Original contributionExpression of the ribosomal proteins Rplp0, Rplp1, and Rplp2 in gynecologic tumors☆
Introduction
Ribosomes are molecular complexes composed of ribosomal RNA and specific proteins known as ribosomal proteins (RPs). An RP is any protein that, in conjunction with the ribosomal RNA (rRNA), makes up the ribosomal subunits involved in translation. Approximately 80 RPs have been described in human cells [1]. It is believed that RPs stabilize specific rRNA structures in mature ribosomal subunits and promote the correct folding of the rRNAs during ribosomal assembly to keep up with the metabolic activities of the cell and the demand for ribosomes.
Most RPs have been classified into subgroups based on their promoter structure, encoded amino acids, and expression profiles [2]. For several decades, protein synthesis has been assumed to be the only function of RPs [3]. Recently, however, it has been suggested that RPs provide a unified control mechanism for transcription and translation, apart from their ribosomal functions. Many RPs may function as transcription factors, as they often contain specific motifs that allow them to bind to both RNA and DNA [4]. RPs have demonstrated great heterogeneity and individual characteristics, as illustrated by their tissue specificity and control by different regulators [2]. Furthermore, a growing number of various secondary functions, besides protein synthesis, have been identified for RPs, including the induction of proliferation, apoptosis, and tumorigenesis [5], [6]. The importance of ribosome function and translational control in tumor progression has been illustrated by studies describing the regulation of ribosome production and the initiation of protein translation by several oncogenes (eg, myc and Hdm2) and tumor suppressors genes (eg, PTEN, pRB, and p53) [7], [8], [9]. Importantly, RP genes have been identified in screens for differentially expressed messenger RNAs (mRNAs) in human disorders, particularly in genetic diseases and cancer [10], [11]. In addition, RP gene mutations have been detected in many genetic diseases, some of which are cancer-related, such as Diamond-Blackfan anemia syndrome, Turner syndrome, Noonan syndrome, Camurati-Engelmann disease, and Bardet-Biedl syndrome [12], [13]. Moreover, high expression levels of a large number of RPs have been detected in human tumors [14]. However, recent investigations have revealed that a general increase in the expression of all RPs is not a hallmark of cancer. Specifically, the expression of some RPs has been shown to be significantly enhanced in tumors (eg, S3, S11, L7, L18, L37, Rplp0, and S6), whereas the expression of other RPs has been shown to be decreased in cancer (eg, S12, S24, L32, and L35a) [11], [15], [16], [17]. Furthermore, the expression level of some RPs is increased in some types of cancer and unchanged in others [18]. Therefore, it is arbitrary and unwise to assume that increased RP mRNA levels are simply a consequence of the high proliferation rate of tumor cells [19].
Interestingly, we have recently identified the RP Rplp1 in a genetic screen for immortalizing genes in primary cells [20]. Our interest in Rplp1 comes not only from its ability to induce immortalization in primary cells but also from its ability to transform previously immortalized cell lines. Rplp1 belongs to a group of acidic RPs termed P proteins, which also includes Rplp0 and Rplp2. P proteins are unique and specific in comparison with the other RPs [2]. Human ribosomal P proteins preferentially form Rplp1-Rplp2 heterodimers that attach to Rplp0 through the Rplp1 protein [21]. The interaction between Rplp1 and Rplp2 that generates the Rplp1-Rplp2 heterodimer seems to be the crucial step in the efficient assembly of the functional GTPase-associated center of the ribosome. P proteins are strongly expressed in normal lymph nodes, skin, spleen, and fetal brain tissue, expressed at lower levels in normal lung, bladder, and placenta, and not expressed in normal colon, kidney, and bone marrow [2]. The role of P proteins in several immune-mediated diseases has also been established. Autoantibodies against the P proteins are detectable in systemic lupus erythematosus, severe hepatitis, and nephritis [21], [22]. Studies have suggested that the P proteins may be considered an important factor for clinical diagnosis and evaluation of disease activity for these diseases [23]. Furthermore, the inhibition of Rplp1 and Rplp2 can result in a decrease in the proliferation rate in several cancer cell types, suggesting that P proteins can play a role in proliferation [24], [25]. Of particular interest, Rplp1 was one of the 17 mRNAs found to be up-regulated in tumor tissue in a global gene expression profile [26]. However, the protein level expression of P proteins in human tumors and their involvement in cancer have not yet been explored.
Endometrial cancer is one of the most common gynecologic cancers, and its incidence rate has been increasing [27]. This cancer is frequently diagnosed at an early stage, and the disease related-death rate has remained very low for decades [28]. In contrast, approximately 75% of the ovarian cancer cases are diagnosed in the advanced stages, and the disease has a fairly poor prognosis [29].
In the present investigation, we mainly focused on P protein expression in gynecologic malignancies but also in other cancer types. To our knowledge, this is the first study demonstrating that Rplp0, Rplp1, and Rplp2 are specifically up-regulated at the protein level in a high percentage of tumor tissues. Importantly, our results suggest that P proteins are involved in human cancer and may be useful as prognosis markers in specific subtypes of gynecologic carcinomas.
Section snippets
mRNA extraction and reverse transcriptase polymerase chain reaction
Normal and tumor tissue from 18 patients with endometrial cancers were randomly selected from the Tumor Bank at the Pathology Department of Vall d'Hebron Hospital (Barcelona, Spain). Biopsied samples stored at the bank are routinely collected, snap frozen, and stored at −80°C immediately after surgery. In addition, 6 patients diagnosed with benign endometrial tissue, 8 patients with ovarian tumors, 21 patients with colon carcinoma, and 11 patients with kidney cancer were also selected for our
Expression of Rplp0, Rplp1, and Rplp2 mRNA
The mRNA expression levels of Rplp0, Rplp1, and Rplp2 were examined in 18 patients diagnosed with endometrial carcinoma. The expression of Rplp0, Rplp1, and Rplp2 was significantly up-regulated in 22% (4/18; P = .03), 27% (5/18; P = .002), and 27% (5/18; P = .01) of the tumors, respectively, compared with normal tissues from the same patient (Fig. 1A-C). Importantly, in most patients, the increased expression of the mRNAs for each RP occurred simultaneously. In some patients, the 3 mRNAs
Discussion
The RP genes are considered essential, and genetic defects in these genes could cause serious problems in the translational apparatus. Because some RPs have been shown to play a role in apoptosis, proliferation, and/or tumorigenesis, RPs may function as oncogenes or tumor suppressor genes [7]. However, only a few reports have examined the correlation between the expression of RPs at the protein level and human cancer, possibly due to the lack of antibodies against most RPs. One of these reports
Acknowledgments
We thank T. Moline and R. Somoza for their technical assistance. We also thank the Tumor Bank of the Pathology Department (Hospital Vall d'Hebron) for providing the tumor samples analyzed. We are very grateful to Dr García-Ballesta for providing the P protein antibody and to J.A. Leal for preparing the manuscript.
References (40)
- et al.
A complete map of the human ribosomal protein genes: assignment of 80 genes to the cytogenetic map and implications for human disorders
Genomics
(2001) Extraribosomal functions of ribosomal proteins
Trends Biochem Sci
(1996)- et al.
Ribosomal protein S9 is a novel B23/NPM-binding protein required for normal cell proliferation
J Biol Chem
(2008) - et al.
Regulation of p53 translation and induction after DNA damage by ribosomal protein L26 and nucleolin
Cell
(2005) - et al.
Ribosomal stress couples the unfolded protein response to p53-dependent cell cycle arrest
J Biol Chem
(2006) - et al.
Abnormalities of the large ribosomal subunit protein, Rpl35a, in Diamond-Blackfan anemia
Blood
(2008) - et al.
Ribosomal protein L5 and l11 mutations are associated with cleft palate and abnormal thumbs in Diamond-Blackfan anemia patients
Am J Hum Genet
(2008) - et al.
Rplp1 bypasses replicative senescence and contributes to transformation
Exp Cell Res
(2009) The acidic ribosomal P proteins
Int J Biochem Cell Biol
(2002)- et al.
Evaluation of assays for the detection of autoantibodies to the ribosomal P proteins
Clin Immunol
(2000)
Surgical stage I endometrial cancer: predictors of distant failure and death
Gynecol Oncol
Amplification of tissue by construction of tissue microarrays
Exp Mol Pathol
Prognostic significance of p53 mutation in suboptimally resected advanced ovarian carcinoma treated with the combination chemotherapy of paclitaxel and carboplatin
Cancer Lett
Associations between p53 overexpression and multiple measures of clinical outcome in high-risk, early stage or suboptimally-resected, advanced stage epithelial ovarian cancers. A Gynecologic Oncology Group study
Gynecol Oncol
The multifunctional nucleolus
Nat Rev Mol Cell Biol
Characteristics and clustering of human ribosomal protein genes
BMC Genomics
Involvement of ribosomal proteins in regulating cell growth and apoptosis: translational modulation or recruitment for extraribosomal activity?
Immunol Cell Biol
Inhibition of HDM2 and activation of p53 by ribosomal protein L23
Mol Cell Biol
Does the ribosome translate cancer?
Nat Rev Cancer
Loss-of-function genetic screening identifies a cluster of ribosomal proteins regulating p53 function
Carcinogenesis
Cited by (64)
Identification of a novel alternatively spliced isoform of the ribosomal uL10 protein
2023, Biochimica et Biophysica Acta - Gene Regulatory MechanismsTargeting the nucleolus as a therapeutic strategy in human disease
2023, Trends in Biochemical SciencesExtra-Ribosome Functions of Ribosomal Proteins
2022, Encyclopedia of Cell Biology: Volume 1-6, Second EditionCellular molecular and proteomic profiling deciphers the SIRT1 controlled cell death pathways in esophageal adenocarcinoma cells
2021, Cancer Treatment and Research CommunicationsCitation Excerpt :For example, 60S acidic ribosomal protein PO was upregulated. This entity has been reported to be overexpressed in gynecological tumors [42]. In hepatocellular carcinoma, it was observed that when EZH2, which is involved in controlling cell proliferation was downregulated, this protein was upregulated [43].
- ☆
This research was supported by Marató TV3 Grant 052130-TV3 (Matilde E. LLeonart). Matilde E. LLeonart is a Fondo de Investigación Sanitario investigator (CP03/00101).
- 1
Both authors have contributed equally to this work.