PELP1 knockdown impedes estrogen-mediated tumor growth. Nude mice implanted with estrogen pellets were injected subcutaneously with MCF-7 cells. After 4 weeks, xenografts were treated with control-siRNA-DOPC or PELP1-siRNA-DOPC. Tumor growth was measured at weekly intervals. (A) Immunohistochemistry (IHC) analysis of PELP1 expression in tumors treated with control or PELP1-siRNA-DOPC (left panel). (B) Tumor volume. (C) Levels of H3K4me2, H2K9me2 and H3K9ac epigenetic marks were analyzed by IHC in tumors treated with control or PELP1-siRNA-DOPC; quantitation performed as described in Materials and methods. Bar: standard error of the mean. *P < 0.05, **P < 0.001. DOPC, 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine; PELP1, proline glutamic acid and leucine-rich protein 1.