Effects of Mdm2 on coactivation of ERα by GRIP (SRC-2). ZR-75 cells were treated with DMSO or 10 nM E2, and transfected with pMGripwt/VPERα and iCT or iMdm2 oligonucleotides (A) or pMGripwt/VP16-Mdm2, empty vectors and hERα (B), and luciferase activity was determined as described in the Materials and Methods. ZR-75 cells were treated with DMSO or 10 nM E2, transfected with pMGripLXXLL/VPERα and iCT or iMdm2 oligonucleotides (C) or pMGripLXXLL/VP16-Mdm2, empty vectors and ERα (D), and luciferase activity determined as described in the Materials and Methods. Results are expressed as means ± SE for at least 3 replicate determinations for each treatment group, and significantly (p<0.05) enhanced interactions by ERα (*) or decreased activity by iMdm2 (**) are indicated.