SIX1 Promotes Proliferation and Invasion of Breast Cancer Cells / 中国生物化学与分子生物学报

ABSTRACT

Sine oculis homeobox homolog 1 (SIX1) is involved in the regulation of many kinds of tumors and plays an important role in the occurrence and development of breast cancer, but the exact mechanism remains to be explored. In this study, we analyzed the expression of SIX1 in breast cancer, and investigated the role of SIX1 in the proliferation and invasion of breast cancer cells. TCGA database and GEPIA2 showed that the expression of SIX1 in breast cancer was significantly higher than that in normal tissues, which was confirmed in different molecular subtypes of breast cancer, including Basal-like, HER2, Luminal A and Luminal B (P < 0. 05). Besides, the analysis of HPA database also showed that the expression of SIX1 was significantly upregulated in breast cancer, and the difference was statistically significant (P < 0. 001). After interfering with the expression of SIX1 in the breast cancer cell line MDA-MB-231 and overexpressing SIX1 in MCF-7, the growth curve and EdU results showed that the proliferation of breast cancer cells was inhibited after knocking down SIX1, while overexpression of SIX1 could promote the proliferation ability (the growth curve assays P < 0. 05; EdU assays P < 0. 001). Besides, Transwell assays showed that SIX1 could enhance the invasion ability of breast cancer cells (P < 0. 001). In TCGA database we defined the high and low expression populations according to the upper and lower quartiles of SIX1 gene expression, and differentially expressed genes were found to be associated with metabolism and stem cell regulatory pathways. For further confirmation, high-throughput RNA deep sequencing (RNA-seq) was conducted using SIX1-knockdown cells, and analysis also showed that SIX1 was closely related to metabolism, stem cell regulation and EMT pathways. We selected several representative genes, MYC, SNAI2 and EGFR, to examine their associations with SIX1 expression and prognosis in patients with clinical breast cancer using published GEO datasets and KM-plotter, we found that SIX1 was positively correlated with the expression of MYC, SNAI2 and EGFR, and the high expression of SIX1, MYC, SNAI2 and EGFR is not conducive to the survival of breast cancer patients. GCBI, GeneMANIA and String online tools were conducted to predict the associated genes, lncRNA and miRNA of SIX1. Collectively, our study initially revealed the role of SIX1 in breast cancer and its regulatory mechanism, providing new insights for further studies.