# 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.

## Key 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.