Genetic inactivation of ERK1 and ERK2 in chondrocytes promotes bone growth and enlarges the spinal canal

Activating mutations in FGFR3 cause the most common forms of human dwarfism: achondroplasia and thanatophoric dysplasia. In mouse models of achondroplasia, recent studies have implicated the ERK MAPK pathway, a pathway activated by FGFR3, in creating reduced bone growth. Our recent studies have indicated that increased Fgfr3 and ERK MAPK signaling in chondrocytes also causes premature synchondrosis closure in the cranial base and vertebrae, accounting for the sometimes fatal stenosis of the foramen magnum and spinal canal in achondroplasia. Conversely, whether the decrease--or inactivation--of ERK1 and ERK2 promotes bone growth and delays synchondrosis closure remains to be investigated. In this study, we inactivated ERK2 in the chondrocytes of ERK1-null mice using the Col2a1-Cre and Col2a1-CreER transgenes. We found that the genetic inactivation of ERK1 and ERK2 in chondrocytes enhances the growth of cartilaginous skeletal elements. We also found that the postnatal inactivation of ERK1 and ERK2 in chondrocytes delays synchondrosis closure and enlarges the spinal canal. These observations make ERK1 and ERK2 an attractive target for the treatment of achondroplasia and other FGFR3-related skeletal syndromes.

Betulinic acid inhibits endotoxin-stimulated phosphorylation cascade and pro-inflammatory prostaglandin E(2) production in human peripheral blood mononuclear cells

BACKGROUND AND PURPOSE

Betulinic acid (BA) is a naturally occurring triterpenoid widely distributed throughout the plant kingdom. We previously reported that BA inhibits lipopolysaccharide (LPS)-induced interleukin-6 production through modulation of nuclear factor κB (NF-κB) in human peripheral blood mononuclear cells (hPBMCs). This study attempted to identify other mechanisms through which BA modulates LPS signalling in mononuclear cells. The effects of BA on signalling pathways downstream were focused on in this study.

EXPERIMENTAL APPROACH

We determined the ability of BA to interfere with p38 and extracellular regulated kinase (ERK) phosphorylation as well as Akt phosphorylation and nuclear factor-κB activation using LPS-activated hPBMCs as an in vitro model. LPS-induced endotoxin shock in mice was the in vivo model employed.

KEY RESULTS

BA inhibited LPS-induced COX-2 protein expression and prostaglandin E(2) production and also attenuated LPS-induced ERK and Akt phosphorylation, but not p38 in hPBMCs. BA abolished LPS-induced IκBα phosphorylation and thus normalized the levels of IκBα in cytosol. BA also inhibited LPS-induced reactive oxygen species formation and lactate dehydrogenase release. Interestingly, BA improved the life span of mice in endotoxin shock and also inhibited PGE(2) production and myeloperoxidase activity in vivo.

CONCLUSIONS AND IMPLICATIONS

BA modulates LPS-induced COX-2 expression in hPBMCs by inhibiting ERK and Akt pathways as well as by modulating IκBα phosphorylation. At the same time, no cell toxicity was observed. The effect of the drug was confirmed through in vivo experiments. The study gives an insight into the molecular mechanisms of BA.

A dopamine D1 receptor-dependent β-arrestin signaling complex potentially regulates morphine-induced psychomotor activation but not reward in mice

Morphine is a widely used analgesic in humans that is associated with multiple untoward effects, such as addiction and physical dependence. In rodent models, morphine also induces locomotor activity. These effects likely involve functionally selective mechanisms. Indeed, G protein-coupled receptor desensitization and adaptor protein β-arrestin 2 (βarr2) through its interaction with the μ-opioid receptor regulates the analgesic but not the rewarding properties of morphine. However, βarr2 is also required for morphine-induced locomotor activity in mice, but the exact cellular and molecular mechanisms that mediate this arrestin-dependent behavior are not understood. In this study, we show that βarr2 is required for morphine-induced locomotor activity in a dopamine D1 receptor (D1R)-dependent manner and that a βarr2/phospho-ERK (βarr2/pERK) signaling complex may mediate this behavior. Systemic administration of SL327, an MEK inhibitor, inhibits morphine-induced locomotion in wild-type mice in a dose-dependent manner. Acute morphine administration to mice promotes the formation of a βarr2/pERK signaling complex. Morphine-induced locomotor activity and formation of the βarr2/pERK signaling complex is blunted in D1R knockout (D1-KO) mice and is presumably independent of D2 dopamine receptors. However, D1Rs are not required for morphine-induced reward as D1-KO mice show the same conditioned place preference for morphine as do control mice. Taken together, these results suggest a potential role for a D1R-dependent βarr2/pERK signaling complex in selectively mediating the locomotor-stimulating but not the rewarding properties of morphine.

Pancreatic adenocarcinoma upregulated factor promotes metastasis by regulating TLR/CXCR4 activation

Pancreatic adenocarcinoma upregulated factor (PAUF) is overproduced in certain types of cancer. However, little is known of the tumorigenic function of PAUF. In this study, we report the X-ray crystal structure of PAUF and reveal that PAUF is a mammalian lectin normally found in plant lectins. We also identify PAUF as an endogenous ligand of Toll-like receptor 2 (TLR2) and TLR4 by screening extracellular domain receptor pools. We further confirmed the specificity of the PAUF-TLR2 interaction. PAUF induces extracellular signal-regulated kinase (ERK) phosphorylation and activates the IKK-β-mediated TPL2/MEK/ERK signaling pathway through TLR2. In agreement with the result of TLR2-mediated ERK activation by PAUF, PAUF induces increased expression of the protumorigenic cytokines RANTES and MIF in THP-1 cells. However, PAUF does not fully activate Iκ-B-α signaling pathways in THP-1 cells, and fails to translocate the p65 subunit of the nuclear factor-κB (NF-κB) complex into the nucleus, resulting in no NF-κB activation. Surprisingly, we found that PAUF also associated with the CXC chemokine receptor (CXCR4)-TLR2 complex and inhibited CXCR4-dependent, TLR2-mediated NF-κB activation. Together, these findings suggest that the new cancer-associated ligand, PAUF, may activate TLR-mediated ERK signaling to produce the protumorigenic cytokines, but inhibits TLR-mediated NF-κB signaling, thereby facilitating tumor growth and escape from innate immune surveillance.

Duration and magnitude of extracellular signal-regulated protein kinase phosphorylation determine adipogenesis or osteogenesis in human bone marrow-derived stem cells

PURPOSE

Imbalances between osteogenic and adipogenic differentiation leads to diseases such as osteoporosis. The aim of our study was to demonstrate the differences in extracellular signal-regulated kinase (ERK) phosphorylation during both adipogenesis and osteogenesis of human bone marrow-derived stem cells (BMSCs).

MATERIALS AND METHODS

Using troglitazone, GW9662 and U0126, we investigated their role in hBMSC differentiation to adipogenic and osteogenic fates.

RESULTS

ERK1/2 inhibition by U0126 suppressed proliferator-activated receptor (PPAR)γ expression and lipid accumulation, while it decreased the mRNA expression of adipogenic genes (lipoprotein lipase, PPARγ, and adipocyte protein) and osteogenic genes (type I collagen and osteopontin). ERK phosphorylation was transient and decreased during adipogenesis, whereas it occurred steadily during osteogenesis. Troglitazone, a PPARγ agonist, induced adipogenesis by inhibiting ERK phosphorylation even in an osteogenic medium, suggesting that ERK signaling needs to be shut off in order to proceed with adipose cell commitment. Cell proliferation was greatly increased in osteogenesis but was not changed during adipogenesis, indicating that ERK might play different roles in cellular proliferation and differentiation between the two committed cell types.

CONCLUSION

The duration and magnitude of ERK activation might be a crucial factor for the balance between adipogenesis and osteogenesis in human bone marrow-derived stem cells.

Morphine modulation of thrombospondin levels in astrocytes and its implications for neurite outgrowth and synapse formation

Opioid receptor signaling via EGF receptor (EGFR) transactivation and ERK/MAPK phosphorylation initiates diverse cellular responses that are cell type-dependent. In astrocytes, multiple μ opioid receptor-mediated mechanisms of ERK activation exist that are temporally distinctive and feature different outcomes. Upon discovering that chronic opiate treatment of rats down-regulates thrombospondin 1 (TSP1) expression in the nucleus accumbens and cortex, we investigated the mechanism of action of this modulation in astrocytes. TSP1 is synthesized in astrocytes and is released into the extracellular matrix where it is known to play a role in synapse formation and neurite outgrowth. Acute morphine (hours) reduced TSP1 levels in astrocytes. Chronic (days) opioids repressed TSP1 gene expression and reduced its protein levels by μ opioid receptor and ERK-dependent mechanisms in astrocytes. Morphine also depleted TSP1 levels stimulated by TGFβ1 and abolished ERK activation induced by this factor. Chronic morphine treatment of astrocyte-neuron co-cultures reduced neurite outgrowth and synapse formation. Therefore, inhibitory actions of morphine were detected after both acute and chronic treatments. An acute mechanism of morphine signaling to ERK that entails depletion of TSP1 levels was suggested by inhibition of morphine activation of ERK by a function-blocking TSP1 antibody. This raises the novel possibility that acute morphine uses TSP1 as a source of EGF-like ligands to activate EGFR. Chronic morphine inhibition of TSP1 is reminiscent of the negative effect of μ opioids on EGFR-induced astrocyte proliferation via a phospho-ERK feedback inhibition mechanism. Both of these variations of classical EGFR transactivation may enable opiates to diminish neurite outgrowth and synapse formation.

Osteopontin is required for unloading-induced osteoclast recruitment and modulation of RANKL expression during tooth drift-associated bone remodeling, but not for super-eruption

Unloading of teeth results in extensive alveolar bone remodeling, causing teeth to move in both vertical ("super-eruption") and horizontal direction ("drift"). In order to decipher the molecular mechanisms of unloading-induced bone remodeling during tooth movement, we focused on the role of osteopontin (OPN) in the un-opposed molar model, comparing wild-type (WT) and OPN-null mice. Our data indicated that OPN was not required for the continuous eruption of un-opposed teeth while OPN was necessary for the drift of teeth. OPN expression and osteoclast counts were greatly increased on alveolar bone surfaces facing the direction of the drift in WT mice, while osteoclast counts were diminished in OPN-/- mice. RANKL expression in the distal periodontal ligament of WT molars increased significantly by day 6 following unloading, while overall levels of RANKL expression were decreased in both WT and OPN-null mice. In vitro treatment of MC3T3 cells, WT BMCs and OPN-/- BMCs with recombinant OPN resulted in significantly increased RANKL expression in all three cell types. The PI3K and MEK/ERK pathway inhibitors Ly294002 and U0126 reduced RANKL expression levels in vitro. Treatment of BMCs and MC3T3 with OPN also resulted in increased ERK phosphorylation and reduced OPG levels. Together, our studies suggest that increased OPN expression during unloading-induced drifting of teeth enhances localized RANKL expression and osteoclast activity on drift-direction alveolar bone surfaces via extracellular matrix signaling pathways.

Hypoxia increases Annexin A2 expression in osteoblastic cells via VEGF and ERK

Vascular endothelial growth factor (VEGF)-stimulated angiogenesis is critical for endochondral ossification that occurs during bone development and bone repair. Under these circumstances, VEGF production appears to be driven by low oxygen tension, under the control of the hypoxia-inducible factor-α family of transcription factors (HIF-α). Annexin 2 (AnxA2) a calcium-dependent phospholipid binding protein has been implicated in VEGF-mediated retinal neovascularization and is upregulated by VEGF in choroid retinal endothelial cells. AnxA2 is also expressed in cells of the osteoblast lineage and chondrocytes and may play a role in matrix mineralization. In this paper, we examined the effects of hypoxia (1% O(2)) and VEGF on the expression of AnxA2 in osteoblastic MC3T3-E1 cells. Hypoxia, desferrioxamine (hypoxia mimetic), and recombinant VEGF all increased AnxA2 mRNA and protein levels in osteoblastic cells. The hypoxia-induced increase in AnxA2 was inhibited by a blocking antibody to VEGF-R1; however, VEGF(120), a VEGF-R1 agonist, demonstrated no influence upon Anxa2 expression. This suggests that VEGF induction of Annexin A2 is not mediated via VEGF-R1 agonism alone but by VEGF-R1 and Neuropilin-1 or Neuropilin-2 heterodimers. In addition, we demonstrated that VEGF-stimulated changes in AnxA2 expression via a pathway involving Src and MEK kinase. These data demonstrate that AnxA2 expression in osteoblasts is under the control of VEGF, which may have implications for both angiogenesis and bone mineralization under low oxygen conditions.

Na+/H+ exchanger regulatory factor-1 is involved in chemokine receptor homodimer CCR5 internalization and signal transduction but does not affect CXCR4 homodimer or CXCR4-CCR5 heterodimer

Chemokine receptors are members of the G protein-coupled receptor (GPCR) family. CCR5 is also the principal co-receptor for macrophage-tropic strains of human immunodeficiency virus, type 1 (HIV-1), and efforts have been made to develop ligands to inhibit HIV-1 infection by promoting CCR5 receptor endocytosis. Given the nature of GPCRs and their propensity to form oligomers, one can consider ligand-based therapies as unselective in terms of the oligomeric composition of complexes. For example, a ligand targeting a CCR5 homomer could likely induce signal transduction on a heteromeric CCR5-CXCR4. Other avenues could therefore be explored. We identified a receptor adaptor interacting specifically with one receptor complex but not others. NHERF1, an adaptor known for its role in desensitization, internalization, and regulation of the ERK signaling cascade for several GPCRs, interacts via its PDZ2 domain with the CCR5 homodimer but not with the CXCR4-CCR5 heterodimer or CXCR4 homodimer. To further characterize this interaction, we also show that NHERF1 increases the CCR5 recruitment of arrestin2 following stimulation. NHERF1 is also involved in CCR5 internalization, as we demonstrate that co-expression of constructs bearing the PDZ2 domain can block CCR5 internalization. We also show that NHERF1 potentiates RANTES (regulated on activation normal T cell expressed and secreted)-induced ERK1/2 phosphorylation via CCR5 activation and that this activation requires NHERF1 but not arrestin2. Taken together, our results suggest that oligomeric receptor complexes can associate specifically with partners and that in this case NHERF1 could represent an interesting new target for the regulation of CCR5 internalization and potentially HIV infection.

Pim3 negatively regulates glucose-stimulated insulin secretion

Pancreatic β-cell response to glucose stimulation is governed by tightly regulated signaling pathways which have not been fully characterized. A screen for novel signaling intermediates identified Pim3 as a glucose-responsive gene in the β cell, and here, we characterize its role in the regulation of β-cell function. Pim3 expression in the β-cell was first observed through microarray analysis on glucose-stimulated murine insulinoma (MIN6) cells where expression was strongly and transiently induced. In the pancreas, Pim3 expression exhibited similar dynamics and was restricted to the β cell. Perturbation of Pim3 function resulted in enhanced glucose-stimulated insulin secretion, both in MIN6 cells and in isolated islets from Pim3-/- mice, where the augmentation was specifically seen in the second phase of secretion. Consequently, Pim3-/- mice displayed an increased glucose tolerance in vivo. Interestingly, Pim3-/- mice also exhibited increased insulin sensitivity. Glucose stimulation of isolated Pim3-/- islets resulted in increased phosphorylation of ERK1/2, a kinase involved in regulating β-cell response to glucose. Pim3 was also found to physically interact with SOCS6 and SOCS6 levels were strongly reduced in Pim3-/- islets. Overexpression of SOCS6 inhibited glucose-induced ERK1/2 activation, strongly suggesting that Pim3 regulates ERK1/2 activity through SOCS6. These data reveal that Pim3 is a novel glucose-responsive gene in the β cell that negatively regulates insulin secretion by inhibiting the activation of ERK1/2, and through its effect on insulin sensitivity, has potentially a more global function in glucose homeostasis.

Treatment with histone deacetylase inhibitor attenuates MAP kinase mediated liver injury in a lethal model of septic shock

BACKGROUND

Despite global efforts to improve the treatment of sepsis, it remains a leading cause of morbidity and mortality in intensive care units. We have previously shown that suberoylanilide hydroxamic acid (SAHA), a histone deacetylase inhibitor, markedly improves survival in a murine model of lipopolysaccharide (LPS)-induced shock. SAHA has anti-inflammatory properties that have not been fully characterized. The liver plays an important role in the production of acute phase reactants involved in the inflammatory cascade and is also one of the major organs that can become dysfunctional in septic shock. The purpose of this study was to assess the effect of SAHA treatment on MAP kinases and associated inflammatory markers in murine liver after LPS-induced injury.

METHODS

C57B1/6J mice were randomly divided into three groups: (A) experimental-given intraperitoneal (i.p.) SAHA (50 mg/kg) in dimethyl sulfoxide (DMSO) vehicle solution (n = 12); (B) control- given vehicle only (n = 12), and; (C) sham-given no treatment (n = 7). Two hours later, experimental and control mice were injected with LPS (20 mg/kg, i.p.) and experimental mice received a second dose of SAHA. Livers were harvested at 3, 24, and 48 h for analysis of inflammatory markers using Western Blot, Polymerase Chain Reaction (PCR), and Enzyme-Linked Immunosorbent Assay (ELISA) techniques.

RESULTS

After 3 h, the livers of animals treated with SAHA showed significantly (P < 0.05) decreased expression of the pro-inflammatory MAP kinases phosphorylated p38, phosphorylated ERK, myeloperoxidase and interleukin-6, and increased levels of the anti-inflammatory interleukin-10 compared with controls. Phospho-p38 expression remained low in the SAHA treated groups at 24 and 48 h.

CONCLUSION

Administration of SAHA is associated with attenuation of MAPK activation and alteration of inflammatory and anti-inflammatory markers in murine liver after a lethal LPS insult. The suppression of MAPK activity is rapid (within 3 h), and is sustained for up to 48 h post-treatment. These results may in part account for the improvement in survival shown in this model.

Disruption of cell spreading by the activation of MEK/ERK pathway is dependent on AP-1 activity

We previously reported that the disruption of cell spreading by v-Crk was dependent on the activation of the MEK/ERK pathway. Here we demonstrate that the activation of that pathway is sufficient to suppress cell spreading. The MEK/ERK pathway regulates the activity of various proteins including AP-1, which is a transcriptional factor composed of heterodimeric proteins. To examine whether AP-1 activity is required for the suppression of cell spreading by the activation of the MEK/ERK pathway, we expressed BATF, which is a negative regulator of AP-1. The expression of BATF clearly restored cell spreading that was suppressed by the activation of MEK/ERK pathway. In addition, a disrupted formation of stress fibers and focal adhesions by such activation was restored by the suppression of AP-1. Our results define an essential role of the MEK/ERK/AP-1 pathway in the disruption of actin cytoskeleton and cell spreading.

A potential role for adiponectin receptor 2 (AdipoR2) in the regulation of alcohol intake

The anterior cingulate cortex (ACC) has been implicated in alcohol and drug addiction. We recently identified the small G protein K-ras as an alcohol-regulated gene in the ACC by gene expression analysis. We show here that the adiponectin receptor 2 (AdipoR2) was differentially regulated by alcohol in the ACC in a K-ras-dependent manner. Additionally, withdrawal-associated increased drinking was attenuated in AdipoR2 null mice. Intracellular recordings revealed that adiponectin increased the excitability of ACC neurons and that this effect was more pronounced during alcohol withdrawal, suggesting that AdipoR2 signaling may contribute to increased ACC activity. Altogether, the data implicate K-ras-regulated pathways involving AdipoR2 in the cellular and behavioral actions of alcohol that may contribute to overactivity of the ACC during withdrawal and excessive alcohol drinking.

RasGRP1 is essential for ras activation by the tumor promoter 12-O-tetradecanoylphorbol-13-acetate in epidermal keratinocytes

RasGRP1 is a guanine nucleotide exchange factor for Ras that binds with high affinity to diacylglycerol analogs like the phorbol esters. Recently, we demonstrated a role for RasGRP1 in skin carcinogenesis and suggested its participation in the action of tumor-promoting phorbol esters like 12-O-tetradecanoylphorbol-13-acetate (TPA) on Ras pathways in epidermal cells. Given the importance of Ras in carcinogenesis, we sought to discern whether RasGRP1 was a critical pathway in Ras activation, using a RasGRP1 knockout (KO) mouse model to examine the response of keratinocytes to TPA. In contrast to the effect seen in wild type keratinocytes, Ras(GTP) levels were barely detected in RasGRP1 KO cells even after 60 min of exposure to phorbol esters. The lack of response was rescued by enforced expression of RasGRP1. Furthermore, small hairpin RNA-induced silencing of RasGRP1 abrogated the effect of TPA on Ras. Analysis of Ras isoforms showed that both H-Ras and N-Ras depended on RasGRP1 for activation by TPA, whereas activation of K-Ras could not be detected. Although RasGRP1 was dispensable for ERK activation in response to TPA, JNK activation was reduced in the KO keratinocytes. Notably, TPA-induced phosphorylation of JNK2, but not JNK1, was reduced by RasGRP1 depletion. These data identify RasGRP1 as a critical molecule in the activation of Ras by TPA in primary mouse keratinocytes and suggest JNK2 as one of the relevant downstream targets. Given the role of TPA as a skin tumor promoter, our findings provide additional support for a role for RasGRP1 in skin carcinogenesis.

Leucine-rich repeat kinase 2 induces alpha-synuclein expression via the extracellular signal-regulated kinase pathway

Mutations in leucine-rich repeat kinase 2 (LRRK2) are the most frequent cause of autosomal-dominant Parkinson's disease (PD). The second known autosomal-dominant PD gene (SNCA) encodes alpha-synuclein, which is deposited in Lewy bodies, the neuropathological hallmark of PD. LRRK2 contains a kinase domain with homology to mitogen-activated protein kinase kinase kinases (MAPKKKs) and its activity has been suggested to be a key factor in LRRK2-associated PD. Here we investigated the role of LRRK2 in signal transduction pathways to identify putative PD-relevant downstream targets. Over-expression of wild-type [wt]LRRK2 in human embryonic kidney HEK293 cells selectively activated the extracellular signal-regulated kinase (ERK) module. PD-associated mutants G2019S and R1441C, but not kinase-dead LRRK2, induced ERK phosphorylation to the same extent as [wt]LRRK2, indicating that this effect is kinase-dependent. However, ERK activation by mutant R1441C and G2019S was significantly slower than that for [wt]LRRK2, despite similar levels of expression. Furthermore, induction of the ERK module by LRRK2 was associated to a small but significant induction of SNCA, which was suppressed by treatment with the selective MAPK/ERK kinase inhibitor U0126. This pathway linking the two dominant PD genes LRRK2 and SNCA may offer an interesting target for drug therapy in both familial and sporadic disease.

Neurodegenerative influence of oxidative stress in the retina of a murine model of diabetes

AIMS/HYPOTHESIS

Diabetic retinopathy is a progressive neurodegenerative disease, but the underlying mechanism is still obscure. Here, we focused on oxidative stress in the retina, and analysed its influence on retinal neurodegeneration, using an antioxidant, lutein.

METHODS

C57BL/6 mice with streptozotocin-induced diabetes were constantly fed either a lutein-supplemented diet or a control diet from the onset of diabetes, and their metabolic data were recorded. In 1-month-diabetic mice, reactive oxygen species (ROS) in the retina were measured using dihydroethidium and visual function was evaluated by electroretinograms. Levels of activated extracellular signal-regulated kinase (ERK), synaptophysin and brain-derived neurotrophic factor (BDNF) were also measured by immunoblotting in the retina of 1-month-diabetic mice. In the retinal sections of 4-month-diabetic mice, histological changes, cleaved caspase-3 and TUNEL staining were analysed.

RESULTS

Lutein did not affect the metabolic status of the diabetic mice, but it prevented ROS generation in the retina and the visual impairment induced by diabetes. ERK activation, the subsequent synaptophysin reduction, and the BDNF depletion in the diabetic retina were all prevented by lutein. Later, in 4-month-diabetic mice, a decrease in the thickness of the inner plexiform and nuclear layers, and ganglion cell number, together with increase in cleaved caspase-3- and TUNEL-positive cells, were avoided in the retina of lutein-fed mice.

CONCLUSIONS/INTERPRETATION

The results indicated that local oxidative stress that has a neurodegenerative influence in the diabetic retina is prevented by constant intake of a lutein-supplemented diet. The antioxidant, lutein may be a potential therapeutic approach to protect visual function in diabetes.

Gender-dependent differential phosphorylation in the ERK signaling pathway is associated with increased MMP2 activity in rat aortic smooth muscle cells

BACKGROUND

The present experiments were conducted to explore the role of mitogen-activated protein kinase (MAPK) pathways, potential upstream regulators of MMPs, in abdominal aortic aneurysms (AAAs).

METHODS

Rat aortic smooth muscle cells (RASMCs) from males and females were treated with media containing interleukin (IL)-1beta (2 ng/mL), a concentration known to be present in AAAs. Levels of both total and phosphorylated (activated) extracellular signal-regulated kinase (ERK), c-Jun amino terminal kinase/stress-activated protein kinase (JNK/SAPK), and p38 were examined by Western blotting at various time intervals up to 60 min. Similar experiments were conducted following exposure of RASMCs to elastase (6 U/mL), a concentration known to induce AAA formation in rodents. Finally, media was assayed for MMP activity by zymography.

RESULTS

Total ERK (t-ERK) was consistently no different in females compared with males prior to or following IL-1beta exposure. In contrast, levels of phosphorylated ERK (p-ERK) were significantly higher in males than females throughout the postexposure period (P < 0.0001). Levels of t-p38, p-p38, and t-JNK were not altered in a gender-dependent manner. The lack of p-JNK levels detected in both male and female RASMCs did not allow for conclusions to be drawn regarding gender disparities in this pathway. Results were similar following RASMC elastase exposure, although t-ERK levels were consistently higher in females than males (P < 0.0001). Pro-MMP2 levels were significantly higher (P = 0.0035) in males than females at each time point following elastase exposure.

CONCLUSIONS

These data provide evidence implicating alterations in p-ERK signaling via the up-regulation of MMPs as a potential explanation for gender-related discrepancies in AAA formation.

Natural angiogenesis inhibitor signals through Erk5 activation of peroxisome proliferator-activated receptor gamma (PPARgamma)

Erk-5, a member of the MAPK superfamily, has a catalytic domain similar to Erk1/2 and a unique C-terminal domain enabling binding with transcription factors. Aberrant vascularization in the Erk5-null mice suggested a link to angiogenesis. Ectopic expression of constitutively active Erk5 blocks endothelial cell morphogenesis and causes HIF1-alpha destabilization/degradation. However the mechanisms by which endogenous Erk5 regulates angiogenesis remain unknown. We show that Erk5 and its activating kinase MEK5 are the upstream mediators of the anti-angiogenic signal by the natural angiogenesis inhibitor, pigment epithelial-derived factor (PEDF). We demonstrate that Erk5 phosphorylation allows activation of PPARgamma transcription factor by displacement of SMRT co-repressor. PPARgamma, in turn is critical for NFkappaB activation, PEDF-dependent apoptosis, and anti-angiogenesis. The dominant negative MEK5 mutant and Erk5 shRNA diminished PEDF-dependent apoptosis, inhibition of the endothelial cell chemotaxis, and angiogenesis. This is the first evidence of Erk5-dependent transduction of signals by endogenous angiogenesis inhibitors.

Poly(ADP-ribose) polymerase (PARP)-1-independent apoptosis-inducing factor (AIF) release and cell death are induced by eleostearic acid and blocked by alpha-tocopherol and MEK inhibition

Poly(ADP-ribose)polymerase-1 (PARP-1) is thought to be required for apoptosis-inducing factor (AIF) release from mitochondria in caspase-independent apoptosis. The mechanism by which AIF is released through PARP-1 remains unclear. Here, we provide evidence that PARP-1-independent AIF release and cell death are induced by a trienoic fatty acid, alpha-eleostearic acid (alpha-ESA). Alpha-ESA induced the caspase-independent and AIF-initiated apoptotic death of neuronal cell lines, independently of PARP-1 activation. The cell death was inhibited by the MEK inhibitor U0126 and by knockdown of MEK using small interfering RNA. However, inhibitors for JNK, p38 inhibitors, calpain, phospholipase A(2), and phosphatidylinositol 3-kinase, did not block cell death. AIF was translocated to the nucleus after the induction of apoptosis by alpha-ESA in differentiated PC12 cells without activating caspase-3 and PARP-1. The alpha-ESA-mediated cell death was not inhibited by PARP inhibitor 3,4-dihydro-5-[4-(1-piperidinyl)butoxyl]-1(2H)-isoquinoline and by knockdown of PARP-1 using small interfering RNA. Unlike N-methyl-N'-nitro-N-nitrosoguanidine treatment, histone-phosphorylated histone 2AX was not phosphorylated by alpha-ESA, which suggests no DNA damage. Overexpression of Bcl-2 did not inhibit the cell death. alpha-ESA caused a small quantity of superoxide production in the mitochondria, resulting in the reduction of mitochondrial membrane potential, both of which were blocked by a trace amount of alpha-tocopherol localized in the mitochondria. Our results demonstrate that alpha-ESA induces PARP-1-independent AIF release and cell death without activating Bax, cytochrome c, and caspase-3. MEK is also a key molecule, although the link between ERK, AIF release, and cell death remains unknown. Finding molecules that regulate AIF release may be an important therapeutic target for the treatment of neuronal injury.

Zinc deficiency and neurodevelopment: the case of neurons

Zinc is essential for normal brain development. Gestational severe zinc deficiency can lead to overt fetal brain malformations. Although not teratogenic, suboptimal zinc nutrition during gestation can have long-term effects on the offspring's nervous system. This article will review current knowledge on the role of zinc in modulating neurogenesis and neuronal apoptosis as well as the proposed underlying mechanisms. A decrease in neuronal zinc causes cell cycle arrest, which in part involves a deregulation of select signals (ERK1/2, p53, and NF-kappaB). Zinc deficiency also induces apoptotic neuronal death through the intrinsic (mitochondrial) pathway, which can be triggered by the activation of the zinc-regulated enzyme caspase-3, and as a consequence of abnormal regulation of prosurvival signals (ERK1/2 and NF-kappaB). Alterations in the finely tuned processes of neurogenesis, neuronal migration, differentiation, and apoptosis, which involve the developmental shaping of the nervous system, could have a long-term impact on brain health. Zinc deficiency during gestation, even at the marginal levels observed in human populations, could increase the risk for behavioral/neurological disorders in infancy, adolescence, and adulthood.

Insulin augments gonadotropin-releasing hormone induction of translation in LbetaT2 cells

The integrated signaling of insulin and gonadotropin-releasing hormone in the pituitary gonadotropes may have a profound bearing on reproductive function, although the cross-receptor signaling mechanisms are unclear. We demonstrate that the insulin receptor is constitutively localized to non-caveolar lipid raft microdomains in the pituitary gonadotrope cell line LbetaT2. The localization to rafts is consistent with similar localization of the GnRH receptor. Insulin receptor phosphorylation occurs in raft domains and activates the downstream signaling targets Insulin Receptor Substrate1 and Akt/Protein Kinase B. Although insulin alone does not strongly activate the extracellular signal-regulated kinase second messenger cascade, co-stimulation potentiates the phosphorylation of the extracellular signal-regulated kinase by gonadotropin-releasing hormone. The co-stimulatory effect of insulin and gonadotropin-releasing hormone is also evident in increased activation of cap-dependent translation. In contrast, co-stimulation attenuates Akt/Protein Kinase B activation. Our results show that both gonadotropin-releasing hormone and insulin are capable of mutually altering their respective regulatory signaling cascades. We suggest that this provides a mechanism to integrate neuropeptide and energy homeostatic signals to modulate reproductive function.

Spots and stripes: pleomorphic patterning of stem cells via p-ERK-dependent cell chemotaxis shown by feather morphogenesis and mathematical simulation

A key issue in stem cell biology is the differentiation of homogeneous stem cells towards different fates which are also organized into desired configurations. Little is known about the mechanisms underlying the process of periodic patterning. Feather explants offer a fundamental and testable model in which multi-potential cells are organized into hexagonally arranged primordia and the spacing between primordia. Previous work explored roles of a Turing reaction-diffusion mechanism in establishing chemical patterns. Here we show that a continuum of feather patterns, ranging from stripes to spots, can be obtained when the level of p-ERK activity is adjusted with chemical inhibitors. The patterns are dose-dependent, tissue stage-dependent, and irreversible. Analyses show that ERK activity-dependent mesenchymal cell chemotaxis is essential for converting micro-signaling centers into stable feather primordia. A mathematical model based on short-range activation, long-range inhibition, and cell chemotaxis is developed and shown to simulate observed experimental results. This generic cell behavior model can be applied to model stem cell patterning behavior at large.

Tregs utilize beta-galactoside-binding protein to transiently inhibit PI3K/p21ras activity of human CD8+ T cells to block their TCR-mediated ERK activity and proliferation

Regulatory T cells (Tregs) and beta-galactoside-binding protein (betaGBP), a regulatory protein often found expressed at sites of immunological privilege, have similar functions. Their presence affects the outcome of harmful autoimmunity and cancers, including experimental autoimmune encephalomyelitis and malignant gliomas. Here we report a novel pathway by which Tregs express and utilize betaGBP to control CD8(+) T cell responses partially activating TCR signaling but blocking PI3K activity. As a result, this leads to a loss of p21(ras), ERK and Akt activities despite activation of TCR proximal signals, such as phosphorylation of CD3zeta, Zap70, Lat and PKCtheta. Although non-processive TCR signaling often leads to cell anergy, Tregs/betaGBP did not affect cell viability. Instead, betaGBP/Tregs transiently prevented activation of CD8(+) T cells with self-antigens, while keeping their responses to xenogeneic antigens unaffected.

Induction of protein tyrosine kinase 6 in mouse intestinal crypt epithelial cells promotes DNA damage-induced apoptosis

BACKGROUND & AIMS

Protein tyrosine kinase 6 (PTK6) is expressed in epithelial linings of the gastrointestinal tract. PTK6 sensitizes the nontransformed Rat1a fibroblast cell line to apoptotic stimuli. The aim of this study was to determine if PTK6 regulates apoptosis in vivo after DNA damage in the small intestine.

METHODS

Wild-type and Ptk6(-/-) mice were subjected to gamma-irradiation; intestinal tissues were collected, protein was isolated, and samples were fixed for immunohistochemical analyses at 0, 6, and 72 hours after the mice were irradiated. Expression of PTK6 was examined in the small intestine before and after irradiation. Apoptosis and proliferation were compared between wild-type and Ptk6(-/-) mice. Expression and activation of prosurvival signaling proteins were assessed.

RESULTS

Irradiation induced PTK6 in crypt epithelial cells of the small intestine in wild-type mice. Induction of PTK6 corresponded with DNA damage-induced apoptosis in the wild-type small intestine. Following irradiation, the apoptotic response was impaired in the intestinal crypts of Ptk6(-/-) mice. Increased activation of AKT and extracellular signal-regulated kinase (ERK)1/2 and increased inhibitory phosphorylation of the proapoptotic protein BAD were detected in Ptk6(-/-) mice after irradiation. In response to the induction of apoptosis, compensatory proliferation increased in the small intestines of wild-type mice but not in Ptk6(-/-) mice at 6 hours after irradiation.

CONCLUSIONS

PTK6 is a stress-induced kinase that promotes apoptosis by inhibiting prosurvival signaling. After DNA damage, induction of PTK6 is required for efficient apoptosis and inhibition of AKT and ERK1/2.