Developmental expression of PAM (protein associated with MYC) in the rodent brain

A Systematic Review of Circulatory microRNAs in Major Depressive Disorder: Potential Biomarkers for Disease Prognosis

Major depressive disorder (MDD) is a neuropsychiatric disorder, which remains challenging to diagnose and manage due to its complex endophenotype. In this aspect, circulatory microRNAs (cimiRNAs) offer great potential as biomarkers and may provide new insights for MDD diagnosis. Therefore, we systemically reviewed the literature to explore various cimiRNAs contributing to MDD diagnosis and underlying molecular pathways. A comprehensive literature survey was conducted, employing four databases from 2012 to January 2021. Out of 1004 records, 157 reports were accessed for eligibility criteria, and 32 reports meeting our inclusion criteria were considered for in-silico analysis. This study identified 99 dysregulated cimiRNAs in MDD patients, out of which 20 cimiRNAs found in multiple reports were selected for in-silico analysis. KEGG pathway analysis indicated activation of ALS, MAPK, p53, and P13K-Akt signaling pathways, while gene ontology analysis demonstrated that most protein targets were associated with transcription. In addition, chromosomal location analysis showed clustering of dysregulated cimiRNAs at proximity 3p22-p21, 9q22.32, and 17q11.2, proposing their coregulation with specific transcription factors primarily involved in MDD physiology. Further analysis of transcription factor sites revealed the existence of HIF-1, REST, and TAL1 in most cimiRNAs. These transcription factors are proposed to target genes linked with MDD, hypothesizing that first-wave cimiRNA dysregulation may trigger the second wave of transcription-wide changes, altering the protein expressions of MDD-affected cells. Overall, this systematic review presented a list of dysregulated cimiRNAs in MDD, notably miR-24-3p, let 7a-5p, miR-26a-5p, miR135a, miR-425-3p, miR-132, miR-124 and miR-16-5p as the most prominent cimiRNAs. However, various constraints did not permit us to make firm conclusions on the clinical significance of these cimiRNAs, suggesting the need for more research on single blood compartment to identify the biomarker potential of consistently dysregulated cimiRNAs in MDD, as well as the therapeutic implications of these in-silico insights.

Myc binding protein 2 suppresses M2-like phenotypes in macrophages during zymosan-induced inflammation in mice

MYCBP2 is an E3 ubiquitin ligase, which is well characterized as a key element in the inhibition of neuronal growth, synapse formation and synaptic strength by regulating several signaling pathways. Although MYCBP2 was suspected to be expressed also in immune cells, to date nothing is known about its role in inflammation. We used Multi-epitope ligand cartography (MELC), a method for multiple sequential immunohistology, to show that MYCBP2 is strongly expressed in monocyte-derived macrophages during zymosan-induced inflammation. We generated a myeloid-specific knockout mouse and found that loss of MYCBP2 in myeloid cells reduced nociceptive (painful) behavior during the resolution phase (1-3 days after zymosan injection). Quantitative MELC analyses and flow cytometric analysis showed an increased number of CD206-expressing macrophages in the inflamed paw tissue. Fittingly, CD206 and arginase 1 expression was upregulated in MYCBP2-deficient bone marrow-derived macrophages after polarization with IL10 or IL4. The regulation of protein expression in these macrophages by MYCBP2 varied depending on the polarization signal. The increased IL10-induced CD206 expression in MYCBP2-deficient macrophages was mediated by p38 MAPK, while IL4-induced CD206 expression in MYCBP2-deficient macrophages was mediated by protein kinase A.

The PHR proteins: intracellular signaling hubs in neuronal development and axon degeneration

During development, a coordinated and integrated series of events must be accomplished in order to generate functional neural circuits. Axons must navigate toward target cells, build synaptic connections, and terminate outgrowth. The PHR proteins (consisting of mammalian Phr1/MYCBP2, Drosophila Highwire and C. elegans RPM-1) function in each of these events in development. Here, we review PHR function across species, as well as the myriad of signaling pathways PHR proteins regulate. These findings collectively suggest that the PHR proteins are intracellular signaling hubs, a concept we explore in depth. Consistent with prominent developmental functions, genetic links have begun to emerge between PHR signaling networks and neurodevelopmental disorders, such as autism, schizophrenia and intellectual disability. Finally, we discuss the recent and important finding that PHR proteins regulate axon degeneration, which has further heightened interest in this fascinating group of molecules.

MYCBP2 Is a Guanosine Exchange Factor for Ran Protein and Determines Its Localization in Neurons of Dorsal Root Ganglia

The small GTPase Ran coordinates retrograde axonal transport in neurons, spindle assembly during mitosis, and the nucleo-cytoplasmic transport of mRNA. Its localization is tightly regulated by the GTPase-activating protein RanGAP1 and the nuclear guanosine exchange factor (GEF) RCC1. We show that loss of the neuronal E3 ubiquitin ligase MYCBP2 caused the up-regulation of Ran and RanGAP1 in dorsal root ganglia (DRG) under basal conditions and during inflammatory hyperalgesia. SUMOylated RanGAP1 physically interacted with MYCBP2 and inhibited its E3 ubiquitin ligase activity. Stimulation of neurons induced a RanGAP1-dependent translocation of MYCBP2 to the nucleus. In the nucleus of DRG neurons MYCBP2 co-localized with Ran and facilitated through its RCC1-like domain the GDP/GTP exchange of Ran. In accordance with the necessity of a GEF to promote GTP-binding and nuclear export of Ran, the nuclear localization of Ran was strongly increased in MYCBP2-deficient DRGs. The finding that other GEFs for Ran besides RCC1 exist gives new insights in the complexity of the regulation of the Ran signaling pathway.

MiR-1247-5p is overexpressed in castration resistant prostate cancer and targets MYCBP2

BACKGROUND

Recently, there has been increasing attention on the role of microRNAs (miRNAs) in cancer development. Several expression profiling studies have provided evidence of aberrant expression of miRNAs in prostate cancer and have highlighted the potential use of specific miRNA expression signatures as prognostic or predictive markers. Here we report an expression analysis of miR-1247-5p, miR-1249, miR-1269a, miR-1271-5p, miR-1290, miR-1291, and miR-1299.

METHODS

qRT-PCR was performed to validate the differential expression of miRNAs in clinical samples, and the effect of miR-1247-5p was studied in prostate cancer cell lines transiently transfected with a miR-1247-5p mimic. The expression of miR-1247-5p's putative target MYCBP2 was evaluated by qRT-PCR and Western blotting, and the interaction of the miRNA with the target gene was assessed using a luciferase assay.

RESULTS

We found a significant up-regulation of miR-1247-5p in castration-resistant prostate cancer (CRPC) samples compared to non-malignant prostate. The expression of miR-1247-5p was subsequently studied in prostate cancer (PC) cell lines where an up-regulation of miR-1247-5p was observed in the androgen-independent PC-3 model. Target prediction analysis for miR-1247-5p performed online revealed that MYCBP2 (myc-binding protein 2) was a high-scoring potential target. Functional studies in vitro performed using PC-3 and LNCaP models confirmed the down-regulation of MYCBP2 at the mRNA and protein levels, and a luciferase assay showed interaction between the miRNA and target gene.

CONCLUSION

miR-1247-5p is overexpressed in CRPC and targets MYCBP2.

Regulation of neuronal functions by the E3-ubiquitinligase protein associated with MYC (MYCBP2)

The E3-ubiquitinligase MYCBP2 regulates neuronal growth, synaptogenesis and synaptic plasticity by modulating several signaling pathways including the p38 MAPK signaling cascade. We found that loss of MYCBP2 in peripheral sensory neurons inhibits the internalization of transient receptor potential vanilloid receptor 1 (TRPV1) in a p38 MAPK-dependent manner. This prevented desensitization of activity-induced calcium increases and prolongs formalin-induced thermal hyperalgesia in mice. Besides its function in pain perception TRPV1 is also involved in the regulation of neuronal growth. Therefore, the observed effect of MYCBP2 on TRPV1 internalization could be part of the mechanisms underlying its well documented regulatory role in neuronal growth. The clarification of the mechanism is important for the understanding of the different MYCBP2-functions in diverse neuronal subpopulations and species.

The ubiquitin ligase MYCBP2 regulates transient receptor potential vanilloid receptor 1 (TRPV1) internalization through inhibition of p38 MAPK signaling

The E3 ubiquitin ligase MYCBP2 negatively regulates neuronal growth, synaptogenesis, and synaptic strength. More recently it was shown that MYCBP2 is also involved in receptor and ion channel internalization. We found that mice with a MYCBP2-deficiency in peripheral sensory neurons show prolonged thermal hyperalgesia. Loss of MYCBP2 constitutively activated p38 MAPK and increased expression of several proteins involved in receptor trafficking. Surprisingly, loss of MYCBP2 inhibited internalization of transient receptor potential vanilloid receptor 1 (TRPV1) and prevented desensitization of capsaicin-induced calcium increases. Lack of desensitization, TRPV internalization and prolonged hyperalgesia were reversed by inhibition of p38 MAPK. The effects were TRPV-specific, since neither mustard oil-induced desensitization nor behavioral responses to mechanical stimuli were affected. In summary, we show here for the first time that p38 MAPK activation can inhibit activity-induced ion channel internalization and that MYCBP2 regulates internalization of TRPV1 in peripheral sensory neurons as well as duration of thermal hyperalgesia through p38 MAPK.

Toponomics analysis of functional interactions of the ubiquitin ligase PAM (Protein Associated with Myc) during spinal nociceptive processing

Protein associated with Myc (PAM) is a giant E3 ubiquitin ligase of 510 kDa. Although the role of PAM during neuronal development is well established, very little is known about its function in the regulation of synaptic strength. Here we used multiepitope ligand cartography (MELC) to study protein network profiles associated with PAM during the modulation of synaptic strength. MELC is a novel imaging technology that utilizes biomathematical tools to describe protein networks after consecutive immunohistochemical visualization of up to 100 proteins on the same sample. As an in vivo model to modulate synaptic strength we used the formalin test, a common model for acute and inflammatory pain. MELC analysis was performed with 37 different antibodies or fluorescence tags on spinal cord slices and led to the identification of 1390 PAM-related motifs that distinguish untreated and formalin-treated spinal cords. The majority of these motifs related to ubiquitin-dependent processes and/or the actin cytoskeleton. We detected an intermittent colocalization of PAM and ubiquitin with TSC2, a known substrate of PAM, and the glutamate receptors mGluR5 and GLUR1. Importantly these complexes were detected exclusively in the presence of F-actin. A direct PAM/F-actin interaction was confirmed by colocalization and cosedimentation. The binding of PAM toward F-actin varied strongly between the PAM splice forms found in rat spinal cords. PAM did not ubiquitylate actin or alter actin polymerization and depolymerization. However, F-actin decreased the ubiquitin ligase activity of purified PAM. Because PAM activation is known to involve its translocation, the binding of PAM to F-actin may serve to control its subcellular localization as well as its activity. Taken together we show that defining protein network profiles by topological proteomics analysis is a useful tool to identify previously unknown protein/protein interactions that underlie synaptic processes.

The RCC1 domain of protein associated with Myc (PAM) interacts with and regulates KCC2

GABAergic and glycinergic function is dependent on neuronal intracellular chloride. The neuron-specific electroneutral potassium (K(+)) and chloride (Cl(-)) cotransporter (KCC2), is a key regulator of neuronal Cl(-), yet little is known about KCC2 regulation. Using yeast two-hybrid, we identified Protein Associated with Myc (PAM) as a binding partner of KCC2. The RCC1 (Regulator of Chromatin Condensation) domain of PAM binds to the carboxyl terminus of KCC2, as demonstrated through yeast two-hybrid and GST-pull-down assays. RCC1/PAM and full-length KCC2 coimmunoprecipitate following heterologous co-expression in HEK293 cells. Additionally, (86)Rb/K(+) uptake assays in this model system show that RCC1/PAM causes increased KCC2-mediated flux. After narrowing down RCC1/PAM binding to a 20 amino acid region on the KCC2 carboxyl terminus, we created a point mutant in this region to eliminate interaction between the KCC2 carboxyl terminus and RCC1/PAM. This same mutation abolishes N-ethylmaleimide activation of KCC2, suggesting that PAM plays a role in modulating KCC2 function.

The requirement for Phr1 in CNS axon tract formation reveals the corticostriatal boundary as a choice point for cortical axons

Phr1 is the single well-conserved murine ortholog of the invertebrate ubiquitin ligase genes highwire (in Drosophila) and rpm-1 (in Caenorhabditis elegans). The function and mechanism of action of highwire and rpm-1 are similar--both cell-autonomously regulate synaptogenesis by down-regulating the ortholog of the mitogen-activated protein kinase kinase kinase dual leucine zipper kinase (MAPKKK DLK). Here, using a targeted conditional mutant, we demonstrate that Phr1 also plays essential roles in mammalian neural development. As in invertebrates, Phr1 functions cell-autonomously to sculpt motor nerve terminals. In addition, Phr1 plays essential roles in the formation of major CNS axon tracts including those of the internal capsule, in part via cell-nonautonomous mechanisms, and these results reveal a choice point for cortical axons at the corticostriatal boundary. Furthermore, whereas the neurite morphology phenotypes of highwire and rpm-1 are suppressed by loss of DLK in flies and worms, Phr1-dependent CNS defects persist in Phr1, DLK double mutants. Thus, in the mammalian nervous system Phr1 is required for formation of major CNS axon tracts via a mechanism that is both cell-nonautonomous and independent of DLK.

DFsn collaborates with Highwire to down-regulate the Wallenda/DLK kinase and restrain synaptic terminal growth

Background

The growth of new synapses shapes the initial formation and subsequent rearrangement of neural circuitry. Genetic studies have demonstrated that the ubiquitin ligase Highwire restrains synaptic terminal growth by down-regulating the MAP kinase kinase kinase Wallenda/dual leucine zipper kinase (DLK). To investigate the mechanism of Highwire action, we have identified DFsn as a binding partner of Highwire and characterized the roles of DFsn in synapse development, synaptic transmission, and the regulation of Wallenda/DLK kinase abundance.

Results

We identified DFsn as an F-box protein that binds to the RING-domain ubiquitin ligase Highwire and that can localize to the Drosophila neuromuscular junction. Loss-of-function mutants for DFsn have a phenotype that is very similar to highwire mutants – there is a dramatic overgrowth of synaptic termini, with a large increase in the number of synaptic boutons and branches. In addition, synaptic transmission is impaired in DFsn mutants. Genetic interactions between DFsn and highwire mutants indicate that DFsn and Highwire collaborate to restrain synaptic terminal growth. Finally, DFsn regulates the levels of the Wallenda/DLK kinase, and wallenda is necessary for DFsn-dependent synaptic terminal overgrowth.

Conclusion

The F-box protein DFsn binds the ubiquitin ligase Highwire and is required to down-regulate the levels of the Wallenda/DLK kinase and restrain synaptic terminal growth. We propose that DFsn and Highwire participate in an evolutionarily conserved ubiquitin ligase complex whose substrates regulate the structure and function of synapses.

Alternative splicing in protein associated with Myc (Pam) influences its binding to c-Myc

We recently identified Pam (for protein associated with c-Myc), as a binding partner for the tuberous sclerosis complex (TSC) protein tuberin in brain. The highly conserved Pam homologs in Drosophila and C. elegans are neuron-specific proteins that regulate synaptic growth. The Pam gene contains 83 exons and encodes a 4,641-amino-acid polypeptide with a predicted molecular weight of approximately 510 kDa. In a previous study, we demonstrated that Pam is expressed as two forms, approximately 450 kDa in rat embryonic and a approximately 350 kDa in rat adult brain. Here we have extended that work to show the approximately 450 kDa form is expressed in rat embryonic kidney, heart, and lung and in rat cell lines, and the approximately 350 kDa form is expressed in adult rat tissues as well as in human and mouse brain and human and mouse cell lines. To understand the size difference, we investigated alternative splicing of Pam in brain and detected six isoforms in the Myc-binding region resulting from splicing of exon 53, and three new exons, 52A, 56, and 56A. We also demonstrate that the presence of exon 52A in Pam significantly enhances binding to Myc, suggesting functional importance of this alternative splicing. The presence of Pam in many cellular compartments, its spliced variants, as well as its multiple binding partners, including tuberin, make it a complex, yet intriguing protein in the nervous system.

Histidine Residues 912 and 913 in Protein Associated with Myc Are Necessary for the Inhibition of Adenylyl Cyclase Activity

We reported previously that protein associated with Myc (PAM) interacts with the C2 domain of type V adenylyl cyclase (ACV-C2) and that purified PAM is a potent inhibitor of Galphas-stimulated ACV activity (J Biol Chem 276:47583-47589, 2001). The present study was conducted to identify the region in PAM that inhibits ACV activity and to determine whether its binding with the ACV-C2 is necessary and sufficient to inhibit the enzyme. Coexpression of ACV and full-length PAM or its N-terminal third (PAM-N) in COS-7 cells inhibited isoproterenol-stimulated cAMP accumulation. Deletion of the RCC1 homology domains in PAM-N abolished its ability to inhibit isoproterenol-stimulated cAMP formation in cells. Purified GST fusion protein of the second RCC1 homology domain (RHD2) of PAM was sufficient to bind with ACV-C2 and inhibit Galphas-stimulated ACV activity. In addition, deletion of 11 amino acids in GST-RHD2 obliterated its ability to bind with and inhibit ACV. The C terminus of the RHD2 domain bound with ACV-C2 without inhibiting enzyme activity. Furthermore, substitution of His912 and His913 with alanine in the GST-RHD2 obliterated its ability to inhibit ACV without altering binding to ACV-C2. Likewise, H912/913A mutants of both PAM-N and full-length PAM did not inhibit cAMP formation in cells. Thus, the RHD2 domain of PAM is sufficient to inhibit Galphas-stimulated ACV activity and the binding of RHD2 to ACV-C2 is necessary but not sufficient for this inhibition. Moreover, His912 and His913 in PAM are critical for inhibiting ACV.

PAM mediates sustained inhibition of cAMP signaling by sphingosine-1-phosphate

PAM (Protein Associated with Myc) is an almost ubiquitously expressed protein that is one of the most potent inhibitors of adenylyl cyclase activity known so far. Here we show that PAM is localized at the endoplasmic reticulum in HeLa cells and that upon serum treatment PAM is recruited to the plasma membrane, causing an inhibition of adenylyl cyclase activity. We purified the serum factor that induced PAM translocation and identified it as sphingosine-1-phosphate (S1P). Within 15 min after incubation with S1P, PAM appeared at the plasma membrane and was detectable for up to 120 min. Sphingosine-1-phosphate induced adenylyl cyclase inhibition in two phases: an initial (1-10 min) and a late (20-240 min) phase. The initial adenylyl cyclase inhibition was Gi-mediated and PAM independent. In the late phase, adenylyl cyclase inhibition was PAM dependent and attenuated cyclic AMP (cAMP) signaling by various cAMP-elevating signals. This makes PAM the longest lasting nontranscriptional regulator of adenylyl cyclase activity known to date and presents a novel mechanism for the temporal regulation of cAMP signaling.

Protein associated with Myc (PAM) is involved in spinal nociceptive processing

PAM (protein associated with Myc) is a potent inhibitor of adenylyl cyclases (ACs) which is primarily expressed in neurones. Here we describe that PAM is highly expressed in dorsal horn neurones and motoneuron of the spinal cord, as well as in neurones of dorsal root ganglia in adult rats. PAM mRNA expression is differentially regulated during development in both spinal cord and dorsal root ganglia of rats, being strongest during the major respective synaptogenic periods. In adult rats, PAM expression was up-regulated in the spinal cord after peripheral nociceptive stimulation using zymosan and formalin injection, suggesting a role for PAM in spinal nociceptive processing. Since PAM inhibited Galphas-stimulated AC activity in dorsal root ganglia as well as spinal cord lysates, we hypothesized that PAM may reduce spinal nociceptive processing by inhibition of cAMP-dependent signalling. Accordingly, intrathecal treatment with antisense but not sense oligonucleotides against PAM increased basal and Galphas-stimulated AC activity in the spinal cord and enhanced formalin-induced nociceptive behaviour in adult rats. Taken together our findings demonstrate that PAM is involved in spinal nociceptive processing.

Highwire Regulates Presynaptic BMP Signaling Essential for Synaptic Growth

Highwire (Hiw), a putative RING finger E3 ubiquitin ligase, negatively regulates synaptic growth at the neuromuscular junction (NMJ) in Drosophila. hiw mutants have dramatically larger synaptic size and increased numbers of synaptic boutons. Here we show that Hiw binds to the Smad protein Medea (Med). Med is part of a presynaptic bone morphogenetic protein (BMP) signaling cascade consisting of three receptor subunits, Wit, Tkv, and Sax, in addition to the Smad transcription factor Mad. When compared to wild-type, mutants of BMP signaling components have smaller NMJ size, reduced neurotransmitter release, and aberrant synaptic ultrastructure. BMP signaling mutants suppress the excessive synaptic growth in hiw mutants. Activation of BMP signaling, which in wild-type does not cause additional growth, in hiw mutants does lead to further synaptic expansion. These results reveal a balance between positive BMP signaling and negative regulation by Highwire, governing the growth of neuromuscular synapses.

Evidence for a conserved function in synapse formation reveals Phr1 as a candidate gene for respiratory failure in newborn mice

Genetic studies using a set of overlapping deletions centered at the piebald locus on distal mouse chromosome 14 have defined a genomic region associated with respiratory distress and lethality at birth. We have isolated and characterized the candidate gene Phr1 that is located within the respiratory distress critical genomic interval. Phr1 is the ortholog of the human Protein Associated with Myc as well as Drosophila highwire and Caenorhabditis elegans regulator of presynaptic morphology 1. Phr1 is expressed in the embryonic and postnatal nervous system. In mice lacking Phr1, the phrenic nerve failed to completely innervate the diaphragm. In addition, nerve terminal morphology was severely disrupted, comparable with the synaptic defects seen in the Drosophila hiw and C. elegans rpm-1 mutants. Although intercostal muscles were completely innervated, they also showed dysmorphic nerve terminals. In addition, sensory neuron terminals in the diaphragm were abnormal. The neuromuscular junctions showed excessive sprouting of nerve terminals, consistent with inadequate presynaptic stimulation of the muscle. On the basis of the abnormal neuronal morphology seen in mice, Drosophila, and C. elegans, we propose that Phr1 plays a conserved role in synaptic development and is a candidate gene for respiratory distress and ventilatory disorders that arise from defective neuronal control of breathing.

Pam and its ortholog highwire interact with and may negatively regulate the TSC1.TSC2 complex

Tuberous Sclerosis Complex (TSC) is an autosomal dominant disorder associated with mutations in TSC1, which codes for hamartin, or TSC2, which codes for tuberin. The brain is one of the most severely affected organs, and CNS lesions include cortical tubers and subependymal giant cell astrocytomas, resulting in mental retardation and seizures. Tuberin and hamartin function together as a complex in mammals and Drosophila. We report here the association of Pam, a protein identified as an interactor of Myc, with the tuberin-hamartin complex in the brain. The C terminus of Pam containing the RING zinc finger motif binds to tuberin. Pam is expressed in embryonic and adult brain as well as in cultured neurons. Pam has two forms in the rat CNS, an approximately 450-kDa form expressed in early embryonic stages and an approximately 350-kDa form observed in the postnatal period. In cortical neurons, Pam co-localizes with tuberin and hamartin in neurites and growth cones. Although Pam function(s) are yet to be defined, the highly conserved Pam homologs, HIW (Drosophila) and RPM-1 (Caenorhabditis elegans), are neuron-specific proteins that regulate synaptic growth. Here we show that HIW can genetically interact with the Tsc1.Tsc2 complex in Drosophila and could negatively regulate Tsc1.Tsc2 activity. Based on genetic studies, HIW has been implicated in ubiquitination, possibly functioning as an E3 ubiquitin ligase through the RING zinc finger domain. Therefore, we hypothesize that Pam, through its interaction with tuberin, could regulate the ubiquitination and proteasomal degradation of the tuberin-hamartin complex particularly in the CNS.