In clinical treatment, HNSCC patients with recurrence and/or metastasis have an extremely low survival rate: the median overall survival rate is only 1 year [22], thus, the metastasis and migration of HNSCC cells have been one of the most concerns for HNSCC treatment. In this study, we demonstrated that FSCN1 was a reliable biomarker for HNSCC diagnosis and prognosis. Bioinformatic studies have been wildly used to access the survival associations of genes[4, 23–33]. Our data suggested that the overall survival rate of HNSCC patients was significantly associated with the expression of FSCN1 in HNSCC tissues. The prognostic potential of FSCN1 has been reported in other types of cancers. In colon cancer, FSCN1 has been found to be positively correlated with survival[34]. The FSCN1 gene was also suggested as an important predictor of early-stage breast cancer [35]. In addition, FSCN1 expression was associated with significantly poorer overall survival of epithelial ovarian cancer patients [36]. In renal cell carcinoma, FSCN1 was overexpressed in tumor tissues compared to non-tumor tissues. It is also associated with poor overall survival and recurrence-free survival in renal cell carcinoma, [37]. In all of these analyses, high expression of FSCN1 was associated with a worse prognosis and most of the studies revealed that FSCN1 expression was independent of age, tumor size, and clinical TNM stage, which were consistent with our results. As for the subtype of HNSCC, a study focused on HNSCC in the tongue found that FSCN1 is an effective biomarker of poor prognosis and a potential therapeutic target in human tongue HNSCC[38]. In our study, we study all types of HNSCC as a whole and further demonstrated that the FSCN1 was not only useful for tongue HNSCC but also for other HNSCC. All these bioinformatic studies demonstrated that FSCN1 might be valuable for clinical cancer prognosis. Nevertheless, we suggested that it is not certain whether this molecule has clinical or therapeutic relevance and can be applied for clinical HNSCC treatment. Our study did not test the therapeutic relevance and the clinical part of the study only provided an observation, not necessarily proving that it can be a biomarker and potentially be better than current biomarkers. Therefore, we should be cautious when drawing any conclusions.
A previous study reported FSCN1 as a potential therapeutic target of lung squamous cell carcinoma and suggested that FSCN1 impact immune and inflammation in the tumor microenvironment[39]. As another type of squamous cell carcinoma, HNSCC might have a similar impact on the immune and inflammation in the tumor microenvironment as lung cancer. In this study, we found that FSCN1 was potentially associated with B cells and T cell infiltration levels. Our results did not validate the functional role of FSCN1 in the regulation of tumor immune microenvironment in HNSCC. However, its expression in HNSCC could still be a biological sign of the changes in the immune response. The changes in immune cell infiltration levels can contribute to the metastasis of the HNSCC. The tumor extracellular matrix (ECM) of HNSCC is significantly different from that of normal tissue[40]. The ECM components upregulated in HNSCC can impact several cancer hallmarks, such as sustaining proliferative signaling, promoting angiogenesis, facilitating invasion and metastasis, modulating growth suppressor activity, and suppressing antitumor immunity. Furthermore, the tumor ECM has been implicated in treatment resistance, making it a potential therapeutic target. Malignant epithelial cells and stromal cells in HNSCC interact through signaling, which leads to the increased production of components of the ECM. These ECM components provide a substrate for carcinoma cell migration, modulate the cytokine environment, and aid in immune evasion. Therefore, we suggested that, as an actin-binding protein mediating the formation of actin-based cellular protrusions, FSCN1 might be involved in the ECM pathways thereby affecting tumor microenvironment and immune cell infiltration levels. In clinical treatment, many different therapies might be applied to inhibit cancer cells [41]. In cancer treatment, many clinical factors might affect cancer metastasis by either regulating cancer cells or the immune system such as the use of anaesthetics or traditional medicines [42–48]. The potential regulation of FSCN1 on immune cells might contribute to the effects of these factors on cancers. Yet, further studies are required to identify the direct impact of FSCN1 on immune cells.
Moreover, we not only analyzed data from the TCGA but also collected clinical samples and validated the expression. Commonly used QPCR and western blotting assay were conducted in many previous studies [49, 50], which provided reliable results. We also used immunochemistry staining [51] to visualize the expression of FSCN1 in HNSCC tissues. One of the most significant findings of this study was that FSCN1 was found to be the essential molecule for HNSCC cell migration. It was not surprising that FSCN1 potentially affected cancer cell migration because FSCN1 has long been defined as a fascin actin-bundling protein that is responsible for the migration or relocation of cells [7–9]. Animal models have been widely used in research previously [52–54]. For the FSCN1 study, an in vivo study using the orthotopic xenografts mice model indicated that FSCN1 could promote cancer cell invasion and metastasis [37]. Another study revealed that FSCN1 could affect gastric cancer migration and invasion [55]. However, so far, few studies have focused on the role of FSCN1 in HNSCC migration.
We notice that a previous study reported that FSCN1 is an effective marker of poor prognosis and a potential therapeutic target in human tongue squamous cell carcinoma[38], yet, the previous study focused on tongue squamous cell carcinoma, while our study expanded the application of FSCN1 to general HNSCN. In addition, we have used multiple cancer cell lines to support the role of FSCN1 in cancer migration, which has never been done before. The correlation of HSCN1 expression and velocity of migration of the eight HNSCC cell lines we tested strongly suggested that FSCN1 was a key molecule for HNSCC cell migration. We validated the promoting effect of FSCN1 on HNSCC cell migration by overexpressing FSCN1 in two of the low FSCN1 cell lines with low migration velocity. We further confirmed the functional effect of FSCN1 by knocking down FSCN1 in two of the high FSCN1 cell lines with high migration velocity. These results were consistent with the previous conclusion that FSCN1 regulated cancer cell migration and metastasis. Furthermore, most of the previous studies investigated cancer cell migration using wound-healing or transwell assay, which determined the migration of a group of cancer cells as a whole. Our study was the first to investigate the role of FSCN1 by tracking individual cell migration. Nevertheless, although we obtain the velocity of individual cell migration, we were not able to determine the expression of FSCN1 in the cell we recorded.
This study aimed to validate the role of FSCN1 in HNSCC cell migration, but the mechanisms underlying these effects were not clear. The enrichment analysis revealed several potential mechanisms, such as the PI3K − Akt signaling pathway, which required further validation with experimental evidence. In addition, as the FSCN1 might play a role in intercellular communications, many cancer-related ion channels, such as VGSC[56–58], TRP[59, 60], and TPCs[61, 62], might also contribute to the effects of FSCN1 on cancer cells and need further investigation in the future.