Cucurbitacin E inhibits esophageal carcinoma cell proliferation, migration, and invasion by suppressing Rac1 expression through PI3K/AKT/mTOR pathway.

ABSTRACT

As an oxygenated tetracyclic triterpenoid, Cucurbitacin E (CuE) possesses potential antitumor properties in sorts of malignancies. However, its effect on human esophageal carcinoma cells has not been previously unearthed, and the mechanism underlying its anticarcinoma activity remains vague. Hence, this study was arranged to probe the function of CuE on esophageal carcinoma cells and its specific mechanism. Human esophageal carcinoma cells (ECA109 and EC9706) and human normal esophageal epithelial cells (Het-1A) were selected for subsequent experiments. The expression levels of Rac1 in esophageal carcinoma cells were measured. After transfection of sh-Rac1 or pCDNA3.1-Rac1, esophageal carcinoma cells were exposed to CuE. Then, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and 5-ethynyl-2'-deoxyuridine staining were utilized for measurement of cell proliferation ability, cell scratch assay for inspection of cell migration rate, and Transwell for detection of cell invasion ability. The phosphorylation levels of protein kinase B and mTOR were analyzed by Western blot. Rac1 was highly expressed in esophageal carcinoma cells. Transfection of sh-Rac1 in esophageal carcinoma cells resulted in suppression on cell proliferation, migration, and invasion, as well as downregulated phosphorylation levels of AKT and mammalian target of rapamycin (mTOR) in esophageal carcinoma cells, while transfection of pCDNA3.1-Rac1 had an opposite effect, implicating that Rac1 can promote the viability of esophageal carcinoma cells. Esophageal carcinoma cells subjected to CuE treatment had decreased expression of Rac1, suppressed cell viability, and decreased phosphorylation levels of AKT and mTOR. Transfection of pCDNA3.1-Rac1 and CuE treatment in esophageal carcinoma cells enhanced viability of esophageal carcinoma cells and promoted the phosphorylation levels of AKT and mTOR in comparison with cells treated with CuE alone. CuE inhibits proliferation, invasion, and migration of esophageal carcinoma cells via downregulating Rac1 to block the phosphoinositide 3-kinase/AKT/mTOR pathway.