Significance of the expression of proliferation-associated nucleolar antigen p120 in human colorectal tumors

Human NOP2/NSUN1 regulates ribosome biogenesis through non-catalytic complex formation with box C/D snoRNPs

5-Methylcytosine (m⁵C) is a base modification broadly found on various RNAs in the human transcriptome. In eukaryotes, m⁵C is catalyzed by enzymes of the NSUN family composed of seven human members (NSUN1-7). NOP2/NSUN1 has been primarily characterized in budding yeast as an essential ribosome biogenesis factor required for the deposition of m⁵C on the 25S ribosomal RNA (rRNA). Although human NOP2/NSUN1 has been known to be an oncogene overexpressed in several types of cancer, its functions and substrates remain poorly characterized. Here, we used a miCLIP-seq approach to identify human NOP2/NSUN1 RNA substrates. Our analysis revealed that NOP2/NSUN1 catalyzes the deposition of m⁵C at position 4447 on the 28S rRNA. We also find that NOP2/NSUN1 binds to the 5′ETS region of the pre-rRNA transcript and regulates pre-rRNA processing through non-catalytic complex formation with box C/D snoRNAs. We provide evidence that NOP2/NSUN1 facilitates the recruitment of U3 and U8 snoRNAs to pre-90S ribosomal particles and their stable assembly into snoRNP complexes. Remarkably, expression of both WT and catalytically inactive NOP2/NSUN1 in knockdown background rescues the rRNA processing defects and the stable assembly of box C/D snoRNP complexes, suggesting that NOP2/NSUN1-mediated deposition of m⁵C on rRNA is not required for ribosome synthesis.

Upregulated expression of NOP2 predicts worse prognosis of gastric adenocarcinoma by promoting tumor growth

Background

: NOP2 nucleolar protein plays a crucial role in early embryo development and cell proliferation. The role of NOP2 in human gastric adenocarcinoma has not been elucidated. In the present study, we aimed to examine the expression levels of NOP2 and dissected whether NOP2 expression was associated with aggressive clinicopathological outcomes of patients with gastric adenocarcinoma.

Methods

: Clinicopathological analysis was performed in patients with gastric adenocarcinoma. Expression of NOP2 was tested by immunohistochemistry staining and quantitative RT-PCR. The prognostic role of NOP2 in gastric adenocarcinoma patients was assessed by univariate and multivariate analysis. The effect of NOP2 on cell proliferation was examined through cellular experiments and mice models.

Results

: NOP2 expression was elevated in gastric adenocarcinoma tissues compared to normal gastric tissues. High expression of NOP2 was significantly correlated with tumor size, invasion depth, and lymph node metastasis. Moreover, patients with high NOP2 expression had poorer overall survival, and NOP2 was identified as an independent prognosis factor. Using the gastric adenocarcinoma cells, we found that NOP2 can promote tumor cell proliferation both in vitro and in vivo.

Conclusions

: Overexpression of NOP2 significantly correlates with a poorer prognosis of gastric adenocarcinoma patients and suggested the potential of NOP2, which may serve as a novel prognostic biomarker in gastric adenocarcinoma.

Effect of NOP2 knockdown on colon cancer cell proliferation, migration, and invasion

Background

Proliferation-associated nucleolar protein p120 (NOP2) has been proven to be a promising tumor cell maker, but it has not been specifically studied in colon cancer. This study aims to investigate the role and action mechanism of NOP2 in colon cancer.

Methods

Fluorescence quantitative PCR and western blot assays were used to evaluate the expression of NOP2. NOP2 siRNA was transfected into HCT116, LOVO, and CCK-8 cells, and transwell assays were performed to evaluate the cell proliferation, migration, and invasion. Transcriptome sequencing of both the NOP2 knockdown and negative control (NC) groups was performed.

Results

NOP2 expression is significantly upregulated in colon cancer tissues and cells compared with that in the healthy controls. The proliferation, migration, and invasion of the colon cancer cells were significantly suppressed in the NOP2 knockdown group compared with those in the NC group (P<0.05). Transcriptome sequencing showed that ASMTL and C6orf52 were significantly downregulated, while MUC19, TXK, APOBEC2, and RBM44 were upregulated in both of the two NOP2 silenced colon cancer cells relative to those in the control. Gene Ontology (GO) analysis showed that NOP2 knockdown mainly induced differential expression of the genes involved in positive regulation of T cell-mediated cytotoxicity and thiamine metabolism. Kyoto Encyclopedia of Genes and Genomes analysis showed that the gene pathways most significantly affected by NOP2 knockdown were Cytokine-cytokine receptor interaction, Type I diabetes mellitus, Taste transduction, and Systemic lupus erythematosus.

Conclusions

NOP2 promotes proliferation, migration, and invasion of colon cancer cells, and the underlying mechanisms may be related to TXK tyrosine kinase.

The dynamic RNA modification 5-methylcytosine and its emerging role as an epitranscriptomic mark

It is a well‐known fact that RNA is the target of a plethora of modifications which currently amount to over a hundred. The vast majority of these modifications was observed in the two most abundant classes of RNA, rRNA and tRNA. With the recent advance in mapping technologies, modifications have been discovered also in mRNA and in less abundant non‐coding RNA species. These developments have sparked renewed interest in elucidating the nature and functions of those “epitransciptomic” modifications in RNA. N6‐methyladenosine (m⁶A) is the best understood and most frequent mark of mRNA with demonstrated functions ranging from pre‐mRNA processing, translation, miRNA biogenesis to mRNA decay. By contrast, much less research has been conducted on 5‐methylcytosine (m5C), which was detected in tRNAs and rRNAs and more recently in poly(A)RNAs. In this review, we discuss recent developments in the discovery of m5C RNA methylomes, the functions of m5C as well as the proteins installing, translating and manipulating this modification. Although our knowledge about m5C in RNA transcripts is just beginning to consolidate, it has become clear that cytosine methylation represents a powerful mechanistic strategy to regulate cellular processes on an epitranscriptomic level.

This article is categorized under:

RNA Processing > RNA Editing and Modification

RNA Interactions with Proteins and Other Molecules > Protein–RNA Interactions: Functional Implications

RNA Processing > tRNA Processing

RNA Turnover and Surveillance > Regulation of RNA Stability

Eukaryotic rRNA Modification by Yeast 5-Methylcytosine-Methyltransferases and Human Proliferation-Associated Antigen p120

Modified nucleotide 5-methylcytosine (m5C) is frequently present in various eukaryotic RNAs, including tRNAs, rRNAs and in other non-coding RNAs, as well as in mRNAs. RNA:m5C-methyltranferases (MTases) Nop2 from S. cerevisiae and human proliferation-associated nucleolar antigen p120 are both members of a protein family called Nop2/NSUN/NOL1. Protein p120 is well-known as a tumor marker which is over-expressed in various cancer tissues. Using a combination of RNA bisulfite sequencing and HPLC-MS/MS analysis, we demonstrated here that p120 displays an RNA:m5C- MTase activity, which restores m5C formation at position 2870 in domain V of 25S rRNA in a nop2Δ yeast strain. We also confirm that yeast proteins Nop2p and Rcm1p catalyze the formation of m5C in domains V and IV, respectively. In addition, we do not find any evidence of m5C residues in yeast 18S rRNA. We also performed functional complementation of Nop2-deficient yeasts by human p120 and studied the importance of different sequence and structural domains of Nop2 and p120 for yeast growth and m5C-MTase activity. Chimeric protein formed by Nop2 and p120 fragments revealed the importance of Nop2 N-terminal domain for correct protein localization and its cellular function. We also validated that the presence of Nop2, rather than the m5C modification in rRNA itself, is required for pre-rRNA processing. Our results corroborate that Nop2 belongs to the large family of pre-ribosomal proteins and possesses two related functions in pre-rRNA processing: as an essential factor for cleavages and m5C:RNA:modification. These results support the notion of quality control during ribosome synthesis by such modification enzymes.

Alterations of the apical junctional complex and actin cytoskeleton and their role in colorectal cancer progression

Colorectal cancer represents the fourth highest mortality rate among cancer types worldwide. An understanding of the molecular mechanisms that regulate their progression can prevents or reduces mortality due to this disease. Epithelial cells present an apical junctional complex connected to the actin cytoskeleton, which maintains the dynamic properties of this complex, tissue architecture and cell homeostasis. Several studies have indicated that apical junctional complex alterations and actin cytoskeleton disorganization play a critical role in epithelial cancer progression. However, few studies have examined the existence of an interrelation between these 2 components, particularly in colorectal cancer. This review discusses the recent progress toward elucidating the role of alterations of apical junctional complex constituents and of modifications of actin cytoskeleton organization and discusses how these events are interlinked to modulate cellular responses related to colorectal cancer progression toward successful metastasis.

Potential role of microsomal prostaglandin E synthase-1 in tumorigenesis

Microsomal prostaglandin E2 synthase-1 (mPGES-1) is a stimulus-inducible enzyme that functions downstream of cyclooxygenase (COX)-2 in the PGE2-biosynthetic pathway. Given the accumulating evidence that COX-2-derived PGE2 participates in the development of various tumors, including colorectal cancer, we herein examined the potential involvement of mPGES-1 in tumorigenesis. Immunohistochemical analyses demonstrated the expression of both COX-2 and mPGES-1 in human colon cancer tissues. HCA-7, a human colorectal adenocarcinoma cell line that displays COX-2- and PGE2-dependent proliferation, expressed both COX-2 and mPGES-1 constitutively. Treatment of HCA-7 cells with an mPGES-1 inhibitor or antisense oligonucleotide attenuated, whereas overexpression of mPGES-1 accelerated, PGE2 production and cell proliferation. Moreover, cotransfection of COX-2 and mPGES-1 into HEK293 cells resulted in cellular transformation manifested by colony formation in soft agar culture and tumor formation when implanted subcutaneously into nude mice. cDNA array analyses revealed that this mPGES-1-directed cellular transformation was accompanied by changes in the expression of a variety of genes related to proliferation, morphology, adhesion, and the cell cycle. These results collectively suggest that aberrant expression of mPGES-1 in combination with COX-2 can contribute to tumorigenesis.

Expression of nucleolar protein p120 predicts poor prognosis in patients with stage I lung adenocarcinoma

BACKGROUND

P120 is a proliferation-associated nucleolar protein found in most human malignant tumors, but not in resting normal cells. In our previous studies, the expression of p120 was statistically correlated with the proliferation capacity in human lung cancer cells and could be a prognostic marker for resected lung adenocarcinoma.

PATIENTS AND METHODS

The expression levels of p120 in tumors were assessed by immunohistochemistry in 59 patients with stage I lung adenocarcinoma who underwent radical resection. Using clinical follow-up data, the prognostic significance of p120 calculated by labeling indices was evaluated using Cox's proportional hazard model.

RESULTS

A mean +/- SD of the labeling index of p120 was 35.3+/-14.4%. No significant correlation was found between the expression levels of p120 and clinicopathological factors. Using a cutoff value of 35% in the labeling index of p120, patients with high expression of p120 experienced early recurrence and shorter survival compared with those having low expression of p120 (P = 0.04). Multivariate analysis revealed that p120 served as an independent and strongest prognostic factor for resected lung adenocarcinoma (P = 0.033).

CONCLUSION

This article provides the first evidence that the expression levels of p120 in tumor tissues can be used as an independent and powerful prognostic marker for resected stage I lung adenocarcinoma.

p120 expression provides a reliable indication of the rapidity of cell duplication in cancer cells independently of tumour origin

p120 is a nucleolar protein that has been immunocytochemically detected in rapidly proliferating cells of a variety of human malignancies. In the present study, the relationship between p120 expression and the rapidity of cell proliferation was evaluated in 48 human tumours of different origins. The cell proliferation rate of cancer cells was determined by quantitative analysis of AgNOR proteins. p120 immunostaining and AgNOR protein quantity were measured by image cytometry and a highly significant correlation was found between the two variables, as evaluated by linear regression analysis (r=0.98, p<0.0001). The relationship between p120 expression and the rapidity of cell duplication was also studied in vitro, in six human cancer cell lines derived from different tumour types, characterized by various doubling times (ranging from 20 to 77 h). p120 expression was determined on western blots using specific anti-p120 monoclonal antibodies. Densitometric analysis revealed a highly significant inverse correlation between the integrated optical density values of the chemoluminescence bands at 120 kD and the cell line doubling times (r=-0.93; p=0.007). The same result was obtained in situ by correlating p120 immunostaining of the cytological preparations obtained from the six cancer cell lines with the corresponding doubling time (r=-0.98, p<0.0001). These results indicate that in cancer cells, the quantitative expression of p120 is directly related to the rapidity of cell duplication, independently of the tumour origin.

Prognostic value of nucleolar protein p120 in patients with resected lung adenocarcinoma

PURPOSE

In this study we investigated the prognostic significance of proliferation-associated nucleolar protein p120 in primary resected lung adenocarcinoma because it reflects tumor growth fractions in vitro.

PATIENTS AND METHODS

Expression levels of p120 in tumors were assessed by immunohistochemistry in 74 patients who underwent radical resection. With clinical follow-up data, the prognostic significance of p120 calculated by labeling indices was evaluated using the Cox proportional hazards model.

RESULTS

p120 protein was clearly detected in nucleoli of adenocarcinoma cells. Its expression levels widely varied in each sample from 8.5% to 67. 2%, with a mean +/- SD of 35.2% +/- 15.1%. No significant correlation was found between expression levels of p120 and clinicopathologic factors. However, the expression levels of p120 were negatively correlated with the tumor doubling time calculated with retrospective chest roentgenograms. Using a cutoff value of 35% in the labeling index of p120, patients with high expression of p120 experienced early recurrence and shorter survival compared with those who had low expression of p120. Multivariate analysis showed that p120 served as an independent, as well as the strongest, prognostic factor for resected lung adenocarcinoma.

CONCLUSION

This report provides the first evidence that expression levels of p120 in tumor tissues can be used as an independent and powerful prognostic marker for resected lung adenocarcinoma.

The prognostic significance of proliferation-associated nucleolar protein p120 expression in prostate adenocarcinoma: a comparison with cyclins A and B1, Ki-67, proliferating cell nuclear antigen, and p34cdc2

BACKGROUND

In this study, the authors evaluated the prognostic significance of the expression of nucleolar antigen p120, along with other cell proliferation-associated proteins, in prostate adenocarcinomas (PACs) and compared the results with previously reported data on p34cdc2 cyclin-dependent kinase (p34 cdk).

METHODS

Archival sections from 132 PACs were immunostained with monoclonal antibodies against p120, cyclin A, cyclin B1, Ki-67, and proliferating cell nuclear antigen (PCNA). The DNA content of each tumor was determined by the Feulgen method using image analysis. The immunohistochemistry (IHC) results were correlated with tumor grade, stage, margin positivity, metastasis, ploidy, and postsurgical disease recurrence.

RESULTS

The overall positivity for the various proteins follows: p120, 36%; cyclin A, 35%; cyclin B1, 43%; Ki-67, 46%; and PCNA, 32%. p120 correlated with grade (P = 0.004), stage (P = 0.01), ploidy (P = 0.02), margin positivity (P = 0.03), and metastasis (P = 0.004). Cyclin B1 correlated with ploidy (P = 0.04) and grade (P = 0.05), Ki-67 with grade (P = 0.02) and margins (P = 0.03), and PCNA with grade (P = 0.01). Significant coexpression among these proteins was noted, as was a significant association between the expression of these markers and that previously reported for p34 cdk. In univariate analysis, p120 (P = 0.01), cyclin A (P = 0.01) and p34 cdk (P = 0.002) correlated with disease recurrence. In multivariate analysis of all these proteins, only p34 cdk independently predicted postsurgical recurrence (P = 0.05).

CONCLUSIONS

Nucleolar antigen p120 expression appears to be an additional marker of aggressiveness in PACs. The significant coexpression of the various cell cycle regulatory proteins support their collective role in tumor cell proliferation, with p34 cdk positivity being an independent predictor of postsurgical recurrence.