Arrestins in apoptosis

Genome-wide CRISPR screening identifies a role for ARRDC3 in TRP53-mediated responses

Whole-genome screens using CRISPR technologies are powerful tools to identify novel tumour suppressors as well as factors that impact responses of malignant cells to anti-cancer agents. Applying this methodology to lymphoma cells, we conducted a genome-wide screen to identify novel inhibitors of tumour expansion that are induced by the tumour suppressor TRP53. We discovered that the absence of Arrestin domain containing 3 (ARRDC3) increases the survival and long-term competitiveness of MYC-driven lymphoma cells when treated with anti-cancer agents that activate TRP53. Deleting Arrdc3 in mice caused perinatal lethality due to various developmental abnormalities, including cardiac defects. Notably, the absence of ARRDC3 markedly accelerated MYC-driven lymphoma development. Thus, ARRDC3 is a new mediator of TRP53-mediated suppression of tumour expansion, and this discovery may open new avenues to harness this process for cancer therapy.

Coordination games in cancer

We propose a model of cancer initiation and progression where tumor growth is modulated by an evolutionary coordination game. Evolutionary games of cancer are widely used to model frequency-dependent cell interactions with the most studied games being the Prisoner's Dilemma and public goods games. Coordination games, by their more obscure and less evocative nature, are left understudied, despite the fact that, as we argue, they offer great potential in understanding and treating cancer. In this paper we present the conditions under which coordination games between cancer cells evolve, we propose aspects of cancer that can be modeled as results of coordination games, and explore the ways through which coordination games of cancer can be exploited for therapy.

Coordination games in cancer

We propose a model of cancer initiation and progression where tumor growth is modulated by an evolutionary coordination game. Evolutionary games of cancer are widely used to model frequency-dependent cell interactions with the most studied games being the Prisoner's Dilemma and public goods games. Coordination games, by their more obscure and less evocative nature, are left understudied, despite the fact that, as we argue, they offer great potential in understanding and treating cancer. In this paper we present the conditions under which coordination games between cancer cells evolve, we propose aspects of cancer that can be modeled as results of coordination games, and explore the ways through which coordination games of cancer can be exploited for therapy.

Ruthenium(II)/Benzonitrile Complex Induces Cytotoxic Effect in Sarcoma-180 Cells by Caspase-Mediated and Tp53/p21-Mediated Apoptosis, with Moderate Brine Shrimp Toxicity

Ruthenium(II)/benzonitrile complexes have demonstrated promising anticancer properties. Considering that there are no specific therapies for treating sarcoma, we decided to evaluate the cytotoxic, genotoxic, and lethal effects of cis-[RuCl(BzCN)(phen)(dppb)]PF₆ (BzCN = benzonitrile; phen = 1,10-phenanthroline; dppb = 1,4-bis-(diphenylphosphino)butane), as well as the mechanism of cell death induction that occurs against murine sarcoma-180 tumor. Thus, MTT assay was applied to assess the ruthenium cytotoxicity, showing that the compound is a more potent inhibitor for the sarcoma-180 tumor cell viability than normal cells (lymphocytes). The comet assay indicated low genotoxic for normal cells. cis-[RuCl(BzCN)(phen)(dppb)]PF₆ also showed moderate lethality in Artemia salina. The complex induced cell cycle arrest in the G0/G1 phase in sarcoma-180 cells. In addition, the complex caused S180 cells to die by apoptosis by an increase in Annexin-V-positive cells and morphological changes typical of apoptotic cells. Additionally, cis-[RuCl(BzCN)(phen)(dppb)]PF₆ increased the gene expression of Bax, Casp3, and Tp53 in S180 cells. By using a western blot, we observed an increased protein level of TNF-R2, Bax, and p21. In conclusion, cis-[RuCl(BzCN)(phen)(dppb)]PF₆ is active and selective for sarcoma-180 cells, leading to cell cycle arrest at the G0/G1 and cell death through a caspases-mediated and Tp53/p21-mediated pathway.

Beta-arrestins operate an on/off control switch for focal adhesion kinase activity

Focal adhesion kinase (FAK) regulates key biological processes downstream of G protein-coupled receptors (GPCRs) in normal and cancer cells, but the modes of kinase activation by these receptors remain unclear. We report that after GPCR stimulation, FAK activation is controlled by a sequence of events depending on the scaffolding proteins β-arrestins and G proteins. Depletion of β-arrestins results in a marked increase in FAK autophosphorylation and focal adhesion number. We demonstrate that β-arrestins interact directly with FAK and inhibit its autophosphorylation in resting cells. Both FAK-β-arrestin interaction and FAK inhibition require the FERM domain of FAK. Following the stimulation of the angiotensin receptor AT1AR and subsequent translocation of the FAK-β-arrestin complex to the plasma membrane, β-arrestin interaction with the adaptor AP-2 releases inactive FAK from the inhibitory complex, allowing its activation by receptor-stimulated G proteins and activation of downstream FAK effectors. Release and activation of FAK in response to angiotensin are prevented by an AP-2-binding deficient β-arrestin and by a specific inhibitor of β-arrestin/AP-2 interaction; this inhibitor also prevents FAK activation in response to vasopressin. This previously unrecognized mechanism of FAK regulation involving a dual role of β-arrestins, which inhibit FAK in resting cells while driving its activation at the plasma membrane by GPCR-stimulated G proteins, opens new potential therapeutic perspectives in cancers with up-regulated FAK.

Cleavage of arrestin-3 by caspases attenuates cell death by precluding arrestin-dependent JNK activation

The two non-visual subtypes, arrestin-2 and arrestin-3, are ubiquitously expressed and bind hundreds of G protein-coupled receptors. In addition, these arrestins also interact with dozens of non-receptor signaling proteins, including c-Src, ERK and JNK, that regulate cell death and survival. Arrestin-3 facilitates the activation of JNK family kinases, which are important players in the regulation of apoptosis. Here we show that arrestin-3 is specifically cleaved at Asp366, Asp405 and Asp406 by caspases during the apoptotic cell death. This results in the generation of one main cleavage product, arrestin-3-(1-366). The formation of this fragment occurs in a dose-dependent manner with the increase of fraction of apoptotic cells upon etoposide treatment. In contrast to a caspase-resistant mutant (D366/405/406E) the arrestin-3-(1-366) fragment reduces the apoptosis of etoposide-treated cells. We found that caspase cleavage did not affect the binding of the arrestin-3 to JNK3, but prevented facilitation of its activation, in contrast to the caspase-resistant mutant, which facilitated JNK activation similar to WT arrestin-3, likely due to decreased binding of the upstream kinases ASK1 and MKK4/7. The data suggest that caspase-generated arrestin-3-(1-366) prevents the signaling in the ASK1-MKK4/7-JNK1/2/3 cascade and protects cells, thereby suppressing apoptosis.

GSK-3 inhibitors enhance TRAIL-mediated apoptosis in human gastric adenocarcinoma cells

Resistance to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis has been reported in some cancer cells, including AGS human gastric adenocarcinoma cells. Reducing this resistance might shed light on the treatment of human gastric adenocarcinoma. In this study, we examined whether glycogen synthase kinase-3 (GSK-3) inhibitors can restore TRAIL responsiveness in gastric adenocarcinoma cells. The effect of two GSK-3 inhibitors, SB-415286, and LiCl, on apoptosis signaling of TRAIL in human gastric adenocarcinoma cell lines and primary gastric epithelial cells was analyzed. Both inhibitors can sensitize gastric adenocarcinoma cells, but not primary gastric epithelial cells, to TRAIL-induced apoptosis by increasing caspase-8 activity and its downstream signal transmission. Adding p53 siRNA can downregulate GSK-3 inhibitor-related sensitization to TRAIL-induced apoptosis and caspase-3 activity. GSK-3 inhibitors strongly activate the phosphorylation of JNK. Inhibition of JNK leads to earlier and more intense apoptosis, showing that the activation of JNK may provide anti-apoptotic equilibrium of pro-apoptotic cells. Our observations indicate that GSK-3 inhibitors can sentize AGS gastric adenocarcinoma cells to TRAIL-induced apoptosis. Therefore, in certain types of gastric adenocarcinoma, GSK-3 inhibitor might enhance the antitumor activity of TRAIL and mightbe a promising candidate for the treatment of certain types of gastric adenocarcinoma.

Poly-dimensional network comparative analysis reveals the pure pharmacological mechanism of baicalin in the targeted network of mouse cerebral ischemia

AIM

This study aimed to investigate the pure pharmacological mechanisms of baicalin/baicalein (BA) in the targeted network of mouse cerebral ischemia using a poly-dimensional network comparative analysis.

METHODS

Eighty mice with induced focal cerebral ischemia were randomly divided into four groups: BA, Concha Margaritifera (CM), vehicle and sham group. A poly-dimensional comparative analysis of the expression levels of 374 stroke-related genes in each of the four groups was performed using MetaCore.

RESULTS

BA significantly reduced the ischemic infarct volume (P<0.05), whereas CM was ineffective. Two processes and 10 network nodes were shared between "BA vs CM" and vehicle, but there were no overlapping pathways. Two pathways, three processes and 12 network nodes overlapped in "BA vs CM" and BA. The pure pharmacological mechanism of BA resulted in targeting of pathways related to development, G-protein signaling, apoptosis, signal transduction and immunity. The biological processes affected by BA were primarily found to correlate with apoptotic, anti-apoptotic and neurophysiological processes. Three network nodes changed from up-regulation to down-regulation, while mitogen-activated protein kinase kinase 6 (MAP2K6, also known as MEK6) changed from down-regulation to up-regulation in "BA vs CM" and vehicle. The changed nodes were all related to cell death and development.

CONCLUSION

The pure pharmacological mechanism of BA is related to immunity, apoptosis, development, cytoskeletal remodeling, transduction and neurophysiology, as ascertained using a poly-dimensional network comparative analysis.

β-arrestins regulate gonadotropin receptor-mediated cell proliferation and apoptosis by controlling different FSHR or LHCGR intracellular signaling in the hGL5 cell line

Gonadotropin signaling classically involves proliferative, steroidogenic and apoptotic stimuli. In this study, we used the human granulosa cell line hGL5 to demonstrate how follicle-stimulating hormone (FSH) and luteinizing hormone (LH) differently control proliferative or apoptotic signals, revealing novel intrinsic properties of their receptors (FSHR, LHCGR). We found that, in this tumor-like cell line, the expression of endogenous FSHR and LHCGR is serum-dependent, but both receptors were unable to activate the canonical cAMP/PKA pathway upon gonadotropin stimulation, failing to produce cAMP, progesterone and G protein-coupled receptor (GPCR)-mediated apoptosis in vitro. Conversely, ligand treatment resulted in FSHR- and LHCGR-mediated ERK1/2 phosphorylation and cell proliferation due to receptor coupling to β-arrestins. The inactive cAMP/PKA pathway was unlocked by siRNA-mediated knock-down of β-arrestin 1 and 2, leading to progesterone synthesis and apoptosis. Surprisingly, FSH, but not LH treatment accelerated the cAMP/PKA-mediated apoptosis after β-arrestin silencing, an effect which could be reproduced by overexpressing the FSHR, but not the LHCGR. This work demonstrates that the expression of FSHR and LHCGR can be induced in hGL5 cells but that the FSHR-dependent cAMP/PKA pathway is constitutively silenced, possibly to protect cells from FSHR-cAMP-PKA-induced apoptosis. Also, we revealed previously unrecognized features intrinsic to the two structurally similar gonadotropin receptors, oppositely resulting in the regulation of life and death signals in vitro.

β-arrestin2 regulates TRAIL-induced HepG2 cell apoptosis via the Src-extracellular signal-regulated signaling pathway

β-arrestins, including β-arrestin1 and β‑arrestin2, two ubiquitously expressed members of the arrestin family in various types of tissue, are adaptor proteins that modulate the desensitization and trafficking of seven membrane‑spanning receptors. Recently, β‑arrestins have been shown to bind to numerous signaling molecules, including c‑Src and mitogen‑activated protein kinase family members. In addition, accumulating evidence has suggested that β‑arrestins are involved in the anti‑apoptosis signaling pathway by associating with kinases, such as Akt and ERK, and altering their activities. However, the role of β‑arrestins in tumor necrosis factor‑related apoptosis‑inducing ligand (TRAIL)‑induced apoptosis remains unclear. In the present study, β‑arrestin2, but not β‑arrestin1, was observed to modulate TRAIL‑triggered HepG2 cell apoptosis by regulating activation of the Src‑extracellular signal‑regulated kinase (ERK) signaling pathway. Using overexpression and RNA interference experiments, β‑arrestin2 was demonstrated to prevent TRAIL‑induced HepG2 cell apoptosis. Additionally, β‑arrestin2 exerted an additive effect on TRAIL‑induced activation of Src and ERK. Furthermore, downregulating β‑arrestin2 expression attenuated the TRAIL‑induced activation of Src and ERK survival signaling and enhanced TRAIL‑induced apoptosis. PP2, a pharmacological inhibitor of Src, reduced activation of the Src‑ERK signaling pathway and enhanced TRAIL‑induced HepG2 cell apoptosis. Co-immunoprecipitation experiments demonstrated a physical association between β‑arrestin2 and Src, and TRAIL stimulation resulted in enhanced quantities of the β‑arrestin2/Src complex. A notable interaction was identified between β‑arrestin2 and death receptors (DR)4 and 5, but only in the presence of TRAIL stimulation. To the best of our knowledge, these findings are the first to demonstrate that β‑arrestin2 mediates TRAIL‑induced apoptosis by combing with DRs and Src, and regulates the activation of Src‑ERK signaling in HepG2 cells. It is hypothesized that the formation of a signaling complex comprising DR, β‑arrestin2 and Src is required for the action of TRAIL on HepG2 cell apoptosis, which provides a novel insight into analyzing the effects of β‑arrestin2 on protecting cells from TRAIL‑induced apoptosis.