Coactivator of estrogen receptor-mediated transcription and a corepressor of other nuclear hormone receptors and sequence-specific transcription factors (PubMed:14963108). Plays a role in estrogen receptor (ER) genomic activity when present in the nuclear compartment by activating the ER target genes in a hormonal stimulation dependent manner. Can facilitate ER non-genomic signaling via SRC and PI3K interaction in the cytosol. Plays a role in E2-mediated cell cycle progression by interacting with RB1. May have important functional implications in ER/growth factor cross-talk. Interacts with several growth factor signaling components including EGFR and HRS. Functions as the key stabilizing component of the Five Friends of Methylated CHTOP (5FMC) complex; the 5FMC complex is recruited to ZNF148 by methylated CHTOP, leading to desumoylation of ZNF148 and subsequent transactivation of ZNF148 target genes. Component of the PELP1 complex involved in the nucleolar steps of 28S rRNA maturation and the subsequent nucleoplasmic transit of the pre-60S ribosomal subunit. Regulates pre-60S association of the critical remodeling factor MDN1 (PubMed:21326211). May promote tumorigenesis via its interaction with and modulation of several oncogenes including SRC, PI3K, STAT3 and EGFR. Plays a role in cancer cell metastasis via its ability to modulate E2-mediated cytoskeleton changes and cell migration via its interaction with SRC and PI3K. {ECO:0000269|PubMed:11481323, ECO:0000269|PubMed:12682072, ECO:0000269|PubMed:14963108, ECO:0000269|PubMed:15374949, ECO:0000269|PubMed:15456770, ECO:0000269|PubMed:15579769, ECO:0000269|PubMed:15994929, ECO:0000269|PubMed:16140940, ECO:0000269|PubMed:16352611, ECO:0000269|PubMed:16574651, ECO:0000269|PubMed:21326211, ECO:0000269|PubMed:22872859}. This is the function of ENSG00000141456 (PELP1, proline, glutamate and leucine rich protein 1).