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. However, its function in DNA damage has been questioned. 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. Involved in both estrogen receptor-regulated gene transcription and estrogen-stimulated G1/S cell-cycle transition. 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. Component of the KMT2 family MLL2/MLL3 complex, at least composed of the histone methyltransferases KMT2D and/or KMT2C, the common complex 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. Interacts with NCOA1, ESR1, NR3C1, AR. 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.