Oncogenic B-RafV600E inhibits apoptosis and promotes ERK-dependent inactivation of Bad and Bim

Recent studies have revealed that B-Raf mutations are very common in malignant melanoma and are required for tumor growth and maintenance. The majority of melanoma-associated B-Raf mutations involve a single point mutation, V600E, which results in greatly elevated B-Raf kinase activity and constitutive activation of MAPK/ERK downstream. Here we show that B-Raf(V600E) increases resistance to apoptosis induced by chemotherapeutic drugs and promotes ERK-dependent phosphorylation of the BH3-only proteins Bim and Bad that are involved in setting thresholds for apoptosis. ERK-dependent phosphorylation of Bim resulted in degradation of this BH3-only protein, whereas phosphorylation of Bad has previously been shown to result in its sequestration by 14-3-3 proteins. Consistent with this, inhibition of ERK activity in a panel of melanoma cell lines resulted in stabilization of Bim and dephosphorylation of Bad. Furthermore, apoptosis induced through overexpression of Bad or Bim was efficiently blocked by coexpression of mutant B-Raf(V600E). However, small interfering RNA-mediated silencing of Bim and Bad expression conferred only modest protection against cytotoxic drugs, whereas oncogenic B-Raf strongly protected against the same stimuli. These observations suggest that B-Raf-initiated inactivation of Bad and Bim only partly contributes to the anti-apoptotic activities of this oncogene and that other points within the cell death machinery are also targeted by deregulated ERK signaling.     

PLX4032, a potent inhibitor of the B-Raf V600E oncogene, selectively inhibits V600E-positive melanomas

Targeted intervention of the B-Raf V600E gene product that is prominent in melanoma has been met with modest success. Here, we characterize the pharmacological properties of PLX4032, a next-generation inhibitor with exquisite specificity against the V600E oncogene and striking anti-melanoma activity. PLX4032 induces potent cell cycle arrest, inhibits proliferation, and initiates apoptosis exclusively in V600E-positive cells in a variety of in vitro experimental systems; follow-up xenograft studies demonstrate extreme selectivity and efficacy against melanoma tumors bearing the V600E oncoproduct. The collective data support further exploration of PLX4032 as a candidate drug for patients with metastatic melanoma; accordingly, validation of PLX4032 as a therapeutic tool for patients with melanoma is now underway in advanced human (Phase III) clinical trials.     

Protecting mitochondria via inhibiting VDAC1 oligomerization alleviates ferroptosis in acetaminophen-induced acute liver injury

Cell Biology and Toxicology - Acetaminophen (APAP) overdose is a common cause of drug-induced liver injury (DILI). Ferroptosis has been recently implicated in APAP-induced liver injury (AILI)....     

The discovery of potent and selective pyridopyrimidin-7-one based inhibitors of B-RafV600E kinase

Herein we describe the discovery of a novel series of ATP competitive B-Raf inhibitors via structure based drug design (SBDD). These pyridopyrimidin-7-one based inhibitors exhibit both excellent cellular potency and striking B-Raf selectivity. Optimization led to the identification of compound 17, a potent, selective and orally available agent with excellent pharmacokinetic properties and robust tumor growth inhibition in xenograft studies.     

Highly potent and selective 3-N-methylquinazoline-4(3H)-one based inhibitors of B-RafV600E kinase

Herein we describe the design of a novel series of ATP competitive B-Raf inhibitors via structure-based methods. These 3-N-methylquinazoline-4(3H)-one based inhibitors exhibit both excellent cellular potency and striking B-Raf selectivity. Optimization led to the identification of compound 16, a potent, selective and orally available agent with excellent pharmacokinetic properties and robust tumor growth inhibition in xenograft studies. Our work also demonstrates that by replacing an aryl amide with an aryl sulfonamide, a multikinase inhibitor such as AZ-628, can be converted to a selective B-Raf inhibitor, a finding that should have broad application in kinase drug discovery.     

Kupffer细胞在APAP所致肝损伤中作用研究进展

对乙酰氨基酚所致肝损伤(acetaminophen-induced liver injury, AILI)是一类普遍的药物源性肝损伤(drug-induced liver injury, DILI),是造成急性肝衰竭(acute liver failure, AIF)的主要原因。Kupffer细胞为肝脏固有巨噬细胞,是机体先天免疫重要组成部分。Kupffer具有促炎和抗炎的双重作用,通过识别损伤相关模式分子(damage-associated molecular patterns, DAMPs)激活细胞内炎症信号,释放促炎因子、抗炎因子和趋化因子。Kupffer在AILI氧化应激、细胞招募、炎症反应、肝再生和纤维化等过程起着重要作用,对AILI的发生、发展及转归有着重要的影响。     

Divergent effects of RIP1 or RIP3 blockade in murine models of acute liver injury

Necroptosis is a recently described Caspase 8-independent method of cell death that denotes organized cellular necrosis. The roles of RIP1 and RIP3 in mediating hepatocyte death from acute liver injury are incompletely defined. Effects of necroptosis blockade were studied by separately targeting RIP1 and RIP3 in diverse murine models of acute liver injury. Blockade of necroptosis had disparate effects on disease outcome depending on the precise etiology of liver injury and component of the necrosome targeted. In ConA-induced autoimmune hepatitis, RIP3 deletion was protective, whereas RIP1 inhibition exacerbated disease, accelerated animal death, and was associated with increased hepatocyte apoptosis. Conversely, in acetaminophen-mediated liver injury, blockade of either RIP1 or RIP3 was protective and was associated with lower NLRP3 inflammasome activation. Our work highlights the fact that diverse modes of acute liver injury have differing requirements for RIP1 and RIP3; moreover, within a single injury model, RIP1 and RIP3 blockade can have diametrically opposite effects on tissue damage, suggesting that interference with distinct components of the necrosome must be considered separately.The etiologies of acute liver injury are diverse and its overall public health burden is considerable. Liver injury from acetaminophen (APAP) overdose is the most common cause of death from over-the-counter drugs and is the leading cause of acute liver failure in the developed world.^{1, 2, 3} Hepatic dysfunction from autoimmune hepatitis has a prevalence of 10–20/100 000.^{4, 5} Other etiologies of acute liver failure include idiosyncratic reaction to medications such as tetracycline, severe viral or alcoholic hepatitis, acute fatty liver of pregnancy, and idiopathic causes. Clinical complications resulting from liver failure include hepatic encephalopathy, impaired protein synthesis, and coagulopathies. Moreover, there are no effective means to reverse liver failure once advanced disease sets in – regardless of etiology – and transplantation frequently remains the only option for survival.⁶Concanavalin-A (ConA) is a lectin derived from the jack-bean plant with a unique ability to induce hepatitis in a well-described murine model of acute hepatic injury. ConA stimulates mouse CD4⁺ T-cell subsets to mediate insult to hepatocytes. The resulting cytokine release can further lead to recruitment and activation of innate inflammatory mediators, which perpetuate an insidious cycle of inflammation and hepatocellular injury.^{7, 8, 9}APAP is a widely used analgesic and antipyretic. Although usually considered safe at therapeutic doses, at higher doses APAP causes acute liver failure characterized by centrilobular hepatic necrosis.^{1, 10} At therapeutic doses, >90% of APAP is metabolized by glucuronidation and sulphation and its metabolites are excreted via the renal system. Of the remaining APAP, roughly 2% is excreted intact in the urine, and approximately 8% is metabolized by the cytochrome P450 system to N-acetyl-p-benzo-quinone imine (NAPQI), which is highly reactive.^{11, 12} Hepatic glutathione (GSH) then induces the formation of a safely excretable APAP-protein adduct. However, at toxic doses of APAP, GSH becomes depleted and NAPQI is able to exert harmful effects by forming covalent bonds with mitochondrial proteins, inhibiting the Ca²⁺-Mg²⁺-ATPase and inducing mitochondrial dysfunction.^{1, 2} This disturbance leads to a decrease in ATP synthesis, disruption of cellular membrane, and eventually hepatocyte death.¹³Although GSH depletion and the resulting toxic metabolites are prerequisites for APAP hepatotoxicity, there is evidence that the severity of liver injury may depend on subsequent participation of innate immunity.^{10, 14, 15, 16} In particular, APAP-induced injury has been reported to be contingent on activation of the NLRP3 inflammasome via DAMPs released from injured hepatocytes. Inflammasome activation cleaves Caspase 1 inducing IL-1β release and galvanizing intrahepatic neutrophils and inflammatory monocytes, which exacerbate injury.¹⁷ However, alternate studies using transgenic mice suggest that NLRP3 inflammasome is largely dispensable for APAP toxicity.¹⁸ Thus the role of inflammasome activation in APAP toxicity is controversial and may be dependent on the precise experimental conditions or strain of mice employed.Apoptosis and necrosis are classically understood processes of cell death that denote either organized Caspase 8-dependent programmed cell death or non-programmed disorganized death, respectively. In contrast to necrosis, which leads to the release of DAMPs and sustains inflammation, apoptosis produces cell fragments called apoptotic bodies, which phagocytic cells are able to engulf before the contents of the cell can spill out onto the surrounding space and activate innate immunity. ‘Necroptosis'' is a recently described Caspase 8-independent method of cell death that denotes organized cellular necrosis. Necroptosis requires the co-activation of RIP1 and RIP3 kinases. Both in vitro and in vivo investigations have suggested that APAP can induce cellular demise via necrosis or Caspase 8-dependent apoptosis, which is determined, in part, by ATP availability from glycolysis.¹⁹ Zhang et al.²⁰ recently confirmed that RIP1 is necessary in APAP-induced necroptosis. Similarly, Takemoto et al.²¹ showed that RIP1 inhibition protects against reactive oxygen species (ROS)-induced hepatotoxicity in APAP-induced acute liver injury. Further, a recent report suggested that selective inhibition of RIP3 using the anticancer drug Dabrafenib alleviates APAP injury.²²In the ConA model of acute liver injury, experiments using apoptosis-resistant mice expressing mutant FADD revealed that ConA alone induced primarily necrotic cell death, whereas ConA combined with d-galactosamine induced apoptosis and necrotic cell death.²³ Zhou et al.²⁴ reported that Necrostatin-1 (Nec-1) prevents autoimmune hepatitis in mice via RIP1- and autophagy-related pathways. Another recent report investigated the role of RIP1, RIP3, and PARP-1 in murine autoimmune hepatitis. This study found that in cases where death of mouse hepatocytes is dependent on TRAIL and NKT cells, PARP-1 activity was positively correlated with liver injury and hepatitis was prevented both by RIP1 or PARP-1 inhibitors.²⁵ Our goal in the current study was to investigate, in parallel, the effects of RIP1 and RIP3 blockade in diverse models of acute liver injury. Our work suggests that modulating necroptosis may have divergent effects, depending on the etiology of hepatic injury and the specific component of the necrosome being targeted.     

Cyclophilin D deficiency protects against acetaminophen-induced oxidant stress and liver injury

Acetaminophen (APAP) hepatotoxicity is the main cause of acute liver failure in humans. Although mitochondrial oxidant stress and induction of the mitochondrial permeability transition (MPT) have been implicated in APAP-induced hepatotoxicity, the link between these events is unclear. To investigate this, this study evaluated APAP hepatotoxicity in mice deficient of cyclophilin D, a protein component of the MPT. Treatment of wild type mice with APAP resulted in focal centrilobular necrosis, nuclear DNA fragmentation and formation of reactive oxygen (elevated glutathione disulphide levels) and peroxynitrite (nitrotyrosine immunostaining) in the liver. CypD-deficient (Ppif(-/-)) mice were completely protected against APAP-induced liver injury and DNA fragmentation. Oxidant stress and peroxynitrite formation were blunted but not eliminated in CypD-deficient mice. Thus, mitochondrial oxidative stress and induction of the MPT are critical events in APAP hepatotoxicity in vivo and at least part of the APAP-induced oxidant stress and peroxynitrite formation occurs downstream of the MPT.     

The Cdk inhibitor p21 is required for necrosis,but it inhibits apoptosis following toxin-induced liver injury

Liver injury and repair were examined in wild type, p21Waf1/Cip1, and p27Kip1-deficient mice following carbon tetrachloride (CCl4) administration. In wild type liver, p21 expression is induced in a biphasic manner following injection of CCl4, with an early peak of p21 expression occurring in pericentral hepatocytes at 6 h, prior to evidence of injury, and a second peak succeeding regenerative proliferation. In contrast, p27 is present throughout the quiescent liver, but its expression decreases following CCl4 injection. Surprisingly, p21-deficient animals were resistant to CCl4-induced necrotic injury, indicating that rapid induction of p21 in pericentral hepatocytes following CCl4 injection contributes to subsequent necrosis. Expression of cytochrome P450 2E1, which plays an essential role in CCl4-induced necrotic injury, was not affected in p21-deficient mice. Although they had the least injury, p21-deficient mice had the highest levels of hepatic proliferation that correlated with increases in hyperphosphorylated retinoblastoma protein and Cyclin A gene expression. Increased replication in p21-deficient livers was counteracted by an increase in hepatocyte apoptosis as detected by caspase-3 activation. p21 plays distinct and opposing roles regulating hepatocyte survival during injury and subsequent repair, with early induction of p21 contributing to necrotic injury and later expression to cessation of proliferation and hepatocyte survival.     

Upregulation of miRNA-223-3p ameliorates RIP3-mediated necroptosis and inflammatory responses via targeting RIP3 after spinal cord injury

Spinal cord injury (SCI) has been a major burden on the society because of the high rate of disability. Receptor-interacting protein 3 (RIP3)-mediated necroptosis is a newly discovered pathway of programmed cell death and is involved in multiple pathologies of various human diseases. Micro RNAs (miRNAs) have been shown to be a potential target for therapeutic interventions after SCI. The aim of the present study is to explore the potential role of miR-223-3p and possible mechanism in SCI. We found that miR-223-3p was significantly downregulated in spinal neurons after H₂O ₂-induced damage, while RIP3-mediated necroptosis was elevated. Accordingly, RIP3-mediated necroptosis and the inflammatory factor secretion could be significantly inhibited by Nec-1 treatment. In adittion, overexpression of miR-223-3p in spinal neurons protected against H ₂O ₂-induced necroptosis, and ablation of miR-223-3p exhibited the opposite effect. We found that miR-223-3p bound to the 3′-untranslated region of RIP3 mRNA to negatively regulate the expression of RIP3. Moreover, the activated RIP3 reversed the inhibition of RIP3 and MLKL expression and the levels of TNF-α, IL-1β, and lactate dehydrogenase, which were induced by transfection with miR-223-3p in a H ₂O ₂-induced model. Finally, these results indicate that miR-223-3p negatively regulates the RIP3 necroptotic signaling cascades and inflammatory factor secretion, which significantly relieves injury of spinal neurons. The miR-223-3p/RIP3 pathway offers a novel therapeutic target for the protection of spinal neurons after SCI.     

Purification and characterization of Manduca sexta serpin-6: a serine proteinase inhibitor that selectively inhibits prophenoloxidase-activating proteinase-3

The proteolytic activation of prophenoloxidase (proPO) is a critical defense mechanism in insects and crustaceans. We have isolated three prophenoloxidase-activating proteinases (PAPs) from cuticular extracts or hemolymph of Manduca sexta pharate pupae, which are negatively regulated by serpin-1J and serpin-3. To test if other serpins may also inhibit the PAPs, we fractionated the induced hemolymph by ammonium sulfate precipitation, gel filtration, and lectin affinity chromatography. A 47 kDa protein, designated M. sexta serpin-6, was identified in concanavalin A-bound fractions, which formed an SDS-stable complex with PAP-3. This inhibitor, not recognized by the serpin-1 or serpin-3 antibodies, was further purified on HPLC anion exchange and hydroxylapatite columns. The molecular mass and isoelectric point of serpin-6 were found to be 46,710 +/- 10 Da and 5.4. While its amino terminus was blocked, we obtained five internal peptide sequences, one of which is highly similar to M. sexta serpins-1, -2, and -3. Serpin-6 strongly inhibited PAP-3 but not PAP-1 or PAP-2, suggesting that the proPO activation by PAPs is differentially regulated by multiple serpins. When included in the reaction mixture containing proPO, PAP-3, and its cofactor, serpin-6 efficiently blocked the cleavage activation of proPO.     

Depletion of activated hepatic stellate cell correlates with severe liver damage and abnormal liver regeneration in acetaminophen-induced liver injury

Hepatic stellate cells (HSCs) are important part of the local 'stem cell niche' for hepatic progenitor cells (HPCs) and hepatocytes. However, it is unclear as to whether the products of activated HSCs are required to attenuate hepatocyte injury, enhance liver regeneration, or both. In this study, we performed 'loss of function' studies by depleting activated HSCs with gliotoxin. It was demonstrated that a significantly severe liver damage and declined survival rate were correlated with depletion of activated HSCs. Furthermore, diminishing HSC activation resulted in a 3-fold increase in hepatocyte apoptosis and a 66% decrease in the number of proliferating hepatocytes. This was accompanied by a dramatic decrease in the expression levels of five genes known to be up-regulated during hepatocyte replication. In particular, it was found that depletion of activated HSCs inhibited oval cell reaction that was confirmed by decreased numbers of Pank-positive cells around the portal tracts and lowered gene expression level of cytokeratin 19 (CK19) in gliotoxin-treated liver. These data provide clear evidence that the activated HSCs are involved in both hepatocyte death and proliferation of hepatocytes and HPCs in acetaminophen (APAP)-induced acute liver injury.     

Chlorogenic acid,a dietary polyphenol,protects acetaminophen-induced liver injury and its mechanism

Chlorogenic acid (CGA) is one of the most abundant dietary polyphenols, possessing well-known antioxidant capacity. The present study is designed to observe the protection provided by CGA against acetaminophen (AP)-induced liver injury in mice in vivo and the underlying mechanisms engaged in this process. Serum transaminases analysis and liver histological evaluation demonstrated the protection of CGA against AP-induced liver injury. CGA treatment decreased the increased number of liver apoptotic cells induced by AP in a dose-dependent manner. CGA also inhibited AP-induced cleaved activation of caspase-3, 7. Moreover, CGA reversed AP-decreased liver reduced glutathione (GSH) levels, glutamate-cysteine ligase (GCL) and glutathione reductase activity. Further results showed that CGA increased mRNA and protein expression of the catalytic subunit of GCL (GCLC), thioredoxin (Trx) 1/2 and thioredoxin reductase (TrxR) 1. Furthermore, CGA abrogated AP-induced phospholyated activation of ERK1/2, c-Jun N-terminal kinase (JNK), p38 kinases and molecular signals upstream. The results of this study demonstrate that CGA counteracts AP-induced liver injury at various levels by preventing apoptosis and oxidative stress damage, and more specifically, both the GSH and Trx antioxidant systems and the mitogen-activated protein kinase (MAPK) signaling cascade appear to be engaged in this protective mechanism.     

Discovery and structure-activity relationship of auriculatone: A potent hepatoprotective agent against acetaminophen-induced liver injury

Acetaminophen (APAP, paracetamol) overdose has been the most frequent cause of drug-induced liver failure. APAP-induced liver toxicity can be fatal in many cases even with treatment of the clinically used N-acetylcysteine (NAC), and the need for novel therapeutic agents is apparent. Through evaluating the hepatoprotective effects of the co-occurring substances present in oleanolic acid tablets which have been used in China for decades as an adjuvant therapy for acute and chronic hepatitis, auriculatone was found to protect HL-7702 cells from APAP-induced liver injury comparable to NAC at the concentration of 10 μM. Structure activity relationship on auriculatone and its analogs showed that absence of the C17 carboxyl group of auriculatone was essential to achieve good hepatoprotective activity, and that the C3-OH, C16 carbonyl and C12-C13 olefinic group were critical for retaining the exceptional activity of auriculatone. Any modifications in the current investigation were all detrimental to the hepatoprotective activity. Docking and drug-metabolizing activity studies demonstrated that CYP3A4 was likely the main target of auriculatone, and that auriculatone elicited the hepatoprotective effect possibly through inhibiting CYP3A4’s metabolism of APAP to the toxic metabolite NAPQI. The work may pave the way for the use of auriculatone in the treatment of APAP-induced liver injury.     

Stem cell factor and c-kit are involved in hepatic recovery after acetaminophen-induced liver injury in mice

Stem cell factor (SCF) and its receptor c-kit are important in hematopoiesis and cellular proliferation. c-kit has also been identified as a cell surface marker for progenitor cells. We have previously shown that there is a large reservoir of hepatic SCF, and this molecule plays a significant role in liver regeneration after 70% hepatectomy. In the current study, we further examined the expression of SCF and c-kit in acetaminophen (APAP)-induced liver injury in C57BL/6J mice or SCF-deficient sl-sld mice and their appropriate wild-type controls. Following APAP-induced liver injury, c-kit mRNA expression increased, with peak levels detected 48 h postinjury. Hepatic SCF mRNA levels after APAP injury were also increased, with peak levels seen 16 h post-APAP. The mortality rate in SCF-deficient mice treated with APAP was significantly higher than that of wild-type mice; furthermore, administration of exogenous SCF significantly reduced the mortality of APAP-treated wild-type mice. Bromodeoxyuridine incorporation experiments showed that SCF significantly increased hepatocyte proliferation at 48 and 72 h in APAP-treated mice. SCF inhibited APAP-induced hepatocyte apoptosis and increased Bcl-2 and Bcl-xL expression, suggesting that this decrease in hepatocyte apoptosis is mediated through Bcl-2 and Bcl-xL. In summary, SCF and c-kit expression was increased after APAP-induced liver injury. Administration of exogenous SCF reduces mortality in APAP-treated mice, increases hepatocyte proliferation, and prevents hepatocyte apoptosis induced by APAP, suggesting that these molecules are important in the liver's recovery from these injuries.     

Hypothermic oxygenated perfusion inhibits HECTD3-mediated TRAF3 polyubiquitination to alleviate DCD liver ischemia-reperfusion injury

Ischemia-reperfusion injury (IRI) is an inevitable and serious clinical problem in donations after heart death (DCD) liver transplantation. Excessive sterile inflammation plays a fateful role in liver IRI. Hypothermic oxygenated perfusion (HOPE), as an emerging organ preservation technology, has a better preservation effect than cold storage (CS) for reducing liver IRI, in which regulating inflammation is one of the main mechanisms. HECTD3, a new E3 ubiquitin ligase, and TRAF3 have an essential role in inflammation. However, little is known about HECTD3 and TRAF3 in HOPE-regulated liver IRI. Here, we aimed to investigate the effects of HOPE on liver IRI in a DCD rat model and explore the roles of HECTD3 and TRAF3 in its pathogenesis. We found that HOPE significantly improved liver damage, including hepatocyte and liver sinusoidal endothelial cell injury, and reduced DCD liver inflammation. Mechanistically, both the DOC and HECT domains of HECTD3 directly interacted with TRAF3, and the catalytic Cys (C832) in the HECT domain promoted the K63-linked polyubiquitination of TRAF3 at Lys138. Further, the ubiquitinated TRAF3 at Lys138 increased oxidative stress and activated the NF-κB inflammation pathway to induce liver IRI in BRL-3A cells under hypoxia/reoxygenation conditions. Finally, we confirmed that the expression of HECTD3 and TRAF3 was obviously increased in human DCD liver transplantation specimens. Overall, these findings demonstrated that HOPE can protect against DCD liver transplantation-induced-liver IRI by reducing inflammation via HECTD3-mediated TRAF3 K63-linked polyubiquitination. Therefore, HOPE regulating the HECTD3/TRAF3 pathway is a novel target for improving IRI in DCD liver transplantation.Subject terms: Molecular biology, Diseases     

Selective BRAFV600E inhibitor PLX4720, requires TRAIL assistance to overcome oncogenic PIK3CA resistance

Documented sensitivity of melanoma cells to PLX4720, a selective BRAFV600E inhibitor, is based on the presence of mutant BRAF(V600E) alone, while wt-BRAF or mutated KRAS result in cell proliferation. In colon cancer appearance of oncogenic alterations is complex , since BRAF, like KRAS mutations, tend to co-exist with those in PIK3CA and mutated PI3K has been shown to interfere with the successful application of MEK inhibitors. When PLX4720 was used to treat colon tumours, results were not encouraging and herein we attempt to understand the cause of this recorded resistance and discover rational therapeutic combinations to resensitize oncogene driven tumours to apoptosis. Treatment of two genetically different BRAF(V600E) mutant colon cancer cell lines with PLX4720 conferred complete resistance to cell death. Even though p-MAPK/ ERK kinase (MEK) suppression was achieved, TRAIL, an apoptosis inducing agent, was used synergistically in order to achieve cell death by apoptosis in RKO(BRAFV600E/PIK3CAH1047) cells. In contrast, for the same level of apoptosis in HT29(BRAFV600E/PIK3CAP449T) cells, TRAIL was combined with 17-AAG, an Hsp90 inhibitor. For cells where PLX4720 was completely ineffective, 17-AAG was alternatively used to target mutant BRAF(V600E). TRAIL dependence on the constitutive activation of BRAF(V600E) is emphasised through the overexpression of BRAF(V600E) in the permissive genetic background of colon adenocarcinoma Caco-2 cells. Pharmacological suppression of the PI3K pathway further enhances the synergistic effect between TRAIL and PLX4720 in RKO cells, indicating the presence of PIK3CA(MT) as the inhibitory factor. Another rational combination includes 17-AAG synergism with TRAIL in a BRAF(V600E) mutant dependent manner to commit cells to apoptosis, through DR5 and the amplification of the apoptotic pathway. We have successfully utilised combinations of two chemically unrelated BRAF(V600E) inhibitors in combination with TRAIL in a BRAF(V600E) mutated background and provided insight for new anti-cancer strategies where the activated PI3KCA mutation oncogene should be suppressed.     

Acteoside inhibits apoptosis in D-galactosamine and lipopolysaccharide-induced liver injury.

We assessed the effect of acteoside, a naturally occurring antioxidative phenylethanoid, on hepatic apoptosis and the subsequent liver failure induced by D-Galactosamine (D-GalN) and lipopolysaccharide (LPS). A co-administration of D-GalN (700 mg/kg) and LPS (35 microg/kg) to mice evoked typical hepatic apoptosis characterized by DNA fragmentation and apoptotic body formation, resulting in fulminant hepatitis and lethality of mice. Pre-administration of acteoside at 10 or 50 mg/kg subcutaneously at 12 and 1 h prior to D-GalN/LPS intoxication significantly inhibited hepatic apoptosis, hepatitis and lethality. Tumor necrosis factor-alpha (TNF-alpha) secreted from LPS-stimulated macrophages is an important mediator of apoptosis in this model. Acteoside showed no apparent effect on the marked elevation of serum TNF-alpha, but it partially prevented in vitro TNF-alpha (100 ng/ml)-induced cell death in D-GalN (0.5 mM)-sensitized hepatocytes at the concentrations of 50, 100 and 200 microM. These results indicated that D-GalN/LPS-induced hepatic apoptosis can be blocked by an exogenous antioxidant, suggesting the involvement of reactive oxygen intermediates (ROIs) in TNF-alpha-dependent hepatic apoptosis.     

The BRAFV600E inhibitor,PLX4032, increases type I collagen synthesis in melanoma cells

Vertical growth phase (VGP) melanoma is frequently metastatic, a process mediated by changes in gene expression, which are directed by signal transduction pathways in the tumor cells. A prominent signaling pathway is the Ras-Raf-Mek-Erk MAPK pathway, which increases expression of genes that promote melanoma progression. Many melanomas harbor a mutation in this pathway, BRAF^V600E, which constitutively activates MAPK signaling and expression of downstream target genes that facilitate tumor progression. In BRAF^V600E melanoma, the small molecule inhibitor, vemurafenib (PLX4032), has revolutionized therapy for melanoma by inducing rapid tumor regression. This compound down-regulates the expression of many genes. However, in this study, we document that blocking the Ras-Raf-Mek-Erk MAPK pathway, either with an ERK (PLX4032) or a MEK (U1026) signaling inhibitor, in BRAF^V600E human and murine melanoma cell lines increases collagen synthesis in vitro and collagen deposition in vivo. Since TGFß signaling is a major mediator of collagen synthesis, we examined whether blocking TGFß signaling with a small molecule inhibitor would block this increase in collagen. However, there was minimal reduction in collagen synthesis in response to blocking TGFß signaling, suggesting additional mechanism(s), which may include activation of the p38 MAPK pathway. Presently, it is unclear whether this increased collagen synthesis and deposition in melanomas represent a therapeutic benefit or an unwanted “off target” effect of inhibiting the Ras-Raf-Erk-Mek pathway.     

The serine threonine kinase RIP3: lost and found

Receptor-interacting protein kinase-3 (RIP3, or RIPK3) is an essential protein in the “programmed”, or “regulated” necrosis cell death pathway that is activated in response to death receptor ligands and other types of cellular stress. Programmed necrotic cell death is distinguished from its apoptotic counterpart in that it is not characterized by the activation of caspases; unlike apoptosis, programmed necrosis results in plasma membrane rupture, thus spilling the contents of the cell and triggering the activation of the immune system and inflammation. Here we discuss findings, including our own recent data, which show that RIP3 protein expression is absent in many cancer cell lines. The recent data suggests that the lack of RIP3 expression in a majority of these deficient cell lines is due to methylation-dependent silencing, which limits the responses of these cells to pro-necrotic stimuli. Importantly, RIP3 expression may be restored in many cancer cells through the use of hypomethylating agents, such as decitabine. The potential implications of loss of RIP3 expression in cancer are explored, along with possible consequences for chemotherapeutic response. [BMB Reports 2015; 48(6): 303-312]