High SIGLEC9 Expression Levels in Cervical Cancer Correlate with Immune Cell Infiltration

Abstract Background: In this work, the sialic acid-binding Ig-like lectin 9 (SIGLEC9) was used to examine the diagnostic utility and underlying processes of cervical cancer. Methods: The TNM plot database were used to analyze the association of SIGLEC9 expression levels in normal, tumor and metastatic. Immunohistochemical Staining and western blotting of SIGLEC9 were performed in 40 cervical cancer patients and 30 patients with uterine fibroids. Moreover, we analyzed the correlation between SIGLEC9 and tumor markers. Furthermore, signaling pathways linked to SIGLEC9 expression were discovered using the Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes Enrichment (KEGG), and Gene Set Enrichment Analysis (GSEA). The relative immune cell infiltrations of each sample were assessed using the estimate method and the CIBERSORT algorithm. We verified the relationship between SIGLEC9 and Treg by immunohistochemistry. Then we revealed how SIGLEC9 functions in macrophages through single-cell analysis. Moreover, we collected some genes directly interacting with SIGLEC9 from four protein-interaction network databases. In addition, we used the the Cancer Genome Atlas (TCGA) and Gene Expression Omnibus database (GEO) databases to analyze the association of MUC1 expression levels with tumor stages. We know 20 kinds of sialyltransferases, and their expressions in cervical cancer were analyzed by TCGA database, and verified by GEO database. Lastly, immunohistochemical staining of MUC1 and ST3GAL1 was performed in 40 cervical cancer patients. And we used ROC to analyze the diagnostics of SIGLEC9, MUC1, ST3GAL1, and ST6GAL1 in cervical cancer. Results: SIGLEC9 is strongly expressed in cervical cancer. The immunohistochemical staining and Western blotting of tissue sections from 40 cervical cancer patients and 30 patients with uterine fibroids showed that SIGLEC9 was highly expressed in cervical cancer. Moreover, SIGLEC9 was associated with the tumor marker CA125 by forest map. Furthermore, the SIGLEC9 expression level was positively correlated with Treg activation by the estimate method and the CIBERSORT algorithm. Immunohistochemistry verified that siglec9 was positively correlated with Treg. SIGLEC9 expression was also positively correlated with major immune checkpoints. Through single-cell analysis, we found that the SIGLEC9 gene is related to the ability of macrophages to process antigens. Furthermore, the PPI analysis showed that SIGLEC9 was correlated with MUC1. TCGA databases showed that MUC1 was highly expressed in the cervical cancer group. According to TCGA and GEO databases, ST3GAL-I and ST6GAL-I are highly expressed in cervical cancer. And immunohistochemical staining of MUC1 and ST3GAL1 was highly expressed in cervical cancer patients. Lastly, SIGLEC9, MUC1, ST3GAL1, and ST6GAL1 have high diagnostic values by ROC. Conclusion: These findings imply that SIGLEC9 is a cervical cancer diagnostic marker and may one day be used as an immunotherapy target for cervical cancer patients.