• Cutaneous vasculitis and immune complexes in severe bronchiectasis.

      Hilton, A M; Hasleton, Philip S; Bradlow, A; Leahy, B C; Cooper, K Michael; Moore, M; Departments of Chest Medicine and Pathology, Wythenshawe Hospital (1984-03)
      Four patients with severe bronchiectasis (chronic bronchial suppuration) are described who developed cutaneous lesions associated with exacerbations of their respiratory disease. The skin abnormalities consisted of purpuric lesions in three patients and an erythematous vasculitis in one. Circulating immune complexes were present in all patients and in three skin biopsy specimens showed deposition of C3, IgG, and IgA in dermal blood vessels. Haemophilus influenzae had been isolated from the sputum of all four patients and in two patients was present at the time the cutaneous lesions appeared. It is suggested that local immune complex deposition was responsible for the skin lesions which occurred during acute exacerbations of bronchiectasis.
    • CXCR4 mediated chemotaxis is regulated by 5T4 oncofetal glycoprotein in mouse embryonic cells.

      Southgate, Thomas D; McGinn, Owen J; Castro, Fernanda V; Rutkowski, Andrzej J; Al-Muftah, Mariam; Marinov, Georgi; Smethurst, Graeme J; Shaw, David M; Ward, Christopher M; Miller, Crispin J; et al. (2010)
      5T4 oncofetal molecules are highly expressed during development and upregulated in cancer while showing only low levels in some adult tissues. Upregulation of 5T4 expression is a marker of loss of pluripotency in the early differentiation of embryonic stem (ES) cells and forms an integrated component of an epithelial-mesenchymal transition, a process important during embryonic development and metastatic spread of epithelial tumors. Investigation of the transcriptional changes in early ES differentiation showed upregulation of CXCL12 and down-regulation of a cell surface protease, CD26, which cleaves this chemokine. CXCL12 binds to the widely expressed CXCR4 and regulates key aspects of development, stem cell motility and tumour metastasis to tissues with high levels of CXCL12. We show that the 5T4 glycoprotein is required for optimal functional cell surface expression of the chemokine receptor CXCR4 and CXCL12 mediated chemotaxis in differentiating murine embryonic stem cells and embryo fibroblasts (MEF). Cell surface expression of 5T4 and CXCR4 molecules is co-localized in differentiating ES cells and MEF. By contrast, differentiating ES and MEF derived from 5T4 knockout (KO) mice show only intracellular CXCR4 expression but infection with adenovirus encoding mouse 5T4 restores CXCL12 chemotaxis and surface co-localization with 5T4 molecules. A series of chimeric constructs with interchanged domains of 5T4 and the glycoprotein CD44 were used to map the 5T4 sequences relevant for CXCR4 membrane expression and function in 5T4KO MEF. These data identified the 5T4 transmembrane domain as sufficient and necessary to enable CXCR4 cell surface expression and chemotaxis. Furthermore, some monoclonal antibodies against m5T4 can inhibit CXCL12 chemotaxis of differentiating ES cells and MEF which is not mediated by simple antigenic modulation. Collectively, these data support a molecular interaction of 5T4 and CXCR4 occurring at the cell surface which directly facilitates the biological response to CXCL12. The regulation of CXCR4 surface expression by 5T4 molecules is a novel means to control responses to the chemokine CXCL12 for example during embryogenesis but can also be selected to advantage the spread of a 5T4 positive tumor from its primary site.
    • Cyclical eosinophilia: a manifestation of periodic haemopoiesis?

      Davies, J; Geary, C; Testa, Nydia G; Pumphrey, R (1985-09)
      A patient is described who has had a marked eosinophilia of unknown cause for 9 years in association with episodic facial swelling. Weekly blood counts for 8 months showed cyclical variations in eosinophils, neutrophils and monocytes (mean cycle length 35 d). Marrow culture studies showed fluctuation in the incidence of granulocyte-macrophage colonies (GM-CFC), and the proportion of eosinophil colonies was higher than the values reported for normals. The blood lymphocyte T4/T8 ratio was reversed, due to an increase of T8+ cells. It is suggested that this condition is a rare form of periodic haemopoiesis.
    • Cyclin D1 promotes androgen-dependent DNA damage repair in prostate cancer cells.

      Casimiro, M; Di Sante, G; Ju, X; Li, Z; Chen, K; Crosariol, M; Yaman, I; Gormley, M; Meng, H; Lisanti, Michael P; et al. (2015-11-18)
      Therapy resistance and poor outcome in prostate cancer is associated with increased expression of Cyclin D1. Androgens promote DNA double strand break repair to reduce DNA damage, and cyclin D1 was also shown to enhance DNA damage repair (DDR). In this study, we investigated the significance of cyclin D1 in androgen-induced DDR using established prostate cancer cells and prostate tissues from cyclinD1 knockout mice. We demonstrate that endogenous cyclin D1 further diminished the dihydrotestosterone (DHT)-dependent reduction of gammaH2AX foci in vitro. We also show that cyclin D1 was required for the androgen-dependent DNA damage response both in vitro and in vivo. Furthermore, cyclin D1 was required for androgen-enhanced DDR and radioresistance of prostate cancer cells. Moreover, microarray analysis of primary prostate epithelial cells from cyclin D1-deficient and wild-type mice demonstrated that most of the DHT-dependent gene expression changes are also cyclin D1-dependent. Collectively, our findings suggest that the hormone-mediated recruitment of cyclin D1 to sites of DDR may facilitate the resistance of prostate cancer cells to DNA damage therapies, and highlight the need to explore other therapeutic approaches in prostate cancer to prevent or overcome drug resistance.
    • Cyclin D1, Id1 and EMT in breast cancer.

      Tobin, Nicholas P; Sims, A H; Lundgren, Katja L; Lehn, Sophie; Landberg, Göran; University of Manchester, Manchester, UK. (2011)
      Cyclin D1 is a well-characterised cell cycle regulator with established oncogenic capabilities. Despite these properties, studies report contrasting links to tumour aggressiveness. It has previously been shown that silencing cyclin D1 increases the migratory capacity of MDA-MB-231 breast cancer cells with concomitant increase in 'inhibitor of differentiation 1' (ID1) gene expression. Id1 is known to be associated with more invasive features of cancer and with the epithelial-mesenchymal transition (EMT). Here, we sought to determine if the increase in cell motility following cyclin D1 silencing was mediated by Id1 and enhanced EMT-features. To further substantiate these findings we aimed to delineate the link between CCND1, ID1 and EMT, as well as clinical properties in primary breast cancer.
    • Cyclin-dependent kinase inhibitors and basement membrane interact to regulate breast epithelial cell differentiation and acinar morphogenesis.

      Coppock, H A; Gilham, David E; Howell, Anthony; Clarke, Robert B; Centre for Molecular Medicine, University of Manchester, Manchester, UK. (2007-10)
      OBJECTIVE: The cyclin-dependent kinase inhibitors (CDKIs), p21(CIP1) and p27(KIP1) regulate growth and differentiation in diverse tissue types. We aimed to determine whether p21(CIP1) or p27(KIP1) could induce a terminally differentiated phenotype in breast cells, and to examine if CDKI expression is regulated by basement membrane interactions. MATERIALS AND METHODS: Effects of increased CDKI expression on the phenotype of MCF-10A breast epithelial cells were examined by retroviral transduction of p21(CIP1) or p27(KIP1) cDNA. RESULTS: Overexpression of p21(CIP1) or p27(KIP1) reduced MCF-10A growth rates in monolayer cultures, altered cellular morphology and stimulated accumulation of neutral lipid droplets, suggesting partial lactational differentiation. However, markers of luminal differentiation (oestrogen and progesterone receptors, alpha-lactalbumin, beta-casein and adipophilin) were absent when examined by reverse transcriptase-polymerase chain reaction and immunohistochemistry. Cell-basement membrane contacts are known to be essential for full mammary epithelial cell differentiation and therefore parental MCF-10A cells were cultured on a basement membrane preparation (Matrigel) in which they form acini. Immunocytochemistry showed that Ki67, the cell proliferation marker, was initially expressed at high levels and as growth decreased p27(KIP1) expression steadily increased. Surprisingly, p21(CIP1) was highest at the early stages of acinus growth and was detected in proliferating cells, as demonstrated by colocalization in dual Ki67/p21(CIP1) immunofluorescence. Overexpression of p21(CIP1) or p27(KIP1) impaired formation of acini, whereas their knockdown, using siRNA, increased acinus formation. CONCLUSION: We conclude that both p21(CIP1) and p27(KIP1) induce partial secretory differentiation of mammary cells in monolayer, but during acinus morphogenesis in 3D culture they have a highly regulated temporal expression pattern.
    • Cyclin-mediated export of human Orc1.

      Laman, Heike; Peters, Gordon; Jones, Nic; Molecular Oncology Laboratory, Gene Regulation Laboratory, Imperial Cancer Research Fund, 44 Lincoln's Inn Fields, London, WC2A 3PX, United Kingdom. (2001-12-10)
      Viral cyclin/cdk6 complexes interact with and phosphorylate human Orc1, a component of the origin recognition complex (ORC) that functions in DNA replication. Here we assess the effect that viral cyclin has on the intracellular location of human Orc1, which is present in both nuclear and cytoplasmic pools. Overexpression of K cyclin or cyclin A results in Crm1-dependent export of Orc1 to the cytoplasm, and this process is dependent on the phosphorylation status of several cdk target sites in Orc1. These findings support a model where S phase promoting cyclin activity drives the export of a component of replication complexes.
    • Cyclooxygenase-dependent tumor growth through evasion of immunity.

      Zelenay, Santiago; van der Veen, A; Böttcher, J; Snelgrove, K; Rogers, N; Acton, S; Chakravarty, P; Girotti, Maria Romina; Marais, Richard; Quezada, S; et al. (2015-09-10)
      The mechanisms by which melanoma and other cancer cells evade anti-tumor immunity remain incompletely understood. Here, we show that the growth of tumors formed by mutant Braf(V600E) mouse melanoma cells in an immunocompetent host requires their production of prostaglandin E2, which suppresses immunity and fuels tumor-promoting inflammation. Genetic ablation of cyclooxygenases (COX) or prostaglandin E synthases in Braf(V600E) mouse melanoma cells, as well as in Nras(G12D) melanoma or in breast or colorectal cancer cells, renders them susceptible to immune control and provokes a shift in the tumor inflammatory profile toward classic anti-cancer immune pathways. This mouse COX-dependent inflammatory signature is remarkably conserved in human cutaneous melanoma biopsies, arguing for COX activity as a driver of immune suppression across species. Pre-clinical data demonstrate that inhibition of COX synergizes with anti-PD-1 blockade in inducing eradication of tumors, implying that COX inhibitors could be useful adjuvants for immune-based therapies in cancer patients.
    • Cyclophosphamide as an adjuvant to X-rays in treatment of a radioresistant solid tumor of the rat, hepatoma H-4-II-E.

      Moore, James V; Rowley, Roy; Hopkins, Harold A; Ritenour, E Russell; Looney, William B; Paterson Laboratories, Christie Hospital and Holt Radium Institute, Manchester (1979-09)
    • Cyclophosphamide decreases O6-alkylguanine-DNA alkyltransferase activity in peripheral lymphocytes of patients undergoing bone marrow transplantation.

      Lee, Siow Ming; Crowther, Derek; Scarffe, J Howard; Dougal, Mark; Elder, Rhoderick H; Rafferty, Joseph A; Margison, Geoffrey P; CRC Department of Carcinogenesis, Paterson Institute for Cancer Research, Manchester, UK. (1992-08)
      O6-alkylguanine-DNA-alkyltransferase (ATase) levels were measured in extracts of peripheral blood lymphocytes taken at various times during chemotherapy from 19 patients with various haematological malignancies. Seven patients with advanced Hodgkin's disease received preparative treatment consisting of cyclophosphamide (1.5 g m-2, daily) administered on days 1 to 4 and BCNU (600 mg m-2) on day 5 prior to autologous bone marrow rescue (ABMR) delivered on day 7. Treatment in the remaining 12 patients consisted of cyclophosphamide (1.8 g m-2, daily) given on days 1 and 2 followed at day 4 with total body irradiation (TBI) administered in six fractions over the subsequent 3 days to a total dose of 1200 cGy prior to bone marrow transplantation. In the Hodgkin's group, significant decreases in ATase activity were seen during the cyclophosphamide treatment, and the median ATase nadir was 32% (range 0% to 57%) of pretreatment levels following 4 days of cyclophosphamide. In one patient, no ATase activity was detectable following the 4th cyclophosphamide treatment. ATase activities decreased further after BCNU administration to a median of 19% (range 0% to 32%) of pretreatment levels. Extensive cyclophosphamide-induced reduction of lymphocyte ATase levels was also seen in the other group of 12 patients treated with cyclophosphamide/TBI: postcyclophosphamide median ATase nadir was 35% (range 12% to 78%) of the pretreatment levels. No ATase depletion was seen when cyclophosphamide (up to 10 mM) was incubated for 2 h with pure recombinant human ATase in vitro whereas ATase activity was reduced by 90% on preincubation with 100 microns acrolein or with greater than 1 mM phosphoramide mustard. This suggests that a cyclophosphamide-induced decrease in ATase levels in human peripheral lymphocytes in vivo may be due to depletion mediated by the production of intracellular acrolein. Since ATase appears to be a principal mechanism in cellular resistance to the cytotoxic effects of BCNU and related alkylating agents, these observations suggest that a cyclophosphamide-induced reduction in ATase activity may be an additional factor in the effectiveness of the combined sequential therapy.
    • Cyclophosphamide inhibition of anti-CD40 monoclonal antibody-based therapy of B cell lymphoma is dependent on CD11b+ cells.

      Honeychurch, Jamie; Glennie, Martin J; Illidge, Timothy M; Cancer Research UK Oncology Unit, Tenovus Research Laboratory, Cancer Sciences Division, School of Medicine, Southampton General Hospital, Southampton, Hampshire. (2005-08-15)
      Monoclonal antibody (mAb)-based immunotherapy is now established as an important option for treating some cancers. The antitumor effects may be further enhanced by combining mAb with conventional chemotherapy. Certain novel immunomodulatory mAbs such as anti-CD40 have shown significant activity in preclinical models. We therefore assessed the efficacy of combining anti-CD40 mAb, known to elicit CTL responses against murine lymphoma models with the commonly used cytotoxic drug, cyclophosphamide. Using the syngeneic tumor model, BCL1, we have shown that timing of cyclophosphamide relative to mAb is critical to therapeutic outcome. Pretreatment with cyclophosphamide 7 to 10 days prior to mAb results in markedly reduced survival levels, similar to that achieved with cyclophosphamide alone. Conversely, when anti-CD40 is given before cyclophosphamide, the level of tumor protection was moderately increased. In vivo tracking experiments reveal that pretreatment with cyclophosphamide leads to diminished CTL expansion, as well as an increased number of CD11b+ cells that display an activated phenotype. These latter cells are able to inhibit T-cell proliferation, at least in part via production of nitric oxide, but do not induce T-cell apoptosis. Furthermore, adoptive transfer of the induced CD11b+ cells is sufficient to inhibit anti-CD40 therapy in tumor-bearing recipients. We have shown that the timing of cyclophosphamide relative to mAb administration is critical to the therapeutic outcome, and although the combination can improve survival, cyclophosphamide given prior to immunotherapy may generate a population of myeloid cells that can interfere with CTL responses and compromise the therapeutic outcome.
    • Cysteine cathepsin protease inhibition: an update on its diagnostic, prognostic and therapeutic potential in cancer

      Soond, SM; Kozhevnikova, MV; Townsend, Paul A; Zamyatnin, AA; Institute of Molecular Medicine, Sechenov First Moscow State Medical University, Trubetskaya str. 8-2, 119991 Moscow, Russia. (2019)
      In keeping with recent developments in basic research; the importance of the Cathepsins as targets in cancer therapy have taken on increasing importance and given rise to a number of key areas of interest in the clinical setting. In keeping with driving basic research in this area in a translational direction; recent findings have given rise to a number of exciting developments in the areas of cancer diagnosis; prognosis and therapeutic development. As a fast-moving area of research; the focus of this review brings together the latest findings and highlights the translational significance of these developments.
    • Cytogenetic changes during the early stages of liver carcinogenesis in Chinese hamster: an in vivo--in vitro comparison.

      Swindell, J A; Ockey, Charles H; Paterson Laboratories, Christie Hospital and Holt Radium Institute, Manchester UK (1983-09)
      Cytogenetic changes were investigated during the early stages of hepatic adenocarcinoma development in Chinese hamsters injected with a single dose of dimethylnitrosamine (DMN). An in vivo-in vitro comparison was made from 7 to 35 weeks after injection. A partial hepatectomy was used to stimulate mitosis for in vivo analysis, and the excised liver, grown to the primary culture stage, was used for chromosome analysis in vitro. Aneuploidy, tetraploidy, and chromosome aberrations increased significantly in the hepatic cells of DMN-treated animals in vivo, with no significant change over the 7- to 35-week period. No differences, however, could be detected between the primary cultures of control and DMN-treated animals because of an inherent tendency for all cultures to develop aneuploid stem lines at an early stage in culture. A preferential involvement of chromosome #6 in the single trisomic state was demonstrated in vitro and to a minor extent in vivo. The relevance of increased aneuploidy in early carcinogenesis and the differences between the in vivo and in vitro results are discussed.
    • Cytogenetic studies of workers exposed to styrene: a review.

      Scott, David; Department of Cancer Genetics, Paterson Institute for Cancer Research, Christie Hospital NHS Trust, Manchester, United Kingdom. (1993)
      In 17 of 50 cytogenetic studies (on chromosomal aberrations, micronucleus formation and sister chromatid exchange) in peripheral blood lymphocytes from a total of 667 workers in industries in which there is exposure to styrene, significant increases in the frequency of chromosomal damage have been reported when compared with unexposed controls. The positive or negative outcome of these studies is, however, unrelated to the extent of exposure to styrene. Furthermore, in the 17 investigations in which positive results were found, there is no convincing evidence of a positive dose-response relationship, in spite of the wide ranges of exposure and different methods of measurement. There are also serious discrepancies between findings on the chromosomal damaging effects of styrene in human lymphocytes in vitro and the types of damage reported in exposed workers. The findings are not consistent with the interpretation that styrene is responsible for the observed effects in workers. Several other chemicals identified in the environment of styrene workers have been reported to induce chromosomal damage in vitro and/or in vivo.
    • A cytogenetic study of male breast cancer.

      Mitchell, Erika L D; Cancer Genetics Department, Paterson Institute for Cancer Research, Christie Hospital, Manchester, England. (1990-07-01)
      In a direct preparation from a male breast carcinoma two populations of cells were present, one hypodiploid (range 25-34) and the other hypertriploid (range 56-84). Twenty-two marker chromosomes were recognized. One of these, dic(5:11)(p14:q23) was present in one or two copies in every cell and has not been reported in any other case of breast cancer. There was a consistent monosomy of chromosome 7 and, in the hypertriploid cells, a gain of one to three copies of chromosome 3. The breakpoint 11q23 is a rare, folate-sensitive fragile site but was not expressed in peripheral blood cell lymphocytes from the patient.
    • Cytokeratin expression in epithelial cells isolated from the crypt and villus regions of the rodent small intestine.

      Flint, Neil; Pemberton, P W; Lobley, R W; Evans, Gareth S; CRC Department of Epithelial Biology, Paterson Institute for Cancer Research, Christie Hospital (NHS) Trust, Manchester, UK. (1994-01)
      Many physiological and structural features of epithelium in the small intestine are regulated during their transit from the crypt base to the villus tip. This crypt-villus axis is an important model for the study of the regulation of cell proliferation and differentiation. We have investigated the expression of cytokeratins in purified epithelial cells from the proliferative (crypt) and differentiated (villus) regions of this tissue. Three polypeptides were identified (cytokeratins 8, 18 and 19) as well as a fourth, 46 kDa polypeptide with similar electrophoretic characteristics to the recently identified cytokeratin 20. The distribution of these molecules was found to vary along the crypt-villus axis, with cytokeratin 18 being restricted to the proliferative crypt and cytokeratins 8 and 19 demonstrating more uniform distributions. The 46 kDa component was found to be expressed predominantly within the villus epithelium. Although there is no substantial evidence of a direct role for cytokeratins in the process of epithelial differentiation, these data suggest that differential expression of cytokeratins is associated with changes in intestinal epithelial differentiation.
    • Cytokine stimulation and the choice of promoter are critical factors for the efficient transduction of mouse T cells with HIV-1 vectors.

      Gilham, David E; Lie-A-Ling, Michael; Taylor, Naomi; Hawkins, Robert E; Cell Therapy Group, Cancer Research UK Department of Medical Oncology, University of Manchester, Manchester Academic Health Science Centre, Manchester, UK. dgilham@picr.man.ac.uk (2010-02)
      BACKGROUND: HIV-1 fails to successfully infect mouse T cells as a result of several blocks in the viral replication cycle. We investigated whether this also impacted on the use of HIV-1 derived lentiviral vectors for stable gene transfer into mouse T cells. METHODS: Freshly isolated primary mouse T cells were immediately mixed with lentiviral vectors encoding an enhanced green fluorescent protein marker gene and transduction frequency was determined after 5 days of culture. RESULTS: Optimal transduction required both mouse T cell activation and cytokine support. Furthermore, transduction was also dependent upon the promoter chosen, with the rank order of potency being PGK > EF1 > SFFV > CMV. HIV-1 lentiviral vectors also efficiently transduced cytokine-stimulated T cells (in the absence of antibody driven T cell activation), albeit with a lower level of transgene expression compared to fully-activated T cells. CONCLUSIONS: The present study demonstrates that primary mouse T cells can be efficiently transduced with HIV-1 lentiviral vectors, opening up prospects for their use in mouse models of gene-modified adoptive cellular therapy.
    • Cytokine-mediated protein kinase C activation is a signal for lineage determination in bipotential granulocyte macrophage colony-forming cells.

      Whetton, Anthony D; Heyworth, Clare M; Nicholls, S E; Evans, C A; Lord, J M; Dexter, T Michael; Owen-Lynch, P J; Department of Biochemistry and Applied Molecular Biology, UMIST, Manchester, United Kingdom. (1994-05)
      Granulocyte macrophage colony-forming cells (GM-CFC) have the potential to develop into either macrophages and/or neutrophils. With a highly enriched population of these cells we have found that although GM-CFC are equally responsive to macrophage colony stimulating factor (M-CSF) and stem cell factor (SCF) in terms of DNA synthesis, M-CSF stimulated the development of colonies containing macrophages in soft gel assays, while SCF promoted neutrophilic colony formation. When SCF and M-CSF were combined, mainly macrophage development was stimulated both in soft agar colony-forming assays and liquid cultures. An analysis of some potential signaling mechanisms associated with cytokine-mediated developmental decisions in GM-CFC revealed that M-CSF, but not SCF, was able to chronically stimulate phosphatidylcholine breakdown and diacylglycerol production, indicating that protein kinase C (PKC) may be involved in the action of M-CSF. Furthermore, M-CSF, but not SCF, can increase the levels of PKC alpha (PKC alpha) expression and stimulate the translocation of PKC alpha to the nucleus. When the PKC inhibitor, calphostin C, was added to GM-CFC cultured in M-CSF then predominantly neutrophils were produced, conversely PKC activators added with SCF stimulated macrophage development. The data indicate a role for PKC in M-CSF-stimulated macrophage development from GM-CFC.
    • The cytoplasmic filaments of the nuclear pore complex are dispensable for selective nuclear protein import.

      Walther, Tobias C; Pickersgill, Helen; Cordes, Volker C; Goldberg, Martin W; Allen, Terence D; Mattaj, Iain W; Fornerod, Maarten; Gene Expression Program, EMBL, D-69117 Heidelberg, Germany. (2002-07-08)
      The nuclear pore complex (NPC) mediates bidirectional macromolecular traffic between the nucleus and cytoplasm in eukaryotic cells. Eight filaments project from the NPC into the cytoplasm and are proposed to function in nuclear import. We investigated the localization and function of two nucleoporins on the cytoplasmic face of the NPC, CAN/Nup214 and RanBP2/Nup358. Consistent with previous data, RanBP2 was localized at the cytoplasmic filaments. In contrast, CAN was localized near the cytoplasmic coaxial ring. Unexpectedly, extensive blocking of RanBP2 with gold-conjugated antibodies failed to inhibit nuclear import. Therefore, RanBP2-deficient NPCs were generated by in vitro nuclear assembly in RanBP2-depleted Xenopus egg extracts. NPCs were formed that lacked cytoplasmic filaments, but that retained CAN. These nuclei efficiently imported nuclear localization sequence (NLS) or M9 substrates. NPCs lacking CAN retained RanBP2 and cytoplasmic filaments, and showed a minor NLS import defect. NPCs deficient in both CAN and RanBP2 displayed no cytoplasmic filaments and had a strikingly immature cytoplasmic appearance. However, they showed only a slight reduction in NLS-mediated import, no change in M9-mediated import, and were normal in growth and DNA replication. We conclude that RanBP2 is the major nucleoporin component of the cytoplasmic filaments of the NPC, and that these filaments do not have an essential role in importin alpha/beta- or transportin-dependent import.