Resibufogenin converts RB protein to the unphosphorylated form with down-regulation of cyclin D1 expression.

<p>(A) The effect of resibufogenin on the expression of phosphorylated RB (p-RB (Ser⁷⁸⁰) and p-RB (Ser^807/811)), RB, cyclin D1 and cyclin E. Cells were treated with resibufogenin at the indicated concentrations for 24 h and analysed by Western blotting. (B) Time-course study on the phosphorylation status of RB protein and the expression of cyclin D1. Cells were treated with 5 μM resibufogenin (R) for 1, 2, 3, 6, 9 or 24 h and analysed by Western blotting. In both figures, RB or GAPDH was used as a loading control for protein quantitation. UT, untreated; DM, treated with DMSO. The band intensity was measured and normalized by RB or GAPDH, and the protein levels are shown at the bottom of each blot.