Although extensive research efforts have been focused on this field in past decades, the screening of ESCC and accurate prediction against complicated ESCC patients still remain an open issue. Recently, studies have found that the expression of certain genes was highly related to the occurrence and development of ESCC. Moreover, single-cell transcriptome analysis technology has been initially applied to ESCC. However, most works only focused on single cell or limited genes, and the predictive ability was barely narrow. Herein, we combined methylation, mRNA and single cell, to explore the role of specific genes in the potential development mechanism of ESCC and the immune microenvironment.
In the last years, the extracellular matrix (ECM) has been reported as playing a relevant role in ESCC development (Palumbo et al. 2020; Wang et al. 2017). The GO enrichment analysis revealed that the biological processes of hypomethylated/high-expression genes were involved in the regulation of extracellular structure organization, regulation of ERK1 and ERK2 cascade, endodermal cell differentiation, endoderm development, chemokine − mediated signaling pathway, response to chemokine, cellular response to chemokine, ossification, interleukin − 1 production and collagen metabolic process. Our results agree with the fact that carcinoma cell metastasis and invasion are closely associated with abnormal cell adhesion, endodermal cell division and nuclear division (Chai et al. 2019; Han et al. 2020; Zhang et al. 2019). Indeed, this is consistent with the research results that ECM remodeling creates a reorganized environment that promotes tumor progression by destabilizing cell polarity and cell–cell adhesions and by increasing growth factor signaling, which impact on tumor gene expression, differentiation, proliferation, migration (Paszek et al. 2005). Furthermore, the enriched KEGG pathways of hypomethylated highly expressed genes were mainly linked to Cytokine − cytokine receptor interaction, ECM − receptor interaction, IL − 17 signaling pathway, Viral protein interaction with cytokine and cytokine receptor, TNF signaling pathway. It has been demonstrated that ESCC TME is enriched for pro-inflammatory cytokines, chemokines, and growth factors, and their complex cross-talk with their receptors influences the development and progression of ESCC (Diakowska et al. 2013). The cytokines and chemokines secreted by the immune cells such as JAK/STAT, NF-κβ, NOTCH to mediate various properties of cancer hallmarks, mediate cancer-stromal interactions and activate several downstream effector pathways (Nisar et al. 2020). Furthermore, cancer cells secret Monocyte chemoattractant protein-1 (MCP-1/CCL2) into TME and product pro-angiogenic factors (Koide et al. 2004). The other immunosuppressive T cells, such as Tregs and Th17, are recruited by tumor cell-derived chemokines CCL17 and CCL22 and are known to promote ESCC pathogenesis (Xia et al. 2013). In particular, the presence of increased Tregs in the ESCC TME is associated with invasion, metastases, disease severity, decreased survival, and thus considered of prognostic significance (Jiao et al. 2012; Chen et al. 2012). Together, these data suggested that inflammatory cytokine play an essential role in ESCC proliferation, angiogenesis, and metastasis, and regulation of tumor immune microenvironment is helpful for prognosis.
The PPI network of hypomethylated/high-expression genes provides an approach to identifying the functional associations between them and the top six hub genes were selected from this: COL1A1, COL1A2, COL5A1, COL5A2, COL11A1, THBS2. Collagens, a family of 28 members, is the main structural protein of the extracellular matrix consisting of three subtypes, namely fibrillar collagens, non-fibril forming collagens, and fibril-associated collagens (Ricard-Blum 2011). COL1A1, COL1A2, COL5A1, COL5A2, COL11A1 are members of the collagen family, and the dysregulation may represent a basis for cancer invasion and migration. COL1A1 and COL1A2 are two types of type I COL, and the most ECM proteins are comprised of fibrillar collagens (Yamauchi et al. 2018). Recent studies have suggested that COL1A1 was up-regulated in several cancers, including colorectal cancer (Zhang et al. 2018), cervical cancer (Liu et al. 2017), oral squamous cancer and gastric cancer (He et al. 2018; Wang et al. 2018). In pancreatic cancer, COL1A2 was highly expressed (Wu et al. 2019). In ESCC, COL1A1 was negatively correlated with miR-133a-3p, which directly inhibit proliferation and metastasis, and promot the apoptosis of ESCC cells (Yin et al. 2019). It has been reported that PDGF receptor-beta increased the expression of COL1A2 through Akt/mTORC1 signaling pathway (Das et al. 2017). Collagen type V (COL5) is classified as a regulatory fibril-forming collagen, and is formed by the combinations of three different chains, namely COL5A1, COL5A2, and COL5A3 (Nardo et al. 2014). COL5 presents in most connective tissue matrices and plays a functional role in some cancers including breast cancer and pancreatic ductal adenocarcinoma (Chai et al. 2016). A study has revealed the peak role of COL11A1 and THBS2 in a metastasis-associated gene expressing signature (Liu et al. 2018). Notably, in patients with advanced pathological T (T3-T4) stage and lymph node metastases, high COL11A1 expression accounted for 69.1% and 72.5% respectively. Suggesting that up-regulated COL11A1 might take part in the process of invasiveness and regional migration (Zhang et al. 2018).
Alternatively, we leveraged the power of single-cell genomics to characterize the heterogenous cell types and states in the tumor microenvironment. We linked clusters to specific cell types including Effector memory CD8 T cells, Intermediate monocytes, Myeloid dendritic cells, Non − Vd2 gd T cells,Plasmablasts, Progenitor cells, Switched memory B cells, T regulatory cells. The 19th cluster cells highly expressing hub genes were annotated " SRP − dependent cotranslational protein targeting to membrane". The targeting of proteins to a membrane that occurs during translation and is dependent upon two key components, the signal-recognition particle (SRP) and the SRP receptor. SRP is a cytosolic particle that transiently binds to the endoplasmic reticulum (ER) signal sequence in a nascent protein, to the large ribosomal unit, and to the SRP receptor in the ER membrane (Costa et al. 2018). These results gave evidence for the role of 19th cluster cells in protein-targeting efficiency and specificity. KEGG analysis also revealed the connection between 19th cluster cells and ribosome and antigen processing and presentation. The MHC class I antigen presentation system enables T cell immunosurveillance of cancers and viruses. It's reported that 40S ribosomal protein S28 (RPS28) knockdown sensitizes tumor cells for T cell targeting by increasing DRiP synthesis, which degrade to A substantial fraction of the immunopeptidome (Wei et al. 2018).
In summary, our research offers a comprehensive bioinformatics analysis of aberrantly methylated DEGs associated with multiple signaling pathways that may be involved in the occurrence and development of ESCC.In addition, the six most modified hub genes were identified, including COL1A1, COL1A2, COL5A1, COL5A2, COL11A1 and THBS2. Then we performed a genomic analysis on the ESCC single cell datasets and clarified the function of cell clusters expressing hub genes specifically. These new discoveries may provide insights for unraveling the pathogenesis of ESCC, and these candidate genes may be optimal abnormal methylation-based biomarkers for the precise diagnosis and treatment of ESCC. Further molecular biological experiments are required to verify the function of the identified candidate genes in ESCC.