Knocking-down the expression of nucleostemin significantly decreases rate of proliferation of rat bone marrow stromal stem cells in an apparently p53-independent manner

GNL3 is an evolutionarily conserved stem cell gene influencing cell proliferation, animal growth and regeneration in the hydrozoan Hydractinia

Nucleostemin (NS) is a vertebrate gene preferentially expressed in stem and cancer cells, which acts to regulate cell cycle progression, genome stability and ribosome biogenesis. NS and its paralogous gene, GNL3-like (GNL3L), arose in the vertebrate clade after a duplication event from their orthologous gene, G protein Nucleolar 3 (GNL3). Research on invertebrate GNL3, however, has been limited. To gain a greater understanding of the evolution and functions of the GNL3 gene, we have performed studies in the hydrozoan cnidarian Hydractinia symbiolongicarpus, a colonial hydroid that continuously generates pluripotent stem cells throughout its life cycle and presents impressive regenerative abilities. We show that Hydractinia GNL3 is expressed in stem and germline cells. The knockdown of GNL3 reduces the number of mitotic and S-phase cells in Hydractinia larvae of different ages. Genome editing of Hydractinia GNL3 via CRISPR/Cas9 resulted in colonies with reduced growth rates, polyps with impaired regeneration capabilities, gonadal morphological defects, and low sperm motility. Collectively, our study shows that GNL3 is an evolutionarily conserved stem cell and germline gene involved in cell proliferation, animal growth, regeneration and sexual reproduction in Hydractinia, and sheds new light into the evolution of GNL3 and of stem cell systems.

Danggui Buxue Tang promotes the adhesion and migration of bone marrow stromal cells via the focal adhesion pathway in vitro

ETHNOPHARMACOLOGY RELEVANCE

Danggui Buxue Tang has been used in China to treat clinical anemia for more than 800 years. However, there is no scientific report on its effect on bone marrow stromal cells.

AIM OF THE STUDY

Here, we aimed to explore the effect of Danggui Buxue Tang on bone marrow stromal cell adhesion and migration.

MATERIALS AND METHODS

Bone marrow stromal cells were used as a model to evaluate the effect of Danggui Buxue Tang on the adhesion and migration of bone marrow stromal cells. RNA-sequencing, quantitative polymerase chain reaction, and western blotting were used to detect and confirm the expression of genes related to the focal adhesion pathway before and after drug delivery.

RESULTS

Danggui Buxue Tang significantly increased the number of bone marrow stromal cells. After 12 days of 16 mg/mL Danggui Buxue Tang treatment, bone marrow stromal cells were significantly increased (by 0.527 ± 0.008 fold; p < 0.001) as compared to the control group (0.180 ± 0.019). The effect was not due to enhanced cell proliferation, as there was no difference in the cell cycle (p > 0.05). The adhesion area of a single cell was doubled by Danggui Buxue Tang treatment (p < 0.001), and the time required for cell adhesion to a Petri dish was shortened. Thus, Danggui Buxue Tang increases the number of bone marrow stromal cells by promoting adhesion. Danggui Buxue Tang also significantly promoted bone marrow stromal cell migration (p <  0.001). Transcript analysis revealed that the focal adhesion and PI3K-Akt signaling pathways were activated. Expression analysis confirmed that the gene and protein expression of focal adhesion-related factors were upregulated.

CONCLUSION

Danggui Buxue Tangaffects bone marrow stromal cell adhesion and migration by enhancing the focal adhesion pathway in vitro, and bone marrow stromal cells are a target of DBT-regulated hematopoiesis, and the active ingredients of DBT involved in the effects require further investigation.

Differential expression of nucleostemin in the cytoplasm and nuclei of normal and cancerous cell lines

Studies conducted in the past decade have reported nucleostemin (NS) as a nucleolar protein that has a role in self-renewal and cell cycle regulation in cancer/stem cells, but is absent in differentiated cells. The localization and expression patterns of NS have always been disputed, as reports indicate its varied levels among tissues and cells. This study evaluates the expression and localization pattern of NS in normal cells, cancer cell lines, and stem cells. Our findings revealed that the expression of NS was high in cancers originating from the skin and liver compared to the normal cell lines. NS knockdown effects the proliferation of normal cell lines, similar to cancerous cell lines. The localization pattern of NS was analyzed by immunofluorescence, which showed that NS was localized in the nuclei of normal cell lines but is present both in the nucleus and the cytoplasm of cancerous/stem cell lines. Interestingly, we observed that siNS cancerous cell lines had lower NS in the cytoplasm, which did not salvage the reduction in proliferation caused by siNS. We postulate that the loss of NS in the nucleus inhibits the proliferative ability of both normal and cancerous cells at similar rates, although the role of NS in the cytoplasm apart from proliferation needs to be further explored.

Exogenous Expression of Nt-3 and TrkC Genes in Bone Marrow Stromal Cells Elevated the Survival Rate of the Cells in the Course of Neural Differentiation

Bone marrow stromal cells (BMSCs) are attractive cellular sources for cell therapy of many diseases, specifically neurodegenerative ones. The potential capability of BMSCs could be further augmented by enhancing their neuroprotective property, differentiation potential, and survival rate subsequent to transplantation. Therefore, a concurrent upregulation of neurotrophin-3 (NT-3) and its high affinity receptor, tyrosin kinase C (TrkC), was utilized in our study. BMSCs were cotransfected with pDsRed1-N1-NT-3 and pCMX-TrkC plasmids before induction of neural differentiation. pEGFP-N1-transfected BMSCs were also employed as a control. Real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR) was employed for gene expression analysis. Cell viability was evaluated by MTT assay, while apoptosis rate was assessed by flow cytometry after PI and Annexin V staining. NT-3 and TrkC mRNA levels were greatly elevated following cotransfection of cells with pDsRed1-N1-NT-3 and pCMX-TrkC vectors. The expression of neural markers (i.e., NFM, and NeuroD1) was augmented in cotransfected BMSCs, compared to the control ones, after neural induction. At each time point, the viability and apoptosis rates of the cells over-expressing NT-3 and TrkC showed increased and reduced patterns, respectively. Our data demonstrated that NT-3/TrkC-co-transfected BMSCs, compared to those of intact cells, could be more beneficial graft candidates for the upcoming treatment strategies of neurogenic disorders due to their increased viability and expression of neural markers. This may be due to their increased level of neural differentiation potential and/or their enhanced rate of survival and/or their useful capacity to secrete NT-3.

Gene expression profiling of NB4 cells following knockdown of nucleostemin using DNA microarrays

Nucleostemin (NS) is mainly expressed in stem and tumor cells, and is necessary for the maintenance of their self-renewal and proliferation. Originally, NS was thought to exert its effects through inhibiting p53, while recent studies have revealed that NS is also able to function independently of p53. The present study performed a gene expression profiling analysis of p53‑mutant NB4 leukeima cells following knockdown of NS in order to elucidate the p53‑independent NS pathway. NS expression was silenced using lentivirus‑mediated RNA interference technology, and gene expression profiling of NB4 cells was performed by DNA microarray analysis. A total of 1,953 genes were identified to be differentially expressed (fold change ≥2 or ≤0.5) following knockdown of NS expression. Furthermore, reverse‑transcription quantitative polymerase chain reaction analysis was used to detect the expression of certain candidate genes, and the results were in agreement with the micaroarray data. Pathway analysis indicated that aberrant genes were enhanced in endoplasmic, c‑Jun N‑terminal kinase and mineral absorption pathways. The present study shed light on the mechanisms of the p54‑independent NS pathway in NB4 cells and provided a foundation for the discovery of promising targets for the treatment of p53-mutant leukemia.

Balancing self-renewal against genome preservation in stem cells: How do they manage to have the cake and eat it too?

Stem cells are endowed with the awesome power of self-renewal and multi-lineage differentiation that allows them to be major contributors to tissue homeostasis. Owing to their longevity and self-renewal capacity, they are also faced with a higher risk of genomic damage compared to differentiated cells. Damage on the genome, if not prevented or repaired properly, will threaten the survival of stem cells and culminate in organ failure, premature aging, or cancer formation. It is therefore of paramount importance that stem cells remain genomically stable throughout life. Given their unique biological and functional requirement, stem cells are thought to manage genotoxic stress somewhat differently from non-stem cells. The focus of this article is to review the current knowledge on how stem cells escape the barrage of oxidative and replicative DNA damage to stay in self-renewal. A clear statement on this subject should help us better understand tissue regeneration, aging, and cancer.

p53 Configures the G2/M Arrest Response of Nucleostemin-Deficient Cells

Nucleostemin (NS) protects the genome from replication-induced DNA damage and has an indispensable role in maintaining the continuous proliferation of both p53-wild-type and mutant cells. Yet, some outcomes of NS-deficient cells appear to be shaped by their p53 status, which stimulates conflicting claims on the role of p53 in executing the NS function. This disparity was conveniently attributed to the usual suspect of cell-type variations. To provide a definitive resolution, we investigated the interplay between NS and p53 in two pairs of isogenic cells, that is, genetically modified mouse embryonic fibroblast (MEF) cells and HCT116 human colon cancer cells. In MEF cells, p53 deletion further compromises rather than rescues the proliferative potential of NS-depleted cells without changing their G2/M arrest fate before prophase entry. The detrimental effect of p53 loss in NS-depleted MEF cells correlates with a dramatic increase of polyploid giant cells (PGCs) (up to 24%), which indicates aberrant mitosis. To determine how p53 shapes the response of cells to NS depletion at the molecular level, we showed that p53 turns on the expression of reprimo and MDM2 in NS-deficient MEF cells. In absence of p53, NS-deficient MEF cells exhibit increased levels of phosphorylated cdc2 (Y15) protein and cyclin B1. In cancer (HCT116) cells, NS loss leads to G2/M arrest under both p53wt and p53ko conditions and increases phosphorylated cdc2 more in p53ko than in p53wt cells, as it does in MEF cells. Unlike its effect in MEF cells, NS depletion decreases tumor growth and increases the expression of reprimo and cyclin B1 in a p53-independent manner in HCT116 cells. Our data indicate that the p53 status of NS-deficient cells orchestrates how they respond to G2/M arrest in a normal versus cancer cell distinct fashion.

Turning a new page on nucleostemin and self-renewal

A quintessential trait of stem cells is embedded in their ability to self-renew without incurring DNA damage as a result of genome replication. One key self-renewal factor is the nucleolar GTP-binding protein nucleostemin (also known as guanine-nucleotide-binding protein-like 3, GNL3, in invertebrate species). Several studies have recently pointed to an unexpected role of nucleostemin in safeguarding the genome integrity of stem and cancer cells. Since its discovery, the predominant presence of nucleostemin in the nucleolus has led to the notion that it might function in the card-carrying event of the nucleolus--the biogenesis of ribosomes. As tantalizing as this might be, a ribosomal role of nucleostemin is refuted by evidence from recent studies, which argues that nucleostemin depletion triggers a primary event of DNA damage in S phase cells that then leads to ribosomal perturbation. Furthermore, there have been conflicting reports regarding the p53 dependency of nucleostemin activity and the cell cycle arrest profile of nucleostemin-depleted cells. In this Commentary, I propose a model that explains how the many contradictory observations surrounding nucleostemin can be reconciled and suggest that this protein might not be as multi-tasking as has been previously perceived. The story of nucleostemin highlights the complexity of the underlying molecular events associated with the appearance of any cell biological phenotype and also signifies a new understanding of the genome maintenance program in stem cells.

Concomitant upregulation of nucleostemin and downregulation of Sox2 and Klf4 in gastric adenocarcinoma

Nucleostemin (NS) is a nucleolar protein involved in stem cell (SC) self-renewal by controlling cell cycle progression. In addition to SCs, NS is also expressed in some highly proliferating cells including several adult stem cells and cancer cell lines. NS knock-down in different cell lines demonstrated its cell type-dependent function in arresting cell cycle in either G1 or G2/M phases. Here, we have evaluated the expression of NS and iPS genes in 36 gastric cancer and their matched marginal nontumor tissues by means of real-time polymerase chain reaction (RT-PCR). We have also examined a potential causative role of NS in gastric tumorigenesis by suppressing its expression in a gastric cancer cell line, AGS. Our data revealed that NS expression level is much higher in tumor tissues (p = 0.046), especially in high-grade ones (p < 0.001), whereas the expression of Klf4 and Sox2 is downregulated in tumor tissues compared to marginal nontumor samples (p < 0.001). Furthermore, NS suppression in the AGS cell line caused some morphological alterations, a cell cycle arrest at G1 phase, and an upregulation of iPS genes: Nanog, Sox2, and Klf4. Based on our results, NS overexpression seems to have a causative role in gastric tumorigenesis and/or progression, and it could be considered as a potential tumor marker for diagnosis, molecular classification, and molecular therapy of gastric adenocarcinoma.

Nucleostemin depletion induces post-g1 arrest apoptosis in chronic myelogenous leukemia k562 cells

PURPOSE

Despite significant improvements in treatment of chronic myelogenous leukemia (CML), the emergence of leukemic stem cell (LSC) concept questioned efficacy of current therapeutical protocols. Remaining issue on CML includes finding and targeting of the key genes responsible for self-renewal and proliferation of LSCs. Nucleostemin (NS) is a new protein localized in the nucleolus of most stem cells and tumor cells which regulates their self-renewal and cell cycle progression. The aim of this study was to investigate effects of NS knocking down in K562 cell line as an in vitro model of CML.

METHODS

NS gene silencing was performed using a specific small interfering RNA (NS-siRNA). The gene expression level of NS was evaluated by RT-PCR. The viability and growth rate of K562 cells were determined by trypan blue exclusion test. Cell cycle distribution of the cells was analyzed by flow cytometry.

RESULTS

Our results showed that NS knocking down inhibited proliferation and viability of K562 cells in a time-dependent manner. Cell cycle studies revealed that NS depletion resulted in G(1) cell cycle arrest at short times of transfection (24 h) followed with apoptosis at longer times (48 and 72 h), suggest that post-G1 arrest apoptosis is occurred in K562 cells.

CONCLUSION

Overall, these results point to essential role of NS in K562 cells, thus, this gene might be considered as a promising target for treatment of CML.

Nucleostemin deletion reveals an essential mechanism that maintains the genomic stability of stem and progenitor cells

Stem and progenitor cells maintain a robust DNA replication program during the tissue expansion phase of embryogenesis. The unique mechanism that protects them from the increased risk of replication-induced DNA damage, and hence permits self-renewal, remains unclear. To determine whether the genome integrity of stem/progenitor cells is safeguarded by mechanisms involving molecules beyond the core DNA repair machinery, we created a nucleostemin (a stem and cancer cell-enriched protein) conditional-null allele and showed that neural-specific knockout of nucleostemin predisposes embryos to spontaneous DNA damage that leads to severe brain defects in vivo. In cultured neural stem cells, depletion of nucleostemin triggers replication-dependent DNA damage and perturbs self-renewal, whereas overexpression of nucleostemin shows a protective effect against hydroxyurea-induced DNA damage. Mechanistic studies performed in mouse embryonic fibroblast cells showed that loss of nucleostemin triggers DNA damage and growth arrest independently of the p53 status or rRNA synthesis. Instead, nucleostemin is directly recruited to DNA damage sites and regulates the recruitment of the core repair protein, RAD51, to hydroxyurea-induced foci. This work establishes the primary function of nucleostemin in maintaining the genomic stability of actively dividing stem/progenitor cells by promoting the recruitment of RAD51 to stalled replication-induced DNA damage foci.

Regional differences in stem cell/progenitor cell populations from the mouse achilles tendon

Specific niches may affect how cells from different regions contribute to tendon biology, particularly in regard to the healing of certain tendinopathies. The objectives of this study are to determine whether distinct subpopulations of stem/progenitor cells are found within the tendon proper and the epi- and paratenon, the peritenon, as well as to characterize these stem/progenitor cell populations. In this study, we hypothesized that tendon stem/progenitor cells exist in each region, that these populations possess distinct features, and that these populations while multipotent could have differing potentials. To test this hypothesis, stem/progenitor cells were isolated and characterized from the peritenon and tendon proper of mouse Achilles tendons. Colony-forming unit and multipotency assays, as well as flow cytometry, and real-time quantitative polymerase chain reaction analyses of stem cell markers were performed. Significantly, more stem/progenitor cell colonies were observed from cells derived from the tendon proper relative to the peritenon. Analysis of surface markers for stem/progenitor cells from both regions indicated that they were Sca1(+) (stem cell marker), Cd90(+) and Cd44(+) (fibroblast markers), Cd18(-) (leukocyte marker), Cd34(-) (hematopoietic and vascular marker), and Cd133(-) (perivascular marker). Tendon proper stem/progenitor cells had increased expression levels for tenomodulin (Tnmd) and scleraxis (Scx), indicative of enrichment of stem/progenitor cells of a tendon origin. In contrast, cells of the peritenon demonstrated relative increases in the vascular (endomucin) and pericyte (Cd133) markers relative to cells from the tendon proper. Stem/progenitor cells from both regions were multipotent (adipogenic, chondrogenic, osteogenic, and tenogenic). These findings demonstrated that different progenitor populations exist within discrete niches of the Achilles tendon-tendon proper versus peritenon. Overall, these data support the hypothesis that the progenitor pools from both regions have distinct properties and contain enriched progenitor subpopulations of different origins. Moreover, in considering their roles in tendon healing more broadly, they are potential cell sources that may differentially contribute to intrinsic and extrinsic tendon repair mechanisms. That is, intrinsic repair may require a progenitor class with predominant tendon marker expression, while extrinsic repair may involve a progenitor class recruited from perivascular cells of the peritenon.

A nucleostemin-like GTPase required for normal apical and floral meristem development in Arabidopsis

Stem cell activities have to be terminated during flower development. A nucleostemin-like 1 gene, NSN1, is described in Arabidopsis. NSN1 is a midsize nucleolar GTPase required for proper termination of stem cell activities during flower development.

Mammalian nucleostemin (NS) is preferentially expressed in stem cells and acts to promote cell cycle progression. In plants, stem cell activities have to be terminated during flower development, and this process requires the activation of AGAMOUS (AG) gene expression. Here, a nucleostemin-like 1 gene, NSN1, is shown to be required for flower development in Arabidopsis. The NSN1 mRNA was found in the inflorescence meristem and floral primordia, and its protein was localized to the nucleoli. Both heterozygous and homozygous plants developed defective flowers on inflorescences that were eventually terminated by the formation of carpelloid flowers. Overexpression of NSN1 resulted in loss of apical dominance and formation of defective flowers. Expression of the AG gene was found to be up-regulated in nsn1. The carpelloid flower defect of nsn1 was suppressed by the ag mutation in the nsn1 ag double mutant, whereas double mutants of nsn1 apetala2 (ap2) displayed enhanced defective floral phenotypes. These results suggest that in the delicately balanced regulatory network, NSN1 acts to repress AG and plays an additive role with AP2 in floral organ specification. As a midsize nucleolar GTPase, NSN1 represents a new class of regulatory proteins required for flower development in Arabidopsis.

An off-target nucleostemin RNAi inhibits growth in human glioblastoma-derived cancer stem cells

Glioblastomas (GBM) may contain a variable proportion of active cancer stem cells (CSCs) capable of self-renewal, of aggregating into CD133⁺ neurospheres, and to develop intracranial tumors that phenocopy the original ones. We hypothesized that nucleostemin may contribute to cancer stem cell biology as these cells share characteristics with normal stem cells. Here we report that nucleostemin is expressed in GBM-CSCs isolated from patient samples, and that its expression, conversely to what it has been described for ordinary stem cells, does not disappear when cells are differentiated. The significance of nucleostemin expression in CSCs was addressed by targeting the corresponding mRNA using lentivirally transduced short hairpin RNA (shRNA). In doing so, we found an off-target nucleostemin RNAi (shRNA22) that abolishes proliferation and induces apoptosis in GBM-CSCs. Furthermore, in the presence of shRNA22, GBM-CSCs failed to form neurospheres in vitro or grow on soft agar. When these cells are xenotransplanted into the brains of nude rats, tumor development is significantly delayed. Attempts were made to identify the primary target/s of shRNA22, suggesting a transcription factor involved in one of the MAP-kinases signaling-pathways or multiple targets. The use of this shRNA may contribute to develop new therapeutic approaches for this incurable type of brain tumor.

Suppression of Myc oncogenic activity by nucleostemin haploinsufficiency

Nucleostemin (NS), a nucleolar GTPase, is highly expressed in stem/progenitor cells and in most cancer cells. However, little is known about the regulation of its expression. Here, we identify the NS gene as a novel direct transcriptional target of the c-Myc oncoprotein. We show that Myc overexpression enhances NS transcription in cultured cells and in pre-neoplastic B cells from Eμ-myc transgenic mice. Consistent with NS being downstream of Myc, NS expression parallels that of Myc in a large panel of human cancer cell lines. Using chromatin immunoprecipitation we show that c-Myc binds to a well-conserved E-box in the NS promoter. Critically, we show NS haploinsufficiency profoundly delays Myc-induced cancer formation in vivo. NS+/-Eμ-myc transgenic mice have much slower rates of B-cell lymphoma development, with life spans twice that of their wild-type littermates. Moreover, we demonstrate that NS is essential for the proliferation of Myc-overexpressing cells in cultured cells and in vivo: impaired lymphoma development was associated with a drastic decrease of c-Myc-induced proliferation of pre-tumoural B cells. Finally, we provide evidence that in cell culture NS controls cell proliferation independently of p53 and that NS haploinsufficiency significantly delays lymphomagenesis in p53-deficient mice. Together these data indicate that NS functions downstream of Myc as a rate-limiting regulator of cell proliferation and transformation, independently from its putative role within the p53 pathway. Targeting NS is therefore expected to compromise early tumour development irrespectively of the p53 status.

Nucleostemin affects the proliferation but not differentiation of oral squamous cell carcinoma cells

Nucleostemin (NS) has been reported as essential for stem and cancer cell proliferation. To investigate the significance of NS in oral squamous cell carcinomas (OSCCs), we examined NS expression in neoplastic tissue of the tongue and in OSCC cell lines. Nucleostemin expression in the histological samples showed positive correlation with Ki-67 expression. Furthermore, NS expression was associated with cellular proliferation in OSCC cell lines using siRNA, which upregulated p27, a cyclin-dependent kinase inhibitor. Regarding OSCC differentiation, NS expression did not influence cornification or oral epithelial differentiation markers such as involucrin and cytokeratin19. Thus, NS is widely expressed in normal and neoplastic oral epithelial tissues, and is likely a marker of proliferation.

Differential expression of nucleostemin, a stem cell marker, and its variants in different types of brain tumors

Nucleostemin (NS) is implicated in the control of stem and cancer cell proliferation. In the present study, we have examined the expression of NS and its spliced variants in various brain tumors. Total RNA was extracted from 59 brain tumor samples, and the expression of different NS spliced variants was measured by semi-quantitative RT-PCR. The subcellular distribution of NS protein in brain tumors was further examined by immunohistochemistry. Furthermore, to decipher the potential involvement of NS in brain tumorogenesis, its expression was knocked-down by means of RNA interference (RNAi) in two malignant glioma (U-87MG and A172), one astrocytoma (1321N1) and one medulloblastoma (DAOY) cell lines. The alterations in cell-cycle progression of the treated cells were then analyzed by flow cytometry. Our data revealed that NS and its variants are widely expressed in different types of brain tumors. Among the NS spliced variants, variant "1" and variant "3" were detected in the majority of tumor samples, whereas variant "2" was only detectable in few samples. Moreover, the intensity of the expression was correlated with the grade of the tumors (P < 0.05). Accordingly, the expression was much higher in glial tumors compared to that of meningiomas. As expected, a nucleolar/nucleoplasmic localization of NS protein was observed in the examined tumor samples. RNAi results revealed a significant reduction of NS expression along with a moderate blockade of the cell cycle in G(2)/M and S phases of NS-siRNA treated cells. All in all, our data suggest a potential role for NS in tumorogenesis of brain cancers.

Slug/SNAI2 regulates cell proliferation and invasiveness of metastatic prostate cancer cell lines

Many metastatic cancers recapitulate the epithelial-to-mesenchymal transition (EMT) resulting in enhanced cell motility and invasiveness. The EMT is regulated by several transcription factors, including the zinc finger protein SNAI2, also named Slug, which appears to exert additional functions during development and cancer progression. We have studied the function of SNAI2 in prostate cancer cells. Quantitative RT-PCR analysis showed strong SNAI2 expression particularly in the PC-3 and PC3-16 prostate carcinoma cell lines. Knockdown of SNAI2 by specific siRNA induced changes in EMT markers and inhibited invasion of both cell lines into a matrigel matrix. SNAI2 siRNA-treated cells did not tolerate detachment from the culture plates, likely at least in part due to downregulation of integrin alpha6beta4. SNAI2 knockdown disturbed the microtubular and actin cytoskeletons, especially severely in PC-3 cells, resulting in grossly enlarged, flattened, and sometimes multinuclear cells. Knockdown also decreased cell proliferation, with a prominent G0/G1 arrest in PC3-16. Together, our data imply that SNAI2 exerts strong effects on the cytoskeleton and adhesion of those prostate cancer cells that express it and is necessary for their proliferation and invasiveness.

Snail regulates cell survival and inhibits cellular senescence in human metastatic prostate cancer cell lines

The epithelial-mesenchymal transition (EMT) is regarded as an important step in cancer metastasis. Snail, a master regulator of EMT, has been recently proposed to act additionally as a cell survival factor and inducer of motility. We have investigated the function of Snail (SNAI1) in prostate cancer cells by downregulating its expression via short (21-mer) interfering RNA (siRNA) and measuring the consequences on EMT markers, cell viability, death, cell cycle, senescence, attachment, and invasivity. Of eight carcinoma cell lines, the prostate carcinoma cell lines LNCaP and PC-3 showed the highest and moderate expression of SNAI1 mRNA, respectively, as measured by quantitative RT-PCR. Long-term knockdown of Snail induced a severe decline in cell numbers in LNCaP and PC-3 and caspase activity was accordingly enhanced in both cell lines. In addition, suppression of Snail expression induced senescence in LNCaP cells. SNAI1-siRNA-treated cells did not tolerate detachment from the extracellular matrix, probably due to downregulation of integrin α6. Expression of E-cadherin, vimentin, and fibronectin was also affected. Invasiveness of PC-3 cells was not significantly diminished by Snail knockdown. Our data suggest that Snail acts primarily as a survival factor and inhibitor of cellular senescence in prostate cancer cell lines. We therefore propose that Snail can act as early driver of prostate cancer progression.

Differential effects of Nucleostemin suppression on cell cycle arrest and apoptosis in the bladder cancer cell lines 5637 and SW1710

OBJECTIVES

The Nucleostemin (NS) gene encodes a nucleolar protein enriched in adult and embryonic stem cells. NS is thought to regulate cancer cell proliferation, but the mechanisms involved are poorly understood. In this study, we have investigated the role of NS in bladder cancer.

MATERIALS AND METHODS

Expression of NS was determined by quantitative reverse transcription-polymerase chain reaction in bladder carcinoma cell lines and in normal uro-epithelial cell cultures. We used an RNAi strategy to investigate the function of NS in two selected carcinoma cell lines.

RESULTS

High NS expression was found in most bladder carcinoma cell lines and normal uro-epithelial cells. Knockdown of NS expression induced a severe decline in cell proliferation in 5637 and SW1710 cell lines, both with mutant p53. Apoptosis was more strongly enhanced in 5637 cells lacking RB1 than in SW1710 cells lacking p16(INK4A). Moreover, NS-siRNA-treated 5637 cells accumulated mainly in G(2)/M, whereas SW1710 cells arrested in G(0)/G(1).

CONCLUSION

Our data indicate that NS expression is necessary for cell proliferation and evasion of apoptosis in bladder cancer cells, independent of its effect on p53. Also, we speculate that the precise effect of NS on cell cycle regulation may relate to functional status of RB1 and CDKN2A/p16(INK4A).

Nucleostemin as a possible progenitor marker of corneal epithelial cells

PURPOSE

Nucleostemin, a nuclear protein involved in the regulation of cell cycle and proliferation, is a candidate marker for various stem cells. We examined the expression of nucleostemin as a marker of differentiation and senescence in corneal epithelial progenitor cells.

METHODS

Nucleostemin expression in normal mouse corneal epithelium was examined by RT-PCR, as well as in cultured mouse corneal epithelial cells by immunohistochemistry. Co-expression with the progenitor markers p63 and Bmi-1, cytokeratin 14 and 19, the proliferating marker Ki67, differentiation markers cytokeratin 12 and involucrin, and with the senescent marker SA-beta-gal were examined by immunohistochemistry. Correlation of cellular size and nucleostemin expression was also examined.

RESULTS

Nucleostemin expression was detected in mouse corneal epithelium by RT-PCR. Immunohistochemistry revealed that nucleostemin was expressed predominantly in basal and suprabasal cells of the whole cornea. The expression of nucleostemin was not associated with the expression of Ki67, K14, and K19, but with the expression of Bmi-1 and particularly with p63. Nucleostemin was not co-expressed with SA-beta-gal in same cell.

CONCLUSIONS

Nucleostemin can be used as a progenitor marker analogous to p63.