When overexpressed, a novel centrosomal protein, RanBPM, causes ectopic microtubule nucleation similar to gamma-tubulin

ATM-Mediated translocation of RanBPM regulates DNA damage response by stabilizing p21 in non-small cell lung cancer cells

PURPOSE

Platinum-based chemotherapy remains a standard-of-care for most patients with advanced non-small cell lung cancer (NSCLC). DNA damage response (DDR) induced by platinum or Etoposide activated a panel of cell cycle-regulatory proteins including p21 through p53 pathway. Previous studies have reported that RanBPM has been involved in various cellular processes such as DDR by interacting with multiple proteins. However, the underlying mechanism remains unclear.

METHODS

NSCLC tissue microarrays were used for assessing the expression of RanBPM by immunohistochemical staining. The roles of RanBPM in the DDR of NSCLC progression was examined in in vitro cell lines and in vivo animal models. The regulation of RanBPM on protein stability and ubiquitination levels were investigated by immunoblots and in vivo ubiquitylation assay.

RESULTS

The level of p21 or RanBPM is lower in NSCLC than non-malignant tissues and has a highly positive correlation. Mechanistically, RanBPM protein physically interacts with p21, and RanBPM deubiquitinates p21 by recruiting a deubiquitinase USP11 to maintain protein stability of p21. RanBPM silencing significantly decreased p21 protein level. Conversely, RanBPM overexpression led to the accumulation of endogenous p21 protein regardless of p53 status. Functionally, RanBPM regulates DDR in a p21-dependent manner. Furthermore, DNA damage significantly promoted the nuclear translocation of RanBPM protein through ATM signaling pathways.

CONCLUSION

RanBPM is a novel regulator of P21 protein stability, and plays a critical role in the regulation of DDR.

The genetics of autism spectrum disorder in an East African familial cohort

Autism spectrum disorder (ASD) is a group of complex neurodevelopmental conditions affecting communication and social interaction in 2.3% of children. Studies that demonstrated its complex genetic architecture have been mainly performed in populations of European ancestry. We investigate the genetics of ASD in an East African cohort (129 individuals) from a population with higher prevalence (5%). Whole-genome sequencing identified 2.13 million private variants in the cohort and potentially pathogenic variants in known ASD genes (including CACNA1C, CHD7, FMR1, and TCF7L2). Admixture analysis demonstrated that the cohort comprises two ancestral populations, African and Eurasian. Admixture mapping discovered 10 regions that confer ASD risk on the African haplotypes, containing several known ASD genes. The increased ASD prevalence in this population suggests decreased heterogeneity in the underlying genetic etiology, enabling risk allele identification. Our approach emphasizes the power of African genetic variation and admixture analysis to inform the architecture of complex disorders.

Analysis of Ser/Thr Kinase HASPIN-Interacting Proteins in the Spermatids

HASPIN is predominantly expressed in spermatids, and plays an important role in cell division in somatic and meiotic cells through histone H3 phosphorylation. The literature published to date has suggested that HASPIN may play multiple roles in cells. Here, 10 gene products from the mouse testis cDNA library that interact with HASPIN were isolated using the two-hybrid system. Among them, CENPJ/CPAP, KPNA6/importin alpha 6, and C1QBP/HABP1 were analyzed in detail for their interactions with HASPIN, with HASPIN phosphorylated C1QBP as the substrate. The results indicated that HASPIN is involved in spermatogenesis through the phosphorylation of C1QBP in spermatids, and also may be involved in the formation of centrosomes.

RNA-Seq analysis in giant pandas reveals the differential expression of multiple genes involved in cataract formation

BACKGROUND

The giant panda (Ailuropoda melanoleuca) is an endangered mammalian species native to China. Fewer than 2500 giant pandas are known to exist, many of which are bred in captivity as a means to preserve and repopulate the species. Like other captive mammals, giant pandas acquire age-related cataracts, reducing their quality of life. Recent comparative genome-wide methylation analysis revealed 110 differentially methylated genes associated with cataract formation including six also associated with the formation of age-related cataracts in humans.

RESULTS

To investigate the pathological pathway in greater detail, here we used RNA-Seq analysis to investigate the differential expression profiles of genes in three giant pandas with cataracts and three healthy controls. We identified more than 700 differentially expressed genes, 29 of which were selected for further analysis based on their low q-value. We found that many of the genes encoded regulatory and signaling proteins associated with the control of cell growth, migration, differentiation and apoptosis, supporting previous research indicating a key role for apoptosis in cataract formation.

CONCLUSION

The identification of genes involved in the formation of age-related cataracts could facilitate the development of predictive markers, preventative measures and even new therapies to improve the life of captive animals.

Designing a highly immunogenic multi epitope based subunit vaccine against Bacillus cereus

Objective

Serious non-gastrointestinal-tract infections and food poisoning are caused by Bacillus cereus. Vaccination against B. cereus is very important. The aim of this study was to identify and analyze B and T cell epitopes for chromate transporter protein of the bacteria.

Methods

Multiple sequence alignment with the Clustal Omega method was used to identify conserved regions and Geneious Prime was used to produce a consensus sequence. T and B cell epitopes were predicted by various computational tools from the NetCTL and Immune Epitope Database (IEDB), respectively.

Results

Altogether, 6 HTL cells and 11 CTL epitopes were predicted. This vaccine's molecular docking is done with Patch Dock and LigPlot to verify interactions. The immune server (C-IMMSIM) was used to develop In silico immune response in order to assess the multi-epitope vaccine's immunogenic profile.

Conclusion

We designed universal vaccine against B. cereus responsible for food poisoning. The disease may be avoided with the aid of the proposed epitope-based vaccine.

Principal Postulates of Centrosomal Biology. Version 2020

The centrosome, which consists of two centrioles surrounded by pericentriolar material, is a unique structure that has retained its main features in organisms of various taxonomic groups from unicellular algae to mammals over one billion years of evolution. In addition to the most noticeable function of organizing the microtubule system in mitosis and interphase, the centrosome performs many other cell functions. In particular, centrioles are the basis for the formation of sensitive primary cilia and motile cilia and flagella. Another principal function of centrosomes is the concentration in one place of regulatory proteins responsible for the cell's progression along the cell cycle. Despite the existing exceptions, the functioning of the centrosome is subject to general principles, which are discussed in this review.

Ran GTPase: A Key Player in Tumor Progression and Metastasis

Ran (Ras-related nuclear protein) GTPase is a member of the Ras superfamily. Like all the GTPases, Ran cycles between an active (GTP-bound) and inactive (GDP-bound) state. However, Ran lacks the CAAX motif at its C-terminus, a feature of other small GTPases that ensures a plasma membrane localization, and largely traffics between the nucleus and the cytoplasm. Ran regulates nucleo-cytoplasmic transport of molecules through the nuclear pore complex and controls cell cycle progression through the regulation of microtubule polymerization and mitotic spindle formation. The disruption of Ran expression has been linked to cancer at different levels - from cancer initiation to metastasis. In the present review, we discuss the contribution of Ran in the acquisition of three hallmarks of cancer, namely, proliferative signaling, resistance to apoptosis, and invasion/metastasis, and highlight its prognostic value in cancer patients. In addition, we discuss the use of this GTPase as a therapeutic target in cancer.

Actin waves transport RanGTP to the neurite tip to regulate non-centrosomal microtubules in neurons

Microtubules (MTs) are the most abundant cytoskeleton in neurons, and control multiple facets of their development. While the MT-organizing center (MTOC) in mitotic cells is typically located at the centrosome, the MTOC in neurons switches to non-centrosomal sites. A handful of cellular components have been shown to promote non-centrosomal MT (ncMT) formation in neurons, yet the regulation mechanism remains unknown. Here, we demonstrate that the small GTPase Ran is a key regulator of ncMTs in neurons. Using an optogenetic tool that enables light-induced local production of RanGTP, we demonstrate that RanGTP promotes ncMT plus-end growth along the neurite. Additionally, we discovered that actin waves drive the anterograde transport of RanGTP. Pharmacological disruption of actin waves abolishes the enrichment of RanGTP and reduces growing ncMT plus-ends at the neurite tip. These observations identify a novel regulation mechanism for ncMTs and pinpoint an indirect connection between the actin and MT cytoskeletons in neurons.

MoRBP9 Encoding a Ran-Binding Protein Microtubule-Organizing Center Is Required for Asexual Reproduction and Infection in the Rice Blast Pathogen Magnaporthe oryzae

Like many fungal pathogens, the conidium and appressorium play key roles during polycyclic dissemination and infection of Magnaporthe oryzae. Ran-binding protein microtubule-organizing center (RanBPM) is a highly conserved nucleocytoplasmic protein. In animalia, RanBPM has been implicated in apoptosis, cell morphology, and transcription. However, the functional roles of RanBPM, encoded by MGG_00753 (named MoRBP9) in M. oryzae, have not been elucidated. Here, the deletion mutant ΔMorbp9 for MoRBP9 was generated via homologous recombination to investigate the functions of this gene. The ΔMorbp9 exhibited normal conidial germination and vegetative growth but dramatically reduced conidiation compared with the wild type, suggesting that MoRBP9 is involved in conidial production. ΔMorbp9 conidia failed to produce appressoria on hydrophobic surfaces, whereas ΔMorbp9 still developed aberrantly shaped appressorium-like structures at hyphal tips on the same surface, suggesting that MoRBP9 is involved in the morphology of appressorium-like structures from hyphal tips and is critical for development of appressorium from germ tubes. Taken together, our results indicated that MoRBP9 played a pleiotropic role in polycyclic dissemination and infection-related morphogenesis of M. oryzae.

Cell signalling pathway regulation by RanBPM: molecular insights and disease implications

RanBPM (Ran-binding protein M, also called RanBP9) is an evolutionarily conserved, ubiquitous protein which localizes to both nucleus and cytoplasm. RanBPM has been implicated in the regulation of a number of signalling pathways to regulate several cellular processes such as apoptosis, cell adhesion, migration as well as transcription, and plays a critical role during development. In addition, RanBPM has been shown to regulate pathways implicated in cancer and Alzheimer's disease, implying that RanBPM has important functions in both normal and pathological development. While its functions in these processes are still poorly understood, RanBPM has been identified as a component of a large complex, termed the CTLH (C-terminal to LisH) complex. The yeast homologue of this complex functions as an E3 ubiquitin ligase that targets enzymes of the gluconeogenesis pathway. While the CTLH complex E3 ubiquitin ligase activity and substrates still remain to be characterized, the high level of conservation between the complexes in yeast and mammals infers that the CTLH complex could also serve to promote the degradation of specific substrates through ubiquitination, therefore suggesting the possibility that RanBPM's various functions may be mediated through the activity of the CTLH complex.

Role of Bicaudal C1 in renal gluconeogenesis and its novel interaction with the CTLH complex

Altered glucose and lipid metabolism fuel cystic growth in polycystic kidneys, but the cause of these perturbations is unclear. Renal cysts also associate with mutations in Bicaudal C1 (Bicc1) or in its self-polymerizing sterile alpha motif (SAM). Here, we found that Bicc1 maintains normoglycemia and the expression of the gluconeogenic enzymes FBP1 and PEPCK in kidneys. A proteomic screen revealed that Bicc1 interacts with the C-Terminal to Lis-Homology domain (CTLH) complex. Since the orthologous Gid complex in S. cerevisae targets FBP1 and PEPCK for degradation, we mapped the topology among CTLH subunits and found that SAM-mediated binding controls Bicc1 protein levels, whereas Bicc1 inhibited the accumulation of several CTLH subunits. Under the conditions analyzed, Bicc1 increased FBP1 protein levels independently of the CTLH complex. Besides linking Bicc1 to cell metabolism, our findings reveal new layers of complexity in the regulation of renal gluconeogenesis compared to lower eukaryotes.

Polycystic kidney diseases (PKD) are incurable inherited chronic disorders marked by fluid-filled cysts that frequently cause renal failure. A glycolytic metabolism reminiscent of cancerous cells accelerates cystic growth, but the mechanism underlying such metabolic re-wiring is poorly understood. PKD-like cystic kidneys also develop in mice that lack the RNA-binding protein Bicaudal-C (Bicc1), and mutations in a single copy of human BICC1 associate with renal cystic dysplasia. Here, we report that Bicc1 regulates renal gluconeogenesis. A screen for interacting factors revealed that Bicc1 binds the C-Terminal to Lis-Homology domain (CTLH) complex, which in lower eukaryotes mediates degradation of gluconeogenic enzymes. By contrast, Bicc1 and the mammalian CTLH complex regulated each other, and Bicc1 stimulated the accumulation of the rate-limiting gluconeogenic enzyme even in cells depleted of CTLH subunits. Our finding that Bicc1 is required for normoglycemia implies that renal gluconeogenesis may be important to inhibit cyst formation.

Proteomic Profiling of Microtubule Self-organization in M-phase

Microtubules (MTs) and associated proteins can self-organize into complex structures such as the bipolar spindle, a process in which RanGTP plays a major role. Addition of RanGTP to M-phase Xenopus egg extracts promotes the nucleation and self-organization of MTs into asters and bipolar-like structures in the absence of centrosomes or chromosomes. We show here that the complex proteome of these RanGTP-induced MT assemblies is similar to that of mitotic spindles. Using proteomic profiling we show that MT self-organization in the M-phase cytoplasm involves the non-linear and non-stoichiometric recruitment of proteins from specific functional groups. Our study provides for the first time a temporal understanding of the protein dynamics driving MT self-organization in M-phase.

Scorpins in the DNA Damage Response

The DNA Damage Response (DDR) is a complex signaling network that comes into play when cells experience genotoxic stress. Upon DNA damage, cellular signaling pathways are rewired to slow down cell cycle progression and allow recovery. However, when the damage is beyond repair, cells activate complex and still not fully understood mechanisms, leading to a complete proliferative arrest or cell death. Several conventional and novel anti-neoplastic treatments rely on causing DNA damage or on the inhibition of the DDR in cancer cells. However, the identification of molecular determinants directing cancer cells toward recovery or death upon DNA damage is still far from complete, and it is object of intense investigation. SPRY-containing RAN binding Proteins (Scorpins) RANBP9 and RANBP10 are evolutionarily conserved and ubiquitously expressed proteins whose biological functions are still debated. RANBP9 has been previously implicated in cell proliferation, survival, apoptosis and migration. Recent studies also showed that RANBP9 is involved in the Ataxia Telangiectasia Mutated (ATM) signaling upon DNA damage. Accordingly, cells lacking RANBP9 show increased sensitivity to genotoxic treatment. Although there is no published evidence, extensive protein similarities suggest that RANBP10 might have partially overlapping functions with RANBP9. Like RANBP9, RANBP10 bears sites putative target of PIK-kinases and high throughput studies found RANBP10 to be phosphorylated following genotoxic stress. Therefore, this second Scorpin might be another overlooked player of the DDR alone or in combination with RANBP9. This review focuses on the relatively unknown role played by RANBP9 and RANBP10 in responding to genotoxic stress.

High levels of centrosomal protein 55 expression is associated with poor clinical prognosis in patients with cervical cancer

Centrosomal protein 55 (CEP55) has been proposed to have a role in tumor development. However, the expression pattern and clinical relevance of CEP55 has, to the best of our knowledge, not yet been investigated in cervical cancer. The mRNA levels of CEP55 in cervical cancer tissues and paired adjacent non-cancerous tissues were examined by reverse transcription-quantitative polymerase chain reaction (RT-qPCR). The present study assessed the association between immunohistochemical staining of CEP55 and clinicopathological characteristics and survival rates of patients. Compared with the adjacent non-cancerous tissues, CEP55 expression was significantly increased in cervical tumor tissues, as demonstrated by the results of RT-qPCR. High expression of CEP55 was significantly associated with lymph node metastasis (P=0.008) and advanced tumor stage (P=0.010). Furthermore, CEP55 overexpression in cervical cancer specimens was significantly associated with poor 5-year overall and recurrence-free survival rates (P=0.021 and P=0.010, respectively). The results of multivariate Cox regression analysis revealed that CEP55 expression was a significant, independent predictor for the survival of patients with cervical cancer (hazard ratio=3.057; P=0.035). These data indicated that high CEP55 expression was associated with lymph node metastasis and was an independent predictive factor for an unfavorable prognosis in patients with cervical carcinoma.

RanBPM: a potential therapeutic target for modulating diverse physiological disorders

The Ran-binding protein microtubule-organizing center (RanBPM) is a highly conserved nucleocytoplasmic protein involved in a variety of intracellular signaling pathways that control diverse cellular functions. RanBPM interacts with proteins that are linked to various diseases, including Alzheimer's disease (AD), schizophrenia (SCZ), and cancer. In this article, we define the characteristics of the scaffolding protein RanBPM and focus on its interaction partners in diverse physiological disorders, such as neurological diseases, fertility disorders, and cancer.

Samp1, a RanGTP binding transmembrane protein in the inner nuclear membrane

Samp1 is a transmembrane protein of the inner nuclear membrane (INM), which interacts with the nuclear lamina and the Linker of Nucleoskeleton and Cytoskeleton (LINC) complex in interphase and during mitosis, it localizes to the mitotic spindle. Samp1 was recently found to coprecipitate a protein complex containing Ran, a GTPase with fundamental regulatory functions both in interphase and in mitosis. To investigate the interaction between Samp1 and Ran in further detail, we have designed and expressed recombinant fusion proteins of the Chaetomium thermophilum homolog of Samp1 (Ct.Samp1) and human Ran. Pulldown experiments show that Samp1 binds directly to Ran and that Samp1 binds better to RanGTP compared to RanGDP. Samp1 also preferred RanGTP over RanGDP in living tsBN2 cells. We also show that the Ran binding domain is located between amino acids 75–135 in the nucleoplasmically exposed N-terminal tail of Samp1. This domain is unique for Samp1, without homology in any other proteins in fungi or metazoa. Samp1 is the first known transmembrane protein that binds to Ran and could provide a unique local binding site for RanGTP in the INM. Samp1 overexpression resulted in increased Ran concentrations in the nuclear periphery supporting this idea.

Difficulty in obtaining the complete mRNA coding sequence at 5' region (5' end mRNA artifact): Causes, consequences in biology and medicine and possible solutions for obtaining the actual amino acid sequence of proteins (Review)

The known difficulty in obtaining the actual full length, complete sequence of a messenger RNA (mRNA) may lead to the erroneous determination of its coding sequence at the 5' region (5' end mRNA artifact), and consequently to the wrong assignment of the translation start codon, leading to the inaccurate prediction of the encoded polypeptide at its amino terminus. Among the known human genes whose study was affected by this artifact, we can include disco interacting protein 2 homolog A (DIP2A; KIAA0184), Down syndrome critical region 1 (DSCR1), SON DNA binding protein (SON), trefoil factor 3 (TFF3) and URB1 ribosome biogenesis 1 homolog (URB1; KIAA0539) on chromosome 21, as well as receptor for activated C kinase 1 (RACK1, also known as GNB2L1), glutaminyl‑tRNA synthetase (QARS) and tyrosyl-DNA phosphodiesterase 2 (TDP2) along with another 474 loci, including interleukin 16 (IL16). In this review, we discuss the causes of this issue, its quantitative incidence in biomedical research, the consequences in biology and medicine, and the possible solutions for obtaining the actual amino acid sequence of proteins in the post-genomics era.

Metaphase Spindle Assembly

A microtubule-based bipolar spindle is required for error-free chromosome segregation during cell division. In this review I discuss the molecular mechanisms required for the assembly of this dynamic micrometer-scale structure in animal cells.

RanBPM inhibits BLT2-mediated IL-8 production and invasiveness in aggressive breast cancer cells

RanBPM is a scaffolding protein that regulates several cellular processes by interacting with various proteins. Previously, we reported that RanBPM acts as a negative regulator of BLT2, a low-affinity leukotriene B₄ receptor; thus, it interferes with BLT2-mediated cell motility. In the present study, we observed that the expression levels of RanBPM were markedly reduced in the highly aggressive MDA-MB-435 and MDA-MB-231 human breast cancer cell lines compared with those in non-invasive MCF-7 cells. Additionally, we found that the restoration of RanBPM levels suppressed the invasiveness of these aggressive breast cancer cells in a manner dependent on BLT2 activation. In contrast, the knockdown of endogenous RanBPM by shRNA strongly promoted invasiveness in non-invasive MCF-7 cells. We also observed that RanBPM suppressed the invasiveness of aggressive breast cancer cells by inhibiting BLT2-mediated reactive oxygen species (ROS) generation and IL-8 production. Taken together, our results suggest that RanBPM acts as a negative regulator of BLT2, thus attenuating the invasiveness of aggressive breast cancer cells.

Ran Binding Protein 9 (RanBP9) is a novel mediator of cellular DNA damage response in lung cancer cells

Ran Binding Protein 9 (RanBP9, also known as RanBPM) is an evolutionary conserved scaffold protein present both in the nucleus and the cytoplasm of cells whose biological functions remain elusive. We show that active ATM phosphorylates RanBP9 on at least two different residues (S181 and S603). In response to IR, RanBP9 rapidly accumulates into the nucleus of lung cancer cells, but this nuclear accumulation is prevented by ATM inhibition. RanBP9 stable silencing in three different lung cancer cell lines significantly affects the DNA Damage Response (DDR), resulting in delayed activation of key components of the cellular response to IR such as ATM itself, Chk2, γH2AX, and p53. Accordingly, abrogation of RanBP9 expression reduces homologous recombination-dependent DNA repair efficiency, causing an abnormal activation of IR-induced senescence and apoptosis. In summary, here we report that RanBP9 is a novel mediator of the cellular DDR, whose accumulation into the nucleus upon IR is dependent on ATM kinase activity. RanBP9 absence hampers the molecular mechanisms leading to efficient repair of damaged DNA, resulting in enhanced sensitivity to genotoxic stress. These findings suggest that targeting RanBP9 might enhance lung cancer cell sensitivity to genotoxic anti-neoplastic treatment.

Cell Adhesion Molecules and Ubiquitination-Functions and Significance

Cell adhesion molecules of the immunoglobulin (Ig) superfamily represent the biggest group of cell adhesion molecules. They have been analyzed since approximately 40 years ago and most of them have been shown to play a role in tumor progression and in the nervous system. All members of the Ig superfamily are intensively posttranslationally modified. However, many aspects of their cellular functions are not yet known. Since a few years ago it is known that some of the Ig superfamily members are modified by ubiquitin. Ubiquitination has classically been described as a proteasomal degradation signal but during the last years it became obvious that it can regulate many other processes including internalization of cell surface molecules and lysosomal sorting. The purpose of this review is to summarize the current knowledge about the ubiquitination of cell adhesion molecules of the Ig superfamily and to discuss its potential physiological roles in tumorigenesis and in the nervous system.

The CCDC55 couples cannabinoid receptor CNR1 to a putative DISC1 schizophrenia pathway

PURPOSE

Our previous study suggested that the coiled coil domain-containing 55 gene (CCDC55), also named as NSRP1 (nuclear speckle splicing regulatory protein 1 (NSRP1)), was encompassed in a haplotype block spanning over the serotonin transporter (5-HTT) gene in patients with schizophrenia (SCZ). However, the neurobiological function of CCDC55 gene remains unknown. This study aims to uncover the potential role of CCDC55 in SCZ-associated molecular pathways.

EXPERIMENTAL DESIGN

Using molecular cloning, sequencing and immune blotting to identify basic properties, yeast two-hybrid screening and glutathione S-transferase (GST) pull-down assay to test protein-protein interaction, and confocal laser scanning microscopy (CSLM) to show intracellular interaction of proteins.

PRINCIPAL FINDINGS

(i) CCDC55 is expressed as a nuclear protein in human neuronal cells; (ii) Protein-protein interaction analyses showed CCDC55 physically interacted with Ran binding protein 9 (RanBP9) and disrupted in schizophrenia 1 (DISC1); (iii) CCDC55 and RanBP9 co-localized in the nucleus of human neuronal cells; (iv) CCDC55 also interacted with the cannabinoid receptor 1 (CNR1), and with the brain cannabinoid receptor-interacting protein 1a (CNRIP1a); (v) CNR1 activation in differentiated human neuronal cells resulted in an altered RanBP9 localization.

CONCLUSION

CCDC55 may be involved in a functional bridging between the CNR1 activation and the DISC1/RanBP9-associated pathways.

Identification of Ran-binding protein M as a stanniocalcin 2 interacting protein and implications for androgen receptor activity

Stanniocalcin (STC), a glycoprotein hormone originally discovered in fish, has been implicated in calcium and phosphate homeostasis. While fishes and mammals possess two STC homologs (STC1 and STC2), the physiological roles of STC2 are largely unknown compared with those of STC1. In this study, we identified Ran-binding protein M (RanBPM) as a novel binding partner of STC2 using yeast two-hybrid screening. The interaction between STC2 and RanBPM was confirmed in mammalian cells by immunoprecipitation. STC2 enhanced the RanBPM-mediated transactivation of liganded androgen receptor (AR), but not thyroid receptor β, glucocorticoid receptor, or estrogen receptor β. We also found that AR interacted with RanBPM in both the absence and presence of testosterone (T). Furthermore, we discovered that STC2 recruits RanBPM/AR complex in T-dependent manner. Taken together, our findings suggest that STC2 is a novel RanBPM-interacting protein that promotes AR transactivation.

RAN-binding protein 9 is involved in alternative splicing and is critical for male germ cell development and male fertility

As a member of the large Ran-binding protein family, Ran-binding protein 9 (RANBP9) has been suggested to play a critical role in diverse cellular functions in somatic cell lineages in vitro, and this is further supported by the neonatal lethality phenotype in Ranbp9 global knockout mice. However, the exact molecular actions of RANBP9 remain largely unknown. By inactivation of Ranbp9 specifically in testicular somatic and spermatogenic cells, we discovered that Ranbp9 was dispensable for Sertoli cell development and functions, but critical for male germ cell development and male fertility. RIP-Seq and proteomic analyses revealed that RANBP9 was associated with multiple key splicing factors and directly targeted >2,300 mRNAs in spermatocytes and round spermatids. Many of the RANBP9 target and non-target mRNAs either displayed aberrant splicing patterns or were dysregulated in the absence of Ranbp9. Our data uncovered a novel role of Ranbp9 in regulating alternative splicing in spermatogenic cells, which is critical for normal spermatogenesis and male fertility.

Male fertility depends on successful production of functional sperm. Sperm are produced through spermatogenesis, a process of male germ cell proliferation and differentiation in the testis. Most of the genes involved in spermatogenesis are transcribed and processed into multiple isoforms, which are mainly achieved through alternative splicing. The testis-specific transcriptome, characterized by male germ cell-specific alternative splicing patterns, has been shown to be essential for successful spermatogenesis. However, how these male germ cells-specific alternative splicing events are regulated remains largely unknown. Here, we report that RANBP9 is involved in alternative splicing events that are critical for male germ cell development, and dysfunction of RANBP9 leads to disrupted spermatogenesis and compromised male fertility.

RanBP9 overexpression accelerates loss of dendritic spines in a mouse model of Alzheimer's disease

We previously demonstrated that RanBP9 overexpression increased Aβ generation and amyloid plaque burden, subsequently leading to robust reductions in the levels of several synaptic proteins as well as deficits in the learning and memory skills in a mouse model of Alzheimer's disease (AD). In the present study, we found striking reduction of spinophilin-immunoreactive puncta (52%, p<0.001) and spinophilin area (62.5%, p<0.001) in the primary cortical neurons derived from RanBP9 transgenic mice (RanBP9-Tg) compared to wild-type (WT) neurons. Similar results were confirmed in WT cortical neurons transfected with EGFP-RanBP9. At 6-months of age, the total spine density in the cortex of RanBP9 single transgenic, APΔE9 double transgenic and APΔE9/RanBP9 triple transgenic mice was similar to WT mice. However, in the hippocampus the spine density was significantly reduced (27%, p<0.05) in the triple transgenic mice compared to WT mice due to reduced number of thin spines (33%, p<0.05) and mushroom spines (22%, p<0.05). This suggests that RanBP9 overexpression in the APΔE9 mice accelerates loss of spines and that the hippocampus is more vulnerable. At 12-months of age, the cortex showed significant reductions in total spine density in the RanBP9 (22%, p<0.05), APΔE9 (19%, p<0.05) and APΔE9/RanBP9 (33%, p<0.01) mice compared to WT controls due to reductions in mushroom and thin spines. Similarly, in the hippocampus the total spine density was reduced in the RanBP9 (23%, p<0.05), APΔE9 (26%, p<0.05) and APΔE9/RanBP9 (39%, p<0.01) mice due to reductions in thin and mushroom spines. Most importantly, RanBP9 overexpression in the APΔE9 mice further exacerbated the reductions in spine density in both the cortex (14%, p<0.05) and the hippocampus (16%, p<0.05). Because dendritic spines are considered physical traces of memory, loss of spines due to RanBP9 provided the physical basis for the learning and memory deficits. Since RanBP9 protein levels are increased in AD brains, RanBP9 might play a crucial role in the loss of spines and synapses in AD.

Aggresome formation is regulated by RanBPM through an interaction with HDAC6

In conditions of proteasomal impairment, the build-up of damaged or misfolded proteins activates a cellular response leading to the recruitment of damaged proteins into perinuclear aggregates called aggresomes. Aggresome formation involves the retrograde transport of cargo proteins along the microtubule network and is dependent on the histone deacetylase HDAC6. Here we show that ionizing radiation (IR) promotes Ran-Binding Protein M (RanBPM) relocalization into discrete perinuclear foci where it co-localizes with aggresome components ubiquitin, dynein and HDAC6, suggesting that the RanBPM perinuclear clusters correspond to aggresomes. RanBPM was also recruited to aggresomes following treatment with the proteasome inhibitor MG132 and the DNA-damaging agent etoposide. Strikingly, aggresome formation by HDAC6 was markedly impaired in RanBPM shRNA cells, but was restored by re-expression of RanBPM. RanBPM was found to interact with HDAC6 and to inhibit its deacetylase activity. This interaction was abrogated by a RanBPM deletion of its LisH/CTLH domain, which also prevented aggresome formation, suggesting that RanBPM promotes aggresome formation through an association with HDAC6. Our results suggest that RanBPM regulates HDAC6 activity and is a central regulator of aggresome formation.

Functional Interactions between BM88/Cend1, Ran-binding protein M and Dyrk1B kinase affect cyclin D1 levels and cell cycle progression/exit in mouse neuroblastoma cells

BM88/Cend1 is a neuronal-lineage specific modulator with a pivotal role in coordination of cell cycle exit and differentiation of neuronal precursors. In the current study we identified the signal transduction scaffolding protein Ran-binding protein M (RanBPM) as a BM88/Cend1 binding partner and showed that BM88/Cend1, RanBPM and the dual specificity tyrosine-phosphorylation regulated kinase 1B (Dyrk1B) are expressed in mouse brain as well as in cultured embryonic cortical neurons while RanBPM can form complexes with either of the two other proteins. To elucidate a potential mechanism involving BM88/Cend1, RanBPM and Dyrk1B in cell cycle progression/exit, we transiently co-expressed these proteins in mouse neuroblastoma Neuro 2a cells. We found that the BM88/Cend1-dependent or Dyrk1B-dependent down-regulation of cyclin D1 is reversed following their functional interaction with RanBPM. More specifically, functional interaction of RanBPM with either BM88/Cend1 or Dyrk1B stabilizes cyclin D1 in the nucleus and promotes 5-bromo-2'-deoxyuridine (BrdU) incorporation as a measure of enhanced cell proliferation. However, the RanBPM-dependent Dyrk1B cytosolic retention and degradation is reverted in the presence of Cend1 resulting in cyclin D1 destabilization. Co-expression of RanBPM with either BM88/Cend1 or Dyrk1B also had a negative effect on Neuro 2a cell differentiation. Our results suggest that functional interactions between BM88/Cend1, RanBPM and Dyrk1B affect the balance between cellular proliferation and differentiation in Neuro 2a cells and indicate that a potentially similar mechanism may influence cell cycle progression/exit and differentiation of neuronal precursors.

RanBPM interacts with TβRI, TRAF6 and curbs TGF induced nuclear accumulation of TβRI

Transforming growth factor β (TGF-β), a cytokine, and its receptors play a vital role during normal embryogenesis, cell proliferation, differentiation, apoptosis and migration. Ran-binding protein in the microtubule-organizing center (RanBPM) serves as a scaffold protein that has been shown to interact with many other proteins, such as MET, Axl/Sky, TRAF6, IFNR, TrKA and TrkB in addition to p75NTR. In the current study, we have identified RanBPM as a novel binding partner of TβRI by yeast two-hybrid assay. The TβRI and RanBPM association was confirmed by co-immunoprecipitation and GST pull-down experiments. Additionally, expression of RanBPM abrogated the interaction between TβRI and TRAF6. Furthermore, RanBPM could depress TGF-β induced TRAF6 ubiquitination, subsequent NF-κB signaling pathway, and block TGF-β induced TβRI nuclear accumulation. Taken together, our results reveal that RanBPM may modulate TGF-β-mediated downstream signaling and biological functions.

Karyotype-phenotype correlation in partial trisomies of the short arm of chromosome 6: a family case report and review of the literature

The first child (proband) of nonconsanguineous Caucasian parents underwent genetic investigation because she was affected with congenital choanal atresia, heart defects and kidney hyposplasia with mild transient renal insufficiency. The direct DNA sequencing after PCR of the CHD7 gene, which is thought to be responsible for approximately 60-70% of the cases of CHARGE syndrome/association, found no mutations. The cytogenetic analysis (standard GTG banding karyotype) revealed the presence of extrachromosomal material on 10q. The chromosome analysis was completed with array CGH (30 kb resolution), MLPA and FISH, which allowed the identification of three 6p regions (6p.25.3p23 × 3): 2 of these regions are normally located on chromosome 6, and the third region is translocated to the long arm of chromosome 10. The same chromosomal rearrangement was subsequently found in the father, who was affected with congenital ptosis and progressive hearing loss, and in the proband's sister, the second child, who presented at birth with choanal atresia and congenital heart defects. The mutated karyotypes, which were directly inherited, are thought to be responsible for a variable phenotype, including craniofacial dysmorphisms, choanal atresia, congenital ptosis, sensorineural hearing loss, heart defects, developmental delay, and renal dysfunction. Nevertheless, to achieve a complete audiological assessment of the father, he underwent further investigation that revealed an increased level of the coagulation factor XIII (300% increased activity), fluctuating levels of fibrin D-dimer degradation products (from 296 to 1,587 ng/ml) and a homoplasmic mitochondrial DNA mutation: T961G in the MTRNR1 (12S rRNA) gene. He was made a candidate for cochlear implantation. Preoperative high-resolution computed tomography and magnetic resonance imaging of the temporal bone revealed the presence of an Arnold-Chiari malformation type I. To the best of our knowledge, this study is the second report on partial 6p trisomy that involves the 10q terminal region. Furthermore, we report the first case of documented Arnold-Chiari malformation type I and increased factor XIII activity associated with 6p trisomy. We present a comprehensive report of the familial cases and an exhaustive literature review.

RanBPM protein acts as a negative regulator of BLT2 receptor to attenuate BLT2-mediated cell motility

BLT2, a low affinity receptor for leukotriene B4 (LTB4), is a member of the G protein-coupled receptor family and is involved in many signal transduction pathways associated with various cellular phenotypes, including chemotactic motility. However, the regulatory mechanism for BLT2 has not yet been demonstrated. To understand the regulatory mechanism of BLT2, we screened and identified the proteins that bind to BLT2. Using a yeast two-hybrid assay with the BLT2 C-terminal domain as bait, we found that RanBPM, a previously proposed scaffold protein, interacts with BLT2. We demonstrated the specific interaction between BLT2 and RanBPM by GST pulldown assay and co-immunoprecipitation assay. To elucidate the biological function of the RanBPM-BLT2 interaction, we evaluated the effects of RanBPM overexpression or knockdown. We found that BLT2-mediated motility was severely attenuated by RanBPM overexpression and that knockdown of endogenous RanBPM by shRNA strongly promoted BLT2-mediated motility, suggesting a negative regulatory function of RanBPM toward BLT2. Furthermore, we observed that the addition of BLT2 ligands caused the dissociation of BLT2 and RanBPM, thus releasing the negative regulatory effect of RanBPM. Finally, we propose that Akt-induced BLT2 phosphorylation at residue Thr(355), which occurs after the addition of BLT2 ligands, is a potential mechanism by which BLT2 dissociates from RanBPM, resulting in stimulation of BLT2 signaling. Taken together, our results suggest that RanBPM acts as a negative regulator of BLT2 signaling to attenuate BLT2-mediated cell motility.

Regulation of ecto-apyrase CD39 (ENTPD1) expression by phosphodiesterase III (PDE3)

The ectoenzyme CD39 suppresses thrombosis and inflammation by suppressing ATP and ADP to AMP. However, mechanisms of CD39 transcriptional and post-translational regulation are not well known. Here we show that CD39 levels are modulated by inhibition of phosphodiesterase 3 (PDE3). RAW macrophages and human umbilical vein endothelial cells (HUVECs) were treated with the PDE3 inhibitors cilostazol and milrinone, then analyzed using qRT-PCR, immunoprecipitation/Western blot, immunofluorescent staining, radio-thin-layer chromatography, a malachite green assay, and ELISA. HUVECs expressed elevated CD39 protein (2-fold [P<0.05] for cilostazol and 2.5-fold [P<0.01] for milrinone), while macrophage CD39 mRNA and protein were both elevated after PDE3 inhibition. HUVEC ATPase activity increased by 25% with cilostazol and milrinone treatment (P<0.05 and P<0.01, respectively), as did ADPase activity (47% and 61%, P<0.001). There was also a dose-dependent elevation of soluble CD39 after treatment with 8-Br-cAMP, with maximal elevation of 60% more CD39 present compared to controls (1 mM, P<0.001). Protein harvested after 8-Br-cAMP treatment showed that ubiquitination of CD39 was decreased by 43% compared to controls. A DMSO or PBS vehicle control was included for each experiment based on solubility of cilostazol, milrinone, and 8-Br-cAMP. These results indicate that PDE3 inhibition regulates endothelial CD39 at a post-translational level.

RanBPM, a scaffolding protein for gametogenesis

RanBPM is a multimodular scaffold protein that interacts with a great variety of molecules including nuclear, cytoplasmic, and membrane proteins. By building multiprotein complexes, RanBPM is thought to regulate various signaling pathways, especially in the immune and nervous system. However, the diversity of these interactions does not facilitate the identification of its precise mechanism of action, and therefore the physiological role of RanBPM still remains unclear. Recently, RanBPM has been shown to be critical for the fertility of both genders in mouse. Although mechanistically it is still unclear how RanBPM affects gametogenesis, the data collected so far suggest that it is a key player in this process. Here, we examine the RanBPM sterility phenotype in the context of other genetic mutations affecting mouse gametogenesis to investigate whether this scaffold protein affects the function of other known proteins whose deficiency results in similar sterility phenotypes.

Centaurin-α₂ interacts with β-tubulin and stabilizes microtubules

Centaurin-α₂ is a GTPase-activating protein for ARF (ARFGAP) showing a diffuse cytoplasmic localization capable to translocate to membrane, where it binds phosphatidylinositols. Taking into account that Centaurin-α₂ can localize in cytoplasm and that its cytoplasmatic function is not well defined, we searched for further interactors by yeast two-hybrid assay to investigate its biological function. We identified a further Centaurin-α₂ interacting protein, β-Tubulin, by yeast two-hybrid assay. The interaction, involving the C-terminal region of β-Tubulin, has been confirmed by coimmunoprecipitation experiments. After Centaurin-α₂ overexpression in HeLa cells and extraction of soluble (αβ dimers) and insoluble (microtubules) fractions of Tubulin, we observed that Centaurin-α₂ mainly interacts with the polymerized Tubulin fraction, besides colocalizing with microtubules (MTs) in cytoplasm accordingly. Even following the depolimerizing Tubulin treatments Centaurin-α₂ remains mainly associated to nocodazole- and cold-resistant MTs. We found an increase of MT stability in transfected HeLa cells, evaluating as marker of stability the level of MT acetylation. In vitro assays using purified Centaurin-α₂ and tubulin confirmed that Centaurin-α₂ promotes tubulin assembly and increases microtubule stability. The biological effect of Centaurin-α₂ overexpression, assessed through the detection of an increased number of mitotic HeLa cells with bipolar spindles and with the correct number of centrosomes in both dividing and not dividing cells, is consistent with the Centaurin-α₂ role on MT stabilization. Centaurin-α₂ interacts with β-Tubulin and it mainly associates to MTs, resistant to destabilizing agents, in vitro and in cell. We propose Centaurin-α₂ as a new microtubule-associated protein (MAP) increasing MT stability.

Protein phosphatase 1γ isoforms linked interactions in the brain

Posttranslational protein modifications, in particular reversible protein phosphorylation, are important regulatory mechanisms involved in cellular signaling transduction pathways. Thousands of human proteins are phosphorylatable and the tight regulation of phosphorylation states is crucial for cell maintenance and development. Protein phosphorylation occurs primarily on serine, threonine, and tyrosine residues, through the antagonistic actions of protein kinases and phosphatases. The catalytic subunit of protein phosphatase 1 (PP1), a major Ser/Thr-phosphatase, associates with a large variety of regulatory subunits that define substrate specificity and determine specific cellular pathway responses. PP1 has been shown to bind to different proteins in the brain in order to execute key and differential functions. This work reports the identification of proteins expressed in the human brain that interact with PP1γ1 and PP1γ2 isoforms by the yeast two-hybrid method. An extensive search of PP1-binding motifs was performed for the proteins identified, revealing already known PP1 regulators but also novel interactors. Moreover, our results were integrated with the data of PP1γ interacting proteins from several public web databases, permitting the development of physical maps of the novel interactions. The PP1γ interactome thus obtained allowed for the identification of novel PP1 interacting proteins, supporting novel functions of PP1γ isoforms in the human brain.

RanBPM expression regulates transcriptional pathways involved in development and tumorigenesis

RanBPM is a ubiquitous protein that has been reported to regulate several cellular processes through interactions with various proteins. However, it is not known whether RanBPM may regulate gene expression patterns. As it has been shown that RanBPM interacts with a number of transcription factors, we hypothesized that it may have wide ranging effects on gene expression that may explain its function. To test this hypothesis, we generated stable RanBPM shRNA cell lines to analyze the effect of RanBPM on global gene expression. Microarray analyses were conducted comparing the gene expression profile of Hela and HCT116 RanBPM shRNA cells versus control shRNA cells. We identified 167 annotated genes significantly up- or down-regulated in the two cell lines. Analysis of the gene set revealed that down-regulation of RanBPM led to gene expression changes that affect regulation of cell, tissue, and organ development and morphology, as well as biological processes implicated in tumorigenesis. Analysis of Transcription Factor Binding Sites (TFBS) present in the gene set identified several significantly over-represented transcription factors of the Forkhead, HMG, and Homeodomain families of transcription factors, which have previously been demonstrated as having important roles in development and tumorigenesis. In addition, the combined results of these analyses suggested that several signaling pathways were affected by RanBPM down-regulation, including ERK1/2, Wnt, Notch, and PI3K/Akt pathways. Lastly, analysis of selected target genes by quantitative RT-qPCR confirmed the changes revealed by microarray. Several of the genes up-regulated in RanBPM shRNA cells encode proteins with known oncogenic functions, such as the RON tyrosine kinase, the adhesion molecule L1CAM, and transcription factor ELF3/ESE-1, suggesting that RanBPM functions as a tumor suppressor to prevent deregulated expression of these genes. Altogether, these results suggest that RanBPM does indeed function to regulate many genomic events that regulate embryonic, tissue, and cellular development as well as those involved in cancer development and progression.

Interactions of an Arabidopsis RanBPM homologue with LisH-CTLH domain proteins revealed high conservation of CTLH complexes in eukaryotes

BACKGROUND

RanBPM (Ran-binding protein in the microtubule-organizing centre) was originally reported as a centrosome-associated protein in human cells. However, RanBPM protein containing highly conserved SPRY, LisH, CTLH and CRA domains is currently considered as a scaffolding protein with multiple cellular functions. A plant homologue of RanBPM has not yet been characterized.

RESULTS

Based on sequence similarity, we identified a homologue of the human RanBPM in Arabidopsis thaliana. AtRanBPM protein has highly conserved SPRY, LisH, CTLH and CRA domains. Cell fractionation showed that endogenous AtRanBPM or expressed GFP-AtRanBPM are mainly cytoplasmic proteins with only a minor portion detectable in microsomal fractions. AtRanBPM was identified predominantly in the form of soluble cytoplasmic complexes ~230-500 kDa in size. Immunopurification of AtRanBPM followed by mass spectrometric analysis identified proteins containing LisH and CRA domains; LisH, CRA, RING-U-box domains and a transducin/WD40 repeats in a complex with AtRanBPM. Homologues of identified proteins are known to be components of the C-terminal to the LisH motif (CTLH) complexes in humans and budding yeast. Microscopic analysis of GFP-AtRanBPM in vivo and immunofluorescence localization of endogenous AtRanBPM protein in cultured cells and seedlings of Arabidopsis showed mainly cytoplasmic and nuclear localization. Absence of colocalization with γ-tubulin was consistent with the biochemical data and suggests another than a centrosomal role of the AtRanBPM protein.

CONCLUSION

We showed that as yet uncharacterized Arabidopsis RanBPM protein physically interacts with LisH-CTLH domain-containing proteins. The newly identified high molecular weight cytoplasmic protein complexes of AtRanBPM showed homology with CTLH types of complexes described in mammals and budding yeast. Although the exact functions of the CTLH complexes in scaffolding of protein degradation, in protein interactions and in signalling from the periphery to the cell centre are not yet fully understood, structural conservation of the complexes across eukaryotes suggests their important biological role.

Targeting the hedgehog signaling pathway with interacting peptides to Patched-1

BACKGROUND

The hedgehog (Hh) signaling pathway is aberrantly activated in many cancers. Overproduction of sonic hedgehog (Shh), a ligand in the Hh pathway, increases Hh signaling activity by inhibiting Patched-1 (Ptch1), a suppressive receptor in the Hh pathway. The purpose of this study was to establish a novel strategy for treating pancreatic cancer and other Hh-dependent cancers through control of the tumor-suppressive function of Ptch1.

METHODS

We synthesized seven interacting peptides to the amino-acid sequence of the Ptch1 docking site for Shh. Human pancreatic cancer cell lines (AsPC-1, SUIT2) were cultured in the presence or absence of the peptides. Cell proliferation was assessed by cell counting and by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The activity of the Hh pathway was estimated by real-time polymerase chain reaction of the target gene product Gli1. To confirm their anti-tumor activity in vivo, the effect of the peptides in a mouse model of pancreatic cancer was determined. Finally, the Hh signaling activity of the xenograft was examined.

RESULTS

Three of the interacting peptides to Ptch1 suppressed the proliferation of the two pancreatic cancer cell lines and decreased the expression of Gli1, both in vitro and in vivo.

CONCLUSIONS

This study suggests that interacting peptides to Ptch1 may be a new tool for controlling the Hh-dependent growth of pancreatic cancer.

Diverse roles of the scaffolding protein RanBPM

Ran-binding protein microtubule-organizing center (RanBPM) appears to function as a scaffolding protein in several signal transduction pathways. RanBPM is a crucial component of multiprotein complexes that regulate the cellular function by modulating and/or assembling with a wide range of proteins in different intracellular regions and thereby mediate diverse cellular functions. This suggests a role for RanBPM as a scaffolding protein. In this article, we have summarized the diverse functions of RanBPM and its interacting partners that have been investigated to date. Also, we have categorized the role of RanBPM into four divisions: RanBPM as a modulator/protein stabilizer, regulator of transcription activity, cell cycle and neurological functions.

Expression of nucleocytoplasmic transport machinery: clues to regulation of spermatogenic development

Spermatogenesis is one example of a developmental process which requires tight control of gene expression to achieve normal growth and sustain function. This review is based on the principle that events in spermatogenesis are controlled by changes in the distribution of proteins between the nuclear and cytoplasmic compartments. Through analysis of the regulated production of nucleocytoplasmic transport machinery in mammalian spermatogenesis, this review addresses the concept that access to the nucleus is tightly controlled to enable and prevent differentiation. A broad review of nuclear transport components is presented, outlining the different categories of machinery required for import, export and non-nuclear functions. In addition, the complexity of nomenclature is addressed by the provision of a concise yet comprehensive listing of information that will aid in comparative studies of different transport proteins and the genes which encode them. We review a suite of existing transcriptional analyses which identify common and distinct patterns of transport machinery expression, showing how these can be linked with key events in spermatogenic development. The additional importance of this for human fertility is considered, in light of data that identify which importin and nuclear transport machinery components are present in testicular cancer specimens, while also providing an indication of how their presence (and absence) may be considered as potential mediators of oncogenesis. This article is part of a Special Issue entitled: Regulation of Signaling and Cellular Fate through Modulation of Nuclear Protein Import.

Identification of the human testis protein phosphatase 1 interactome

Protein phosphorylation is a critical regulatory mechanism in cellular signalling. To this end, PP1 is a major eukaryotic serine/threonine-specific phosphatase whose cellular functions, in turn, depend on complexes it forms with PP1 interacting proteins-PIPs. The importance of the testis/sperm-enriched variant, PP1γ2, in sperm motility and spermatogenesis has previously been shown. Given the key role of PIPs, it is imperative to identify the physiologically relevant PIPs in testis and sperm. Hence, we performed Yeast Two-Hybrid screens of a human testis cDNA library using as baits the different PP1 isoforms and also a proteomic approach aimed at identifying PP1γ2 binding proteins. To the best of our knowledge this is the largest data set of the human testis PP1 interactome. We report the identification of 77 proteins in human testis and 7 proteins in human sperm that bind PP1. The data obtained increased the known PP1 interactome by reporting 72 novel interactions. Confirmation of the interaction of PP1 with 5 different proteins was also further validated by co-immunoprecipitation or protein overlays. The data here presented provides important insights towards the function of these proteins and opens new possibilities for future research. In fact, such diversity in PP1 regulators makes them excellent targets for pharmacological intervention.

p73-Binding Partners and Their Functional Significance

p73 is one of the tumor-suppressor p53 family of nuclear transcription factor. As expected from the structural similarity between p53 and p73, p73 has a tumor-suppressive function. However, p73 was rarely mutated in human primary tumors. Under normal physiological conditions, p73 is kept at an extremely low level to allow cells normal growth. In response to a certain subset of DNA damages, p73 is induced dramatically and transactivates an overlapping set of p53-target genes implicated in the promotion of cell cycle arrest and/or apoptotic cell death. Cells undergo cell cycle arrest and/or apoptotic cell death depending on the type and strength of DNA damages. p73 is regulated largely through the posttranslational modifications such as phosphorylation and acetylation. These chemical modifications are tightly linked to direct protein-protein interactions. In the present paper, the authors describe the functional significance of the protein-protein interactions in the regulation of proapoptotic p73.

Stability and function of mammalian lethal giant larvae-1 oncoprotein are regulated by the scaffolding protein RanBPM

The evolutionarily conserved lethal giant larvae (Lgl) tumor suppressor gene has an essential role in establishing apical-basal cell polarity, cell proliferation, differentiation, and tissue organization. However, the precise molecular mechanism by which the Lgl carries out its function remains obscure. In the current study, we have identified Ran-binding protein M (RanBPM) as a novel binding partner of Mgl-1, a mammalian homolog of Drosophila tumor suppressor protein lethal (2) giant larvae (L(2)gl) by yeast two-hybrid screening. RanBPM seems to act as a scaffolding protein with a modulatory function with respect to Mgl-1. The Mgl-1 and RanBPM association was confirmed by co-immunoprecipitation and GST pull-down experiments. Additionally, expression of RanBPM resulted in inhibition of Mgl-1 degradation, and thereby extended the half-life of Mgl-1. Furthermore, the ability of Mgl-1 activity in cell migration and colony formation assay was enhanced by RanBPM. Taken together, our findings reveal that RanBPM plays a novel role in regulating Mgl-1 stability and contributes to its biological function as a tumor suppressor.

The Drosophila gene RanBPM functions in the mushroom body to regulate larval behavior

BACKGROUND

In vertebrates, Ran-Binding Protein in the Microtubule Organizing Center (RanBPM) appears to function as a scaffolding protein in a variety of signal transduction pathways. In Drosophila, RanBPM is implicated in the regulation of germ line stem cell (GSC) niche organization in the ovary. Here, we addressed the role of RanBPM in nervous system function in the context of Drosophila larval behavior.

METHODOLOGY/PRINCIPAL FINDINGS

We report that in Drosophila, RanBPM is required for larval feeding, light-induced changes in locomotion, and viability. RanBPM is highly expressed in the Kenyon cells of the larval mushroom body (MB), a structure well studied for its role in associative learning in Drosophila and other insects. RanBPM mutants do not display major disruption in nervous system morphology besides reduced proliferation. Expression of the RanBPM gene in the Kenyon cells is sufficient to rescue all behavioral phenotypes. Through genetic epistasis experiments, we demonstrate that RanBPM participates with the Drosophila orthologue of the Fragile X Mental Retardation Protein (FMRP) in the development of neuromuscular junction (NMJ).

CONCLUSIONS/SIGNIFICANCE

We demonstrate that the RanBPM gene functions in the MB neurons for larval behavior. Our results suggest a role for this gene in an FMRP-dependent process. Taken together our findings point to a novel role for the MB in larval behavior.

RanBPM contributes to TrkB signaling and regulates brain-derived neurotrophic factor-induced neuronal morphogenesis and survival

Tropomyosin-related kinase (Trk) B is a receptor tyrosine kinase for brain-derived neurotrophic factor (BDNF) which plays a critical role in neuronal survival, differentiation and morphogenesis. Ran-binding protein in the microtubule-organizing center (RanBPM) is a cytosolic scaffold protein that has been shown to interact with protein-tyrosine kinase receptor MET, Axl/Sky, and TrkA in addition to the pan-neurotrophin receptor pan-neurotrophin receptor 75 kDa. In this study, we report RanBPM is a novel TrkB-interacting protein that contributes to BDNF-induced MAPK and Akt activation together with neuronal morphogenesis and survival. Over-expression of RanBPM in PC1210 cells (PC12 cells stably over-expressing TrkB) can significantly enhance BDNF-induced MAPK and Akt activation. Moreover, RanBPM can promote BDNF-induced hippocampal neuronal morphogenesis and enhance BDNF-mediated trophic effects after serum deprivation, while siRNA knock down of RanBPM in cells has the opposite effects. Together, these results suggest that RanBPM may modulate TrkB-mediated downstream signaling and biological functions.

RanBPM regulates the progression of neuronal precursors through M-phase at the surface of the neocortical ventricular zone

Many of the mitoses that produce pyramidal neurons in neocortex occur at the dorsolateral surface of the lateral ventricles in the embryo. RanBPM was found in a yeast two-hybrid screen to potentially interact with citron kinase (CITK), a protein shown previously to localize to the surface of the lateral ventricles and to be essential to neurogenic mitoses. Similar to its localization in epithelia, RanBPM protein is concentrated at the adherens junctions in developing neocortex. The biochemical interaction between CITK and RanBPM was confirmed in coimmunoprecipitation and protein overlay experiments. To test for a functional role of RanPBM in vivo, we used in utero RNAi. RanBPM RNAi decreased the polarization of CITK to the ventricular surface, increased the number of cells in mitosis, and decreased the number of cells in cytokinesis. Finally, the effect of RanBPM knockdown on mitosis was reversed in embryos mutant for CITK. Together, these results indicate that RanBPM, potentially through interaction with CITK, plays a role in the progression of neocortical precursors through M-phase at the ventricular surface.

Activation of the Ran GTPase is subject to growth factor regulation and can give rise to cellular transformation

Although the small GTPase Ran is best known for its roles in nucleocytoplasmic transport, mitotic spindle assembly, and nuclear envelope formation, recent studies have demonstrated the overexpression of Ran in multiple tumor types and that its expression is correlated with a poor patient prognosis, providing evidence for the importance of this GTPase in cell growth regulation. Here we show that Ran is subject to growth factor regulation by demonstrating that it is activated in a serum-dependent manner in human breast cancer cells and, in particular, in response to heregulin, a growth factor that activates the Neu/ErbB2 tyrosine kinase. The heregulin-dependent activation of Ran requires mTOR (mammalian target of rapamycin) and stimulates the capped RNA binding capability of the cap-binding complex in the nucleus, thus influencing gene expression at the level of mRNA processing. We further demonstrate that the excessive activation of Ran has important consequences for cell growth by showing that a novel, activated Ran mutant is sufficient to transform NIH-3T3 cells in an mTOR- and epidermal growth factor receptor-dependent manner and that Ran-transformed cells form tumors in mice.

RanBPM is an acetylcholinesterase-interacting protein that translocates into the nucleus during apoptosis

Acetylcholinesterase (AChE) expression may be induced during apoptosis in various cell types. Here, we used the C-terminal of AChE to screen the human fetal brain library and found that it interacted with Ran-binding protein in the microtubule-organizing center (RanBPM). This interaction was further confirmed by coimmunoprecipitation analysis. In HEK293T cells, RanBPM and AChE were heterogeneously expressed in the cisplatin-untreated cytoplasmic extracts and in the cisplatin-treated cytoplasmic or nuclear extracts. Our previous studies performed using morphologic methods have shown that AChE translocates from the cytoplasm to the nucleus during apoptosis. Taken together, these results suggest that RanBPM is an AChE-interacting protein that is translocated from the cytoplasm into the nucleus during apoptosis, similar to the translocation observed in case of AChE.

The microtubule modulator RanBP10 plays a critical role in regulation of platelet discoid shape and degranulation

Terminally mature megakaryocytes undergo dramatic cellular reorganization to produce hundreds of virtually identical platelets. A hallmark feature of this process is the generation of an elaborate system of branched protrusions called proplatelets. We recently identified RanBP10 as a tubulin-binding protein that is concentrated along polymerized microtubules in mature megakaryocytes. RanBP10 depletion in vitro caused the disturbance of polymerized filaments. Here we study the function of RanBP10 in vivo by generating deficient mice using a gene-trap approach. Mutant mice show normal platelet counts, and fetal liver-derived megakaryocytes reveal only slightly reduced proplatelet formation. However, ultrastructural analysis unveiled a significantly increased geometric axis ratio for resting platelets, and many platelets exhibited disorders in microtubule filament numbers and localization. Mutant mice showed a markedly prolonged bleeding time. Granule release, a process that depends on internal contraction of the microtubule marginal coil, also was reduced. Flow cytometry analysis revealed reduced expression of CD62P and CD63 after PAR4-peptide stimulation. These data suggest that RanBP10 plays an essential role in hemostasis and in maintaining microtubule dynamics with respect to both platelet shape and function.

Muscle giants: molecular scaffolds in sarcomerogenesis

Myofibrillogenesis in striated muscles is a highly complex process that depends on the coordinated assembly and integration of a large number of contractile, cytoskeletal, and signaling proteins into regular arrays, the sarcomeres. It is also associated with the stereotypical assembly of the sarcoplasmic reticulum and the transverse tubules around each sarcomere. Three giant, muscle-specific proteins, titin (3-4 MDa), nebulin (600-800 kDa), and obscurin (approximately 720-900 kDa), have been proposed to play important roles in the assembly and stabilization of sarcomeres. There is a large amount of data showing that each of these molecules interacts with several to many different protein ligands, regulating their activity and localizing them to particular sites within or surrounding sarcomeres. Consistent with this, mutations in each of these proteins have been linked to skeletal and cardiac myopathies or to muscular dystrophies. The evidence that any of them plays a role as a "molecular template," "molecular blueprint," or "molecular ruler" is less definitive, however. Here we review the structure and function of titin, nebulin, and obscurin, with the literature supporting a role for them as scaffolding molecules and the contradictory evidence regarding their roles as molecular guides in sarcomerogenesis.