Introduction
Yes-associated protein 1 (
YAP1) expression and nuclear localization have been found to be increased in various cancers [
1−
4].
YAP1 is one of the most important effectors of the Hippo signaling pathway and is involved in crosstalk with other cancer-promoting pathways. The Hippo pathway plays a crucial role in organ size control and tissue regeneration [
5]. The roles of Hippo pathway dysregulation in tumorigenesis and cancer progression have been widely reported [
6]. As a potent oncogene activated in many cancers,
YAP1 has a negatively regulated downstream target in the Hippo signaling pathway and functions as a transcriptional coactivator involved in the regulation of cell growth, proliferation, and apoptosis [
2,
7−
9].
YAP1 plays a key role as a tumor suppressor in the Hippo signaling pathway and enhances gene transcription by binding to transcription factors [
10]. Specifically,
YAP1 contributes to cancer development by promoting malignant phenotypes, the expansion of cancer stem cells, and drug resistance of cancer cells.
YAP1 is considered a potent oncogene closely linked to the progression of several cancer types [
11,
12], and
YAP1 overexpression in cancer cell lines can also promote tumor growth [
13,
14]. Therefore,
YAP1 promotes tumorigenesis, but the underlying mechanisms by which
YAP1 exerts this effect require further exploration.
Telomeres are cellular nucleoprotein complexes, and their main function is to maintain chromosomal integrity and genomic stability [
15]. A telomere is a ribonucleoprotein complex composed of 2 main core subunits: telomerase reverse transcriptase (
TERT), which constitutes the catalytic subunit, and a functional telomerase RNA component (
TR or
TERC) that provides a template for telomerase elongation [
16]. A positive correlation between
TERT mRNA levels and telomerase activity has been reported, suggesting that telomerase is primarily regulated by
TERT expression [
17]. Telomerase is active in adult germ-line tissues, immortal cells [
18], and most malignant tumors [
19].
TERT induces stemness of cancer cells to promote metastasis and recurrence [
20]. In cancer cells, the upregulation of
TERT transcriptional activity has been reported [
21].
TERT overexpression has been detected in more than 80% to 90% of human cancers [
15]. Thus,
TERT overexpression may represent the mechanism by which cancer cells prevent telomere shortening and become immortal [
22]. Zhang et al. [
23] recently reported that
YAP1 regulates
TERT expression, and that hyperactivation of
YAP1 promotes telomerase activity and increases telomeric length, causing an increase in
TERT expression. They also showed that
TERT expression was positively correlated with
YAP1 activation in liver cancer tissues. Several studies have reported that
TERT overexpression contributes to cancer progression [
24]. Therefore,
YAP1 promotes
TERT expression, which may contribute to tumor progression [
25]. However, several studies have highlighted the importance of
TERC in cancer because of findings indicating that
TERC expression may be highly upregulated in a variety of cancers [
26−
30]. Although
TERC is associated with the development of several diseases, its underlying mechanisms in cancer are poorly understood. In addition, the correlation between the expression of
YAP1 and telomerase-associated genes in cancer has not been completely explored.
In the present study, we analyzed YAP1 expression in normal and different types of tumor tissues based on The Cancer Genome Atlas (TCGA) data using online databases and tools. We also evaluated the prognostic value of YAP1 expression its correlation with the expression of 2 major telomerase components (TERT and TERC) in various cancer types on the basis of TCGA data.
Materials and Methods
Gene Expression Profiling Interactive Analysis Database Analysis
The Gene Expression Profiling Interactive Analysis (GEPIA) database (
https://gepia.cancer-pku.cn/index.html), which is a web server tool consisting of 8,587 normal and 9,736 tumor tissue samples from the TCGA and GTEx projects [
31−
33], was used to analyze differences in
YAP1 expression between normal and tumor tissue based on RNA sequencing. We represented expression of the
YAP1 profile across various cancers and paired normal tissues. We also analyzed the survival curves, including overall survival (OS), which refers to the duration of patient survival from the date of disease treatment, and disease-free survival (DFS), which denotes relapse-free survival, according to
YAP1 gene expression by using the log-rank and Mantel-Cox tests for different cancer types via the GEPIA database.
PrognoScan Database Analysis
The PrognoScan database (
http://www.abren.net/PrognoScan/), a platform for evaluating potential tumor markers, is widely used to evaluate biological relationships between gene expression and patient prognosis such as OS and DFS [
34]. It includes a large-scale collection of publicly available cancer microarray datasets with clinical information. We used this PrognoScan database to analyze the prognostic value of
YAP1 in various cancers based on the hazard ratio (HR) and log-rank
p-values.
Tumor Immune Estimation Resource Database Analysis
The Tumor Immune Estimation Resource (TIMER) database (
https://cistrome.shinyapps.io/timer/) for systematic analysis was used to explore gene correlations in various cancers. The TIMER database consists of 10,897 samples across 32 cancer types from TCGA to estimate the relationship of cancer signaling pathway genes. Spearman correlation analysis of these samples was performed to determine the relationship between
YAP1 expression and telomerase (
TERT and
TERC) [
35].
Statistical Analysis
Gene expression data from the GEPIA were explored with online tools. Survival curves were generated with GEPIA and PrognoScan online tools. The correlations of gene expression were evaluated in the TIMER database using Spearman correlation analysis. All results are presented with p-values from the log-rank test. Statistical significance of the data (p-values) was provided by the program.
Results
mRNA Expression Levels of YAP1 in Various Types of Cancer
To determine differences in
YAP1 expression between tumor and normal tissue,
YAP1 expression in normal samples and multiple cancer types was analyzed using the GEPIA database. The mRNA expression levels of
YAP1 were higher in cholangiocarcinoma (CHOL), lymphoid neoplasm diffuse large B-cell lymphoma (DLBC), glioblastoma multiforme (GBM), pancreatic adenocarcinoma (PAAD), stomach adenocarcinoma, and thymoma (THYM) than in non-tumor tissues (
Figure 1A). However, the mRNA expression levels of
YAP1 were lower in adrenocortical carcinoma (ACC), bladder urothelial carcinoma (BLCA), cervical squamous cell carcinoma, pheochromocytoma and paraganglioma, uterine corpus endometrial carcinoma, and uterine carcinosarcoma than in non-tumor tissues (
Figure 1B). These results suggested that
YAP1 was differentially expressed between tissue samples of various cancers and non-tumor tissues.
Prognostic Significance of YAP1 Expression in Various Types of Cancer
We investigated whether
YAP1 expression was correlated with the prognosis in various cancer types. Therefore, the effect of
YAP1 expression on survival rates was evaluated using the GEPIA and PrognoScan databases. The OS rates of patients with different types of cancers that overexpressed or underexpressed
YAP1 were compared. The results revealed shorter OS with a worse prognosis in patients with high
YAP1 expression than in those with ACC (HR, 0.009;
p=0.006) and PAAD (HR, 0.006;
p=0.005) who had low
YAP1 expression (
Figure 2A,
B). Moreover, the DFS rates between patients with low and high
YAP1 expression were compared. High
YAP1 expression was associated with poorer DFS in patients with ACC (HR, 0.000;
p=0.000) and BLCA (HR, 0.037;
p=0.036) (
Figure 2C,
D). In other cancer types,
YAP1 did not have any prognostic value (Table S1). To further examine the prognostic potential of
YAP1 in different cancer types, we analyzed the PrognoScan database. The analysis indicated a worse prognosis in cancers of the bladder, brain, breast, colorectal, esophagus, and lung (Table S2). These results suggest that
YAP1 expression affects cancer prognosis.
Correlation between YAP1 Expression and Telomerase in Various Types of Cancer
To determine the correlation between
YAP1 expression and
TERT and
TERC, we analyzed the data included in the TIMER database. As shown in
Table 1, the analysis indicated
YAP1 expression was negatively correlated with
TERT in BLCA, breast invasive carcinoma (BRCA), CHOL, colon adenocarcinoma (COAD), brain lower grade glioma (LGG), lung adenocarcinoma (LUAD,), mesothelioma (MESO), prostate adenocarcinoma (PRAD), rectal adenocarcinoma (READ), sarcoma (SARC), testicular germ cell tumors (TGCT), thyroid carcinoma (THCA), and THYM. Moreover,
YAP1 expression was negatively correlated with
TERC in BLCA, BRCA, DLBC, GBM, head and neck squamous cell carcinoma (HNSC), LUAD, lung squamous cell carcinoma (LUSC), MESO, ovarian serous cystadenocarcinoma (OV), PRAD, READ, TGCT and THYM (
Table 2). However,
YAP1 expression was positively correlated with
TERT activity in OV and uveal melanoma (UVM). These results suggested that
YAP1 expression was correlated with
TERT and
TERC in different cancer types.
Discussion
In the past decade, previous studies have focused on determining
YAP1 expression to improve the understanding of its prognostic significance and potential effect on various cancer types.
YAP1 is a potent oncogene [
24], and its levels are frequently increased in many cancer types [
1,
14,
36−
38]. The expression and role of
YAP1 in cancer are cell type-dependent, and its expression may contribute to cancer development [
2,
6,
9,
39]. Upregulation of
YAP1 expression has been observed in multiple cancer types.
YAP1 overexpression has been reported in patients with hepatocellular carcinoma (HCC), colorectal cancers, LUAD, ovarian cancer, and prostate cancer [
2,
3,
14,
40]. These findings suggest the potential oncogenic role of
YAP1 in multiple cancer types.
Zhang et al. [
41] performed the immunohistochemical analyzes of primary esophageal squamous cell carcinoma tumor resection samples from patients, and reported that overexpression of
YAP1 was associated with tumor relative to adjacent tissue samples. In addition, Collak et al. [
42] identified overexpression of
YAP1 in nuclear and cytosolic of benign prostates using immunohistochemistry, whereas moderate expression of
YAP1 was found in cellular locations of prostate intraepithelial neoplasia and prostate cancer. These findings show differences in expression levels of
YAP1 across cancer tissue samples, and are consistent with those presented in this study.
In this study, we showed that the prognostic value of
YAP1 expression was significant in various cancer types. Importantly, our data provide evidence that
YAP1 expression is correlated with telomerase (
TERT and
TERC) expression in various cancer types. Previous studies have reported that
YAP1 is a prognostic marker for OS and DFS in HCC [
2].
YAP1 expression is a remarkable predictor of poor prognosis in HCC patients with negative keratin 19 cells [
9].
YAP1 expression has also been significantly correlated with a poor prognosis in OV [
6,
36,
43,
44]. However, our results showed that
YAP1 expression did not have a prognostic role in various cancers, including HCC and OSC, based on TCGA data. Interestingly, higher expression of
YAP1 predicted poorer OS in patients with ACC and PAAD, and poorer DFS in patients with ACC and BLCA. According to these results, we suggest that higher expression of
YAP1 may be significantly correlated to a poorer prognosis in various cancers.
Telomerase is active in adult germ-line tissues, immortal cells [
18], and most types of malignant tumors [
19]. It is upregulated during tumorigenesis through the transcriptional regulation of
TERT in up to 90% of cancers [
45−
48]. Upregulation of
TERC is an early event in tumorigenesis, and
TERC could be more closely correlated with tumor grade than telomerase activity or
TERT expression [
49−
55].
TERC activity is associated with cancer, but its underlying mechanisms are poorly understood. This is the first study to explore the correlations between
YAP1 expression and telomerase expression (
TERT and
TERC) in various cancer types. Our data indicated that
YAP1 expression was negatively correlated with
TERT in BLCA, BRCA, CHOL, COAD, LGG, MESO, PRAD, READ, SARC, TGCT, THCA, and THYM.
YAP1 expression was positively correlated with
TERT in OV and UVM, but negatively correlated with
TERC in BLCA, BRCA, DLBC, GBM, HNSC, LIHC, LUSC, MESO, OV, PRAD, READ, TGCT, and THYM. Our findings may suggest that
YAP1 expression affects
TERT and
TERC expression in different cancer types. However, further investigation should be performed to elucidate the potential role of
YAP1 and telomere-related gene expression, which may contribute to novel research and therapies for treating various cancer types. Our results indicate that
YAP1 expression is correlated with 2 major components of telomerase, and is associated with a poor prognosis in various cancer types.
In this study, we attempted to confirm the clinical value of YAP1 expression in various cancer types and its effect on telomerase. Although YAP1 expression was different in many cancer types, the detailed mechanism underlying YAP1 regulation should be established in future studies.
Article information
Ethics Approval
Not applicable.
Conflicts of Interest
The authors have no conflicts of interest to declare.
Funding
This research was supported by the National Research Foundation Grant funded by the Korean Government (NRF-2021R1C1C1003333 to HSJ).
Availability of Data
All data generated or analyzed during this study are included in this published article. Other data may be requested through the corresponding author.
Authors’ Contributions
Conceptualization: SJH, JK; Data curation: SJH, JK; Formal analysis: SJH, JK; Funding acquisition: SJH; Investigation: HRK, KY, CWS; Methodology: HRK, KY, CWS; Project administration: HRK, KY, CWS; Resources: HRK, KY, CWS; Software: HRK, KY, CWS; Supervision: HRK, KY, CWS; Validation: HRK, KY; Visualization: HRK, KY; Writing–original draft: all authors; Writing–review & editing: all authors.
