The MLL4-ASCOM complex (an MLL4 complex, composed of the core MLL4 complex, consisting of KMT2D and the WRAD subcomplex of WDR5, RBBP5, ASH2L, and DPY30, and accessory subunits PAXIP1, PAGR1, NCOA6, and KDM6A) and/or the MLL3-ASCOM complex (same composition as the MLL4-ASCOM except for the catalytic subunit KMT2C) are recruited to ligand- and coactivator-bound PPARG:RXRA heterodimer to PPARG target gene loci. While most of the functional studies were done in mouse, as described below, the physical interaction between KMT2D and PPARG was confirmed by co-immunoprecipitation of the endogenous complex from human prostate cancer cell lines (Zhai et al. 2022).

In differentiating mouse brown adipocytes, KMT2D (MLL4) mainly binds to active enhancers that are prevalently bound by both CEBP and PPARG, or at least by one of the two adipogenic transcription factors - the experiment did not distinguish between CEBPA and CEBPB (Lee et al. 2013). In mouse differentiating adipocytes, the non-catalytic subunits of KMT2C (MLL3)- and MLL4-ASCOM complexes were shown to co-immunoprecipitate with the complex of PPARG and RXRA (Lee et al. 2008). The MLL4 complex physically interacts with PPARG in mouse differentiating brown adipocytes (Lee et al. 2013). A flavonoid, kaempferol, is a PPARG antagonist that prevents rosiglitazone-induced association of Mll4 with Pparg at Pparg target loci in mouse adipocytes (Park et al. 2022).

By ChIP, at day 2 of mouse brown adipocyte differentiation, more than half of MLL4 binding sites overlap with binding sites for CEBPB, CEBPA, and PPARG (Lee et al. 2013). Association of PPARG1 and PPARG2 with KMT2D requires a PPARG agonist such as rosiglitazone (Kim et al. 2016). KMT2D binds to PPARG2 more robustly than to PPARG1 (Kim et al. 2016). The interaction between PPARG2 and KMT2D is diminished in the presence of the ABL1 inhibitor imatinib (Kim et al. 2016). ABL1-dependent phosphorylation of PPARG2 enhances association of PPARG with KMT2D in mouse liver carcinoma cells. Imatinib, an inhibitor of ABL1 kinase, decreases association between PPARG2 and RBBP5, a component of the MLL4 complex and other KMT2 complexes (Kim et al. 2016). Imatinib significantly decreases the recruitment of KMT2D to PPREs (peroxisome proliferator response elements) in the PPARG, CD36, CIDEC and SCD gene loci (Kim et al. 2016).

The MLL4-ASCOM and MLL3-ASCOM complexes or their components were shown to bind to regulatory elements of the following adipogenesis genes regulated by PPARG in adipocytes and/or steatotic hepatocytes:

ACSS3 gene (Kim et al. 2016: based on ChIP-seq for KMT2D and PPARG in mouse hepatocytes)

AGPAT2 gene (Kim et al. 2016: based on ChIP-seq for KMT2D and PPARG in mouse hepatocytes)

CD36 gene (Kim et al. 2016: based on ChIP-seq for KMT2D and PPARG in mouse hepatocytes)

CEBPA gene (Cho et al. 2009: by ChIP assay in mouse embryonic fibroblasts - MEFs, endogenous PAXIP1 - PTIP, an accessory subunit of MLL3 and MLL4 complexes, associates with the CEBPA gene promoter with a signal peak around the transcription start site; in mouse white preadipocyte line 3T3-L1, PAXIP1 is enriched around the transcription start sites of CEBPA before and after the onset of differentiation; in differentiating mouse brown preadipocytes, KMT2D is enriched around the transcription start site of CEBPA in a PAXIP1-dependent manner; Lee et al. 2013: KMT2D binds the CEBPA gene locus in differentiating mouse brown adipocytes)

CIDEC gene (Kim et al. 2016: based on ChIP-seq for KMT2D and PPARG in mouse hepatocytes)

ELOVL5 gene (Kim et al. 2016: based on ChIP-seq for KMT2D and PPARG in mouse hepatocytes)

FABP4 gene (Qi et al. 2003: by ChIP, NCOA6 binds to the FABP4 gene locus in a PPARG-dependent manner in mouse embryonic fibroblasts - MEFs - stimulated to differentiate into adipocytes; Lee et al. 2008: by ChIP, KMT2C and KMT2D, as well as NCOA6, bind the FABP4 gene locus in mouse fibroblasts induced to differentiate into adipocytes; the recruitment of components of MLL3/4-ASCOM complexes - KMT2C, KMT2D, WDR5, RBBP5, ASH2L, DPY30, NCOA6, PAXIP1, and KDM6A - is dependent on direct interaction of MLL3-ASCOM and MLL4-ASCOM with the PPARG:RXRA heterodimer; Lee et al. 2013: MLL4 binds the FABP4 gene locus in differentiating mouse brown adipocytes)

GPAM gene (Kim et al. 2016: based on ChIP-seq for KMT2D and PPARG in mouse hepatocytes)

LPL gene (Lee et al. 2013: mouse Mll4 complex was shown to bind to Lpl gene locus in differentiating mouse brown adipocytes)

PLIN2 gene (Kim et al. 2016: based on ChIP-seq for KMT2D and PPARG in mouse hepatocytes)

PPARG gene (Cho et al. 2009: by ChIP in mouse embryonic fibroblasts (MEFs), PAXIP1 (PTIP) and PAGR1 (PA1), accessory subunits of the MLL3 and MLL4 complexes, as well as the obligatory subunit RBBP5 and the catalytic subunit KMT2D are found associated with the PPARG1 but not PPARG2 promoter; PPARG1 is the only isoform of PPARG expressed in MEFs; in mouse white preadipocyte line 3T3-L1, PAXIP1 is enriched around the transcription start sites of PPARG1 and PPARG2 before and after the onset of differentiation; in differentiating mouse brown preadipocytes, KMT2D is enriched around the transcription start sites of PPARG1 and PPARG2 in a PAXIP1-dependent manner; Lee et al. 2013: KMT2D binds the PPARG gene locus in differentiating mouse brown adipocytes)

SCD gene (also known as SCD1, Kim et al. 2016: based on ChIP-seq for KMT2D and PPARG in mouse hepatocytes)

SCD5 gene (also known as SCD2 or SCD4, Scd4 in mouse; Kim et al. 2016: based on ChIP-seq for KMT2D and PPARG in mouse hepatocytes)

THRSP gene (Kim et al. 2016: based on ChIP-seq for KMT2D and PPARG in mouse hepatocytes).

While PPARG-mediated recruitment of MLL3/MLL4 complexes to PPARG target genes ACSL1, ADIPOQ, ANGPTL4, DGAT2, LIPE, LPIN1, MGLL, PDK4, PEX11A, PLIN1, PLIN4, PNPLA2 has not been reported, the expression of these genes, as well as the genes for which more direct evidence was available (ACSS3, AGPAT2, CD36, CEBPA, CIDEC, ELOVL5, FABP4, GPAM, LPL, PLIN2, PPARG, SCD, SCD5, and THRSP), is severely reduced in differentiating mouse brown preadipocytes expressing histone H3.3 K4M mutant or Kmt2c (Mll3) and Kmt2d (Mll4) with deleted SET domains (Jang et al. 2019: RNA-seq, supplementary information). Therefore, these genes are also annotated as direct MLL3/MLL4 targets.

UCP1 gene (Lee et al. 2013: KMT2D binds the UCP1 gene locus in differentiating mouse brown adipocytes).

KMT2D was also shown to bind the UCP1 and KLF15 gene loci in differentiating mouse brown adipocytes, while it was largely absent from the CEBPB gene locus (Lee et al. 2013). KLF15 has not been reported as a PPARG target gene, while UCP1 gene was reported to be co-regulated by EBF2 and PPARG (Stine et al. 2016).