Extracellular Signal-regulated Kinase Cascade Research Articles

Bile acid metabolites enhance expression of cathelicidin antimicrobial peptide in airway epithelium through activation of the TGR5-ERK1/2 pathway

Signals for the maintenance of epithelial homeostasis are provided in part by commensal bacteria metabolites, that promote tissue homeostasis in the gut and remote organs as microbiota metabolites enter the bloodstream. In our study, we investigated the effects of bile acid metabolites, 3-oxolithocholic acid (3-oxoLCA), alloisolithocholic acid (AILCA) and isolithocholic acid (ILCA) produced from lithocholic acid (LCA) by microbiota, on the regulation of innate immune responses connected to the expression of host defense peptide cathelicidin in lung epithelial cells. The bile acid metabolites enhanced expression of cathelicidin at low concentrations in human bronchial epithelial cell line BCi-NS1.1 and primary bronchial/tracheal cells (HBEpC), indicating physiological relevance for modulation of innate immunity in airway epithelium by bile acid metabolites. Our study concentrated on deciphering signaling pathways regulating expression of human cathelicidin, revealing that LCA and 3-oxoLCA activate the surface G protein-coupled bile acid receptor 1 (TGR5, Takeda-G-protein-receptor-5)—extracellular signal-regulated kinase (ERK1/2) cascade, rather than the nuclear receptors, aryl hydrocarbon receptor, farnesoid X receptor and vitamin D3 receptor in bronchial epithelium. Overall, our study provides new insights into the modulation of innate immune responses by microbiota bile acid metabolites in the gut-lung axis, highlighting the differences in epithelial responses between different tissues.

The ERK Signaling Cascade Inhibits Gonadotropin-Stimulated Steroidogenesis.

The response of granulosa cells to Luteinizing Hormone (LH) and Follicle- Stimulating Hormone (FSH) is mediated mainly by cAMP/protein kinase A (PKA) signaling. Notably, the activity of the extracellular signal-regulated kinase (ERK) signaling cascade is elevated in response to these stimuli as well. We studied the involvement of the ERK cascade in LH- and FSH-induced steroidogenesis in two granulosa-derived cell lines, rLHR-4 and rFSHR-17, respectively. We found that stimulation of these cells with the appropriate gonadotropin induced ERK activation as well as progesterone production downstream of PKA. Inhibition of ERK activity enhanced gonadotropin-stimulated progesterone production, which was correlated with increased expression of the Steroidogenic Acute Regulatory Protein (StAR), a key regulator of progesterone synthesis. Therefore, it is likely that gonadotropin-stimulated progesterone formation is regulated by a pathway that includes PKA and StAR, and this process is down-regulated by ERK, due to attenuation of StAR expression. Our results suggest that activation of PKA signaling by gonadotropins not only induces steroidogenesis but also activates down-regulation machinery involving the ERK cascade. The activation of ERK by gonadotropins as well as by other agents may be a key mechanism for the modulation of gonadotropin-induced steroidogenesis.

Limonin, a natural ERK2 agonist, protects against ischemic acute kidney injury.

Acute kidney injury (AKI) is a refractory clinical syndrome with limited effective treatments. Amid AKI, activation of the extracellular signal-regulated kinase (ERK) cascade plays a critical role in promoting kidney repair and regeneration. However, a mature ERK agonist in treating kidney disease remains lacking. This study identified limonin, a member of the class of compounds known as furanolactones, as a natural ERK2 activator. Employing a multidisciplinary approach, we systemically dissected how limonin mitigates AKI. Compared to vehicles, pretreatment of limonin significantly preserved kidney functions after ischemic AKI. We revealed that ERK2 is a significant protein linked to the limonin's active binding sites through structural analysis. The molecular docking study showed a high binding affinity between limonin and ERK2, which was confirmed by the cellular thermal shift assay and microscale thermophoresis. Mechanistically, we further validated that limonin promoted tubular cell proliferation and reduced cell apoptosis after AKI by activating ERK signaling pathway in vivo. In vitro and ex vivo, blockade of ERK abolished limonin's capacity of preventing tubular cell death under hypoxia stress. Our results indicated that limonin is a novel ERK2 activator with strong translational potential in preventing or mitigating AKI.

Abstract 108: Altered Erk / Klf4-mediated Control Of Agrp And Metabolic Rate During Obesity

Resting metabolic rate (RMR) adaptation contributes to the maintenance of human obesity, yet mechanisms controlling RMR in lean vs obese states remain poorly defined. Leptin contributes to RMR control in part through suppression of inhibitory Agouti-related peptide (AgRP) neurotransmission in the hypothalamic arcuate nucleus (ARC). Within AgRP neurons, leptin activates the extracellular signal-regulated kinase (ERK) cascade, which is thought to interrupt Agrp transcription through interference with the Krüppel-like factor 4 (KLF4) transcription factor, and our published data support altered ARC ERK signaling during obesity. We therefore hypothesized a role for ERK/KLF4 signaling within AgRP neurons for the suppression of AgRP transcription and thereby stimulation of RMR in the lean state, and changes in this pathway during obesity. In the GT1-7 cell model of AgRP neurons, leptin increased the phosphorylated ERK (pERK)/ERK ratio (n=4, 1 uM, 15 min +89% p<0.05) and reduced Agrp mRNA (n=4, 1 uM, 1 hr -43.0% p<0.05); similarly, siRNA knockdown of Klf4 reduced Agrp mRNA (n=4, -21.6% p<0.05). In lean adult C57BL/6J mice, leptin increased the ARC pERK/ERK ratio (n=8, 1 ug/g ip 16.5-fold p<0.05) and stimulated RMR (n=11, 2 ug/g ip 30 min +43.8% p<0.05). Lean transgenic mice with conditional deletion of KLF4 from AgRP neurons ( Agrp -Cre x Klf4 flox ) exhibited increased RMR (n=13 KO +13.48% vs controls n=22 p<0.05). These findings support the model that ERK inhibition of KLF4 within AgRP neurons mechanistically contributes to leptin-mediated control of Agrp and RMR in the lean state. Ten weeks of high fat feeding strongly increases endogenous plasma leptin in C57BL/6J mice, and this treatment increased the ARC pERK/ERK ratio (n=5 +54.4% p<0.05), yet ARC KLF4 was increased (n=6 +74.6% p<0.05) and Agrp mRNA was not suppressed (n=4 +1.6-fold, p=ns). Therefore, these data also support the concept that loss of ERK-mediated suppression of KLF4 within the AgRP neuron during obesity may contribute to the pathogenesis of RMR adaptation.

The GPCR–β-arrestin complex allosterically activates C-Raf by binding its amino terminus

G protein–coupled receptors (GPCRs) convert external stimuli into cellular signals through heterotrimeric guanine nucleotide-binding proteins (G-proteins) and β-arrestins (βarrs). In a βarr-dependent signaling pathway, βarrs link GPCRs to various downstream signaling partners, such as the Raf–mitogen-activated protein kinase extracellular signal–regulated kinase–extracellular signal-regulated kinase cascade. Agonist-stimulated GPCR–βarr complexes have been shown to interact with C-Raf and are thought to initiate the mitogen-activated protein kinase pathway through simple tethering of these signaling partners. However, recent evidence shows that in addition to canonical scaffolding functions, βarrs can allosterically activate downstream targets, such as the nonreceptor tyrosine kinase Src. Here, we demonstrate the direct allosteric activation of C-Raf by GPCR–βarr1 complexes in vitro. Furthermore, we show that βarr1 in complex with a synthetic phosphopeptide mimicking the human V2 vasopressin receptor tail that binds and functionally activates βarrs also allosterically activates C-Raf. We reveal that the interaction between the phosphorylated GPCR C terminus and βarr1 is necessary and sufficient for C-Raf activation. Interestingly, the interaction between βarr1 and C-Raf was considerably reduced in the presence of excess activated H-Ras, a small GTPase known to activate C-Raf, suggesting that H-Ras and βarr1 bind to the same region on C-Raf. Furthermore, we found that βarr1 interacts with the Ras-binding domain of C-Raf. Taken together, these data suggest that in addition to canonical scaffolding functions, GPCR–βarr complexes directly allosterically activate C-Raf by binding to its amino terminus. This work provides novel insights into how βarrs regulate effector molecules to activate downstream signaling pathways.

Identification and functional prediction of long noncoding RNAs related to intramuscular fat content in Laiwu pigs.

ObjectiveIntramuscular fat (IMF) is a critical economic indicator of pork quality. Studies on IMF among different pig breeds have been performed via high-throughput sequencing, but comparisons within the same pig breed remain unreported.MethodsThis study was performed to explore the gene profile and identify candidate long noncoding RNA (lncRNAs) and mRNAs associated with IMF deposition among Laiwu pigs with different IMF contents. Based on the longissimus dorsi muscle IMF content, eight pigs from the same breed and management were selected and divided into two groups: a high IMF (>12%, H) and low IMF group (<5%, L). Whole-transcriptome sequencing was performed to explore the differentially expressed (DE) genes between these two groups.ResultsThe IMF content varied greatly among Laiwu pig individuals (2.17% to 13.93%). Seventeen DE lncRNAs (11 upregulated and 6 downregulated) and 180 mRNAs (112 upregulated and 68 downregulated) were found. Gene Ontology analysis indicated that the following biological processes played an important role in IMF deposition: fatty acid and lipid biosynthetic processes; the extracellular signal-regulated kinase cascade; and white fat cell differentiation. In addition, the peroxisome proliferator-activated receptor, phosphatidylinositol-3-kinase-protein kinase B, and mammalian target of rapamycin pathways were enriched in the pathway analysis. Intersection analysis of the target genes of DE lncRNAs and mRNAs revealed seven candidate genes associated with IMF accumulation. Five DE lncRNAs and 20 DE mRNAs based on the pig quantitative trait locus database were identified and shown to be related to fat deposition. The expression of five DE lncRNAs and mRNAs was verified by quantitative real time polymerase chain reaction (qRT-PCR). The results of qRT-PCR and RNA-sequencing were consistent.ConclusionThese results demonstrated that the different IMF contents among pig individuals may be due to the DE lncRNAs and mRNAs associated with lipid droplets and fat deposition.

Striatal transcriptome changes linked to drug-induced repetitive behaviors.

Disruptive or excessive repetitive motor patterns (stereotypies) are cardinal symptoms in numerous neuropsychiatric disorders. Stereotypies are also evoked by psychomotor stimulants such as amphetamine. The acquisition of motor sequences is paralleled by changes in activity patterns in the striatum, and stereotypies have been linked to abnormal plasticity in these reinforcement-related circuits. Here, we designed experiments in mice to identify transcriptomic changes that underlie striatal plasticity occurring alongside the development of drug-induced stereotypic behavior. We identified three schedules of amphetamine treatment inducing different degrees of stereotypy and used bulk RNAseq to compare striatal gene expression changes among groups of mice treated with the different drug-dose schedules and vehicle-treated, cage-mate controls. Mice were identified as naïve, sensitized, or tolerant to drug-induced stereotypy. All drug-treated groups exhibited expression changes in genes that encode members of the extracellular signal-regulated kinase (ERK) cascades known to regulate psychomotor stimulant responses. In the sensitized group with the most prolonged stereotypy, we found dysregulation of 20 genes that were not changed in other groups. Gene set enrichment analysis indicated highly significant overlap with genes regulated by neuregulin 1 (Nrg1). Nrg1 is known to be a schizophrenia and autism susceptibility gene that encodes a ligand for Erb-B receptors, which are involved in neuronal migration, myelination, and cell survival, including that of dopamine-containing neurons. Stimulant abuse is a risk factor for schizophrenia onset, and these two disorders share behavioral stereotypy phenotypes. Our results raise the possibility that drug-induced sensitization of the Nrg1 signaling pathway might underlie these links.

Dopamine D1 and Glutamate Receptors Co-operate With Brain-Derived Neurotrophic Factor (BDNF) and TrkB to Modulate ERK Signaling in Adult Striatal Slices.

In the striatum, the input nucleus of the basal ganglia, the extracellular-signal-regulated kinase (ERK) pathway, necessary for various forms of behavioral plasticity, is triggered by the combined engagement of dopamine D1 and ionotropic glutamate receptors. In this study, we investigated the potential crosstalk between glutamatergic, dopaminergic, and brain-derived neurotrophic factor (BDNF)-TrkB inputs to ERK cascade by using an ex vivo model of mouse striatal slices. Our results confirmed that the concomitant stimulation of D1 and glutamate receptors is necessary to activate ERK in striatal medium spiny neurons (MSNs). Moreover, we found that ERK activation is significantly enhanced when BDNF is co-applied either with glutamate or the D1 agonist SKF38393, supporting the idea of possible integration between BDNF, glutamate, and D1R-mediated signaling. Interestingly, ERK activation via BDNF-TrkB is upregulated upon blockade of either AMPAR/NMDAR or D1 receptors, suggesting a negative regulatory action of these two neurotransmitter systems on BDNF-mediated signaling. However, the observed enhancement of ERK1/2 phosphorylation does not result in corresponding downstream signaling changes at the nuclear level. Conversely, the TrkB antagonist cyclotraxin B partially prevents glutamate- and D1-mediated ERK activation. Altogether, these results suggest a complex and unexpected interaction among dopaminergic, glutamatergic, and BDNF receptor systems to modulate the ERK pathway in striatal neurons.

The protein kinase MAP3K19 phosphorylates MAP2Ks and thereby activates ERK and JNK kinases and increases viability of KRAS-mutant lung cancer cells

Identifying additional mitogen-activated protein kinase (MAPK) pathway regulators is invaluable in aiding our understanding of the complex signaling networks that regulate cellular processes, including cell proliferation and survival. Here, using in vitro kinase assays and by expressing WT or kinase-dead MAPK kinase kinase 19 (MAP3K19) in the HEK293T cell line and assessing activation of the extracellular signal-regulated kinase (ERK) and JUN N-terminal kinase (JNK) signaling pathways, we defined MAP3K19 as a novel regulator of MAPK signaling. We also observed that overexpression of WT MAP3K19 activates both the ERK and JNK pathways in a panel of cancer cell lines. Furthermore, MAP3K19 sustained ERK pathway activation in the presence of inhibitors targeting the RAF proto-oncogene Ser/Thr protein kinase (RAF) and MAPK/ERK kinase, indicating that MAP3K19 activates ERK via a RAF-independent mechanism. Findings from in vitro and in-cell kinase assays demonstrate that MAP3K19 is a kinase that directly phosphorylates both MAPK/ERK kinase (MEK) and MAPK kinase 7 (MKK7). Results from an short-hairpin RNA screen indicated that MAP3K19 is essential for maintaining survival in KRAS-mutant cancers; therefore, we depleted or inhibited MAP3K19 in KRAS-mutant cancer cell lines and observed that this reduces viability and decreases ERK and JNK pathway activation. In summary, our results reveal that MAP3K19 directly activates the ERK and JNK cascades and highlight a role for this kinase in maintaining survival of KRAS-mutant lung cancer cells.

High Expression of Integrin α3 Predicts Poor Prognosis and Promotes Tumor Metastasis and Angiogenesis by Activating the c-Src/Extracellular Signal-Regulated Protein Kinase/Focal Adhesion Kinase Signaling Pathway in Cervical Cancer.

Background: Cervical cancer remains a leading cause of death in women due to metastasis to distant tissues and organs. Integrins are involved in cancer metastasis. However, whether integrin α3 participates in cervical cancer metastasis is under investigation. In this study, we explored the effect and detailed mechanism through which integrin α3 regulates cervical cell migration, invasion, and angiogenesis.Methods: First, we explored the mRNA and protein expression levels of integrin α3 in cervical cancer cell lines and tissue samples obtained from patients. After knocking down the expression of integrin α3 using shRNA, the proliferation, migration, and invasion of cervical cancer cells, as well as the possible signaling pathways involved, were investigated in vitro. In addition, tube formation, proliferation, and migration of human umbilical vein endothelial cells were tested to identify their effect on angiogenesis. Zebrafish tumor migration and nude mouse lung metastasis models were utilized for the in vivo analysis.Results: We examined samples from 142 patients with cervical cancer and 20 normal cervixes. Integrin α3 was highly expressed in patients and predicted poor overall survival and disease-free survival. In SiHa cells, treatment with integrin α3 shRNA induced the phosphorylation of protein focal adhesion kinase and enhanced focal adhesion. These events were mediated by the activation of c-Src and extracellular signal-regulated protein kinase cascades. Consequently, integrin α3 increased the migratory ability of SiHa cells. In addition, knockdown of integrin α3 decreased the tube formation, proliferation, and migration of human umbilical vein endothelial cells, as well as the levels of matrix metalloproteinase-9, indicating its effect on angiogenesis. Stable transfection with integrin α3 shRNA reduced the migratory ability of SiHa cells in the zebrafish model and diminished lung metastasis in the xenograft mouse model.Conclusion: Integrin α3 recruits the c-Src/extracellular signal-regulated protein kinase cascade, leading to phosphorylation of focal adhesion kinase. Moreover, it regulates focal adhesion, endowing cervical cancer cells with potentiated migratory and invasive ability, and promotes angiogenesis via matrix metalloproteinase-9. Our findings may shed light on the mechanism involved in cervical cancer metastasis and highlight integrin α3 as a candidate prognostic biomarker and therapeutic target in patients with cervical cancer.

Behavioral abnormalities and phosphorylation deficits of extracellular signal-regulated kinases 1 and 2 in rat offspring of the maternal immune activation model

Extracellular signal-regulated kinase (ERK) signal transduction is known to be associated with neurogenesis and neuronal differentiation and as such may be related to the synaptic plasticity associated with cognitive function. Although antipsychotic drug studies have suggested a potential role for the ERK cascade in schizophrenia, the mechanistic basis is unknown. The maternal immune activation (MIA) rat model is a well-known to simulate many of the clinical symptoms of schizophrenia, including cognitive deficits, but a role in this model for dynamic changes in ERK has not been established. In this study, polyinosinic:polycytidylic acid was administered to rats intravenously at a dose of 10 mg/kg on embryonic day 9.5 to produce MIA. The effect of MIA on behavior and ERK phosphorylation within the prefrontal cortex and the hippocampus of adolescent and adult offspring were explored. We also examined neurofilaments, a marker of neurogenesis, which have been reported to be modulated by ERK signaling. The results demonstrate an age- and region-specific profile of ERK expression and phosphorylation and suggest possible relationships among ERK, neurofilament expression, and cognitive performance in schizophrenia.

Soya-cerebroside reduces IL-1β-induced MMP-1 production in chondrocytes and inhibits cartilage degradation: implications for the treatment of osteoarthritis

ABSTRACTOsteoarthritis (OA) commonly affects the synovial joint and is characterized by degradation of articular cartilage, which is largely mobilized by increased matrix metalloproteinase (MMP) activity. Soya-cerebroside, an extract of Cordyceps militaris, inhibits inflammatory cytokine production and monocyte migration in human synovial fibroblasts, although its effects are uncertain on MMP expression in chondrocytes and cartilage degradation. In this study, soya-cerebroside antagonized interleukin 1 beta (IL-1β)-induced MMP-1 production in chondrocytes, without cytotoxic effects. Functional genomic data confirm high levels of MMP-1 expression in OA tissue compared with normal tissue. Soya-cerebroside reduced MMP-1 expression via the focal adhesion kinase (FAK), mitogen-activated protein kinase (MEK), extracellular signal-regulated kinase (ERK) and AP-1 signalling pathways. In addition, soya-cerebroside suppressed IL-1β-promoted MMP-1 expression and cartilage degradation in animal models. Our report is the first to reveal that soya-cerebroside reduces MMP-1 production in chondrocytes and protects cartilage degradation through the FAK, MEK, ERK, and AP-1 signalling cascade.

Молекулярные механизмы апоптоза нейтрофилов (обзор литературы)

В обзоре представлены современные данные о механизмах инициации, регуляции и выполнении процесса апоптоза нейтрофилов с участием «рецепторов смерти», митохондрий, белков семейства Bcl-2, PI3-K (phosphatidylinositol 3-kinase), протеинкиназных каскадов p38 MAPK (mitogen-activated protein kinase), ERK (extracellular signal regulated kinase) и JNK (c-Jun N-terminal kinase), протеинкиназ А, В и С, сAMP, белков теплового шока, NF-kB (nuclear factor-kB), кальпаинов, каспаз и их ингибиторов, активных форм кислорода и других факторов. Предложена гипотетическая модель вовлечения апоптотических процессов в регуляцию дифференцировки и реактивности нейтрофилов. This review presented recent data on initiation, regulation, and execution of neutrophil apoptosis with participation of «death receptors», mitochondria, Bcl-2 family proteins, PI3-K (phosphatidylinositol 3-kinase), p38 MAPK (mitogen-activated protein kinase), ERK (extracellular signal regulated kinase) and JNK (c-Jun N-terminal kinase) cascades, protein kinases A, B and C, сAMP, heat shock proteins, NF-kB (nuclear factor-kB), calpains, caspases and theirs inhibitors, reactive oxygen species, and other factors. A speculative model of the apoptotic processes involvement in the regulation of neutrophil differentiation and reactivity was proposed.

Insulin Antagonizes LPS-Induced Inflammatory Responses by Activating SR-A1/ERK Axis in Macrophages.

Insulin is a key regulator of metabolism and inflammation in the body. However, the mechanism of the anti-inflammatory effect of insulin is not fully understood. In the present study, we investigated the role of the class A1 scavenger receptor (SR-A1), a prototypic member of the pattern recognition receptor family, in the insulin-mediated suppression of inflammatory responses in macrophages. Our murine in vivo studies show that insulin can attenuate lipopolysaccharide (LPS)-induced endotoxemia in a SR-A1-dependent manner, and this was consistent with our in vitro results which demonstrate that the SR-A1 is necessary for insulin to antagonize the LPS-induced inflammatory responses in macrophages. The effect of SR-A1 on the anti-inflammatory action of insulin might be associated with the activation of the extracellular signal-regulated kinases (ERK) signaling pathway in macrophages. Insulin could inhibit macrophage polarization to a pro-inflammatory phenotype via the SR-A1/ERK cascade. Collectively, our results suggest that SR-A1 may be a pivotal element for the anti-inflammation effect of insulin in macrophages.

BMP2/7 heterodimer enhances osteogenic differentiation of rat BMSCs via ERK signaling compared with respective homodimers.

Bone morphogenetic protein (BMP)2/7 heterodimer shows greater efficacy in enhancing bone regeneration. However, the precise mechanism and the role of mitogen-activated protein kinase (MAPK) signaling network in BMP2/7-driven osteogenesis remain ambiguous. In this study, we evaluated the effects of BMP2/7 heterodimers on osteoblastic differentiation in rat bone marrow mesenchymal stem cells (BMSCs), with the aim to elaborate how MAPKs might be involved in this cellular process by treatment of rat BMSCs with BMP2/-7 with a special signal-pathway inhibitor. We found that BMP2/7 heterodimer induced a much stronger osteogenic response in rat BMSCs compared with either homodimer. Most interestingly, extracellular signal-regulated kinase (ERK) demonstrated a highly sustained phosphorylation and activation in the BMP2/7 heterodimer treatment groups, and inhibition of ERK cascades using U0126 special inhibitor that significantly reduced the activity of ALP and calcium mineralization to a substantial degree in rat BMSCs treated with BMP2/7 heterodimers. Collectively, we demonstrate that BMP2/7 heterodimer shows a potent ability to stimulate osteogenesis in rat BMSCs. The activated ERK signaling pathway involved in this process may contribute partially to an increased osteogenic potency of heterodimeric BMP2/7 growth factors.

A novel benzamide derivative protects ligature-induced alveolar bone erosion by inhibiting NFATc1-mediated osteoclastogenesis

Since elevated osteoclast formation and/or activity by inhibitory responses against pathogens leads to diverse osteolytic bone diseases including periodontitis, inhibition of osteoclast differentiation and bone resorption has been a primary therapeutic strategy. In this study, we investigated the therapeutic potential of a novel benzamide-linked molecule, OCLI-070, for preventing alveolar bone loss in mice with ligature-induced experimental periodontitis. OCLI-070 inhibited osteoclast formation by acting on both early and late stages of differentiation, and attenuated the induction of nuclear factor of activated T-cells, cytoplasmic 1 (NFATc1) and the expression of osteoclast-specific genes. In addition, OCLI-070 significantly suppressed the formation of actin rings and resorption pits. Analysis of the inhibitory action of OCLI-070 showed that it markedly suppressed receptor activator of nuclear factor-κB ligand (RANKL)-induced extracellular signal-regulated kinase (ERK) and NF-κB signaling cascades. Moreover, OCLI-070 prevented ligature-induced alveolar bone erosion in mice by suppressing osteoclast formation. These findings demonstrate that OCLI-070 attenuated osteoclast differentiation and function as well as ligature-induced bone erosion by inhibiting RANKL-mediated ERK and NF-κB signaling pathways.

Ras-Mediated Activation of the Raf Family Kinases.

The extracellular signal-regulated kinase (ERK) cascade comprised of the Raf, MEK, and ERK protein kinases constitutes a key effector cascade used by the Ras GTPases to relay signals regulating cell growth, survival, proliferation, and differentiation. Of the ERK cascade components, the regulation of the Raf kinases is by far the most complex, involving changes in subcellular localization, protein and lipid interactions, as well as alterations in the Raf phosphorylation state. The Raf kinases interact directly with active, membrane-localized Ras, and this interaction is often the first step in the Raf activation process, which ultimately results in ERK activation and the downstream phosphorylation of cellular targets that will specify a particular biological response. Here, we will examine our current understanding of how Ras promotes Raf activation, focusing on the molecular mechanisms that contribute to the Raf activation/inactivation cycle.

KIAA1522 overexpression promotes tumorigenicity and metastasis of esophageal cancer cells through potentiating the ERK activity.

Esophageal squamous cell carcinoma (ESCC) is a highly malignant tumor associated with a poor prognosis, and the molecular mechanisms underlying its formation and progression remain poorly understood. KIAA1522 is upregulated in various tumor tissues, but its function is unknown. Alterations in KIAA1522 expression and its implication in ESCC are currently unclear. In this study, an immunohistochemical analysis of ESCC tissues showed that KIAA1522 was highly expressed in 46% (157/342) of ESCC specimens and that its expression was inversely correlated with the degree of differentiation (P=0.03). Furthermore, small interfering RNA-mediated silencing of KIAA1522 revealed that overexpression of this protein reinforced malignant cell proliferation and anoikis resistance of ESCC cells in vitro. More importantly, KIAA1522 depletion significantly suppressed the growth of ESCC xenograft tumors and lung metastasis of ESCC cells in nude mice. At the molecular level, inhibition of KIAA1522 expression markedly reduced the phosphorylated extracellular signal-regulated kinase (ERK) levels in both suspended and adherent ESCC cells, suggesting that KIAA1522 might promote cell proliferation and survival via the ERK cascade. Taken together, these data suggest that upregulation of KIAA1522 might enhance tumorigenicity and metastasis of ESCC cells through potentiating the ERK activity. Thus, aberrant expression of KIAA1522 plays oncogenic roles in ESCC and might serve as a novel molecular target in ESCC treatment.

Muscarinic receptor regulates extracellular signal regulated kinase by two modes of arrestin binding

Binding of agonists to G-protein-coupled receptors (GPCRs) activates heterotrimeric G proteins and downstream signaling. Agonist-bound GPCRs are then phosphorylated by protein kinases and bound by arrestin to trigger desensitization and endocytosis. Arrestin plays another important signaling function. It recruits and regulates activity of an extracellular signal-regulated kinase (ERK) cascade. However, molecular details and timing of ERK activation remain fundamental unanswered questions that limit understanding of how arrestin-dependent GPCR signaling controls cell functions. Here we validate and model a system that tracks the dynamics of interactions of arrestin with receptors and of ERK activation using optical reporters. Our intermolecular FRET measurements in living cells are consistent with β-arrestin binding to M1 muscarinic acetylcholine receptors (M1Rs) in two different binding modes, transient and stable. The stable mode persists for minutes after agonist removal. The choice of mode is governed by phosphorylation on key residues in the third intracellular loop of the receptor. We detect a similar intramolecular conformational change in arrestin in either binding mode. It develops within seconds of arrestin binding to the M1 receptor, and it reverses within seconds of arrestin unbinding from the transient binding mode. Furthermore, we observed that, when stably bound to phosphorylated M1R, β-arrestin scaffolds and activates MEK-dependent ERK. In contrast, when transiently bound, β-arrestin reduces ERK activity via recruitment of a protein phosphatase. All this ERK signaling develops at the plasma membrane. In this scaffolding hypothesis, a shifting balance between the two arrestin binding modes determines the degree of ERK activation at the membrane.

Polymeric immunoglobulin receptor promotes tumor growth in hepatocellular carcinoma.

Our findings reveal the molecular mechanism by which pIgR promotes cancer malignancy, suggest the clinical potential of targeting this pathway in HCC, and provide new insight into the oncogenic role of immunoglobulin receptors. (Hepatology 2017;65:1948-1962).