ETS-domain transcription factor Elk-1 mediates neuronal survival: SMN as a potential target

Prolonged STAT1 activation in neurons drives a pathological transcriptional response

Neurons require physiological IFN-γ signaling to maintain central nervous system (CNS) homeostasis, however, pathological IFN-γ signaling can cause CNS pathologies. The downstream signaling mechanisms that cause these drastically different outcomes in neurons has not been well studied. We hypothesized that different levels of IFN-γ signaling in neurons results in differential activation of its downstream transcription factor, signal transducer and activator of transduction 1 (STAT1), causing varying outcomes. Using primary cortical neurons, we showed that physiological IFN-γ elicited brief and transient STAT1 activation, whereas pathological IFN-γ induced prolonged STAT1 activation, which primed the pathway to be more responsive to a subsequent IFN-γ challenge. This is an IFN-γ specific response, as other IFNs and cytokines did not elicit such STAT1 activation nor priming in neurons. Additionally, we did not see the same effect in microglia or astrocytes, suggesting this non-canonical IFN-γ/STAT1 signaling is unique to neurons. Prolonged STAT1 activation was facilitated by continuous janus kinase (JAK) activity, even in the absence of IFN-γ. Finally, although IFN-γ initially induced a canonical IFN-γ transcriptional response in neurons, pathological levels of IFN-γ caused long-term changes in synaptic pathway transcripts. Overall, these findings suggest that IFN-γ signaling occurs via non-canonical mechanisms in neurons, and differential STAT1 activation may explain how neurons have both homeostatic and pathological responses to IFN-γ signaling.

ERK MAPK signaling pathway inhibition as a potential target to prevent autophagy alterations in Spinal Muscular Atrophy motoneurons

Spinal Muscular Atrophy (SMA) is a severe genetic neuromuscular disorder that occurs in childhood and is caused by misexpression of the survival motor neuron (SMN) protein. SMN reduction induces spinal cord motoneuron (MN) degeneration, which leads to progressive muscular atrophy and weakness. The link between SMN deficiency and the molecular mechanisms altered in SMA cells remains unclear. Autophagy, deregulation of intracellular survival pathways and ERK hyperphosphorylation may contribute to SMN-reduced MNs collapse, offering a useful strategy to develop new therapies to prevent neurodegeneration in SMA. Using SMA MN in vitro models, the effect of pharmacological inhibition of PI3K/Akt and ERK MAPK pathways on SMN and autophagy markers modulation was studied by western blot analysis and RT-qPCR. Experiments involved primary cultures of mouse SMA spinal cord MNs and differentiated SMA human MNs derived from induced pluripotent stem cells (iPSCs). Inhibition of the PI3K/Akt and the ERK MAPK pathways reduced SMN protein and mRNA levels. Importantly, mTOR phosphorylation, p62, and LC3-II autophagy markers protein level were decreased after ERK MAPK pharmacological inhibition. Furthermore, the intracellular calcium chelator BAPTA prevented ERK hyperphosphorylation in SMA cells. Our results propose a link between intracellular calcium, signaling pathways, and autophagy in SMA MNs, suggesting that ERK hyperphosphorylation may contribute to autophagy deregulation in SMN-reduced MNs.

ZIP12 Contributes to Hypoxic Pulmonary Hypertension by Driving Phenotypic Switching of Pulmonary Artery Smooth Muscle Cells

ABSTRACT

ZIP12, a plasmalemmal zinc transporter, reportedly promotes pulmonary vascular remodeling (PVR) by enhancing proliferation of pulmonary artery smooth muscle cells (PASMCs). However, the mechanisms of ZIP12 facilitating PASMCs proliferation remain incompletely appreciated. It has been acknowledged that proliferation-predisposing phenotypic switching of PASMCs can lead to PVR. Given that hypoxia triggers phenotypic switching of PASMCs and ZIP12 mediates PVR, this study aims to explore whether ZIP12-mediated phenotypic switching of PASMCs contributes to hypoxia-induced PVR. Rats were exposed to hypoxia (10% O2) for 3 weeks to induce PVR, and primary rat PASMCs were cultured under hypoxic condition (3% O2) for 48 hours to induce proliferation. Immunofluorescence, quantitative reverse transcription-polymerase chain reaction, and Western blot analysis were performed to detect the expression of target mRNAs and proteins. EdU incorporation and 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium assay were conducted to measure the proliferation of PASMCs. Hypoxia upregulated ZIP12 expression (both mRNA and protein) in pulmonary arteries and PASMCs. Knockdown of ZIP12 inhibited phenotypic switching of PASMCs induced by hypoxia. We propose that HIF-1α/ZIP12/pERK pathway could represent a novel mechanism underlying hypoxia-induced phenotypic switching of PASMCs. Therapeutic targeting of ZIP12 could be exploited to treat PVR.

The effects of surface functionality and size of gold nanoparticles on neuronal toxicity, apoptosis, ROS production and cellular/suborgan biodistribution

Gold nanoparticles are emerging as promising nanomaterials to create nanoscale therapeutic delivery systems. The aim of the study was to synthesis of highly monodisperse and stable gold nanoparticles functionalized with polyethyleneimine (PEI) and polyethylene glycol (PEG), multiparametric investigation of their neuronal toxicological effects and evaluation of the cellular/suborgan biodistribution. Gold nanoparticles (AuNP₂₀ and AuNP₅₀) were synthesized and their surfaces were electrostatically modified by PEI and PEG. Dorsal root ganglion (DRG) sensory neurones were isolated from BALB/c mice. Cell viability, apoptosis and ROS production were evaluated in vitro. Cellular and suborgan biodisribution of the AuNPs were investigated using inductively coupled plasma mass spectrometry (ICP-MS) technique. PEI and PEG surface coating increased both biocompatibility and biodistribution of the AuNPs. ICP-MS measurements showed the presence of gold in liver, spleen, kidney, heart, blood and brain within a 30 days period. The size and surface chemistry of the AuNPs are important parameters for potential nanoteranostic applications in the future studies.

Decreased MicroRNA-150 Exacerbates Neuronal Apoptosis in the Diabetic Retina

Diabetic retinopathy (DR) is a chronic complication associated with diabetes and the number one cause of blindness in working adults in the US. More than 90% of diabetic patients have obesity-associated type 2 diabetes (T2D), and 60% of T2D patients will develop DR. Photoreceptors undergo apoptosis shortly after the onset of diabetes, which contributes to the retinal dysfunction and microvascular complications leading to vision impairment. However, how diabetic insults cause photoreceptor apoptosis remains unclear. In this study, obesity-associated T2D mice and cultured photoreceptors were used to investigate how decreased microRNA-150 (miR-150) and its downstream target were involved in photoreceptor apoptosis. In the T2D retina, miR-150 was decreased with its target ETS-domain transcription factor (ELK1) and phosphorylated ELK1 at threonine 417 (pELK1_T417) upregulated. In cultured photoreceptors, treatments with palmitic acid (PA), to mimic a high-fat environment, decreased miR-150 but upregulated ELK1, pELK1_T417, and the translocation of pELK1_T417 from the cytoplasm to the cell nucleus. Deletion of miR-150 (miR-150^-/-) exacerbates T2D- or PA-induced photoreceptor apoptosis. Blocking the expression of ELK1 with small interfering RNA (siRNA) for Elk1 did not rescue PA-induced photoreceptor apoptosis. Translocation of pELK1_T417 from cytoplasm-to-nucleus appears to be the key step of diabetic insult-elicited photoreceptor apoptosis.

Sex dependent glial-specific changes in the chromatin accessibility landscape in late-onset Alzheimer's disease brains

BACKGROUND

In the post-GWAS era, there is an unmet need to decode the underpinning genetic etiologies of late-onset Alzheimer's disease (LOAD) and translate the associations to causation.

METHODS

We conducted ATAC-seq profiling using NeuN sorted-nuclei from 40 frozen brain tissues to determine LOAD-specific changes in chromatin accessibility landscape in a cell-type specific manner.

RESULTS

We identified 211 LOAD-specific differential chromatin accessibility sites in neuronal-nuclei, four of which overlapped with LOAD-GWAS regions (±100 kb of SNP). While the non-neuronal nuclei did not show LOAD-specific differences, stratification by sex identified 842 LOAD-specific chromatin accessibility sites in females. Seven of these sex-dependent sites in the non-neuronal samples overlapped LOAD-GWAS regions including APOE. LOAD loci were functionally validated using single-nuclei RNA-seq datasets.

CONCLUSIONS

Using brain sorted-nuclei enabled the identification of sex-dependent cell type-specific LOAD alterations in chromatin structure. These findings enhance the interpretation of LOAD-GWAS discoveries, provide potential pathomechanisms, and suggest novel LOAD-loci.

ETS-Domain Transcription Factor Elk-1 Regulates Stemness Genes in Brain Tumors and CD133+ BrainTumor-Initiating Cells

Elk-1, a member of the ternary complex factors (TCFs) within the ETS (E26 transformation-specific) domain superfamily, is a transcription factor implicated in neuroprotection, neurodegeneration, and brain tumor proliferation. Except for known targets, c-fos and egr-1, few targets of Elk-1 have been identified. Interestingly, SMN, SOD1, and PSEN1 promoters were shown to be regulated by Elk-1. On the other hand, Elk-1 was shown to regulate the CD133 gene, which is highly expressed in brain-tumor-initiating cells (BTICs) and used as a marker for separating this cancer stem cell population. In this study, we have carried out microarray analysis in SH-SY5Y cells overexpressing Elk-1-VP16, which has revealed a large number of genes significantly regulated by Elk-1 that function in nervous system development, embryonic development, pluripotency, apoptosis, survival, and proliferation. Among these, we have shown that genes related to pluripotency, such as Sox2, Nanog, and Oct4, were indeed regulated by Elk-1, and in the context of brain tumors, we further showed that Elk-1 overexpression in CD133+ BTIC population results in the upregulation of these genes. When Elk-1 expression is silenced, the expression of these stemness genes is decreased. We propose that Elk-1 is a transcription factor upstream of these genes, regulating the self-renewal of CD133+ BTICs.

Nuclear Respiratory Factor 1 (NRF1) Transcriptional Activity-Driven Gene Signature Association with Severity of Astrocytoma and Poor Prognosis of Glioblastoma

Despite tremendous progress in understanding the pathobiology of astrocytoma, major gaps remain in our knowledge of the molecular basis underlying the aggressiveness of high-grade astrocytoma (glioblastoma - GBM). Recently, we and others have shown nuclear respiratory factor 1 (NRF1) transcription factor being highly active in human cancers, but its role in astrocytoma remains unknown. Therefore, the purpose of this study was to uncover the role of NRF1 in the progression of GBM. NRF1 has higher mRNA expression and transcription factor activity in astrocytoma compared to non-tumor brain tissue. NRF1 activity also correlated with the aggressiveness of cancer. Increased NRF1 TF activity coupled with overexpression of RHOG was associated with poor survival of GBM patients. NRF1 activity was associated with transcriptomic signatures of neurogenesis, cell stemness, epithelial-mesenchymal transition and cell cycle progression. Overexpression of CDK4, AKT1, APAF1, HDAC1, NBN, TGFB1, & TNFRSF1A and downregulation of CASP3, IL7, STXBP1 and OPA1 predicted GBM malignancy in high expressors of NRF1 activity. Increased expression of the NRF1 motif containing genes, H6PD, NAT10, NBEAL2, and RNF19B predicted poor survival of IDH1 wild-type GBM patients. Poor survival outcomes and resistance to Temozolomide therapy were associated with higher NRF1 expression including its targets - LDHA, ZMAT3, NSUN2, ARMC5, NDEL1, CLPTM1L, ALKBH5, YIPF5, PPP2CA, and TFG. These findings suggest that aberrant NRF1 activity may contribute to the pathogenesis of GBM and severity of astrocytoma. Further analyses of NRF1 gene signatures will pave the way for next generation targeted therapies and drug combination strategies for GBM patients.

Early epigenomic and transcriptional changes reveal Elk-1 transcription factor as a therapeutic target in Huntington's disease

Huntington's disease (HD) is a chronic neurodegenerative disorder characterized by a late clinical onset despite ubiquitous expression of the mutant Huntingtin gene (HTT) from birth. Transcriptional dysregulation is a pivotal feature of HD. Yet, the genes that are altered in the prodromal period and their regulators, which present opportunities for therapeutic intervention, remain to be elucidated. Using transcriptional and chromatin profiling, we found aberrant transcription and changes in histone H3K27acetylation in the striatum of R6/1 mice during the presymptomatic disease stages. Integrating these data, we identified the Elk-1 transcription factor as a candidate regulator of prodromal changes in HD. Exogenous expression of Elk-1 exerted beneficial effects in a primary striatal cell culture model of HD, and adeno-associated virus-mediated Elk-1 overexpression alleviated transcriptional dysregulation in R6/1 mice. Collectively, our work demonstrates that aberrant gene expression precedes overt disease onset in HD, identifies the Elk-1 transcription factor as a key regulator linked to early epigenetic and transcriptional changes in HD, and presents evidence for Elk-1 as a target for alleviating molecular pathology in HD.

Bladder Cancer-Specific Nuclear Matrix Proteins-4 May Be a Potential Biomarker for Non-Muscle-Invasive Bladder Cancer Detection

Aims

Bladder cancer–specific nuclear matrix protein-4 (BLCA-4) is a protein expressed mainly in bladder cancer tissues. Therefore, the aim of this study was to investigate its assisting diagnostic potential in non-muscle-invasive bladder cancer (NMIBC).

Methods

Twenty patients with NMIBC, 20 with benign prostatic hyperplasia (BPH), and 20 normal controls were included in this study. Blood and urine samples were collected from all patients. Moreover, cancer foci and adjacent tissue samples were collected from NMIBC patients, and normal bladder tissue samples were collected from patients with BPH. A competitive enzyme-linked immunosorbent assay was used to determine the BLCA-4 level in serum and urine, and immunohistochemistry was used to examine BLCA-4 expression in bladder cancer, adjacent, and normal tissues.

Results

Median urinary BLCA-4 levels in the NMIBC, BPH, and normal control groups were 0.759 ng/mL, 0.309 ng/mL, and 0.171 ng/mL, respectively. Urinary BLCA-4 level was significantly higher in the NMIBC group than in the other 2 groups (P < 0.01); meanwhile, the BPH group was higher than the normal control group (P < 0.05). Median serum BLCA-4 levels in the NMIBC, BPH, and normal control groups were 5.680 ng/mL, 5.928 ng/mL, and 5.473 ng/mL, respectively, showing no significant difference among groups (P > 0.05).

Conclusion

As a new marker of bladder cancer, urinary BLCA-4 level detection might apply for clinical diagnosis or postoperative monitoring for NMIBC.

Modulation of transcriptional activity in brain lower grade glioma by alternative splicing

Proteins that modify the activity of transcription factors (TFs) are often called modulators and play a vital role in gene transcriptional regulation. Alternative splicing is a critical step of gene processing, and differentially spliced isoforms may have different functions. Alternative splicing can modulate gene function by adding or removing certain protein domains and thereby influence the activity of a protein. The objective of this study is to investigate the role of alternative splicing in modulating the transcriptional regulation in brain lower grade glioma (LGG), especially transcription factor ELK1, which is closely related to various disorders, including Alzheimer’s disease and Down syndrome. The results showed that changes in the exon inclusion ratio of proteins APP and STK16 are associated with changes in the expression correlation between ELK1 and its targets. In addition, the structural features of the two modulators are strongly associated with the pathological impact of exon inclusion. The results of our analysis suggest that alternatively spliced proteins have different functions in modifying transcription factors and can thereby induce the dysregulation of multiple genes.

Functionalized gold nanoparticles manifested as potent carriers for nucleolar targeting

It is generally known that gold nanoparticles are localised in the cytoplasm and, if synthesised in small sizes or functionalized with specific proteins, they enter the cell nucleus. However, there is no report emphasising the importance of surface functionalization in their accumulation in the nucleolus. Here, for the first time in the literature, it is proposed that functionalization of gold nanoparticles with a thin layer of polyethyleneimine (PEI) spearheads them to the nucleolus of hard-to-transfect post-mitotic dorsal root ganglion neurones in a size-independent manner. As a potential for theranostic applications, it was found that functionalization with a thin layer of PEI affected the emission signal intensity of gold nanoparticles so that the cellular biodistribution of nanoparticles was visualised clearly under both confocal and two-photon microscopes.

LPA1 Mediates Antidepressant-Induced ERK1/2 Signaling and Protection from Oxidative Stress in Glial Cells

Antidepressants have been shown to affect glial cell functions and intracellular signaling through mechanisms that are still not completely understood. In the present study, we provide evidence that in glial cells the lysophosphatidic acid (LPA) receptor LPA1 mediates antidepressant-induced growth factor receptor transactivation, ERK1/2 signaling, and protection from oxidative stress. Thus, in C6 glioma cells and rat cortical astrocytes, ERK1/2 activation induced by either amitriptyline or mianserin was antagonized by Ki16425 and VPC 12249 (S), which block LPA1 and LPA3 receptors, and by AM966, which selectively blocks LPA1 Cell depletion of LPA1 with siRNA treatment markedly reduced antidepressant- and LPA-induced ERK1/2 phosphorylation. LPA1 blockade prevented antidepressant-induced phosphorylation of the transcription factors CREB and Elk-1. Antidepressants and LPA signaling to ERK1/2 was abrogated by cell treatment with pertussis toxin and by the inhibition of fibroblast growth factor (FGF) receptor (FGF-R) and platelet-derived growth factor receptor (PDGF-R) tyrosine kinases. Both Ki16425 and AM966 suppressed antidepressant-induced phosphorylation of FGF-R. Moreover, blockade of LPA1 or inhibition of FGF-R and PDGF-R activities prevented antidepressant-stimulated Akt and GSK-3β phosphorylations. Mianserin protected C6 glioma cells and astrocytes from apoptotic cell death induced by H2O2, as indicated by increased cell viability, decreased expression of cleaved caspase 3, reduced cleavage of poly-ADP ribose polymerase and inhibition of DNA fragmentation. The protective effects of mianserin were antagonized by AM966. These data indicate that LPA1 constitutes a novel molecular target of the regulatory actions of tricyclic and tetracyclic antidepressants in glial cells.

PTPN21 exerts pro-neuronal survival and neuritic elongation via ErbB4/NRG3 signaling

Although expression quantitative trait locus, eQTL, serves as an explicit indicator of gene-gene associations, challenges remain to disentangle the mechanisms by which genetic variations alter gene expression. Here we combined eQTL and molecular analyses to identify an association between two seemingly non-associated genes in brain expression data from BXD inbred mice, namely Ptpn21 and Nrg3. Using biotinylated receptor tracking and immunoprecipitation analyses, we determined that PTPN21 de-phosphorylates the upstream receptor tyrosine kinase ErbB4 leading to the up-regulation of its downstream signaling. Conversely, kinase-dead ErbB4 (K751R) or phosphatase-dead PTPN21 (C1108S) mutants impede PTPN21-dependent signaling. Furthermore, PTPN21 also induced Elk-1 activation in embryonic cortical neurons and a novel Elk-1 binding motif was identified in a region located 1919bp upstream of the NRG3 initiation codon. This enables PTPN21 to promote NRG3 expression through Elk-1, which provides a biochemical mechanism for the PTPN21-NRG3 association identified by eQTL. Biologically, PTPN21 positively influences cortical neuronal survival and, similar to Elk-1, it also enhances neuritic length. Our combined approaches show for the first time, a link between NRG3 and PTPN21 within a signaling cascade. This may explain why these two seemingly unrelated genes have previously been identified as risk genes for schizophrenia.

ELK1 transcription factor linked to dysregulated striatal mu opioid receptor signaling network and OPRM1 polymorphism in human heroin abusers

BACKGROUND

Abuse of heroin and prescription opiate medications has grown to disturbing levels. Opioids mediate their effects through mu opioid receptors (MOR), but minimal information exists regarding MOR-related striatal signaling relevant to the human condition. The striatum is a structure central to reward and habitual behavior and neurobiological changes in this region are thought to underlie the pathophysiology of addiction disorders.

METHODS

We examined molecular mechanisms related to MOR in postmortem human brain striatal specimens from a homogenous European Caucasian population of heroin abusers and control subjects and in an animal model of heroin self-administration. Expression of ets-like kinase 1 (ELK1) was examined in relation to polymorphism of the MOR gene OPRM1 and drug history.

RESULTS

A characteristic feature of heroin abusers was decreased expression of MOR and extracellular regulated kinase signaling networks, concomitant with dysregulation of the downstream transcription factor ELK1. Striatal ELK1 in heroin abusers associated with the polymorphism rs2075572 in OPRM1 in a genotype dose-dependent manner and correlated with documented history of heroin use, an effect reproduced in an animal model that emphasizes a direct relationship between repeated heroin exposure and ELK1 dysregulation. A central role of ELK1 was evidenced by an unbiased whole transcriptome microarray that revealed ~20% of downregulated genes in human heroin abusers are ELK1 targets. Using chromatin immune precipitation, we confirmed decreased ELK1 promoter occupancy of the target gene Use1.

CONCLUSIONS

ELK1 is a potential key transcriptional regulatory factor in striatal disturbances associated with heroin abuse and relevant to genetic mutation of OPRM1.

Shift from extracellular signal-regulated kinase to AKT/cAMP response element-binding protein pathway increases survival-motor-neuron expression in spinal-muscular-atrophy-like mice and patient cells

Spinal muscular atrophy (SMA), a recessive neurodegenerative disease, is characterized by the selective loss of spinal motor neurons. No available therapy exists for SMA, which represents one of the leading genetic causes of death in childhood. SMA is caused by a mutation of the survival-of-motor-neuron 1 (SMN1) gene, leading to a quantitative defect in the survival-motor-neuron (SMN) protein expression. All patients retain one or more copies of the SMN2 gene, which modulates the disease severity by producing a small amount of stable SMN protein. We reported recently that NMDA receptor activation, directly in the spinal cord, significantly enhanced the transcription rate of the SMN2 genes in a mouse model of very severe SMA (referred as type 1) by a mechanism that involved AKT/CREB pathway activation. Here, we provide the first compelling evidence for a competition between the MEK/ERK/Elk-1 and the phosphatidylinositol 3-kinase/AKT/CREB signaling pathways for SMN2 gene regulation in the spinal cord of type 1 SMA-like mice. The inhibition of the MEK/ERK/Elk-1 pathway promotes the AKT/CREB pathway activation, leading to (1) an enhanced SMN expression in the spinal cord of SMA-like mice and in human SMA myotubes and (2) a 2.8-fold lifespan extension in SMA-like mice. Furthermore, we identified a crosstalk between ERK and AKT signaling pathways that involves the calcium-dependent modulation of CaMKII activity. Together, all these data open new perspectives to the therapeutic strategy for SMA patients.

SMA-MAP: a plasma protein panel for spinal muscular atrophy

Objectives

Spinal Muscular Atrophy (SMA) presents challenges in (i) monitoring disease activity and predicting progression, (ii) designing trials that allow rapid assessment of candidate therapies, and (iii) understanding molecular causes and consequences of the disease. Validated biomarkers of SMA motor and non-motor function would offer utility in addressing these challenges. Our objectives were (i) to discover additional markers from the Biomarkers for SMA (BforSMA) study using an immunoassay platform, and (ii) to validate the putative biomarkers in an independent cohort of SMA patients collected from a multi-site natural history study (NHS).

Methods

BforSMA study plasma samples (N = 129) were analyzed by immunoassay to identify new analytes correlating to SMA motor function. These immunoassays included the strongest candidate biomarkers identified previously by chromatography. We selected 35 biomarkers to validate in an independent cohort SMA type 1, 2, and 3 samples (N = 158) from an SMA NHS. The putative biomarkers were tested for association to multiple motor scales and to pulmonary function, neurophysiology, strength, and quality of life measures. We implemented a Tobit model to predict SMA motor function scores.

Results

12 of the 35 putative SMA biomarkers were significantly associated (p<0.05) with motor function, with a 13^th analyte being nearly significant. Several other analytes associated with non-motor SMA outcome measures. From these 35 biomarkers, 27 analytes were selected for inclusion in a commercial panel (SMA-MAP) for association with motor and other functional measures.

Conclusions

Discovery and validation using independent cohorts yielded a set of SMA biomarkers significantly associated with motor function and other measures of SMA disease activity. A commercial SMA-MAP biomarker panel was generated for further testing in other SMA collections and interventional trials. Future work includes evaluating the panel in other neuromuscular diseases, for pharmacodynamic responsiveness to experimental SMA therapies, and for predicting functional changes over time in SMA patients.

Net expression inhibits the growth of pancreatic ductal adenocarcinoma cell PL45 in vitro and in vivo

Pancreatic ductal adenocarcinoma has a poor prognosis due to late diagnosis and a lack of effective therapeutic options. Thus, it is important to better understand its molecular mechanisms and to develop more effective treatments for the disease. The ternary complex factor Net, which exerts its strong inhibitory function on transcription of proto-oncogene gene c-fos by forming ternary complexes with a second transcription factor, has been suspected of being involved in pancreatic cancer and other tumors biology. In this study, we found that the majority of pancreatic ductal adenocarcinoma tissues and cell lines had weak or no expression of Net, whereas significantly high level of Net expression occurred in paired adjacent normal tissues we studied. Furthermore, using in vitro and in vivo model systems, we found that overexpression of Net inhibited cell growth and survival and induced cell apoptosis in human pancreatic ductal adenocarcinoma cell PL45; the mechanisms by which Net inhibited the cell cycle progression were mainly through P21-Cyclin D1/CDK4 Pathway. Our data thus suggested that Net might play an important role in pancreatic carcinogenesis, possibly by acting as a tumor suppressor gene.

Phospho-Ser383-Elk-1 is localized to the mitotic spindles during cell cycle and interacts with mitotic kinase Aurora-A

Elk-1 is a member of the E-twenty-six (ETS) domain superfamily of transcription factors and has been traditionally associated with mitogen-induced immediate early gene transcription upon phosphorylation by mitogen activated protein kinases (ERK/MAPK). Elk-1 is not only upregulated but also phosphorylated in brain tumour cells. However, in this study, we show for the first time that S383-phosphorylated Elk-1 (P-S383-Elk-1) is associated with mitotic spindle poles from metaphase through telophase and relocates to the spindle midbody during cytokinesis, while Thr417Ala mutation is associated with DNA throughout mitosis. Serine 383 phosphorylation appears to be important for polar localization of Elk-1, since exogenous protein including serine-to-alanine mutation was seen to be distributed throughout the spindle fibres. We further show that Elk-1 interacts with the cell cycle kinase Aurora-A, and when Aurora inhibitors are used, P-S383-Elk-1 fails to localize to the poles and remains associated with DNA. Apart from one transcriptional repressor molecule, Kaiso, this is the first time a transactivator was shown to possess such mitotic localization and interaction. The functional significance and detailed mechanism of this cell cycle-related localization of Elk-1 are yet to be determined.

Rab7 mutants associated with Charcot-Marie-Tooth disease cause delayed growth factor receptor transport and altered endosomal and nuclear signaling

Rab7 belongs to the Ras superfamily of small GTPases and is a master regulator of early to late endocytic membrane transport. Four missense mutations in the late endosomal Rab7 GTPase (L129F, K157N, N161T, and V162M) cause the autosomal dominant peripheral neuropathy Charcot-Marie-Tooth type 2B (CMT2B) disease. As yet, the pathological mechanisms connecting mutant Rab7 protein expression to altered neuronal function are undefined. Here, we analyze the effects of Rab7 CMT2B mutants on epidermal growth factor (EGF)-dependent intracellular signaling and trafficking. Three different cell lines expressing Rab7 CMT2B mutants and stimulated with EGF exhibited delayed trafficking of EGF to LAMP1-positive late endosomes and lysosomes and slowed EGF receptor (EGFR) degradation. Expression of all Rab7 CMT2B mutants altered the Rab7 activation cycle, leading to enhanced and prolonged EGFR signaling as well as variable increases in p38 and ERK1/2 activation. However, due to reduced nuclear translocation of p38 and ERK1/2, the downstream nuclear activation of Elk-1 was decreased along with the expression of immediate early genes like c-fos and Egr-1 by the disease mutants. In conclusion, our results demonstrate that Rab7 CMT2B mutants impair growth factor receptor trafficking and, in turn, alter p38 and ERK1/2 signaling from perinuclear, clustered signaling endosomes. The resulting down-regulation of EGFR-dependent nuclear transcription that is crucial for normal axon outgrowth and peripheral innervation offers a crucial new mechanistic insight into disease pathogenesis that is relevant to other neurodegenerative diseases.

Serum response factor modulates neuron survival during peripheral axon injury

Background

The transcription factor SRF (serum response factor) mediates neuronal survival in vitro. However, data available so far suggest that SRF is largely dispensable for neuron survival during physiological brain function.

Findings

Here, we demonstrate that upon neuronal injury, that is facial nerve transection, constitutively-active SRF-VP16 enhances motorneuron survival. SRF-VP16 suppressed active caspase 3 abundance in vitro and enhanced neuron survival upon camptothecin induced apoptosis. Following nerve fiber injury in vitro, SRF-VP16 improved survival of neurons and re-growth of severed neurites. Further, SRF-VP16 enhanced immune responses (that is microglia and T cell activation) associated with neuronal injury in vivo. Genome-wide transcriptomics identified target genes associated with axonal injury and modulated by SRF-VP16.

Conclusion

In sum, this is a first report describing a neuronal injury-related survival function for SRF.

Activation of Elk-1 participates as a neuroprotective compensatory mechanism in models of Huntington's disease

The transcription factor Elk-1 has been revealed as neuroprotective against toxic stimuli. In this study, we explored the neuroprotective capacity of Elk-1 in Huntington's disease. To this aim, we used two exon-1 mutant huntingtin (mhtt) mouse models (R6/1 and R6/2), and a full-length mhtt striatal cell model (STHdh(Q111/Q111) ). Analysis of Elk-1 and pElk-1(Ser383) in the striatum of R6 mice revealed increased levels during the disease progression. Similarly, Elk-1 and pElk-1(Ser383) levels were increased in STHdh(Q111/Q111) cells when compared with wild-type cells. In addition, we observed a predominant nuclear localization of Elk-1 in STHdh(Q111/Q111) cells, and in the striatum of 30-week-old R6/1 mice. Nuclear Elk-1 did not colocalize with mhtt aggregates, suggesting a higher transcriptional activity. In agreement, the knock-down of Elk-1 decreased immediate early genes expression in STHdh(Q111/Q111) cells, but not in wild-type cells. Interestingly, reduction of Elk-1 levels by siRNAs transfection promoted cell death and caspase 3 cleavage in STHdh(Q111/Q111) cells, but not in wild-type cells. In summary, we propose that increased protein levels, phosphorylation and nuclear localization of Elk-1 observed in exon-1 and full-length Huntington's disease models could be a compensatory mechanism activated by striatal cells in response to the presence of mhtt that contributes to neuroprotection.

Elk-1 interacts with dynein upon serum stimulation but independent of serine 383 phosphorylation

Elk-1 belongs to the Ternary Complex Factor (TCF) subfamily of the ETS (from E26 viral oncogene) domain superfamily of transcription factors, and has been known as a regulator of mitogen-induced immediate early gene transcription upon Mitogen Activated Protein Kinase (MAPK) activation. Elk-1 has been previously shown to interact with neuronal microtubules, and here we show that P-S383-Elk-1, in addition to co-localizing with motor proteins kinesin, Eg5 and Mitotik Kinesin-Like Protein (MKLP) at the mitotic spindles, it physically interacts with dynein in a serum induction-dependent but Ser383 phosphorylation-independent manner.