E2F1 and neoplasm: As a tumor-suppressive miRNA, miR-449a inhibits cell growth and proliferation in a retinoblastoma (Rb)-dependent manner by directly targeting key factors involved in cell cycle progression, such as HDAC119, cyclin D123, CDC25A24, cyclin-dependent kinase 6 (CDK6)20 and E2F transcription factor 1 (E2F1)24.