cTnI is a structural protein in the contractile apparatus of myocardial cells. It has been demonstrated to be one of the most specific and sensitive biomarkers for myocardial injury. Its measurement can also serve as a valid diagnostic tool for clinical screening, early identification, timely assessment and monitoring of cardiotoxicity induced by chemo-, radio-, or immuno-therapy for cancer sufferers (22–24). This is the most reported association between cancer and cTnI. Although cTnI has been reported to present abnormal expression in non-small cell lung cancer tissues and human carcinoma cells (14), its roles in cancers are still unknown. Previously, we demonstrated that cTnI is located in nucleus in adult mouse and human fetal hearts, and found it is associated with the regulation of genes such as PDEs, PGC-1a, ND5 and ATP2A2 (20, 25, 26). This provides new directions for us to have a closer understanding of the role of gene TNNI3.
KIRP is the second most common kidney cancer following clear cell renal cell carcinoma, and ranks second in terms of morbidity rate. KIRP patients, however, are often excluded from molecular investigation due to limited number of cases (27). Therefore, there is indeed an urgency to identify effective diagnostic and prognostic biomarkers for improving survival outcomes of KIRP patients. In the present study, we revealed that the expression of TNNI3 extremely increased in KIRP samples as opposed to normal samples from TCGA datasets. As a result, the KIRP patients were classified into TNNI3-low and TNNI3-high groups. Although we did not found TNNI3 was directly related to survival outcomes in the KIRP patients, we demonstrated the expression of TNNI3-related genes were closely associated with tumor progression and survival outcomes in KIRP. We firstly selected out 835 DEgenes including TNNI3 itself among TNNI3-low and TNNI3-high KIRP patients. Of the DEgenes, 361 genes were positively or negatively related to TNNI3 in expression. Based on the results of univariate Cox regression analysis, log-rank test and LASSO analysis, we found six genes, including PTPRH, RYR2, PLA2G5, LGR5, DMRT3 and ACTG2, were associated with survival outcomes. PTPRH, LGR5 and DMRT3 were furthermore selected as the signature genes via multivariable Cox regression analysis. Hence, we constructed a prognostic risk score formula and stratified KIRP patients into high-risk and low-risk groups based on their risk scores. We demonstrated that the overall survival was shorter for the high-risk patients as compared to the low-risk ones. Collectively, these findings indicate the predictive value of PTPRH, LGR5 and DMRT3 for assessing the prognosis of KIRP patients.
To gain insight into the molecular mechanisms of PTPRH, LGR5 and DMRT3, the genes which potentially interacted with the three genes were predicted by STRING, and gene-gene interaction networks were obtained. A total of 31 genes in the network were taken into the subsequent GO and KEGG analysis. GO analysis indicated that the three genes were mostly associated with canonical Wnt signaling pathway. KEGG pathway analysis also indicated the association with Wnt signaling pathway. Moreover, KEGG analysis showed that these genes were potentially related to cancers such as breast cancer, gastric cancer, endometrial cancer, and prostate cancer etc. Wnt family is a group of proteins that can affect various cellular functions such as organogenesis, stem cell regeneration, and cell survival (28). Activation of Wnt signaling is essential for tumor progression and survival, even in the presence of anti-neoplastic agents or anti-tumoral immune response (29). To date, Wnt signaling pathway was reported to be involved in various cancers such as colorectal cancer (30), endometrial cancer (31), breast cancer (32), non-small cell lung cancer (33), and kidney cancer (34). These evidence could well support our GO and KEGG results in this study.
The key to activate Wnt pathway signaling is the accumulation of cytoplasmic β-catenin that presents in different forms and locations in the cell (29). Protein coding gene LGR5 potentiates canonical Wnt/β-catenin signaling and is a stem cell marker in intestinal epithelia, hair follicles, and hepatocytes. etc. (35–37). LGR5 is reportedly over-expressed in human colorectal adenomas and cancers (38–40), as well as in other solid tumors such as basal cell carcinoma, hepatocellular carcinoma and neuroblastoma (41, 42). LGR5 expression predicts adverse prognosis in patients with colorectal cancers (43). In our study, β-catenin and LGR5 showed increased expression in the presence of TNNI3 over-expression in 786-O cells. This evidence suggested that TNNI3 might activate Wnt signaling pathway. In addition, we found TNNI3 could accelerate the migration of 786-O cells and enhance their proliferation ability via wound-healing and CCK-8 assays. These results indicated that TNNI3 might be an adverse gene for kidney cancer.