唾液酸免疫球蛋白型凝集素-15促进结直肠癌细胞增殖和迁移并抑制肿瘤组织中CD4+与CD8+T细胞浸润

唾液酸免疫球蛋白型凝集素-15(sialic acid-binding immunoglobulin-type lectin-15,Siglec-15)属于Siglecs家族的一员,是一种新型免疫抑制分子。Siglec-15在多种人类肿瘤细胞和肿瘤相关巨噬细胞中高表达,但Siglec-15在结直肠癌(colorectal cancer,CRC)中的生物学功能及其对免疫微环境的影响尚不明确。本文旨在分析Siglec-15异常表达对CRC细胞功能及CD4⁺T细胞、CD8⁺T细胞浸润的影响。首先,分析TCGA数据库中结直肠癌与正常组织中Siglec-15 mRNA表达水平,并对52例人CRC与配对癌旁组织进行免疫组织化学染色(IHC),发现Siglec-15在CRC中的表达水平高于癌旁组织(P<0.01)。CCK8和划痕愈合结果显示,敲低Siglec-15能抑制人CRC细胞SW480增殖(P<0.01)和迁移(P<0.05)。磁珠分选小鼠脾的CD8⁺T细胞并与小鼠CRC细胞MC38共培养,发现MC38细胞过表达Siglec-15能抑制CD8⁺T细胞对其的杀伤以及IFN-γ和TNF-α的分泌(P<0.01)。小鼠荷瘤结果表明,过表达Siglec-15可以促进小鼠肿瘤生长(P<0.05)。单样本基因集富集分析、荷瘤小鼠肿瘤组织及人结直肠癌组织IHC分析均表明,Siglec-15高表达时,肿瘤微环境中CD4⁺T细胞、CD8⁺T细胞浸润减少(P<0.05)。综上所述,Siglec-15可能通过促进CRC细胞增殖迁移以及抑制CD4⁺T细胞、CD8⁺T细胞浸润促进结直肠癌进展。本文为探究Siglec-15在CRC中的免疫抑制作用提供了一些新的实验依据。

Siglec-15 Promotes the Proliferation and Migration of Colorectal Cancer Cells and Inhibits the Infiltration of CD4+ andCD8+ T Cells in Tumor Tissues

Sialic acid binding immunoglobulin type lectin-15 (Siglec-15), one of the Siglec gene family members, is a new immunosuppressive molecule. Siglec-15 is highly expressed in a variety of human tumor cells and tumor-associated macrophages, but the biological function of Siglec-15 in colorectal cancer (CRC) and its effect on the tumor immune microenvironment remains poorly understood. This study aimed to investigate the effects of aberrant expression of Siglec-15 on the biological behaviors of CRC cells and the infiltration of CD4⁺ T and CD8⁺ T cells. Firstly, mRNA expression level of Siglec-15 was assessed in human CRC tissues from the TCGA database. IHC staining was performed to detect Siglec-15 expression in 52 cases of human CRC and paired adjacent tissues. We found that the expression level of Siglec-15 in CRC was significantly higher than that in adjacent tissues (P<0.01). CCK8 assay and wound healing assay showed that knocking down Siglec-15 could inhibit the proliferation (P<0.01) and migration (P<0.05) of SW480 cells. CD8⁺ T cells were isolated from mouse spleen with anti-CD8 magnetic beads, and co-cultured with mouse MC38 CRC cells. It was found that overexpression of Siglec-15 in MC38 cells could inhibit CD8⁺ T-cell-mediated killing of tumor cells and inhibit the secretion of IFN-γ and TNF-α (P<0.01). Subsequent in vivo experiments showed that overexpression of Siglec-15 promoted tumor growth in tumor-bearing mice (P<0.05). In addition, high level of Siglec-15 in CRC tissues is associated with decreasing infiltration of CD4⁺ T cells and CD8⁺ T cells in the tumor microenvironment after single sample gene set enrichment analysis and IHC analysis of mouse xenograft tumor tissues and human CRC tissues (P<0.05). In conclusion, Siglec-15 may contribute to the progression of colorectal cancer through promoting the proliferation and migration of CRC cells and hampering CD4⁺ T cells and CD8⁺ T cells infiltration into tumor microenvironment. This study provides some new experimental basis for exploring the immunosuppressive effect of Siglec-15 in CRC.