RNAi knockdown of human kinetochore protein CENP-H

Protein Complexes in the Nucleus: The Control of Chromosome Segregation

Mistakes in the process of cell division can lead to the loss, gain or rearrangement of chromosomes. Significant chromosomal abnormalities are usually lethal to the cells and cause spontaneous miscarriages. However, in some cases, defects in the spindle assembly checkpoint lead to severe diseases, such as cancer and birth and development defects, including Down's syndrome. The timely and accurate control of chromosome segregation in mitosis relies on the spindle assembly checkpoint (SAC), an evolutionary conserved, self-regulated signalling system present in higher organisms. The spindle assembly checkpoint is orchestrated by dynamic interactions between spindle microtubules and the kinetochore , a multiprotein complex that constitutes the site for attachment of chromosomes to microtubule polymers to pull sister chromatids apart during cell division. This chapter discusses the current molecular understanding of the essential, highly dynamic molecular interactions underpinning spindle assembly checkpoint signalling and how the complex choreography of interactions can be coordinated in time and space to finely regulate the process. The potential of targeting this signalling pathway to interfere with the abnormal segregation of chromosomes, which occurs in diverse malignancies and the new opportunities that recent technological developments are opening up for a deeper understanding of the spindle assembly checkpoint are also discussed.

CENP-H regulates the cell growth of human hepatocellular carcinoma cells through the mitochondrial apoptotic pathway

The genomic alterations of hepatocellular carcinoma (HCC) are still unclear. Centromere protein-H (CENP-H) has been shown to be associated with many solid tumors. Our previous study found that CENP-H was upregulated in HCC and was related to patient prognosis. However, the biological functions of CENP-H in HCC and the possible underlying mechanisms have not been well elucidated. In the present study, we demonstrated that CENP-H knockdown inhibited the proliferation of Hep3B cells and decreased colony formation ability of single cells in vitro. Furthermore, CENP-H knockdown induced Hep3B cell apoptosis, and apoptotic bodies were observed using transmission electron microscopy. The protein expression of cleaved caspase-3 was upregulated in Hep3B cells after CENP-H knockdown. Additionally, a Bax/Bcl-2 ratio imbalance with a significant increase of Bax and a substantial decrease of Bcl-2 at both the mRNA and protein levels were determined in this study. In an animal experiment, CENP-H knockdown blocked the growth of Hep3B subcutaneous xenografts. Immunohistochemistry revealed that the protein expression of cleaved caspase-3 and Bax was increased, whereas the protein expression of Bcl-2 and Ki-67 was decreased in subcutaneous xenografts of the CENP-H-knockdown group. In summary, CENP-H may be involved in cell proliferation and apoptosis of HCC cells through the mitochondrial apoptotic pathway. Combined with previous studies, the data provide a new perspective on HCC development and progression.

CenpH regulates meiotic G2/M transition by modulating the APC/CCdh1-cyclin B1 pathway in oocytes

Meiotic resumption (G2/M transition) and progression through meiosis I (MI) are two key stages for producing fertilization-competent eggs. Here, we report that CenpH, a component of the kinetochore inner plate, is responsible for G2/M transition in meiotic mouse oocytes. Depletion of CenpH by morpholino injection decreased cyclin B1 levels, resulting in attenuation of maturation-promoting factor (MPF) activation, and severely compromised meiotic resumption. CenpH protects cyclin B1 from destruction by competing with the action of APC/C^Cdh1. Impaired G2/M transition after CenpH depletion could be rescued by expression of exogenous cyclin B1. Unexpectedly, blocking CenpH did not affect spindle organization and meiotic cell cycle progression after germinal vesicle breakdown. Our findings reveal a novel role of CenpH in regulating meiotic G2/M transition by acting via the APC/C^Cdh1-cyclin B1 pathway.

Summary: CenpH, a component of the kinetochore inner plate protein, is necessary for cyclin B1 stabilization and is responsible for the G2/M transition in meiotic mouse oocytes.

Low expression of spindle checkpoint protein, Cenp-E, causes numerical chromosomal abnormalities in HepG-2 human hepatoma cells

The aim of the present study was to investigate the expression, localization and role of centromere-associated protein E (Cenp-E) in hepatoma cells. The Cenp-E mRNA expression levels in the HepG-2 human hepatocellular carcinoma and LO2 normal hepatic cell lines following treatment with nocodazole were detected by reverse transcription-quantitative polymerase chain reaction (RT-qPCR). Furthermore, the localization and expression of Cenp-E protein in the two cell types was visualized using indirect immunofluorescence. RT-qPCR was also performed to detect the Cenp-E mRNA expression levels in LO2 cells before and after RNA interference. Additional evaluation of the function of interfered cells was performed using indirect immunofluorescence. The results of RT-qPCR demonstrated that the protein expression levels of Cenp-E in the two cell lines prior to treatment with nocodazole were not significantly different (P>0.05). However, the upregulation of Cenp-E expression levels in the LO2 cells was significantly higher compared with that in the HepG-2 cells during cell division (P<0.05). Indirect immunofluorescence analysis indicated that the Cenp-E protein was predominantly located in the nucleus, and that Cenp-E protein expression in nuclei with abnormal mitosis was markedly lower compared with that in nuclei exhibiting normal mitosis. Indirect immunofluorescence also determined that the ratio of dyskaryosis was significantly higher in cells that had undergone Cenp-E interference compared with normal cells. Thus, the present study indicated that the low expression of Cenp-E mRNA may be an important reason for numerical chromosomal abnormalities in human hepatoma cells.

The EHEC-host interactome reveals novel targets for the translocated intimin receptor

Enterohemorrhagic E. coli (EHEC) manipulate their human host through at least 39 effector proteins which hijack host processes through direct protein-protein interactions (PPIs). To identify their protein targets in the host cells, we performed yeast two-hybrid screens, allowing us to find 48 high-confidence protein-protein interactions between 15 EHEC effectors and 47 human host proteins. In comparison to other bacteria and viruses we found that EHEC effectors bind more frequently to hub proteins as well as to proteins that participate in a higher number of protein complexes. The data set includes six new interactions that involve the translocated intimin receptor (TIR), namely HPCAL1, HPCAL4, NCALD, ARRB1, PDE6D, and STK16. We compared these TIR interactions in EHEC and enteropathogenic E. coli (EPEC) and found that five interactions were conserved. Notably, the conserved interactions included those of serine/threonine kinase 16 (STK16), hippocalcin-like 1 (HPCAL1) as well as neurocalcin-delta (NCALD). These proteins co-localize with the infection sites of EPEC. Furthermore, our results suggest putative functions of poorly characterized effectors (EspJ, EspY1). In particular, we observed that EspJ is connected to the microtubule system while EspY1 appears to be involved in apoptosis/cell cycle regulation.

A regulatory effect of INMAP on centromere proteins: antisense INMAP induces CENP-B variation and centromeric halo

CENP-B is a highly conserved protein that facilitates the assembly of specific centromere structures both in interphase nuclei and on mitotic chromosomes. INMAP is a conserved protein that localizes at nucleus in interphase cells and at mitotic apparatus in mitotic cells. Our previous results showed that INMAP over-expression leads to spindle defects, mitotic arrest and formation of polycentrosomal and multinuclear cells, indicating that INMAP may modulate the function of (a) key protein(s) in mitotic apparatus. In this study, we demonstrate that INMAP interacts with CENP-B and promotes cleavage of the N-terminal DNA binding domain from CENP-B. The cleaved CENP-B cannot associate with centromeres and thus lose its centromere-related functions. Consistent with these results, CENP-B in INMAP knockdown cells becomes more diffused around kinetochores. Although INMAP knockdown cells do not exhibit gross defects in mitotic spindle formation, these cells go through mitosis, especially prophase and metaphase, with different relative timing, indicating subtle abnormality. These results identify INMAP as a model regulator of CENP-B and support the notion that INMAP regulates mitosis through modulating CENP-B-mediated centromere organization.

Overexpression of CENP-H as a novel prognostic biomarker for human hepatocellular carcinoma progression and patient survival

Centromere protein H (CENP-H) has been shown to be significantly upregulated in many types of cancers and is associated with disrupted cell cycle regulation, cell proliferation and genetic instability. The aim of the present study was to explore the expression and localization of CENP-H in hepatocellular carcinoma (HCC) and determine whether its overexpression is a prognostic biomarker for HCC. Reverse transcription-polymerase chain reaction (pcr), real-time qPCR and western blotting were used to compare CENP-H expression at the mRNA and protein levels in HCC samples and corresponding adjacent non-cancerous samples. CENP-H protein levels were determined in 60 paired paraffin-embedded HCC tissues using immunohistochemistry (IHC), and the correlation with clinicopathological features and patient prognosis was analyzed. In addition, an immunofluorescence assay was performed to test the expression and localization of CENP-H protein in HCC cells. Results showed that levels of CENP-H mRNA and protein were higher in HCC samples than in the corresponding adjacent non-cancerous samples. In 60 paired paraffin-embedded tissues, CENP-H was upregulated in the HCC samples (38/60, 63.3%) relative to the adjacent non-cancerous samples (21/60, 35%, P=0.003), and a higher level of upregulation was associated with tumor size (P=0.032); higher histological grade (P=0.001); more advanced TNM stage (P=0.002) and Chinese clinical stage (P=0.008); and poorer prognosis. In addition, consistent with the results of IHC, the immunofluorescence assay showed that CENP-H was localized in the nucleus of Hep3B cells. CENP-H was overexpressed in HCC, and its level of upregulation was an independent prognostic indicator, suggesting that CENP-H may be an effective therapeutic strategy for the treatment of HCC.

Clinical Significance of CENP-H Expression in Uterine Cervical Cancer

Objective

This work aims to investigate the expression pattern and clinicopathologic significance of centromere protein H (CENP-H) in uterine cervical cancer (UCC).

Methods

The level of CENP-H expression in the paraffin sections of 62 UCC cases was determined by the SP immunohistochemical method, with complete clinicopathologic data in all cases. Statistical analysis was conducted to evaluate the prognostic and diagnostic significance of CENP-H using SPSS13.0 software package.

Results

Immunohistochemical assay showed strong CENP-H expression in 61.29% (38/62) of the paraffin-embedded cervical cancer tissues. Statistical analysis revealed a strong correlation between the CENP-H expression and the clinical classification (P=0.038) of the cervical carcinoma. The expression increased with rise of the stages. The analysis of Cox proportional hazards regression model suggested that CENP-H expression (P=0.002) and tumor stage (P=0.001) were independent prognostic markers for the survival of UCC patients. The survival analysis showed that the survival rate was significantly lower in patients with high expression of CENP-H than in those with low expression of CENP-H (P=0.001).

Conclusions

CENP-H is likely to be a valuable marker for carcinogenesis and progression of UCC. It might be used as the important diagnostic and prognostic marker for cervical carcinoma patients, especially for those at early stage.

Role of centromere protein H and Ki67 in relapse-free survival of patients after primary surgery for hypopharyngeal cancer

PURPOSE

Centromere protein H (CENP-H) and Ki67 are overexpressed in some malignancies, but whether they are predictors of survival after primary resection for hypopharyngeal squamous cell carcinoma (HSCC) remains unknown.

METHODS

We assessed immunohistochemical expression of CENP-H and Ki67 in 112 HSCC specimens collected between March 2003 and March 2005 for analysis by clinical characteristics. The Kaplan-Meier method was used to analyze relapse-free survival and logistic multivariate regression to determine risk factors of relapse-free survival. Cholecystokinin octapeptide assays and flow cytometry were used to examine cell proliferation and apoptosis after siRNA inhibition of CENP-H in HSCC cells.

RESULTS

Overall, 50 (44.6%) HSCC specimens showed upregulated CENP-H expression and 69 (61.6%) upregulated Ki67. An increased CENP-H protein level was associated with advanced cancer stage and alcohol history (P=0.012 and P=0.048, respectively) but an increased Ki67 protein level only with advanced cancer stage (P=0.021). Increased CENP-H or Ki67 were associated with short relapse-free survival (P<0.001 or P=0.009, respectively) and were independent predictors of relapse-free survival (P=0.001 and P=0.018, respectively). siRNA knockdown of CENP-H mRNA inhibited cell proliferation and promoted cancer cell apoptosis in vitro.

CONCLUSIONS

Upregulated CENP-H and Ki67 levels are significantly associated with short relapse-free survival in HSCC. These factors may be predictors of a relapsing phenotype in HSSC cases.

Sp1 and Sp3 are involved in the full transcriptional activity of centromere protein H in human nasopharyngeal carcinoma cells

The overexpression of centromere protein H (CENPH), one of the fundamental components of the human active kinetochore, has been shown to be closely associated with human cancers. However, the mechanism of its transcriptional regulation has not been reported. The aim of the present study was to investigate the regulatory elements for the transcriptional regulation of CENPH in nasopharyngeal carcinoma cells. To characterize the CENPH promoter and identify regulatory elements, we cloned 1015 bp (-975/+40 bp) of the 5'-flanking region of the CENPH gene from immortalized normal nasopharyngeal epithelial cells (Bmi-1/NPEC). Functional analysis established a minimal region (-140/-87 bp) involved in the regulation of human CENPH promoter activity. Through site-directed mutagenesis, a transactivation assay, chromatin immunoprecipitation, and electrophoretic mobility shift assay, we found that the Sp1/Sp3 transcription factors could bind to the CENPH promoter in vitro and in vivo, and that they regulated CENPH promoter activation in human nasopharyngeal carcinoma cells. Furthermore, Sp1 and Sp3 were highly expressed in nasopharyngeal carcinoma cells. Knockdown of Sp1 and Sp3 by small interfering RNA or inhibition of Sp1 and Sp3 activity by mithramycin A decreased CENPH mRNA expression, whereas the exogenous expression of Sp1 and Sp3 upregulated CENPH mRNA expression. Taken together, our results indicate that Sp1 and Sp3 bind to the CENPH minimal promoter and function as a regulator of the transcription of CENPH in human nasopharyngeal carcinomas.

ShRNA-targeted centromere protein A inhibits hepatocellular carcinoma growth

Background

Centromere protein A (CENP-A) plays important roles in cell-cycle regulation and genetic stability. Herein, we aimed to investigate its expression pattern, clinical significance, and biological function in hepatocellular carcinoma (HCC).

Methodology/Principal Findings

CENP-A expression at the mRNA and protein levels was examined in 20 pairs of fresh HCCs and corresponding nontumor liver tissues. Immunohistochemistry for CENP-A was performed on 80 paraffin-embedded HCC specimens, and the clinical significance of its expression was analyzed. A human HCC cell line HepG2 with high abundance of CENP-A was used to study the effects of manipulating CENP-A on HCC growth. Quantitative real-time polymerase chain reaction arrays and Western blot analysis were employed to identify the cell-cycle control- and apoptosis-related genes regulated by CENP-A. The results showed that CENP-A was aberrantly overexpressed in HCCs relative to adjacent nontumor tissues. This overexpression was significantly associated with positive serum HBsAg status, increased histological grade, high Ki-67 index and P53 immunopositivity. Knockdown of CENP-A in HepG2 cells reduced cell proliferation, blocked cell cycle at the G1 phase, and increased apoptosis. The antiproliferative effects of CENP-A silencing were also observed in vivo. Conversely, CENP-A overexpression promoted HCC cell growth and reduced apoptosis. Furthermore, many genes implicated in cell-cycle regulation and apoptosis, including CHK2, P21waf1, P27 Kip1, SKP2, cyclin G1, MDM2, Bcl-2, and Bax, were deregulated by manipulating CENP-A.

Conclusions/Significance

Overexpression of CENP-A is frequently observed in HCC. Targeting CENP-A can inhibit HCC growth, likely through the regulation of a large number genes involved in cell-cycle progression and apoptosis, and thereby represents a potential therapeutic strategy for this malignancy.

Interruption of cenph causes mitotic failure and embryonic death, and its haploinsufficiency suppresses cancer in zebrafish

Kinetochore proteins associate with centromeric DNA and spindle microtubules and play essential roles in chromosome segregation during mitosis. In this study, we uncovered a zebrafish mutant, stagnant and curly (stac), that carries the Tol2 transposon element inserted at the kinetochore protein H (cenph) locus. Mutant embryos exhibit discernible cell death as early as 20 hours postfertilization, extensive apoptosis, and upward curly tail during the pharyngula period and deform around 5 days postfertilization. The stac mutant phenotype can be rescued by cenph mRNA overexpression and mimicked by cenph knockdown with antisense morpholinos, suggesting the responsibility of cenph deficiency for stac mutants. We demonstrate that the intrinsic apoptosis pathway is hyperactivated in stac mutants and that p53 knockdown partially blocks excess apoptosis in stac mutants. Mitotic cells in stac mutants show chromosome missegregation and are usually arrested in G(2)/M phase. Furthermore, compared with wild type siblings, heterozygous stac fish develop invasive tumors at a dramatically reduced rate, suggesting a reduced cancer risk. Taken together, our findings uncover an essential role of cenph in mitosis and embryonic development and its association with tumor development.

Centromere protein H is a novel prognostic marker for human nonsmall cell lung cancer progression and overall patient survival

BACKGROUND

Lung cancer is 1 of the leading causes of cancer death worldwide, and the high mortality from this disease is caused mainly by the lack of efficient diagnostic strategies for early-stage lung cancer. The objective of the current study was to investigate the expression pattern and clinicopathologic significance of centromere protein H (CENP-H) in patients with nonsmall cell lung cancer (NSCLC).

METHODS

The expression profile of CENP-H in normal lung epithelial cells, NSCLC cell lines, NSCLC tissues, and adjacent noncancerous lung tissues were detected by reverse transcription-polymerase chain reaction (RT-PCR), real-time RT-PCR, and Western blot analysis. The expression level of CENP-H in 223 NSCLC tissues was measured by immunohistochemistry staining. Statistical analysis was performed to evaluate the clinicopathologic significance of CENP-H.

RESULTS

The expression level of CENP-H was much higher in cancer cell lines and lung cancer tissues than that in normal cells and adjacent noncancerous lung tissues, respectively. Immunohistochemical analysis revealed positive CENP-H expression in 118 of 223 NSCLC tissues (52.9%). Statistical analysis revealed that CENP-H expression was correlated strongly with clinical stage (P=.018), tumor classification (P=.03), and Ki-67 expression (P < .001). Patients with lower CENP-H expression had better overall survival than patients with higher CENP-H expression. Further analysis suggested that CENP-H could predict prognosis only in patients with early-stage disease. Multivariate analysis suggested that CENP-H expression was an independent prognostic marker for survival in patients with NSCLC.

CONCLUSIONS

The current results demonstrated that high CENP-H protein expression was related to poor outcome in patients with NSCLC. CENP-H may be used as a prognostic biomarker for patients lung patients, especially those with early-stage NSCLC.

LINE retrotransposon RNA is an essential structural and functional epigenetic component of a core neocentromeric chromatin

We have previously identified and characterized the phenomenon of ectopic human centromeres, known as neocentromeres. Human neocentromeres form epigenetically at euchromatic chromosomal sites and are structurally and functionally similar to normal human centromeres. Recent studies have indicated that neocentromere formation provides a major mechanism for centromere repositioning, karyotype evolution, and speciation. Using a marker chromosome mardel(10) containing a neocentromere formed at the normal chromosomal 10q25 region, we have previously mapped a 330-kb CENP-A–binding domain and described an increased prevalence of L1 retrotransposons in the underlying DNA sequences of the CENP-A–binding clusters. Here, we investigated the potential role of the L1 retrotransposons in the regulation of neocentromere activity. Determination of the transcriptional activity of a panel of full-length L1s (FL-L1s) across a 6-Mb region spanning the 10q25 neocentromere chromatin identified one of the FL-L1 retrotransposons, designated FL-L1b and residing centrally within the CENP-A–binding clusters, to be transcriptionally active. We demonstrated the direct incorporation of the FL-L1b RNA transcripts into the CENP-A–associated chromatin. RNAi-mediated knockdown of the FL-L1b RNA transcripts led to a reduction in CENP-A binding and an impaired mitotic function of the 10q25 neocentromere. These results indicate that LINE retrotransposon RNA is a previously undescribed essential structural and functional component of the neocentromeric chromatin and that retrotransposable elements may serve as a critical epigenetic determinant in the chromatin remodelling events leading to neocentromere formation.

The centromere is an essential chromosomal structure for the correct segregation of chromosomes during cell division. Normal human centromeres comprise a 171-bp α-satellite DNA arranged into tandem and higher-order arrays. Neocentromeres are fully functional centromeres that form epigenetically on noncentromeric regions of the chromosomes, with recent evidence indicating an important role they play in centromere repositioning, karyotype evolution, and speciation. Neocentromeres contain fully definable DNA sequences and provide a tractable system for the molecular analysis of the centromere chromatin. Here, the authors investigate the role of epigenetic determinants in the regulation of neocentromere structure and function. They identify that a retrotransposable DNA element found within the neocentromere domain is actively transcribed and that the transcribed RNA is essential for the structural and functional integrity of the neocentromere. This study defines a previously undescribed epigenetic determinant that regulates the neocentromeric chromatin and provides insight into the mechanism of neocentromere formation and centromere repositioning.

Prognostic relevance of Centromere protein H expression in esophageal carcinoma

Background

Many kinetochore proteins have been shown to be associated with human cancers. The aim of the present study was to clarify the expression of Centromere protein H (CENP-H), one of the fundamental components of the human active kinetochore, in esophageal carcinoma and its correlation with clinicopathological features.

Methods

We examined the expression of CENP-H in immortalized esophageal epithelial cells as well as in esophageal carcinoma cells, and in 12 cases of esophageal carcinoma tissues and the paired normal esophageal tissues by RT-PCR and Western blot analysis. In addition, we analyzed CENP-H protein expression in 177 clinicopathologically characterized esophageal carcinoma cases by immunohistochemistry. Statistical analyses were applied to test for prognostic and diagnostic associations.

Results

The level of CENP-H mRNA and protein were higher in the immortalized cells, cancer cell lines and most cancer tissues than in normal control tissues. Immunohistochemistry showed that CENP-H was expressed in 127 of 171 ESCC cases (74.3%) and in 3 of 6 esophageal adenocarcinoma cases (50%). Statistical analysis of ESCC cases showed that there was a significant difference of CENP-H expression in patients categorized according to gender (P = 0.013), stage (P = 0.023) and T classification (P = 0.019). Patients with lower CENP-H expression had longer overall survival time than those with higher CENP-H expression. Multivariate analysis suggested that CENP-H expression was an independent prognostic marker for esophageal carcinoma patients. A prognostic value of CENP-H was also found in the subgroup of T3~T4 and N0 tumor classification.

Conclusion

Our results suggest that CENP-H protein is a valuable marker of esophageal carcinoma progression. CENP-H might be used as a valuable prognostic marker for esophageal carcinoma patients.