This study, for the first time, constructed a prognostic model using immune-related miRNAs and validated its accurate, potent performance. We firstly analyzed the key modules associated with prognosis of PC using WGCNA, and then adopted differential analysis to obtain 1,826 up-regulated and 1,276 down-regulated genes in PC comparing with normal tissues. Spearman correlation coefficient was calculated and 700 immune-related miRNAs were found. Uni- and multi-variate COX regression analyses were performed to screen immune-related miRNA associated with OS. Eventually, a 7-miRNA-based prognostic model for PC was generated and a model-based risk scoring system was established with excellent performance detected by KM, ROC, distribution plot of survival status in subgroups, and uni- and multi-variate COX regression analyses. Furthermore, a miRNA-mRNA network was built using the Cytoscape3.8.0 software, according to the 99 target genes obtained from the predicted mRNAs of the 7 model miRNAs and key module genes. Moreover, immune cell infiltration was analyzed using the TIMER in the subgroups stratified by the model-based risk score, and dendritic cells were found as the most significantly different immune infiltrate in TME of the subgroups. Wilcoxon test also indicated correlation of the risk score with expression of immune checkpoint genes, including TNFSF9, TNFRSF9, KIR3DL1, HAVCR2, CD276, especially CD80. GSEA showed the remarkably enriched signaling pathways in the two subgroups.
There have been multiple studies devoted to constructing prognostic models for PC. For instance, Weng W et al. [27] established a prognostic model for PC using 14 significant mRNAs; Yan J et al. [28] reported a 4-gene-based prognostic model for PC according to the transcriptome data; Liu B et al. [29] constructed a 5-mRNA prognostic model for PC, which was immune-associated; Chen S and Jia Y [30–31] obtained a prognostic model based on miRNAs.
Currently, prognostic miRNAs for PC have been extensively studied. Guo S et al. [32] reported that high expression levels of miR-21, miR-212, miR-675, miR-142-5p, miR-204 and low expression levels of miR-148a, miR-187, let-7g were associated with poor prognosis of PC. In that study, they also found several other miRNAs of prognostic significance, including miR-30a-3p, miR-105, miR-127, miR-187, miR-452, miR-518a-2, miR-155, miR-203, miR-210, miR-222, miR-200c, miR-302 and miR-15a. Tesfaye AA et al. [33] revealed that the down-regulation of miR-183, miR-34a and the up-regulation of miR-1290, miR-155, miR-203, miR-222, miR-10b predicted a poor survival outcome of PC. Additionally, high expression levels of miR-142-5p, miR-21 led to significantly prolonged survival in patients with PC, and the miRNAs involved in p53, COX2 pathways were demonstrated to be associated with prognosis as well. Gablo NA et al. [34] confirmed miR-21 as an oncogene in PC and revealed that increased expression of miR-21 and miR155 was associated with the decline in survival, liver metastasis, lymph node status and increased resistance to Gemcitabine.
In the current study, we successfully established a prognostic model using 7 immune-related miRNAs. Lu XG et al. [35] found that expression of miR-550a in severe acute pancreatitis was down-regulated in patients combining with acute lung injury compared with patients without acute lung injury. Qin S et al. [36] revealed that miR-3613-5p was prognostic for renal clear cell carcinoma, which was also observed in the study by Zhan Y et al. [37] Ma J et al. [38] also reported miR-3613-5p as a prognostic biomarker for pancreatic carcinoma and found that the target genes of miR-3613-5p might be correlated with the p53 signaling pathway. Research also found that miR-3613-5p was a key miRNA in cell malignancy of liver cancer induced by aflatoxin B1 [39]. Wang X et al. [40] found that miR-221-3p was independent of the prognosis of hepatocellular carcinoma (HCC), while Wang J et al. [41] reported the key role of miR-221-3p in thyroid cancer. Moreover, Fang R et al. [42] established a prognostic model for breast cancer based on 13 miRNAs including miR-221-3p. Abak A et al. [43] analyzed breast biopsy samples and found increased expression of miR-221-3p in tumor tissue compared to that in adjacent normal tissue. Xie L et al.[44] adopted high-throughput sequencing from peripheral blood mononuclear cells in small cell osteosarcoma and detected dysregulation of miR-221-3p. Kandhavelu J et al. [45] found that miR-424-5p was associated with 10 biomarkers of colon carcinoma, while only two of them, including microtubule-associated protein-2 (MAP2) and cyclin gene (CCN) D1, were experimentally validated. Liang Y et al. [46] identified miR-424-5p as a potential prognostic biomarker for gastric cancer. In the meantime, Liu W et al. [47] experimentally validated that the up-regulation of miR-424-5p induced by astragaloside IV could inhibit the epithelial-mesenchymal transition (EMT) and angiogenesis in gastric cancer, thereby to play a role in treatment of this cancer. Wang S et al. [48] found and validated the role of miR-424-5p as a factor in prognosis of HCC. Xu F et al.[49] also reported miR-424-5p played a vital role in onset of bile duct carcinoma. Additionally, miR-424-5p might reverse the progression of thyroid cancer via regulating clusterin (CLU) and apolipoprotein (APO) [50]. Ranjha R et al. [51] found decreased expression of miR-491-3p in ulcerative colitis located in the rectal sigmoid colon region than expression in ulcerative colitis located in the ascending colon. circANKRD36 might interact with miR-3614-3p to participate in Type 2 Diabetes and inflammation, supporting their role as potential biomarkers [52]. miR-1179 inhibited the in vivo growth of PC by down-regulating the expression of E2F transcription factor 5 [53]. Moreover, miR-1179 could suppress the growth and invasion of thyroid, gastric, esophageal squamous-cell carcinoma, non-small cell lung, cervical, breast, and nasopharyngeal carcinomas via regulating downstream target genes [54–60].
To conclude, this is the first study that constructed a prognostic model for PC using immune-related miRNAs, aiming to provide a new direction for clinical prognosis of PC. The current study still has some deficiencies, such as lack of validation by molecular biology or relevant clinical trials. Additionally, the miR-491-3p and miR-550a-3-5p have not been fully studied in the field of tumor, requiring further in-depth research.