Abstract
miR-203 act as tumor repressor by inhibiting cell proliferation and is repressed in a variety of human tumors, although the molecular mechanisms responsible have not been elucidated. Here, we reveal that miR-203 is regulated by E2F1, an important transcription factor that can induce cell proliferation by controlling cell cycle progression. We found that miR-203 expression was induced by cisplatin, which also induced E2F1 protein accumulation in esophageal squamous cell carcinoma (ESCC) cell lines. miR-203 expression was elevated upon activation of ectopic E2F1, whereas this induction was abolished when the E2F1 gene was silenced. Moreover, with luciferase reporter assays and chromatin immunoprecipitation (ChIP) assays, we demonstrated that E2F1 transactivates miR-203 by directly binding to the miR-203 gene promoter. In addition, we found that miR-203 inhibited cell proliferation by inducing G1/S cell cycle arrest, but not apoptosis, in ESCC cell lines. Finally, we observed that miR-203 negatively inhibited the expression of CDK6, subsequently decreasing E2F1 expression possibly through Rb phosphorylation. Taken together, our data show that cancer-related miR-203 is a novel transcriptional target of E2F1 and that it regulates cell cycle arrest by participating in a feedback loop with E2F1.