Quantitative assessment of Siglec-15 expression in lung, breast, head, and neck squamous cell carcinoma and bladder cancer

The expression characteristic and prognostic role of Siglec-15 in lung adenocarcinoma

Sialic acid-binding immunoglobulin-like lectin-15 (Siglec-15) has been identified as an immune suppressor and a promising candidate for immunotherapy of cancer management. However, the association between Siglec-15 expression and clinicopathological features of lung adenocarcinoma (LUAD), especially the prognostic role, is not fully elucidated. In this present study, a serial of bioinformatics analyses in both tissue and cell levels were conducted to provide an overview of Siglec-15 expression. Real-time quantitative PCR (qPCR) test, western blotting assay, and immunohistochemistry (IHC) analyses were conducted to evaluate the expression of Siglec-15 in LUAD. Survival analysis and Kaplan-Meier curve were employed to describe the prognostic parameters of LUAD. The results of bioinformatics analyses demonstrated the up-regulation of Siglec-15 expression in LUAD. The data of qPCR, western blotting, and IHC analyses further proved that the expression of Siglec-15 in LUAD tissues was significantly increased than that in noncancerous tissues. Moreover, the expression level of Siglec-15 protein in LUAD was substantially associated with TNM stage. LUAD cases with up-regulated Siglec-15 expression, positive N status, and advance TNM stage suffered a critical unfavorable prognosis. In conclusion, Siglec-15 could be identified as a novel prognostic biomarker in LUAD and targeting Siglec-15 may provide a promising strategy for LUAD immunotherapy.

Siglec 15 as a biomarker or a druggable molecule for non-small cell lung cancer

Lung cancer has been the main cause of cancer mortality worldwide. Furthermore, lung cancer rates of new cases per year evidenced a large incidence of this neoplasm in both men and women. Because there is no biomarker for early detection, it is frequently detected late, at an advanced state. The introduction of multiple lines of tyrosine kinase inhibitors in patients with EGFR, ALK, ROS1, and NTRK mutations has modified the therapy of lung cancer. Immunotherapy advances have resulted in substantial improvements in overall survival and disease-free survival, making immune checkpoint inhibitors (ICIs) a potential option for lung cancer treatment. Current PD-1/PD-L1/CTLA-4 immunotherapies have resulted in important response and survival rates. However, existing medicines only function in around 20% of unselected, advanced NSCLC patients, and primary and acquired resistance remain unsolved obstacles. Therefore, precise predictive indicators must be identified to choose the best patients for ICI treatment. Thus, Sialic acid-binding immunoglobulin-like lectin 15 (Siglec-15) stands out as a potential tumor biomarker, with distinctive expression in normal tissues, in tumor immune involvement, and a high structural similarity to PD-L1. Understanding the tumor immune response and the search for new therapeutic targets leads to the improvement of therapeutic pathways directed at the tumor microenvironment. The present review aims to analyze Siglec-15 potential as a diagnostic, prognostic, and response biomarker in lung cancer, considering its results evidenced in the current literature.

Siglec15 is a prognostic indicator and a potential tumor-related macrophage regulator that is involved in the suppressive immunomicroenvironment in gliomas

Background

Siglec15 is rising as a promising immunotherapeutic target in bladder, breast, gastric, and pancreatic cancers. The aim of the present study is to explore the prognostic value and immunotherapeutic possibilities of Siglec15 in gliomas using bioinformatics and clinicopathological methods.

Methods

The bioinformatics approach was used to examine Siglec15 mRNA expression in gliomas based on TCGA, CGGA, and GEO datasets. Then, the predictive value of Siglec15 expression on progression-free survival time (PFST) and overall survival time (OST) in glioma patients was comprehensively described.The TCGA database was screened for differentially expressed genes (DEGs) between the high and low Siglec15 expression groups, and enrichment analysis of the DEGs was performed. The Siglec15 protein expression and its prognostic impact in 92 glioma samples were explored using immunohistochemistry Next, the relationships between Siglec15 expression and infiltrating immune cells, immune regulators and multiple immune checkpoints were analysed.

Results

Bioinformatics analyses showed that high Siglec15 levels predicted poor clinical prognosis and adverse recurrence time in glioma patients. In the immunohistochemical study serving as a validation set, Siglec15 protein overexpression was found in 33.3% (10/30) of WHO grade II, 56% (14/25) of WHO grade III, and 70.3% (26/37) of WHO grade IV gliomas respectively. Siglec15 protein overexpression was also found to be an independent prognostic indicator detrimental to the PFST and OST of glioma patients. Enrichment analysis showed that the DEGs were mainly involved in pathways associated with immune function, including leukocyte transendothelial migration, focal adhesion, ECM receptor interaction, and T-cell receptor signaling pathways. In addition, high Siglec15 expression was related to M2 tumor-associated macrophages (TAMs), N2 tumor-infiltrating neutrophils, suppressive tumor immune microenvironment, and multiple immune checkpoint molecules. Immunofluorescence analysis confirmed the colocalization of Siglec15 and CD163 on TAMs.

Conclusion

Siglec15 overexpression is common in gliomas and predicts an adverse recurrence time and overall survival time. Siglec15 is a potential target for immunotherapy and a potential TAMs regulator that is involved in the suppressed immunomicroenvironment in gliomas.

Dynamic change in Siglec-15 expression in peritumoral macrophages confers an immunosuppressive microenvironment and poor outcome in glioma

Background

Sialic acid-binding immunoglobulin-like lectin-15 (Siglec-15) was reported to be a novel immune checkpoint molecule comparable to programmed cell death 1 ligand 1 (PD-L1). However, its expression profile and immunosuppressive mechanisms in the glioma tumor microenvironment have not yet been fully explored.

Objectives

To identify the expression profile and potential function of Siglec-15 in glioma tumor microenvironment.

Methods

We investigated Siglec-15 and PD-L1 expression in tumor tissues from 60 human glioma patients and GL261 tumor models. Next, Siglec-15 knockout macrophages and mice were used to elucidate the immunosuppressive mechanism of Siglec-15 impacting macrophage function.

Results

Our results demonstrated that high levels of Siglec-15 in tumor tissues was positively correlated with poor survival in glioma patients. Siglec-15 was predominantly expressed on peritumoral CD68⁺ tumor-associated macrophages, which accumulated to the highest level in grade II glioma and then declined as grade increased. The Siglec-15 expression pattern was mutually exclusive with that of PD-L1 in glioma tissues, and the number of Siglec-15⁺PD-L1^- samples (n = 45) was greater than the number of Siglec-15^-PD-L1⁺ samples (n = 4). The dynamic change in and tissue localization of Siglec-15 expression were confirmed in GL261 tumor models. Importantly, after Siglec15 gene knockout, macrophages exhibited enhanced capacities for phagocytosis, antigen cross-presentation and initiation of antigen-specific CD8⁺ T-lymphocyte responses.

Conclusion

Our findings suggested that Siglec-15 could be a valuable prognostic factor and potential target for glioma patients. In addition, our data first identified dynamic changes in Siglec-15 expression and distribution in human glioma tissues, indicating that the timing of Siglec-15 blockade is critical to achieve an effective combination with other immune checkpoint inhibitors in clinical practice.

Tamoxifen Modulates the Immune Landscape of the Tumour Microenvironment: The Paired Siglec-5/14 Checkpoint in Anti-Tumour Immunity in an In Vitro Model of Breast Cancer

Since the role of sialome–Siglec axis has been described as a regulatory checkpoint of immune homeostasis, the promotion of stimulatory or inhibitory Siglec-related mechanisms is crucial in cancer progression and therapy. Here, we investigated the effect of tamoxifen on the sialic acid–Siglec interplay and its significance in immune conversion in breast cancer. To mimic the tumour microenvironment, we used oestrogen-dependent or oestrogen-independent breast cancer cells/THP-1 monocytes transwell co-cultures exposed to tamoxifen and/or β-estradiol. We found changes in the cytokine profiles accompanied by immune phenotype switching, as measured by the expression of arginase-1. The immunomodulatory effects of tamoxifen in THP-1 cells occurred with the altered SIGLEC5 and SIGLEC14 genes and the expression of their products, as confirmed by RT-PCR and flow cytometry. Additionally, exposure to tamoxifen increased the binding of Siglec-5 and Siglec-14 fusion proteins to breast cancer cells; however, these effects appeared to be unassociated with oestrogen dependency. Our results suggest that tamoxifen-induced alterations in the immune activity of breast cancer reflect a crosstalk between the Siglec-expressing cells and the tumour’s sialome. Given the distribution of Siglec-5/14, the expression profile of inhibitory and activatory Siglecs in breast cancer patients may be useful in the verification of therapeutic strategies and predicting the tumour’s behaviour and the patient’s overall survival.

Significance of Siglec-15 expression in colorectal cancer: association with advanced disease stage and fewer tumor-infiltrating lymphocytes

Siglec-15, a novel immune suppressor, is upregulated in many human cancers. The aim of this study was to explore the expression of Siglec-15 in colorectal cancer (CRC), and investigate whether Siglec-15 could be a potential target for cancer immunotherapy in patients with CRC. We performed immunohistochemical analyses of Siglec-15 on a cohort of 805 patients with CRC and made comparisons between clinicopathological characteristics, PD-L1 expression, CD3, CD8, CD45RO tumor-infiltrating lymphocytes (TILs), and prognosis. We found that Siglec-15 expression was commonly detected in tumor cells (48.3%) and tumor-associated stromal cells (33.4%), and was more frequently observed than PD-L1 expression in tumor cells. In contrast, Siglec-15 expression was weakly and scarcely found in normal mucosa (13%). Siglec-15 overexpression in tumor cells was associated with advanced TNM stage (p = 0.020). Co-expression of Siglec-15 and PD-L1 in tumor cells was found in 14.4% of patients, and Siglec-15 expression was detected in almost half of PD-L1 negative cases. Elevated Siglec-15 expression in tumor and stromal cells was associated with sparser CD45RO and CD8 TILs (p = 0.035 and p = 0.004, respectively). The expression of Siglec-15 did not have prognostic significance. In summary, compared to PD-L1, Siglec-15 protein expression is more prevalent in CRC and is associated with advanced disease stage and fewer TILs. These findings support Siglec-15 as a potential cancer immunotherapy target, in addition to PD-1/PD-L1 inhibitors, in patients with CRC.