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. Mediates cap-independent translation of specific viral IRESs (internal ribosomal entry site). Regulates cell proliferation, differentiation, and survival. Isoform 1 suppresses apoptosis whereas isoform 2 promotes cell differentiation. Isoform 2 is undetectable whereas isoform 1 is strongly expressed in cancer cells (at protein level). Isoform 1 and isoform 2 are widely expressed, including heart, brain, lung, pancreas, skeletal muscle, kidney, placenta and liver. 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 NCL/nucleolin. 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. Interacts with AKT1.