A, pcDNA vector- and PELP1-expressing clones were stimulated with E2 for 20 h. Total lysates were analyzed for the phosphorylation status of pRb by Western blotting with pRb. B, pcDNA and PELP1 clones were stimulated with E2 for different periods, and the kinetics of pRb phosphorylation were analyzed by Western blotting. The arrows point to the hyperphosphorylated form of pRb (pRbPhos). C, pcDNA and PELP1 clones were treated with E2 for 6 or 8 h, and total cell lysates were analyzed for the status of phosphorylation of pRb using phosphorylation site-specific antibodies. D, pcDNA and PELP1 clones were pretreated with or without ICI 182780 for 30 min and then with or without E2 for 8 h. The status of pRb phosphorylation at Ser-807/Ser-811 was analyzed by Western blotting (W).