Uridine-cytidine kinase 2 (UCK2): A potential diagnostic and prognostic biomarker for lung cancer

Abstract

Lung cancer has the highest morbidity and mortality among all cancers. Discovery of early diagnostic and prognostic biomarkers of lung cancer can greatly facilitate the survival rate and reduce its mortality. In our study, by analyzing Gene Expression Omnibus and Oncomine databases, we found a novel potential oncogene uridine-cytidine kinase 2 (UCK2), which was overexpressed in lung tumor tissues compared to adjacent nontumor tissues or normal lung. Then we confirmed this finding in clinical samples. Specifically, UCK2 was identified as highly expressed in stage IA lung cancer with a high diagnostic accuracy (area under the receiver operating characteristic curve > 0.9). We also found that high UCK2 expression was related to poorer clinicopathological features, such as higher T stage and N stage and higher probability of early recurrence. Furthermore, we found that patients with high UCK2 expression had poorer first progression survival and overall survival than patients with low UCK2 expression. Univariate and multivariate Cox regression analyses showed that UCK2 was an independent risk factor related with worse DFS and OS. By gene set enrichment analysis, tumor-associated biological processes and signaling pathways were enriched in the UCK2 overexpression group, which indicated that UCK2 might play a vital role in lung cancer. Furthermore, in cytology experiments, we found that knockdown of UCK2 could suppress the proliferation and migration of lung cancer cells. In conclusion, our study indicated that UCK2 might be a potential early diagnostic and prognostic biomarker for lung cancer.

Keywords: biomarker; early diagnosis; lung cancer; prognosis; uridine-cytidine kinase 2.

Figure 1

Uridine‐cytidine kinase 2 (UCK2) was upregulated in various cancers. A, The Oncomine database was used to explore UCK2 expression in cancer and normal tissues. Two‐fold change, top 10% gene rank, and P value <.001 was set as the threshold. Red and blue indicates UCK2 upregulation and downregulation, respectively. B, 12 GEO datasets were used to explore UCK2 expression. Expression was transformed into log2 (probe intensities) and showed as the mean ± SE. *P < .05; ***P < .001

Figure 2

Uridine‐cytidine kinase 2 (UCK2) is overexpressed in lung cancer. A, Analysis of UCK2 expression in normal lung and non‐small cell lung cancer (NSCLC) in GSE33532. ****P < .0001, unpaired t test. B,C, Analysis of UCK2 expression in normal lung and different pathological subtypes of lung cancer in GSE30219. ***P < .001, one‐way ANOVA followed by Dunnett's test. D, Oncomine datasets showing UCK2 expression in lung cancer; red denotes significant overexpression. E,F, UCK2 mRNA expression in 37 lung cancer tissues and adjacent nontumor tissues were explored by real‐time PCR. ***P < .001. G, UCK2 mRNA expression in human bronchial epithelial cell BEAS‐2B and lung cancer cell lines. ***P < .001. H, UCK2 expression in lung cancer patients with and without tobacco smoking history. ****P < .0001. I, UCK2 expression in EGFR‐mutated and EGFR nonmutated lung cancer tissue. **P < .01; ****P < .0001. ADC, adenocarcinoma; BAS, basaloid; CARCI, carcinoid tumor; LCC, large cell carcinoma; LCNE, large cell neuroendocrine tumor; SCC, squamous cell carcinoma; SCLC, small cell lung cancer

Figure 3

Immunohistochemistry of lung cancer tissues. A,B, Representative images of lung cancer patients by immunohistochemistry (magnification, 100×; 200×). C, Total scores of lung cancer and adjacent nontumor tissues of adenocarcinoma (ADC) patients. D, Total score of lung cancer and adjacent nontumor tissues of squamous cell carcinoma (SCC) patients. E, Plot of the distribution of uridine‐cytidine kinase 2 (UCK2) expression in tumor tissues and adjacent nontumor tissues of ADC patients. F, Plot of the distribution of UCK2 expression in tumor tissues and adjacent non‐tumor tissues of SCC patients. G, Overall survival curves for ADC patients with high (n = 70) and low (n = 18) UCK2 expression. H, Overall survival curves for SCC patients with high (n = 63) and low (n = 11) UCK2 expression. ****P < .0001. IHC, immunohistochemistry

Figure 4

Diagnostic value of uridine‐cytidine kinase 2 (UCK2) in lung cancer. A,B, Receiver operating characteristic plots for all lung cancer patients in GSE33532 (A) and all lung cancer patients in GSE30219 (B). C,D, UCK2 expression in normal lung and stage IA lung cancer in GSE33532 (C) and GSE30219 (D). E,F, Stage IA lung cancer patients in GSE33532 (E) and GSE30219 (F). AUC, area under the receiver operating characteristic curve; NSCLC, non‐small cell lung cancer

Figure 5

Higher uridine‐cytidine kinase 2 (UCK2) expression predicted poorer first progression survival in lung cancer patients. A, All lung cancer patients (n = 982). B, Adenocarcinoma patients (n = 461). C, Squamous cell carcinoma patients (n = 141). D, AJCC T1N0M0 stage lung cancer patients (n = 50). HR, hazard ratio

Figure 6

Higher uridine‐cytidine kinase 2 (UCK2) expression predicted poorer overall survival in lung cancer patients. A, All lung cancer patients (n = 1926). B, Adenocarcinoma patients (n = 720). C, Squamous cell carcinoma patients (n = 524). D, AJCC T1N0M0 stage lung cancer patients (n = 244). HR, hazard ratio

Figure 7

Knockdown of uridine‐cytidine kinase 2 (UCK2) suppressed proliferation and migration of lung cancer cells. A, RT‐qPCR analysis of cells with UCK2 knockdown. B, Knockdown of UCK2 suppressed proliferation of lung cancer cells indicated by CCK‐8 assay. C,D, Knockdown of UCK2 suppressed migration of lung cancer cells as indicated by wound healing assays. **P < .01, ***P < .001. NC, normal control; OD, optical density

Figure 8

Uridine‐cytidine kinase 2 (UCK2) enriched cell cycle G₂/M checkpoint, DNA repair, mitotic spindle process, MTOR1 signaling, MYC, and E2F targets in lung cancer. The role of UCK2 in biological processes was investigated by gene set enrichment analysis on the GSE33532 dataset with functional gene set files (c5.all.v5.1.symbols.gmt). UCK2 high expression enriched (A) G₂/M checkpoint, (B) DNA repair, (C) mitotic spindle, (D) MTOR1 signaling, (E) MYC targets, (F) E2F targets. FDR, false discovery rate; NES, normal enrichment score