First, differential expression analysis showed that GALNT14 was highly expressed in KIRC tissues, and this was verified in the CCLE database. The results of the clinicopathological analysis showed that GALNT14 expression differed significantly in clinical stage, T stage, distant metastasis, and survival status. In addition, the UALCAN results showed that GALNT14 methylation was under-expressed in KIRC. The OS outcome of the Kaplan-Meier curve also showed that high GALNT14 expression was associated with better outcomes in patients with KIRC. In addition, univariate and multivariate Cox analyses suggested that GALNT14 may be a biomarker for the prognosis of KIRC. Subsequently, Genegen network analysis demonstrated that GALNT14 was associated with multiple MUC genes. Finally, the results of GSEA revealed that GALNT14 overexpression regulates KIRC mainly through histidine metabolism, peroxidase, renin-angiotensin system and other pathways. In conclusion, GALNT14 may serve as a potential marker for prognostic and therapeutic targets of KIRC.
Our work is the first to suggest that GALNT14 is a KIRC protective factor. The results of differential expression analysis and Cox regression analysis showed that GALNT14 high expression was significantly different in clinical-grade, T stage and distant metastasis. Further, the overexpression of GALNT14 is associated with a low T grade. In other words, GALNT14 upregulation inhibited the size and extent of the primary KIRC tumor. In the stage, Hillman et al. [2] proposed that GALNT14 is expressed in several cancers, including ovarian cancer, and its upregulation promotes clinical progression in high-grade serous cancer. Beyond that, most patients with KIRC are diagnosed with metastases, particularly to the lung, bone, and brain[17, 18]. We speculated that the high expression of GALNT14 in KIRC may affect the biological functions of tumor cell proliferation, invasion and metastasis.
In addition, we found that GALNT14 expression was significantly associated with survival in patients with KIRC. Correlation analysis between clinicopathologic features of GALNT14 and KIRC showed that GALNT14 was significantly associated with OS and DFS in patients with KIRC. So far, studies have reported the effect of GALNT14 on survival in patients with other cancers. Taking esophageal cancer, lung cancer and liver cancer as examples, Tsou et al. [9, 19] noted that the GALNT14 "TT + TG" genotype resulted in a longer OS in patients. Besides, Kwon et al. [20] indicated that patients with GALNT14 overexpression had poor DFS. What’s more, Lin et al. [10] suggested that in patients with positive anti-HCV antibodies, the GALNT14 TT genotype was associated with longer OS. Therefore, we suggested that GALNT14 overexpression may affect the progression of cancers. Unfortunately, the prognostic value of GALNT14 expression in lung cancer and HCC is known[20, 21], but its prognostic value in other cancers, including renal cancer, remains unknown.
Our Cox analysis suggests that GALNT14 may serve as an independent good prognostic biomarker for KIRC. Indeed, GALNT14 is not the only protective factor for KIRC. Zhang et al. [22] indicated that ACE2 is one of the protective factors of KIRC, and ACE2 down-regulation is associated with poor OS and tumor progression in KIRC. Correspondingly, there are other genes that may act as protective factors for KIRC. For example, Qiu et al. [23] proposed that the high expression of PHYH improves the survival of patients with KIRC mainly by affecting peroxisomes and may serve as a potential prognostic molecular marker. In brief, there is not only one protective factor in each cancer. Absolutely, protective factors are not just present in KIRC or in a particular type of cancer, but in a wide range of cancers. For instance, Jiang et al. [24] found that overexpression of PTGD was positively correlated with early TNM, suggesting that this gene may be a protective prognostic factor for breast cancer. Moreover, the survival rate of cervical cancer patients with high KIR3DL1 transcription levels in tumor tissues is significantly higher than that of cervical cancer patients with low/moderate transcription levels, suggesting that KIR3DL1 is a protective factor of cervical cancer[25]. Collectively, protective factors exist not only in cancers of the urinary system, but also in cancers of other systems. Thus, we propose that the most intuitive manifestation of cancer affecting protective factors is to inhibit the metastasis and spread of cancer cells, thus improving the OS of cancer patients.
According to univariate and multivariate analysis, GALNT14 was predicted to be a novel biomarker in KIRC samples. GALNT14-mediated protein glycosylation has been reported to be associated with tumor development and malignant transformation[20, 26]. In addition, Wang et al. [27] pointed out that cancer-specific glycation changes are mainly based on the abnormal expression and activity of related glycosyltransferases, which provides theoretical support for our belief that the glycation of KIRC is mainly based on the abnormal expression and activity of GALNT14. We know that GALNT14 encodes the glycosyltransferase GalNA-T14, which is involved in O-chain glycosylation after protein translation[26]. O-glycosylation is a type of glycosylation that plays an important role in cell growth, differentiation, transformation, adhesion and tumor immune monitoring[27–29]. In detail, DeDarya et al. [13] proposed that abnormal expression of GALNTs would lead to abnormal glycation of cancer cells, which would interfere with cell adhesion, migration and proliferation and promote tumor development. Besides, in melanoma cells, non-small cell lung cancer, and pancreatic cancer, high GALNT14 expression enhances O-glycation of DR4 and DR5, thereby reducing tumor cell sensitivity to TRAIL[30]. Hence, GALNT14 overexpression interacts with glycosylation to influence cancer progression in various systems of the body. In conclusion, we suggest that GALNT14 affects a variety of tumor cell functions, including proliferation, apoptosis, invasion, and metastasis, by altering glycation, and further affects the genesis and development of KIRC.
Moreover, by UALCAN analysis, we found that GALNT14 methylation was down-expression in KIRC, and different DNA methylation patterns differed in pathological grade, clinical stage and other clinical indicators. To our knowledge, DNA methylation has been identified as a potential target for diagnostic, prognostic and predictive biomarkers in cancer[31, 32]. Nevertheless, the PubMed database of 14 biomarkers used to measure gene methylation does not include GALNT14[31]. Thus, the correlation between GALNT14 methylation and the clinicopathological characteristics of KIRC explored in this study is the first to date, which will provide a reference for subsequent related studies. Altogether, methylation markers play an important role in the diagnosis and prediction of survival of solid tumors[33–35], which is why we explored the relationship between GALNT14 methylation and KIRC in this study. To our surprise, Chen et al. [3] proposed that the hypomethylation of oncogenes plays an indispensable role in the carcinogenesis process. In addition, Li et al. [33] proposed that the abnormal methylation contributing to cancer is common in all types of cancer. Interestingly, abnormal enhancer hypermethylation has been shown to be a predictor of poor survival in patients with KIRC[31, 36], which could fully explain the role of GALNT14 as a protective factor in KIRC. Similarly, studies have shown that the increase of hypermethylation is associated with a higher stage and grade of KIRC[3, 37], which is consistent with our finding. Therefore, we estimate that GALNT14 methylation may affect its function and thus contribute to the early diagnosis and prognosis of KIRC.
Finally, we used GSEA analysis to identify the pathway by which GALNT14 affects KIRC. The results showed that GALNT14 was highly expressed in histidine metabolism, peroxisome, renin-angiotensin system and other pathways. Our results are similar to those of Wang et al. [38], who identified three important pathways associated with KIRC, namely, arginine and proline metabolism, aldosterone-regulated sodium reabsorption, and oxidative phosphorylation. This suggests that GALNT14 plays an important role in the metabolic pathway of the KIRC enrichment pathway, which is consistent with the physiological function of the kidney. Previous studies have suggested a strong link between cancer and metabolism, with one even pointing to kidney cancer as a disorder of cell metabolism[16]. Recent research has shown that the characteristic that distinguishes KIRC from other types of tumors is its specific metabolic changes[39]. In terms of amino acid metabolism, it has been reported that the deletion of the 3P chromosome in clear cell renal cell carcinoma leads to the inactivation of FHIT gene[40], so we speculate that this may be the reason why the histidine metabolic pathway is in the first place. Besides, Weiss et al. [41] proposed that tryptophan is catabolized by the renin pathway and that the renin metabolites have immunosuppressive effects. In addition, Liu et al. [5] have shown that tryptophan depletion leads to apoptosis through an accumulation of KP metabolites. Therefore, we speculate that GALNT14 may reduce tryptophan metabolism to maintain the immune function of patients, thereby limiting the proliferation of KIRC primary tumor. Then, in terms of fatty acid metabolism, Hillman et al. [2] showed that KIRC is associated with abnormal fatty acid metabolism. Interestingly, reduced fatty acids in KIRC were associated with increased tumor invasion and poor prognosis[41]. This suggests that the high expression of GALNT14 in KIRC may inhibit the expression of fatty acid synthase, leading to the higher OS in patients with GALNT14 upregulation. Surprisingly, there are also reports of dysregulation of carbon metabolism in KIRC[6]. This is basically consistent with our findings in KIRC enrichment analysis that GALNT14 overexpression affects glucose metabolism. KIRC has been reported to enhance uptake of glucose transporters, leading to glucose accumulation and further promoting tumor progression[39], so inhibition of gluconeogenesis will promote the development of RCC. In a word, we suggest that GALNT14 overexpression in KIRC reduces the absorptive activity of glucose transporter and accelerates glucose decomposition. Hence, we hypothesized that GALNT14 regulates the occurrence of KIRC through the above metabolism-related pathways. However, the prognosis of high GALNT14 expression is limited to KIRC Ⅰ and IV stages, and further experiments are needed.