Its association with the histone methyltransferase MLL2/MLL3 complex is suggesting a role in epigenetic transcriptional activation. However, in association with PAXIP1/PTIP is proposed to function at least in part independently of the MLL2/MLL3 complex. Proposed to be recruited by PAXIP1 to sites of DNA damage where the PAGR1:PAXIP1 complex is required for cell survival in response to DNA damage independently of the MLL2/MLL3 complex (PubMed:19124460). However, its function in DNA damage has been questioned (PubMed:26744420). During immunoglobulin class switching in activated B-cells is involved in transcription regulation of downstream switch regions at the immunoglobulin heavy-chain (Igh) locus independently of the MLL2/MLL3 complex (PubMed:26744420). Involved in both estrogen receptor-regulated gene transcription and estrogen-stimulated G1/S cell-cycle transition (By similarity). Acts as transcriptional cofactor for nuclear hormone receptors. Inhibits the induction properties of several steroid receptors such as NR3C1, AR and PPARG; the mechanism of inhibition appears to be gene-dependent (By similarity). May be involved in the regulation of the BMP pathway in extraembryonic development (PubMed:24633704). Component of the KMT2 family MLL2/MLL3 complex, at least composed of the histone methyltransferases KMT2D and/or KMT2C, the common subunits ASH2L, RBBP5, WDR5 and DPY30, and the complex type-specific subunits PAXIP1/PTIP, PAGR1, NCOA6 and KDM6A; PAXIP1 is required for the association with the MLL2/MLL3 complex (By similarity). Forms a constitutive complex with PAXIP1/PTIP independently of the MLL2/MLL3 complex (PubMed:19124460, PubMed:26744420). Interacts with NCOA1, ESR1, NR3C1, AR (By similarity). Expression first detected at 5.0-6.0 dpc in the extraembryonic region, at 7.5 dpc detected within the chorion; later the expression is expanding to the entire embryo. Normal germ layer specification and developmental patterning but limited anterior development and arrest by 8.5 dpc, likely due at least in part to defects in extraembryonic tissue. The terminology of MLL proteins in mammalia is not consistent also concerning the terminology of MLL protein-containing complexes. The decribed MLL2/MLL3 complex is commonly described as MLL3/MLL4 complex in literature.