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Research Article: Observational Study

Adenylate kinase 7 is a prognostic indicator of overall survival in ovarian cancer

Zhang, Xue-ying PhDa; Zhou, Li-li PhDb; Jiao, Yan PhDc; Li, Yan-qing PhDd; Guan, Yi-nuo PhDe; Zhao, Yue-chen PhDf; Zheng, Lian-wen PhDa,∗

Editor(s): Wane., Daryle

Author Information
doi: 10.1097/MD.0000000000024134
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1 Introduction

Ovarian cancer (OC) is 1 of the 3 most common gynecological tumors in women. It is the fifth most common cause of cancer death in women worldwide.[1] The prodromal manifestations of OC are always nonspecific, which makes it difficult to distinguish from other carcinomatosis.[2] Additionally, the current screening strategies for the diagnosis of early-stage OC, including transvaginal ultrasound, computed tomography, detection of tumor marker CA125, and detection of BRCA gene mutation, are apparently ineffective in reducing the mortality rate of OC.[2,3] Consequently, early stage diagnosis of OC is uncommon leading to a poor prognosis with a 5-year OS rate of < 30%.[4,5] Thus, there is an urgent requirement to detect a biomarker for tumor prognosis.

The mechanism of pathogenesis of OC is complex. Recently, a study found that the ciliated epithelial cells in the fallopian tube underwent periodic proliferation and differentiation during the menstrual cycle, which could be 1 of the mechanisms involved in the pathogenesis of OC.[6] In recent years, researchers have become interested in the role of cilia in various human diseases, including tumorigenesis. It has been shown that primary cilia are involved in cell-cycle regulation and further implicated in tumor progression.[7,8] Adenylate kinase 7 (AK7), a cytosolic isoform of adenylate kinase (AK) isoenzymes located on chromosome 14q32, is known to have a tissue-restricted expression pattern and is expressed in cilia-rich tissues in the epithelium.[9]

However, there is no direct evidence showing an association between AK7 and tumor progression and prognosis, possibly via the regulation of cilia function. In this study, we retrospectively analyzed the data from The Cancer Genome Atlas (TCGA) cohort and assessed the correlation between AK7 levels and clinicopathological symptoms of OC to evaluate the prognostic value (PV) of AK7 in OC. We also performed GSEA to explore relevant signaling pathways.

2 Materials and methods

2.1 Data extraction from the TCGA database

We extracted cancerous ovarian tissues (n = 308; OC group) and normal ovarian tissues (n = 88; CON group) from the TCGA database to determine AK7 levels and the PV by RNAseq (Illumina HiSeq). The high and low AK7 expression groups were classified based on the median value of AK7.

2.2 Statistical analysis

Statistical analysis was performed using R software (version 3.5.2). The c2 test assessed the correlation between AK7 levels and the clinical symptoms of OC. Kaplan–Meier curve was used to compare the OS between the AK7 expression groups. The independent PV of AK7 in OC was determined via Cox regression analyses. A value of P < .05 implied statistical significance.

GSEA. In GSEA, target genes are ranked according to predetermined gene sets based on the differential expression between the 2 sample groups, followed by the assessment of the position of the predetermined gene sets in the sorting table.[10] Here, we used GSEA 3.0 for patient data analysis. Permutation analysis was done to obtain normalized enrichment score (NES).

2.3 Ethics approval

This study did not require ethics approval since all clinical data were from public databases.

3 Results

3.1 Patient characteristics

Table 1 shows the demographic, clinical symptoms, and gene expression data of patients in the OC group.

Table 1 - Demographic and clinical characteristics of TCGA cohort.
Characteristics Numbers of cases
 <55 113 (36.69)
 >=55 195 (63.31)
 NA 17 (5.52)
 Bilateral 212 (68.83)
 Left 37 (12.01)
 Right 42 (13.64)
 NA 2 (0.65)
 I 1 (0.32)
 II 22 (7.14)
 III 245 (79.55)
 IV 38 (12.34)
Longest dimension
 Large 124 (46.1)
 Small 145 (53.9)
Lymphatic invasion
 NA 180 (58.44)
 NO 44 (14.29)
 YES 84 (27.27)
Histologic grade
 NA 2 (0.65)
 G1 1 (0.32)
 G2 37 (12.01)
 G3 261 (84.74)
 G4 1 (0.32)
 GB 2 (0.65)
 GX 4 (1.3)
New type
 NA 145 (47.08)
 Locoregional 4 (1.3)
 Metastatic 1 (0.32)
 Progression 12 (3.9)
 Recurrence 146 (47.4)
Sample type
 Primary Tumor 303 (98.38)
 Recurrent Tumor 5 (1.62)
Vital status
 Deceased 184 (59.74)
 Living 124 (40.26)
 High 154 (50)
 Low 154 (50)
NA = not available, AK7 = Adenylate kinase, TCGA = the Cancer Genome Atlas.

3.2 AK7 expression and association with clinicopathological variables

We found a substantially downregulated AK7 levels in the OC group than the CON group (P < .05). Furthermore, there was a marked difference in AK7 levels based on patient age (Fig. 1). Patients with OC were classified into high and low AK7 expression groups. Table 2 describes their clinicopathological parameters and OS. We found that low AK7 levels were correlated with patient age (P = .0093).

Figure 1
Figure 1:
AK7 expression in OC. Boxplots show the difference in AK7 expression grouped by stage, histological grade, new type, vital status, subdivision, lymphatic invasion, and patient age. AK7 = adenylate kinase 7.
Table 2 - Association of AK7 mRNA expression in ovarian cancer tissues with clinicopathologic variables.
AK7 mRNA expression
Parameter Variable N High % Low % χ2 P value
Age <55 113 68 (44.16) 45 (29.22) 6.7652 .0093
>=55 195 86 (55.84) 109 (70.78)
Subdivision Bilateral 212 111 (74.5) 101 (71.13) 4.0109 .1346
Left 37 22 (14.77) 15 (10.56)
Right 42 16 (10.74) 26 (18.31)
Stage I 1 1 (0.65) 0 (0) 2.2183 .5284
II 22 12 (7.79) 10 (6.58)
III 245 125 (81.17) 120 (78.95)
IV 38 16 (10.39) 22 (14.47)
Longest dimension Large 124 60 (43.8) 64 (48.48) 0.4212 .5164
Small 145 77 (56.2) 68 (51.52)
Lymphatic invasion No 44 18 (27.27) 26 (41.94) 2.4315 .1189
Yes 84 48 (72.73) 36 (58.06)
Histologic grade G1 1 0 (0) 1 (0.66) 5.5678 .3506
G2 37 24 (15.58) 13 (8.55)
G3 261 126 (81.82) 135 (88.82)
G4 1 1 (0.65) 0 (0)
GB 2 1 (0.65) 1 (0.66)
GX 4 2 (1.3) 2 (1.32)
New type Locoregional 4 4 (4.82) 0 (0) 5.3073 .1506
Metastatic 1 0 (0) 1 (1.25)
Progression 12 5 (6.02) 7 (8.75)
Recurrence 146 74 (89.16) 72 (90)
Sample type Primary Tumor 303 151 (98.05) 152 (98.7) 0 1
Recurrent Tumor 5 3 (1.95) 2 (1.3)
Vital status Deceased 184 92 (59.74) 92 (59.74) 0 1
Living 124 62 (40.26) 62 (40.26)
AK7 = Adenylate kinase 7, N = number.

3.3 Low AK7 expression as an independent prognostic factor for poor OS

Low AK7 levels were related to poor OS (P = .019; Fig. 2), especially in those with late-stage OC (P = .014) but not early-stage OC (P = .62); G3/G4 grade (P = .011) but not G1/G2 grade (P = .97); old age (P = .018) but not young age (P = .83; Fig. 2). The results of the univariate analysis showed that patient age and AK7 levels were related to poor OS (Table 3). Further multivariate analysis estimated the independent PV of low AK7 levels for poor OS of OC (HR: 1.34, 95% CI: 1-1.8, P = .048; Table 3).

Figure 2
Figure 2:
The PV of AK7 in patients with OC. Kaplan-Meier curves for the survival of patients with OC based on AK7 expression in cancerous ovarian tissues. AK7 = adenylate kinase 7.
Table 3 - Univariate and multivariate analyses of overall survival in patients with ovarian cancer.
Univariate analysis Multivariate analysis
Parameters Hazard Ratio CI 95 P value Hazard Ratio CI 95 P value
Age 1.63 1.19–2.24 .003 1.57 1.14–2.16 .005
Subdivision 0.84 0.67–1.04 .101
Stage 1.09 0.8–1.5 .581
Longest dimension 1.12 0.82–1.52 .485
Lymphatic invasion 1.02 0.85–1.23 .798
Histologic grade 1.12 0.88–1.42 .349
New type 0.99 0.63–1.55 .951
Sample type 0.43 0.11–1.73 .235
AK7 1.41 1.06–1.89 .02 1.34 1–1.8 .048
AK7 = adenylate kinase 7.

3.4 AK7-related signaling pathway

The results of GSEA showed a marked difference in the enrichment of MSigDB Collection (NOM P < .05; Table 4). The essential signaling pathways, including EMT, apical junction, TGF-b signaling, UV response, and myogenesis, were chosen based on NES. These signaling pathways were all enriched in low AK7 expression phenotype (Table 4 and Fig. 3).

Table 4 - GSEA enrichment plot in low ABCB9 phenotype.
Gene set ES NES NOM P-value
HALLMARK_epithelial mesenchymal transition 0.64390194 1.8245728 .019880716
HALLMARK_UV response 0.41891807 1.5772356 .029940119
HALLMARK_TGF-beta signaling 0.48144048 1.5725749 .03952569
HALLMARK_myogenesis 0.43896723 1.5351363 .043052837
HALLMARK_apical junction 0.3967964 1.5181613 .042
ES = enrichment score, NES = normalized enrichment score, NOM = nominal.

Figure 3
Figure 3:
Enrichment plots from gene set enrichment analysis.

4 Discussion

Several complex factors interact to influence the pathogenesis and progression of OC, including genetic factors, reproductive factors, environmental factors, and so on.[11] Among these pathogenic factors, cilia were found to be involved in ovarian tumorigenesis. Cilia are sensory and motor organelles extending from the cellular surface and have long been considered as a degraded organelle.[12] Accumulating evidence has shown that primary cilia structure dysfunction may cause a series of multisystemic developmental disorders known as ciliopathies and multifactorial human diseases, including cancer.[13,14] It has been shown that primary cilia have a dual role in regulating tumorigenesis, whereas the loss of primary cilia and abnormally activated cilia regulation of hedgehog signaling pathway has been associated with the progression and prognosis of various tumors, including pancreas, breast, prostate, ovarian cancer, and so on.[15–17] Shpak performed bioinformatics analysis to study the gene expression patterns of cilia in OC and identified 354 cilia genes abnormally expressed in OC tissues, indicating an important role of ciliary disruption in the development of OC.[14] However, there is still a lack of in vivo experimental data to verify this hypothesis.

The maintenance of proper cilia structure and function requires ATP hydrolysis, which is done by the AK family.[9] Based on recent studies, AK7, a cytosolic human AK isoform, was found to be associated with ciliary homeostasis. The mutation of AK7 in primary ciliary dyskinesia (PCD) was found in both humans and murine species.[18,19] However, there is still a lack of research on the association between AK7 and human cancer. It has been speculated that ciliary dysfunction mediates the effects of AK7 on the genesis, progress, and prognosis of different types of cancer, including OC.

Here, we detected a substantially downregulated expression of AK7 in cancerous ovarian tissues than with normal ovarian tissues, which was also associated with patient age based on the analysis of high and low AK7 groups. Milara identified a downregulated AK7 expression at both RNA and protein levels and found that it was associated with PCD.[18] Consistently, Angeles observed the phenotypes of PCD in AK7-deficient mice.[19] These findings are consistent with our hypothesis that lower AK7 expression may cause ciliary structure disorder or dysfunction, further affecting the progression and prognosis of OC.

Also, patients who expressed lower levels of AK7 in OC tissues were more prone to have a poorer prognosis, particularly those with late-stage disease, G3/G4 grade, and old age. Also, late-stage diagnosis is related to a poor prognosis. Thus, AK7 might act as a novel indicator of OC prognosis. Moreover, the onset age of epithelial ovarian cancer, the most common and malignant type of OC, was 62 years and older patients with lower AK7 levels had a worse prognosis, suggesting a valuable role of AK7 in the diagnosis of epithelial ovarian cancer.[2] Cox regression analysis revealed that low AK7 levels had a significant PV in patients with OC.

Our investigations are focused on the identification of novel biomarkers of cancers to track their onset and development. This is the first study to detect a relationship between AK7 levels and OS in patients with OC. The results of our study have shown that downregulated AK7 levels are related to poor OS in OC and has an independent PV in OC. These results provide a new insight that AK7 plays a valuable role in the prognosis of OC, which might be mediated by ciliary structure disorder and function and lays a foundation for further investigation.

Author contributions

Conceptualization: XZ, LZ.

Data curation: LZ, YL.

Formal analysis: XZ, YJ.

Funding acquisition: LZ.

Investigation: LZ, XZ, YJ, ZY.

Methodology: YL, YJ.

Project administration: XZ, YL.

Resources: YL, ZY, YG, YZ.

Software: YJ.

Supervision: YZ.

Validation: YZ, YG.

Visualization: ZY, YG.

Writing – original draft: XZ.

Writing – review & editing: LZ.


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adenylate kinase 7; ovarian cancer; prognosis; the Cancer Genome Atlas

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