Functional characterization of nidogen-2 (NID2) in nasopharyngeal carcinoma (NPC) and esophageal squamous cell carcinoma (ESCC)

Abstract

The deregulation of genetics and epigenetics contributes to the multifactorial development of cancer. Among which, the promoter hypermethylation of tumor suppressor genes (TSGs) and metastasis suppressor genes (MSGs) has been well-studied and is known to be a key driver of tumorigenesis and metastasis in several cancers, including nasopharyngeal carcinoma (NPC) and esophageal squamous cell carcinoma (ESCC). Nidogen-2 (NID2) has been identified as a candidate TSG/MSG from methylome studies of NPC and ESCC. Both genome-wide methylation profiling and gene-specific methylation-sensitive high-resolution melting assays have confirmed the hypermethylation of the NID2 promoter in NPC and ESCC biopsies and cell lines. The NID2 protein is a key constituent of the basement membrane that stabilizes the macromolecule networks in the extracellular matrix. Hence, its absence may have catastrophic consequences such as the increased invasiveness and metastatic ability of the cancer cells. Although the promoter hypermethylation of NID2 has been reported in several cancers, little is known about its functional roles and mechanisms, particularly in NPC and ESCC. The present study was carried out to investigate the functional roles of NID2 in the pathogenesis of NPC and ESCC. NID2 was found to be down-regulated in clinical samples and cell lines of both cancers. To characterize the roles of NID2 in the two cancers, the lentiviral transduction system was used to re-express it in NPC and ESCC cells for use in subsequent in vitro and in vivo functional analyses. NID2 re-expression was found to suppress the clonogenic survival of both NPC and ESCC cells. Furthermore, the cell wound healing, migration, and invasion abilities were also impeded upon NID2 re-expression. More importantly, the in vivo metastasis assay demonstrated that the re-expression of NID2 in HONE1-Luc cells significantly inhibits liver metastasis. Mechanistic studies of the signaling pathways also confirmed NID2 re-expression in NPC and ESCC cells to suppress the integrin/FAK/PLCγ and EGFR/Akt pathways, both of which are known to regulate cancer metastasis. The utility of NID2 as a methylation or serum biomarker was also investigated. In summary, the results of this study suggest that NID2 suppresses clonogenicity, migration, invasion, and metastasis in NPC and ESCC, most likely through the down-regulation of integrins and EGFR pathways. The study thus enhances our understanding of the mechanistic roles of NID2 and offers novel insights into its crucial metastasis suppression roles in cancer.