Nucleotide exchange factor SIL1 promotes the progress of breast cancer cells via regulating the cell cycle and apoptosis

Breast cancer, as one of the most malignant tumors, poses a serious threat to the lives of females. Nucleotide exchange factor SIL1 is an important regulator of endoplasmic reticulum function that might have a specific role in tumor progression. In this study, we aimed to investigate the effect of SIL1 on the proliferation, apoptosis, and metastasis of human breast cancer. SIL1-specific small interfering RNA was transfected into two breast cancer cell lines, MCF7 and MDA-MB-231, to generate SIL1 knockdown cells. Clone formation and Cell Counting Kit-8 assays were performed to determine cell proliferation. Wound healing and transwell assays were used to detect the cell migration and invasion, respectively. Cell cycle and apoptosis were determined by flow cytometry. The messenger RNA and protein levels of target genes were analyzed using quantitative real-time PCR and western blot. According to the results of TCGA and GTEx database analysis, we determined that SIL1 was overexpressed in 1085 breast cancer samples compared with 291 normal samples. Knockdown of SIL1 inhibited the proliferation, migration, and invasion of MCF7 and MDA-MB-231 cells, accordingly. The cell cycle was blocked at the G1 phase following transfection of SIL1-specific small interfering RNA through the inhibition of Cyclin D1, CDK4, and CDK6. SIL1 knockdown induced apoptosis and also promoted the activity of Caspase9 and Bax. Furthermore, SIL1 was able to promote phosphorylation of ERK1/2. Based on these results, SIL1 might act as an oncogene and accelerate the progression of human breast cancer.