PinX1 is recruited to the mitotic chromosome periphery by Nucleolin and facilitates chromosome congression

Nuclear p120 catenin is a component of the perichromosomal layer and coordinates sister chromatid segregation during mitosis in lung cancer cells

Abnormal expression of p120 catenin is associated with the malignant phenotype in human lung cancer. Numerous studies have focused on the function of p120 catenin in the juxta-membrane compartment. However, the role of nuclear p120 catenin remains unclear. In this study, the dynamic changes in nuclear p120 catenin localization during cell cycle progression were investigated. Immunofluorescent staining, FACS analysis, and western blotting revealed that nuclear p120 catenin is a major architectural constituent of the chromosome periphery during mitosis. During mitosis, granule-like p120 catenin dispersed into a cloudy-like structure and formed cordon-like structures surrounding the condensed chromosomes to create the peri-chromosomal layer. Interestingly, lumican and p120 catenin colocalized at the spindle fiber where the perichromosomal layer connects to the condensed chromosomes during mitosis. Furthermore, downregulation of p120 catenin using a specific siRNA induced cell cycle stalling in the G2/M phase and promoted aneuploidy. This study validates the role of nuclear p120 catenin in the formation of the chromosome periphery and reveals the p120 catenin-lumican interaction may couple orientation of cell division with the segregation of sister chromatids during mitosis. Our data suggest the protective role of p120 catenin in maintaining the integrity of chromosomes, and also warrants further studies to evaluate the contribution of the loss of p120 catenin to the creation of gene rearrangement in cancer evolution and tumor progression.

Could nucleolin and nucleophosmin levels be prognostic indicators in non-small cell lung cancer?

Aim: Lung cancer is the leading cause of mortality from cancer across the world. In this study, the use of serum nucleolin (NCL) and nucleophosmin (NPM1) levels as a marker in the diagnosis, prognosis and treatment response evaluation in lung cancer was investigated. Materials and Method: NCL and NPM1 levels of serum samples taken before chemotherapy and after 3-4 courses of chemotherapy from the control group and the patients diagnosed with lung cancer were studied using ELISA method. Results: Serum NCL and NPM1 levels of the patients were higher than of the controls (p = 0.085 for NCL, p = 0.000 for NPM1). NCL and NPM1 levels by histopathologic type were significantly higher in adenocarcinoma than in squamous cell carcinoma (p < 0.05 for each). In view of the treatment responses to chemotherapeutic agents, there was a statistically insignificant difference between the values before and after chemotherapy (p > 0.05 for each). Conclusion: High serum NCL and NPM1 levels were found to correlate with poor prognosis, poor treatment response and low survival rate. It can be concluded that serum NCL and NPM1 levels in lung cancer can be used as diagnostic and prognostic markers for the disease.

Electrochemiluminescence Biosensor for Nucleolin Imaging in a Single Tumor Cell Combined with Synergetic Therapy of Tumor

Nucleolin, a nuclear biological multifunctional protein, plays significant roles in modulating the proliferation, survival, and apoptosis of tumor cells. Different from the traditional electrochemiluminescence (ECL) method, a new ECL biosensor was built to perform ECL imaging of nucleolin in a single HeLa cell with high sensitivity and throughput. Briefly, mesoporous silica nanoparticles (MSN) loaded with doxorubicin (DOX) and phorbol 12-myristate 13-acetate (PMA) were used as drug carriers and could be specifically opened by nucleolin in a HeLa cell. PMA then induced the HeLa cell to produce reactive oxygen species (ROS) and realized ECL imaging of nucleolin. After that, ROS could damage DNA and proteins of the tumor cell and DOX could induce the apoptosis of HeLa cells by inhibiting genetic material, nucleic acid, synthesis. HeLa cells were then efficiently killed by DOX and ROS in a synergetic pathway. Herein, a new ECL biosensor for ECL imaging of nucleolin in a single HeLa cell and synergetic tumor therapy was built.

An exploration of aptamer internalization mechanisms and their applications in drug delivery

INTRODUCTION

As 'chemical antibodies', aptamers have some advantages, such as lack of immunogenicity, rapid tissue penetration, cell internalization and so on. Consequently, more and more aptamers have been screened out by the systematic evolution of ligands through exponential enrichment for the desired cells or membrane receptors. On the basis of the result, researchers use aptamers to guide drug targeting to the desired cells and internalization in vivo.

AREAS COVERED

In this review, we explore the mechanisms of cargo- or aptamer-mediated internalization, and then briefly summarize five strategies for exploring the mechanism of aptamer internalization. Finally, we focus on four types of applications involving aptamer internalization: aptamers as drugs, aptamers as chemical drug-delivery systems, aptamer-based chimeras and aptamer-conjugated nanoparticles or block copolymer micelles.

EXPERT OPINION

Two aptamer-internalization mechanisms are known, namely receptor-mediated endocytosis and macropinocytosis. The latter mechanism, which is has only been verified in the internalization of nucleolin aptamer shuttles between the nucleus and cytoplasm, may be important for nuclear internalization and cargo molecule escape from the endosomal compartment. Thus, it is feasible to use some strategies to further explore the macropinocytosis internalization mechanism and then to screen for aptamers similar to the nucleolin aptamer for use with the desired cell types as a targeted delivery tool.

Enterovirus 71 3C Promotes Apoptosis through Cleavage of PinX1, a Telomere Binding Protein

Enterovirus 71 (EV71) is an emerging pathogen causing hand, foot, and mouth disease (HFMD) and fatal neurological diseases in infants and young children due to their underdeveloped immunocompetence. EV71 infection can induce cellular apoptosis through a variety of pathways, which promotes EV71 release. The viral protease 3C plays an important role in EV71-induced apoptosis. However, the molecular mechanism responsible for 3C-triggered apoptosis remains elusive. Here, we found that EV71 3C directly interacted with PinX1, a telomere binding protein. Furthermore, 3C cleaved PinX1 at the site of Q50-G51 pair through its protease activity. Overexpression of PinX1 reduced the level of EV71-induced apoptosis and EV71 release, whereas depletion of PinX1 by small interfering RNA promoted apoptosis induced by etoposide and increased EV71 release. Taken together, our study uncovered a mechanism that EV71 utilizes to promote host cell apoptosis through cleavage of cellular protein PinX1 by 3C.

IMPORTANCE

EV71 3C plays an important role in processing viral proteins and interacting with host cells. In this study, we showed that 3C promoted apoptosis through cleaving PinX1, a telomere binding protein, and that this cleavage facilitated EV71 release. Our study demonstrated that PinX1 plays an important role in EV71 release and revealed a novel mechanism that EV71 utilizes to induce apoptosis. This finding is important in understanding EV71-host cell interactions and has potential impact on understanding other enterovirus-host cell interactions.

Roles of nucleolin. Focus on cancer and anti-cancer therapy

Nucleolin, a multifunctional protein distributed in the nucleolus, participates in many modulations including rDNA transcription, RNA metabolism, and ribosome assembly. Nucleolin is also found in the cytoplasm and on the cell membrane, and surface nucleolin can bind to various ligands to affect many physiological functions. The expression and localization of nucleolin is often abnormal in cancers, as the differential distribution of nucleolin in cancer can influence the carcinogenesis, proliferation, survival, and metastasis of cancer cells, leading to the cancer progression. Thus, nucleolin may be a novel and promising target for anti-cancer treatment. Here, we describe how nucleolin act functions in cancer development and describe nucleolin-dependent anti-cancer therapies.

Biological significance of PinX1 telomerase inhibitor in esophageal carcinoma treatment

In the present study, to investigate the expression of PinX1 gene and its functional effects in human esophageal carcinoma (Eca)-109 cell line, expression vectors of human PinX1 (pEGFP-C3-PinX1) and its small interfering RNA (PinX1-FAM-siRNA) were constructed and transfected into Eca-109 cells using Lipofectamine 2000. Firstly, the mRNA expression level of PinX1 was examined using reverse transcription-polymerase chain reaction (RT-PCR). Once successful transfection was achieved, the effects on the mRNA level of human telomerase reverse transcriptase (hTERT), telomerase activity, cell proliferation and apoptosis were examined by semi-quantitative RT-PCR, stretch PCR, MTT assay and flow cytometry, respectively. Analysis of restriction and sequencing demonstrated that the recombining plasmids were successfully constructed. The results also indicated that transfection with pEGFP-C3-PinX1 and PinX1-FAM-siRNA into Eca-109 cells significantly increased PinX1 mRNA, decreased hTERT mRNA by 29.9% (P<0.05), and significantly reduced telomerase activity (P<0.05), inhibited cell growth, and increased the cell apoptotic index from 19.27±0.76 to 49.73±2%. The transfected PinX1-FAM-SiRNA exhibited PinX1 mRNA expression levels that were significantly decreased by 70% (P<0.05), whereas the remaining characteristics of Eca-109 cells, including cell growth, mRNA level of hTERT, telomerase activity and cell apoptotic index were not altered. Exogenous PinX1 has been demonstrated to be highly expressed in human Eca. PinX1 can inhibit human telomerase activity and the expression of hTERT mRNA, reduce tumor cell growth and induce apoptosis. Notably, these inhibitory functions were inhibited by silencing PinX1 in Eca with PinX1-FAM-siRNA. PinX1 was successfully increased and decreased in the present study, demonstrating that it may be a potential telomerase activity inhibitor. As PinX1 is an endogenous telomerase inhibitor, it may be used as a novel tumor-targeted gene therapy.

Expression of Nucleolin Affects Microtubule Dynamics

Nucleolin is present in diverse cellular compartments and is involved in a variety of cellular processes from nucleolar structure and function to intracellular trafficking, cell adhesion and migration. Recently, nucleolin has been localized at the mature centriole where it is involved in microtubule nucleation and anchoring. Although this new function of nucleolin linked to microtubule regulation has been identified, the global effects of nucleolin on microtubule dynamics have not been addressed yet. In the present study, we analyzed the roles of nucleolin protein levels on global microtubule dynamics by tracking the EB3 microtubule plus end binding protein in live cells. We have found that during microtubule growth phases, nucleolin affects both the speed and life time of polymerization and by analyzing catastrophe events, we showed that nucleolin reduces catastrophe frequency. This new property of nucleolin was then confirmed in a cold induced microtubule depolymerization experiment in which we have found that cold resistant microtubules were totally destabilized in nucleolin depleted cells. Altogether, our data demonstrate a new function of nucleolin on microtubule stabilization, thus bringing novel insights into understanding the multifunctional properties of nucleolin in healthy and cancer cells.

Sharing the mitotic pre-ribosomal particles between daughter cells

Ribosome biogenesis is a fundamental multistep process initiated by the synthesis of 90S pre-ribosomal particles in the nucleoli of higher eukaryotes. Even though synthesis of ribosomes stops during mitosis while nucleoli disappear, mitotic pre-ribosomal particles persist as observed in prenucleolar bodies (PNBs) during telophase. To further understand the relationship between the nucleolus and the PNBs, the presence and the fate of the mitotic pre-ribosomal particles during cell division was investigated. We demonstrate that the recently synthesized 45S precursor ribosomal RNAs (pre-rRNAs) but also the 32S and 30S pre-rRNAs are maintained during mitosis and associated with the chromosome periphery together with pre-rRNA processing factors. Maturation of the mitotic pre-ribosomal particles, as assessed by the stability of the mitotic pre-rRNAs, is transiently arrested during mitosis by a cyclin-dependent kinase (CDK)1-cyclin B-dependent mechanism and may be restored by CDK inhibitor treatments. At the M/G1 transition, the resumption of mitotic pre-rRNA processing in PNBs does not induce the disappearance of PNBs that only occurs when functional nucleoli reform. Strikingly, during their maturation process, mitotic pre-rRNAs localize in reforming nucleoli.

The telomere/telomerase binding factor PinX1 regulates paclitaxel sensitivity depending on spindle assembly checkpoint in human cervical squamous cell carcinomas

Paclitaxel is a main ingredient in the combination chemotherapy treatment of advanced human cervical squamous cell carcinomas. We investigated the roles and underlying molecular mechanisms of PinX1 in cervical squamous cell carcinomas (CSCC) cells response to paclitaxel and its clinical significances. The expression dynamics of PinX1 was first examined by immunohistochemistry in 122 advanced CSCC patients treated with cisplatin/paclitaxel chemotherapy. The expression of PinX1 was significantly associated with the effects of cisplatin/paclitaxel chemotherapy in advanced CSCCs (P<0.05). High expression of PinX1 correlated with CSCC's response to cisplatin/paclitaxel chemotherapy, and was an independent predictor of shortened survival (P<0.05). A series of in vivo and in vitro assays were performed to elucidate the function of PinX1 on CSCC cells chemosensitivity to paclitaxel and underlying mechanisms. In CSCC cells, the levels of PinX1 were only associated with the cytotoxicity and sensitivity of paclitaxel, in which knockdown of PinX1 dramatically enhanced paclitaxel cytotoxicity, whereas the reestablishment of PinX1 levels substantially reduced the paclitaxel-induced killing effect. In addition, we identified that the ability of PinX1 to stabilize the tension between sister kinetochores and maintain the spindle assembly checkpoint was the main reason CSCC cells undergo apoptosis when treated with paclitaxel, and further studies demonstrated that shortened distance between sisters kinetochores by nocodazole confers upon PinX1-replenished cells a sensitivity to the death inducing paclitaxel effects. Furthermore, our study of CSCC cells xenografts in nude mice confirmed the role of PinX1 in paclitaxel sensitivity in vivo. Our data reveal that PinX1 could be used as a novel predictor for CSCC patient response to paclitaxel, and the role of PinX1-mediated paclitaxel sensitivity might represent a new direction for the development of a new generation of microtubule drugs.

PinX1 regulation of telomerase activity and apoptosis in nasopharyngeal carcinoma cells

BACKGROUND

Human interacting protein X1 (PinX1) has been identified as a critical telomerase inhibitor and proposed to be a putative tumor suppressor gene. Loss of PinX1 has been found in a large variety of malignancies, however, its function in inhibiting telomerase activity of tumor cells is not well documented. Here we show that PinX1 is essential for down-regulation telomerase activity of nasopharyngeal carcinoma.

METHODS

Expression vectors of human PinX1 (pEGFP-C3-PinX1) and its small interfering RNA (PinX1-FAM-siRNA) were constructed and transfected into NPC. Their effects on mRNA of telomerase catalytic subunit (hTERT), telomerase activity, cell proliferation, cell migration, wound healing, cell cycles and apoptosis were examined using semi-quantitative RT-PCR, stretch PCR, MTT assay, Transwell, scratch assay and flow cytometry, respectively.

RESULTS

Transfection of pEGFP-C3-PinX1 and PinX1-FAM-siRNA increased and reduced PinX1 mRNA by 1.6-fold and 70%, respectively. Over-expression of PinX1 decreased hTERT mRNA by 21%, reduced telomerase activity, inhibited cell growth, migration and wound healing ability, arrested cells in G0/G1 phase, and increased apoptotic index. In contrast, down-regulation of PinX1 did not alter the above characteristics.

CONCLUSIONS

PinX1 may play important roles in NPC proliferation, migration and apoptosis and has application potential in tumor-targeted gene therapy.

Continual expression throughout the cell cycle and downregulation upon adipogenic differentiation makes nucleostemin a vital human MSC proliferation marker

Nucleostemin (NS) is a nucleolar protein expressed in stem and cancer cells. In combination with nuclear/nucleolar proteins, NS has been demonstrated to be involved in cell-cycle regulation and telomere maintenance. NS expression reflects the cell's proliferation state indicating that the cell is active in the cell cycle, whereas NS signals disappear upon differentiation. This study analyzes the spatio-temporal (nucleolar/nuclear localization during interphase and M-phase) NS remodeling in two distinct human mesenchymal stem cell (MSC) populations to discriminate the NS differences, if any, throughout their stem cell and differentiation states. Beside its prominent multilobular nucleolar localization in interphase cells, coexistence of NS with chromosome arms during mitosis was also observed. Disruption of mitotic microtubules induced dissociation of NS from the chromosome arms and scattered it into the cytoplasm. Compared to deciduous dental pulp MSCs, NS mRNA expression gradually decreased upon aging in umbilical cord stroma-derived MSCs as culture time increased. Following adipogenic differentiation of the latter, NS signals gradually disappeared in both dividing and non-dividing cells, even before the morphological and functional signs of adipogenic transformation appeared. Quantitative NS mRNA measurements showed that MSCs from two sources exhibit a strong nucleostemin expression similar to embryonic stem cells. In conclusion, apart from its novel chromosomal localization shown in this study, nucleolar NS can be considered as a marker that indicates the proliferation/differentiation states in human MSCs. Moreover, differences in the relative NS protein and mRNA levels may reflect the degree of proliferation and can be used to characterize in vitro expansion capabilities.

The nuclear scaffold protein SAF-A is required for kinetochore-microtubule attachment and contributes to the targeting of Aurora-A to mitotic spindles

Segregation of chromosomes during cell division requires correct formation of mitotic spindles. Here, we show that a scaffold attachment factor A (SAF-A), also known as heterogeneous nuclear ribonucleoprotein-U, contributes to the attachment of spindle microtubules (MTs) to kinetochores and spindle organization. During mitosis, SAF-A was localized at the spindles, spindle midzone and cytoplasmic bridge. Depletion of SAF-A by RNA interference induced mitotic delay and defects in chromosome alignment and spindle assembly. We found that SAF-A specifically co-immunoprecipitated with the chromosome peripheral protein nucleolin and the spindle regulators Aurora-A and TPX2, indicating that SAF-A is associated with nucleolin and the Aurora-A-TPX2 complex. SAF-A was colocalized with TPX2 and Aurora-A in spindle poles and MTs. Elimination of TPX2 or Aurora-A from cells abolished the association of SAF-A with the mitotic spindle. Interestingly, SAF-A can bind to MTs and contributes to the targeting of Aurora-A to mitotic spindle MTs. Our finding indicates that SAF-A is a novel spindle regulator that plays an essential role in kinetochore-MT attachment and mitotic spindle organization.

Plk1-mediated mitotic phosphorylation of PinX1 regulates its stability

PinX1 was originally identified as a Pin2/TRF1-interacting protein that suppresses telomerase activity via its telomerase inhibitor domain (TID) and regulates the nucleolar localization of TRF1 in telomerase-positive cells. In addition to its telomeric localization, PinX1 can be found in the nucleoli of human cells. Our recent studies have shown that PinX1 localizes to the chromosome periphery and kinetochores in mitosis. Depletion of PinX1 results in lagging chromosomes in mitosis and micronuclei in interphase. However, less is known about the post-translational modification of PinX1 in mitosis. Here, we show that Polo-like kinase 1 (Plk1) is a novel interacting protein of PinX1. Plk1 interacts with and phosphorylates PinX1 in vivo and in vitro. Overexpression of Plk1 promotes protein turnover of PinX1, a process that depends on ubiquitin-associated proteasomal degradation. Depletion of Plk1 using siRNA increases the stability of PinX1 at protein level in mitosis. Moreover, Plk1-mediated phosphorylation of PinX1 at five phosphorylation sites is essential for its Plk1-induced degradation. These findings suggest that Plk1 may negatively regulate the stability of PinX1 by mitotic phosphorylation.

The chromosome peripheral proteins play an active role in chromosome dynamics

The chromosome periphery is a chromosomal structure that covers the surface of mitotic chromosomes. The structure and function of the chromosome periphery has been poorly understood since its first description in 1882. It has, however, been proposed to be an insulator or barrier to protect chromosomes from subcellular substances and to act as a carrier of nuclear and nucleolar components to direct their equal distribution to daughter cells because most chromosome peripheral proteins (CPPs) are derived from the nucleolus or nucleus. Until now, more than 30 CPPs were identified in mammalians. Recent immunostaining analyses of CPPs have revealed that the chromosome periphery covers the centromeric region of mitotic chromosomes in addition to telomeres and regions between two sister chromatids. Knockdown analyses of CPPs using RNAi have revealed functions in chromosome dynamics, including cohesion of sister chromatids, kinetochore-microtubule attachments, spindle assembly and chromosome segregation. Because most CPPs are involved in various subcellular events in the nucleolus or nuclear at interphase, a temporal and spatial-specific knockdown method of CPPs in the chromosome periphery will be useful to understand the function of chromosome periphery in cell division.