Morphological heterogeneity and genetic heterogeneity comprise tumor heterogeneity affecting diagnosis and therapy in cancer[20]. Gastric cancer is a highly heterogeneous malignant cancer with virous subtypes and clinical behaviors[21, 22]. Here, we explored tumor heterogeneity at the single cell level in GC using scRNA-seq.
Our result based on scRNA-seq analysis showed that tumors included virous cells, such as malignant cells, tumor infiltrating cells and stromal components. Cell transition trajectory analysis is widely used to explore different cell types at different stages of development and differentiation in several reports[23, 24]. We identified three branches in cell transition trajectory. In this study, common DEGs were analyzed in three branches. Our analysis revealed that these genes were enriched in Coronavirus disease 2019 (COVID-19). COVID-19 is defined as a respiratory tract infection caused by the severe acute respiratory syndrome (SARS) coronavirus (COV), also named SARS-CoV-2[25]. COVID-19 was first found in Central China (Wuhan, the capital of Hubei province) at the end of December 2019[26]. Many reports have explored the relationship of COVID-19 with cancer[27–29]. Hoang, T. et al reported that genetic susceptibility of ACE2 and TMPRSS2 in GC was associated with the susceptibility to COVID-19 infection[30].
The tumor microenvironment (TME) consists of a heterogenous cellular component affecting cancer cell behavior. Sathe, A. et al showed that gastric cancer TME was significantly enriched for stromal cells, macrophages, dendritic cells (DC), and Tregs[31]. Our study also found that cells cluster 5 was main macrophages. We investigated that common DEGs in three branches were associated with neutrophil degranulation, neutrophil activation involved in immune response, neutrophil mediated immunity and neutrophil activation. Increasing studies revealed that neutrophil played a critical role in tumor microenvironment[32–34].
In this study, we used ten tumor differentiation grade-related genes for the first time to establish the prognostic signature including TNFAIP2, MAGEA3, CXCR4, COL1A1, FN1, VCAN, PXDN, COL5A1, MUC13, and RGS2 based on single-cell RNA-seq. More importantly, age, stage and riskscore were independent prognostic factors. To our knowledge, this is the first study that directly revealed that a prognostic risk model based on tumor differentiation grade-related genes may predict prognosis in GC.
Many recent study showed that TNFAIP2, MAGEA3, CXCR4, COL1A1, FN1, VCAN, PXDN, COL5A1, MUC13, and RGS2 could predict overall survival as a single gene biomarker[35–43]. Here, we found that the expression level of TNFAIP2, MAGEA3, CXCR4, COL1A1, FN1, VCAN, PXDN, COL5A1, MUC13, and RGS2 is closely related to the prognosis of GC patients.
Several studies have used PPI network to study the interactome of protein and screen hub genes[44]. Our PPI network studies demonstrated that COL5A1 was a key molecular node. As the collagen family members, high level of COL5A1 is closely associated with the poor prognosis of multiple human tumors[45, 46]. Focused on the molecular role of COL5A1 in malignant cells, investigators have reported that NAT10 promoted GC metastasis via N4-acetylated COL5A1[47]. We also observed that COL5A1 was differentially expressed in GC tissues. A previous study shows that COL5A1 was a cancer-associated fibroblast gene signature as a poor prognostic factor and potential therapeutic target in GC[48]. Given that the correlations of COL5A1 with immune infiltrating cells, our results revealed that COL5A1 was significantly correlated with B cell memory, dendritic cells-activated, macrophage M0, macrophage M2, plasma cells, and T cells follicular helper, suggesting its role in regulating TME. However, this study has no enough clinical samples to validate this prognostic signature using our experimental data.