Suppression Of Protein Kinase Research Articles

Protein kinase A type II-α regulatory subunit regulates the response of prostate cancer cells to taxane treatment

In the last decade taxane-based therapy has emerged as a standard of care for hormone-refractory prostate cancer. Nevertheless, a significant fraction of tumors show no appreciable response to the treatment, while the others develop resistance and recur. Despite years of intense research, the mechanisms of taxane resistance in prostate cancer and other malignancies are poorly understood and remain a topic of intense investigation. We have used improved mutagenesis via random insertion of a strong promoter to search for events, which enable survival of prostate cancer cells after Taxol exposure. High-throughput mapping of the integration sites pointed to the PRKAR2A gene, which codes for a type II-α regulatory subunit of protein kinase A, as a candidate modulator of drug response. Both full-length and N-terminally truncated forms of the PRKAR2A gene product markedly increased survival of prostate cancer cells lines treated with Taxol and Taxotere. Suppression of protein kinase A enzymatic activity is the likely mechanism of action of the overexpressed proteins. Accordingly, protein kinase A inhibitor PKI (6–22) amide reduced toxicity of Taxol to prostate cancer cells. Our findings support the role of protein kinase A and its constituent proteins in cell response to chemotherapy.

Highly expressed protein kinase A inhibitor α and suppression of protein kinase A may potentiate acetaminophen-induced hepatotoxicity

Drug-induced hepatotoxicity is a serious adverse effect with high morbidity and mortality rates but substantial individual to individual variation is observed in its severity. Here we sought to discover factors determining the susceptibility to acetaminophen (APAP)-induced hepatotoxicity by comparing the global gene expression profile (27,342 genes) in pre-dose blood before APAP administration between susceptible and resistant animals (N=5) grouped based on the severity of hepatotoxicity. Forty-one genes were expressed differently (>1.5 fold change and p<0.05) between susceptible and resistant groups. Among them, protein kinase (cAMP-dependent) inhibitor alpha, Pkia, a member of protein kinase A (PKA) inhibitor family, was found to be most significantly and highly expressed in susceptible animals (∼3.5 fold with p<0.01). To investigate the effects of PKA inhibition on APAP-induced hepatotoxicity, we pre-treated H-89, a potent and selective inhibitor of PKA, prior to APAP administration in vivo. As a result, H-89 pretreatment significantly potentiated APAP-induced hepatotoxicity as determined by the increased serum alanine transaminase. These results were further corroborated by the exacerbation of APAP-induced glutathione depletion, suppression of antioxidant enzyme system, superoxide dismutase 1 and glutathione peroxidase 1, and peroxynitrite generation in the liver following H-89 pretreatment, reflecting that PKA may be involved in the protection against, or attenuation of APAP-induced hepatotoxicity, and Pkia can be employed to screen individuals susceptible to APAP-induced hepatotoxicity.

Mitochondrial APE1/Ref-1 suppressed protein kinase C-induced mitochondrial dysfunction in mouse endothelial cells

Protein kinase C (PKC) induces mitochondrial dysfunction, which is an important pathological factor in cardiovascular diseases. The role of apurinic/apyrimidinic endonuclease-1/redox factor-1 (APE1/Ref-1) on PKC-induced mitochondrial dysfunction has not been variously investigated. In this study, phorbol 12-myristate 13-acetate (PMA), an activator of protein kinase C, induced mitochondrial hyperpolarization and reactive oxygen species generation and also increased mitochondrial translocation of APE1/Ref-1. APE1/Ref-1 overexpression suppressed PMA-induced mitochondrial dysfunction. In contrast, gene silencing of APE1/Ref-1 increased the sensitivity of mitochondrial dysfunction. Moreover, mitochondrial targeting sequence (MTS)-fused APE1/Ref-1 more effectively suppressed PMA-induced mitochondrial dysfunctions. These results suggest that mitochondrial APE1/Ref-1 is contributed to the protective role to protein kinase C-induced mitochondrial dysfunction in endothelial cells.

Discovery of an obesity susceptibility gene, KSR2, provides new insight into energy homeostasis pathways.

Obesity is a heterogeneous condition with considerable heritability. Multiple adiposity genes have now been identified through genome-wide association studies and studies of rare forms obesity caused by single-gene mutations. Several of these monogenic forms of obesity seem to replicate mouse obesity phenotypes, with notable examples including obesity caused by inactivating mutations in leptin, the leptin receptor, and the melanocortin-4 receptor. A large-scale screen for additional obese phenotypes in mice found that targeted deletion of Ksr2 leads to obesity,1 suggesting a role for Ksr2 in energy homeostasis. Ksr2 encodes the scaffolding protein kinase suppressor of ras 2 (KSR2), which may regulate multiple signaling pathways by binding kinases, such as Raf and AMP-activated protein kinase (AMPK). In this article, Pearce et al2 hypothesize that genetic variants in KSR2 may contribute to the development of severe, early onset obesity in humans. Using a combination of Sanger and whole-exome sequencing, the authors sequenced the coding region and intron/exon boundaries of KSR2 to identify rare variants (minor allele frequency, <0.5%) in 2101 individuals of mixed European ancestry who developed severe obesity before 10 years and in 1536 controls from a UK population-based study. They also performed a small replication study (238 cases and 1117 controls) and sequenced KSR2 in family members of severely obese probands to determine whether KSR2 variants cosegregated with overweight/obesity …

Inhibition of cell growth by BrMC through inactivation of Akt in HER-2/neu-overexpressing breast cancer cells.

We previously reported that chrysin (ChR) and its analogs induced cell cycle arrest and apoptosis in human estrogen receptor-positive/-negative breast cancer cells. However, it was unknown whether 8-bromo-7-methoxychrysin (BrMC), a novel synthetic ChR analog, inhibited the cell growth of human epidermal growth factor receptor 2 (HER-2)/neu-overexpressing breast cancers. In the present study, it was demonstrated that BrMC preferentially inhibited the cell viability of HER-2/neu-overexpressing MDA-MB-453 and BT-474 cells. Western blot analysis revealed that HER-2/neu expression and tyrosine phosphorylation were inhibited by BrMC in a concentration-dependent manner; whereas the proteasome inhibitor, MG-132, significantly prevented BrMC-induced HER-2/neu depletion and cell death in MDA-MB-453 cells. This directly indicated that BrMC-induced HER-2/neu depletion and cell growth inhibition was mediated by a proteasomal pathway. BrMC significantly downregulated the expression of cyclin D1, cyclin E and CDK4, followed by the suppression of protein kinase B phosphorylation and downstream effectors, GSK-3β and β-catenin. A colony formation assay also confirmed the growth-inhibitory effects of BrMC. Thus, these findings clearly demonstrate the anticancer activity of BrMC against human HER-2/neu-overexpressing breast cancer cells. Thus, these findings clearly demonstrate the anticancer activity of BrMC against human HER 2/neu-overexpressing breast cancer cells, and highlight BrMC as a promising candidate for breast cancer therapy.

Suppression of protein kinase C-ζ attenuates vascular leakage via prevention of tight junction protein decrease in diabetic retinopathy

To investigate the effect of protein kinase C (PKC)-ζ inhibition on vascular leakage in diabetic retinopathy, streptozotocin-induced diabetic mice were intravitreously injected with siPKC-ζ. According to the fluorescein angiography of the retinal vessels, suppression of PKC-ζ effectively attenuated vascular leakage in diabetic retina. Further evaluation on the retina with western blot analysis and immunohistochemistry revealed accompanying restoration of tight junction proteins on retinal vessels. As two major contributors to vascular leakage in diabetic retinopathy, vascular endothelial growth factor (VEGF) and advanced glycation end products (AGEs) were investigated on the tight junction protein expression in endothelial cells. Inhibition of PKC-ζ attenuated VEGF-induced decrease of tight junction proteins and accompanying hyperpermeability in human retinal microvascular endothelial cells (HRMECs). PKC-ζ inhibition also attenuated AGE-induced decrease of tight junction proteins in HRMECs. Our findings suggest that inhibition of PKC-ζ could be an alternative treatment option for compromised blood-retinal barrier in diabetic retinopathy.

Suppression of protein kinase C theta contributes to enhanced myogenesis In vitro via IRS1 and ERK1/2 phosphorylation

BackgroundDifferentiation and fusion of skeletal muscle myoblasts into multi-nucleated myotubes is required for neonatal development and regeneration in adult skeletal muscle. Herein, we report novel findings that protein kinase C theta (PKCθ) regulates myoblast differentiation via phosphorylation of insulin receptor substrate-1 and ERK1/2.ResultsIn this study, PKCθ knockdown (PKCθshRNA) myotubes had reduced inhibitory insulin receptor substrate-1 ser1095 phosphorylation, enhanced myoblast differentiation and cell fusion, and increased rates of protein synthesis as determined by [3H] phenylalanine incorporation. Phosphorylation of insulin receptor substrate-1 ser632/635 and extracellular signal-regulated kinase1/2 (ERK1/2) was increased in PKCθshRNA cells, with no change in ERK5 phosphorylation, highlighting a PKCθ-regulated myogenic pathway. Inhibition of PI3-kinase prevented cell differentiation and fusion in control cells, which was attenuated in PKCθshRNA cells. Thus, with reduced PKCθ, differentiation and fusion occur in the absence of PI3-kinase activity. Inhibition of the ERK kinase, MEK1/2, impaired differentiation and cell fusion in control cells. Differentiation was preserved in PKCθshRNA cells treated with a MEK1/2 inhibitor, although cell fusion was blunted, indicating PKCθ regulates differentiation via IRS1 and ERK1/2, and this occurs independently of MEK1/2 activation.ConclusionCellular signaling regulating the myogenic program and protein synthesis are complex and intertwined. These studies suggest that PKCθ regulates myogenic and protein synthetic signaling via the modulation of IRS1and ERK1/2 phosphorylation. Myotubes lacking PKCθ had increased rates of protein synthesis and enhanced myotube development despite reduced activation of the canonical anabolic-signaling pathway. Further investigation of PKCθ regulated signaling may reveal important interactions regulating skeletal muscle health in an insulin resistant state.

Ssanghwa-tang, an oriental herbal cocktail, exerts anti-melanogenic activity by suppression of the p38 MAPK and PKA signaling pathways in B16F10 cells

BackgroundSsanghwa-tang (SHT) is a widely used medication for the treatment of fatigue, pain, inflammation, hypothermia, erectile dysfunction, cancer, and osteoporosis in Asia, however, role of SHT on the melanin synthesis has not been checked previously. Thus, the present study was designed to determine the effect of SHT on α-melanocyte stimulating hormone (α-MSH)-induced melanogensis and its mechanisms of action in murine B16F10 melanoma cells.MethodCellular melanin content and tyrosinase activity in murine B16F10 melanoma cells were determined after α-MSH stimulation with or without pre-treatment of SHT at the concentration of 250 and 500 μg/ml. Expression level of tyrosinase, tyrosinase-related protein 1 (TRP-1), TRP-2, microphthalmia-associated transcription factor (MITF), and activation of c-AMP-dependent protein kinase (PKA), c-AMP-related element binding protein (CREB), and mitogen-activated protein kinases (MAPKs) were examined by Western blot analysis.ResultsSHT significantly inhibited α-MSH-induced melanin synthesis and tyrosinase activity, and also decreased α-MSH-induced expression of MITF, tyrosinase, and TRP-1. In addition, SHT remarkably suppressed tyrosinase, CRE, and MITF luciferase reporter activity in a resting state as well as in α-MSH-stimulating condition. Phosphorylation of p38 MAPK by α-MSH stimulation was efficiently blocked by SHT pre-treatment. Moreover, SHT as an herbal cocktail showed synergistic anti-melanogenic effect compared with that of each single constituent herb.ConclusionSHT efficiently inhibited c-AMP-induced melanin synthesis in B16F10 cells via suppression of PKA and p38 MAPK signaling pathways and subsequently decreased the level of CREB phosphorylation, MITF, and melanogenic enzymes. These results indicate that SHT may be useful as herbal medicine for treating hyperpigmentation and cosmetics as a skin-whitening agent.

Abstract 024: MicroRNAs and Anesthetic Cardioprotection in Diabetes

Introduction: MicroRNAs are endogenous small RNA molecules that regulate a wide range of cellular functions primarily through reduction of target protein expression. Several microRNAs have been shown to play important roles in cardiac injury, and also contribute to the development of diabetic complications and cardiac preconditioning. We utilized a model of the patient-specific induced pluripotent stem cells (iPSCs) differentiated into the cardiac lineage in order to delineate the environmental and cellular mechanisms responsible for overturning anesthetic cardioprotection in diabetes. We hypothesized that miR-21 contributes to cardioprotection conferred by anesthetics in human cardiomyocytes and that diabetic conditions compromise this protection in part via suppression of miR-21. Methods: We have developed and validated a clinically relevant model of cardioprotection using human cardiomyocytes differentiated from the iPSCs derived from non-diabetic individuals (N-CM) and patients with type 2 diabetes mellitus (T2-CM). Results: Our results indicate that cardiomyocytes derived from type 2 diabetes-specific stem cells recapitulate the phenotypic findings from type 2 diabetic patients. For instance, T2-CM exhibited a suppression of protein kinase B (Akt) and activation of glycogen synthase kinase-3β, compared to N-CM; indicating that this pathway is compromised in cardiomyocytes derived from diabetic individuals. In addition, we examined whether isoflurane could delay oxidative stress-induced mitochondrial permeability transition pore (mPTP) opening in T2-CM and found that the effects of isoflurane were significantly attenuated as compared to N-CM. Finally, isoflurane increased miR-21 abundance in N-CM, but not in T2-CM. Summary: Diabetes and hyperglycemia substantially increase perioperative cardiovascular risk, with few mitigating strategies. Our data indicate an important role of miR-21 in isoflurane-induced cardioprotection and its impairment by diabetic conditions that may suggest new therapeutic targets for reducing perioperative cardiovascular morbidity and mortality in high-risk patients.

Reversal of synaptic plasticity and spatial memory deficits in APP/PS1 mice by suppressing protein kinase GCN2

Reversal of synaptic plasticity and spatial memory deficits in APP/PS1 mice by suppressing protein kinase GCN2

Quercetin inhibits transcriptional up-regulation of histamine H1 receptor via suppressing protein kinase C-δ/extracellular signal-regulated kinase/poly(ADP-ribose) polymerase-1 signaling pathway in HeLa cells

It has been reported that the histamine H1 receptor (H1R) gene is up-regulated in patients with allergic rhinitis and H1R expression level strongly correlates with the severity of allergy symptoms. Accordingly compounds that suppress the H1R gene expression are promising as useful anti-allergic medications. Recently, we demonstrated that histamine or phorbol-12-myristate-13-acetate (PMA) stimulation induced the up-regulation of H1R gene expression through the protein kinase Cδ (PKCδ)/extracellular signal-regulated kinase/poly(ADP-ribose) polymerase-1 signaling pathway in HeLa cells expressing H1R endogenously. Quercetin is one of the well-characterized flavonoids and it possesses many biological activities including anti-allergic activity. However, effect of quercetin on H1R signaling is remained unknown. In the present study, we examined the effect of quercetin on histamine- and PMA-induced up-regulation of H1R gene expression in HeLa cells. We also investigated its in vivo effects on the toluene-2,4-diisocyanate (TDI)-sensitized allergy model rats. Quercetin suppressed histamine- and PMA-induced up-regulation of H1R gene expression. Quercetin also inhibited histamine- or PMA-induced phosphorylation of Tyr311 of PKCδ and translocation of PKCδ to the Golgi. Pre-treatment with quercetin for 3weeks suppressed TDI-induced nasal allergy-like symptoms and elevation of H1R mRNA in the nasal mucosa of TDI-sensitized rats. These data suggest that quercetin suppresses H1R gene expression by the suppression of PKCδ activation through the inhibition of its translocation to the Golgi.

Abstract 46: RSK4 Is a Novel Negative Regulator of Endothelial Differentiation via Direct Suppression of Protein Kinase A Activity

Endothelial cells (ECs) differentiation is strictly regulated to generate functional blood vessels. Previously, we demonstrated that Flk1+ cells derived from embryonic stem (ES) cells serve as vascular progenitors and can constructively reproduce the early differentiation of both ECs and Mural cells (MCs; vascular smooth muscle cells and pericytes). We recently reported that cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA) signaling enhanced EC differentiation from Flk1+ vascular progenitors via induction of vascular endothelial growth factor (VEGF) receptors expression. To identify a novel molecule involved in EC differentiation, we performed microarray analyses at various differentiation stages from ES cells to vascular cells; undifferentiated ES cells, Flk1+ vascular progenitors, ECs and MCs. Then, we found that mRNA of p90 ribosomal protein S6 kinase 4 (RSK4) was highly expressed in Flk1+ vascular progenitors and almost diminished during EC differentiation, whereas it remained being expressed in MCs. The addition of a broad-spectrum RSK inhibitor, SL0101, to Flk1+ vascular progenitors enhanced VEGF receptor expression and EC differentiation specifically in the presence of the simultaneous cAMP signal activation. SL0101-elicited EC differentiation was abolished by PKA catalytic subunit alpha (PKAc) knockdown. Specific RSK4 knockdown in Flk1+ vascular progenitors reproduced the effects of SL0101 on EC differentiation via increasing Flk1 expression. RSK4 had potential to bind with PKAc and inhibited PKA activity. Furthermore, an ex vivo whole embryo culture assay showed that SL0101 treatment drastically resulted in increased CD31+ vasculature area, enlarged vessel diameter and defected vascular remodeling in yolk sac. Taken together, these results indicate that RSK4 acts as a novel negative regulator for EC differentiation via inhibition of PKA function. Fine tuning of PKA and Flk1 signaling by RSK4 is critical to normal vascular development. Elucidation of the new-mode cell fate determination by RSK4 would provide novel insights in developmental biology, stem cell biology, and regenerative medicine.

Genetic variants of kinases suppressors of ras (KSR1) to predict survival in patients with ER-alpha positive metastatic breast cancer.

e11018 Background: In addition to its activating role of MAPK pathway, the protein kinase suppressor of ras 1 (KSR1) has been identified as a novel modulator of estrogen receptor alpha (ERα), as silencing of KSR1 in ERα+ breast cancer (BC) cells lines resulted in dowregulation of ERα transcriptional activity in the presence of oestradiol. Our previously data revealed the existence of single nucleotide polymorphisms (SNPs) in EGFR and ERα pathway genes that may predict clinical outcome in ERα positive metastatic BC (mBC) patients. With respect to those findings we aimed to evaluate the clinical implication of KSR1 SNPs on survival in patients with primary ERα+ mBC treated with tamoxifen. Methods: Tumoral DNA was obtained from 222 patients treated with tamoxifen withERα+ invasive BC who had undergone surgery between 1981 and 2003 (median age 56 [28-90]). Three relevant KSR1 SNPs were selected based on public literature resources and databases, including 2 SNPs localised in the regulating 3’untranslated region (rs224190, rs 1075952) and 1 non-synonymous SNP localised in the coding exon 7 region (rs2293180). All SNP were analysed using DNA sequencing with OS and DFS as primary endpoint. Results: The overall median follow-up was 6.4 years.In univariate analysis the rs2241906 SNP was significantly associated with DFS and OS and patients with the TT genotypedemonstrated shorter DFS (2.1 vs. 7.1 months, p=0.005) and OS ( 2.6 vs. 8.4 months p=0.002) than patients with the x/C genotypes. The associations remained significant in the multivariate analysis adjusting age, lymph node status and HER2 status (HR (95%CI): 4.81 (2.00-11.59) and 5.74 (2.29-14.43), for DFS and OS, respectively). The same significant correlation was retrieved with the SNP rs1075952 in linkage disequilibrium with rs2241906 that was used as a control. No relationship was shown between rs2293180 and survival. Conclusions: Our findings demonstrated that KSR1 polymorphisms could arise as a potential marker to predict survival in patients with mBC treated with tamoxifen. The putative role of KSR1 as a modulator of ERα activity could functionally explain our results yielding insight for further studies.

Protein Arginine Methyltransferase 5 (PRMT5) Signaling Suppresses Protein Kinase Cδ- and p38δ-dependent Signaling and Keratinocyte Differentiation

PKCδ is a key regulator of keratinocyte differentiation that activates p38δ phosphorylation leading to increased differentiation as measured by an increased expression of the structural protein involucrin. Our previous studies suggest that p38δ exists in association with protein partners. A major goal is to identify these partners and understand their role in regulating keratinocyte differentiation. In this study we use affinity purification and mass spectrometry to identify protein arginine methyltransferase 5 (PRMT5) as part of the p38δ signaling complex. PRMT5 is an arginine methyltransferase that symmetrically dimethylates arginine residues on target proteins to alter target protein function. We show that PRMT5 knockdown is associated with increased p38δ phosphorylation, suggesting that PRMT5 impacts the p38δ signaling complex. At a functional level we show that PRMT5 inhibits the PKCδ- or 12-O-tetradecanoylphorbol-13-acetate-dependent increase in human involucrin expression, and PRMT5 dimethylates proteins in the p38δ complex. Moreover, PKCδ expression reduces the PRMT5 level, suggesting that PKCδ activates differentiation in part by reducing PRMT5 level. These studies indicate antagonism between the PKCδ and PRMT5 signaling in control of keratinocyte differentiation.

Suppression of Ras/Mapk pathway signaling inhibits Myc-induced lymphomagenesis

Although the Myc transcription factor has been shown necessary for the oncogenic function of Ras, the contribution of Ras pathway signaling to the oncogenic function of Myc remains unresolved. We report the novel findings that Myc alone induced Ras/Mapk pathway signaling, and increased signaling following growth factor stimulation. Deletion of the scaffold protein kinase suppressor of Ras 1 (Ksr1) attenuated signaling through the Ras/Mapk pathway, including activation following Myc induction. B cells that lacked Ksr1 exhibited reduced proliferation and increased cytokine deprivation-induced apoptosis. Overexpression of Myc rescued the proliferation defect of Ksr1-null B cells, but loss of Ksr1 increased sensitivity of B cells to Myc-induced apoptosis. Notably, there was a significant delay in lymphoma development in Ksr1-null mice overexpressing Myc in B cells (Eμ-myc transgenic mice). There was an elevated frequency of p53 inactivation, indicative of increased selective pressure to bypass the p53 tumor suppressor pathway, in Ksr1-null Eμ-myc lymphomas. Therefore, loss of Ksr1 inhibits Ras/Mapk pathway signaling leading to increased Myc-induced B-cell apoptosis, and this results in reduced B-cell transformation and lymphoma development. Our data indicate that suppression of Myc-induced Ras/Mapk pathway signaling significantly impairs Myc oncogenic function. These results fill a significant gap in knowledge about Myc and should open new avenues of therapeutic intervention for Myc-overexpressing malignancies.

Ceramide accumulation and up-regulation of proinflammatory interleukin-1β exemplify lipotoxicity to mediate declines of reproductive efficacy of broiler hens

The study was conducted to delineate fundamental mechanisms that initiate the deleterious effect of fuel overloading on reproductive efficacy of broiler breeder hens. Sixty hens at age 26 wk were fed recommended amounts of feed (160 g/d per hen) or allowed voluntary feeding (approximately 30% more than restriction). At age 35 and 50 wk, hens were sampled for further analyzes. Voluntary feeding resulted in poor egg production, high rate of mortality, and abnormal ovarian structure (mainly overt hierarchical follicle atresia at age 35 wk and ovarian involution at age 50 wk). In contrast to feed-restricted hens, voluntary feeding also induced metabolic dysregulations that comprised enhanced adiposity; hepatic triacylglycerol accumulation; and elevated concentrations of plasma glucose, NEFAs, very low density lipoprotein, triacylglycerol, phospholipids, and sphingomyelin (P < 0.05). Furthermore, hepatic and circulating ceramide and sphingomyelin accumulation, and up-regulation of proinflammatory IL-1β expression in liver and adipose tissues (P < 0.05) systemically manifested the development of lipotoxicity in feed-satiated hens. Lipotoxicity leading to impaired ovarian dysfunctions, including follicle atresia, ovarian regression, and a decline of circulating estradiol levels (P < 0.05) in feed-satiated hens, was further exemplified by ceramide accumulation and up-regulation of IL-1β, serine palmitoyltransferase, and sphingomyelinase transcript abundance, but suppressed protein kinase Akt activation (P < 0.1 to 0.05) within the hierarchical follicles. This study provides the first in vivo evidence of the actions of ceramide and IL-1β in mediating overfeeding-induced follicle atresia and progression of ovarian involution in broiler hens.

Dahuang Zhechong Pill (大黄虫丸) containing serum inhibited platelet-derived growth factor-stimulated vascular smooth muscle cells proliferation by inducing G1 arrest partly via suppressing protein kinase C α-Extracellular regulated kinase 1/2 signaling pathway

To investigate effects of dahuang zhechong pill ( DHZCP) on the cell cycle and the related signal pathways in vascular smooth muscle cells (VSMCs) stimulated by platelet-derived growth factor (PDGF) with the method of serum pharmacology. DNA synthesis in VSMCs was examined by detecting 5'-bromo-2'-deoxyuridine incorporation with the immunocytochemical method. The cycle of VSMCs was evaluated with flow cytometry. Expressions of cyclin D1, p27, protein kinase Cα (PKCα), and phosphorylated extracellular signal regulated kinase 1/2 (ERK1/2) were quantified by Western blot method. DHZCP containing serum significantly inhibited DNA synthesis of PDGF-stimulated VSMCs, arrested the cells in G G(1) phase, modulated the protein expressions of cyclin D D(1) and p27, and suppressed the activation of PKCα and ERK1/2. DHZCP containing serum inhibits VSMCs proliferation via modulating the expressions of cell cycle proteins to arrest the cell in G G(1) phase, which is attributed to, at least in part, suppressing PKCα-ERK1/2 signaling in VSMCs.

Abstract 2325: The crystal structure of the ERK2/norathyriol complex

Abstract Norathyriol is an active metabolite of mangiferin, one of the mango polyphenolic compounds that have been demonstrated to have anti-proliferative and pro-apoptotic activities against human leukemia, as well as human lung, breast, colon and prostate cancer cells. Norathyriol has been reported to inhibit the PMA-induced respiratory burst and aggregation of rat neutrophils by suppressing protein kinase C activity. We show that norathyriol targets extracellular signal-regulated kinase 2 (ERK2), which is activated in response to growth factors and cytokines, and is a key kinase in the Ras/Raf/MAPK signaling pathway, which is deregulated in many cancers. We determined the crystal structure of ERK2 complexed with norathyriol at 1.6 Å resolution. Human recombinant ERK2 was expressed, purified from E.coli and successfully crystallized. The protein crystals were soaked with norathyriol solution prior to the data collection. The norathyriol molecule is clearly visible in the electron density map inside the ATP-binding site below the phosphate-binding loop. Norathyriol is anchored to the ERK2 hinge region that connects the kinase N- and C-lobes by several hydrogen bonds. The side chain carboxyl of the gatekeeper residue Gln105 hydrogen bonded with the 7-OH group of norathyriol. The backbone of Asp106 and Met108 form hydrogen bonds with 6-OH group of norathyriol. We mutated Gln105 to alanine to weaken the norathyriol interaction with ERK2, and showed that the recombinant Q105A mutant exhibited impaired in vitro binding affinity to norathyriol compared with wild type. The Ile31, Val39, and Ala52 residues from the N-lobe contribute to the hydrophobic interactions with the xanthone moiety of norathyriol. These results indicate that norathyriol directly binds to the ATP-binding site of ERK2. The Ras/Raf mutation in many cancers causes the hyperactivation of ERK2 and unregulated cell proliferation. Recent reports indicate that knockdown of ERK2 inhibits growth of tumor cells, suggesting that ERK2 inhibition is a potential approach for the treatment of cancer. Norathyriol thus might be a potential therapeutic and chemopreventive lead compound targeting ERK2 in cancer cells where activation of the ERK2 pathway mediates the anti-apoptotic response. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2325. doi:10.1158/1538-7445.AM2011-2325

Abstract LB-261: Maintenance of aerobic glycolysis provides selective protection from apoptosis upon loss of growth signals or inhibition of BCR-Abl through suppression of p53 activation

Abstract Healthy cells require input from growth factor signaling pathways to maintain cell metabolism and survival. In contrast, cancer cells can maintain growth factor-independent glycolysis and survival through expression of oncogenic kinases, such as BCR-Abl. While disruption of these growth signals through targeted kinase inhibition can promote cancer cell death, therapeutic resistance frequently develops, and further mechanistic understanding is needed. Cell metabolism may play a central role in this cell death pathway, as we have shown that growth factor deprivation leads to decreased glycolysis that promotes apoptosis via p53 activation and induction of the pro-apoptotic protein Puma. However, it has remained unclear how cell metabolism regulates p53 activation. To investigate this, we have utilized a system in which stable overexpression of the glucose transporter Glut1 and hexokinase 1 in hematopoietic cells drives growth factor-independent glycolysis. This system allows us to examine the effects of altered glucose metabolism in the absence of other signaling events activated downstream of growth factor receptors or oncogenic kinases. Here, we extend our findings to demonstrate that elevated glucose metabolism, characteristic of cancer cells, can suppress Protein Kinase C delta-dependent p53 activation to maintain cell survival after growth factor withdrawal. In contrast, DNA damage-induced p53 activation was independent of Protein Kinase C delta and was not metabolically sensitive. Both stresses required phosphorylation of p53 at serine 18 for maximal activity, but each led to a unique pattern of p53 target gene expression, demonstrating distinct activation and response pathways for p53 that were differentially regulated by metabolism. Consistent with oncogenic kinases acting to replace growth factors, treatment of BCR-Abl-expressing cells with the kinase inhibitor imatinib led to reduced glycolysis and p53- and Puma-dependent cell death. Accordingly, maintenance of glucose metabolism inhibited p53 activation and promoted imatinib resistance. Furthermore, inhibition of glycolysis enhanced imatinib sensitivity in BCR-Abl-positive cells expressing wild type p53 but had little effect on p53-null cells. These data demonstrate that distinct pathways regulate p53 after DNA damage and metabolic stress and that inhibition of glucose metabolism may enhance the efficacy of and overcome resistance to targeted molecular cancer therapies. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr LB-261. doi:10.1158/1538-7445.AM2011-LB-261

Compartmentalization of the MAPK scaffold protein KSR1 modulates synaptic plasticity in hippocampal neurons.

ERK1/2 is required for certain forms of synaptic plasticity, including the long-term potentiation of synaptic strength. However, the molecular mechanisms regulating synaptically localized ERK1/2 signaling are poorly understood. Here, we show that the MAPK scaffold protein kinase suppressor of Ras 1 (KSR1) is directly phosphorylated by the downstream kinase ERK1/2. Quantitative Western blot analysis further demonstrates that expression of mutated, feedback-deficient KSR1 promotes sustained ERK1/2 activation in HEK293 cells in response to EGF stimulation, compared to a more transient activation in control cells expressing wild-type KSR1. Immunocytochemistry and confocal imaging of primary hippocampal neurons from newborn C57BL6 mice further show that feedback phosphorylation of KSR1 significantly reduces its localization to dendritic spines. This effect can be reversed by tetrodotoxin (1 μM) or PD184352 (2 μM) treatment, further suggesting that neuronal activity and phosphorylation by ERK1/2 lead to KSR1 removal from the postsynaptic compartment. Consequently, electrophysiological recordings in hippocampal neurons expressing wild-type or feedback-deficient KSR1 demonstrate that KSR1 feedback phosphorylation restricts the potentiation of excitatory postsynaptic currents. Our findings, therefore, suggest that feedback phosphorylation of the scaffold protein KSR1 prevents excessive ERK1/2 signaling in the postsynaptic compartment and thus contributes to maintaining physiological levels of synaptic excitability.