Previous studies suggested the causal effects of cancers for hyperkalemia , as well as the negative influence of hyperkalemia on the prognosis of LSCC . The purpose of our study is to explore the potential molecular mechanisms underlying the clinical association between hyperkalemia and LSCC. Based on the discovery, we made one further step to test the hypothesis that genes promoting hyperkalemia may also play roles in the development of LSCC.
Assisted by using the tool Pathway Studio (www.pathwaystudio.com), we conducted a large-scale literature data mining, covering over 40 million references to identify LSCC and hyperkalemia related genes, proteins, small molecules, and cell types. Based on the mining results, pathway analysis has been conducted to identify common targets and common regulators of LSCC and hyperkalemia. We also discovered a potential cross-network through which LSCC and hyperkalemia may connect with each other and mutually impact their pathologic development.
On the one hand, previous studies showed that LSCC and hyperkalemia influenced by multiple common molecules. For instance, macrophages play a vital role in the development of LSCC and hyperkalemia [7, 8]. Moreover, squamous carcinoma cell lines experiments showed that abnormal TP53 expression could cause hyperkalemia , while the mutation of TP53 has been suggested to play roles in the development of LSCC . On the other hand, LSCC and hyperkalemia have an influence on multiple common molecules. It has been shown that increased calcium content is an indicator of LSCC , while hyperkalemia stimulates enzyme secretion and elevates calcium concentration . It has also been suggested that the amplification and overexpression of MYC have been reported previously in both LSCC and hyperkalemia type carcinoma .
In addition, multiple evidence from previous studies indicated that hyperkalemia and LSCC could be mutual causal factors for each other. As shown in Fig. 3, besides the promotion of calcium , LSCC also activates multiple genes that produce hyperkalemia, including EGFR, EZH2 [5, 14]. These studies partially explain the mechanism that LSCC induces hyperkalemia. On the other hand, hyperkalemia has been shown to stimulate the expression of multiple genes or proteins that promote the development of LSCC. For instance, hyperkalemia patients demonstrated elevated ACE levels , which lead to an increased risk of LSCC . Hyperkalemia also stimulates the expression of PTGS2 , which plays an important role in the rat LSCC  and has been suggested as a therapeutic target for LSCC . These studies indicated that hyperkalemia might be a risk factor that promotes the development of LSCC.
Based on the association study between LSCC and hyperkalemia, it is reasonable to hypothesize that genes promoting hyperkalemia may also play roles in the development of LSCC. Venn diagrams in Fig. 1 showed that 16% (20/125) genes implicated with hyperkalemia have also been suggested an association with LSCC. Fisher exact test showed that the probability that two random gene groups with the same size of genes (i.g., 125 and 397 genes) to have an overlap of 20 is less than 4.98e-15, which supports the hypothesis proposed here.
In addition, mega-analysis discovered one hyperkalemia-specific promoter, SPP1, also presented significantly increased expression in the case of LSCC (p = 2.81e-6; LFC = 2.64) (Table 2, Fig. 4b). MLR analysis results suggested that the population region (country) was a factor that affects the expression level of SPP1 in the case of LSCC (P-value = 0.054). Pathway analysis showed that SPP1 might promote the pathological development of LSCC through the stimulation of the expression of multiple genes, as shown in Fig. 4b. Overexpression of SPP1 was reported to be associated with poor prognosis, progression, migration, and invasion of multiple cancers [20,21,22,23]. The elevated expression of SPP1 could result in the up-regulation of SDC1 signaling (gene colored in red, Fig. 2), which promotes the metastasis in LSCC . Moreover, SPP1 induces increased PLAU production that indirectly activates MMP1, which promotes tumor progression and LSCC cell migration and invasion [25, 26]. The pathway presented in Fig. 4b provides further support for the hypothesis that genes promoting hyperkalemia may also play roles in the development of LSCC. To note, the activities of the genes within the SPP1 signaling pathway (Fig. 4b) have been validated by the mega-analysis using the 11 independent datasets listed in Table 1.
To note, this study was designed to explore the mechanism of LSCC-hyperkalemia mechanism at the molecular level. The shared genetic pathways and molecular targets and regulators may partially explain the mutual influence of LSCC and hyperkalemia. However, our results did not suggest a causal effect of hyperkalemia on LSCC.