A study of correlation between NPM-translocation and apoptosis in cells induced by daunomycin

Nucleolar Stress: hallmarks, sensing mechanism and diseases

The nucleolus is a prominent subnuclear compartment, where ribosome biosynthesis takes place. Recently, the nucleolus has gained attention for its novel role in the regulation of cellular stress. Nucleolar stress is emerging as a new concept, which is characterized by diverse cellular insult-induced abnormalities in nucleolar structure and function, ultimately leading to activation of p53 or other stress signaling pathways and alterations in cell behavior. Despite a number of comprehensive reviews on this concept, straightforward and clear-cut way criteria for a nucleolar stress state, regarding the factors that elicit this state, the morphological and functional alterations as well as the rationale for p53 activation are still missing. Based on literature of the past two decades, we herein summarize the evolution of the concept and provide hallmarks of nucleolar stress. Along with updated information and thorough discussion of existing confusions in the field, we pay particular attention to the current understanding of the sensing mechanisms, i.e., how stress is integrated by p53. In addition, we propose our own emphasis regarding the role of nucleolar protein NPM1 in the hallmarks of nucleolar stress and sensing mechanisms. Finally, the links of nucleolar stress to human diseases are briefly and selectively introduced.

Anti-metastatic and differential effects on protein expression of epigallocatechin-3-gallate in HCCLM6 hepatocellular carcinoma cells

Hepatocellular carcinoma (HCC) is the fifth most common cancer worldwide and the third highest cause of cancer-related mortality in humans. Epigallocatechin-3-gallate (EGCG) has been shown to inhibit the metastatic activity of certain cancer cells. The aim of this study was to determine the effects and molecular mechanism(s) of action of EGCG in human HCC cells. A migration and invasion assay for the metastatic behavior of HCCLM6 cells was performed. The anti-metastatic effects of EGCG were investigated by RT-PCR and gelatin zymography. A total cellular protein profile was obtained using 2-dimensional gel electrophoresis (2-DE), followed by matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF-MS) analyses of proteins with significant differences in expression following treatment with EGCG. The results revealed that EGCG induced apoptosis and inhibited the metastasis of HCCLM6 cells. The anti-metastatic effects of EGCG were associated with the inhibition of matrix metalloproteinase (MMP)-2 and MMP-9 activity. The expression levels of far upstream element (FUSE) binding protein 1 (FUBP1), heat shock protein beta 1 (HSPB1), heat shock 60 kDa protein 1 (chaperonin) (CH60) and nucleophosmin (NPM) proteins, which are associated with metastasis, were significantly altered in the EGCG-treated HCCLM6 cells. The data from the present study suggest that EGCG has potential as a therapeutic agent for the treatment of HCC.

Cucurbitacin B inhibits human breast cancer cell proliferation through disruption of microtubule polymerization and nucleophosmin/B23 translocation

Background

Cucurbitacin B, an oxygenated tetracyclic triterpenoid compound extracted from the Thai medicinal plant Trichosanthes cucumerina L., has been reported to have several biological activities including anti-inflammatory, antimicrobial and anticancer. Cucurbitacin B is great of interest because of its biological activity. This agent inhibits growth of various types of human cancer cells lines.

Methods

In this study, we explored the novel molecular response of cucurbitacin B in human breast cancer cells, MCF-7 and MDA-MB-231. The growth inhibitory effect of cucurbitacin B on breast cancer cells was assessed by MTT assay. The effects of cucurbitacin B on microtubules morphological structure and tubulin polymerization were analyzed using immunofluorescence technique and tubulin polymerization assay kit, respectively. Proteomic analysis was used to identify the target-specific proteins that involved in cucurbitacin B treatment. Some of the differentially expressed genes and protein products were validated by real-time RT-PCR and western blot analysis. Cell cycle distributions and apoptosis were investigated using flow cytometry.

Results

Cucurbitacin B exhibited strong antiproliferative effects against breast cancer cells in a dose-dependent manner. We show that cucurbitacin B prominently alters the cytoskeletal network of breast cancer cells, inducing rapid morphologic changes and improper polymerization of the microtubule network. Moreover, the results of 2D-PAGE, real-time RT-PCR, and western blot analysis revealed that the expression of nucleophosmin/B23 and c-Myc decreased markedly after cucurbitacin B treatment. Immunofluorescence microscopy showed that cucurbitacin B induced translocation of nucleophosmin/B23 from the nucleolus to nucleoplasm. Treatment with cucurbitacin B resulted in cell cycle arrest at G₂/M phase and the enhancement of apoptosis.

Conclusions

Our findings suggest that cucurbitacin B may inhibit the proliferation of human breast cancer cells through disruption of the microtubule network and down-regulation of c-Myc and nucleophosmin/B23 as well as the perturbation in nucleophosmin/B23 trafficking from the nucleolus to nucleoplasm, resulting in G₂/M arrest.

Acute myeloid leukemia with mutated nucleophosmin (NPM1): any hope for a targeted therapy?

Acute myeloid leukemia (AML) carrying nucleophosmin (NPM1) mutations displays distinct molecular and clinical-pathological features that led to its inclusion as provisional entity in 2008 WHO classification of myeloid neoplasms. Since NPM1 mutations behave as a founder genetic lesion in AML, they could be an attractive target for therapeutic intervention. Here, we discuss the potential for developing targeted therapies for NPM1-mutated AML with focus on: (i) interfering with the abnormal traffic of the NPM1 leukemic mutant, i.e., its cytoplasmic dislocation; (ii) disrupting the nucleolar structure/function by interfering with residual wild-type nucleophosmin and other nucleolar components acting as hub proteins; and (iii) evaluating the activity of epigenetic drugs (e.g., 5-azacytidine) or agents acting on differentiation and apoptosis. As quantitative assessment of NPM1 mutated transcript copies now provides the means to measure minimal residual disease, we also discuss the potential for intervening in NPM1-mutated AML before overt hematological relapse occurs (so-called pre-emptive therapy).

Protein B23/nucleophosmin/numatrin nuclear dynamics in relation to protein kinase CK2 and apoptotic activity in prostate cells

Protein B23/nucleophosmin/numatrin (B23) is a key nucleolar/nuclear matrix-associated protein required for cell growth-related functions, such as rRNA synthesis. Protein kinase CK2 (CK2) (formerly casein kinase 2, a protein Ser/Thr kinase signal that is involved in cell growth and cell death) mediates phosphorylation of B23, thereby influencing its functional activity. Here we have delineated the dynamics of B23 and its link to CK2 status in response to altered growth stimuli and induction of apoptosis in cultured prostate cells and in rat prostate cells in vivo. Our studies employing PC-3 and ALVA-41 prostate cancer cells demonstrated colocalization of CK2 and B23 in the nucleus. Further, CK2 and B23 underwent coordinate modulation in the nucleus related to their nucleocytoplasmic shuttling in response to induction of apoptotic activity in cells caused by downregulation of CK2 or by treatment with other apoptosis-inducing agents. These alterations in nuclear association of B23 occurred in the absence of a significant change in the level of cytoplasmic B23. Similar studies in the in vivo model of rat prostate epithelial cells subjected to androgen deprivation (that resulted in loss of nuclear CK2 and induction of apoptosis) demonstrated dynamic modulation of nuclear matrix-associated B23 without a significant change in its cytoplasmic level. These changes were reversed by androgen-mediated growth response in the prostate. Our results suggest that CK2-mediated phosphorylation of B23 is essential for its retention in the nucleus and that coordinated nuclear localization of B23 and CK2 is dynamically regulated in response to altered growth status in the cell.

The genotype nucleophosmin mutated and FLT3-ITD negative is characterized by high bax/bcl-2 ratio and favourable outcome in acute myeloid leukaemia

Nucleophosmin gene (NPM1) mutations characterize acute myeloid leukaemia (AML) with normal karyotype and frequently co-exist with FLT3 internal tandem duplications (ITD). We evaluated bcl-2, bax, NPM1 and FLT3-ITD in 222 AML patients. Bax/bcl-2 ratio >0.35 and NPM1 without FLT3-ITD were significantly associated (P = 0.0001). NPM1-mutated (mt)/FLT3-ITD negative patients showed a higher complete remission (CR) rate (90%, P = 0.0002) and a longer overall survival (OS, P = 0.00007). NPM1-mt/FLT3-ITD negative plus bax/bcl-2 > 0.35 subset showed a very high CR rate (96%), very long OS (P = 0.00005) and disease-free survival (P = 0.004). The favourable prognosis of NPM1-mt/FLT3-ITD negative patients might be explained by a higher bax/bcl-2 ratio.

Inflammation and endothelial dysfunction during aging: role of NF-kappaB

One of the major conceptual advances in our understanding of the pathogenesis of age-associated cardiovascular diseases has been the insight that age-related oxidative stress may promote vascular inflammation even in the absence of traditional risk factors associated with atherogenesis (e.g., hypertension or metabolic diseases). In the present review we summarize recent experimental data suggesting that mitochondrial production of reactive oxygen species, innate immunity, the local TNF-alpha-converting enzyme (TACE)-TNF-alpha, and the renin-angiotensin system may underlie NF-kappaB induction and endothelial activation in aged arteries. The theme that emerges from this review is that multiple proinflammatory pathways converge on NF-kappaB in the aged arterial wall, and that the transcriptional activity of NF-kappaB is regulated by multiple nuclear factors during aging, including nuclear enzymes poly(ADP-ribose) polymerase (PARP-1) and SIRT-1. We also discuss the possibility that nucleophosmin (NPM or nuclear phosphoprotein B23), a known modulator of the cellular oxidative stress response, may also regulate NF-kappaB activity in endothelial cells.

Anticancer effects of ginsenoside Rg1, cinnamic acid, and tanshinone IIA in osteosarcoma MG-63 cells: nuclear matrix downregulation and cytoplasmic trafficking of nucleophosmin

Ginsenoside Rg1, cinnamic acid, and tanshinone IIA are effective anticancer and antioxidant constituents of traditional Chinese herbal medicines of Ginseng (Panax ginseng), Xuanshen (Radix scrophulariae), and Danshen (Salvia mitiorrhiza), respectively. There was insufficient study on molecular mechanisms of anticancer effects of those constituents and their targets were unknown. We chose nucleophosmin as a candidate molecular target because it is frequently mutated and upregulated in various cancer cells. Nucleophosmin is a major nucleolus phosphoprotein that involves in rRNA synthesis, maintaining genomic stability, and normal cell division and its haploinsufficiency makes cell more susceptible to oncogenic assault. Ginsenoside Rg1, cinnamic acid, and tanshinone IIA treatment of osteosarcoma MG-63 cells decreased nucleophosmin expression in nuclear matrix and induced nucleophosmin translocation from nucleolus to nucleoplasm and cytoplasm, a process of dedifferentiating transformed cells. Using immunogold electro-microscopy, we found at the first time that nucleophosmin was localized on nuclear matrix intermediate filaments that had undergone restorational changes after the treatments. Nucleophosmin also functions as a molecular chaperone that might interact with multiple oncogenes and tumor suppressor genes. We found that oncogenes c-myc, c-fos and tumor suppressor genes, P53, Rb were regulated by ginsenoside Rg1, cinnamic acid, and tanshinone IIA as well. In present study, we identified nucleophosmin as a molecular target of the effective anticancer constituents of t Ginseng, Xuanseng, and Danseng that down-regulated nucleophosmin in nuclear matrix, changed its trafficking from nucleolus to cytoplasm, and regulated several oncogenes and tumor suppressor genes. Therefore, we postulate that Ginsenoside Rg1, cinnamic acid, and tanshinone IIA could serve as protective agents in cancer prevention and treatment.

Immunocell-array for molecular dissection of multiple signaling pathways in mammalian cells

The knowledge of signaling pathways that are triggered by physiological and pathological conditions or drug treatment is essential for the comprehension of the biological events that regulate cellular responses. Recently novel platforms based on "reverse-phase protein arrays" have proven to be useful in the study of different pathways, but they still lack the possibility to detect events in the complexity of a cellular context. We developed an "immunocell-array" of cells on chip where, upon cell plating, growing, drug treatment, and fixation, by spotting specific antibodies we can detect the localization and state of hundreds of proteins involved in specific signaling pathways. By applying this technology to mammalian cells we analyzed signaling proteins involved in the response to DNA damage and identified a chromatin remodeling pathway following bleomycin treatment. We propose our technology as a new tool for the array-based multiplexed analysis of signaling pathways in drug response screening, for the proteomics of profiling patient cells, and ultimately for the high throughput screening of antibodies for immunofluorescence applications.

Acute myeloid leukemia carrying cytoplasmic/mutated nucleophosmin (NPMc+ AML): biologic and clinical features

The nucleophosmin (NPM1) gene encodes for a multifunctional nucleocytoplasmic shuttling protein that is localized mainly in the nucleolus. NPM1 mutations occur in 50% to 60% of adult acute myeloid leukemia with normal karyotype (AML-NK) and generate NPM mutants that localize aberrantly in the leukemic-cell cytoplasm, hence the term NPM-cytoplasmic positive (NPMc+ AML). Cytoplasmic NPM accumulation is caused by the concerted action of 2 alterations at mutant C-terminus, that is, changes of tryptophan(s) 288 and 290 (or only 290) and creation of an additional nuclear export signal (NES) motif. NPMc+ AML shows increased frequency in adults and females, wide morphologic spectrum, multilineage involvement, high frequency of FLT3-ITD, CD34 negativity, and a distinct gene-expression profile. Analysis of mutated NPM has important clinical and pathologic applications. Immunohistochemical detection of cytoplasmic NPM predicts NPM1 mutations and helps rationalize cytogenetic/molecular studies in AML. NPM1 mutations in absence of FLT3-ITD identify a prognostically favorable subgroup in the heterogeneous AML-NK category. Due to their frequency and stability, NPM1 mutations may become a new tool for monitoring minimal residual disease in AML-NK. Future studies should focus on clarifying how NPM mutants promote leukemia, integrating NPMc+ AML in the upcoming World Health Organization leukemia classification, and eventually developing specific antileukemic drugs.

State of nucleolar proteins B23/nucleophosmin and UBF in HeLa cells during apoptosis induced by tumor necrosis factor

The structural state of two major nucleolar proteins, UBF and B23/nucleophosmin (both monomeric and oligomeric forms), was for the first time established in HeLa cells treated with apoptosis inducers: tumor necrosis factor (TNF-alpha), emetine, and their combination. The treatment of the cells with either TNF-alpha or emetine did not induce apoptosis and affect the state of UBF and nucleophosmin (both monomers and oligomers). Apoptosis was rather pronounced only if HeLa cells were treated with a mixture of TNF-alpha and emetine. States of the UBF and B23 proteins were analyzed in samples containing 25, 45, and 100% of cells with apoptotic nuclei. It was shown by immunoblotting that TNF-alpha-induced apoptosis of HeLa cells was associated with proteolysis of UBF and production of a 76-kD fragment, the content of which increased in correlation with the fraction of apoptotically changed cells. The N- and C-terminal amino acid sequences of UBF and its 76-kD fragment were characterized, and the site of the apoptosis-induced specific proteolysis was identified. As differentiated from UBF, protein B23 did not undergo proteolytic degradation during the TNF-alpha-induced apoptosis of HeLa cells and its content was unchanged even in the cell fraction with fragmentation of virtually all nuclei. However, the ratio between the monomeric and oligomeric states of B23 protein was changed in apoptotic cells, and apoptosis-specific forms of nucleophosmin were detected.

Nucleophosmin gene mutations are predictors of favorable prognosis in acute myelogenous leukemia with a normal karyotype

Nucleophosmin (NPM1) exon-12 gene mutations are the hallmark of a large acute myelogenous leukemia (AML) subgroup with normal karyotype, but their prognostic value in this AML subset has not yet been determined. We screened 401 AML patients with normal karyotype treated within the German AML Cooperative Group Protocol 99 (AMLCG99) study for NPM1 mutations. Results were related with partial tandem duplications within the MLL gene (MLL-PTD), Fms-like tyrosine kinase 3–length mutations (FLT3-LM), the tyrosine kinase domain of FLT3 (FLT3-TKD), NRAS, KIT, and CEBPA mutations and with clinical characteristics and outcome. NPM1 mutations were detected in 212 (52.9%) of 401 patients. Fourteen mutations, including 8 new variants, were identified. NPM1-mutated cases associated frequently with FLT3 mutations but rarely with other mutations. The NPM1-mutated group had a higher complete remission (CR) rate (70.5% vs 54.7%, P = .003), a trend to a longer overall survival (OS; median 1012 vs 549 days, P = .076), and significantly longer event-free survival (EFS; median 428 vs 336 days; P = .012). The favorable impact of NPM1 mutations on OS and EFS clearly emerged in the large group (264 [66.8%] of 395 cases) of normal-karyotype AML without FLT3-LM. This positive effect was lost in the presence of a concomitant FLT3-LM, since survival of the NPM1+/FLT3-LM+ double positive was similar to NPM1–/FLT3-LM+ cases. In conclusion, this study demonstrates that NPM1+/FLT3-LM– mutations are an independent predictor for a favorable outcome in AML with normal karyotype.

Release of nucleophosmin from the nucleus: Involvement in aloe-emodin-induced human lung non small carcinoma cell apoptosis

Aloe-emodin (1,8-dihydroxy-3-(hydroxymethyl)-anthraquinone) is one of the active constituents from the root and rhizome of Rheum palmatum. Our previous study has demonstrated that aloe-emodin induced a significant change in the expression of lung cancer cell apoptosis-related proteins compared to those of control cells. However, the molecular mechanisms underlying the biological effects of aloe-emodin still remain unknown. Based on these reasons, we were interested in the change of aloe-emodin-induced total protein expression by the proteomics technique during aloe-emodin-induced lung cancer cell apoptosis. Our study applied 2D electrophoresis to analyze the proteins involved in aloe-emodin-induced apoptosis in H460 cells. We found that the release of nucleophosmin from the nucleus to the cytosol and the degradation of nucleophosmin were associated with aloe-emodin-induced H460 cell apoptosis. Our study also demonstrated that the gene expression of nucleophosmin remained unchanged after treatment with aloe-emodin. The aloe-emodin-caused increase in the amount of proform and fragment of nucleophosmin in cytoplasm may be one of the important events for aloe-emodin-induced H460 cell apoptosis.

Molecular pathogenesis of acute promyelocytic leukaemia and APL variants

It has been 12 years since the simultaneous discovery of the unique sensitivity of acute promyelocytic leukaemia (APL) to differentiation therapy with all-trans retinoic acid (ATRA) and the discovery that the retinoic acid receptor alpha (RARalpha) gene was rearranged in APL. Nearly 98% of cases of APL are associated with t(15;17) chromosomal translocation and fusion of the PML gene to that encoding RARalpha to yield an abnormal receptor with the capability of de-regulating gene expression in the haematopoietic cell, causing differentiation block and eventually the development of leukaemia. Since this original discovery, four other translocations were described in APL. In each of these the RARalpha gene is fused to different partner genes, all yielding aberrant nuclear receptors. These fusion proteins share in common the ability to repress rather than activate retinoic acid targets, one so strongly that the result is an ATRA-resistant form of the disease. In addition each of the partner proteins is important for normal cell growth and development. In this chapter we explore the biology of the RARalpha, the fusion proteins created in APL and the normal forms of the partner proteins. Through continued study of this disease it is hoped that novel treatments, potentially more applicable to other forms of leukaemia, may arise.

Regulation of PRAK subcellular location by p38 MAP kinases

The p38 mitogen-activated protein kinase (MAPK) pathway plays an important role in cellular responses to inflammatory stimuli and environmental stress. p38 regulated/activated protein kinase (PRAK, also known as mitogen-activated protein kinase activated protein kinase 5 [MAPKAPK5]) functions downstream of p38alpha and p38beta in mediating the signaling of the p38 pathway. Immunostaining revealed that endogenous PRAK was predominantly localized in the cytoplasm. Interestingly, ectopically expressed PRAK was localized in the nucleus and can be redistributed by coexpression of p38alpha or p38beta to the locations of p38alpha and p38beta. Mutations in the docking groove on p38alpha/p38beta, or the p38-docking site in PRAK, disrupted the PRAK-p38 interaction and impaired the ability of p38alpha and p38beta to redistribute ectopically expressed PRAK, indicating that the location of PRAK could be controlled by its docking interaction with p38alpha and p38beta. Although the majority of PRAK molecules were detected in the cytoplasm, PRAK is consistently shuttling between the cytoplasm and the nucleus. A sequence analysis of PRAK shows that PRAK contains both a putative nuclear export sequence (NES) and a nuclear localization sequence (NLS). The shuttling of PRAK requires NES and NLS motifs in PRAK and can be regulated through cellular activation induced by stress stimuli. The nuclear content of PRAK was reduced after stimulation, which resulted from a decrease in the nuclear import of PRAK and an increase in the nuclear export of PRAK. The nuclear import of PRAK is independent from p38 activation, but the nuclear export requires p38-mediated phosphorylation of PRAK. Thus, the subcellular distribution of PRAK is determined by multiple factors including its own NES and NLS, docking interactions between PRAK and docking proteins, phosphorylation of PRAK, and cellular activation status. The p38 MAPKs not only regulate PRAK activity and PRAK activation-related translocation, but also dock PRAK to selected subcellular locations in resting cells.

Translocations of the RARalpha gene in acute promyelocytic leukemia

Acute promyelocytic leukemia (APL) has been recognized as a distinct clinical entity for over 40 years. Although relatively rare among hematopoietic malignancies (approximately 10% of AML cases), this disease has attracted a particularly good share of attention by becoming the first human cancer in which all-trans-retinoic acid (ATRA), a physiologically active derivative of vitamin A, was able to induce complete remission (CR). ATRA induced remission is not associated with rapid cell death, as in the case of conventional chemotherapy, but with a restoration of the 'normal' granulocytic differentiation pathway. With this remarkable medical success story APL has overnight become a paradigm for the differentiation therapy of cancer. A few years later, excitement with APL was further enhanced by the discovery that a cytogenetic marker for this disease, the t(15:17) reciprocal chromosomal translocation, involves a fusion between the retinoic acid receptor alpha (RARalpha) gene and a previously unknown locus named promyelocytic leukemia (PML). Consequence of this gene rearrangement is expression of the PML-RARalpha chimeric oncoprotein, which is responsible for the cellular transformation as well as ATRA response that is observed in APL. Since this initial discovery, a number of different translocation partner genes of RARalpha have been reported in rarer cases of APL, strongly suggesting that disruption of RARalpha underlies its pathogenesis. This article reviews various rearrangements of the RARalpha gene that have so far been described in literature, functions of the proteins encoded by the different RARalpha partner loci, and implications that these may have for the molecular pathogenesis of APL.

Nuclear apoptotic changes: an overview

Apoptosis is a form of active cell death essential for morphogenesis, development, differentiation, and homeostasis of multicellular organisms. The activation of genetically controlled specific pathways that are highly conserved during evolution results in the characteristic morphological features of apoptosis that are mainly evident in the nucleus. These include chromatin condensation, nuclear shrinkage, and the formation of apoptotic bodies. The morphological changes are the result of molecular alterations, such as DNA and RNA cleavage, post-translational modifications of nuclear proteins, and proteolysis of several polypeptides residing in the nucleus. During the last five years our understanding of the process of apoptosis has dramatically increased. However, the mechanisms that lead to apoptotic changes in the nucleus have been only partially clarified. Here, we shall review the most recent findings that may explain why the nucleus displays these striking modifications. Moreover, we shall take into consideration the emerging evidence about apoptotic events as a trigger for the generation of autoantibodies to nuclear components.

Immunocytochemical localization of nucleophosmin and RH-II/Gu protein in nucleoli of HeLa cells after treatment with actinomycin D

HeLa cells were studied with the use of light microscopical immunocytochemistry to obtain more information on the nucleolar localization of nucleophosmin (B23 protein) and RH-II/Gu protein. In control cells these proteins are colocalized. After structural rearrangement of nucleoli induced by actinomycin D, nucleophosmin was present in the nucleolar periphery and nucleolar peripheral caps. In contrast, RH-II/Gu protein was observed mainly in central regions of nucleoli as a compact body. However, in some nucleoli the proteins colocalized in a small portion of the peripheral nucleolar cap. The proteins were also colocalized in micronucleoli but occasionally RH-II/Gu protein was absent or both proteins were not present.

The N-terminal half of NPM dissociates from nucleoli of HeLa cells after anticancer drug treatments

NPM (nucleophosmin/B23) is a nucleolar phosphoprotein abundant in tumor cells. It dissociates from nucleoli of cells after treatments with various anticancer drugs. To determine the domain of NPM responsible for nucleolar binding, the N- and C-terminal halves of NPM were fused to GFP (green fluorescent protein) and introduced into HeLa cells. The N-terminal half (aa 1-150) of NPM (GFP-NPM(N)) was found localized in the nucleoli. A stable transformant of GFP-NPM(N) in HeLa cells was prepared and tested for association to nucleoli after anticancer drug treatments. GFP-NPM(N) dissociates from nucleoli after treatments with daunomycin, actinomycin D, camptothecin, and toyocamycin. The dissociation is time- and dose-dependent, and correlates with the cytotoxicity induced by the drugs. These results indicate that a stable transformant of GFP-NPM(N) in HeLa cells may be useful for the screening of anticancer drugs.