JIP1 regulates neuronal apoptosis in response to stress

VRK2 kinase pathogenic pathways in cancer and neurological diseases

The VRK2 ser-thr kinase, belonging to the dark kinome, is implicated in the pathogenesis of cancer progression, neurological and psychiatric diseases. The VRK2 gene codes for two isoforms. The main isoform (VRK2A) is mainly located in the cytoplasm, and anchored to different types of membranes, such as the endoplasmic reticulum, mitochondria and nuclear envelope. The VRK2A isoform interacts with signaling modules assembled on scaffold proteins such as JIP1 or KSR1, forming stable complexes and blocking the activation of regulatory signaling pathways by altering their intracellular localization and the balance among them. VRK2 regulates apoptosis, nuclear membrane organization, immune responses, and Cajal bodies. Wild-type VRK2 is overexpressed in tumors and contributes to cancer development. In cells and tumors with low levels of nuclear VRK1, VRK2 generates by alternative splicing a shorter isoform (VRK2B) that lacks the C-terminal hydrophobic tail and permits its relocation to nuclei. Furthermore, rare VRK2 gene variants are associated with different neurological or psychiatric diseases such as schizophrenia, epilepsy, bipolar disorder, depression, autism, circadian clock alterations and insomnia, but their pathogenic mechanism is unknown. These diseases are a likely consequence of an altered balance among different signaling pathways that are regulated by VRK2.

The AICD interactome: implications in neurodevelopment and neurodegeneration

The pathophysiological mechanism involving the proteolytic processing of amyloid precursor protein (APP) and the generation of amyloid plaques is of significant interest in research on Alzheimer's disease (AD). The increasing significance of the downstream AD-related pathophysiological mechanisms has sparked research interest in other products of the APP processing cascades, including the APP intracellular domain (AICD). The potential importance of AICD in various cellular processes in the central nervous system has been established through the identification of its interactors. The interaction between AICD and its physiological binding partners is implicated in cellular events including regulation of transcriptional activity, cytoskeletal dynamics, neuronal growth, APP processing and cellular apoptosis. On the contrary, AICD is also implicated in neurodegeneration, which is a potential outcome of the functional fluctuation of AICD-mediated neuronal processes within the neuronal network. In this review, we summarize the neuronal functions and pathological manifestations of the dynamic AICD interaction network.

Protective effect of Cornuside on OGD/R injury in SH-SY5Y cells and its underlying mechanism

Apoptosis induced by oxygen-glucose deprivation/reperfusion (OGD/R) injury is the main cause of neuronal damage. Cornuside, a small-molecule cyclic enol ether terpene glycoside extracted from the dried fruit of mature Cornus officinalis Sieb. et Zucc., has vigorous anti-apoptotic and antioxidant effects. Previous studies have shown that Cornuside can reduce apoptosis and improve mitochondrial energy metabolism in cortical neurons of rats by inhibiting caspase-3 and calcium release. In this study, we treated SH-SY5Y cells with OGD/R to simulated ischemia/reperfusion (I/R) injury. Using high-throughput transcriptome sequencing, differentially expressed genes were analyzed in the OGD/R group versus the OGD/R + Cornuside (10 μmol/L) group to explore the neuroprotective mechanisms of Cornuside. The differentially expressed genes were mainly enriched in apoptosis signaling pathway, cell cycle, DNA damage and repair, and p38/JNK MAPK and p53 signaling pathways. The results showed that OGD/R significantly reduced the survival of SH-SY5Y cells, induced apoptosis, disrupted the nucleus, promoted the release of ROS, and led to cell cycle arrest. Cornuside reversed OGD/R-induced damage. By upregulating MAPK8IP1 and downregulating MAPK14, TP53INP1, and signaling pathway-related proteins (p-p38, p-JNK, and p-p53), Cornuside ameliorated cell damage induced by p38/JNK MAPK and p53 signaling pathways. Cornuside also downregulated apoptosis regulatory proteins (Bax, Bcl-2, caspase-3, caspase-9, and cytochrome c) and cell cycle regulatory proteins (cyclin B1, cyclin E, and p21).

Colocalization and Interaction Study of Neuronal JNK3, JIP1, and β-Arrestin2 Together with PSD95

c-Jun N-terminal kinases (JNKs) are stress-activated serine/threonine protein kinases belonging to the mitogen-activated protein kinase (MAPK) family. Among them, JNK3 is selectively expressed in the central nervous system, cardiac smooth muscle, and testis. In addition, it is the most responsive JNK isoform to stress stimuli in the brain, and it is involved in synaptic dysfunction, an essential step in neurodegenerative processes. JNK3 pathway is organized in a cascade of amplification in which signal transduction occurs by stepwise, highly controlled phosphorylation. Since different MAPKs share common upstream activators, pathway specificity is guaranteed by scaffold proteins such as JIP1 and β-arrestin2. To better elucidate the physiological mechanisms regulating JNK3 in neurons, and how these interactions may be involved in synaptic (dys)function, we used (i) super-resolution microscopy to demonstrate the colocalization among JNK3-PSD95-JIP1 and JNK3-PSD95-β-arrestin2 in cultured hippocampal neurons, and (ii) co-immunoprecipitation techniques to show that the two scaffold proteins and JNK3 can be found interacting together with PSD95. The protein-protein interactions that govern the formation of these two complexes, JNK3-PSD95-JIP1 and JNK3-PSD95-β-arrestin2, may be used as targets to interfere with their downstream synaptic events.

JNK3 as Therapeutic Target and Biomarker in Neurodegenerative and Neurodevelopmental Brain Diseases

The c-Jun N-terminal kinase 3 (JNK3) is the JNK isoform mainly expressed in the brain. It is the most responsive to many stress stimuli in the central nervous system from ischemia to Aβ oligomers toxicity. JNK3 activity is spatial and temporal organized by its scaffold protein, in particular JIP-1 and β-arrestin-2, which play a crucial role in regulating different cellular functions in different cellular districts. Extensive evidence has highlighted the possibility of exploiting these adaptors to interfere with JNK3 signaling in order to block its action. JNK plays a key role in the first neurodegenerative event, the perturbation of physiological synapse structure and function, known as synaptic dysfunction. Importantly, this is a common mechanism in many different brain pathologies. Synaptic dysfunction and spine loss have been reported to be pharmacologically reversible, opening new therapeutic directions in brain diseases. Being JNK3-detectable at the peripheral level, it could be used as a disease biomarker with the ultimate aim of allowing an early diagnosis of neurodegenerative and neurodevelopment diseases in a still prodromal phase.

Genetic and Molecular Biology of Multiple Sclerosis Among Iranian Patients: An Overview

Multiple sclerosis (MS) is one if the common types of autoimmune disorders in developed countries. Various environmental and genetic factors are associated with initiation and progression of MS. It is believed that the life style changes can be one of the main environmental risk factors. The environmental factors are widely studied and reported, whereas minority of reports have considered the role of genetic factors in biology of MS. Although Iran is a low-risk country in the case of MS prevalence, it has been shown that there was a dramatically rising trend of MS prevalence among Iranian population during recent decades. Therefore, it is required to assess the probable MS risk factors in Iran. In the present study, we summarized all of the reported genes until now which have been associated with MS susceptibility among Iranian patients. To clarify the probable molecular biology of MS progression, we categorized these reported genes based on their cellular functions. This review paves the way of introducing a specific population-based diagnostic panel of genetic markers among the Iranian population for the first time in the world.

Unravelling the genetic basis of schizophrenia and bipolar disorder with GWAS: A systematic review

OBJECTIVES

To systematically review findings of GWAS in schizophrenia (SZ) and in bipolar disorder (BD); and to interpret findings, with a focus on identifying independent replications.

METHOD

PubMed search, selection and review of all independent GWAS in SZ or BD, published since March 2011, i.e. studies using non-overlapping samples within each article, between articles, and with those of the previous review (Li et al., 2012).

RESULTS

From the 22 GWAS included in this review, the genetic associations surviving standard GWAS-significance were for genetic markers in the regions of ACSL3/KCNE4, ADCY2, AMBRA1, ANK3, BRP44, DTL, FBLN1, HHAT, INTS7, LOC392301, LOC645434/NMBR, LOC729457, LRRFIP1, LSM1, MDM1, MHC, MIR2113/POU3F2, NDST3, NKAPL, ODZ4, PGBD1, RENBP, TRANK1, TSPAN18, TWIST2, UGT1A1/HJURP, WHSC1L1/FGFR1 and ZKSCAN4. All genes implicated across both reviews are discussed in terms of their function and implication in neuropsychiatry.

CONCLUSION

Taking all GWAS to date into account, AMBRA1, ANK3, ARNTL, CDH13, EFHD1 (albeit with different alleles), MHC, PLXNA2 and UGT1A1 have been implicated in either disorder in at least two reportedly non-overlapping samples. Additionally, evidence for a SZ/BD common genetic basis is most strongly supported by the implication of ANK3, NDST3, and PLXNA2.

Vaccinia Related Kinase 2 (VRK2) expression in neurological disorders: schizophrenia, epilepsy and multiple sclerosis

BACKGROUND

Schizophrenia (SCZ), epilepsy and Multiple Sclerosis (MS) are neurological disorders with increasing prevalence disturb the patients' lives and are regarded as burdens to the society. As multifactorial disorders, genetic susceptibility factors are involved in their pathogenesis. The Vaccinia-Related Kinase 2 (VRK2) gene codes for a serine threonine kinase recently reported to be contributed in the pathogenesis of some neurological disorders. In the present case-control study we compared the VRK2 gene expression in peripheral blood samples from SCZ, epilepsy and MS patients with normal subjects.

METHOD

A total of 300 subjects comprising 50 patients in each disease category (SCZ, epilepsy and MS) as well as 150 healthy individuals (50 matched controls for each disorder) participated in the current study.

RESULT

The VRK2 blood mRNA expression level was measured using the TaqMan real time PCR. The results demonstrated significant down-regulation of VRK2 gene in SCZ (P<0.0001), epilepsy (P=0.008) and MS (P=0.029) compared with the healthy subjects.

CONCLUSION

Consequently, VRK2 is suggested as a candidate gene for neurological disorders through its role in signaling pathway, the neuronal loss and stress response.

Anti-inflammatory Effect of Glucagon Like Peptide-1 Receptor Agonist, Exendin-4, through Modulation of IB1/JIP1 Expression and JNK Signaling in Stroke

Glucagon like peptide-1 (GLP-1) stimulates glucose-dependent insulin secretion. Dipeptidyl peptidase-4 (DPP-4) inhibitors, which block inactivation of GLP-1, are currently in clinical use for type 2 diabetes mellitus. Recently, GLP-1 has also been reported to have neuroprotective effects in cases of cerebral ischemia. We therefore investigated the neuroprotective effects of GLP-1 receptor (GLP-1R) agonist, exendin-4 (ex-4), after cerebral ischemia-reperfusion injury. Transient middle cerebral artery occlusion (tMCAO) was induced in rats by intracerebroventricular (i.c.v.) administration of ex-4 or ex9-39. Oxygen-glucose deprivation was also induced in primary neurons, bEnd.3 cells, and BV-2. Ischemia-reperfusion injury reduced expression of GLP-1R. Additionally, higher oxidative stress in SOD2 KO mice decreased expression of GLP-1R. Downregulation of GLP-1R by ischemic injury was 70% restored by GLP-1R agonist, ex-4, which resulted in significant reduction of infarct volume. Levels of intracellular cyclic AMP, a second messenger of GLP-1R, were also increased by 2.7-fold as a result of high GLP-1R expression. Moreover, our results showed that ex-4 attenuated pro-inflammatory cyclooxygenase-2 (COX-2) and prostaglandin E₂ after MCAO. C-Jun NH₂ terminal kinase (JNK) signaling, which stimulates activation of COX-2, was 36% inhibited by i.c.v. injection of ex-4 at 24 h. Islet-brain 1 (IB1), a scaffold regulator of JNK, was 1.7-fold increased by ex-4. GLP-1R activation by ex-4 resulted in reduction of COX-2 through increasing IB1 expression, resulting in anti-inflammatory neuroprotection during stroke. Our study suggests that the anti-inflammatory action of GLP-1 could be used as a new strategy for the treatment of neuroinflammation after stroke accompanied by hyperglycemia.

Effects of VRK2 (rs2312147) on white matter connectivity in patients with schizophrenia

Recent genome-wide association studies of schizophrenia reported a novel risk variant, rs2312147 at vaccinia-related kinase 2 gene (VRK2), in multiple Asian and European samples. However, its effect on the brain structure in schizophrenia is little known. We analyzed the brain structure of 36 schizophrenia patients and 18 healthy subjects with regard to rs2312147 genotype groups. Brain magnetic resonance scans for gray matter (GM) and white matter (WM) analysis, and genotype analysis for VRK2 rs2312147, were conducted. The Positive and Negative Syndrome Scale and the Digit Symbol Test were assessed for schizophrenia patients. There was no significant difference in either GM volume or WM connectivity with regard to rs2312147 genotype in healthy subjects. In contrast, we found significant differences in the WM connectivity between rs2312147 CC and CT/TT genotype groups of schizophrenia patients. The related brain areas included the splenium of corpus callosum, the left occipital lobe WM, the internal capsule (left anterior limb and right retrolenticular part), the bilateral temporal lobe WM, the left fornix/stria terminalis, the left cingulate gyrus WM, and the left parietal lobe WM. Voxelwise correlation analysis revealed that the Digit Symbol Test scores (age corrected) correlated with the fractional anisotropy in WM tracts that previously showed significant group differences between the CT/TT and CC genotypes in the rs2312147 CT/TT genotype group, while no significant correlation was found in the CC genotype group. Our data may provide evidence for the effect of VRK2 on WM connectivity in patients with schizophrenia.

Sh3rf2/POSHER protein promotes cell survival by ring-mediated proteasomal degradation of the c-Jun N-terminal kinase scaffold POSH (Plenty of SH3s) protein

We report that Sh3rf2, a homologue of the pro-apoptotic scaffold POSH (Plenty of SH3s), acts as an anti-apoptotic regulator for the c-Jun N-terminal kinase (JNK) pathway. siRNA-mediated knockdown of Sh3rf2 promotes apoptosis of neuronal PC12 cells, cultured cortical neurons, and C6 glioma cells. This death appears to result from activation of JNK signaling. Loss of Sh3rf2 triggers activation of JNK and its target c-Jun. Also, apoptosis promoted by Sh3rf2 knockdown is inhibited by dominant-negative c-Jun as well as by a JNK inhibitor. Investigation of the mechanism by which Sh3rf2 regulates cell survival implicates POSH, a scaffold required for activation of pro-apoptotic JNK/c-Jun signaling. In cells lacking POSH, Sh3rf2 knockdown is unable to activate JNK. We further find that Sh3rf2 binds POSH to reduce its levels by a mechanism that requires the RING domains of both proteins and that appears to involve proteasomal POSH degradation. Conversely, knockdown of Sh3rf2 promotes the stabilization of POSH protein and activation of JNK signaling. Finally, we show that endogenous Sh3rf2 protein rapidly decreases following several different apoptotic stimuli and that knockdown of Sh3rf2 activates the pro-apoptotic JNK pathway in neuronal cells. These findings support a model in which Sh3rf2 promotes proteasomal degradation of pro-apoptotic POSH in healthy cells and in which apoptotic stimuli lead to rapid loss of Sh3rf2 expression, and consequently to stabilization of POSH and JNK activation and cell death. On the basis of these observations, we propose the alternative name POSHER (POSH-eliminating RING protein) for the Sh3rf2 protein.

Common variants at VRK2 and TCF4 conferring risk of schizophrenia

Common sequence variants have recently joined rare structural polymorphisms as genetic factors with strong evidence for association with schizophrenia. Here we extend our previous genome-wide association study and meta-analysis (totalling 7 946 cases and 19 036 controls) by examining an expanded set of variants using an enlarged follow-up sample (up to 10 260 cases and 23 500 controls). In addition to previously reported alleles in the major histocompatibility complex region, near neurogranin (NRGN) and in an intron of transcription factor 4 (TCF4), we find two novel variants showing genome-wide significant association: rs2312147[C], upstream of vaccinia-related kinase 2 (VRK2) [odds ratio (OR) = 1.09, P = 1.9 × 10(-9)] and rs4309482[A], between coiled-coiled domain containing 68 (CCDC68) and TCF4, about 400 kb from the previously described risk allele, but not accounted for by its association (OR = 1.09, P = 7.8 × 10(-9)).

Disassembly of the JIP1/JNK molecular scaffold by caspase-3-mediated cleavage of JIP1 during apoptosis

We report here the cleavage of the c-Jun N-terminal Kinase (JNK) pathway scaffold protein, JNK Interacting Protein-1 (JIP1), by caspases during both Tumour Necrosis Factor-Related Apoptosis-Inducing Ligand (TRAIL) and staurosporine-induced apoptosis in HeLa cells. During the initiation of apoptosis, maximal JNK activation is observed when JIP1 is intact, whereas cleavage of JIP1 correlates with JNK inactivation and progression of apoptosis. JIP1 is cleaved by caspase-3 at two sites, leading to disassembly of the JIP1/JNK complex. Inhibition of JIP1 cleavage by the caspase-3 inhibitor DEVD.fmk inhibits this disassembly, and is accompanied by sustained JNK activation. These data suggest that TRAIL and staurosporine induce JNK activation in a caspase-3-independent manner and that caspase-3-mediated JIP1 cleavage plays a role in JNK inactivation via scaffold disassembly during the execution phase of apoptosis. Caspase-mediated cleavage of JIP scaffold proteins may therefore represent an important mechanism for modulation of JNK signalling during apoptotic cell death.

AP-1 inhibitory peptides are neuroprotective following acute glutamate excitotoxicity in primary cortical neuronal cultures

Neuronal cell death caused by glutamate excitotoxicity is prevalent in various neurological disorders and has been associated with the transcriptional activation of activator protein-1 (AP-1). In this study, we tested 19 recently isolated AP-1 inhibitory peptides, fused to the cell penetrating peptide TAT, for their efficacy in preventing cell death in cortical neuronal cultures following glutamate excitotoxicity. Five peptides (PYC19D-TAT, PYC35D-TAT, PYC36D-TAT, PYC38D-TAT, PYC41D-TAT) displayed neuroprotective activity in concentration responses in both l- and retro-inverso d-isoforms with increasing levels of neuroprotection peaking at 83%. Interestingly, the D-TAT peptide displayed a neuroprotective effect increasing neuronal survival to 25%. Using an AP-1 luciferase reporter assay, we confirmed that the AP-1 inhibitory peptides reduce AP-1 transcriptional activation, and that c-Jun and c-Fos mRNA following glutamate exposure is reduced. In addition, following glutamate exposure the AP-1 inhibitory peptides decreased calpain-mediated alpha-fodrin cleavage, but not neuronal calcium influx. Finally, as neuronal death following glutamate excitotoxicity was transcriptionally independent (actinomycin D insensitive), our data indicate that activation of AP-1 proteins can induce cell death via non-transcriptional pathways. Thus, these peptides have potential application as therapeutics directly or for the rational design of small molecule inhibitors in both apoptotic and necrotic neuronal death associated with AP-1 activation.

Burn-related metabolic and signaling changes in rat brain

Postburn alterations in the morphology and metabolism of brain tissue have been previously reported. It was demonstrated in our previous study that thermal injury decreased glucose usage in rat brain during the ebb phase. The cellular and molecular signaling events that trigger the pathophysiologic alterations, however, have not yet been characterized. In the present report, the authors have examined the effect of burn injury on mitogen-activated protein kinases (MAPKs) activities and insulin signaling in the brain tissue. Rats were subjected to 50% total body surface area full thickness scald injury. Brain samples were collected at 6 hours after injury. Tissue lysates were analyzed for MAPKs activities, insulin receptor substrate (IRS)-1 expression, and Akt activity which were determined by western blot and immunoprecipitation. Burn injury stimulated the stress-responsive components, SAPK/JNK, p38 MAP kinase and p44/42 MAP kinase, and increased IRS-1 expression and Akt activity. There was no change, however, on the phosphorylation of Ser307 of IRS-1 in brain tissue. The present data is consistent with the hypothesis that activation of the three major MAPKs pathways appears to be events involved in the mechanisms of burn injury induced insulin resistance and encephalopathy. Changes in signal transduction pathways in the brain after burn injury provide the underlying molecular mechanism of neurologic abnormalities (burn encephalopathy) that occur in burn patients.

The docking properties of SHIP2 influence both JIP1 tyrosine phosphorylation and JNK activity

SHIP2 (SH2-containing inositol polyphosphate 5-phosphatase 2) is an ubiquitously expressed phosphatidylinositol (3,4,5)-trisphosphate (PtdIns(3,4,5)P(3)) 5-phosphatase which contains various motifs susceptible to mediate protein-protein interaction. In cell models, evidence has been provided that SHIP2 plays a role in insulin and growth factor signaling, cytoskeletal organization, cell adhesion and migration. Herein we describe the c-Jun NH2-terminal kinase (JNK)-interacting protein 1 (JIP1) as a new protein partner of SHIP2. The interaction between SHIP2 and JIP1 was confirmed in both overexpression systems and native cells. Without modifying the association of JIP1 with the MAPKs in the scaffold complex and with no apparent change of Akt phosphorylation, SHIP2 positively modulated the MLK3/JIP1-mediated JNK1 activation. Moreover, SHIP2 positively regulated the tyrosine phosphorylation of JIP1. This up-regulation was prevented by inhibitors of the Src family and Abl kinases, PP2 and Glivec. The effects of SHIP2 on JNK activity and JIP1 tyrosine phosphorylation were independent of the SHIP2 phosphoinositide 5-phosphatase activity, as similar results were obtained when using a SHIP2 catalytic inactive mutant instead of wild-type SHIP2. Together, these data suggest that by its docking properties, SHIP2 can modulate JIP1-mediated JNK pathway signaling.

Modulation of interleukin-1 transcriptional response by the interaction between VRK2 and the JIP1 scaffold protein

Background

Cellular biological responses to specific stimulation are determined by a balance among signaling pathways. Protein interactions are likely to modulate these pathways. Vaccinia-related kinase-2 (VRK2) is a novel human kinase that can modulate different signaling pathways.

Principal Findings

We report that in vivo, the activity of JIP1-JNK complexes is downregulated by VRK2 in response to interleukin-1β. Also the reduction of endogenous VRK2 with shRNA increases the transcriptional response to IL-1β. The JIP1 scaffold protein assembles three consecutive members of a given MAPK pathway forming signaling complexes and their signal can be modulated by interactions with regulatory proteins that remain to be identified. Knocking-down JIP1 with siRNA resulted in elimination of the AP1 transcriptional response to IL-1β. VRK2, a member of novel Ser-Thr kinase family, is able to stably interact with JIP1, TAK1 and MKK7, but not JNK, and can be isolated forming oligomeric complexes with different proportions of TAK1, MKK7β1 and JNK. JIP1 assembles all these proteins in an oligomeric signalosome. VRK2 binding to the JIP1 signalosome prevents the association of JNK and results in a reduction in its phosphorylation and downregulation of AP1-dependent transcription.

Conclusions/Significance

This work suggests that the intracellular level of VRK2 protein can modulate the flow through a signaling pathway and alter the response from a receptor that can be distributed by more than one pathway, and thus contribute to the cellular specificity of the response by forming alternative signaling complexes. Furthermore, the effect might be more general and affect other signaling routes assembled on the JIP1 scaffold protein for which a model is proposed.

Screening of AMP-activated protein kinase alpha2 subunit interacting proteins by bacterial two-hybrid system

AMP-activated protein kinase (AMPK) is a ubiquitous eukaryotic protein kinase regulating cellular metabolism and energy demand. In brain AMPK plays a role as a multidimensional energy sensor and AMPK alpha2 subunit is expressed at higher levels than AMPK alpha1 subunit. In order to identify potential targets of AMPK in brain, we perform bacterial two-hybrid screening of a rat fetal brain cDNA library using AMPK alpha2 subunit as bait. Here, we present seven potential AMPK alpha2 subunit interacting proteins, including 6-phosphofructo-1-kinase (PFK-1), polyubiquitin, cytochrome c oxidase subunit I (COX I), heat shock protein 8 (HSP8), HLA-B-associated transcript 3 (BAT3) isoform 1, protein tyrosine phosphatase receptor type D (PTPRD) and islet-brain 1 (IB1). They are involved in glycolysis, protein degradation, mitochondrial electron transport and apoptosis pathways participating in energy regulation directly or indirectly. These data may provide new insight into further studying the pathways of AMPK energy regulation in brain and possible mechanisms of AMPK-mediated neuroprotective effect.

Vaccinia-related kinase 2 modulates the stress response to hypoxia mediated by TAK1

Hypoxia represents a major stress that requires an immediate cellular response in which different signaling pathways participate. Hypoxia induces an increase in the activity of TAK1, an atypical mitogen-activated protein kinase kinase kinase (MAPKKK), which responds to oxidative stress by triggering cascades leading to the activation of c-Jun N-terminal kinase (JNK). JNK activation by hypoxia requires assembly with the JIP1 scaffold protein, which might also interact with other intracellular proteins that are less well known but that might modulate MAPK signaling. We report that TAK1 is able to form a stable complex with JIP1 and thus regulate the activation of JNK, which in turn determines the cellular stress response to hypoxia. This activation of TAK1-JIP1-JNK is suppressed by vaccinia-related kinase 2 (VRK2). VRK2A is able to interact with TAK1 by its C-terminal region, forming stable complexes. The kinase activity of VRK2 is not necessary for this interaction or the downregulation of AP1-dependent transcription. Furthermore, reduction of the endogenous VRK2 level with short hairpin RNA can increase the response induced by hypoxia, suggesting that the intracellular levels of VRK2 can determine the magnitude of this stress response.

Low-Density Lipoprotein Receptor-Related Protein 8 (LRP8) Is Upregulated in Granulosa Cells of Bovine Dominant Follicle: Molecular Characterization and Spatio-Temporal Expression Studies1

The low-density lipoprotein (LDL) receptor-related protein 8 (LRP8) is a member of the LDL receptor family that participates in endocytosis and signal transduction. We cloned the full-length bovine LRP8 cDNA in granulosa cells (GC) of the dominant follicle (DF) as well as several LRP8 mRNA splicing variants, including a variant that contains a proline-rich cytoplasmic insert (A759-K817) that is involved in intracellular signaling. Expression of the A759-K817 variant was analyzed in the GC of follicles at different developmental stages: the small follicle (SF; 2-4 mm), the DF at Day 5 (D5) of the estrus cycle, ovulatory follicles (OF) 24 h after hCG injection, and corpora lutea (CL) at D5. RT-PCR analysis showed that expression was predominant in the GC of DF compared to other follicles and CL (P<0.0001), whereas the expression of other related receptors, such as LDLR and VLDLR, did not show differences. Temporal analyses of follicular walls from the OF following hCG treatment revealed a decrease in LRP8 mRNA expression starting 12 h post-hCG treatment (P<0.0001). LRP8 protein was exclusively localized to the GC, with higher levels in the DF than in the SF (P<0.05). RELN mRNA, which encodes an LRP8 ligand, was highly expressed in the theca of the DF as compared to the OF (P<0.004), whereas MAPK8IP1 mRNA, which encodes an LRP8 intracellular interacting partner, is expressed in the GC of the DF. These results demonstrate the differential expression patterns of LRP8, RELN, and MAPK8IP1 mRNAs during final follicular growth and ovulation, and suggest that a RELN/LRP8/MAPK8IP1 paracrine interaction regulates follicular growth.

JNK and AP-1 mediate apoptosis induced by bortezomib in HepG2 cells via FasL/caspase-8 and mitochondria-dependent pathways

The proteasome inhibitor bortezomib is an efficacious apoptotic agent in many tumor cells. This paper shows that bortezomib induced apoptosis in human hepatoma HepG2 cells associated with many modifications in the expression of survival or death factors. Although bortezomib increased the level of the protective factors HSP70 and HSP27, the effects of the drug that favour cell death were predominant. These events include accumulation of c-Jun, phospho-c-Jun and p53; increase in FasL level with activation of caspase-8; changes related to members of Bcl-2 family with increase in the level of pro-apoptotic members and decrease in that of anti-apoptotic ones; dissipation of mitochondrial potential with cytochrome c release and activation of caspase-3. In contrast, Chang liver cells exhibited a very low susceptibility to bortezomib-induced apoptosis, which was accompanied by modest modifications in the expression of apoptotic factors. In HepG2 cells bortezomib markedly increased AP-1 activity and the expression of its transcriptional targets such as c-Jun, FasL, BimEL, which are involved in apoptosis. Moreover, AP-1 induced its own production by increasing c-Jun content in the composition of the same AP-1 complex. In addition, bortezomib caused activation of JNK1, which in turn increased the level of phospho-c-Jun as well as stimulated the activation of caspase-3 and t-Bid, two fundamental apoptotic factors. Interestingly, siRNA silencing of c-Jun or JNK1 reduced HepG2 cell susceptibility to apoptosis and prevented the increase in AP-1 activity. Both JNK-1 and AP-1 thus exerted a crucial role in bortezomib-induced apoptosis. Differently, in Chang liver cells the different composition of AP-1 complex as well as the failure of JNK activation seemed to be responsible for the low susceptibility to apoptosis. Given the high susceptibility of hepatoma cells to bortezomib, our results suggest the potential application of this compound in clinical trials for liver cancers.