Cell Cycle-dependent Expression of Centrosomal Ninein-like Protein in Human Cells Is Regulated by the Anaphase-promoting Complex

Combining single-cell and bulk RNA sequencing, NK cell marker genes reveal a prognostic and immune status in pancreatic ductal adenocarcinoma

The NK cell is an important component of the tumor microenvironment of pancreatic ductal adenocarcinoma (PDAC), also plays a significant role in PDAC development. This study aimed to explore the relationship between NK cell marker genes and prognosis, immune response of PDAC patients. By scRNA-seq data, we found the proportion of NK cells were significantly downregulated in PDAC and 373 NK cell marker genes were screened out. By TCGA database, we enrolled 7 NK cell marker genes to construct the signature for predicting prognosis in PDAC patients. Cox analysis identified the signature as an independent factor for pancreatic cancer. Subsequently, the predictive power of signature was validated by 6 GEO datasets and had an excellent evaluation. Our analysis of relationship between the signature and patients' immune status revealed that the signature has a strong correlation with immunocyte infiltration, inflammatory reaction, immune checkpoint inhibitors (ICIs) response. The NK cell marker genes are closely related to the prognosis and immune capacity of PDAC patients, and they have potential value as a therapeutic target.

APC/C-regulated CPT1C promotes tumor progression by upregulating the energy supply and accelerating the G1/S transition

BACKGROUND

In addition to functioning as a precise monitoring mechanism in cell cycle, the anaphase-promoting complex/cyclosome (APC/C) is reported to be involved in regulating multiple metabolic processes by facilitating the ubiquitin-mediated degradation of key enzymes. Fatty acid oxidation is a metabolic pathway utilized by tumor cells that is crucial for malignant progression; however, its association with APC/C remains to be explored.

METHODS

Cell cycle synchronization, immunoblotting, and propidium iodide staining were performed to investigate the carnitine palmitoyltransferase 1 C (CPT1C) expression manner. Proximity ligation assay and co-immunoprecipitation were performed to detect interactions between CPT1C and APC/C. Flow cytometry, 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2 H-tetrazolium, inner salt (MTS) assays, cell-scratch assays, and transwell assays and xenograft transplantation assays were performed to investigate the role of CPT1C in tumor progression in vitro and in vivo. Immunohistochemistry was performed on tumor tissue microarray to evaluate the expression levels of CPT1C and explore its potential clinical value.

RESULTS

We identified CPT1C as a novel APC/C substrate. CPT1C protein levels exhibited cell cycle-dependent fluctuations, peaking at the G1/S boundary. Elevated CPT1C accelerated the G1/S transition, facilitating tumor cell proliferation in vitro and in vivo. Furthermore, CPT1C enhanced fatty acid utilization, upregulated ATP levels, and decreased reactive oxygen species levels, thereby favoring cell survival in a harsh metabolic environment. Clinically, high CPT1C expression correlated with poor survival in patients with esophageal squamous cell carcinoma.

CONCLUSIONS

Overall, our results revealed a novel interplay between fatty acid utilization and cell cycle machinery in tumor cells. Additionally, CPT1C promoted tumor cell proliferation and survival by augmenting cellular ATP levels and preserving redox homeostasis, particularly under metabolic stress. Therefore, CPT1C could be an independent prognostic indicator in esophageal squamous cell carcinoma.

Identification of LINC00654-NINL Regulatory Axis in Diffuse Large B-Cell Lymphoma In Silico Analysis

Background

The long non-coding RNA (lncRNA)-mRNA regulation network plays an important role in the development of diffuse large B-cell lymphoma (DLBCL). This study uses bioinformatics to find an innovative regulation axis in DLBCL that will provide a positive reference for defining the mechanism of disease progression.

Methods

Batch Cox regression was used to screen prognosis-related lncRNAs, and a random forest model was used to identify hub lncRNA. The clinical value of the lncRNA was evaluated and Spearman correlation analysis was used to predict the candidate target genes. Gene Oncology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment were used to define the biological function of the lncRNA. A batch Cox regression model, expression validation, and Spearman correlation analysis were used to select the best downstream target genes. The expression and prognostic value validation of this gene was conducted using public data. Gene Set Enrichment Analysis (GSEA) was performed to explore potential mechanisms for this gene in DLBCL.

Results

LINC00654 was identified as the hub lncRNA and 1443 mRNAs were selected as downstream target genes of the lncRNA. The target genes were enriched in the regulation of GTPase and Notch signaling pathways. After validation, the ninein-like (NINL) gene was selected as the potential target of LINC00654 and the LINC00654-NINL axis was constructed. Patients with better responses to therapy were shown to have high NINL gene expression (p-value = 0.036). NINL also had high expression in the DB cell line and low expression in the OCILY3 cell line. Survival analysis showed that high NINL expression was a risk factor for overall survival (OS) and disease-specific survival (DSS) within older patients and those with advanced-stage cancer. GSEA results showed that NINL may be involved in neutrophil-mediated immunity and NF-κB signaling.

Conclusion

This study identified a novel LncRNA00654-NINL regulatory axis in DLBCL, which could provide a favorable reference for exploring the possible mechanisms of disease progression.

A look into the link between centrosome amplification and breast cancer

Centrosome amplification (CA) is a common feature of human tumors, but it is not clear whether this is a cause or a consequence of cancer. The centrosome amplification observed in tumor cells may be explained by a series of events, such as failure of cell division, dysregulation of centrosome cycle checkpoints, and de novo centriole biogenesis disorder. The formation and progression of breast cancer are characterized by genomic abnormality. The centrosomes in breast cancer cells show characteristic structural aberrations, caused by centrosome amplification, which include: an increase in the number and volume of centrosomes, excessive increase of pericentriolar material (PCM), inappropriate phosphorylation of centrosomal molecular, and centrosome clustering formation induced by the dysregulation of important genes. The mechanism of intracellular centrosome amplification, the impact of which on breast cancer and the latest breast cancer target treatment options for centrosome amplification are exhaustively elaborated in this review.

The dynein adaptor Hook2 plays essential roles in mitotic progression and cytokinesis

Hook proteins are evolutionarily conserved dynein adaptors that promote assembly of highly processive dynein-dynactin motor complexes. Mammals express three Hook paralogs, namely Hook1, Hook2, and Hook3, that have distinct subcellular localizations and expectedly, distinct cellular functions. Here we demonstrate that Hook2 binds to and promotes dynein-dynactin assembly specifically during mitosis. During the late G2 phase, Hook2 mediates dynein-dynactin localization at the nuclear envelope (NE), which is required for centrosome anchoring to the NE. Independent of its binding to dynein, Hook2 regulates microtubule nucleation at the centrosome; accordingly, Hook2-depleted cells have reduced astral microtubules and spindle positioning defects. Besides the centrosome, Hook2 localizes to and recruits dynactin and dynein to the central spindle. Dynactin-dependent targeting of centralspindlin complex to the midzone is abrogated upon Hook2 depletion; accordingly, Hook2 depletion results in cytokinesis failure. We find that the zebrafish Hook2 homologue promotes dynein-dynactin association and was essential for zebrafish early development. Together, these results suggest that Hook2 mediates assembly of the dynein-dynactin complex and regulates mitotic progression and cytokinesis.

The Anaphase Promoting Complex/Cyclosome (APC/C): A Versatile E3 Ubiquitin Ligase

In the present chapter we discuss the essential roles of the human E3 ubiquitin ligase Anaphase Promoting Complex/Cyclosome (APC/C) in mitosis as well as the emerging evidence of important APC/C roles in cellular processes beyond cell division control such as regulation of genomic integrity and cell differentiation of the nervous system. We consider the potential incipient role of APC/C dysregulation in the pathophysiology of the neurological disorder Alzheimer's disease (AD). We also discuss how certain Deoxyribonucleic Acid (DNA) and Ribonucleic Acid (RNA) viruses take control of the host's cell division regulatory system through harnessing APC/C ubiquitin ligase activity and hypothesise the plausible molecular mechanisms underpinning virus manipulation of the APC/C. We also examine how defects in the function of this multisubunit protein assembly drive abnormal cell proliferation and lastly argue the potential of APC/C as a promising therapeutic target for the development of innovative therapies for the treatment of chronic malignancies such as cancer.

Multiple Roles, Multiple Adaptors: Dynein During Cell Cycle

Dynein is an essential protein complex present in most eukaryotes that regulate biological processes ranging from ciliary beating, intracellular transport, to cell division. Elucidating the detailed mechanism of dynein function has been a challenging task owing to its large molecular weight and high complexity of the motor. With the advent of technologies in the last two decades, studies have uncovered a wealth of information about the structural, biochemical, and cell biological roles of this motor protein. Cytoplasmic dynein associates with dynactin through adaptor proteins to mediate retrograde transport of vesicles, mRNA, proteins, and organelles on the microtubule tracts. In a mitotic cell, dynein has multiple localizations, such as at the nuclear envelope, kinetochores, mitotic spindle and spindle poles, and cell cortex. In line with this, dynein regulates multiple events during the cell cycle, such as centrosome separation, nuclear envelope breakdown, spindle assembly checkpoint inactivation, chromosome segregation, and spindle positioning. Here, we provide an overview of dynein structure and function with focus on the roles played by this motor during different stages of the cell cycle. Further, we review in detail the role of dynactin and dynein adaptors that regulate both recruitment and activity of dynein during the cell cycle.

Caveolin-1 Mediates Low-Intensity Ultrasound-Induced Apoptosis via Downregulation of Signal Transducer and Activator of Transcription 3 Phosphorylation in Laryngeal Carcinoma Cells

Low-intensity ultrasound therapy has been found to be a potential tool in the management of malignant tumors in recent years. However, the molecular mechanism underlying low-intensity ultrasound-induced apoptosis is still not clear. In this study, we investigated the effects of low-intensity ultrasound-induced apoptosis in HEp-2 cells. We found that low-intensity ultrasound significantly induced apoptosis, and the expression level of caveolin-1 (Cav-1) was dramatically increased after ultrasound treatment of HEp-2 cells. After inhibiting the expression level of Cav-1 using siRNA transfection, we found that the cellular apoptosis induced by low-intensity ultrasound was significantly suppressed. In addition, inhibition of Cav-1 expression promoted phosphorylation of signal transducer and activator of transcription 3 (STAT3), suggesting that the STAT3 signaling pathway was involved in low-intensity ultrasound-induced apoptosis via Cav-1 regulation. Our results indicate that Cav-1/STAT3 signaling pathway may mediate low-intensity ultrasound-induced apoptosis, and this technology could potentially be used clinically for the treatment of cancers.

Loss of function of the Drosophila Ninein-related centrosomal protein Bsg25D causes mitotic defects and impairs embryonic development

The centrosome-associated proteins Ninein (Nin) and Ninein-like protein (Nlp) play significant roles in microtubule stability, nucleation and anchoring at the centrosome in mammalian cells. Here, we investigate Blastoderm specific gene 25D (Bsg25D), which encodes the only Drosophila protein that is closely related to Nin and Nlp. In early embryos, we find that Bsg25D mRNA and Bsg25D protein are closely associated with centrosomes and astral microtubules. We show that sequences within the coding region and 3′UTR of Bsg25D mRNAs are important for proper localization of this transcript in oogenesis and embryogenesis. Ectopic expression of eGFP-Bsg25D from an unlocalized mRNA disrupts microtubule polarity in mid-oogenesis and compromises the distribution of the axis polarity determinant Gurken. Using total internal reflection fluorescence microscopy, we show that an N-terminal fragment of Bsg25D can bind microtubules in vitro and can move along them, predominantly toward minus-ends. While flies homozygous for a Bsg25D null mutation are viable and fertile, 70% of embryos lacking maternal and zygotic Bsg25D do not hatch and exhibit chromosome segregation defects, as well as detachment of centrosomes from mitotic spindles. We conclude that Bsg25D is a centrosomal protein that, while dispensable for viability, nevertheless helps ensure the integrity of mitotic divisions in Drosophila.

Summary: In humans, mutations in Ninein or Ninein-like protein result in microcephaly and other severe diseases. We show that while flies lacking the Ninein orthologue can survive, many die as embryos with defects in mitosis.

Structural centrosome aberrations favor proliferation by abrogating microtubule-dependent tissue integrity of breast epithelial mammospheres

Structural centrosome aberrations are frequently observed in early stage carcinomas, but their role in malignant transformation is poorly understood. Here, we examined the impact of overexpression of Ninein-like protein (Nlp) on the architecture of polarized epithelia in three-dimensional mammospheres. When Nlp was overexpressed to levels resembling those seen in human tumors, it formed striking centrosome-related bodies (CRBs), which sequestered Ninein and affected the kinetics of microtubule (MT) nucleation and release. In turn, the profound reorganization of the MT cytoskeleton resulted in mislocalization of several adhesion and junction proteins as well as the tumor suppressor Scribble, resulting in the disruption of epithelial polarity, cell-cell interactions and mammosphere architecture. Remarkably, cells harboring Nlp-CRBs displayed an enhanced proliferative response to epidermal growth factor. These results demonstrate that structural centrosome aberrations cause not only the disruption of epithelial polarity but also favor overproliferation, two phenotypes typically associated with human carcinomas.

Targeting Cdc20 as a novel cancer therapeutic strategy

The Anaphase Promoting Complex (APC, also called APC/C) regulates cell cycle progression by forming two closely related, but functionally distinct E3 ubiquitin ligase sub-complexes, APC(Cdc20) and APC(Cdh1), respectively. Emerging evidence has begun to reveal that Cdc20 and Cdh1 have opposing functions in tumorigenesis. Specifically, Cdh1 functions largely as a tumor suppressor, whereas Cdc20 exhibits an oncogenic function, suggesting that Cdc20 could be a promising therapeutic target for combating human cancer. However, the exact underlying molecular mechanisms accounting for their differences in tumorigenesis remain largely unknown. Therefore, in this review, we summarize the downstream substrates of Cdc20 and the critical functions of Cdc20 in cell cycle progression, apoptosis, ciliary disassembly and brain development. Moreover, we briefly describe the upstream regulators of Cdc20 and the oncogenic role of Cdc20 in a variety of human malignancies. Furthermore, we summarize multiple pharmacological Cdc20 inhibitors including TAME and Apcin, and their potential clinical benefits. Taken together, development of specific Cdc20 inhibitors could be a novel strategy for the treatment of human cancers with elevated Cdc20 expression.

Functional characterization of Anaphase Promoting Complex/Cyclosome (APC/C) E3 ubiquitin ligases in tumorigenesis

The Anaphase Promoting Complex/Cyclosome (APC/C) is a multi-subunit E3 ubiquitin ligase that primarily governs cell cycle progression. APC/C is composed of at least 14 core subunits and recruits its substrates for ubiquitination via one of the two adaptor proteins, Cdc20 or Cdh1, in M or M/early G1 phase, respectively. Furthermore, recent studies have shed light on crucial functions for APC/C in maintaining genomic integrity, neuronal differentiation, cellular metabolism and tumorigenesis. To gain better insight into the in vivo physiological functions of APC/C in regulating various cellular processes, particularly development and tumorigenesis, a number of mouse models of APC/C core subunits, coactivators or inhibitors have been established and characterized. However, due to their essential role in cell cycle regulation, most of the germline knockout mice targeting the APC/C pathway are embryonic lethal, indicating the need for generating conditional knockout mouse models to assess the role in tumorigenesis for each APC/C signaling component in specific tissues. In this review, we will first provide a brief introduction of the ubiquitin-proteasome system (UPS) and the biochemical activities and cellular functions of the APC/C E3 ligase. We will then focus primarily on characterizing genetic mouse models used to understand the physiological roles of each APC/C signaling component in embryogenesis, cell proliferation, development and carcinogenesis. Finally, we discuss future research directions to further elucidate the physiological contributions of APC/C components during tumorigenesis and validate their potentials as a novel class of anti-cancer targets.

Nonparametric Bayesian evaluation of differential protein quantification

Arbitrary cutoffs are ubiquitous in quantitative computational proteomics: maximum acceptable MS/MS PSM or peptide q value, minimum ion intensity to calculate a fold change, the minimum number of peptides that must be available to trust the estimated protein fold change (or the minimum number of PSMs that must be available to trust the estimated peptide fold change), and the "significant" fold change cutoff. Here we introduce a novel experimental setup and nonparametric Bayesian algorithm for determining the statistical quality of a proposed differential set of proteins or peptides. By comparing putatively nonchanging case-control evidence to an empirical null distribution derived from a control-control experiment, we successfully avoid some of these common parameters. We then apply our method to evaluating different fold-change rules and find that for our data a 1.2-fold change is the most permissive of the plausible fold-change rules.

Cell cycle-dependent expression of p42.3 promotes mitotic progression in malignant transformed cells

In an earlier study, we cloned the p42.3 gene and showed that its expression was specific to tumors in a number of tumor cell lines and primary tumor tissues. However, the biological role and function of this gene remains largely unknown. In this study, p42.3 expression was found to be cell cycle-dependent at both the mRNA and protein levels in several human tumor cell lines. Typically, abundant expression was detected at G1 and M phases compared with S and G2 phases. Expression peaked at early G1 phase then decreased drastically at late G1, S, and G2. Furthermore, transfection of the p42.3 gene into NIH3T3 cells promoted malignant transformation, accompanied by accelerated mitotic progression and altered chromosome segregation. It was also observed that Cyclin B1 was upregulated and Cdc2-Tyr15 was downregulated following p42.3 overexpression in NIH3T3 cells. Combined, these results indicate that p42.3 as a cell cycle-regulated gene contributes to promoting cell cycle progression through disruption of mitotic regulation, and may play important roles in malignant transformation.

The mitotic spindle protein SPAG5/Astrin connects to the Usher protein network postmitotically

BACKGROUND

Mutations in the gene for Usher syndrome 2A (USH2A) are causative for non-syndromic retinitis pigmentosa and Usher syndrome, a condition that is the most common cause of combined deaf-blindness. To gain insight into the molecular pathology underlying USH2A-associated retinal degeneration, we aimed to identify interacting proteins of USH2A isoform B (USH2AisoB) in the retina.

RESULTS

We identified the centrosomal and microtubule-associated protein sperm-associated antigen (SPAG)5 in the retina. SPAG5 was also found to interact with another previously described USH2AisoB interaction partner: the centrosomal ninein-like protein NINLisoB. Using In situ hybridization, we found that Spag5 was widely expressed during murine embryonic development, with prominent signals in the eye, cochlea, brain, kidney and liver. SPAG5 expression in adult human tissues was detected by quantitative PCR, which identified expression in the retina, brain, intestine, kidney and testis. In the retina, Spag5, Ush2aisoB and NinlisoB were present at several subcellular structures of photoreceptor cells, and colocalized at the basal bodies.

CONCLUSIONS

Based on these results and on the suggested roles for USH proteins in vesicle transport and providing structural support to both the inner ear and the retina, we hypothesize that SPAG5, USH2AisoB and NINLisoB may function together in microtubule-based cytoplasmic trafficking of proteins that are essential for cilium formation, maintenance and/or function.

IQGAP1 interacts with Aurora-A and enhances its stability and its role in cancer

IQGAP1, a ubiquitously expressed scaffold protein, has been identified in a wide range of organisms. It participates in multiple aspects of cellular events by binding to and regulating numerous interacting proteins. In our present study, we identified a new IQGAP1 binding protein named Aurora-A which is an oncogenic protein and overexpressed in various types of human tumors. In vitro analysis with GST-Aurora-A fusion proteins showed a physical interaction between Aurora-A and IQGAP1. Moreover, the binding also occurred in HeLa cells as endogenous Aurora-A co-immunoprecipitated with IQGAP1 from the cell lysates. Overexpression of IQGAP1 resulted in an elevation of both expression and activity of Aurora-A kinase. Endogenous IQGAP1 knockdown by siRNA promoted Aurora-A degradation whereas IQGAP1 overexpression enhanced the stability of Aurora-A. Additionally, we documented that the IQGAP1-induced cell proliferation was suppressed by knocking down Aurora-A expression. Taken together, our results showed an unidentified relationship between Aurora-A and IQGAP1, and provided a new insight into the molecular mechanism by which IQGAP1 played a regulatory role in cancer.

Overexpression of centrosomal protein Nlp confers breast carcinoma resistance to paclitaxel

Nlp (ninein-like protein), an important molecule involved in centrosome maturation and spindle formation, plays an important role in tumorigenesis and its abnormal expression was recently observed in human breast and lung cancers. In this study, the correlation between overexpression of Nlp and paclitaxel chemosensitivity was investigated to explore the mechanisms of resistance to paclitaxel and to understand the effect of Nlp upon apoptosis induced by chemotherapeutic agents. Nlp expression vector was stably transfected into breast cancer MCF-7 cells. With Nlp overexpression, the survival rates, cell cycle distributions and apoptosis were analyzed in transfected MCF-7 cells by MTT test and FCM approach. The immunofluorescent assay was employed to detect the changes of microtubule after paclitaxel treatment. Immunoblotting analysis was used to examine expression of centrosomal proteins and apoptosis associated proteins. Subsequently, Nlp expression was retrospectively examined with 55 breast cancer samples derived from paclitaxel treated patients. Interestingly, the survival rates of MCF-7 cells with Nlp overexpressing were higher than that of control after paclitaxel treatment. Nlp overexpression promoted G2-M arrest and attenuated apoptosis induced by paclitaxel, which was coupled with elevated Bcl-2 protein. Nlp expression significantly lessened the microtubule polymerization and bundling elicited by paclitaxel attributing to alteration on the structure or dynamics of β-tubulin but not on its expression. The breast cancer patients with high expression of Nlp were likely resistant to the treatment of paclitaxel, as the response rate in Nlp negative patients was 62.5%, whereas was 58.3 and 15.8% in Nlp (+) and Nlp (++) patients respectively (p = 0.015). Nlp expression was positive correlated with those of Plk1 and PCNA. These findings provide insights into more rational chemotherapeutic regimens in clinical practice, and more effective approaches might be developed through targeting Nlp to increase chemotherapeutic sensitivity.

REV7 is required for anaphase-promoting complex-dependent ubiquitination and degradation of translesion DNA polymerase REV1

REV1 is a Y-family polymerase specialized for replicating across DNA lesions at the stalled replication folk. Due to the high error rate of REV1-dependent translesion DNA synthesis (TLS), tight regulation of REV1 activity is essential. Here, we show that human REV1 undergoes proteosomal degradation mediated by the E3 ubiquitin ligase known as anaphase-promoting complex (APC). REV1 associates with APC. Overexpression of APC coactivator CDH1 or CDC20 promotes polyubiquitination and proteosomal degradation of REV1. Surprisingly, polyubiquitination of REV1 also requires REV7, a TLS accessory protein that interacts with REV1 and other TLS polymerases. The N-terminal region of REV1 contains both the APC degron and an additional REV7-binding domain. Depletion of REV7 by RNA interference stabilizes REV1 by preventing polyubiquitination, whereas overexpression of REV7 augments REV1 degradation. Taken together, our findings suggest a role of REV7 in governing REV1 stability and interplay between TLS and APC-dependent proteolysis.

The role of centrosomal Nlp in the control of mitotic progression and tumourigenesis

The human centrosomal ninein-like protein (Nlp) is a new member of the γ-tubulin complexes binding proteins (GTBPs) that is essential for proper execution of various mitotic events. The primary function of Nlp is to promote microtubule nucleation that contributes to centrosome maturation, spindle formation and chromosome segregation. Its subcellular localisation and protein stability are regulated by several crucial mitotic kinases, such as Plk1, Nek2, Cdc2 and Aurora B. Several lines of evidence have linked Nlp to human cancer. Deregulation of Nlp in cell models results in aberrant spindle, chromosomal missegregation and multinulei, and induces chromosomal instability and renders cells tumourigenic. Overexpression of Nlp induces anchorage-independent growth and immortalised primary cell transformation. In addition, we first demonstrate that the expression of Nlp is elevated primarily due to NLP gene amplification in human breast cancer and lung carcinoma. Consistently, transgenic mice overexpressing Nlp display spontaneous tumours in breast, ovary and testicle, and show rapid onset of radiation-induced lymphoma, indicating that Nlp is involved in tumourigenesis. This review summarises our current knowledge of physiological roles of Nlp, with an emphasis on its potentials in tumourigenesis.

Processive ubiquitin chain formation by the anaphase-promoting complex

Progression through mitosis requires the sequential ubiquitination of cell cycle regulators by the anaphase-promoting complex, resulting in their proteasomal degradation. Although several mechanisms contribute to APC/C regulation during mitosis, the APC/C is able to discriminate between its many substrates by exploiting differences in the processivity of ubiquitin chain assembly. Here, we discuss how the APC/C achieves processive ubiquitin chain formation to trigger the sequential degradation of cell cycle regulators during mitosis.

Aurora B interaction of centrosomal Nlp regulates cytokinesis

Cytokinesis is a fundamental cellular process, which ensures equal abscission and fosters diploid progenies. Aberrant cytokinesis may result in genomic instability and cell transformation. However, the underlying regulatory machinery of cytokinesis is largely undefined. Here, we demonstrate that Nlp (Ninein-like protein), a recently identified BRCA1-associated centrosomal protein that is required for centrosomes maturation at interphase and spindle formation in mitosis, also contributes to the accomplishment of cytokinesis. Through immunofluorescent analysis, Nlp is found to localize at midbody during cytokinesis. Depletion of endogenous Nlp triggers aborted division and subsequently leads to multinucleated phenotypes. Nlp can be recruited by Aurora B to the midbody apparatus via their physical association at the late stage of mitosis. Disruption of their interaction induces aborted cytokinesis. Importantly, Nlp is characterized as a novel substrate of Aurora B and can be phosphorylated by Aurora B. The specific phosphorylation sites are mapped at Ser-185, Ser-448, and Ser-585. The phosphorylation at Ser-448 and Ser-585 is likely required for Nlp association with Aurora B and localization at midbody. Meanwhile, the phosphorylation at Ser-185 is vital to Nlp protein stability. Disruptions of these phosphorylation sites abolish cytokinesis and lead to chromosomal instability. Collectively, these observations demonstrate that regulation of Nlp by Aurora B is critical for the completion of cytokinesis, providing novel insights into understanding the machinery of cell cycle progression.

Centrosomal Nlp is an oncogenic protein that is gene-amplified in human tumors and causes spontaneous tumorigenesis in transgenic mice

Disruption of mitotic events contributes greatly to genomic instability and results in mutator phenotypes. Indeed, abnormalities of mitotic components are closely associated with malignant transformation and tumorigenesis. Here we show that ninein-like protein (Nlp), a recently identified BRCA1-associated centrosomal protein involved in microtubule nucleation and spindle formation, is an oncogenic protein. Nlp was found to be overexpressed in approximately 80% of human breast and lung carcinomas analyzed. In human lung cancers, this deregulated expression was associated with NLP gene amplification. Further analysis revealed that Nlp exhibited strong oncogenic properties; for example, it conferred to NIH3T3 rodent fibroblasts the capacity for anchorage-independent growth in vitro and tumor formation in nude mice. Consistent with these data, transgenic mice overexpressing Nlp displayed spontaneous tumorigenesis in the breast, ovary, and testicle within 60 weeks. In addition, Nlp overexpression induced more rapid onset of radiation-induced lymphoma. Furthermore, mouse embryonic fibroblasts (MEFs) derived from Nlp transgenic mice showed centrosome amplification, suggesting that Nlp overexpression mimics BRCA1 loss. These findings demonstrate that Nlp abnormalities may contribute to genomic instability and tumorigenesis and suggest that Nlp might serve as a potential biomarker for clinical diagnosis and therapeutic target.

BRCA1 interaction of centrosomal protein Nlp is required for successful mitotic progression

Breast cancer susceptibility gene BRCA1 is implicated in the control of mitotic progression, although the underlying mechanism(s) remains to be further defined. Deficiency of BRCA1 function leads to disrupted mitotic machinery and genomic instability. Here, we show that BRCA1 physically interacts and colocalizes with Nlp, an important molecule involved in centrosome maturation and spindle formation. Interestingly, Nlp centrosomal localization and its protein stability are regulated by normal cellular BRCA1 function because cells containing BRCA1 mutations or silenced for endogenous BRCA1 exhibit disrupted Nlp colocalization to centrosomes and enhanced Nlp degradation. Its is likely that the BRCA1 regulation of Nlp stability involves Plk1 suppression. Inhibition of endogenous Nlp via the small interfering RNA approach results in aberrant spindle formation, aborted chromosomal segregation, and aneuploidy, which mimic the phenotypes of disrupted BRCA1. Thus, BRCA1 interaction of Nlp might be required for the successful mitotic progression, and abnormalities of Nlp lead to genomic instability.

Adenoviral-mediated gene transfer of Gadd45a results in suppression by inducing apoptosis and cell cycle arrest in pancreatic cancer cell

BACKGROUND

The extremely poor prognosis of patients with pancreatic ductal adenocarcinoma indicates the need for novel therapeutic approaches. The growth arrest and DNA damage-inducible (Gadd) gene Gadd45a is a member of a group of genes that are induced by DNA damaging agents and growth arrest signals.

METHODS

We evaluated the biological activity of Gadd45a in pancreatic ductal adenocarcinoma cancer-derived cell lines and assessed the efficacy of a combined treatment with adenoviral-mediated expression of Gadd45a (Ad-G45a) and anticancer drug (Etoposide, cisplatin, 5-fluorouracil, respectively) for the PANC1 cell line.

RESULTS

Gadd45a is variously expressed in cell lines derived from pancreatic ductal adenocarcinoma cancer and adenoviral-mediated expression of Gadd45a (Ad-G45a) in these cells results in apoptosis via caspase activation and cell-cycle arrest in the G2/M phase. Gadd45a significantly increased the chemosensitivity of PANC1, which may be due to abundant apoptosis induction and cell cycle arrest. By combinational treatment of Ad-G45a infection and chemotherapeutics, Gadd45a expression was elevated to a higher extent in cancer cells with wild-type p53 than in that with knocked-out p53 status, indicating a higher chemosensitivity to cancer chemotherapy.

CONCLUSIONS

Gadd45a may be a promising candidate for use in cancer gene therapy in combination with chemotherapeutic agents.

Aurora-A interacts with Cyclin B1 and enhances its stability

The mitotic regulator Aurora-A is an oncogenic protein that is over-expressed in many types of human tumors. However, the underlying mechanism through which Aurora-A promotes tumorigenesis remains unclear. Here, we show that overexpression of Aurora-A causes an elevation of Cyclin B1 expression. Cyclin B1 degradation is delayed in Aurora-A over-expressing cells, which depends on Aurora-A kinase activity. In contrast, Aurora-A RNAi enhances Cyclin B1 degradation. Furthermore, we found that Aurora-A interacts with Cyclin B1, and that Aurora-A overexpression reduces the interaction of Cyclin B1 with APC subunits. In human esophageal squamous cell carcinomas (ESCC), overexpression of Aurora-A was correlated with deregulated expression of Cyclin B1. Taken together, these findings suggest that overexpression of Aurora-A may stabilize Cyclin B1 through inhibiting its degradation. These results provide new insight into the mechanism of how deregulated Aurora-A contributes to genomic instability and carcinogenesis.

Increased expression of Nlp, a potential oncogene in ovarian cancer, and its implication in carcinogenesis

OBJECTIVE

Nlp (Ninein-like protein), a novel centrosome protein involved in microtubule nucleation, has been studied extensively in our laboratory, and its overexpression has been found in some human tumors. To understand the role of Nlp in human ovarian cancer development, we studied the correlation of Nlp expression with clinicopathological parameters and survival in epithelial ovarian cancer, and the impact of Nlp overexpression on ovarian cancer cells.

METHODS

Nlp expression in normal, borderline, benign and malignant epithelial ovarian tissues was examined by immunohistochemistry. The correlation between Nlp expression and tumor grade, FIGO stage and histological type was also evaluated. Survival was calculated using Kaplan-Meier estimates. Cell proliferation and apoptosis were assayed after stable transfection of pEGFP-C3-Nlp or empty vector in human ovarian cancer cell line SKOV3.

RESULTS

Nlp was positive in 1 of 10 (10%) normal ovarian tissues, 5 of 34 (14.7%) benign tumors, 9 of 26 (34.6%) borderline tumors and 73 of 131 (56.0%) ovarian tumors. Nlp immunoreactivity intensity significantly correlated with tumor grade, but not with FIGO stage or histological type. Kaplan-Meier curves showed that Nlp overexpression was marginally associated with decreased overall survival. Overexpression of Nlp enhanced proliferation and inhibited apoptosis induced by paclitaxel in the SKOV3 cell line.

CONCLUSIONS

Overexpression of Nlp in ovarian tumors raises the possibility that Nlp may play a role in ovarian carcinogenesis.

BRCA1 regulates caveolin-1 expression and inhibits cell invasiveness

BRCA1 is involved in multiple biological processes including DNA damage repair, cell growth, apoptosis, and transcriptional activation. Also, BRCA1 plays key roles in inhibiting cancer progression. Caveolin-1 is identified as a tumor suppressor and regulates the invasiveness of cells. However, the interactions between BRCA1 and caveolin-1 remain largely unknown. We have investigated the potential function of BRCA1 in regulation of caveolin-1 gene expression and its subcellular localization as well. The observations from RT-PCR, transfection, RNAi, and luciferase assays implied that BRCA1 could elevate caveolin-1 mRNA levels via transactivation of the caveolin-1 promoter region. Additionally, immunofluorescent approach showed that BRCA1 might inhibit the invasiveness and metastatic abilities of mammalian cells by inducing the redistribution of caveolin-1 from the cytoplasm to the cell membrane.