Ran-binding Protein Research Articles

Inflammatory myofibroblastic tumor with RANBP2 and ALKgene rearrangement: a report of two cases and literature review

Inflammatory myofibroblastic tumors (IMTs) are categorized as intermediate biologic neoplasms, whereas IMTs with genetic features of ran-binding protein 2 (RANBP2) and anaplastic lymphoma kinase (ALK) rearrangement (IMT-RAs) are possibly related to a more aggressive clinical course. However, fewer than 10 cases of IMT-RA have been reported to date. Herein, we present 2 new cases of IMT-RA in which both tumors recurred quickly after primary surgery; one patient died 3 months later from the disease, and the other patient has been living with the disease for 12 months. IMT-RAs are characterized by noncohesive epithelioid and rounded tumoral cell morphology, commonly derived from pelvic and peritoneal cavities, and frequently show larger tumor sizes. The relation between the clinicopathologic features and poor prognosis of IMT-RA is discussed.Virtual slidesThe virtual slide(s) for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/3314123381007714

HIV-1 and SUMOylation

Background The HIV virus hijacks cellular machineries to replicate. Post-translational modifications, like acetylation, phosphorylation or ubiquitination, are no exception. We are interested in studying the interplay between HIV and the SUMOylation pathway. SUMOylation occurs via an enzymatic cascade requiring an E1 activating enzyme (SAE1/SAE2 heterodimer) and an E2 conjugating enzyme (Ubc9). This modification is reversible thanks to SUMO isopeptidases (SENPs). Despite Ubc9 alone being sufficient to transfer SUMO moieties to acceptor lysine residues in vitro, E3 SUMO ligases promote specificity and/or efficiency of SUMOylation in vivo. So far, several E3 SUMO ligases have been characterized, such as nuclear pore complex component Ran-binding protein 2 (RanBP2) and protein-inhibitor of activated STAT (PIAS) family proteins. We have recently shown that HIV integrase, the viral enzyme that is responsible for viral genome integration into host cellular chromosome, is SUMOylated, and that virions harboring a SUMOylation-defective integrase are less infectious than WT viruses. Our data suggest that this modification is important for efficient viral replication.

Sphingosine Kinase 1 Serves as a Pro-Viral Factor by Regulating Viral RNA Synthesis and Nuclear Export of Viral Ribonucleoprotein Complex upon Influenza Virus Infection

Influenza continues to pose a threat to humans by causing significant morbidity and mortality. Thus, it is imperative to investigate mechanisms by which influenza virus manipulates the function of host factors and cellular signal pathways. In this study, we demonstrate that influenza virus increases the expression and activation of sphingosine kinase (SK) 1, which in turn regulates diverse cellular signaling pathways. Inhibition of SK suppressed virus-induced NF-κB activation and markedly reduced the synthesis of viral RNAs and proteins. Further, SK blockade interfered with activation of Ran-binding protein 3 (RanBP3), a cofactor of chromosome region maintenance 1 (CRM1), to inhibit CRM1-mediated nuclear export of the influenza viral ribonucleoprotein complex. In support of this observation, SK inhibition altered the phosphorylation of ERK, p90RSK, and AKT, which is the upstream signal of RanBP3/CRM1 activation. Collectively, these results indicate that SK is a key pro-viral factor regulating multiple cellular signal pathways triggered by influenza virus infection.

AKT activation drives the nuclear localization of CSE1L and a pro-oncogenic transcriptional activation in ovarian cancer cells

The human homolog of the yeast cse1 gene (CSE1L) is over-expressed in ovarian cancer. CSE1L forms complex with Ran and importin-α and has roles in nucleocytoplasmic traffic and gene expression. CSE1L accumulated in the nucleus of ovarian cancer cell lines, while it was localized also in the cytoplasm of other cancer cell lines. Nuclear localization depended on AKT, which was constitutively active in ovarian cancer cells, as the CSE1L protein translocated to the cytoplasm when AKT was inactivated. Moreover, the expression of a constitutively active AKT forced the translocation of CSE1L from the cytoplasm to the nucleus in other cancer cells. Nuclear accrual of CSE1L was associated to the nuclear accumulation of the phosphorylated Ran Binding protein 3 (RanBP3), which depended on AKT as well. Also in samples of human ovarian cancer, AKT activation was associated to nuclear accumulation of CSE1L and phosphorylation of RanBP3. Expression profiling of ovarian cancer cells after CSE1L silencing showed that CSE1L was required for the expression of genes promoting invasion and metastasis. In agreement, CSE1L silencing impaired motility and invasiveness of ovarian cancer cells. Altogether these data show that in ovarian cancer cells activated AKT by affecting RanBP3 phosphorylation determines the nuclear accumulation of CSE1L and likely the nuclear concentration of transcription factors conveying pro-oncogenic signals.

Distinct and Atypical Intrinsic and Extrinsic Cell Death Pathways between Photoreceptor Cell Types upon Specific Ablation of Ranbp2 in Cone Photoreceptors

Non-autonomous cell-death is a cardinal feature of the disintegration of neural networks in neurodegenerative diseases, but the molecular bases of this process are poorly understood. The neural retina comprises a mosaic of rod and cone photoreceptors. Cone and rod photoreceptors degenerate upon rod-specific expression of heterogeneous mutations in functionally distinct genes, whereas cone-specific mutations are thought to cause only cone demise. Here we show that conditional ablation in cone photoreceptors of Ran-binding protein-2 (Ranbp2), a cell context-dependent pleiotropic protein linked to neuroprotection, familial necrotic encephalopathies, acute transverse myelitis and tumor-suppression, promotes early electrophysiological deficits, subcellular erosive destruction and non-apoptotic death of cones, whereas rod photoreceptors undergo cone-dependent non-autonomous apoptosis. Cone-specific Ranbp2 ablation causes the temporal activation of a cone-intrinsic molecular cascade highlighted by the early activation of metalloproteinase 11/stromelysin-3 and up-regulation of Crx and CoREST, followed by the down-modulation of cone-specific phototransduction genes, transient up-regulation of regulatory/survival genes and activation of caspase-7 without apoptosis. Conversely, PARP1+-apoptotic rods develop upon sequential activation of caspase-9 and caspase-3 and loss of membrane permeability. Rod photoreceptor demise ceases upon cone degeneration. These findings reveal novel roles of Ranbp2 in the modulation of intrinsic and extrinsic cell death mechanisms and pathways. They also unveil a novel spatiotemporal paradigm of progression of neurodegeneration upon cell-specific genetic damage whereby a cone to rod non-autonomous death pathway with intrinsically distinct cell-type death manifestations is triggered by cell-specific loss of Ranbp2. Finally, this study casts new light onto cell-death mechanisms that may be shared by human dystrophies with distinct retinal spatial signatures as well as with other etiologically distinct neurodegenerative disorders.

Identification of Host Proteins Involved in Japanese Encephalitis Virus Infection by Quantitative Proteomics Analysis

Japanese encephalitis virus (JEV) enters host cells via receptor-mediated endocytosis and replicates in the cytoplasm of infected cells. To study virus-host cell interactions, we performed a SILAC-based quantitative proteomics study of JEV-infected HeLa cells using a subcellular fractionation strategy. We identified 158 host proteins as differentially regulated by JEV (defined as exhibiting a greater than 1.5-fold change in protein abundance upon JEV infection). The mass spectrometry quantitation data for selected proteins were validated by Western blot and immunofluorescence confocal microscopy. Bioinformatics analyses were used to generate JEV-regulated host response networks consisting of regulated proteins, which included 35 proteins that were newly added based on the results of this study. The JEV infection-induced host response was found to be coordinated primarily through the immune response process, the ubiquitin-proteasome system (UPS), the intracellular membrane system, and lipid metabolism-related proteins. Protein functional studies of selected host proteins using RNA interference-based techniques were carried out in HeLa cells infected with an attenuated or a highly virulent strain of JEV. We demonstrated that the knockdown of interferon-induced transmembrane protein 3 (IFITM3), Ran-binding protein 2 (RANBP2), sterile alpha motif domain-containing protein 9 (SAMD9) and vesicle-associated membrane protein 8 (VAMP8) significantly increased JEV replication. The results presented here not only promote a better understanding of the host response to JEV infection but also highlight multiple potential targets for the development of antiviral agents.

Abstract 4048: Aggresome formation is regulated by RanBPM through an interaction with HDAC6.

Abstract RanBPM (Ran-binding protein M, also called RanBP9) is a nucleocytoplamsic protein that has been implicated in a number of cellular processes including cell adhesion, migration and gene transcription. It has been hypothesized to be a scaffolding protein, but its function remains poorly understood. In previous studies we documented the relocalization of RanBPM from the nucleus to the cytoplasm in response to ionizing radiation (IR) treatment. Subsequent analysis showed that IR triggered cytoplasmic RanBPM relocalization in perinuclear dots or foci often located close to an invagination of the nucleus. Upon further investigation, the RanBPM aggregates were identified as aggresomes, which have not been previously documented to occur in response to IR. Aggresomes are aggregates of misfolded/ubiquitinated proteins resulting from improper protein assembly, aberrant modifications and/or environmental stress. These misfolded/ubiquitinated proteins are normally cleared by chaperone-mediated refolding or by proteasomal degradation through the ubiquitin-proteasome system. In conditions where these systems are impaired or overwhelmed, misfolded proteins accumulate in specific perinuclear structures called aggresome. Further analysis confirmed that the RanBPM foci were indeed aggresomes by assessing co-localization of RanBPM with HDAC6, which is required for aggresome formation. Further, we showed RanBPM also formed aggresome in response to treatment with the proteasome inhibitor MG132. To determine the effect of RanBPM downregulation on aggresome formation, we assessed aggresome formation by HDAC6 in RanBPM shRNA and control shRNA Hela and HEK cells. RanBPM downregulation resulted in significantly lower number of aggresomes both after MG132 and IR treatment, suggesting that RanBPM is essential in aggresome formation. Confocal microscopy analysis showed that RanBPM and HDAC6 co-localize within the aggresome and co-immunoprecipitation studies detected an interaction between the two proteins. Downregulation of RanBPM also resulted in decreased acetylated α-tubulin, suggesting that RanBPM regulates HDAC6 activity. Altogether these results suggest that RanBPM may regulate aggresome formation through an interaction with HDAC6. The molecular details of this regulation are currently under investigation. Citation Format: Louisa Salemi, Ahmad Almawi, Karen Lefebvre, Caroline Schild Poulter. Aggresome formation is regulated by RanBPM through an interaction with HDAC6. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4048. doi:10.1158/1538-7445.AM2013-4048

Kinesin-1 and mitochondrial motility control by discrimination of structurally equivalent but distinct subdomains in Ran-GTP-binding domains of Ran-binding protein 2

The pleckstrin homology (PH) domain is a versatile fold that mediates a variety of protein–protein and protein–phosphatidylinositol lipid interactions. The Ran-binding protein 2 (RanBP2) contains four interspersed Ran GTPase-binding domains (RBDn = 1–4) with close structural homology to the PH domain of Bruton's tyrosine kinase. The RBD2, kinesin-binding domain (KBD) and RBD3 comprise a tripartite domain (R2KR3) of RanBP2 that causes the unfolding, microtubule binding and biphasic activation of kinesin-1, a crucial anterograde motor of mitochondrial motility. However, the interplay between Ran GTPase and R2KR3 of RanBP2 in kinesin-1 activation and mitochondrial motility is elusive. We use structure–function, biochemical, kinetic and cell-based assays with time-lapse live-cell microscopy of over 260 000 mitochondrial-motility-related events to find mutually exclusive subdomains in RBD2 and RBD3 towards Ran GTPase binding, kinesin-1 activation and mitochondrial motility regulation. The RBD2 and RBD3 exhibit Ran-GTP-independent, subdomain and stereochemical-dependent discrimination on the biphasic kinetics of kinesin-1 activation or regulation of mitochondrial motility. Further, KBD alone and R2KR3 stimulate and suppress, respectively, multiple biophysical parameters of mitochondrial motility. The regulation of the bidirectional transport of mitochondria by either KBD or R2KR3 is highly coordinated, because their kinetic effects are accompanied always by changes in mitochondrial motile events of either transport polarity. These studies uncover novel roles in Ran GTPase-independent subdomains of RBD2 and RBD3, and KBD of RanBP2, that confer antagonizing and multi-modal mechanisms of kinesin-1 activation and regulation of mitochondrial motility. These findings open new venues towards the pharmacological harnessing of cooperative and competitive mechanisms regulating kinesins, RanBP2 or mitochondrial motility in disparate human disorders.

Epithelioid inflammatory myofibroblastic sarcoma arising in the pleural cavity

A 57-year-old Japanese man presented with massive right pleural effusion, and a huge tumor arising in the pleural cavity was detected by chest computed tomography. A thoracoscopic tumor biopsy revealed that the tumor protruded extensively into the pleural cavity, and its gross appearance was cystic and glossy. Microscopically, the tumor cells were rounded and epithelioid in shape. Prominent and abundant myxoid stroma was also present together with an inflammatory infiltrate, and the tumor was anaplastic lymphoma kinase (ALK)-immunopositive. Fluorescence in situ hybridization revealed that the Ran-binding protein 2-ALK fusion gene was present. Taken together, these findings supported the diagnosis of epithelioid inflammatory myofibroblastic sarcoma (EIMS), which is a variant of an inflammatory myofibrobrastic tumor. This is the first reported case of an EIMS arising in the pleural cavity.

The role of Ran-binding protein 3 during influenza A virus replication

Influenza A virus vRNP nuclear export is CRM1-dependent. Ran-binding protein 3 (RanBP3) is a Ran-interacting protein that is best known for its role as a cofactor of CRM1-mediated cargo nuclear export. In this study, we investigated the role of RanBP3 during the influenza A virus life cycle. We found that RanBP3 was phosphorylated at Ser58 in the early and late phases of infection. Knockdown of RanBP3 expression led to vRNP nuclear retention, suggesting that RanBP3 is involved in vRNP nuclear export. Moreover, we demonstrated that the function of RanBP3 during vRNP nuclear export is regulated by phosphorylation at Ser58, and that RanBP3 phosphorylation is modulated by both PI3K/Akt and Ras/ERK/RSK pathways in the late phase of viral infection.

Ran GTPase-Independent and Stereochemical Control of Kinesin-1 and Mitochondrial Motility by Domains of Ran-Binding Protein-2

The microtubule-based motor proteins, dynein and kinesin-1, mediate fast mitochondrial trafficking, but the mechanisms underlying the regulation of mitochondrial motility are ill-defined. The Ran-binding protein 2 (RanBP2) is a pleiotropic and multimodular protein, which couples directly with the kinesin-1 isoforms, KIF5B/KIF5C, via its tripartite domains, the kinesin-binding domain (KBD) and the Ran GTPase-binding domains, RBD2 and RBD3. The coupling of RBD2-KBD-RBD3 to kinesin-1 activates its ATPase activity ∼30-fold and with activation kinetics that is biphasic and cooperative. Here, we employ structure-function, biochemical, kinetic and cell-based assays with time-lapse live-cell microscopy of over 260,000 mitochondrial motility-related events to probe the interplay between Ran GTPase and RBD2-KBD-RBD3 on kinesin-1 activation and mitochondrial motility. We uncover mutually exclusive subdomains in RBDs toward Ran GTPase binding, kinesin-1 activation and modulation of mitochondria motility. The RBDs exhibit Ran-GTP-independent, subdomain and stereochemical-dependent discrimination on the biphasic activation kinetics of kinesin-1 or regulation of mitochondrial motility. Remarkably, RBD2-KBD-RBD3 and KBD alone exert opposing effects on the equilibrium between the stationary and motile phases of mitochondria and multiple biophysical parameters of mitochondrial motility. Further, the regulation of the bidirectional transport of mitochondria by either RBD2-KBD-RBD3 or KBD is highly coordinated, since their effects are accompanied always by changes in motile biophysical parameters of opposite-polarity. These studies uncover Ran GTPase-independent antagonizing and multimodal mechanisms of kinesin-1 activation and regulation of mitochondrial motility by distinct domains of RanBP2. Further, they open new venues toward the pharmacological harnessing of mechanisms regulating kinesins, mitochondrial motility or RanBP2 in a variety of disparate disorders.

RanBPM Is an Inhibitor of ERK Signaling

Ran-binding protein M (RanBPM) is a nucleocytoplasmic protein of yet unknown function. We have previously shown that RanBPM inhibits expression of the anti-apoptotic factor Bcl-2 and promotes apoptosis induced by DNA damage. Here we show that the effects of RanBPM on Bcl-2 expression occur through a regulation of the ERK signaling pathway. Transient and stable down-regulation of RanBPM stimulated ERK phosphorylation, leading to Bcl-2 up-regulation, while re-expression of RanBPM reversed these effects. RanBPM was found to inhibit MEK and ERK activation induced by ectopic expression of active RasV12. Activation of ERK by active c-Raf was also prevented by RanBPM. Expression of RanBPM correlated with a marked decrease in the protein levels of ectopically expressed active c-Raf and also affected the expression of endogenous c-Raf. RanBPM formed a complex with both active c-Raf, consisting of the C-terminal kinase domain, and endogenous c-Raf in mammalian cells. In addition, RanBPM was found to decrease the binding of Hsp90 to c-Raf. Finally, we show that loss of RanBPM expression confers increased cell proliferation and cell migration properties to HEK293 cells. Altogether, these findings establish RanBPM as a novel inhibitor of the ERK pathway through an interaction with the c-Raf complex and a regulation of c-Raf stability, and provide evidence that RanBPM loss of expression results in constitutive activation of the ERK pathway and promotes cellular events leading to cellular transformation and tumorigenesis.

Sgk1 enhances RANBP1 transcript levels and decreases taxol sensitivity in RKO colon carcinoma cells

The serum- and glucocorticoid-regulated kinase (Sgk1) is essential for hormonal regulation of epithelial sodium channel-mediated sodium transport and is involved in the transduction of growth factor-dependent cell survival and proliferation signals. Growing evidence now points to Sgk1 as a key element in the development and/or progression of human cancer. To gain insight into the mechanisms through which Sgk1 regulates cell proliferation, we adopted a proteomic approach to identify up- or downregulated proteins after Sgk1-specific RNA silencing. Among several proteins, the abundance of which was found to be up- or downregulated upon Sgk1 silencing, we focused our attention of RAN-binding protein 1 (RANBP1), a major effector of the GTPase RAN. We report that Sgk1-dependent regulation of RANBP1 has functional consequences on both mitotic microtubule activity and taxol sensitivity of cancer cells.

RANBP9 (RAN binding protein 9)

Review on RANBP9 (RAN binding protein 9), with data on DNA, on the protein encoded, and where the gene is implicated.

Ranbp2 haploinsufficiency mediates distinct cellular and biochemical phenotypes in brain and retinal dopaminergic and glia cells elicited by the Parkinsonian neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)

Many components and pathways transducing multifaceted and deleterious effects of stress stimuli remain ill-defined. The Ran-binding protein 2 (RanBP2) interactome modulates the expression of a range of clinical and cell-context-dependent manifestations upon a variety of stressors. We examined the role of Ranbp2 haploinsufficiency on cellular and metabolic manifestations linked to tyrosine-hydroxylase (TH+) dopaminergic neurons and glial cells of the brain and retina upon acute challenge to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), a parkinsonian neurotoxin, which models facets of Parkinson disease. MPTP led to stronger akinetic parkinsonism and slower recovery in Ranbp2 +/− than wild-type mice without viability changes of brain TH+-neurons of either genotype, with the exception of transient nuclear atypia via changes in chromatin condensation of Ranbp2 +/− TH+-neurons. Conversely, the number of wild-type retinal TH+-amacrine neurons compared to Ranbp2 +/− underwent milder declines without apoptosis followed by stronger recoveries without neurogenesis. These phenotypes were accompanied by a stronger rise of EdU+-proliferative cells and non-proliferative gliosis of GFAP+-Müller cells in wild-type than Ranbp2 +/− that outlasted the MPTP-insult. Finally, MPTP-treated wild-type and Ranbp2 +/− mice present distinct metabolic footprints in the brain or selective regions thereof, such as striatum, that are supportive of RanBP2-mediated regulation of interdependent metabolic pathways of lysine, cholesterol, free-fatty acids, or their β-oxidation. These studies demonstrate contrasting gene-environment phenodeviances and roles of Ranbp2 between dopaminergic and glial cells of the brain and retina upon oxidative stress-elicited signaling and factors triggering a continuum of metabolic and cellular manifestations and proxies linked to oxidative stress, and chorioretinal and neurological disorders such as Parkinson.Electronic supplementary materialThe online version of this article (doi:10.1007/s00018-012-1071-9) contains supplementary material, which is available to authorized users.

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

BackgroundRanBPM (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.ResultsBased 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.ConclusionWe 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.

Recurrent Acute Necrotizing Encephalopathy in a Korean Child

Acute necrotizing encephalopathy is characterized by fever, seizures, acute encephalopathy, and rapid progression to coma. It is usually associated with viral illness and shows characteristic brain magnetic resonance imaging features, including symmetrical involvement of bilateral thalami, brain stem, white matter, and cerebellum. After the first report of recurrent or familial cases in 2003, similar cases were found exclusively in American and European regions. The association with Ran-binding protein 2 gene was identified in 75% of familial or recurrent cases. This report describes a previous healthy 22-month-old boy who recurrently manifested typical clinical and radiological characteristics of acute necrotizing encephalopathy. His neurological outcome worsened with repeated episodes. There was no family history of acute necrotizing encephalopathy and no mutation in the coding region of Ran-binding protein 2 (RANBP2) gene. This is the first reported case of recurrent acute necrotizing encephalopathy in a non-Caucasian family.

Abstract LB-77: Crm1-mediated nucleocytoplasmic transport inhibition perturbs multiple cellular pathways to trigger melanoma cell apoptosis

Abstract Development of multiple resistance mechanisms in melanomas has necessitated the identification of novel drug targets, which when inhibited could impact multiple cellular pathways thus circumventing potential resistance mechanisms. By performing cDNA-microarray analysis, we identified four key components of the nucleocytoplasmic transport machinery, Chromosome Region Maintenance 1 (Crm1), Ran-GTPase, Ran-GTPase Activating Protein 1 (RanGAP1) and Ran Binding Protein 1 (RanBP1) to be overexpressed in human melanoma metastases. Crm1 inhibition, employing the highly specific Crm1 inhibitor Leptomycin B (LMB) induced a dramatic depletion of pro-survival/cytoplasmic Erk1/2 and p90RSK1 and mediated persistent Erk signaling hyperactivation. Consistently, Crm1 inhibition inflicted extensive apoptosis in melanoma cells while sparing immortalized melanocytes and primary lung fibroblasts. Apoptosis required both the intrinsic and extrinsic apoptotic pathways and was associated with a nuclear entrapment and down-regulation of anti-apoptotic Survivin. Apoptosis was preceded by a G1 cell-cycle arrest and even though Crm1 inhibition mediated dramatic p53 and p21 induction exclusively in wild-type p53 melanoma cells, latter's silencing or inactivation failed to alleviate ensuing apoptosis. Notably, Crm1 inhibition elicited cell line specific, G1 to S progression-retarding changes in the expression of multiple cell-cycle regulatory proteins (Cdk2, Cdk4, p27, p16 and p18) thus potentially explaining p53 dispensability. Based on our results, we propose Crm1 as a potential therapeutic target in human melanoma, whose inhibition initiates a multitude of cell context-dependent molecular events to trigger G1-arrest followed by massive apoptosis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-77. doi:1538-7445.AM2012-LB-77

Identification and characterization of novel factors regulating kinesin‐1 activation and mitochondria dynamics

The Ran‐binding protein 2 (RanBP2) is a mosaic and pleiotropic protein, which associates in vitro and in vivo with the conventional microtubule‐based motor and kinesin‐1 isoforms, KIF5B/KIF5C. We showed previously that the kinesin‐binding domain (KBD) together with the flanking Ran‐binding domains 2 and 3 (RBD2, RBD3) of RanBP2 directly jump‐start and boost the ATPase motor activity of kinesin‐1, a motor implicated in mitochondria transport. The goal of this study is to define the roles of RBD2 and RBD3 of RanBP2 and Ran GTPase in kinesin‐1 activation in vitro and multiple biophysical parameters of mitochondria motility in live cells. We show that the activation of kinesin‐1 by RBD2‐KBDRBD3 is Ran GTPase independent; yet mutations in RBD2‐KBDRBD3 and abolishing its interaction with Ran GTPase suppress the Michaelis‐Menton and partially affect the allosteric activation phases of kinesin‐1. These effects lead to a ~20% reduction of kinesin‐1 activity (kcat). In live cells, KBD alone stimulates the motility, displacement, frequency of change in direction, motility persistence and anterograde velocity of mitochondria, whereas a mutant KBD construct has no effect. In contrast, RBD2‐KBDRBD3 of RanBP2, but not mutant constructs, suppress all these biophysical parameters of mitochondria motility. Further, there is stereochemical specificity between RBD2 and RBD3 in certain parameters of regulation of mitochondria motility. These studies uncover novel Ran GTPase‐independent functions of RBD2, RBD3 and KBD of RanBP2 in kinesin‐1 activation and regulation of mitochondria motility.NIH support GM083165 & EY019492 and RPB

Identification and functional analysis of Zranb2 as a novel Smad‐binding protein that suppresses BMP signaling

Smads 1/5/8 transduce the major intracellular signaling of bone morphogenetic proteins (BMPs). In the present study, we analyzed Smad1-binding proteins in HEK293T cells using a proteomic technique and identified the protein, zinc-finger, RAN-binding domain-containing protein 2 (ZRANB2). Zranb2 interacted strongly with Smad1, Smad5, and Smad8 and weakly with Smad4. The overexpression of Zranb2 inhibited BMP activities in C2C12 myoblasts in vitro, and the injection of Zranb2 mRNA into zebrafish embryos induced weak dorsalization. Deletion analyses of Zranb2 indicated that the serine/arginine-rich (SR) domain and the glutamine-rich domain were required for the inhibition of BMP activity and the interaction with Smad1, respectively. Zranb2 was found to be localized in the nucleus; however, the SR domain-deleted mutant localized to the cytoplasm. The knockdown of endogenous Zranb2 in C2C12 cells enhanced BMP activity. Zranb2 suppressed Smad transcriptional activity without affecting Smad phosphorylation, nuclear localization, or DNA binding. Taken together, these findings suggested that Zranb2 is a novel BMP suppressor that forms a complex with Smads in the nucleus.