The downregulation of SASH1 expression promotes breast cancer occurrence and invasion accompanied by the activation of PI3K-Akt-mTOR signaling pathway.

SASH1 (SAM and SH3 domain containing 1) has been increasingly reported as a tumor suppressor gene. However, there is limited research on the role of SASH1 in breast cancer. This manuscript aims to investigate the mechanism of SASH1 in the occurrence, development, and prognosis of breast cancer. Firstly, we obtained RNA-sequencing data of the tumors from the Genomic Data Commons data portal website, along with the corresponding clinical information of patients. Pan-cancer analysis was performed to analyze the expression of SASH1 across all tumors. Univariate Cox regression analysis was used to assess the correlation between SASH1 expression and the prognosis of breast cancer patients. Then, immunohistochemistry was utilized to evaluate the expression levels of SASH1, p-Akt, p-PI3K, and p-mTOR in breast cancer tissue. Finally, a cell assay was employed to analyze the impact of SASH1 on the proliferation and invasion of breast cancer cells (MDA-MB-231). The results revealed that SASH1 expression is decreased in BRCA, LUSC, LUAD, CESC, ESCA, and COAD. Meta-analysis also found that SASH1 is downregulated in most tumor tissues, and the expression level of SASH1 in breast cancer was significantly lower than that in the control group (OR = 0.14, 95% CI = 0.08-0.25; P < 0.001). Further experimental validation showed that SASH1 expression is significantly downregulated in breast cancer tissue (38.33%, 23/60), and the overexpression of SASH1 can inhibit the proliferation and invasion of breast cancer cells accompanied by the suppression of PI3K-Akt-mTOR signaling pathway. Additionally, SASH1 overexpression can improve OS and RFS of breast cancer patients.