Prolonged activation of ERK1,2 induces FADD-independent caspase 8 activation and cell death

A guide to ERK dynamics, part 2: downstream decoding

Signaling by the extracellular signal-regulated kinase (ERK) pathway controls many cellular processes, including cell division, death, and differentiation. In this second installment of a two-part review, we address the question of how the ERK pathway exerts distinct and context-specific effects on multiple processes. We discuss how the dynamics of ERK activity induce selective changes in gene expression programs, with insights from both experiments and computational models. With a focus on single-cell biosensor-based studies, we summarize four major functional modes for ERK signaling in tissues: adjusting the size of cell populations, gradient-based patterning, wave propagation of morphological changes, and diversification of cellular gene expression states. These modes of operation are disrupted in cancer and other related diseases and represent potential targets for therapeutic intervention. By understanding the dynamic mechanisms involved in ERK signaling, there is potential for pharmacological strategies that not only simply inhibit ERK, but also restore functional activity patterns and improve disease outcomes.

Quercetin induces dual specificity phosphatase 5 via serum response factor

The phytochemical quercetin has gained attention for its antiinflammatory and anti-tumorigenic properties in various types of cancer. Tumorigenesis involves the aberrant regulation of kinase/phosphatase, highlighting the importance of maintaining homeostasis. Dual Specificity Phosphatase (DUSP) plays a crucial role in controlling the phosphorylation of ERK. The current study aimed to clone the DUSP5 promoter, and investigate its transcriptional activity in the presence of quercetin. The results revealed that quercetin-induced DUSP5 expression is associated with the serum response factor (SRF) binding site located in the DUSP5 promoter. The deletion of this site abolished the luciferase activity induced by quercetin, indicating its vital role in quercetin-induced DUSP5 expression. SRF protein is a transcription factor that potentially contributes to quercetin-induced DUSP5 expression at the transcriptional level. Additionally, quercetin enhanced SRF binding activity without changing its expression. These findings provide evidence of how quercetin affects anti-cancer activity in colorectal tumorigenesis by inducing SRF transcription factor activity, thereby increasing DUSP5 expression at the transcriptional level. This study highlights the importance of investigating the molecular mechanisms underlying the anti-cancer properties of quercetin, and suggests its potential use in cancer therapy. [BMB Reports 2023; 56(9): 508-513].

Prolactin-induced protein (PIP) increases the sensitivity of breast cancer cells to drug-induced apoptosis

We have previously shown that high expression of prolactin-induced protein (PIP) correlates with the response of breast cancer (BC) patients to standard adjuvant chemotherapy (doxorubicin and cyclophosphamide), which suggests that the absence of this glycoprotein is associated with resistance of tumor cells to chemotherapy. Therefore, in the present study, we analyzed the impact of PIP expression on resistance of BC cells to anti-cancer drugs and its biological role in BC progression. Expression of PIP and apoptotic genes in BC cell lines was analyzed using real-time PCR and Western blotting. PIP was detected in BC tissue specimens using immunohistochemistry. The tumorigenicity of cancer cells was analyzed by the in vivo tumor growth assay. Apoptotic cells were detected based on caspase-3 activation, Annexin V binding and TUNEL assay. The interaction of PIP with BC cells was analyzed using flow cytometry. Using two cellular models of BC (i.e. T47D cells with the knockdown of the PIP gene and MDA-MB-231 cells overexpressing PIP), we found that high expression of PIP resulted in (1) increased sensitivity of BC cells to apoptosis induced by doxorubicin (DOX), 4-hydroperoxycyclophosphamide (4-HC), and paclitaxel (PAX), and (2) improved efficacy of anti-cancer therapy with DOX in the xenograft mice model. Accordingly, a clinical study revealed that BC patients with higher PIP expression were characterized by longer 5-year overall survival and disease-free survival. Subsequent studies showed that PIP up-regulated the expression of the following pro-apoptotic genes: CRADD, DAPK1, FASLG, CD40 and BNIP2. This pro-apoptotic activity is mediated by secreted PIP and most probably involves the specific surface receptor. This study demonstrates that a high expression level of PIP sensitizes BC cells to anti-cancer drugs. Increased sensitivity to chemotherapy is the result of pro-apoptotic activity of PIP, which is evidenced by up-regulation of specific pro-apoptotic genes. As high expression of PIP significantly correlated with a better response of patients to anti-cancer drugs, this glycoprotein can be a marker for the prognostic evaluation of adjuvant chemotherapy.

IKKε knockout alleviates angiotensin II-induced apoptosis and excessive autophagy in vascular smooth muscle cells by regulating the ERK1/2 pathway

Inhibitor of nuclear factor-κB kinase subunit ε (IKKε) is an important signal regulator in the formation of abdominal aortic aneurysm (AAA). However, the underlying mechanism remains to be elucidated. Therefore, the present study aimed to investigate the mechanism underlying IKKε function in AAA formation by studying apoptosis and autophagy in angiotensin II (Ang II)-induced vascular smooth muscle cells (VSMCs). AngII was used to stimulate VSMCs for 24 h to simulate the process of AAA formation. VSMCs were transfected with IKKε small interfering RNA to investigate the effect of IKKε on AAA formation, cell apoptosis and autophagy. IKKε deficiency led to reduced mitochondrial damage and apoptosis in VSMCs in the early stage of apoptosis in vitro, as demonstrated using a JC-1 probe. IKKε deficiency also reduced autophagy and decreased the formation of autophagic vacuoles in VSMCs, demonstrated using transmission electron microscopy. The decrease in apoptosis caused by IKKε knockdown was reversed when the autophagic flow was blocked using bafilomycin A1. Western blot analysis further revealed that IKKε deficiency negatively regulated the ERK1/2 signaling pathway to reduce autophagy. Collectively, the results of the present study revealed that IKKε played a key role in apoptosis by inducing excessive autophagy, thereby potentially contributing to AAA formation. These findings further revealed the mechanism underlying IKKε function in the formation of AAA.

ROS-ERK Pathway as Dual Mediators of Cellular Injury and Autophagy-Associated Adaptive Response in Urinary Protein-Irritated Renal Tubular Epithelial Cells

ERK, an extracellular signal-regulated protein kinase, is involved in various biological responses, such as cell proliferation and differentiation, cell morphology maintenance, cytoskeletal construction, apoptosis, and canceration of cells. In this study, we focused on ERK pathway on cellular injury and autophagy-associated adaptive response in urinary protein-irritated renal tubular epithelial cells and explored the potential mechanisms underlying it. By using antioxidants N-acetylcysteine and catalase, we found that ERK pathway was activated by a reactive oxygen species- (ROS-) dependent mechanism after exposure to urinary proteins. What is more, ERK inhibitor U0126 could decrease the release of neutrophil gelatinase-associated lipocalin (NGAL), kidney injury molecule-1 (KIM-1), and the number of apoptotic cells induced by urinary proteins, indicating the damaging effects of ERK pathway in mediating cellular injury and apoptosis in HK-2 cells. Interestingly, we also found that the increased expression of microtubule-associated protein 1 light chain 3 (LC3)-II (a key marker of autophagy) and the decreased expression of p62 (autophagic substrate) induced by urinary proteins were reversed by U0126, suggesting autophagy was activated by ERK pathway. Furthermore, rapamycin reduced urinary protein-induced NGAL and KIM-1 secretion and cell growth inhibition, while chloroquine played the opposite effect, indicating that autophagy activation by ERK pathway was an adaptive response in the exposure to urinary proteins. Taken together, our results indicate that activated ROS-ERK pathway can induce cellular injury and in the meantime provide an autophagy-associated adaptive response in urinary protein-irritated renal tubular epithelial cells.

Traditional Uyghur medicine Quercus infectoria galls water extract triggers apoptosis and autophagic cell death in colorectal cancer cells

Background

The water extract of Quercuse infectoria galls (QIG) is the active ingredient of Uyghur medicine Xipayi Kui Jie’an (KJA) which has promising therapeutic effects on Ulcerative Colitis (UC) as an alternative medicine. Considering the relationship between UC and the development of colorectal cancer (CRC), the present work aims to explore the direct anti-CRC activity of QIG extract.

Methods

CCK8 assay and flow cytometry were used to detect cytotoxicity and apoptosis. Transmission electron microscopy (TEM), flow cytometry, laser confocal and western blotting were performed to examine autophagy. We also adopted Reactive Oxygen Assay kit, as well as transwell and wound healing tests to study the underlying mechanism of QIG against CRC cells.

Results

First, we found that QIG extract could suppress the viability of CRC cells and trigger caspases-dependent apoptosis. Subsequently, we proved for the first time that QIG extract also triggered autophagic cell death in CRC cells, which together with apoptosis contributed to the cytotoxic effect on CRC cells. Further investigation revealed that QIG-induced cytotoxicity associated with intracellular ROS accumulation which could suppress the AKT/mTOR signaling pathway, and then induce autophagy and inhibit cell growth. Besides, Erk signaling pathway was also involved in the process of autophagic cell death. Moreover, QIG extract also influenced EMT process and inhibited CRC cell migration.

Conclusion

Altogether, this study provides a basis for the utilization of QIG as an alternative medicine for CRC prevention and treatment.

SYPL1 Inhibits Apoptosis in Pancreatic Ductal Adenocarcinoma via Suppression of ROS-Induced ERK Activation

Synaptophysin-like 1 (SYPL1) is a neuroendocrine-related protein. The role of SYPL1 in pancreatic ductal adenocarcinoma (PDAC) and the underlying molecular mechanism remain unclarified. Here, after analyzing five datasets (GSE15471, GSE16515, GSE28735, TCGA, and PACA-AU) and 78 PDAC patients from Sun Yat-sen University Cancer Center, we demonstrated that SYPL1 was upregulated in PDAC and that a high level of SYPL1 indicated poor prognosis. Bioinformatics analysis implied that SYPL1 was related to cell proliferation and cell death. To validate these findings, gain-of-function and loss-of-function experiments were carried out, and we found that SYPL1 promoted cell proliferation in vitro and in vivo and that it protected cells from apoptosis. Mechanistic studies revealed that sustained extracellular-regulated protein kinase (ERK) activation was responsible for the cell death resulting from knockdown of SYPL1. In addition, bioinformatics analysis showed that the expression of SYPL1 positively correlated with antioxidant activity. Reactive oxygen species (ROS) were upregulated in cells with SYPL1 knockdown and vice versa. Upregulated ROS led to ERK activation and cell death. These results suggest that SYPL1 plays a vital role in PDAC and promotes cancer cell survival by suppressing ROS-induced ERK activation.

Targeting ERK-Hippo Interplay in Cancer Therapy

Extracellular signal-regulated kinase (ERK) is a part of the mitogen-activated protein kinase (MAPK) signaling pathway which allows the transduction of various cellular signals to final effectors and regulation of elementary cellular processes. Deregulation of the MAPK signaling occurs under many pathological conditions including neurodegenerative disorders, metabolic syndromes and cancers. Targeted inhibition of individual kinases of the MAPK signaling pathway using synthetic compounds represents a promising way to effective anti-cancer therapy. Cross-talk of the MAPK signaling pathway with other proteins and signaling pathways have a crucial impact on clinical outcomes of targeted therapies and plays important role during development of drug resistance in cancers. We discuss cross-talk of the MAPK/ERK signaling pathway with other signaling pathways, in particular interplay with the Hippo/MST pathway. We demonstrate the mechanism of cell death induction shared between MAPK/ERK and Hippo/MST signaling pathways and discuss the potential of combination targeting of these pathways in the development of more effective anti-cancer therapies.

Cardio-facio-cutaneous syndrome-associated pathogenic MAP2K1 variants activate autophagy

MAP2K1 encodes mitogen-activated protein kinase 1 (MEK1). Mutations in MAP2K1 lead to continuous activation of MEK/ERK signaling pathway, giving rise to cardio-facio-cutaneous syndrome (CFCS). However, the molecular mechanisms of abnormal activation of MEK/ERK signaling pathway and the role of autophagy, if any, in manifesting CFCS in MAP2K mutants remain unclear. Here, we report three Chinese children with CFCS having MAP2K1 pathogenic variants, identified by exome sequencing. They presented with dysmorphic facial features, seizures, psychomotor retardation, and short stature. Additionally, the third child showed pulmonary valve stenosis, multiple skeletal deformities, and osteoporosis. Whole exome sequencing revealed two heterozygous missense mutations in exon 3 of MAP2K1 (c.383G>T; p.Gly128Val and c.389A>G; p.Tyr130Cys), as well as a novel heterozygous missense variant (c.170A>T; p.Lys57Met) in exon 2 of MAP2K1. In SH-SY5Y cells, we identified, for the first time, that MAP2K1 mutations can activate the p-ERK-dependent cell cycle progression and autophagy, and cause CFCS. Our results extended the mutational spectrum of MAP2K1, examined the role of MEK1 protein in nerve cell functions, and demonstrated, for the first time, that autophagy may mediate the altered MAP2K1 function, leading to CFCS phenotypes.

New application of in silico methods in identifying mechanisms of action and key components of anti-cancer herbal formulation YIV-906 (PHY906)

YIV-906 (formally PHY906, KD018) is a four-herb formulation that is currently being developed to improve the therapeutic index and ameliorate the side effects of many chemotherapeutic drugs including sorafenib, irinotecan, and capecitabine. However, as a promising anti-cancer adjuvant, the molecular mechanism of action of YIV-906 remains unrevealed due to its multi-component and multi-target features. Since YIV-906 has been shown to induce apoptosis and autophagy in cancer cells through modulating the negative regulators of ERK1/2, namely DUSPs, it is of great interest to elucidate the key components that cause the therapeutic effect of YIV-906. In this work, we investigated the mechanism of YIV-906 inhibiting DUSPs, using a broad spectrum of molecular modelling techniques, including molecular docking, molecular dynamics (MD) simulations, and binding free energy calculations. In total, MD simulations and binding free energy calculations were performed for 99 DUSP-ligand complexes. We found that some herbal components or their metabolites could inhibit DUSPs. Based on the docking scores and binding free energies, the sulfation and glucuronidation metabolites of the S ingredient in YIV-906 play a leading role in inhibiting DUSPs, although several original herbal chemicals with carboxyl groups from the P and Z ingredients also make contributions to this inhibitory effect. It is not a surprise that the electrostatic interaction plays the dominant role in the ligand binding process, given the fact that several charged residues reside in the binding pockets of DUSPs. Our MD simulation results demonstrate that the sulfate moieties and carboxyl moieties of the advantageous ligands from YIV-906 can occupy the enzymes' catalytic sites, mimicking the endogenous phosphate substrates of DUSPs. As such, the ligand binding can inhibit the association of DUSPs and ERK1/2, which in turn reduces the dephosphorylation of ERK1/2 and causes cell cycle arrest in the tumor. Our modelling study provides useful insights into the rational design of highly potent anti-cancer drugs targeting DUSPs. Finally, we have demonstrated that multi-scale molecular modelling techniques are able to elucidate molecular mechanisms involving complex molecular systems.

Derrone induces autophagic cell death through induction of ROS and ERK in A549 cells

We studied the effect of derrone (DR), one of the major compounds of unripe fruits of Cudrania tricuspidata, on cancer cell death. DR inhibited cell growth of various cancer cells, and that was partially associated with apoptosis in A549 cells. DR showed the autophagic features, such as the conversion of LC3-I to LC3-II, the formation of autophagosome and the downregulation of SQSTM1/p62 (p62). The treatment of autophagy inhibitor reversed DR-mediated cell death, suggesting that DR induces autophagic cell death. The increase of cytoplasmic Ca2+ and ROS by DR treatment significantly influences the formation of autophagosomes; however, only ROS scavengers significantly rescued the reduced cell viability. Additional results revealed that treatment of DR induces sustained phosphorylation of ERK and the inhibition of ERK phosphorylation using U0126 (ERK inhibitor) markedly attenuated DR-induced cell death. Overall, these results suggest that DR induces autophagic cell death through intracellular ROS and sustained ERK phosphorylation in A549 cells.

The ER stress sensor IRE1 and MAP kinase ERK modulate autophagy induction in cells infected with coronavirus infectious bronchitis virus

Coronavirus infection induces the generation of autophagosomes, and certain host proteins regulating cellular autophagy are hijacked by some coronaviruses to facilitate the formation of double membrane vesicles. However, mechanisms underlying coronavirus-induced autophagy remain largely unknown. In this study, we demonstrate that autophagosome formation and apparent autophagic flux are induced in cells infected with infectious bronchitis virus (IBV) - a gammacoronavirus. Notably, IBV-induced autophagy was dependent on autophagy related 5 (ATG5) but not beclin1 (BECN1), although both are essential proteins in the canonical autophagy pathway. Moreover, the ER stress sensor inositol requiring enzyme 1 (IRE1), but not its substrate X-box protein 1 (XBP1), was also essential for the induction of autophagy during IBV infection. Finally, the anti-apoptotic extracellular signal-regulated kinase 1/2 (ERK1/2) also contributed to IBV-induced autophagy. Our findings add new knowledge to the regulatory mechanisms governing coronavirus-induced autophagy, highlighting an extensive cross-talk among cellular signaling pathways during coronavirus infection.

Early intervention with gastrodin reduces striatal neurotoxicity in adult rats with experimentally‑induced diabetes mellitus

Glutamate-induced excitotoxicity in the striatum has an important role in neurodegenerative diseases. It has been reported that diabetes mellitus (DM) induces excitotoxicity in striatal neurons, although the underlying mechanism remains to be fully elucidated. The present study aimed to investigate the effect of gastrodin on DM-induced excitotoxicity in the striatal neurons of diabetic rats. Adult Sprague-Dawley rats were divided into control, diabetic, and gastrodin intervention groups. Diabetes in the rats was induced with a single intraperitoneal injection of streptozotocin (65 mg/kg). In the gastrodin groups, the rats were gavaged with 60 or 120 mg/kg/day gastrodin for 6 weeks, 3 weeks following the induction of diabetes. Pathological alterations in the striatum were assessed using hematoxylin and eosin (H&E) staining. The protein expression levels of phosphorylated (p)-extracellular signal-regulated kinase (ERK)1/2, p-mitogen-activated protein kinase kinase (MEK)1/2, tyrosine receptor kinase B (TrKB) and brain-derived neurotrophic factor (BDNF) in the striatal neurons were evaluated by western blotting and double immunofluorescence. Additionally, the extracellular levels of glutamate were measured by microanalysis followed by high-pressure-liquid-chromatography. In diabetic rats, striatal neuronal degeneration was evident following H&E staining, which revealed the common occurrence of pyknotic nuclei. This was coupled with an increase in glutamate levels in the striatal tissues. The protein expression levels of p-ERK1/2, p-MEK1/2, TrKB and BDNF in the striatal tissues were significantly increased in the diabetic rats compared with those in the normal rats. In the gastrodin groups, degeneration of the striatal neurons was ameliorated. Furthermore, the expression levels of glutamate, p-ERK1/2, p-MEK1/2, TrKB and BDNF in the striatal neurons were decreased. From these findings, it was concluded that reduced neurotoxicity in striatal neurons following treatment with gastrodin may be attributed to its suppressive effects on the expression of p-ERK1/2, p-MEK1/2, BDNF and TrKB.

Mitochondrial Hyperactivation and Enhanced ROS Production are Involved in Toxicity Induced by Oncogenic Kinases Over-Signaling

Targeted therapy is an effective, rational, and safe approach to solid and hematological tumors treatment. Unfortunately, a significant fraction of patients treated with tyrosine kinase inhibitors (TKI) relapses mainly because of gene amplification, mutations, or other bypass mechanisms. Recently a growing number of papers showed how, in some cases, resistance due to oncogene overexpression may be associated with drug addiction: cells able to proliferate in the presence of high TKI doses become also TKI dependent, undergoing cellular stress, and apoptosis/death upon drug withdrawal. Notably, if a sub-cellular population survives TKI discontinuation it is also partially re-sensitized to the same drug. Thus, it is possible that a subset of patients relapsing upon TKI treatment may benefit from a discontinuous therapeutic schedule. We focused on two different hematologic malignancies, chronic myeloid leukemia (CML) and anaplastic large cell lymphoma (ALCL), both successfully treatable with TKIs. The two models utilized (LAMA and SUP-M2) differed in having oncogene overexpression as the sole cause of drug resistance (CML), or additionally carrying kinase domain mutations (ALCL). In both cases drug withdrawal caused a sudden overload of oncogenic signal, enhanced mitochondria activity, induced the release of a high amount of reactive oxygen species (ROS), and caused genotoxic stress and massive cell death. In LAMA cells (CML) we could rescue the cells from death by partially blocking downstream oncogenic signaling or lowering ROS detrimental effect by adding reduced glutathione.

Angiotensin-converting enzyme Ance is cooperatively regulated by Mad and Pannier in Drosophila imaginal discs

Angiotensin-converting enzyme (ACE) is an evolutionarily conserved peptidyl dipeptidase. Mammalian ACE converts angiotensin I to the active vasoconstrictor angiotensin II, thus playing a critical role for homeostasis of the renin-angiotensin system. In Drosophila, the ACE homolog Ance is expressed in specific regions of developing organs, but its regulatory mechanism has not been identified. Here we provide evidence that Ance expression is regulated by a combination of Mad and Pannier (Pnr) in imaginal discs. We demonstrate that Ance expression in eye and wing discs depends on Dpp signaling. The Mad binding site of Ance regulatory region is essential for Ance expression. Ance expression in imaginal discs is also regulated by the GATA family transcription factor Pnr. Pnr directly regulates Ance expression by binding to a GATA site of Ance enhancer. In addition, Pnr and Mad physically and genetically interact. Ance null mutants are morphologically normal but show genetic interaction with dpp mutants. Furthermore, we show that human SMAD2 and GATA4 physically interact and ACE expression in HEK293 cells is regulated by SMAD2 and GATA4. Taken together, this study reveals a cooperative mechanism of Ance regulation by Mad and Pnr. Our data also suggest a conserved transcriptional regulation of human ACE.

Anthocyanins/anthocyanidins and colorectal cancer: What is behind the scenes?

Colorectal cancer (CRC) is one of the most common cause of cancer death. Phytochemicals, especially anthocyanins/anthocyanidins (A/A), have gathered attention of the scientific community owing to their anti-inflammatory, antioxidant, and cancer-inhibitory properties. In this review, we discussed the possible mechanisms whereby A/A exhibit intestinal anticarcinogenic characteristics. Anthocyanins/anthocyanidins inhibit the pro-inflammatory NF-κB pathway, attenuate Wnt signaling and suppress abnormal epithelial cell proliferation. In addition, A/A induce mitochondrial-mediated apoptosis and downregulate Akt/mTOR (mammalian target of rapamycin) pathway. Furthermore, activation of AMP-activated protein kinase (AMPK) and sirtuin 1 (SIRT1) also contributes to the anti-carcinogenic effects of A/A. Finally, downregulation of metalloproteinases (MMPs) by A/A inhibits tumor invasion and metastasis. In conclusion, A/A exert their anti-tumor effects against colorectal carcinogenesis via multiple mechanisms, providing insights into the use of A/A as a natural chemopreventive intervention on major colorectal carcinogenesis.

An immediate-late gene expression module decodes ERK signal duration

The RAF‐MEK‐ERK signalling pathway controls fundamental, often opposing cellular processes such as proliferation and apoptosis. Signal duration has been identified to play a decisive role in these cell fate decisions. However, it remains unclear how the different early and late responding gene expression modules can discriminate short and long signals. We obtained both protein phosphorylation and gene expression time course data from HEK293 cells carrying an inducible construct of the proto‐oncogene RAF. By mathematical modelling, we identified a new gene expression module of immediate–late genes (ILGs) distinct in gene expression dynamics and function. We find that mRNA longevity enables these ILGs to respond late and thus translate ERK signal duration into response amplitude. Despite their late response, their GC‐rich promoter structure suggested and metabolic labelling with 4SU confirmed that transcription of ILGs is induced immediately. A comparative analysis shows that the principle of duration decoding is conserved in PC12 cells and MCF7 cells, two paradigm cell systems for ERK signal duration. Altogether, our findings suggest that ILGs function as a gene expression module to decode ERK signal duration.

Grape seed extracts modify the outcome of oxaliplatin in colon cancer cells by interfering with cellular mechanisms of drug cytotoxicity

Grape seed extracts are commonly utilized as dietary supplements for their antioxidant properties, even from cancer patients. However, whether these natural extracts interfere with chemotherapeutics utilized in colon cancer treatment is still poorly investigated. The cytotoxicity of extracts from Italia and Palieri cultivars either alone or in combination with oxaliplatin was evaluated in colon cancer cells. Grape seed extracts displayed anti-proliferative activity depending on the concentration utilized through apoptosis induction. In combination, they affected the activation of Erk1/2 and counteracted the intrinsic and the extrinsic pathway of apoptosis, the DNA damage and the generation of ROS induced by oxaliplatin. Noteworthy grape seed extracts strongly enhanced the uptake of oxaliplatin into all cells, by affecting the cell transport system of platinum. The addition of these natural extracts to oxaliplatin strongly reduced the cellular response to oxaliplatin and allowed a huge accumulation of platinum into cells. Here, we shed light on the chemical biology underlying the combination of grape seed extracts and oxaliplatin, demonstrating that they might be detrimental to oxaliplatin effectiveness in colon cancer therapy.

Analysis of ERK3 intracellular localization: dynamic distribution during mitosis and apoptosis

Extracellular signal-regulated kinases (ERK) 1, 2 and 3 are involved in cell proliferation and differentiation, and apoptosis; although ERK1/2 have been widely studied, limited knowledge on ERK3 is available. The present work aimed at investigating ERK3 distribution during cell cycle and apoptosis in human tumor HeLa cells. The analysis performed by double immunofluorescence and immunoelectron microscopy revealed that during interphase ERK3 is mainly resident in the nucleoplasm in association with ribonuclear proteins involved in early pre-mRNA splicing, it undergoes cell cycle-dependent redistribution and, during apoptosis, it remains in the nucleus in the form of massive nuclear aggregates, then moves to the cytoplasm and is finally extruded.

Moxifloxacin and ciprofloxacin induces S-phase arrest and augments apoptotic effects of cisplatin in human pancreatic cancer cells via ERK activation

Background

Pancreatic cancer, one of the most dreadful gastrointestinal tract malignancies, with the current chemotherapeutic drugs has posed a major impediment owing to poor prognosis and chemo-resistance thereby suggesting critical need for additional drugs as therapeutics in combating the situation. Fluoroquinolones have shown promising and significant anti-tumor effects on several carcinoma cell lines.

Methods

Previously, we reported growth inhibitory effects of fourth generation fluoroquinolone Gatifloxacin, while in the current study we have investigated the anti-proliferative and apoptosis-inducing mechanism of older generation fluoroquinolones Moxifloxacin and Ciprofloxacin on the pancreatic cancer cell-lines MIA PaCa-2 and Panc-1. Cytotoxicity was measured by MTT assay. Apoptosis induction was evaluated using annexin assay, cell cycle assay and activation of caspase-3, 8, 9 were measured by western blotting and enzyme activity assay.

Results

Herein, we found that both the fluoroquinolones suppressed the proliferation of pancreatic cancer cells by causing S-phase arrest and apoptosis. Blockade in S-phase of cell cycle was associated with decrease in the levels of p27, p21, CDK2, cyclin-A and cyclin-E. Herein we also observed triggering of extrinsic as well as intrinsic mitochondrial apoptotic pathway as suggested by the activation of caspase-8, 9, 3, and Bid respectively. All this was accompanied by downregulation of antiapoptotic protein Bcl-xL and upregulation of proapoptotic protein Bak. Our results strongly suggest the role of extracellular-signal-regulated kinases (ERK1/2), but not p53, p38 and c-JUN N-terminal kinase (JNK) in fluoroquinolone induced growth inhibitory effects in both the cell lines. Additionally, we also found both the fluoroquinolones to augment the apoptotic effects of broad spectrum anticancer drug Cisplatin via ERK.

Conclusion

The fact that these fluoroquinolones synergize the effect of cisplatin opens new insight into therapeutic index in treatment of pancreatic cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1560-y) contains supplementary material, which is available to authorized users.

Hippocampal cell fate regulation by chronic cocaine during periods of adolescent vulnerability: Consequences of cocaine exposure during adolescence on behavioral despair in adulthood

Given that adolescence represents a critical moment for shaping adult behavior and may predispose to disease vulnerability later in life, the aim of this study was to find a vulnerable period during adolescence in which hippocampal cell fate regulation was altered by cocaine exposure, and to evaluate the long-term consequences of a cocaine experience during adolescence in affecting hippocampal plasticity and behavioral despair in adulthood. Study I: Male rats were treated with cocaine (15mg/kg, i.p.) or saline for 7 consecutive days during adolescence (early post-natal day (PND) 33-39, mid PND 40-46, late PND 47-53). Hippocampal plasticity (i.e., cell fate regulation, cell genesis) was evaluated 24h after the last treatment dose during the course of adolescence (PND 40, PND 47, PND 54). Study II: The consequences of cocaine exposure during adolescence (PND 33-39 or PND 33-46; 7 or 14days) were measured in adulthood at the behavioral (i.e., forced swim test, PND 62-63) and molecular (hippocampal cell markers, PND 64) levels. Chronic cocaine during early adolescence dysregulated FADD forms only in the hippocampus (HC), as compared to other brain regions, and during mid adolescence, impaired cell proliferation (Ki-67) and increased PARP-1 cleavage (a cell death maker) in the HC. Interestingly, chronic cocaine exposure during adolescence did not alter the time adult rats spent immobile in the forced swim test. These results suggest that this paradigm of chronic cocaine administration during adolescence did not contribute to the later manifestation of behavioral despair (i.e., one pro-depressive symptom) as measured by the forced swim test in adulthood.

PHY906(KD018), an adjuvant based on a 1800-year-old Chinese medicine, enhanced the anti-tumor activity of Sorafenib by changing the tumor microenvironment

PHY906 (KD018) is a four-herb Chinese Medicine Formula. It has been shown to potentially enhance the therapeutic indices of different class anticancer agents in vivo. Here, PHY906 is reported to enhance the anti-tumor activity of Sorafenib in nude mice bearing HepG2 xenografts. Among the four herbal ingredients of PHY906, Scutellaria baicalensis Georgi (S) and Paeonia lactiflora Pall (P) are required; however, S plays a more important role than P in increasing tumor apoptosis induced by Sorafenib with an increase of mouse(m)FasL and human(h)FasR expression. PHY906 may potentiate Sorafenib action by increasing hMCP1 expression and enhancing infiltration of macrophages into tumors with a higher M1/M2 (tumor rejection) signature expression pattern, as well as affect autophagy by increasing AMPKα-P and ULK1-S555-P of tumors. Depletion of macrophage could counteract PHY906 to potentiate the anti-tumor activity of Sorafenib. It was reported that tumor cells with higher levels of ERK1/2-P are more susceptible to Sorafenib, and the S component of PHY906 may increase ERK1/2-P via inhibition of ERK1/2 phosphatase in HepG2 tumors. PHY906 may potentiate the anti-hepatoma activity of Sorafenib by multiple mechanisms targeting on the inflammatory state of microenvironment of tumor tissue through two major ingredients (P and S) of PHY906.

The neuroprotective effect of maltol against oxidative stress on rat retinal neuronal cells

PURPOSE

Maltol (3-hydroxy-2-methyl-4-pyrone), formed by the thermal degradation of starch, is found in coffee, caramelized foods, and Korean ginseng root. This study investigated whether maltol could rescue neuroretinal cells from oxidative injury in vitro.

METHODS

R28 cells, which are rat embryonic precursor neuroretinal cells, were exposed to hydrogen peroxide (H2O2, 0.0 to 1.5 mM) as an oxidative stress with or without maltol (0.0 to 1.0 mM). Cell viability was monitored with the lactate dehydrogenase assay and apoptosis was examined by the terminal deoxynucleotide transferase-mediated terminal uridine deoxynucleotidyl transferase nick end-labeling (TUNEL) method. To investigate the neuroprotective mechanism of maltol, the expression and phosphorylation of nuclear factor-kappa B (NF-κB), extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38 were evaluated by Western immunoblot analysis.

RESULTS

R28 cells exposed to H2O2 were found to have decreased viability in a dose- and time-dependent manner. However, H2O2-induced cytotoxicity was decreased with the addition of maltol. When R28 cells were exposed to 1.0 mM H2O2 for 24 hours, the cytotoxicity was 60.69 ± 5.71%. However, the cytotoxicity was reduced in the presence of 1.0 mM maltol. This H2O2-induced cytotoxicity caused apoptosis of R28 cells, characterized by DNA fragmentation. Apoptosis of oxidatively-stressed R28 cells with 1.0 mM H2O2 was decreased with 1.0 mM maltol, as determined by the TUNEL method. Western blot analysis showed that treatment with maltol reduced phosphorylation of NF-κB, ERK, and JNK, but not p38. The neuroprotective effects of maltol seemed to be related to attenuated expression of NF-κB, ERK, and JNK.

CONCLUSIONS

Maltol not only increased cell viability but also attenuated DNA fragmentation. The results obtained here show that maltol has neuroprotective effects against hypoxia-induced neuroretinal cell damage in R28 cells, and its effects may act through the NF-κB and mitogen-activated protein kinase signaling pathways.

Kaempferol Downregulates Insulin-like Growth Factor-I Receptor and ErbB3 Signaling in HT-29 Human Colon Cancer Cells

BACKGROUND

Novel dietary agents for colon cancer prevention and therapy are desired. Kaempferol, a flavonol, has been reported to possess anticancer activity. However, little is known about the molecular mechanisms of the anticancer effects of kaempferol. The aim of this study was to determine the inhibitory effect of kaempferol on growth factor-induced proliferation and to elucidate its underlying mechanisms in the HT-29 human colon cancer cell line.

METHODS

To assess the effects of kaempferol and/or growth factors [insulin-like growth factor (IGF)-I and heregulin (HRG)-β], cells were cultured with or without 60 μmol/L kaempferol and/or 10 nmol/L IGF-I or 20 μg/L HRG-β. Cell proliferation, DNA synthesis, and apoptosis were determined by a cell viability assay, a [(3)H]thymidine incorporation assay, and Annexin-V staining, respectively. Western blotting, immunoprecipitation, and an in vitro kinase assay were conducted to evaluate expression and activation of various signaling molecules involved in the IGF-I receptor (IGF-IR) and ErbB3 signaling pathways.

RESULTS

IGF-I and HRG-β stimulated HT-29 cell growth but did not abrogate kaempferol-induced growth inhibition and apoptosis. Kaempferol reduced IGF-II secretion, HRG expression and phosphorylation of Akt and extracellular signal-regulated kinase (ERK)-1/2. Kaempferol reduced IGF-I- and HRG-β-induced phosphorylation of the IGF-IR and ErbB3, their association with p85, and phosphatidylinositol 3-kinase (PI3K) activity. Additionally, kaempferol inhibited IGF-I- and HRG-β-induced phosphorylation of Akt and ERK-1/2.

CONCLUSIONS

The results demonstrate that kaempferol downregulates activation of PI3K/Akt and ERK-1/2 pathways by inhibiting IGF-IR and ErbB3 signaling in HT-29 cells. We suggest that kaempferol could be a useful chemopreventive agent against colon cancer.

Kaempferol Downregulates Insulin-like Growth Factor-I Receptor and ErbB3 Signaling in HT-29 Human Colon Cancer Cells

Background:

Novel dietary agents for colon cancer prevention and therapy are desired. Kaempferol, a flavonol, has been reported to possess anticancer activity. However, little is known about the molecular mechanisms of the anticancer effects of kaempferol. The aim of this study was to determine the inhibitory effect of kaempferol on growth factor-induced proliferation and to elucidate its underlying mechanisms in the HT-29 human colon cancer cell line.

Methods:

To assess the effects of kaempferol and/or growth factors [insulin-like growth factor (IGF)-I and heregulin (HRG)-β], cells were cultured with or without 60 μmol/L kaempferol and/or 10 nmol/L IGF-I or 20 μg/L HRG-β. Cell proliferation, DNA synthesis, and apoptosis were determined by a cell viability assay, a [³H]thymidine incorporation assay, and Annexin-V staining, respectively. Western blotting, immunoprecipitation, and an in vitro kinase assay were conducted to evaluate expression and activation of various signaling molecules involved in the IGF-I receptor (IGF-IR) and ErbB3 signaling pathways.

Results:

IGF-I and HRG-β stimulated HT-29 cell growth but did not abrogate kaempferol-induced growth inhibition and apoptosis. Kaempferol reduced IGF-II secretion, HRG expression and phosphorylation of Akt and extracellular signal-regulated kinase (ERK)-1/2. Kaempferol reduced IGF-I- and HRG-β-induced phosphorylation of the IGF-IR and ErbB3, their association with p85, and phosphatidylinositol 3-kinase (PI3K) activity. Additionally, kaempferol inhibited IGF-I- and HRG-β-induced phosphorylation of Akt and ERK-1/2.

Conclusions:

The results demonstrate that kaempferol downregulates activation of PI3K/Akt and ERK-1/2 pathways by inhibiting IGF-IR and ErbB3 signaling in HT-29 cells. We suggest that kaempferol could be a useful chemopreventive agent against colon cancer.

The neurotoxicity of 5-S-cysteinyldopamine is mediated by the early activation of ERK1/2 followed by the subsequent activation of ASK1/JNK1/2 pro-apoptotic signalling

5-S-cysteinyldopamine is an endogenous neurotoxin with relevance to Parkinson's disease. The present study shows for the first time that the endogenous formation of 5-S-cysteinyldopamine in the Parkinsonian brain may be causally related to nigrostriatal tract degeneration.

Quercetin induces mitochondrial-derived apoptosis via reactive oxygen species-mediated ERK activation in HL-60 leukemia cells and xenograft

Quercetin is a plant-derived bioflavonoid that was recently shown to have multiple anticancer activities in various solid tumors. Here, novel molecular mechanisms through which quercetin exerts its anticancer effects in acute myeloid leukemia (AML) cells were investigated. Results from Western blot and flow cytometric assays revealed that quercetin significantly induced caspase-8, caspase-9, and caspase-3 activation, poly ADP-ribose polymerase (PARP) cleavage, and mitochondrial membrane depolarization in HL-60 AML cells. The induction of PARP cleavage by quercetin was also observed in other AML cell lines: THP-1, MV4-11, and U937. Moreover, treatment of HL-60 cells with quercetin induced sustained activation of extracellular signal-regulated kinase (ERK), and inhibition of ERK by an ERK inhibitor significantly abolished quercetin-induced cell apoptosis. MitoSOX red and 2',7'-dichlorofluorescin fluorescence, respectively, showed that mitochondrial superoxide and intracellular peroxide levels were higher in quercetin-treated HL-60 cells compared with the control group. Moreover, both N-acetylcysteine and the superoxide dismutase mimetic, MnTBAP, reversed quercetin-induced intracellular reactive oxygen species production, ERK activation, and subsequent cell death. The in vivo xenograft mice experiments revealed that quercetin significantly reduced tumor growth through inducing intratumoral oxidative stress while activating the ERK pathway and subsequent cell apoptosis in mice with HL-60 tumor xenografts. In conclusions, our results indicated that quercetin induced cell death of HL-60 cells in vitro and in vivo through induction of intracellular oxidative stress following activation of an ERK-mediated apoptosis pathway.

Human immunodeficiency virus-1 (HIV-1)-mediated apoptosis: new therapeutic targets

HIV has posed a significant challenge due to the ability of the virus to both impair and evade the host’s immune system. One of the most important mechanisms it has employed to do so is the modulation of the host’s native apoptotic pathways and mechanisms. Viral proteins alter normal apoptotic signaling resulting in increased viral load and the formation of viral reservoirs which ultimately increase infectivity. Both the host’s pro- and anti-apoptotic responses are regulated by the interactions of viral proteins with cell surface receptors or apoptotic pathway components. This dynamic has led to the development of therapies aimed at altering the ability of the virus to modulate apoptotic pathways. These therapies are aimed at preventing or inhibiting viral infection, or treating viral associated pathologies. These drugs target both the viral proteins and the apoptotic pathways of the host. This review will examine the cell types targeted by HIV, the surface receptors exploited by the virus and the mechanisms whereby HIV encoded proteins influence the apoptotic pathways. The viral manipulation of the hosts’ cell type to evade the immune system, establish viral reservoirs and enhance viral proliferation will be reviewed. The pathologies associated with the ability of HIV to alter apoptotic signaling and the drugs and therapies currently under development that target the ability of apoptotic signaling within HIV infection will also be discussed.

Network analysis of differential Ras isoform mutation effects on intestinal epithelial responses to TNF-α

Tumor necrosis factor alpha (TNF-α) is an inflammatory cytokine that can elicit distinct cellular behaviors under different molecular contexts. Mitogen activated protein kinase (MAPK) pathways, especially the extracellular signal-regulated kinase (Erk) pathway, help to integrate influences from the environmental context, and therefore modulate the phenotypic effect of TNF-α exposure. To test how variations in flux through the Erk pathway modulate TNF-α-elicited phenotypes in a complex physiological environment, we exposed mice with different Ras mutations (K-Ras activation, N-Ras activation, and N-Ras ablation) to TNF-α and observed phenotypic and signaling changes in the intestinal epithelium. Hyperactivation of Mek1, an Erk kinase, was observed in the intestine of mice with K-Ras activation and, surprisingly, in N-Ras null mice. Nevertheless, these similar Mek1 outputs did not give rise to the same phenotype, as N-Ras null intestine was hypersensitive to TNF-α-induced intestinal cell death while K-Ras mutant intestine was not. A systems biology approach applied to sample the network state revealed that the signaling contexts presented by these two Ras isoform mutations were different. Consistent with our experimental data, N-Ras ablation induced a signaling network state that was mathematically predicted to be pro-death, while K-Ras activation did not. Further modeling by constrained Fuzzy Logic (cFL) revealed that N-Ras and K-Ras activate the signaling network with different downstream distributions and dynamics, with N-Ras effects being more transient and diverted more towards PI3K-Akt signaling and K-Ras effects being more sustained and broadly activating many pathways. Our study highlights the necessity to consider both environmental and genomic contexts of signaling pathway activation in dictating phenotypic responses, and demonstrates how modeling can provide insight into complex in vivo biological mechanisms, such as the complex interplay between K-Ras and N-Ras in their downstream effects.

Effects of Hominis placenta on LPS-induced cell toxicity in BV2 microglial cells

ETHNOPHARMACOLOGICAL RELEVANCE

Hominis placenta (HP) dried placenta extracted from pregnant women after delivery has been widely used to treat chronic inflammatory diseases. HP has been reported to be effective to alleviate the arthritic symptoms by modulating the expression of inflammatory factors in adjuvant-induced arthritis rats. However, the mechanism of action of HP is unknown. Neuroinflammation has been implicated in the pathogenesis of several neurodegenerative disease, including Alzheimer's disease (AD), Parkinson's disease (PD) and amyotropic lateral sclerosis (ALS). Activated microglia produce large amounts of toxic soluble factors, which can be responsible for the neurodegenerative disease. Chronic microglial activation leads to neuroinflammation, which contributes to neuronal dysfunction, injury and loss in these diseases. Lipopolysaccharide (LPS) is widely used for neuroinflammation caused by microglial activation of immune cells in the central nervous system (CNS) and subsequent release of inflammatory or neurotoxic factors. In the present study, we investigated the effects and signaling pathway of HP in the LPS induced BV2 microglial cells.

MATERIALS AND METHOD

BV2 microglial cells were pretreated with 50 μM HP for 2h prior to 2 μg/ml LPS for 15 min. Cell viability was determined by MTT assay. The level of protein expression was analyzed by western blot. Immunofluorescence was performed with an anti-COX2 antibody in BV2 cells.

RESULTS

HP decreased LPS-induced microglial cell death by 24% and inhibited LPS-induced activation of c-Jun N-terminal kinase (JNK) by 23% and p42/44MAP kinase (ERK) by 34% treatment of LPS. In addition, HP attenuated LPS-induced pro-inflammatory proteins such as iNOS and COX2 in microglial cells 34% and 28% respectively.

CONCLUSIONS

Our data shows that HP has a protective role against LPS stimulation through inhibition of MAPK signaling and suppression of inflammation caused by neurotoxin including LPS. These findings suggest that HP could be a potential therapeutic agent of neurodegenerative diseases which accompanied with microglial activation.

Mechanistic evaluation of a novel small molecule targeting mitochondria in pancreatic cancer cells

Background

Pancreatic cancer is one of the deadliest cancers with a 5-year survival rate of 6%. Therapeutic options are very limited and there is an unmet medical need for safe and efficacious treatments. Cancer cell metabolism and mitochondria provide unexplored targets for this disease. We recently identified a novel class of triphenylphosphonium salts, TP compounds, with broad- spectrum anticancer properties. We examined the ability of our prototypical compound TP421– chosen for its fluorescent properties – to inhibit the growth of pancreatic cancer cells and further investigated the molecular mechanisms by which it exerts its anticancer effects.

Methodology/Principal Findings

TP421 exhibited sub-micromolar IC₅₀ values in all the pancreatic cancer cell lines tested using MTT and colony formation assays. TP421 localized predominantly to mitochondria and induced G₀/G₁ arrest, ROS accumulation, and activation of several stress-regulated kinases. Caspase and PARP-1 cleavage were observed indicating an apoptotic response while LC3B-II and p62 were accumulated indicating inhibition of autophagy. Furthermore, TP421 induced de-phosphorylation of key signaling molecules involved in FAK mediated adhesion that correlated with inhibition of cell migration.

Conclusions/Significance

TP421 is a representative compound of a new promising class of mitochondrial-targeted agents useful for pancreatic cancer treatment. Because of their unique mechanism of action and efficacy further development is warranted.

Oncogenic KRAS and BRAF activation of the MEK/ERK signaling pathway promotes expression of dual-specificity phosphatase 4 (DUSP4/MKP2) resulting in nuclear ERK1/2 inhibition

Gain-of-function mutations in KRAS and BRAF genes are found in up to 50% of colorectal cancers. These mutations result in the activation of the BRAF/MEK signaling pathway culminating in the stimulation of ERK1/2 mitogen-activated protein kinases. Upon activation, ERK1/2 translocate from the cytoplasm to the nucleus. This process has been shown to be required for the induction of many cellular responses, although the molecular mechanisms regulating ERK nuclear function, especially under oncogenic stimulation, remain to be explored. Herein, we examined the spatiotemporal regulation of ERK1/2 activity upon oncogenic activation of KRAS(G12V) and BRAF(V600E) in normal intestinal epithelial crypt cells (IECs). Results demonstrate that expression of these oncogenes markedly stimulated ERK1/2 activities and morphologically transformed IECs. Importantly however, ERK phosphorylation was not observed in the nucleus, but restricted to the cytoplasm of KRAS(G12V)- and BRAF(V600E)-transformed IECs. The absence of nuclear ERK phosphorylation was due to a vanadate-sensitive phosphatase activity. Nuclear ERK dephosphorylation was found to be tightly correlated with the rapid expression of DUSP4 phosphatase induced in an MEK-dependent manner. In addition, MEK-dependent phosphorylation of T361, T363, S390 and S395 residues highly stabilized DUSP4 protein. Finally, in human colorectal cancer cells, ERK1/2 activities were also confined to the cytoplasm and treatment with pervanadate reactivated ERK1/2 in the nucleus. Accordingly, DUSP4 mRNAs were found to be highly expressed, in an MEK-dependent manner, in all colorectal cancer cells analyzed. These findings indicate that DUSP4 functions as part of a negative feedback mechanism in the control of the duration and magnitude of nuclear ERK activation during intestinal tumorigenesis.

Sirolimus enhances cyclosporine a-induced cytotoxicity in human renal glomerular mesangial cells

End Stage Renal Disease (ESRD) is an ever increasing problem worldwide. However the mechanisms underlying disease progression are not fully elucidated. This work addressed nephrotoxicity induced by the immunosuppressive agents' cyclosporine A (CsA) and sirolimus (SRL). Nephrotoxicity is the major limiting factor in long term use of CsA. SRL causes less nephrotoxicity than CsA. Therefore investigations into the differential effects of these agents may identify potential mechanisms of nephrotoxicity and means to prevent ESRD induced by therapeutic drugs. Using ELISA, Western blotting, quantitative PCR and a reporter gene assay we detailed the differential effects of CsA and SRL in human renal mesangial cells. CsA treatment increased profibrotic TGF-β1 secretion in human mesangial cells whereas SRL did not, indicating a role for TGF-β in CsA toxicity. However we observed a synergistic nephrotoxic effect when CsA and SRL were co-administered. These synergistic alterations may have been due to an increase in CTGF which was not evident when the immunosuppressive drugs were used alone. The CsA/SRL combination therapy significantly enhanced Smad signalling and altered the extracellular matrix regulator matrix metalloproteinase 9 (MMP-9). Inhibition of the ERK 1/2 pathway, attenuated these CsA/SRL induced alterations indicating a potentially significant role for this pathway.

Decreased proliferation of adult hippocampal stem cells during cocaine withdrawal: possible role of the cell fate regulator FADD

The current study uses an extended access rat model of cocaine self-administration (5-h session per day, 14 days), which elicits several features manifested during the transition to human addiction, to study the neural adaptations associated with cocaine withdrawal. Given that the hippocampus is thought to have an important role in maintaining addictive behavior and appears to be especially relevant to mechanisms associated with withdrawal, this study attempted to understand how extended access to cocaine impacts the hippocampus at the cellular and molecular levels, and how these alterations change over the course of withdrawal (1, 14, and 28 days). Therefore, at the cellular level, we examined the effects of cocaine withdrawal on cell proliferation (Ki-67+ and NeuroD+ cells) in the DG. At the molecular level, we employed a 'discovery' approach with gene expression profiling in the DG to uncover novel molecules possibly implicated in the neural adaptations that take place during cocaine withdrawal. Our results suggest that decreased hippocampal cell proliferation might participate in the adaptations associated with drug removal and identifies 14 days as a critical time-point of cocaine withdrawal. At the 14-day time-point, gene expression profiling of the DG revealed the dysregulation of several genes associated with cell fate regulation, highlighting two new neurobiological correlates (Ascl-1 and Dnmt3b) that accompany cessation of drug exposure. Moreover, the results point to Fas-Associated protein with Death Domain (FADD), a molecular marker previously associated with the propensity to substance abuse and cocaine sensitization, as a key cell fate regulator during cocaine withdrawal. Identifying molecules that may have a role in the restructuring of the hippocampus following substance abuse provides a better understanding of the adaptations associated with cocaine withdrawal and identifies novel targets for therapeutic intervention.

Strong negative feedback from Erk to Raf confers robustness to MAPK signalling

This study shows that MAPK signalling is robust against protein level changes due to a strong negative feedback from Erk to Raf. Surprisingly, robustness is provided through a fast post-translational mechanism although variation of Erk levels occurs on a timescale of days.

MAPK signalling is robust against variation in protein level.

Robustness is mediated by a negative feedback to Raf.

Loss of negative feedback due to mutation in B-Raf opens the door for targeted intervention.

Protein levels within signal transduction pathways vary strongly from cell to cell. For example, it has been reported that concentrations of the last kinase within the MAPK signalling module, Erk, varies about four-fold between clonal cells under the same conditions. In the present study, we analysed how signalling pathways can still process information quantitatively despite strong heterogeneity in protein levels. Mathematical analysis of isolated phosphorylation–dephosphorylation cycles predicts that phosphorylation of a signalling molecule is proportional to the protein concentration. We systematically perturbed the protein levels of Erk in human cell lines by siRNA. We found that the steady-state phosphorylation of Erk is very robust against perturbations of Erk protein level, suggesting that there are mechanisms that provide robustness to the pathway against protein fluctuations. Using mathematical modelling, we identified three potential mechanisms that may provide robustness against fluctuating protein levels:

1. Kinetic effects (saturation of the activating kinase Mek),

2. Transcriptional negative feedbacks,

3. Negative feedbacks on the post-translational level.

By experimental analysis of the systems, which included analysis of Erk phosphorylation under Mek overexpression, measuring transcript levels of negative feedback regulators, and application of generic inhibitors of transcription and translation, we could exclude kinetic effects and transcriptional negative feedback as mechanisms of robustness.

By analysing a panel of cell lines, we found that cells are robust as long as the signal passes through Raf-1. In contrast, cells where the pathway is activated by a mutation in B-Raf lose robustness. Detailed molecular analysis of the system shows that a single post-translational feedback to Raf mediates robustness. Thus, robustness is provided through a fast post-translational mechanism although variation of Erk levels occurs on a timescale of days.

Protein levels within signal transduction pathways vary strongly from cell to cell. Here, we analysed how signalling pathways can still process information quantitatively despite strong heterogeneity in protein levels. We systematically perturbed the protein levels of Erk, the terminal kinase in the MAPK signalling pathway in a panel of human cell lines. We found that the steady-state phosphorylation of Erk is very robust against perturbations of Erk protein level. Although a multitude of mechanisms exist that may provide robustness against fluctuating protein levels, we found that one single feedback from Erk to Raf-1 accounts for the observed robustness. Surprisingly, robustness is provided through a fast post-translational mechanism although variation of Erk levels occurs on a timescale of days.

Effects of bee venom on glutamate-induced toxicity in neuronal and glial cells

Bee venom (BV), which is extracted from honeybees, is used in traditional Korean medical therapy. Several groups have demonstrated the anti-inflammatory effects of BV in osteoarthritis both in vivo and in vitro. Glutamate is the predominant excitatory neurotransmitter in the central nervous system (CNS). Changes in glutamate release and uptake due to alterations in the activity of glutamate transporters have been reported in many neurodegenerative diseases, including Parkinson's disease, Alzheimer's disease, and amyotrophic lateral sclerosis. To assess if BV can prevent glutamate-mediated neurotoxicity, we examined cell viability and signal transduction in glutamate-treated neuronal and microglial cells in the presence and absence of BV. We induced glutamatergic toxicity in neuronal cells and microglial cells and found that BV protected against cell death. Furthermore, BV significantly inhibited the cellular toxicity of glutamate, and pretreatment with BV altered MAP kinase activation (e.g., JNK, ERK, and p38) following exposure to glutamate. These findings suggest that treatment with BV may be helpful in reducing glutamatergic cell toxicity in neurodegenerative diseases.

Regulation of autophagy by kinases

Autophagy is a process of self-degradation that maintains cellular viability during periods of metabolic stress. Although autophagy is considered a survival mechanism when faced with cellular stress, extensive autophagy can also lead to cell death. Aberrations in autophagy are associated with several diseases, including cancer. Therapeutic exploitation of this process requires a clear understanding of its regulation. Although the core molecular components involved in the execution of autophagy are well studied there is limited information on how cellular signaling pathways, particularly kinases, regulate this complex process. Protein kinases are integral to the autophagy process. Atg1, the first autophagy-related protein identified, is a serine/threonine kinase and it is regulated by another serine/threonine kinase mTOR. Emerging studies suggest the participation of many different kinases in regulating various components/steps of this catabolic process. This review focuses on the regulation of autophagy by several kinases with particular emphasis on serine/threonine protein kinases such as mTOR, AMP-activated protein kinase, Akt, mitogen-activated protein kinase (ERK, p38 and JNK) and protein kinase C that are often deregulated in cancer and are important therapeutic targets.

Increased expression of c-Fos by extracellular signal-regulated kinase activation under sustained oxidative stress elicits BimEL upregulation and hepatocyte apoptosis

We previously reported that the inhibition of catalase and glutathione peroxidase activities by treatment with 3-amino-1,2,4-triazole (ATZ) and mercaptosuccinic acid evoked sustained increases in the levels of reactive oxygen species and apoptosis in rat primary hepatocytes. Apoptosis was accompanied by increased expression of BimEL, following activation of extracellular signal-regulated kinase. The aim of this study was to characterize the mechanism underlying hepatocyte apoptosis by identifying the transcription factor that induces BimEL expression. The bim promoter region was cloned into a promoterless-luc vector, and promoter activity was monitored by a luciferase assay. The luciferase activity increased in the presence of ATZ + mercaptosuccinic acid. Pretreatment with a MEK inhibitor, U0126, or an antioxidant, vitamin C, suppressed the promoter activity. Furthermore, ATZ + mercaptosuccinic acid-induced luciferase activity was attenuated by mutation of the activator protein-1 binding site in the bim promoter region. The amounts of total and phosphorylated c-Fos increased over time in the presence of ATZ + mercaptosuccinic acid, whereas the amounts of total and phosphorylated c-Jun remained unchanged. Chromatin immunoprecipitation revealed that both c-Fos and c-Jun localized to the activator protein-1-binding site in the bim promoter region. BimEL expression and hepatocyte apoptosis were suppressed by knockdown of c-Fos and c-Jun, respectively. These results indicate that increases in c-Fos following extracellular signal-regulated kinase activation are critical for BimEL upregulation and apoptosis.

Post-transcriptional regulation of the DUSP6/MKP-3 phosphatase by MEK/ERK signaling and hypoxia

DUSP6/MKP-3 is a cytoplasmic dual-specificity phosphatase specific for the MAP kinases ERK1/2. Previous data have shown that the MEK/ERK axis exerts a retro-control on its own signaling through transcriptional and post-translational regulation of DUSP6. We first confirm the key role of MEK/ERK in maintaining the levels of dusp6 mRNA, while PI3K/mTOR, p38 MAPK, and JNK signaling pathways had no significant effects. We further show that regulation of dusp6 mRNA stability plays a critical role in ERK-dependent regulation of dusp6 expression. Luciferase reporter constructs indicated that MEK/ERK signaling increased the half-life of dusp6 mRNA in a 3'untranslated region (3'UTR)-dependent manner. In addition, hypoxia, a hallmark of tumor growth, was found to increase both endogenous levels of dusp6 mRNA and the stability of the luciferase reporter constructs containing its 3'UTR, in a HIF-1-dependent manner. Nevertheless, a basal ERK activity was required for the response to hypoxia. Finally, Tristetraprolin (TTP), a member of the TIS11 CCCH zinc finger protein family, and PUM2, an homolog of drosophila pumilio, two proteins regulating mRNA stability reduced the levels of endogenous dusp6 mRNA and the activity of the dusp6/3'UTR luciferase reporter constructs. This study shows that post-transcriptional regulation is a key process in the control of DUSP6 expression.

The Ca(2+) channel blocker flunarizine induces caspase-10-dependent apoptosis in Jurkat T-leukemia cells

Flunarizine is a Ca(2+) channel blocker that can be either cytoprotective or cytotoxic, depending on the cell type that is being examined. We show here that flunarizine was cytotoxic for Jurkat T-leukemia cells, as well as for other hematological maligancies, but not for breast or colon carcinoma cells. Treatment of Jurkat cells with flunarizine resulted in caspase-3 activation, poly (ADP-ribose) polymerase cleavage, and laddering of DNA fragments, all of which are hallmarks of apoptosis. Flunarizine-induced DNA fragmentation was inhibited by the caspase-3 inhibitor z-DEVD-fmk, the caspase-8/caspase-10 inhibitor z-IETD-fmk, and the caspase-10 inhibitor z-AEVD-fmk, but was not reduced in caspase-8-deficient Jurkat cells, indicating the involvement of caspase-10 upstream of caspase-3 activation. Interestingly, FADD recruitment to a death receptor was not involved since flunarizine caused DNA fragmentation in FADD-deficient Jurkat cells. Flunarizine treatment of Jurkat cells also resulted in reactive oxygen species production, dissipation of mitochondrial transmembrane potential, release of cytochrome c from mitochondria, and caspase-9 activation, although none of these events were necessary for apoptosis induction. Collectively, these findings indicate that flunarizine triggers apoptosis in Jurkat cells via FADD-independent activation of caspase-10. Flunarizine warrants further investigation as a potential anti-cancer agent for the treatment of hematological malignancies.

HIV-1 viral protein r induces ERK and caspase-8-dependent apoptosis in renal tubular epithelial cells

OBJECTIVE

HIV-associated nephropathy (HIVAN) is the most common cause of end-stage renal disease in persons with HIV/AIDS and is characterized by focal glomerulosclerosis and dysregulated renal tubular epithelial cell (RTEC) proliferation and apoptosis. HIV-1 viral protein r (Vpr) has been implicated in HIV-induced RTEC apoptosis but the mechanisms of Vpr-induced RTEC apoptosis are unknown. The aim of this study was therefore to determine the mechanisms of Vpr-induced apoptosis in RTEC.

METHODS

Apoptosis and caspase activation were analyzed in human RTEC (HK2) after transduction with Vpr-expressing and control lentiviral vectors. Bax and BID were inhibited with lentiviral shRNA, and ERK activation was blocked with the MEK1,2 inhibitor, U0126.

RESULTS

Vpr induced apoptosis as indicated by caspase 3/7 activation, PARP-1 cleavage and mitochondrial injury. Vpr activated both caspases-8 and 9. Inhibition of Bax reduced Vpr-induced apoptosis, as reported in other cell types. Additionally, Vpr-induced cleavage of BID to tBID and suppression of BID expression prevented Vpr-induced apoptosis. Since sustained ERK activation can activate caspase-8 in some cell types, we studied the role of ERK in Vpr-induced caspase-8 activation. Vpr induced sustained ERK activation in HK2 cells and incubation with U0126 reduced Vpr-induced caspase-8 activation, BID cleavage and apoptosis. We detected phosphorylated ERK in RTEC in HIVAN biopsy specimens by immunohistochemistry.

CONCLUSIONS

These studies delineate a novel pathway of Vpr-induced apoptosis in RTEC, which is mediated by sustained ERK activation, resulting in caspase 8-mediated cleavage of BID to tBID, thereby facilitating Bax-mediated mitochondrial injury and apoptosis.

The dual-specificity MAP kinase phosphatases: critical roles in development and cancer

Intracellular signaling by mitogen-activated protein (MAP) kinases (MAPK) is involved in many cellular responses and in the regulation of various physiological and pathological conditions. Tight control of the localization and duration of extracellular-regulated kinase (ERK), c-Jun NH(2)-terminal kinase (JNK), or p38 MAPK activity is thus a fundamental aspect of cell biology. Several members of the dual-specificity phosphatase (DUSPs) family are able to dephosphorylate MAPK isoforms with different specificity, cellular, and tissue localization. Understanding how these phosphatases are themselves regulated during development or in physiological and pathological conditions is therefore fundamental. Over the years, gene deletion and knockdown studies have completed initial in vitro studies and shed a new light on the global and specific roles of DUSPs in vivo. Whereas DUSP1, DUSP2, and DUSP10 appear as crucial players in the regulation of immune responses, other members of the family, like the ERK-specific DUSP6, were shown to play a major role in development. Recent findings on the involvement of DUSPs in cancer progression and resistance will also be discussed.