasis in those cases carrying BRAF mutations that trigger the mitogen-activated protein kinases (MAPK) signaling and unrestrained cell proliferation in the absence of mitogens. Current therapies targeting MAPK are hindered by drug resistance and relapse that rely on metabolic rewiring and Akt activation. To identify new drug candidates against melanoma, we investigated the molecular mechanism of action of the Octopus Kaurna-derived peptide, Octpep-1, in human BRAF(V600E) melanoma cells using proteomics and RNAseq coupled with metabolic analysis. Fluorescence microscopy verified that Octpep-1 tagged with fluorescein enters MM96L and NFF cells and distributes preferentially in the perinuclear area of MM96L cells. Proteomics and RNAseq revealed that Octpep-1 targets PI3K/AKT/mTOR signaling in MM96L cells. In addition, Octpep-1 combined with rapamycin (mTORC1 inhibitor) or LY3214996 (ERK1/2 inhibitor) augmented the cytotoxicity against BRAF(V600E) melanoma cells in comparison with the inhibitors or Octpep-1 alone. Octpep-1-treated MM96L cells displayed reduced glycolysis and mitochondrial respiration when combined with LY3214996. Altogether these data support Octpep-1 as an optimal candidate in combination therapies for melanoma BRAF(V600E) mutations.

Efficient Therapeutic Delivery by a Novel Cell-Penetrating Peptide Derived from Acinus

In this study, we have identified a novel cell-penetrating sequence, termed hAP10, from the C-terminus of the human protein Acinus. hAP10 was able to efficiently enter various normal and cancerous cells, likely through an endocytosis pathway, and to deliver an EGFP cargo to the cell interior. Cell penetration of a peptide, hAP10DR, derived from hAP10 by mutation of an aspartic acid residue to an arginine was dramatically increased. Interestingly, a peptide containing a portion of the heptad leucine repeat region domain of the survival protein AAC-11 (residues 377–399) fused to either hAP10 or hAP10DR was able to induce tumor cells, but not normal cells, death both ex vivo on Sézary patients’ circulating cells and to inhibit tumor growth in vivo in a sub-cutaneous xenograft mouse model for the Sézary syndrome. Combined, our results indicate that hAP10 and hAP10DR may represent promising vehicles for the in vitro or in vivo delivery of bioactive cargos, with potential use in clinical settings.

Combating Proteins with Proteins: Engineering Cell-Penetrating Peptide Antagonists of Amyloid-β Aggregation and Associated Neurotoxicity

A central event that underlies the etiology of Alzheimer's disease (AD) is the self-assembly of the amyloid-β (Aβ) peptide into aggregates termed amyloids. Increasing evidence implicates soluble prefibrillar Aβ oligomers in the neurodegeneration and synaptic dysfunction in AD. Recently we introduced a new class of highly promising antagonists of Aβ amyloidogenesis: designed cell-penetrating peptides (CPPs). These CPPs combine the attractive intrinsic properties of peptides (high target specificity and selectivity, biocompatibility, biodegradability, and ease and low cost of production) with potent therapeutic effects (inhibition of Aβ oligomerization, fiber formation, and neurotoxicity) and highly efficient delivery (to target cells and subcellular organelles).

Combined Knockout of RIPK3 and MLKL Reveals Unexpected Outcome in Tissue Injury and Inflammation

Necroptosis, initially identified as a backup cell death program when apoptosis is hindered, is a prominent feature in the etiology and progression of many human diseases, such as ischemic injury and sepsis. Receptor-interacting protein kinase 3 (RIPK3) is the cardinal regulator of this cell death modality, recruiting and phosphorylating the executioner mixed lineage kinase domain-like protein (MLKL) to signal necroptosis, which is terminated by a cellular plasma membrane rupture and the leakage of intracellular contents from dying cells. Experimental data to date indicate that RIPK3 and MLKL is the core machinery essential for all necroptotic cell death responses. By using CRISPR/Cas9 (clustered regularly interspaced short palindromic repeat/CRISPR-associated protein 9) technology, we showed that Ripk3 and Mlkl knockout and Ripk3/Mlkl double-knockout in necroptosis-sensitive cell lines extensively block susceptibility to necroptosis, in each case to an indistinguishable degree. In vivo studies using Ripk3- or Mlkl-deficient mice validated kidney ischemia reperfusion injury and high-dose tumor necrosis factor (TNF) availability, as druggable targets in necroptotic-mediated pathologies. Here, we demonstrated that Ripk3 or Mlkl-deficient mice are protected to a similar extent from kidney ischemia reperfusion injury and TNF-induced toxicity. Remarkably, in contrast to each single knockout, Ripk3/Mlkl double-deficient mice did not have appreciable protection from either of the above necroptotic-mediated pathologies. Paradoxically, the double-knockout mice resembled, in each case, the vulnerable wild-type mice, revealing novel complexities in the mechanisms of inflammation-driven diseases, due to aberrant cell death.

MDA-7/interleukin 24 (IL-24) in tumor gene therapy: application of tumor penetrating/homing peptides for improvement of the effects

INTRODUCTION

MDA-7/Interleukin-24 (IL-24), as a pleiotropic cytokine, exhibits a specific tumor suppression property that has attracted a great deal of attention. While its anti-tumor induction is mostly attributed to endogenous gene expression, attachment of secreted MDA-7/IL-24 to cognate receptors also triggers the death of cancerous cell via different pathways. Therefore, precise targeting of secreted MDA-7/IL-24 to tumor cells would render it more efficacy and specificity.

AREAS COVERED

In order to target soluble cytokines, particularly MDA-7/IL-24 to the neighbor tumor sites and enhance their therapeutic efficiency, fusing with cell penetrating peptides (CPPs) or Tumor homing peptides (THPs) seems logical due to the improvement of their bystander effects. Although the detailed anti-tumor mechanisms of endogenous mda-7/IL-24 have been largely investigated, the significance of the secreted form in these activities and methods of its improving by CPPs or THPs need more discussion.

EXPERT OPINION

While the employment of CPPs/THPs for the improvement of cytokine gene therapy is desirable, to create fusions of CPPs/THPs with MDA-7/IL-24, some hurdles are not avoidable. Regarding our expertise, herein, the importance of CPPs/THPs, needs for their elegant designing in a fusion structure, and their applications in cytokine gene therapy are discussed with a special focus on mda-7/IL-24.

Glioma targeting peptide in combination with the P53 C terminus inhibits glioma cell proliferation in vitro

Glioma is a prevalent malignant primary brain tumor in adults, the treatment for which remains a challenge due to its high infiltration and recurrence. Hence, treatments that lead to the suppression of glioma cell migration and invasion may be used in addition to surgery to increase the therapeutic outcome. In this study, we aimed to construct a multifunctional protein that would exert an effect on glioma cell proliferation and migration. The protein is named GL1-P53C-11R and it consists of the glioma-targeting peptide GL1 (G), the P53 C terminus (Pc) and the cell-penetrating peptide arginine (R). GL1-P53C-R was expressed with the fusion protein ZZ and immunofluorescence analysis showed effective delivery of the fused ZZ-GL1-P53C-R protein represented as ZZ-GPcR. The ZZ-GPcR exhibited an inhibitory effect on the proliferation, migration and invasion of U87ΔEGFR cells. Western blotting results indicated that it caused significant changes in the expression levels of cell cycle and apoptotic proteins. Flow cytometric analysis showed increase apoptosis. Our findings suggest that the P53C in the fusion protein ZZ-GPcR can enter into glioma cells to exert its inhibitory effect.

Necroptosis and ferroptosis are alternative cell death pathways that operate in acute kidney failure

Ferroptosis is a recently recognized caspase-independent form of regulated cell death that is characterized by the accumulation of lethal lipid ROS produced through iron-dependent lipid peroxidation. Considering that regulation of fatty acid metabolism is responsible for the membrane-resident pool of oxidizable fatty acids that undergo lipid peroxidation in ferroptotic processes, we examined the contribution of the key fatty acid metabolism enzyme, acyl-CoA synthetase long-chain family member 4 (ACSL4), in regulating ferroptosis. By using CRISPR/Cas9 technology, we found that knockout of Acsl4 in ferroptosis-sensitive murine and human cells conferred protection from erastin- and RSL3-induced cell death. In the same cell types, deletion of mixed lineage kinase domain-like (Mlkl) blocked susceptibility to necroptosis, as expected. Surprisingly, these studies also revealed ferroptosis and necroptosis are alternative, in that resistance to one pathway sensitized cells to death via the other pathway. These data suggest a mechanism by which one regulated necrosis pathway compensates for another when either ferroptosis or necroptosis is compromised. We verified the synergistic contributions of ferroptosis and necroptosis to tissue damage during acute organ failure in vivo. Interestingly, in the course of pathophysiological acute ischemic kidney injury, ACSL4 was initially upregulated and its expression level correlated with the severity of tissue damage. Together, our findings reveal ACSL4 to be a reliable biomarker of the emerging cell death modality of ferroptosis, which may also serve as a novel therapeutic target in preventing pathological cell death processes.