Heterodimers of photoreceptor-specific nuclear receptor (PNR/NR2E3) and peroxisome proliferator-activated receptor-γ (PPARγ) are disrupted by retinal disease-associated mutations

Abstract

Photoreceptor-specific nuclear receptor (PNR/NR2E3) and Tailless homolog (TLX/NR2E1) are human orthologs of the NR2E group, a subgroup of phylogenetically related members of the nuclear receptor (NR) superfamily of transcription factors. We assessed the ability of these NRs to form heterodimers with other members of the human NRs representing all major subgroups. The TLX ligand-binding domain (LBD) did not appear to form homodimers or interact directly with any other NR tested. The PNR LBD was able to form homodimers, but also exhibited robust interactions with the LBDs of peroxisome proliferator-activated receptor-γ (PPARγ)/NR1C3 and thyroid hormone receptor b (TRb) TRβ/NR1A2. The binding of PNR to PPARγ was specific for this paralog, as no interaction was observed with the LBDs of PPARα/NR1C1 or PPARδ/NR1C2. In support of these findings, PPARγ and PNR were found to be co-expressed in human retinal tissue extracts and could be co-immunoprecipitated as a native complex. Selected sequence variants in the PNR LBD associated with human retinopathies, or a mutation in the dimerization region of PPARγ LBD associated with familial partial lipodystrophy type 3, were found to disrupt PNR/PPARγ complex formation. Wild-type PNR, but not a PNR309G mutant, was able to repress PPARγ-mediated transcription in reporter assays. In summary, our results reveal novel heterodimer interactions in the NR superfamily, suggesting previously unknown functional interactions of PNR with PPARγ and TRβ that have potential importance in retinal development and disease.

Binding of Per- and Polyfluoro-alkyl Substances to Peroxisome Proliferator-Activated Receptor Gamma

“… 30 − 35 Fulton et al provides direct evidence that PPARγ homodimerizes by using yeast two-hybrid experiments, where the physical interaction between the two PPARγ monomers, and formation of homodimers, has been shown by reporter activation. 30 Todorov et al studied nuclear receptor proteins from CaLu-6 cells probed with the 33 P-labeled human renin Pal3 sequence using electrophoretic mobility-shift assay. 31 The addition of anti-PPARγ antibody in these assays resulted in retardation of two separate protein complex bands.…”

“…PPARγ functions as a regulator for fatty acid storage and glucose metabolism by binding to DNA and acting as a transcription factor. The homodimerization of PPARγ and its biological relevance have been discussed in the literature. − Fulton et al provides direct evidence that PPARγ homodimerizes by using yeast two-hybrid experiments, where the physical interaction between the two PPARγ monomers, and formation of homodimers, has been shown by reporter activation . Todorov et al studied nuclear receptor proteins from CaLu-6 cells probed with the 33 P-labeled human renin Pal3 sequence using electrophoretic mobility-shift assay .…”

PPARs and Tumor Microenvironment: The Emerging Roles of the Metabolic Master Regulators in Tumor Stromal–Epithelial Crosstalk and Carcinogenesis

“…Classically, all PPAR isotypes form heterodimers with RXR to coordinately modulate their target genes [ 165 ]. Nonetheless, PPARs can cooperate with other nuclear receptors such as glucocorticoid receptors, estrogen-related receptors, and photoreceptor-specific nuclear receptors to form atypical heterodimers transiently [ 166 , 167 ]. These atypical heterodimers may regulate the expression of different sets of genes from those of the classical heterodimers, leading to diverse cell fate and behaviors [ 167 ].…”

Binding of Per- and Polyfluoroalkyl Substances (PFAS) to the PPARγ/RXRα–DNA Complex

“…Nuclear receptors (NRs) are a superfamily of ligand-activated transcription factors and have been the focus of many drug discovery programs. One of the most studied NRs is peroxisome proliferator-activator γ (PPARγ) due to its role in glucose metabolism, regulation of adipogenesis, and lipid metabolism. − Even though the biological relevance of PPARγ in its homodimer form has been discussed in the literature, − the known biologically relevant form of PPARγ that controls gene transcription is the heterodimer form, i.e., peroxisome proliferator-activator γ/retinoic X receptor (PPARγ/RXRα). ,, The PPARγ and RXRα proteins, similar to other NR proteins, consist of three main domains: a ligand binding domain (LBD), a DNA binding domain (DBD), and a hinge domain that connects the DNA binding domain (DBD) and the ligand binding domain (LBD). The ligand molecules can bind to the LBD, causing the reorientation of the Helix-12 and consequently aiding in the recruitment of coactivators .…”