E2F1 and breast cancer: Furthermore, western blot demonstrated that upregulation of circAGFG1 enhanced the protein levels of CCNE1 and downstream targets CDK2, pRB, E2F1 and breast cancer stem cells marker CD44, while knockdown of circAGFG1 decreased the levels of these proteins and the effects caused by overexpressing or silencing circAGFG1 could be reversed by miR-195-5p mimics or inhibitors, respectively (Fig. 8d, e).