Expression of ubiquitin-conjugating enzyme E2T in colorectal cancers and clinical implications

Abstract

Ubiquitin-conjugating enzyme E2T (UBE2T) plays a significant role in carcinogenesis. Previous studies have demonstrated that UBE2T promotes the development and progression of numerous types of cancer. However, the association between UBE2T expression and colorectal cancer (CRC) remains unclear. In the present study, UBE2T protein expression was examined in the tissues of patients with CRC via immunohistochemistry. In addition, UBE2T expression data and corresponding clinical information were obtained from The Cancer Genome Atlas (TCGA). In the clinical samples, the associations between UBE2T expression and clinicopathological factors were evaluated by the χ² or Fisher's exact tests. In TCGA data, associations between UBE2T expression and clinical characteristics were evaluated using a logistic regression model. Overall survival was analyzed using Kaplan-Meier and Cox regression analyses. Reverse transcription-quantitative PCR (RT-qPCR) and western blotting assays were used to examine UBE2T expression in normal and CRC cell lines. Gene set enrichment analysis (GSEA) was performed on the dataset from TCGA. UBE2T protein was highly expressed in the cytoplasm of tumor cells in 29/50 clinical samples, whereas in the adjacent normal tissues, it was only highly expressed in 2/50 samples. Furthermore, UBE2T expression was associated with the N classification (P<0.001), clinical TNM stage (P<0.001) and histological grade of tumors (P=0.010). Survival analysis showed an association between high UBE2T expression and poor survival rate in patients with CRC (P=0.002). Cox regression analysis also revealed that UBE2T expression was an independent prognostic factor for these patients (P=0.006). RT-qPCR and western blotting showed that UBE2T was expressed in CRC cell lines at higher levels than that in a normal colon cell line. Analysis of TCGA data revealed that UBE2T was highly expressed in tumor samples compared with normal samples, but was not associated with prognosis. GSEA showed that high expression of UBE2T was associated with the Kyoto Encyclopedia of Genes and Genomes pathways 'cell cycle', 'oxidative phosphorylation', 'DNA replication', 'p53 signaling pathway', 'ubiquitin mediated proteolysis' and 'pentose phosphate pathway'. These results indicate that UBE2T may play an important role in the progression of CRC and serve as a potential prognostic factor during the treatment of cancer.

Keywords: colorectal cancer; prognosis; ubiquitin-conjugating enzyme E2T; ubiquitination.

Figure 1.

UBE2T protein expression in colorectal cancer and adjacent normal tissue samples examined by immunohistochemistry. UBE2T expression at different invasion depths is shown. Scale bar, 250 µm (magnification, ×200). UBE2T, ubiquitin-conjugating enzyme E2T; T1-T4, tumor invasion depth.

Figure 2.

Kaplan-Meier survival curves for 50 patients with colorectal cancer according to UBE2T protein expression in tumor tissue. There was a significant difference in survival between patients with low and high expression of UBE2T. UBE2T, ubiquitin-conjugating enzyme E2.

Figure 3.

UBE2T expression in CRC and normal colorectal cell lines. (A) Reverse transcription-quantitative PCR analysis of UBE2T mRNA expression and (B) western blotting and densitometric analysis of UBE2T protein expression in various human CRC cell lines and one normal colorectal cell line. GAPDH was used as an internal control. Data are presented as the mean ± SD (n=3). **P<0.01, ***P<0.001 and ****P<0.0001 vs. NCM460. UBE2T, ubiquitin-conjugating enzyme E2T; CRC, colorectal cancer.

Figure 4.

UBE2T expression in colorectal cancer based on TCGA data. (A) UBE2T expression in 568 tumor and 44 normal tissues from TCGA database. (B) UBE2T expression in 44 paired tumor and normal tissues from TCGA database. UBE2T, ubiquitin-conjugating enzyme E2T; TCGA, The Cancer Genome Atlas.

Figure 5.

Gene set enrichment analysis of ubiquitin-conjugating enzyme E2T expression. KEGG, Kyoto Encyclopedia of Genes and Genomes.