A Novel Prognostic Signature Based on Cell-In-Cell-Related Genes for Predicting Survival and Tumor Microenvironment in Pancreatic Cancer
Abstract Background: Pancreatic cancer (PC) is a highly malignant tumor featured with high intra-tumoral heterogeneity and poor prognosis. Cell-in-cell (CIC) structures have been reported in multiple tumor types, and their presence is thought to promote clonal selection and tumor evolution. Here, we aimed to establish a CIC-related gene signature for predicting the prognosis and evaluating immune microenvironment in PC. Methods: In this study, the gene expression data, as well as corresponding clinicopathological data of PC and normal pancreatic tissues were collected from The Cancer Genome Atlas (TCGA), Genotype-Tissue Expression (GTEx), International Cancer Genome Consortium (ICGC) and Gene Expression Omnibus (GEO) databases. Differential gene expression analysis, random forest screening, least absolute shrinkage and selection operator (LASSO) regression and multivariate Cox regression analysis were performed on 101 CIC-related genes to construct a prognostic gene signature. The effectiveness and robustness of the prognostic gene signature were evaluated by receiver operating characteristic (ROC) curves, Kaplan-Meier survival analysis and establishing the nomogram model. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses were conducted to annotate the biological functions of the differentially expressed genes (DEGs). Quantitative real-time PCR (qRT-PCR), western blotting and immunohistochemistry (IHC) staining were validated the core gene expression in both mRNA and protein levels. Results: A 4-gene signature was constructed to stratify patients into the low-risk and high-risk groups with distinct survival outcomes, somatic mutation profiles and immune features. The high-risk group had poorer prognosis than did the low-risk group. This signature was found to be an independent prognostic factor for PC patients with favorable predictive efficiency. Functional enrichment analyses showed that numerous terms and pathways associated with invasion and metastasis were enriched in the high-risk group. Moreover, the high-risk group had a higher tumor mutation burdens and lower immune cell infiltrations. KRT7, as the most important risk gene, was significantly associated with the worse prognosis of PC. CIC formation assay performing in PC cell lines indicated that KRT7 expression was correlated with CIC frequency. Conclusions: The signature based on four CIC-related genes could be applicable for predicting the prognosis of PC, and targeting CIC processes may be a potential therapeutic option. Further studies are needed to reveal the underlying molecular mechanisms and biological implications of CIC in PC progression.