Transcytosis-mediated anterograde transport of TrkA receptors is necessary for sympathetic neuron development and function.

In neurons, many membrane proteins, synthesized in cell bodies, must be efficiently delivered to axons to influence neuronal connectivity, synaptic communication, and repair. Previously, we found that axonal targeting of TrkA neurotrophin receptors in sympathetic neurons occurs via an atypical transport mechanism called transcytosis, which relies on TrkA interactions with PTP1B, a protein tyrosine phosphatase. Here, we generated TrkAR685A mice, where TrkA receptor signaling is preserved, but its PTP1B-dependent transcytosis is disrupted to show that this mode of axonal transport is essential for sympathetic neuron development and autonomic function. TrkAR685A mice have decreased axonal TrkA levels in vivo, loss of sympathetic neurons, and reduced innervation of targets. The neuron loss and diminished target innervation phenotypes are specifically restricted to the developmental period when sympathetic neurons are known to rely on the TrkA ligand, nerve growth factor, for trophic support. Postnatal TrkAR685A mice exhibit reduced pupil size and eyelid ptosis, indicative of sympathetic dysfunction. Furthermore, we also observed a significant loss of TrkA-expressing nociceptive neurons in the dorsal root ganglia during development in TrkAR685A mice, suggesting that transcytosis might be a general mechanism for axonal targeting of TrkA receptors. Together, these findings establish the necessity of transcytosis in supplying TrkA receptors to axons, specifically during development, and highlight the physiological relevance of this axon targeting mechanism in the nervous system.

Evaluation of the enzymatic properties of DNA (cytosine-5)-methyltransferase M.ApeKI from archaea in the presence of metal ions.

We previously identified M.ApeKI from Aeropyum pernix K1 as a highly thermostable DNA (cytosine-5)-methyltransferase. M.ApeKI uses the type II restriction-modification system (R-M system), among the best-studied R-M systems. Although endonucleases generally utilize Mg (II) as a cofactor, several reports have shown that MTases exhibit different reactions in the presence of metal ions. This study aim was to evaluate the enzymatic properties of DNA (cytosine-5)-methyltransferase M.ApeKI from archaea in the presence of metal ions. We evaluated the influence of metal ions on the catalytic activity and DNA binding of M.ApeKI. The catalytic activity was inhibited by Cu (II), Mg (II), Mn (II), and Zn (II), each at 5 m m. DNA binding was more strongly inhibited by 5 m m Cu (II) and 10 m m Zn (II). To our knowledge, this is the first report showing that DNA binding of type II MTase is inhibited by metal ions.

Clinical evidence that a dysregulated master neural network modulator may aid in diagnosing schizophrenia.

There are no validated biomarkers for schizophrenia (SCZ), a disorder linked to neural network dysfunction. We demonstrate that collapsin response mediator protein-2 (CRMP2), a master regulator of cytoskeleton and, hence, neural circuitry, may form the basis for a biomarker because its activity is uniquely imbalanced in SCZ patients. CRMP2's activity depends upon its phosphorylation state. While an equilibrium between inactive (phosphorylated) and active (nonphosphorylated) CRMP2 is present in unaffected individuals, we show that SCZ patients are characterized by excess active CRMP2. We examined CRMP2 levels first in postmortem brains (correlated with neuronal morphometrics) and then, because CRMP2 is expressed in lymphocytes as well, in the peripheral blood of SCZ patients versus age-matched unaffected controls. In the brains and, more starkly, in the lymphocytes of SCZ patients <40 y old, we observed that nonphosphorylated CRMP2 was higher than in controls, while phosphorylated CRMP2 remained unchanged from control. In the brain, these changes were associated with dendritic structural abnormalities. The abundance of active CRMP2 with insufficient opposing inactive p-CRMP2 yielded a unique lowering of the p-CRMP2:CRMP2 ratio in SCZ patients, implying a disruption in the normal equilibrium between active and inactive CRMP2. These clinical data suggest that measuring CRMP2 and p-CRMP2 in peripheral blood might reflect intracerebral processes and suggest a rapid, minimally invasive, sensitive, and specific adjunctive diagnostic aid for early SCZ: increased CRMP2 or a decreased p-CRMP2:CRMP2 ratio may help cinch the diagnosis in a newly presenting young patient suspected of SCZ (versus such mimics as mania in bipolar disorder, where the ratio is high).

Methylmercury Induces Apoptosis in Mouse C17.2 Neural Stem Cells through the Induction of OSGIN1 Expression by NRF2.

Methylmercury is a known environmental pollutant that exhibits severe neurotoxic effects. However, the mechanism by which methylmercury causes neurotoxicity remains unclear. To date, we have found that oxidative stress-induced growth inhibitor 1 (OSGIN1), which is induced by oxidative stress and DNA damage, is also induced by methylmercury. Therefore, in this study, we investigated the relationship between methylmercury toxicity and the induction of OSGIN1 expression using C17.2 cells, which are mouse brain neural stem cells. Methylmercury increased both OSGIN1 mRNA and protein levels in a time- and concentration-dependent manner. Moreover, these increases were almost entirely canceled out by pretreatment with actinomycin D, a transcription inhibitor. Furthermore, similar results were obtained from cells in which expression of the transcription factor nuclear factor erythroid 2-related factor 2 (NRF2) was suppressed, indicating that methylmercury induces OSGIN1 expression via NRF2. Methylmercury causes neuronal cell death by inducing apoptosis. Therefore, we next investigated the role of OSGIN1 in methylmercury-induced neuronal cell death using the activation of caspase-3, which is involved in apoptosis induction, as an indicator. As a result, the increase in cleaved caspase-3 (activated form) induced by methylmercury exposure was decreased by suppressing OSGIN1, and the overexpression of OSGIN1 further promoted the increase in cleaved caspase-3 caused by methylmercury. These results suggest, for the first time, that OSGIN1 is a novel factor involved in methylmercury toxicity, and methylmercury induces apoptosis in C17.2 cells through the induction of OSGIN1 expression by NRF2.

FDI-6, a FOXM1 inhibitor, activates the aryl hydrocarbon receptor and suppresses tumorsphere formation.

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that is activated by environmental contaminants such as dioxins and polycyclic aromatic hydrocarbons. Following ligand binding, AhR binds to xenobiotic responsive elements and modulates the transcription of AhR target genes. Multiple studies have shown that AhR plays important roles in a range of cancer cells and is attracting attention as a therapeutic target for cancer treatment. We have previously reported that AhR agonists inhibit tumorsphere formation in an AhR-dependent manner in the MCF-7 breast cancer cell line. In the present study, we found that FDI-6, an inhibitor of the transcription factor Forkhead Box M1 (FOXM1) induced the mRNA expression of AhR target genes, nuclear translocation of AhR, and transcriptional activity of AhR. In addition, FDI-6 dose-dependently reduced the mRNA expression of FOXM1-regulated genes in AhR-expressing MCF-7 cells, although not in AhR-deficient MCF-7 cells. Furthermore, FDI-6 was found to suppress tumorsphere formation via the AhR in MCF-7 cells and HepG2 human liver cancer cell line. On the basis of the findings of this study, we show that FDI-6, a FOXM1 inhibitor, functions as an AhR agonist, and suppresses tumorsphere formation via the AhR.

Aryl Hydrocarbon Receptor Directly Regulates VTCN1 Gene Expression in MCF-7 Cells.

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that mediates the toxicity of dioxins and polycyclic aromatic hydrocarbons. Recent studies have suggested that AhR is involved in cancer immunity. In the present study, we examined whether AhR regulates the expression of immune checkpoint genes in breast cancer cells. We discovered that the mRNA expression of V-set domain containing T cell activation inhibitor 1 (VTCN1) that negatively regulates T cell immunity was upregulated by AhR agonists in breast cancer cell lines, MCF-7 and T47D. Furthermore, AhR knockout or knockdown experiments clearly demonstrated that upregulation of VTCN1 gene expression by 3-methylcholanthrene was AhR dependent. Luciferase reporter and chromatin immunoprecipitation assays revealed that this upregulation of VTCN1 gene expression was induced by the recruitment of AhR to the AhR responsive element in the VTCN1 gene promoter in MCF-7 cells. Taken together, AhR directly regulates VTCN1 gene expression in MCF-7 cells.

Possible Involvement of the Upregulation of ΔNp63 Expression Mediated by HER2-Activated Aryl Hydrocarbon Receptor in Mammosphere Maintenance.

Cancer stem cells (CSCs) contribute to the drug resistance, recurrence, and metastasis of breast cancers. Recently, we demonstrated that HER2 overexpression increases mammosphere formation via the activation of aryl hydrocarbon receptor (AHR). In this study, the objective was to identify the mechanism underlying mammosphere maintenance mediated by HER2 signaling-activated AHR. We compared the chromatin structure of AHR-knockout (AHRKO) HER2-overexpressing MCF-7 (HER2-5) cells with that of wild-type HER2-5 cells; subsequently, we identified TP63, a stemness factor, as a potential target gene of AHR. ΔNp63 mRNA and protein levels were higher in HER2-5 cells than in HER2-5/AHRKO cells. Activation of HER2/HER3 signaling by heregulin treatment increased ΔNp63 mRNA levels, and its induction was decreased by AHR knockdown in HER2-5 cells. The results of the chromatin immunoprecipitation assay revealed an interaction between AHR and the intronic region of TP63, which encodes ΔNp63. A luciferase reporter gene assay with the intronic region of TP63 showed that AHR expression increased reporter activity. Collectively, our findings suggest that HER2-activated AHR upregulates ΔNp63 expression and that this signaling cascade is involved in CSC maintenance in HER2-expressing breast cancers.

Activity-induced secretion of semaphorin 3A mediates learning.

The semaphorin family is a well-characterized family of secreted or membrane-bound proteins that are involved in activity-independent neurodevelopmental processes, such as axon guidance, cell migration, and immune functions. Although semaphorins have recently been demonstrated to regulate activity-dependent synaptic scaling, their roles in Hebbian synaptic plasticity as well as learning and memory remain poorly understood. Here, using a rodent model, we found that an inhibitory avoidance task, a hippocampus-dependent contextual learning paradigm, increased secretion of semaphorin 3A in the hippocampus. Furthermore, the secreted semaphorin 3A in the hippocampus mediated contextual memory formation likely by driving AMPA receptors into hippocampal synapses via the neuropilin1-plexin A4-semaphorin receptor complex. This signaling process involves alteration of the phosphorylation status of collapsin response mediator protein 2, which has been characterized as a downstream molecule in semaphorin signaling. These findings implicate semaphorin family as a regulator of Hebbian synaptic plasticity and learning.

Activation of the aryl hydrocarbon receptor by 3-methylcholanthrene, but not by indirubin, suppresses mammosphere formation via downregulation of CDC20 expression in breast cancer cells.

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that regulates various toxicological and biological functions. We reported previously that 3-methylcholanthrene (3MC), an exogenous AhR agonist, inhibited tumorsphere (mammosphere) formation from breast cancer cell lines, while the endogenous AhR agonist, indirubin, very weakly inhibited this process. However, the difference in inhibition mechanism of mammosphere formation by 3MC or indirubin is still unknown. In this study, we established AhR-re-expressing (KOTR-AhR) cells from AhR knockout MCF-7 cells using the tetracycline (Tet)-inducible gene expression systems. To identify any difference in inhibition of mammosphere formation by 3MC or indirubin, RNA-sequencing (RNA-seq) experiments were performed using KOTR-AhR cells. RNA-seq experiments revealed that cell division cycle 20 (CDC20), which regulates the cell cycle and mitosis, was decreased by 3MC, but not by indirubin, in the presence of AhR expression. Furthermore, the mRNA and protein levels of CDC20 were decreased by 3MC in MCF-7 cells via the AhR. In addition, mammosphere formation was suppressed by small interfering RNA-mediated CDC20 knockdown compared to the negative control in MCF-7 cells. These results suggest that AhR activation by 3MC suppresses mammosphere formation via downregulation of CDC20 expression in breast cancer cells. This study provides useful information for the development of AhR-targeted anti-cancer drugs.

The Differential Selectivity of Aryl Hydrocarbon Receptor (AHR) Agonists towards AHR-Dependent Suppression of Mammosphere Formation and Gene Transcription in Human Breast Cancer Cells.

We had previously reported that treatment with the aryl hydrocarbon receptor (AHR) agonist ß-naphthoflavone (ßNF) suppressed mammosphere formation derived from cancer stem cells in human breast cancer MCF-7 cells (Cancer Lett., 317, 2012, Zhao et al.). Here, using several AHR agonists, we have investigated the association of this suppression with the classical ability to induce AHR-mediated gene transcription in the xenobiotic response element (XRE). The mammosphere formation assays were performed using wild-type and AHR-knockout MCF-7 cells in the presence of AHR agonists including 3-methylcholanthrene (3MC), benzo[a]pyrene (BaP), 7,12-dimethylbenz[a]anthracene (DMBA), 6-formylindolo[3,2-b]carbazole (FICZ), indirubin, indole-3-carbinol (I3C), indole-3-acetic acid (IAA), and kynurenine (KYN), followed by the XRE-reporter gene assays of the agonists. We showed that treatments with 3MC, BaP, and DMBA strongly suppressed mammosphere formation of the stem cells in an AHR-dependent manner, while other agonists showed weaker suppression. In reporter gene assays, the strength or duration of AHR/XRE-mediated gene transcription was found to be dependent on the agonist. Although strong transcriptional activation was observed with 3MC, FICZ, indirubin, I3C, IAA, or KYN after 6 h of treatment, only weak activation was seen with BaP or DMBA. While transcriptional activation was sustained or increased at 24 h with 3MC, BaP, or DMBA, appreciable reduction was observed with the other agonists. In conclusions, the results demonstrated that the suppressive effects of AHR agonists on mammosphere formation do not necessarily correlate with their abilities to induce AHR-mediated gene transcription. Hence, different AHR functions may be differentially induced in an agonist-dependent manner.

NGF Signaling in Endosomes.

During the development of the nervous system, neurons respond to diffusible cues secreted by target cells. Because such target-derived factors regulate development, maturation, and maintenance of axons as well as somatodendritic compartments, signals initiated at distal axons must be retrogradely transmitted toward cell bodies. Neurotrophins, including the nerve growth factor (NGF), provide one of the best-known examples of target-derived growth factors. The cell biological processes of endocytosis and retrograde trafficking of their Trk receptors from growth cones to cell bodies are key mechanisms by which target-derived neurotrophins influence neurons. Evidence accumulated over the past several decades has begun to uncover the molecular mechanisms of formation, transport, and biological functions of these specialized endosomes called "signaling endosomes."

Probing the lithium-response pathway in hiPSCs implicates the phosphoregulatory set-point for a cytoskeletal modulator in bipolar pathogenesis.

The molecular pathogenesis of bipolar disorder (BPD) is poorly understood. Using human-induced pluripotent stem cells (hiPSCs) to unravel such mechanisms in polygenic diseases is generally challenging. However, hiPSCs from BPD patients responsive to lithium offered unique opportunities to discern lithium's target and hence gain molecular insight into BPD. By profiling the proteomics of BDP-hiPSC-derived neurons, we found that lithium alters the phosphorylation state of collapsin response mediator protein-2 (CRMP2). Active nonphosphorylated CRMP2, which binds cytoskeleton, is present throughout the neuron; inactive phosphorylated CRMP2, which dissociates from cytoskeleton, exits dendritic spines. CRMP2 elimination yields aberrant dendritogenesis with diminished spine density and lost lithium responsiveness (LiR). The "set-point" for the ratio of pCRMP2:CRMP2 is elevated uniquely in hiPSC-derived neurons from LiR BPD patients, but not with other psychiatric (including lithium-nonresponsive BPD) and neurological disorders. Lithium (and other pathway modulators) lowers pCRMP2, increasing spine area and density. Human BPD brains show similarly elevated ratios and diminished spine densities; lithium therapy normalizes the ratios and spines. Consistent with such "spine-opathies," human LiR BPD neurons with abnormal ratios evince abnormally steep slopes for calcium flux; lithium normalizes both. Behaviorally, transgenic mice that reproduce lithium's postulated site-of-action in dephosphorylating CRMP2 emulate LiR in BPD. These data suggest that the "lithium response pathway" in BPD governs CRMP2's phosphorylation, which regulates cytoskeletal organization, particularly in spines, modulating neural networks. Aberrations in the posttranslational regulation of this developmentally critical molecule may underlie LiR BPD pathogenesis. Instructively, examining the proteomic profile in hiPSCs of a functional agent-even one whose mechanism-of-action is unknown-might reveal otherwise inscrutable intracellular pathogenic pathways.

Cell Cycle and Apoptosis Regulator 1, CCAR1, Regulates Enhancer-Dependent Nuclear Receptor CAR Transactivation.

The constitutive active/androstane receptor (CAR) controls genes involved in xenochemical metabolism. Although numerous cofactors have been reported to be involved in CAR-mediated transactivation, unknown and poorly defined proteins recruited by CAR have yet to be characterized. In this study, a novel CAR-interacting protein, cell cycle and apoptosis regulator 1 (CCAR1), was identified by coimmunoprecipitation analysis using human hepatocarcinoma HepG2 cells expressing FLAG epitope-tagged CAR. We demonstrated that CCAR1 can act as an enhancer-dependent coactivator of CAR. First, we showed that overexpression of CCAR1 enhanced CAR-induced reporter gene activity with triplicate consensus direct repeat 4 motif (DR4-Luc), xenobiotic-responsive enhancer module (XREM)-enhancer of CYP3A4 (XREM-Luc), and phenobarbital-responsive enhancer module of UDP-glucuronosyltransferases 1A1 (UGT1A1) (gtPBREM)-enhancer of UGT1A1 (gtPBREM-Luc)-driven reporter plasmids but not PBREM-enhancer of CYP2B6 (PBREM-Luc)-driven reporter activity. Furthermore, we showed that knockdown of CCAR1 suppressed CAR-induced UGT1A1 mRNA expression but did not affect CAR-induced CYP2B6 mRNA expression in HepTR/CAR and HepaRG cells. Moreover, CCAR1 could be recruited to the gtPBREM of the UGT1A1 enhancer by CAR but not to the PBREM of the CYP2B6 enhancer. Moreover, we showed that CCAR1 can act as a secondary coactivator by cooperating with the p160 family of steroid receptor coactivators (SRCs). These findings demonstrated CCAR1 to be a novel transcriptional cofactor for CAR and provided insight regarding the mechanism of CAR-mediated gene-selective transactivation.

A functional coupling between CRMP1 and Nav1.7 for retrograde propagation of Semaphorin3A signaling.

Semaphorin3A (Sema3A) is a secreted type of axon guidance molecule that regulates axon wiring through complexes of neuropilin-1 (NRP1) with PlexinA protein receptors. Sema3A regulates the dendritic branching through tetrodotoxin (TTX)-sensitive retrograde axonal transport of PlexA proteins and tropomyosin-related kinase A (TrkA) complex. We here demonstrate that Nav1.7 (encoded by SCN9A), a TTX-sensitive Na+ channel, by coupling with collapsin response mediator protein 1 (CRMP1), mediates the Sema3A-induced retrograde transport. In mouse dorsal root ganglion (DRG) neurons, Sema3A increased co-localization of PlexA4 and TrkA in the growth cones and axons. TTX treatment and RNAi knockdown of Nav1.7 sustained Sema3A-induced colocalized signals of PlexA4 and TrkA in growth cones and suppressed the subsequent localization of PlexA4 and TrkA in distal axons. A similar localization phenotype was observed in crmp1-/- DRG neurons. Sema3A induced colocalization of CRMP1 and Nav1.7 in the growth cones. The half maximal voltage was increased in crmp1-/- neurons when compared to that in wild type. In HEK293 cells, introduction of CRMP1 lowered the threshold of co-expressed exogenous Nav1.7. These results suggest that Nav1.7, by coupling with CRMP1, mediates the axonal retrograde signaling of Sema3A.

Aryl hydrocarbon receptor counteracts pharmacological efficacy of doxorubicin via enhanced AKR1C3 expression in triple negative breast cancer cells.

Triple-negative breast cancer (TNBC) is associated with poor prognosis, because of no effective targeted therapy. In the present study, we demonstrated the crucial role of the aryl hydrocarbon receptor (AhR) in mediating the effects of the chemotherapeutic agent doxorubicin (DOX) in the chemotherapeutic sensitivity of TNBC. Firstly, we established AhR knockout (KO) MDA-MB 231 TNBC cells. The cytotoxic effects of DOX were more pronounced in AhR KO cells than in parental cells. In addition, our results indicated that AhR KO cells showed downregulated expression of DOX-metabolism enzyme, aldo-keto reductase (AKR) 1C3, relative to those of parental cells. Furthermore, AhR was found to enhance AKR1C3 promoter reporter activity, suggesting that AKR1C3 mRNA transcription is activated by AhR. Additionally, our findings confirmed that the downregulation of AKR1C3 expression enhanced DOX sensitivity in MDA-MB 231 cells. Finally, AhR and AKR1C3 expression were positively correlated in human breast cancer. Taken together, our results suggested that AhR is involved in DOX sensitivity by regulating AKR1C3 expression in TNBC cells.

Retrograde signaling via axonal transport through signaling endosomes.

Neurons extend axons far from cell bodies, and retrograde communications from distal axons to cell bodies and/or dendrites play critical roles in the development and maintenance of neuronal circuits. In neurotrophin signaling, the retrograde axonal transport of endosomes containing active ligand-receptor complexes from distal axons to somatodendrite compartments mediates retrograde signaling. However, the generality and specificity of these endosome-based transportations called "signaling endosomes" remain to be elucidated. Here, I summarize the discovery of semaphorin3A signaling endosomes, the first example other than neurotrophins to regulate dendritic development via AMPA receptor GluA2 localization in dendrites. The molecular components of Sema3A and neurotrophin signaling endosomes are distinct, but partially overlap to regulate specific and common cellular events. Because receptors are transported back to the cell bodies, neurons must replenish receptors on the growth cone surface to ensure continued response to the target-derived ligands. Recent findings have demonstrated that retrograde signaling endosomes also induce anterograde delivery of nascent receptors in neurotrophin signaling. The coupling between anterograde and retrograde axonal transport via signaling endosomes therefore plays a critical role in regulating proper neuronal network formation.

Heregulin-induced cell migration is promoted by aryl hydrocarbon receptor in HER2-overexpressing breast cancer cells.

HER2 overexpression accounts for approximately 15-20% of all breast cancers. We have shown that HER2 overexpression leads to elevated expression of the aryl hydrocarbon receptor (AhR) in breast cancer cells. In this study, firstly, we showed that AhR expression was up-regulated by treatment with the HER3 ligand heregulin (HRG) in HER2-overexpressing breast cancer cell lines. Induction of AhR was mediated by transcriptional activation of the region of AhR promoter corresponding to - 190 to - 100 bp. In addition, HRG treatment elicited nuclear translocation of AhR. To investigate the role of AhR in HRG-HER2/HER3 signaling in HER2-overexpressing cells, we established AhR knockout (KO) HER2-overexpressing cells to perform wound-healing assays. HRG-induced cell migration was markedly attenuated by AhR KO. HRG-induced cell migration was associated with increased expression of the inflammatory cytokines interleukin (IL)-6 and IL-8 in wild type cells, but not in AhR KO cells. These results elucidate that AhR is an important factor for the malignancy in HER2 overexpressing breast cancers.

Identification of 10-dehydrooxyglycyuralin E as a selective human estrogen receptor alpha partial agonist.

Selective estrogen receptor modulators (SERMs) act as either agonist or antagonist of estrogen receptor (ER) in a tissue selective manner and have been used in several diseases such as breast cancer, postmenopausal syndrome, osteoporosis, and cardiovascular diseases. However, current SERMs may also increase the risk of serious side effects and trigger drug resistance. Herein, a screening program, that was designed to search for novel SERMs, resulted in the identification of a series of 2-arylbenzofuran-containing compounds that are ligands for ERα, when applying the Gaussia-luciferase reporter assay. One of these compounds, 10-dehydrooxyglycyuralin E (T9) was chemically synthesized. T9 showed anti-estrogenic/proliferative activity in ERα-positive breast cancer cells. Pretreatment of T9 prevented the mRNA expression of GREB1, which is an estrogen response gene. Furthermore, by an in silico docking simulation study we demonstrated that T9 showed interactions directly to ERα. Taken together, these results demonstrated that T9 is a candidate of SERMs and a useful seed compound for the foundation of the selective activity of SERMs.

TrkA mediates retrograde semaphorin 3A signaling through plexin A4 to regulate dendritic branching.

Semaphorin 3A (Sema3A), a secretory semaphorin, exerts various biological actions through a complex between neuropilin-1 and plexin-As (PlexAs). Sema3A induces retrograde signaling, which is involved in regulating dendritic localization of GluA2 (also known as GRIA2), an AMPA receptor subunit. Here, we investigated a possible interaction between retrograde signaling pathways for Sema3A and nerve growth factor (NGF). Sema3A induces colocalization of PlexA4 (also known as PLXNA4) signals with those of tropomyosin-related kinase A (TrkA, also known as NTRK1) in growth cones, and these colocalized signals were then observed along the axons. The time-lapse imaging of PlexA4 and several TrkA mutants showed that the kinase and dynein-binding activity of TrkA were required for Sema3A-induced retrograde transport of the PlexA4-TrkA complex along the axons. The inhibition of the phosphoinositide 3-kinase (PI3K)-Akt signal, a downstream signaling pathway of TrkA, in the distal axon suppressed Sema3A-induced dendritic localization of GluA2. The knockdown of TrkA suppressed Sema3A-induced dendritic localization of GluA2 and that suppressed Sema3A-regulated dendritic branching both in vitro and in vivo These findings suggest that by interacting with PlexA4, TrkA plays a crucial role in redirecting local Sema3A signaling to retrograde axonal transport, thereby regulating dendritic GluA2 localization and patterning.

Tripartite Motif Containing 24 Acts as a Novel Coactivator of the Constitutive Active/Androstane Receptor.

The constitutive androstane receptor (CAR) is a nuclear receptor that acts as a transcription factor for a variety of genes, including genes encoding xenobiotic, steroid, and drug-metabolizing enzymes and transporters. Transactivation of a target gene by a transcription factor is generally mediated through the concerted and stepwise recruitment of various proteins termed coregulators, including coactivators and corepressors. In this study, TRIM24 (also known as transcriptional intermediary factor 1 alpha) was found to interact with the CAR. TRIM24 enhanced the CAR-dependent transactivation in reporter assays using the direct repeat-4 motif, a binding site of the CAR. This enhancement was synergistically augmented in the presence of steroid receptor coactivator (SRC) 1 or SRC2, both of which are coactivators of the CAR. In addition, TRIM24 was recruited to the CAR-binding element of the CYP2B6 promoter together with the CAR. We also noted that knockdown of TRIM24 suppressed CAR-induced CYP2B6 mRNA expression in HepTR/CAR and HepaRG cells and suppressed CAR-induced CYP3A4 mRNA expression in HepaRG cells but not HepTR/CAR cells. From these results, we suggest that TRIM24 is a novel coactivator of the CAR that is involved in cell- and/or promoter- selective transactivation.