A, pRb-defective SAOS2 cells were cultured for 48 h in 5% DCC serum and then transfected with the ERE reporter, ERα, and PELP1 with or without pRb expression vectors. Cells were treated with or without E2 (10−9 m) after 48 h, and luciferase (luc) activity was measured after 24 h of ligand treatment. The inset shows the expression of endogenous PELP1 in SAOS2 cells. B, SAOS2 cells were cotransfected with the PELP1 N-terminal fragment and the pRb expression vector, and ERE-luciferase activity was measured after 24 h of E2 treatment. Con, control; WT, wild-type; PELP-MT, PELP-1 protein containing amino acids 1–605.