Ellagic acid induces esophageal squamous cell carcinoma cell apoptosis by modulating SHP-1/STAT3 signaling

Ellagic acid (EA) has been reported to have antiproliferative and antioxidant properties, but its function in esophageal squamous cell carcinoma (ESCC) has not been investigated yet. In the current study, EA was found have a significant anti-tumor activity in ESCC. In specific, EA inhibited ESCC cell survival in both of a concentration- and time-dependent manner. And our results showed that EA promoted ESCC cell apoptosis, including inducing the cleavages of PARP, and inhibiting the expression of anti-apoptotic proteins. In mechanistic, EA markedly suppressed STAT3-driven luciferase activity, and inhibited both of the endogenous and cytokines-induced STAT3 activation in ESCC cells. Further investigations indicated that EA could significantly upregulate SHP-1 expression, a negative modulator of STAT3 signaling. In contrast, knockdown of SHP-1 could attenuate the effects of EA on inhibiting ESCC cell survival. Moreover, we found that EA could inhibit RNF6 expression, an E3 of SHP-1, and overexpressing RNF6 could also significantly attenuate the effects of EA on inhibiting ESCC cell survival, which further revealed that EA could inhibit STAT3 signaling by modulating RNF6/SHP-1 axis. Our present study indicated that EA could be as a novel STAT3 inhibitor for the treatment of ESCC.