Identification and Analysis of SND1 as an Oncogene and Prognostic Biomarker for Lung Adenocarcinoma

TL;DR

This study identifies SND1 as a cancer-promoting gene in lung adenocarcinoma, showing it is linked to poor patient outcomes and promotes tumor cell growth and spread.

Contribution

The study is the first to demonstrate SND1's role as an oncogene and potential biomarker in lung adenocarcinoma.

Findings

SND1 is overexpressed in lung adenocarcinoma and correlates with poor patient survival.

SND1 is localized in the cytoplasm of cancer cells and is associated with cell cycle progression and DNA replication.

Reducing SND1 expression inhibits cancer cell proliferation, migration, and invasion in laboratory experiments.

Abstract

背景与目的 转录因子（transcription factor, TF）可以结合特异性序列，对下游基因起到促进或抑制的作用，对肿瘤的发生、迁移、侵袭等生物学过程都有重要的影响。葡萄球菌含核酸酶结构域1（Staphylococcal nuclease-containing structural domain 1, SND1）作为一种转录共激活因子，被认为是肿瘤治疗的一个潜在靶点。然而，其在肺腺癌（lung adenocarcinoma, LUAD）中的表达及作用尚不清楚。本研究主要探索SND1作为LUAD癌基因在LUAD中的作用。方法 从癌症基因组图谱（The Cancer Genome Atlas, TCGA）、基因表达综合数据库（Gene Expression Omnibus, GEO）、临床蛋白质组肿瘤分析联盟（Clinical Proteomic Tumor Analysis Consortium, CPTAC）和人类蛋白图库（Human Protein Atlas, HPA）等数据库获取数据，探讨SND1表达与LUAD患者预后、免疫细胞浸润和亚细胞定位的关系；利用EdU法、CCK-8法、流式细胞术、细胞划痕实验、Transwell实验、蛋白印迹实验等体外实验探讨SND1在LUAD中的功能作用。结果 在LUAD中SND1的表达上调，且与患者预后不良有关。SND1主要存在于LUAD细胞的细胞质中。富集分析表明SND1与细胞周期密切相关，包括DNA复制和染色体分离等。免疫细胞浸润分析显示，SND1与多种免疫细胞群有关，包括T细胞、B细胞、细胞毒性细胞和树突状细胞。体外研究表明沉默SND1可抑制LUAD细胞的增殖、侵袭和迁移，下调SND1可阻断G1期细胞周期进程。结论 SND1可能是LUAD重要的预后生物标志物，其可促进LUAD细胞的增殖和迁移。

A: The analysis of genetic changes in SND1 through cBioPortal based on TCGA's LUAD database; B: High mRNA expression of SND1 in LUAD tissues in the TCGA database (UCLCAN); C: The expression of SND1 in paired tumor and normal lung tissues; D: SND1 was highly expressed in tumor tissues as verified in two GEO databases (GSE116959 and GSE68517); E: High protein expression of SND1 in LUAD tissues in the CPTAC database; F: SND1 protein expression in LUAD and normal tissues was examined by immunohistochemistry in the Human Protein Atlas database; G: Expression of SND1 in 20 NSCLC cell lines in CCLE database. SND1: Staphylococcal nuclease-containing structural domain 1; LUAD: lung adenocarcinoma; TCGA: The Cancer Genome Atlas; GEO: Gene Expression Omnibus. ***P<0.001.

A, B: Expression of SND1 in LUAD stratified by tumor stages and lymph node metastases status in the TCGA database (UCLCAN); C: Protein expression levels of SND1 stratified by grades of LUAD in the CPTAC database; D: Kaplan-Meier survival curves for the OS according to the expression levels of SND1 in LUAD; E: ROC curve of SND1 in LUAD based on TCGA database. OS: overall survival; ROC: receiver operating characteristic; AUC: area under the curve; ns: not significant. Compared with normal control group, *P<0.05, ***P<0.001.

A, B: In vivo and intracellular SND1 distribution based on the human protein atlas; C: Confocal fluorescence microscopy to examine the location of SND1 expression in LUAD cells (×100).

A: SND1-related protein interactions networks; B: KEGG enrichment annotation of related genes; C-E: GO enrichment annotation of the related genes, including CC, BP and MF; F: The volcano plot of the DEGs in the high-SND1 expression group vs low-SND1 expression group; G: Regulation of chromosome segregation; H: DNA replication initiation; I: Mitotic spindle assembly; J: Cell cycle DNA replication; K: Mitotic nuclear division. DEGs: differentially expressed genes.

A: Differential expression of 16 immune cells in high SND1 expression group and low SND1 expression group; B: Relationship between SND1 and immune checkpoint genes in LUAD; C-E: Relationship between SND1 expression and stromal score, immune score and estimate score. *P<0.05, **P<0.01, ***P<0.001.

A, B: Expression of SND1 in bronchial epithelial cell lines (BEAS-2B) and four NSCLC cell lines (H1975, A549, PC9 and H1299) at mRNA level and protein level; C: Immunohistochemical staining of SND1 in tumor and non-tumor tissues from ten LUAD patients. Compared with BEAS-2B cell line, *P<0.05, **P<0.01, ***P<0.001.

A: Relative mRNA and protein levels of H1975 and A549 after transfection with si-NC and si-SND1; B: CCK-8 assay of cell proliferation in H1975 and A549 cells after SND1 knockdown; C: EdU assay results of H1975 and A549 after SND1 knockdown (×20); D, E: Cell cycle assay showed that SND1 knockdown induced G1 phase arrest; F, G: The results of scratch and transwell invasion assays showed reduced migration and invasion of SND1 knockdown cells compared with control cells (×10); H: Expression of cycle, migration and invasion-related proteins in the SND1 knockout group compared to controls. *P<0.05, **P<0.01, ***P<0.001. OD: optical density.

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