Expression of RNUDC, a potential nuclear movement protein, in mammalian cells: localization to the Golgi apparatus

Angiomotin regulates prostate cancer cell proliferation by signaling through the Hippo-YAP pathway

Angiomotin (AMOT) is a family of proteins found to be a component of the apical junctional complex of vertebrate epithelial cells and is recently found to play important roles in neurofibromatosis type 2 (NF-2). Whether AMOT plays a role in prostate cancer (PCa) is unknown. AMOT is expressed as two isoforms, AMOTp80 and AMOTp130, which has a 409 aa N-terminal domain that is absent in AMOTp80. Both AMOTp80 and AMOTp130 are expressed in LNCaP and C4-2B4, but at a low to undetectable level in PC3, DU145, and BPH1 cells. Further study showed that AMOTp130 and AMOTp80 have distinct functions in PCa cells. We found that AMOTp80, but not AMOT p130, functioned as a tumor promoter by enhancing PCa cell proliferation. Mechanistic studies showed that AMOTp80 signaled through the Hippo pathway by promoting nuclear translocation of YAP, resulting in an increased expression of YAP target protein BMP4. Moreover, inhibition of BMP receptor activity by LDN-193189 abrogates AMOTp80-mediated cell proliferation. Together, this study reveals a novel mechanism whereby the AMOTp80-Merlin-MST1-LATS-YAP-BMP4 pathway leads to AMOTp80-induced tumor cell proliferation.

Dynamic Phosphorylation of NudC by Aurora B in Cytokinesis

Nuclear distribution protein C (NudC) is a mitotic regulator that plays a role in cytokinesis. However, how NudC is regulated during cytokinesis remains unclear. Here, we show that NudC is phosphorylated by Aurora B, a kinase critical for cell abscission. NudC is co-localized with Aurora B at the midbody and co-immunoprecipitated with Aurora B in mitosis. Inhibition of Aurora B by ZM447439 reduced NudC phosphorylation, suggesting that NudC is an Aurora B substrate in vivo. We identified T40 on NudC as an Aurora B phosphorylation site. NudC depletion resulted in cytokinesis failure with a dramatic elongation of the intercellular bridge between daughter cells, sustained Aurora B activity at the midbody, and reduced cell abscission. These cytokinetic defects can be rescued by the ectopic expression of wild-type NudC. Reconstitution with T40A phospho-defective NudC was found to rescue the cytokinesis defect. In contrast, reconstitution with the T40D phospho-mimetic NudC was inefficient in supporting the completion of cytokinesis. These results suggest that that dynamic phosphorylation of NudC by Aurora B regulates cytokinesis.

The mammalian NudC-like genes: a family with functions other than regulating nuclear distribution

Nuclear distribution gene C homolog (NudC) is a highly conserved gene. It has been identified in different species from fungi to mammals. The high degree of conservation, in special in the nudC domain, suggests that they are genes with essential functions. Most of the identified genes in the family have been implicated in cell division through the regulation of cytoplasmic dynein. As for mammalian genes, human NUDC has been implicated in the migration and proliferation of tumor cells and has therefore been considered a possible therapeutic target. There is evidence suggesting that mammalian NudC is also implicated in the regulation of the inflammatory response and in thrombopoiesis. The presence of these other functions not related to the interaction with molecular motors agrees with that these genes and their products are larger in size than their microbial orthologous, indicating that they have evolved to convey additional features.

The nuclear migration protein NUDF/LIS1 forms a complex with NUDC and BNFA at spindle pole bodies

Nuclear migration depends on microtubules, the dynein motor complex, and regulatory components like LIS1 and NUDC. We sought to identify new binding partners of the fungal LIS1 homolog NUDF to clarify its function in dynein regulation. We therefore analyzed the association between NUDF and NUDC in Aspergillus nidulans. NUDF and NUDC directly interacted in yeast two-hybrid experiments via NUDF's WD40 domain. NUDC-green fluorescent protein (NUDC-GFP) was localized to immobile dots in the cytoplasm and at the hyphal cortex, some of which were spindle pole bodies (SPBs). We showed by bimolecular fluorescence complementation microscopy that NUDC directly interacted with NUDF at SPBs at different stages of the cell cycle. Applying tandem affinity purification, we isolated the NUDF-associated protein BNFA (for binding to NUDF). BNFA was dispensable for growth and for nuclear migration. GFP-BNFA fusions localized to SPBs at different stages of the cell cycle. This localization depended on NUDF, since the loss of NUDF resulted in the cytoplasmic accumulation of BNFA. BNFA did not bind to NUDC in a yeast two-hybrid assay. These results show that the conserved NUDF and NUDC proteins play a concerted role at SPBs at different stages of the cell cycle and that NUDF recruits additional proteins specifically to the dynein complex at SPBs.

Regulation of cell differentiation by hNUDC via a Mpl-dependent mechanism in NIH 3T3 cells

Thrombopoietin receptor (Mpl) belongs to the cytokine receptor surperfamily with a large extracellular N-terminal portion responsible for cytokine recognition and binding. Thrombopoietin (TPO) has so far been the only widely studied cytokine for Mpl. However we have recently identified human NUDC (hNUDC), previously described as a human homolog of a fungal nuclear migration protein, as another putative binding partner of Mpl. The purpose of this study is to test the extent of the functioning of hNUDC by identifying protein-protein interactions with Mpl in mammalian cells. The full-length cDNAs encoding Mpl and hNUDC were cloned into pEGFP-N1 and pDsRed2-N1 respectively which were subsequently expressed as Mpl-EGFP (green) and hNUDC-DsRed (red) fusion proteins. Using ELISA and immunofluorescence studies, we have demonstrated the direct binding of hNUDC to cell surface-captured Mpl. We also observed that hNUDC induced significant changes in cellular morphology in NIH 3T3 cells stably transfected with pMpl-EGFP. Interestingly, these morphological changes were characteristic of cells undergoing megakaryocyte differentiation. Extracellular-signal-regulated protein kinases 1 and 2 (ERK1/2) have been shown to mediate such megakaryocyte-like differentiation. In addition, co-expression of Mpl-EGFP and hNUDC-DsRed led to the release of hNUDC-DsRed into the culture medium.

Expression patterns of LIS1, dynein and their interaction partners dynactin, NudE, NudEL and NudC in human gliomas suggest roles in invasion and proliferation

Diffusely infiltrating gliomas are the most common type of primary intracranial neoplasm in humans. One of the major obstacles to the effective treatment of these tumors is their highly infiltrative growth. However, mechanisms controlling their migration and proliferation are poorly understood. Glioma cells resemble neural progenitors, and we hypothesize that gliomas recapitulate the capacity of migration and proliferation of progenitors that takes place during brain development. Based on recent evidence implicating cytoplasmic dynein and its regulatory proteins in neural progenitor migration and division, we conducted immunohistochemical evaluation of surgically resected human glioma samples for the presence and distribution of these proteins. We examined expression of LIS1, the gene responsible for type I lissencephaly, cytoplasmic dynein and the dynein- and LIS1-interacting factors dynactin, NudE/NudEL and NudC, which play significant roles in neural progenitor cell behavior. We found that each of these proteins is expressed in all histological types and grades of human neuroectodermal tumors examined. Immunohistochemical analysis revealed that the levels of expression varied from cell to cell within each tumor, ranging from very high to undetectable. This stands in contrast to the low levels of diffuse staining seen in non-neoplastic brain tissue. Of particular interest, we noted tumor cells infiltrating the white matter and tumor cells undergoing cell division amongst the cells with notably high expression levels. These findings are compatible with the idea that LIS1 and its interacting proteins play a role in glioma migration and proliferation analogous to their role during brain development.

NudC is required for Plk1 targeting to the kinetochore and chromosome congression

The equal distribution of chromosomes during mitosis is critical for maintaining the integrity of the genome. Essential to this process are the capture of spindle microtubules by kinetochores and the congression of chromosomes to the metaphase plate . Polo-like kinase 1 (Plk1) is a mitotic kinase that has been implicated in microtubule-kinetochore attachment, tension generation at kinetochores, tension-responsive signal transduction, and chromosome congression . The tension-sensitive substrates of Plk1 at the kinetochore are unknown. Here, we demonstrate that human Nuclear distribution protein C (NudC), a 42 kDa protein initially identified in Aspergillus nidulans and shown to be phosphorylated by Plk1 , plays a significant role in regulating kinetochore function. Plk1-phosphorylated NudC colocalizes with Plk1 at the outer plate of the kinetochore. Depletion of NudC reduced end-on microtubule attachments at kinetochores and resulted in defects in chromosome congression at the metaphase plate. Importantly, NudC-deficient cells exhibited mislocalization of Plk1 and the Kinesin-7 motor CENP-E from prometaphase kinetochores. Ectopic expression of wild-type NudC, but not NudC containing mutations in the Plk1 phosphorylation sites, recovered Plk1 localization at the kinetochore and rescued chromosome congression. Thus, NudC functions as both a substrate and a spatial regulator of Plk1 at the kinetochore to promote chromosome congression.

Inhibition of prostate tumor growth by overexpression of NudC, a microtubule motor-associated protein

Microtubules play a central role in coordinating various cellular functions that are orchestrated by their interaction with molecular motors. Anticancer drugs that target microtubule dynamics have been shown to be effective in cancer treatment. However, the effect of microtubule motor-associated molecules on cancer cell proliferation is not clear. Here, we investigated the role of NudC, a nuclear movement protein associated with the microtubule motor dynein, on prostate tumorigenesis. Recombinant adenovirus expressing NudC (Ad-NudC) was used to examine the effects of NudC on the tumorigenicity of prostate cancer cells. Expression of NudC in LNCaP cells inhibited their anchorage-independent growth in a soft agar colony assay. Expression of NudC in DU145 or PC-3 cells inhibited tumor growth in a subcutaneous xenograft model. At the cellular level, expression of NudC in DU145 and PC-3 cells inhibited cell proliferation at 48 h after Ad-NudC infection. FACS analysis of cell cycle distribution showed that 50-60% of Ad-NudC-infected PC-3 cells have a G2/M-phase DNA content compared to about 16-19% in Ad-Luciferase (Ad-Luc)-infected control cells, suggesting that NudC overexpression resulted in aberrant cell cycle progression. Immunofluorescence microscopy revealed a significant increase in cells with a single enlarged nucleus and cells exhibiting multiple nuclei, along with a concomitant increase in cell size in Ad-NudC-infected cells. These results suggest that NudC overexpression led to a block in cell division of prostate cancer cells, and that Ad-NudC may provide a new anticancer drug approach targeting the function of a microtubule motor-associated protein.

A role for Plk1 phosphorylation of NudC in cytokinesis

Polo-like kinase 1 (Plk1) plays essential roles at multiple events during cell division, yet little is known about its physiological substrates. In a cDNA phage display screen using Plk1 C-terminal affinity columns, we identified NudC (nuclear distribution gene C) as a Plk1 binding protein. Here, we characterize the interaction between Plk1 and NudC, show that Plk1 phosphorylates NudC at conserved S274 and S326 residues in vitro, and present evidence that NudC is also a substrate for Plk1 in vivo. Downregulation of NudC by RNA interference results in multiple mitotic defects, including multinucleation and cells arrested at the midbody stage, which are rescued by ectopic expression of wild-type NudC, but not by NudC with mutations in the Plk1 phosphorylation sites. These results suggest that Plk1 phosphorylation of NudC may influence cytokinesis.

Role for NudC, a dynein-associated nuclear movement protein, in mitosis and cytokinesis

NudC, a nuclear movement protein that associates with dynein, was originally cloned as a mitogen-inducible early growth response gene. NudC forms a biochemical complex with components of the dynein/dynactin complex and is suggested to play a role in translocation of nuclei in proliferating neuronal progenitors as well as in migrating neurons in culture. Here, we show that NudC plays multiple roles in mitosis and cytokinesis in cultured mammalian cells. Altering NudC levels by either small interfering RNA-mediated gene silencing or adenovirus-mediated overexpression resulted in multinucleated cells and cells with persistent intercellular connections and disorganized midzone and midbody matrix. These phenotypes suggest a failure in cytokinesis in NudC altered cells. Further, a key mitotic enzyme, polo-like kinase, is mislocalized from the centrosomes and the midbody in NudC altered cells. Gene silencing of nud-1, the Caenorhabditis elegans ortholog of NudC, led to a loss of midzone microtubules and the rapid regression of the cleavage furrow, which resulted in one-celled embryos containing two nuclei. The loss of midzone microtubule organization owing to silencing of the NudC/nud-1 gene in two systems, coupled with the loss of Plk1 from mitotic structures in mammalian cells, provide clues to the cytokinesis defect and the multinucleation phenotype. Our findings suggest that NudC functions in mitosis and cytokinesis, in part by regulating microtubule organization at the midzone and midbody.

The nuclear migration gene NudC and human hematopoiesis

The filamentous fungus Aspergillus nidulans nudC (nuclear distribution C) gene is required for movement of nuclei following mitosis and for normal colony growth. It is highly conserved, structurally and functionally, throughout most of evolution. The human homolog, called HnudC, has been cloned and has an important role in cell proliferation. In hematopoiesis, HNUDC is highly expressed in early hematopoietic precursors and declines during normal differentiation. Stimulation of proliferation of the erythroleukemia cell line TF-1 with GM-CSF enhances HnudC protein and mRNA expression and treatment with antisense (but not sense) oligonucleotides to HnudC mRNA significantly reduces cell division. A significant increase in HNUDC is present in bone marrow aspirates from patients with acute lymphoblastic leukemia (ALL) and acute myelogenous leukemia (AML) compared to the level in normal cellular counterparts, demonstrating dysregulated expression in leukemia. These data support the conclusion that HnudC plays a functional role in promoting hematopoietic cell growth and that it is involved in leukemogenesis.

Analysis of prolactin-modulated gene expression profiles during the Nb2 cell cycle using differential screening techniques

BACKGROUND

Rat Nb2-11C lymphoma cells are dependent on prolactin for proliferation and are widely used to study prolactin signaling pathways. To investigate the role of this hormone in the transcriptional mechanisms that underlie prolactin-stimulated mitogenesis, five different techniques were used to isolate differentially expressed transcripts: mRNA differential display, representational difference analysis (RDA), subtractive suppressive hybridization (SSH), analysis of weakly expressed candidate genes, and differential screening of an organized library.

RESULTS

About 70 transcripts were found to be modulated in Nb2 cells following prolactin treatment. Of these, approximately 20 represent unknown genes. All cDNAs were characterized by northern blot analysis and categorized on the basis of their expression profiles and the functions of the known genes. We compared our data with other cell-cycle-regulated transcripts and found several new potential signaling molecules that may be involved in Nb2 cell growth. In addition, abnormalities in the expression patterns of several transcripts were detected in Nb2 cells, including the constitutive expression of the immediate-early gene EGR-1. Finally, we compared the differential screening techniques in terms of sensitivity, efficiency and occurrence of false positives.

CONCLUSIONS

Using these techniques to determine which genes are differentially expressed in Nb2 lymphoma cells, we have obtained valuable insight into the potential functions of some of these genes in the cell cycle. Although this information is preliminary, comparison with other eukaryotic models of cell-cycle progression enables identification of expression abnormalities and proteins potentially involved in signal transduction, which could indicate new directions for research.

Human munc13 is a diacylglycerol receptor that induces apoptosis and may contribute to renal cell injury in hyperglycemia

We have previously shown that human munc13 (hmunc13) is up-regulated by hyperglycemia under in vitro conditions in human mesangial cell cultures. The purpose of the present study was to determine the cellular function of hmunc13. To do this, we have investigated the subcellular localization of hmunc13 in a transiently transfected renal cell line, opossum kidney cells. We have found that hmunc13 is a cytoplasmic protein and is translocated to the Golgi apparatus after phorbol ester stimulation. In addition, cells transfected with hmunc13 demonstrate apoptosis after treatment with phorbol ester, but cells transfected with an hmunc13 deletion mutant in which the diacylglycerol (C1) binding domain is absent exhibit no change in intracellular distribution and no induction of apoptosis in the presence of phorbol ester stimulation. We conclude that both the diacylglycerol-induced translocation and the apoptosis represent functional activity of hmunc13. We have also demonstrated that munc13-1 and munc13-2 are localized mainly to cortical epithelial cells in rat kidney and both are overexpressed under conditions of hyperglycemia in a streptozotocin-treated diabetic rat model. Taken together, our data suggest that hmunc13 serves as a diacylglycerol-activated, PKC-independent signaling pathway capable of inducing apoptosis and that this pathway may contribute to the renal cell complications of hyperglycemia.

A homolog of the fungal nuclear migration gene nudC is involved in normal and malignant human hematopoiesis

The filamentous fungus Aspergillus nidulans nudC gene has an essential function in movement of nuclei following mitosis and is required for normal colony growth. Here, the molecular cloning and role in hematopoiesis of a human gene (designated HnudC) homologous to A. nidulans nudC is reported. The amino terminus of the larger human protein (HNUDC = 45 kDa) does not overlap with A. nidulans NUDC (22 kDa). However, NUDC and the C-terminal 94 amino acids of HNUDC are 67% identical. The C-terminal region of the HnudC gene fully complements the A. nidulans temperature-sensitive nudC3 mutation, suggesting that nudC has an essential function in cell growth that is conserved from filamentous fungi to humans. In initial studies, HNUDC levels were much higher in erythroid precursors compared to most other human tissues. Therefore, the potential role of HnudC in hematopoiesis was explored. In normal human bone marrow, HNUDC protein and mRNA are highly expressed in early myeloid and erythroid precursors and decline as these cells terminally differentiate. To determine whether hematopoietic growth factors induce HnudC expression, TF-1 cells were stimulated by granulocyte-macrophage colony-stimulating factor. This induced a significant increase in HNUDC protein and HnudC mRNA, suggesting that enhancement of HnudC expression in response to growth factor stimulation may be mediated at the transcription level. Furthermore, HNUDC was significantly enhanced in lysates of bone marrow aspirates from patients with acute myelogenous and acute lymphoblastic leukemia compared to aspirates from normal controls, suggesting that HnudC is involved in malignant hematopoietic cell growth as well. These data demonstrate that HNUDC is highly expressed in normal and malignant human hematopoietic precursors and suggest it is of functional importance in the proliferation of these cells.

The lissencephaly gene product Lis1, a protein involved in neuronal migration, interacts with a nuclear movement protein, NudC

Important clues to how the mammalian cerebral cortex develops are provided by the analysis of genetic diseases that cause cortical malformations [1-5]. People with Miller-Dieker syndrome (MDS) or isolated lissencephaly sequence (ILS) have a hemizygous deletion or mutation in the LIS1 gene [3,6]; both conditions are characterized by a smooth cerebral surface, a thickened cortex with four abnormal layers, and misplaced neurons [7,8]. LIS1 is highly expressed in the ventricular zone and the cortical plate [9,10], and its product, Lis1, has seven WD repeats [3]; several proteins with such repeats have been shown to interact with other polypeptides, giving rise to multiprotein complexes [11]. Lis1 copurifies with platelet-activating factor acetylhydrolase subunits alpha 1 and alpha 2 [12], and with tubulin; it also reduces microtubule catastrophe events in vitro [13]. We used a yeast two-hybrid screen to isolate new Lis1-interacting proteins and found a mammalian ortholog of NudC, a protein required for nuclear movement in Aspergillus nidulans [14]. The specificity of the mammalian NudC-Lis1 interaction was demonstrated by protein-protein interaction assays in vitro and by co-immunoprecipitation from mouse brain extracts. In addition, the murine mNudC and mLis1 genes are coexpressed in the ventricular zone of the forebrain and in the cortical plate. The interaction of Lis1 with NudC, in conjunction with the MDS and ILS phenotypes, raises the possibility that nuclear movement in the ventricular zone is tied to the specification of neuronal fates and thus to cortical architecture.