Partial cleavage of RasGAP by caspases is required for cell survival in mild stress conditions

Transient caspase-mediated activation of caspase-activated DNase causes DNA damage required for phagocytic macrophage differentiation

Phagocytic macrophages are crucial for innate immunity and tissue homeostasis. Most tissue-resident macrophages develop from embryonic precursors that populate every organ before birth to lifelong self-renew. However, the mechanisms for versatile macrophage differentiation remain unknown. Here, we use in vivo genetic and cell biological analysis of the Drosophila larval hematopoietic organ, the lymph gland that produces macrophages. We show that the developmentally regulated transient activation of caspase-activated DNase (CAD)-mediated DNA strand breaks in intermediate progenitors is essential for macrophage differentiation. Insulin receptor-mediated PI3K/Akt signaling regulates the apoptosis signal-regulating kinase 1 (Ask1)/c-Jun kinase (JNK) axis to control sublethal levels of caspase activation, causing DNA strand breaks during macrophage development. Furthermore, caspase activity is also required for embryonic-origin macrophage development and efficient phagocytosis. Our study provides insights into developmental signaling and CAD-mediated DNA strand breaks associated with multifunctional and heterogeneous macrophage differentiation.

Persister cell plasticity in tumour drug resistance

The emergence of therapeutic resistance remains a formidable barrier to durable responses by cancer patients and is a major cause of cancer-related deaths. It is increasingly recognized that non-genetic mechanisms of acquired resistance are important in many cancers. These mechanisms of resistance rely on inherent cellular plasticity where cancer cells can switch between multiple phenotypic states without genetic alterations, providing a dynamic, reversible resistance landscape. Such mechanisms underlie the generation of drug-tolerant persister (DTP) cells, a subpopulation of tumour cells that contributes to heterogeneity within tumours and that supports therapeutic resistance. In this review, we provide an overview of the major features of DTP cells, focusing on phenotypic and metabolic plasticity as two key drivers of tolerance and persistence. We discuss the link between DTP cell plasticity and the potential vulnerability of these cells to ferroptosis. We also discuss the relationship between DTP cells and cells that survive the induction of apoptosis, a process termed anastasis, and discuss the properties of such cells in the context of increased metastatic potential and sensitivity to cell death mechanisms such as ferroptosis.

Apoptotic signaling: Beyond cell death

Apoptosis is the best described form of regulated cell death, and was, until relatively recently, considered irreversible once particular biochemical points-of-no-return were activated. In this manuscript, we examine the mechanisms cells use to escape from a self-amplifying death signaling module. We discuss the role of feedback, dynamics, propagation, and noise in apoptotic signaling. We conclude with a revised model for the role of apoptosis in animal development, homeostasis, and disease.

Death and survival from executioner caspase activation

Executioner caspases are evolutionarily conserved regulators of cell death under apoptotic stress. Activated executioner caspases drive apoptotic cell death through cleavage of diverse protein substrates or pyroptotic cell death in the presence of gasdermin E. On the other hand, activation of executioner caspases can also trigger pro-survival and pro-proliferation signals. In recent years, a growing body of studies have demonstrated that cells can survive from executioner caspase activation in response to stress and that the survivors undergo molecular and phenotypic alterations. This review focuses on death and survival from executioner caspase activation, summarizing the role of executioner caspases in apoptotic and pyroptotic cell death and discussing the potential mechanism and consequences of survival from stress-induced executioner caspase activation.

Cellular stress management by caspases

Cellular stress plays a pivotal role in the onset of numerous human diseases. Consequently, the removal of dysfunctional cells, which undergo excessive stress-induced damage via various cell death pathways, including apoptosis, is essential for maintaining organ integrity and function. The evolutionarily conserved family of cysteine-aspartic-proteases, known as caspases, has been a key player in orchestrating apoptosis. However, recent research has unveiled the capability of these enzymes to govern fundamental cellular processes without triggering cell death. Remarkably, some of these non-lethal functions of caspases may contribute to restoring cellular equilibrium in stressed cells. This manuscript discusses how caspases can function as cellular stress managers and their potential impact on human health and disease. Additionally, it sheds light on the limitations of caspase-based therapies, given our still incomplete understanding of the biology of these enzymes, particularly in non-apoptotic contexts.

Cell survival following direct executioner-caspase activation

Executioner-caspase activation has been considered a point-of-no-return in apoptosis. However, numerous studies report survival from caspase activation after treatment with drugs or radiation. An open question is whether cells can recover from direct caspase activation without pro-survival stress responses induced by drugs. To address this question, we engineered a HeLa cell line to express caspase-3 inducibly and combined it with a quantitative caspase activity reporter. While high caspase activity levels killed all cells and very low levels allowed all cells to live, doses of caspase activity sufficient to kill 15 to 30% of cells nevertheless allowed 70 to 85% to survive. At these doses, neither the rate, nor the peak level, nor the total amount of caspase activity could accurately predict cell death versus survival. Thus, cells can survive direct executioner-caspase activation, and variations in cellular state modify the outcome of potentially lethal caspase activity. Such heterogeneities may underlie incomplete tumor cell killing in response to apoptosis-inducing cancer treatments.

Paradoxical roles of caspase-3 in regulating cell survival, proliferation, and tumorigenesis

Caspase-3 is a widely expressed member of a conserved family of proteins, generally recognized for their activated proteolytic roles in the execution of apoptosis in cells responding to specific extrinsic or intrinsic inducers of this mode of cell death. However, accumulating evidence indicates that caspase-3 also plays key roles in regulating the growth and homeostatic maintenance of both normal and malignant cells and tissues in multicellular organisms. Given that yeast possess an ancestral caspase-like gene suggests that the caspase-3 protein may have acquired different functions later during evolution to better meet the needs of more complex multicellular organisms, but without necessarily losing all of the functions of its ancestral yeast precursor. This review provides an update on what has been learned about these interesting dichotomous roles of caspase-3, their evolution, and their potential relevance to malignant as well as normal cell biology.

The roles of GTPase-activating proteins in regulated cell death and tumor immunity

GTPase-activating protein (GAP) is a negative regulator of GTPase protein that is thought to promote the conversion of the active GTPase-GTP form to the GTPase-GDP form. Based on its ability to regulate GTPase proteins and other domains, GAPs are directly or indirectly involved in various cell requirement processes. We reviewed the existing evidence of GAPs regulating regulated cell death (RCD), mainly apoptosis and autophagy, as well as some novel RCDs, with particular attention to their association in diseases, especially cancer. We also considered that GAPs could affect tumor immunity and attempted to link GAPs, RCD and tumor immunity. A deeper understanding of the GAPs for regulating these processes could lead to the discovery of new therapeutic targets to avoid pathologic cell loss or to mediate cancer cell death.

Signaling by the inhibitory receptor CD200R is rewired by type I interferon

CD200 receptor 1 (CD200R) is an inhibitory immunoreceptor that suppresses Toll-like receptor (TLR)–induced cytokine production through the adaptor protein Dok2 and the GTPase activating protein (GAP) p120-RasGAP, which can be cleaved during mild cellular stress. We found that in the presence of cleaved p120-RasGAP, CD200R lost its capacity to inhibit phosphorylation of ribosomal S6 protein (rpS6), suggesting the reduced activity of mammalian target of rapamycin complex 1 (mTORC1). Furthermore, treatment of human peripheral blood mononuclear cells (PBMC) with interferon-α (IFN-α) resulted in increased amounts of cleaved p120-RasGAP. Upon pretreatment of cells with increasing concentrations of IFN-α, CD200R switched from inhibiting to potentiating the TLR7- and TLR8-induced expression of the gene encoding IFN-γ, a cytokine that is important for innate and adaptive immunity and is implicated in systemic lupus erythematosus (SLE) pathogenesis. PBMC from patients with SLE, a prototypic type I IFN disease, had an increased abundance of cleaved p120-RasGAP compared to that in cells from healthy controls. In a subset of SLE patients, CD200R stopped functioning as an inhibitory receptor or potentiated TLR-induced IFNG mRNA expression. Thus, our data suggest that type I IFN rewires CD200R signaling to be proinflammatory, which could contribute to the perpetuation of inflammation in patients with SLE.

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.

Histone Deacetylase Inhibitor Trichostatin A Suppresses Cell Proliferation and Induces Apoptosis by Regulating the PI3K/AKT Signalling Pathway in Gastric Cancer Cells

BACKGROUND

Gastric cancer, a common malignant tumour worldwide, has a relatively poor prognosis and is a serious threat to human health. Histone Deacetylase Inhibitors (HDACi) are anticancer agents that are known to affect the cell growth of different cancer types. Trichostatin A (TSA) selectively inhibits the class I and II mammalian Histone Deacetylase (HDAC) family enzymes and regulates many cell processes. Still, the underlying mechanisms of HDACs are not fully understood in gastric cancer.

OBJECTIVE

This study aims to investigate the antitumor effect and the mechanism of growth modulation of gastric cancer cells by TSA.

METHODS

The cell proliferation of gastric cancer cells was measured by MTT and BrdU immunofluorescence assays. Soft agar assay was used to detect the colony formation ability of gastric cancer cells. Flow cytometry was used to examine cell cycle and apoptosis. Western blot was employed to detect protein expression of target factors.

RESULTS

TSA inhibits the proliferation of MKN-45 and SGC-7901 cells and leads to significant repression of colony number and size. Flow cytometry assays show TSA induces cell cycle arrest at G1 phase and apoptosis, and TSA effects the expression of related factors in the mitochondrial apoptotic signalling and cell cycle-related regulatory pathways. Furthermore, TSA increased histone H3K27 acetylation and downregulated the expression of PI3K and p-AKT.

CONCLUSION

Downregulating PI3K/AKT pathway activation is involved in TSA-mediated proliferation inhibition of gastric cancer.

Crosstalk of the Caspase Family and Mammalian Target of Rapamycin Signaling

Cell can integrate the caspase family and mammalian target of rapamycin (mTOR) signaling in response to cellular stress triggered by environment. It is necessary here to elucidate the direct response and interaction mechanism between the two signaling pathways in regulating cell survival and determining cell fate under cellular stress. Members of the caspase family are crucial regulators of inflammation, endoplasmic reticulum stress response and apoptosis. mTOR signaling is known to mediate cell growth, nutrition and metabolism. For instance, over-nutrition can cause the hyperactivation of mTOR signaling, which is associated with diabetes. Nutrition deprivation can inhibit mTOR signaling via SH3 domain-binding protein 4. It is striking that Ras GTPase-activating protein 1 is found to mediate cell survival in a caspase-dependent manner against increasing cellular stress, which describes a new model of apoptosis. The components of mTOR signaling-raptor can be cleaved by caspases to control cell growth. In addition, mTOR is identified to coordinate the defense process of the immune system by suppressing the vitality of caspase-1 or regulating other interferon regulatory factors. The present review discusses the roles of the caspase family or mTOR pathway against cellular stress and generalizes their interplay mechanism in cell fate determination.

Chromosome-level de novo assembly of Coprinopsis cinerea A43mut B43mut pab1-1 #326 and genetic variant identification of mutants using Nanopore MinION sequencing

The homokaryotic Coprinopsis cinerea strain A43mut B43mut pab1-1 #326 is a widely used experimental model for developmental studies in mushroom-forming fungi. It can grow on defined artificial media and complete the whole lifecycle within two weeks. The mutations in mating type factors A and B result in the special feature of clamp formation and fruiting without mating. This feature allows investigations and manipulations with a homokaryotic genetic background. Current genome assembly of strain #326 was based on short-read sequencing data and was highly fragmented, leading to the bias in gene annotation and downstream analyses. Here, we report a chromosome-level genome assembly of strain #326. Oxford Nanopore Technology (ONT) MinION sequencing was used to get long reads. Illumina short reads was used to polish the sequences. A combined assembly yield 13 chromosomes and a mitochondrial genome as individual scaffolds. The assembly has 15,250 annotated genes with a high synteny with the C. cinerea strain Okayama-7 #130. This assembly has great improvement on contiguity and annotations. It is a suitable reference for further genomic studies, especially for the genetic, genomic and transcriptomic analyses in ONT long reads. Single nucleotide variants and structural variants in six mutagenized and cisplatin-screened mutants could be identified and validated. A 66 bp deletion in Ras GTPase-activating protein (RasGAP) was found in all mutants. To make a better use of ONT sequencing platform, we modified a high-molecular-weight genomic DNA isolation protocol based on magnetic beads for filamentous fungi. This study showed the use of MinION to construct a fungal reference genome and to perform downstream studies in an individual laboratory. An experimental workflow was proposed, from DNA isolation and whole genome sequencing, to genome assembly and variant calling. Our results provided solutions and parameters for fungal genomic analysis on MinION sequencing platform.

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.

Implementing Patient-Derived Xenografts to Assess the Effectiveness of Cyclin-Dependent Kinase Inhibitors in Glioblastoma

Glioblastoma (GBM) is the most common primary brain tumor with no available cure. As previously described, seliciclib, a first-generation cyclin-dependent kinase (CDK) inhibitor, down-regulates the anti-apoptotic protein, Mcl-1, in GBM, thereby sensitizing GBM cells to the apoptosis-inducing effects of the death receptor ligand, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). Here, we have assessed the efficacy of seliciclib when delivered in combination with the antibody against human death receptor 5, drozitumab, in clinically relevant patient-derived xenograft (PDX) models of GBM. A reduction in viability and significant levels of apoptosis were observed in vitro in human GBM neurospheres following treatment with seliciclib plus drozitumab. While the co-treatment strategy induced a similar effect in PDX models, the dosing regimen required to observe seliciclib-targeted responses in the brain, resulted in lethal toxicity in 45% of animals. Additional studies showed that the second-generation CDK inhibitor, CYC065, with improved potency in comparison to seliciclib, induced a significant decrease in the size of human GBM neurospheres in vitro and was well tolerated in vivo, upon administration at clinically relevant doses. This study highlights the continued need for robust pre-clinical assessment of promising treatment approaches using clinically relevant models.

Caspase Cleavage of Gelsolin Is an Inductive Cue for Pathologic Cardiac Hypertrophy

Background

Cardiac hypertrophy is an adaptive remodeling event that may improve or diminish contractile performance of the heart. Physiologic and pathologic hypertrophy yield distinct outcomes, yet both are dependent on caspase‐directed proteolysis. This suggests that each form of myocardial growth may derive from a specific caspase cleavage event(s). We examined whether caspase 3 cleavage of the actin capping/severing protein gelsolin is essential for the development of pathologic hypertrophy.

Methods and Results

Caspase targeting of gelsolin was established through protein analysis of hypertrophic cardiomyocytes and mass spectrometry mapping of cleavage sites. Pathologic agonists induced late‐stage caspase‐mediated cleavage of gelsolin. The requirement of caspase‐mediated gelsolin cleavage for hypertrophy induction was evaluated in primary cardiomyocytes by cell size analysis, monitoring of prohypertrophy markers, and measurement of hypertrophy‐related transcription activity. The in vivo impact of caspase‐mediated cleavage was investigated by echo‐guided intramyocardial injection of adenoviral‐expressed gelsolin. Expression of the N‐terminal gelsolin caspase cleavage fragment was necessary and sufficient to cause pathologic remodeling in isolated cardiomyocytes and the intact heart, whereas expression of a noncleavable form prevents cardiac remodeling. Alterations in myocardium structure and function were determined by echocardiography and end‐stage cardiomyocyte cell size analysis. Gelsolin secretion was also monitored for its impact on naïve cells using competitive antibody trapping, demonstrating that hypertrophic agonist stimulation of cardiomyocytes leads to gelsolin secretion, which induces hypertrophy in naïve cells.

Conclusions

These results suggest that cell autonomous caspase cleavage of gelsolin is essential for pathologic hypertrophy and that cardiomyocyte secretion of gelsolin may accelerate this negative remodeling response.

Regulating Apoptosis by Degradation: The N-End Rule-Mediated Regulation of Apoptotic Proteolytic Fragments in Mammalian Cells

A pivotal hallmark of some cancer cells is the evasion of apoptotic cell death. Importantly, the initiation of apoptosis often results in the activation of caspases, which, in turn, culminates in the generation of proteolytically-activated protein fragments with potentially new or altered roles. Recent investigations have revealed that the activity of a significant number of the protease-generated, activated, pro-apoptotic protein fragments can be curbed via their selective degradation by the N-end rule degradation pathways. Of note, previous work revealed that several proteolytically-generated, pro-apoptotic fragments are unstable in cells, as their destabilizing N-termini target them for proteasomal degradation via the N-end rule degradation pathways. Remarkably, previous studies also showed that the proteolytically-generated anti-apoptotic Lyn kinase protein fragment is targeted for degradation by the UBR1/UBR2 E3 ubiquitin ligases of the N-end rule pathway in chronic myeloid leukemia cells. Crucially, the degradation of cleaved fragment of Lyn by the N-end rule counters imatinib resistance in these cells, implicating a possible linkage between the N-end rule degradation pathway and imatinib resistance. Herein, we highlight recent studies on the role of the N-end rule proteolytic pathways in regulating apoptosis in mammalian cells, and also discuss some possible future directions with respect to apoptotic proteolysis signaling.

The Role of Apoptotic Signaling in Axon Guidance

Navigating growth cones are exposed to multiple signals simultaneously and have to integrate competing cues into a coherent navigational response. Integration of guidance cues is traditionally thought to occur at the level of cytoskeletal dynamics. Drosophila studies indicate that cells exhibit a low level of continuous caspase protease activation, and that axon guidance cues can activate or suppress caspase activity. We base a model for axon guidance on these observations. By analogy with other systems in which caspase signaling has non-apoptotic functions, we propose that caspase signaling can either reinforce repulsion or negate attraction in response to external guidance cues by cleaving cytoskeletal proteins. Over the course of an entire trajectory, incorrectly navigating axons may pass the threshold for apoptosis and be eliminated, whereas axons making correct decisions will survive. These observations would also explain why neurotrophic factors can act as axon guidance cues and why axon guidance systems such as Slit/Robo signaling may act as tumor suppressors in cancer.

p-Coumaric acid mediated protection of H9c2 cells from Doxorubicin-induced cardiotoxicity: Involvement of augmented Nrf2 and autophagy

Doxorubicin (Dox) is a widely administered chemotherapeutic drug and incidences of cardiotoxicity associated with its administration have been of general concern. Extensive research proposes several mechanisms as a cause of Dox induced cardiotoxicity. However, none of these studies have been able to suggest a find one, cure all antidote for the same. To this end, several studies involving plant based compounds or natural products have gained acclaim for their ability to address at least one factor contributing to drug induced pathogenesis. We had previously reported that p-coumaric (pCA) has a protective effect on Dox induced oxidative stress in rat-derived cardiomyoblasts. In this study we investigated the effects of pCA on the regulation of Nrf-2, mitochondrial viability, autophagy and apoptosis in Doxorubicin treated H9c2 cardiomyocytes. ROS induced mitochondrial stress, changes in mitochondrial membrane potential, loss of membrane integrity; nuclear damage as single/double stranded breaks, autophagy and the effects of pre and co-treatment of pCA on Nrf-2 mediated signaling was evaluated by various approaches. The effect of pCA on drug uptake was evaluated through confocal Raman Spectroscopy. We find that nuclear translocation of Nrf-2 is prominently marked by protein-specific antibody conjugated fluorophore in Dox treated cells especially. Cell survival is mediated to a certain extent by the expression of the anti-apoptotic BCl2 in pCA treated cells. However, mRNA levels of autophagy related (Atg) genes suggest that autophagy plays a decisive role in deciding cellular fate. Caspase-3 activation is also observed in pCA treated cells which suggest an alternative function of caspase-3 in pCA mediated cell survival. Expression of antioxidant enzymes confirm the oxidative stress induced by Dox treatment in cells and the modulation of cell redox homeostasis through treatment with pCA.

RASA1 regulates the function of lymphatic vessel valves in mice

Capillary malformation-arteriovenous malformation (CM-AVM) is a blood and lymphatic vessel (LV) disorder that is caused by inherited inactivating mutations of the RASA1 gene, which encodes p120 RasGAP (RASA1), a negative regulator of the Ras small GTP-binding protein. How RASA1 mutations lead to the LV leakage defects that occur in CM-AVM is not understood. Here, we report that disruption of the Rasa1 gene in adult mice resulted in loss of LV endothelial cells (LECs) specifically from the leaflets of intraluminal valves in collecting LVs. As a result, valves were unable to prevent fluid backflow and the vessels were ineffective pumps. Furthermore, disruption of Rasa1 in midgestation resulted in LEC apoptosis in developing LV valves and consequently failed LV valvulogenesis. Similar phenotypes were observed in induced RASA1-deficient adult mice and embryos expressing a catalytically inactive RASA1R780Q mutation. Thus, RASA1 catalytic activity is essential for the function and development of LV valves. These data provide a partial explanation for LV leakage defects and potentially other LV abnormalities observed in CM-AVM.

Active caspase-3 expression levels as bioindicator of individual radiosensitivity

Several molecules and events involved in cell response to radiation-induced damage have been investigated towards a personalized radiotherapy. Considering the importance of active caspase-3 in the proteolytic cascade that ensures radiation-induced apoptosis execution, this research was designed to evaluate the expression levels of this protein as a bioindicator of individual radiosensitivity. Peripheral blood samples of 10 healthy individuals were gamma-irradiated (cobalt-60 source) with 1, 2 and 4 Gy (control: non-irradiated samples), and active caspase-3 expression levels were measured in lymphocytes, by flow cytometry, ex vivo and after different times of in vitro incubation (24, 48 and 72 hours). Short-term incubation of 24 h was the most adequate condition to evidence correlations between dose radiation and active caspase-3 expression. For each radiation dose, it was observed a significant inter-individual variation in active caspase-3 expression intensity, suggesting that this parameter may be suitable for evidence individual radiosensitivity. The methodology presented and discussed in this work may help to predict healthy tissues response to radiation exposure toward the better patient outcome.

TAT-RasGAP317-326 Enhances Radiosensitivity of Human Carcinoma Cell Lines In Vitro and In Vivo through Promotion of Delayed Mitotic Cell Death

The synthetic peptide TAT-RasGAP_317-326 has been shown to potentiate the efficacy of anti-cancer drugs. In this study, we explored the action of TAT-RasGAP_317-326 when combined with radiation by investigating its radiosensitizing activity in vitro and in vivo. To investigate the modulation of intrinsic radiosensitivity induced by TAT-RasGAP_317-326, clonogenic assays were performed using four human cancer cell lines, HCT116 p53^+/+ (ATCC: CCL-247), HCT116 p53^-/-, PANC-1 (ATCC: CRL-1469) and HeLa (ATCC: CCL-2), as well as one nontumor cell line, HaCaT (CLS: 300493). Next, to investigate tumor growth delay after irradiation, HCT116 cell lines were selected and xenografted onto nude mice that were then treated with TAT-RasGAP_317-326 alone or in combination with radiation or cisplatin. Afterwards, cell cycle and death modulation were investigated by quantification of micronuclei and apoptosis-related protein array. TAT-RasGAP_317-326 radiosensitized all four human carcinoma cell lines tested but displayed no effect on normal cells. It also displayed no effect when administered as monotherapy. This radiosensitizing effect was confirmed in vivo in both p53-positive and p53-negative HCT116 xenografts. TAT-RasGAP_317-326 combined with radiation enhanced the number of cells in S phase and subsequently delayed cell death, but had almost no effect on major apoptosis-related proteins. TAT-RasGAP_317-326 is a radiosensitizing agent that acts on carcinoma cells and its radiosensitizing effect might be mediated, at least in part, by the enhancement of mitotic cell death.

The caspase-3/p120 RasGAP stress-sensing module reduces liver cancer incidence but does not affect overall survival in gamma-irradiated and carcinogen-treated mice

Activation of oncogenes is the initial step in cellular transformation. Oncogenes favor aberrant proliferation, which, at least initially, induces cellular stress. This oncogenic stress can act as a safeguard mechanism against further transformation by inducing senescence or apoptosis. Yet, the few premalignant cells that tolerate and escape these senescent or apoptotic responses are those that will ultimately generate tumors. The caspase-3/p120 RasGAP module is a stress-sensing device that promotes survival under mild stress conditions. A point mutation in RasGAP that prevents its cleavage by caspase-3 inactivates the pro-survival capacity of the device. When the mice homozygous for this mutation (D455A knock-in mice) are patho-physiologically challenged, they experience much stronger cellular damage than their wild-type counterparts and the affected organs rapidly lose their functionality. We reasoned that the caspase-3/p120 RasGAP module could help premalignant cells to cope with oncogenic stress and hence favor the development of tumors. Using gamma-irradiation and N-ethyl-N-nitrosourea (ENU) as tumor initiators, we assessed the survival advantage that the caspase-3/p120 RasGAP module could provide to premalignant cells. No difference in overall mortality between wild-type and D455A knock-in mice were observed. However, the number of ENU-induced liver tumors in the knock-in mice was higher than in control mice. These results indicate that the caspase-3/p120 RasGAP stress-sensing module impacts on carcinogen-induced liver cancer incidence but not sufficiently so as to affect overall survival. Hence, gamma irradiation and ENU-induced tumorigenesis processes do not critically rely on a survival mechanism that contributes to the maintenance of organ homeostasis in stressed healthy tissues.

Whole-eye electrical stimulation therapy preserves visual function and structure in P23H-1 rats

Low-level electrical stimulation to the eye has been shown to be neuroprotective against retinal degeneration in both human and animal subjects, using approaches such as subretinal implants and transcorneal electrical stimulation. In this study, we investigated the benefits of whole-eye electrical stimulation (WES) in a rodent model of retinitis pigmentosa. Transgenic rats with a P23H-1 rhodopsin mutation were treated with 30 min of low-level electrical stimulation (4 μA at 5 Hz; n = 10) or sham stimulation (Sham group; n = 15), twice per week, from 4 to 24 weeks of age. Retinal and visual functions were assessed every 4 weeks using electroretinography and optokinetic tracking, respectively. At the final time point, eyes were enucleated and processed for histology. Separate cohorts were stimulated once for 30 min, and retinal tissue harvested at 1 h and 24 h post-stimulation for real-time PCR detection of growth factors and inflammatory and apoptotic markers. At all time-points after treatment, WES-treated rat eyes exhibited significantly higher spatial frequency thresholds than untreated eyes. Inner retinal function, as measured by ERG oscillatory potentials (OPs), showed significantly improved OP amplitudes at 8 and 12 weeks post-WES compared to Sham eyes. Additionally, while photoreceptor segment and nuclei thicknesses in P23H-1 rats did not change between treatment groups, WES-treated eyes had significantly greater numbers of retinal ganglion cell nuclei than Sham eyes at 20 weeks post-WES. Gene expression levels of brain-derived neurotrophic factor (BDNF), caspase 3, fibroblast growth factor 2 (FGF2), and glutamine synthetase (GS) were significantly higher at 1 h, but not 24 h after WES treatment. Our findings suggest that WES has a beneficial effect on visual function in a rat model of retinal degeneration and that post-receptoral neurons may be particularly responsive to electrical stimulation therapy.

Trophic factors deprivation induces long-term protection of neurons against excitotoxic damage

One of the strategies to induce tolerance of neurons to toxic injury is preconditioning. Preconditioning is caused by a weak damage of cells, which become more resistant to subsequent, more severe damage. We found that preconditioning by deprivation of trophic factors, or deprivation of trophic factor and glucose effectively protects neurons against subsequent toxic effects of glutamate. Deprivation of trophic factors plays a decisive role in the development of resistance, regardless of whether it has been combined with glucose deprivation or not. Neuronal protection is achieved when the deprivation lasts from 30 min to two hours and is kept for a period of from one to five days. Preconditioning is accompanied neuronal secretion of cathepsin B occurs. We suggest that this phenomenon is associated with a more general process of exocytosis of lysosomes triggered by deprivation of trophic factors.

Apoptotic Caspases in Promoting Cancer: Implications from Their Roles in Development and Tissue Homeostasis

Apoptosis, a major form of programmed cell death, is an important mechanism to remove extra or unwanted cells during development. In tissue homeostasis apoptosis also acts as a monitoring machinery to eliminate damaged cells in response to environmental stresses. During these processes, caspases, a group of proteases, have been well defined as key drivers of cell death. However, a wealth of evidence is emerging which supports the existence of many other non-apoptotic functions of these caspases, which are essential not only in proper organism development but also in tissue homeostasis and post-injury recovery. In particular, apoptotic caspases in stress-induced dying cells can activate mitogenic signals leading to proliferation of neighbouring cells, a phenomenon termed apoptosis-induced proliferation. Apparently, such non-apoptotic functions of caspases need to be controlled and restrained in a context-dependent manner during development to prevent their detrimental effects. Intriguingly, accumulating studies suggest that cancer cells are able to utilise these functions of caspases to their advantage to enable their survival, proliferation and metastasis in order to grow and progress. This book chapter will review non-apoptotic functions of the caspases in development and tissue homeostasis with focus on how these cellular processes can be hijacked by cancer cells and contribute to tumourigenesis.

Mitochondria and the hallmarks of cancer

Mitochondria have traditionally been viewed as the powerhouse of the cell, where they serve, amongst other functions, as a major source of ATP generation. More recently, mitochondria have also been shown to have active roles in a variety of other processes, including apoptotic cell death and inflammation. Here we review the various ways in which mitochondrial functions affect cancer. Although there are many diverse types of cancer, hallmarks have been defined that are applicable to most cancer types. We provide an overview of how mitochondrial functions affect some of these hallmarks, which include evasion of cell death, de-regulated bioenergetics, genome instability, tumour-promoting inflammation and metastasis. In addition to discussing the underlying mitochondrial roles in each of these processes, we also highlight the considerable potential of targeting mitochondrial functions to improve cancer treatment.

Possible role of proteases in preconditioning of brain cells to pathological conditions

Preconditioning (PC) is one of the most effective strategies to reduce the severity of cell damage, in particular of nervous tissue cells. Although PC mechanisms are studied insufficiently, it is clear that proteases are involved in them, but their role has yet been not studied in detail. In this work, some mechanisms of a potential recruiting of proteases in PC are considered. Our attention is mainly focused on the protease families of caspases and cathepsins and on protease receptors. We present evidence that just these proteins are involved in the PC of brain cells. A hypothesis is proposed that secreted cathepsin B is involved in the realization of PC through activation of PAR2 receptor.

RasGAP Shields Akt from Deactivating Phosphatases in Fibroblast Growth Factor Signaling but Loses This Ability Once Cleaved by Caspase-3

Fibroblast growth factor receptors (FGFRs) are involved in proliferative and differentiation physiological responses. Deregulation of FGFR-mediated signaling involving the Ras/PI3K/Akt and the Ras/Raf/ERK MAPK pathways is causally involved in the development of several cancers. The caspase-3/p120 RasGAP module is a stress sensor switch. Under mild stress conditions, RasGAP is cleaved by caspase-3 at position 455. The resulting N-terminal fragment, called fragment N, stimulates anti-death signaling. When caspase-3 activity further increases, fragment N is cleaved at position 157. This generates a fragment, called N2, that no longer protects cells. Here, we investigated in Xenopus oocytes the impact of RasGAP and its fragments on FGF1-mediated signaling during G2/M cell cycle transition. RasGAP used its N-terminal Src homology 2 domain to bind FGFR once stimulated by FGF1, and this was necessary for the recruitment of Akt to the FGFR complex. Fragment N, which did not associate with the FGFR complex, favored FGF1-induced ERK stimulation, leading to accelerated G2/M transition. In contrast, fragment N2 bound the FGFR, and this inhibited mTORC2-dependent Akt Ser-473 phosphorylation and ERK2 phosphorylation but not phosphorylation of Akt on Thr-308. This also blocked cell cycle progression. Inhibition of Akt Ser-473 phosphorylation and entry into G2/M was relieved by PHLPP phosphatase inhibition. Hence, full-length RasGAP favors Akt activity by shielding it from deactivating phosphatases. This shielding was abrogated by fragment N2. These results highlight the role played by RasGAP in FGFR signaling and how graded stress intensities, by generating different RasGAP fragments, can positively or negatively impact this signaling.

The caspase-3/p120 RasGAP module generates a NF-κB repressor in response to cellular stress

The NF-κB transcription factor is a master regulator of inflammation. Short-term NF-κB activation is generally beneficial. However, sustained NF-κB may be detrimental, directly causing apoptosis of cells or leading to a persistent damaging inflammatory response. NF-κB activity in stressed cells needs therefore to be controlled for homeostasis maintenance. Here we show that fragment N that is produced by the caspase-3/p120 RasGAP sensor in mildly stressed cells is a potent NF-κB inhibitor. Fragment N decreases the transcriptional activity of NF-κB by promoting its export from the nucleus. Cells unable to generate fragment N displayed increased NF-κB activation upon stress. Knock-in mice expressing the uncleavable RasGAP mutant showed exaggerated NF-κB activation when their epidermis was treated with anthralin, a drug used for the treatment of psoriasis. Our study provides biochemical and genetic evidence of the importance of the caspase-3/p120 RasGAP stress-sensing module in the control of stress-induced NF-κB activation.

Interleukin-1β enhances FasL-induced caspase-3/-7 activity without increasing apoptosis in primary mouse hepatocytes

Sustained inflammation may increase the susceptibility of hepatocytes to apoptotic cell death and therefore exacerbate liver damage. Here we report that the pro-inflammatory cytokine IL-1β sensitizes primary murine hepatocytes to Fas ligand (FasL)-induced caspase-3/-7 activity. This process was dependent on JNK1/2 and the BH3-only proteins Bim and Bid. Mathematical modeling revealed that incubation of hepatocytes with IL-1β depleted the anti-apoptotic Bcl-2 protein pool and thus shifted hepatocytes to mitochondrial type II apoptosis following Fas activation. As a consequence, IL-1β and FasL treatment enhanced cytochrome c release. Surprisingly, despite increased caspase-3/-7 activation, FasL-induced cell death was reduced by IL-1β pre-treatment. This protective effect was independent of JNK1/2, Bim or Bid. Furthermore, elevated caspase-3/-7 activity upon IL-1β and FasL treatment did not result in enhanced PARP cleavage. The protective effect of IL-1β was seen after 3 h of pre-incubation, indicating an anti-apoptotic transcriptional response. Indeed, NF-κB DNA binding was increased in response to IL-1β plus FasL and gene-expression profiling of NF-κB regulated genes revealed a transcriptional and translational upregulation of the caspase-8 inhibitor A20. A mathematical model was developed to explain the contradictious occurrence of both increased caspase-3/-7 activity and elevated cell viability by including a heterogeneous distribution of Bcl-2 proteins and variations in Fas signaling resulting in different subpopulations of hepatocytes.

The activity of the anti-apoptotic fragment generated by the caspase-3/p120 RasGAP stress-sensing module displays strict Akt isoform specificity

The caspase-3/p120 RasGAP module acts as a stress sensor that promotes pro-survival or pro-death signaling depending on the intensity and the duration of the stressful stimuli. Partial cleavage of p120 RasGAP generates a fragment, called fragment N, which protects stressed cells by activating Akt signaling. Akt family members regulate many cellular processes including proliferation, inhibition of apoptosis and metabolism. These cellular processes are regulated by three distinct Akt isoforms: Akt1, Akt2 and Akt3. However, which of these isoforms are required for fragment N mediated protection have not been defined. In this study, we investigated the individual contribution of each isoform in fragment N-mediated cell protection against Fas ligand induced cell death. To this end, DLD1 and HCT116 isogenic cell lines lacking specific Akt isoforms were used. It was found that fragment N could activate Akt1 and Akt2 but that only the former could mediate the protective activity of the RasGAP-derived fragment. Even overexpression of Akt2 or Akt3 could not rescue the inability of fragment N to protect cells lacking Akt1. These results demonstrate a strict Akt isoform requirement for the anti-apoptotic activity of fragment N.

The δ-opioid receptor affects epidermal homeostasis via ERK-dependent inhibition of transcription factor POU2F3

Neuropeptides and their receptors are present in human skin, and their importance for cutaneous homeostasis and during wound healing is increasingly appreciated. However, there is currently a lack of understanding of the molecular mechanisms by which their signaling modulates keratinocyte function. Here, we show that δ-opioid receptor (DOPr) activation inhibits proliferation of human keratinocytes, resulting in decreased epidermal thickness in an organotypic skin model. DOPr signaling markedly delayed induction of keratin intermediate filament (KRT10) during in vitro differentiation and abolished its induction in the organotypic skin model. This was accompanied by deregulation of involucrin (IVL), loricrin, and filaggrin. Analysis of the transcription factor POU2F3, which is involved in regulation of KRT10, IVL, and profilaggrin expression, revealed a DOPr-mediated extracellular signal-regulated kinase (ERK)-dependent downregulation of this factor. We propose that DOPr signaling specifically activates the ERK 1/2 mitogen-activated protein kinase pathway to regulate keratinocyte functions. Complementing our earlier studies in DOPr-deficient mice, these data suggest that DOPr activation in human keratinocytes profoundly influences epidermal morphogenesis and homeostasis.

A WXW motif is required for the anticancer activity of the TAT-RasGAP317-326 peptide

TAT-RasGAP317-326, a cell-permeable 10-amino acid-long peptide derived from the N2 fragment of p120 Ras GTPase-activating protein (RasGAP), sensitizes tumor cells to apoptosis induced by various anticancer therapies. This RasGAP-derived peptide, by targeting the deleted in liver cancer-1 (DLC1) tumor suppressor, also hampers cell migration and invasion by promoting cell adherence and by inhibiting cell movement. Here, we systematically investigated the role of each amino acid within the RasGAP317-326 sequence for the anticancer activities of TAT-RasGAP317-326. We report here that the first three amino acids of this sequence, tryptophan, methionine, and tryptophan (WMW), are necessary and sufficient to sensitize cancer cells to cisplatin-induced apoptosis and to reduce cell migration. The WMW motif was found to be critical for the binding of fragment N2 to DLC1. These results define the interaction mode between the active anticancer sequence of RasGAP and DLC1. This knowledge will facilitate the design of small molecules bearing the tumor-sensitizing and antimetastatic activities of TAT-RasGAP317-326.

RasGAP-derived peptide GAP159 enhances cisplatin-induced cytotoxicity and apoptosis in HCT116 cells

To increase the efficacy of currently used anti-cancer genotoxins, one of the current efforts is to find agents that can sensitize cancer cells to genotoxins so that the efficacious doses of genotoxins can be lowered to reduce deleterious side-effects. In this study, we reported that a synthetic RasGAP-derived peptide GAP159 could enhance the effect of chemotherapeutic agent cisplatin (CDDP) in human colon carcinoma HCT116 cells. Our results showed that GAP159 significantly increased the CDDP-induced cytotoxicity and apoptosis in HCT116 cells. This synergistic effect was associated with the inhibitions of phospho-AKT, phospho-ERK and NF-κB. In mouse colon tumor CT26 animal models, GAP159 combined with CDDP significantly suppressed CT26 tumor growth, and GAP159 alone showed slight inhibitory effect. Our data suggests that co-treatment of GAP159 and chemotherapeutics will become a potential therapeutic strategy for colon cancers.

Fragment N2, a caspase-3-generated RasGAP fragment, inhibits breast cancer metastatic progression

The p120 RasGAP protein negatively regulates Ras via its GAP domain. RasGAP carries several other domains that modulate several signaling molecules such as Rho. RasGAP is also a caspase-3 substrate. One of the caspase-3-generated RasGAP fragments, corresponding to amino acids 158-455 and called fragment N2, was previously reported to specifically sensitize cancer cells to death induced by various anticancer agents. Here, we show that fragment N2 inhibits migration in vitro and that it impairs metastatic progression of breast cancer to the lung. Hence, stress-activated caspase-3 might contribute to the suppression of metastasis through the generation of fragment N2. These results indicate that the activity borne by fragment N2 has a potential therapeutic relevance to counteract the metastatic process.

Visualization of caspase-3-like activity in cells using a genetically encoded fluorescent biosensor activated by protein cleavage

Cytosolic caspase-3-like proteases, such as caspase-3 and caspase-7, have a central role in mediating the progress of apoptosis. Here to conveniently monitor caspase-3-like activity in the multicellular environment, we have developed genetically encoded switch-on fluorescence-base indicators that are cyclized chimeras containing a caspase-3 cleavage site as a switch. When cleaved by caspase-3-like proteases, the non-fluorescent indicator rapidly becomes fluorescent, and thus detects in real-time the activation of such caspases. We generate cultured cells constitutively expressing these chimeras, and all the healthy cells are non-fluorescent. When these cells are exposed to apoptotic stimuli, dead cells show strong fluorescence depending on caspase activation. With these tools, we monitor in real-time caspase-3-like activity in each cell under various conditions, and show for the first time that the environment of cancer cells affects their sensitivity to chemotherapeutic drugs in a modified soft agar assay. These biosensors should enable better understanding of the biological relevance of caspase-3-like proteases.

HDLs protect the MIN6 insulinoma cell line against tunicamycin-induced apoptosis without inhibiting ER stress and without restoring ER functionality

HDLs protect pancreatic beta cells against apoptosis induced by several endoplasmic reticulum (ER) stressors, including thapsigargin, cyclopiazonic acid, palmitate and insulin over-expression. This protection is mediated by the capacity of HDLs to maintain proper ER morphology and ER functions such as protein folding and trafficking. Here, we identified a distinct mode of protection exerted by HDLs in beta cells challenged with tunicamycin (TM), a protein glycosylation inhibitor inducing ER stress. HDLs were found to inhibit apoptosis induced by TM in the MIN6 insulinoma cell line and this correlated with the maintenance of a normal ER morphology. Surprisingly however, this protective response was neither associated with a significant ER stress reduction, nor with restoration of protein folding and trafficking in the ER. These data indicate that HDLs can use at least two mechanisms to protect beta cells against ER stressors. One that relies on the maintenance of ER function and one that operates independently of ER function modulation. The capacity of HDLs to activate several anti-apoptotic pathways in beta cells may explain their ability to efficiently protect these cells against a variety of insults.

Caspase-3 and RasGAP: a stress-sensing survival/demise switch

The final decision on cell fate, survival versus cell death, relies on complex and tightly regulated checkpoint mechanisms. The caspase-3 protease is a predominant player in the execution of apoptosis. However, recent progress has shown that this protease paradoxically can also protect cells from death. Here, we discuss the underappreciated, protective, and prosurvival role of caspase-3 and detail the evidence showing that caspase-3, through differential processing of p120 Ras GTPase-activating protein (RasGAP), can modulate a given set of proteins to generate, depending on the intensity of the input signals, opposite outcomes (survival vs death).

Role of mTOR, Bad, and Survivin in RasGAP Fragment N-Mediated Cell Protection

Partial cleavage of p120 RasGAP by caspase-3 in stressed cells generates an N-terminal fragment, called fragment N, which activates an anti-apoptotic Akt-dependent survival response. Akt regulates several effectors but which of these mediate fragment N-dependent cell protection has not been defined yet. Here we have investigated the role of mTORC1, Bad, and survivin in the capacity of fragment N to protect cells from apoptosis. Neither rapamycin, an inhibitor of mTORC1, nor silencing of raptor, a subunit of the mTORC1 complex, altered the ability of fragment N from inhibiting cisplatin- and Fas ligand-induced death. Cells lacking Bad, despite displaying a stronger resistance to apoptosis, were still protected by fragment N against cisplatin-induced death. Fragment N was also able to protect cells from Fas ligand-induced death in conditions where Bad plays no role in apoptosis regulation. Fragment N expression in cells did neither modulate survivin mRNA nor its protein expression. Moreover, the expression of cytoplasmic survivin, known to exert anti-apoptotic actions in cells, still occurred in UV-B-irradiated epidermis of mouse expressing a caspase-3-resistant RasGAP mutant that cannot produce fragment N. Additionally, survivin function in cell cycle progression was not affected by fragment N. These results indicate that, taken individually, mTOR, Bad, or Survivin are not required for fragment N to protect cells from cell death. We conclude that downstream targets of Akt other than mTORC1, Bad, or survivin mediate fragment N-induced protection or that several Akt effectors can compensate for each other to induce the pro-survival fragment N-dependent response.

Caspase-3 protects stressed organs against cell death

The ability to generate appropriate defense responses is crucial for the survival of an organism exposed to pathogenesis-inducing insults. However, the mechanisms that allow tissues and organs to cope with such stresses are poorly understood. Here we show that caspase-3-knockout mice or caspase inhibitor-treated mice were defective in activating the antiapoptotic Akt kinase in response to various chemical and environmental stresses causing sunburns, cardiomyopathy, or colitis. Defective Akt activation in caspase-3-knockout mice was accompanied by increased cell death and impaired survival in some cases. Mice homozygous for a mutation in RasGAP that prevents its cleavage by caspase-3 exhibited a similar defect in Akt activation, leading to increased apoptosis in stressed organs, marked deterioration of their physiological functions, and stronger disease development. Our results provide evidence for the relevance of caspase-3 as a stress intensity sensor that controls cell fate by either initiating a RasGAP cleavage-dependent cell resistance program or a cell suicide response.

The role of endogenous and exogenous RasGAP-derived fragment N in protecting cardiomyocytes from peroxynitrite-induced apoptosis

Peroxynitrite (PN) is a potent nitrating and oxidizing agent generated during various pathological situations affecting the heart. The negative effects of PN result, at least in part, from its ability to activate caspases and apoptosis. RasGAP is a ubiquitously expressed protein that is cleaved sequentially by caspase-3. At low caspase-3 activity, RasGAP is cleaved into an N-terminal fragment, called fragment N, that protects cells by activating the Ras/PI3K/Akt pathway. At high caspase-3 activity, fragment N is further cleaved and this abrogates its capacity to stimulate the antiapoptotic Akt kinase. Fragment N formation is crucial for the survival of cells exposed to a variety of stresses. Here we investigate the pattern of RasGAP cleavage upon PN stimulation and the capacity of fragment N to protect cardiomyocytes. PN did not lead to sequential cleavage of RasGAP. Indeed, PN did not allow accumulation of fragment N because it induced its rapid cleavage into smaller fragments. No situations were found in cells treated with PN in which the presence of fragment N was associated with survival. However, expression of a caspase-resistant form of fragment N in cardiomyocytes protected them from PN-induced apoptosis. Our results indicate that the antiapoptotic pathway activated by fragment N is effective at inhibiting PN-induced apoptosis (as seen when cardiomyocytes express a capase-3-resistant form of fragment N) but because fragment N is too transiently generated in response to PN, no survival response is effectively produced. This may explain the marked deleterious consequences of PN generation in various organs, including the heart.

RasGAP-derived fragment N increases the resistance of beta cells towards apoptosis in NOD mice and delays the progression from mild to overt diabetes

The caspase-3-generated RasGAP N-terminal fragment (fragment N) inhibits apoptosis in a Ras-PI3K-Akt-dependent manner. Fragment N protects various cell types, including insulin-secreting cells, against different types of stresses. Whether fragment N exerts a protective role during the development of type 1 diabetes is however not known. Non-obese diabetic (NOD) mice represent a well-known model for spontaneous development of type 1 diabetes that shares similarities with the diseases encountered in humans. To assess the role of fragment N in type 1 diabetes development, a transgene encoding fragment N under the control of the rat insulin promoter (RIP) was back-crossed into the NOD background creating the NOD-RIPN strain. Despite a mosaic expression of fragment N in the beta cell population of NOD-RIPN mice, islets isolated from these mice were more resistant to apoptosis than control NOD islets. Islet lymphocytic infiltration and occurrence of a mild increase in glycemia developed with the same kinetics in both strains. However, the period of time separating the mild increase in glycemia and overt diabetes was significantly longer in NOD-RIPN mice compared to the control NOD mice. There was also a significant decrease in the number of apoptotic beta cells in situ at 16 weeks of age in the NOD-RIPN mice. Fragment N exerts therefore a protective effect on beta cells within the pro-diabetogenic NOD background and this prevents a fast progression from mild to overt diabetes.

RasGAP-derived peptide 38GAP potentiates the cytotoxicity of cisplatin through inhibitions of Akt, ERK and NF-κB in colon carcinoma HCT116 cells

To increase the efficacy of currently used anti-cancer genotoxins, a combination use of different drugs is a potential new therapeutical tool. Here, we reported that a synthetic RasGAP-derived peptide 38GAP with RasGAP(301-326) and TAT penetration sequences could enhance the effect of chemotherapeutic agent CDDP in human colon carcinoma HCT116 cells. Our results showed that 38GAP significantly increased the CDDP-induced apoptosis in HCT116 cells. This synergistic effect was associated with abrogation of CDDP-induced G2/M arrest by down-regulations of phospho-Cdc2 and p21, and inhibitions of phospho-AKT, phospho-ERK and NF-κB. In animal models, 38GAP combined with CDDP significantly suppressed CT26 tumor growth, while 38GAP alone showed slight inhibitory effect. Our data suggest that 38GAP in combination with chemotherapeutics will become a potential therapeutic strategy for colon cancers.

Epigallocatechin gallate suppresses lung cancer cell growth through Ras-GTPase-activating protein SH3 domain-binding protein 1

Green tea is a highly popular beverage globally. Green tea contains a number of polyphenol compounds referred to as catechins, and (-)-epigallocatechin gallate (EGCG) is believed to be the major biologically active compound found in green tea. EGCG has been reported to suppress lung cancer, but the molecular mechanisms of the inhibitory effects of EGCG are not clear. We found that EGCG interacted with the Ras-GTPase-activating protein SH3 domain-binding protein 1 (G3BP1) with high binding affinity (K(d) = 0.4 micromol/L). We also showed that EGCG suppressed anchorage-independent growth of H1299 and CL13 lung cancer cells, which contain an abundance of the G3BP1 protein. EGCG was much less effective in suppressing anchorage-independent growth of H460 lung cancer cells, which express much lower levels of G3BP1. Knockdown shG3BP1-transfected H1299 cells exhibited substantially decreased proliferation and anchorage-independent growth. shG3BP1 H1299 cells were resistant to the inhibitory effects of EGCG on growth and colony formation compared with shMock-transfected H1299 cells. EGCG interfered with the interaction of G3BP1 and the Ras-GTPase-activating protein and further suppressed the activation of Ras. Additional results revealed that EGCG effectively attenuated G3BP1 downstream signaling, including extracellular signal-regulated kinase and mitogen-activated protein kinase/extracellular signal-regulated kinase kinase, in wild-type H1299 and shMock H1299 cells but had little effect on H460 or shG3BP1 H1299 cells. Overall, these results strongly indicate that EGCG suppresses lung tumorigenesis through its binding with G3BP1.

Expression of the NH(2)-terminal fragment of RasGAP in pancreatic beta-cells increases their resistance to stresses and protects mice from diabetes

OBJECTIVE

Our laboratory has previously established in vitro that a caspase-generated RasGAP NH(2)-terminal moiety, called fragment N, potently protects cells, including insulinomas, from apoptotic stress. We aimed to determine whether fragment N can increase the resistance of pancreatic beta-cells in a physiological setting.

RESEARCH DESIGN AND METHODS

A mouse line, called rat insulin promoter (RIP)-N, was generated that bears a transgene containing the rat insulin promoter followed by the cDNA-encoding fragment N. The histology, functionality, and resistance to stress of RIP-N islets were then assessed.

RESULTS

Pancreatic beta-cells of RIP-N mice express fragment N, activate Akt, and block nuclear factor kappaB activity without affecting islet cell proliferation or the morphology and cellular composition of islets. Intraperitoneal glucose tolerance tests revealed that RIP-N mice control their glycemia similarly as wild-type mice throughout their lifespan. Moreover, islets isolated from RIP-N mice showed normal glucose-induced insulin secretory capacities. They, however, displayed increased resistance to apoptosis induced by a series of stresses including inflammatory cytokines, fatty acids, and hyperglycemia. RIP-N mice were also protected from multiple low-dose streptozotocin-induced diabetes, and this was associated with reduced in vivo beta-cell apoptosis.

CONCLUSIONS

Fragment N efficiently increases the overall resistance of beta-cells to noxious stimuli without interfering with the physiological functions of the cells. Fragment N and the pathway it regulates represent, therefore, a potential target for the development of antidiabetes tools.

Can't live without them, can live with them: roles of caspases during vital cellular processes

Since the pioneering discovery that the genetic cell death program in C. elegans is executed by the cysteine-aspartate protease (caspase) CED3, caspase activation has become nearly synonymous with apoptosis. A critical mass of data accumulated in the past few years, have clearly established that apoptotic caspases can also participate in a variety of non-apoptotic processes. The roles of caspases during these processes and the regulatory mechanisms that prevent unrestrained caspase activity remain to be fully investigated, and may vary in different cellular contexts. Significantly, some of these processes, such as terminal differentiation of vertebrate lens fiber cells and red blood cells, as well as spermatid terminal differentiation and dendritic pruning of sensory neurons in Drosophila, all involve proteolytic degradation of major cellular compartments, and are conceptually, molecularly, biochemically, and morphologically reminiscent of apoptosis. Moreover, some of these model systems bear added values for the study of caspase activation/apoptosis. For example, the Drosophila sperm differentiation is the only system known in invertebrate which absolutely requires the mitochondrial pathway (i.e. Cyt c). The existence of testis-specific genes for many of the components in the electron transport chain, including Cyt c, facilitates the use of the Drosophila sperm system to investigate possible roles of these otherwise essential proteins in caspase activation. Caspases are also involved in a wide range of other vital processes of non-degenerative nature, indicating that these proteases play much more diverse roles than previously assumed. In this essay, we review genetic, cytological, and molecular studies conducted in Drosophila, vertebrate, and cultured cells, which underlie the foundations of this newly emerging field.

HIV-1 Tat and morphine have interactive effects on oligodendrocyte survival and morphology

Human immunodeficiency virus (HIV)-infected individuals who abuse opiates show faster progression to AIDS, and enhanced incidence of HIV-1 encephalitis. Most opiates with abuse liability are preferential agonists for mu-opioid receptors (MORs), and MORs are expressed on both neurons and glia, including oligodendrocytes (OLs). Tat, gp120, and other viral toxins, cause neurotoxicity in vitro and/or when injected into brain, and co-exposure to opiates can augment HIV-1 protein-induced insults to both glial and neuronal populations. We examined the effects of HIV-1 Tat +/- opiate exposure on OL survival and differentiation. In vivo studies utilized transgenic mice expressing Tat(1-86) regulated by an inducible glial fibrillary acidic protein promoter. Although MBP levels were unchanged on immunoblots, certain structural and apoptotic indices were abnormal. After only 2 days of Tat induction, OLs showed an upregulation of active caspase-3 that was enhanced by morphine exposure. Tat also upregulated TUNEL staining, but only in the presence of morphine. Tat significantly reduced the length of processes in Golgi-Kopsch impregnated OLs. A greater proportion of cells exhibited diminished or aberrant cytoplasmic processes, especially when mice expressing Tat were co-exposed to morphine. Collectively, our data show that OLs in situ are extremely sensitive to effects of Tat +/- morphine, although it is not clear if immature OLs as well as differentiated OLs are targeted equally. Significant elevations in caspase-3 activity and TUNEL labeling, and evidence of increased degeneration/regeneration of OLs exposed to Tat +/- morphine suggest that toxicity toward OLs may be accompanied by heightened OL turnover.