May play a role in a ERBB3-regulated signal transduction pathway. Seems be involved in growth regulation. Acts a corepressor of the androgen receptor (AR) and is regulated by the ERBB3 ligand neuregulin-1/heregulin (HRG). Inhibits transcription of some E2F1-regulated promoters, probably by recruiting histone acetylase (HAT) activity. Binds RNA. Associates with 28S, 18S and 5.8S mature rRNAs, several rRNA precursors and probably U3 small nucleolar RNA. May be involved in regulation of intermediate and late steps of rRNA processing. May be involved in ribosome assembly (By similarity). Mediates cap-independent translation of specific viral IRESs (internal ribosomal entry site). Together with PTBP1 is required for the translation initiation on the foot-and-mouth disease virus (FMDV) IRES. Regulates cell proliferation, differentiation, and survival. Isoform 1 suppresses apoptosis whereas isoform 2 promotes cell differentiation (By similarity). Isoform 2 interacts with the cytoplasmic domain of non-phosphorylated ERBB3; the interaction requires PKC activity. Interacts with AR. Treatment with HRG leads to dissociation from ERBB3 and increases association with AR. Interacts with nucleolin/NCL. Component of a ribonucleoprotein complex containing at least PA2G4, NCL, TOP1, PABPC2, RPLP0, acetylated histone H1 (HIST1H1A or H1F1), histone H1 2/4, RPL4, RPL8, RPL15, RPL18, RPL18A, RPL21, RPL11, RPL12, RPL28, RPL27, RPLP2 and RPL24. Interacts with HDAC2. Interacts with RB1; the interaction is enhanced upon PA2G4 dephosphorylation (By similarity). Interacts with AKT1 (By similarity). Isoform 1 and isoform 2 interact with RNF20 (By similarity). Isoform 2 interacts with HUWE1. Interacts with DNAJC21 (By similarity). Phosphorylation at Ser-361 by PKC/PRKCD regulates its nucleolar localization. Widely expressed. Expressed in proliferating cells. Observed between G1 and mid S phase, decrease toward the end of S phase, and disappear at the S/G2 transition. By mitogens. Phosphorylated on serine and threonine residues. Phosphorylation is enhanced by HRG treatment. Basal phosphorylation is PKC-dependent and HRG-induced phosphorylation is predominantly PKC-independent. Phosphorylation at Ser-361 by PKC/PRKCD regulates its nucleolar localization. Isoform 2 is polyubiquitinated, leading to proteasomal degradation and phosphorylation by PKC/PRKCD enhances polyubiquitination. Belongs to the peptidase M24 family. Although it belongs to the peptidase M24 family, it does not contain metal cofactors and lacks aminopeptidase activity.