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Next-generation retinoid X receptor agonists increase ATRA signaling in organotypic epithelium cultures and have
Nathalia Melo1, Olga V Belyaeva1, Wilhelm K Berger2
1O'Neil Comprehensive Cancer Center, University of Alabama at Birmingham, Birmingham, Alabama, USA; Department of Biochemistry and Molecular Genetics, University of Alabama at Birmingham, Birmingham, Alabama, USA.
Abstract:
Retinoid X receptors (RXRs) are nuclear transcription factors that partner with other nuclear receptors to regulate numerous physiological processes. Although RXR represents a valid therapeutic target, only a few RXR-specific ligands (rexinoids) have been identified, in part due to the lack of clarity on how rexinoids selectively modulate RXR response. Previously, we showed that rexinoid UAB30 potentiates all-trans-retinoic acid (ATRA) signaling in human keratinocytes, in part by stimulating ATRA biosynthesis. Here, we examined the mechanism of action of next-generation rexinoids UAB110 and UAB111 that are more potent in vitro than UAB30 and the FDA-approved Targretin. Both UAB110 and UAB111 enhanced ATRA signaling in human organotypic epithelium at a 50-fold lower concentration than UAB30. This was consistent with the 2- to 5- fold greater increase in ATRA in organotypic epidermis treated with UAB110/111 versus UAB30. Furthermore, at 0.2 μM, UAB110/111 increased the expression of ATRA genes up to 16-fold stronger than Targretin. The less toxic and more potent UAB110 also induced more changes in differential gene expression than Targretin. Additionally, our hydrogen deuterium exchange mass spectrometry analysis showed that both ligands reduced the dynamics of the ligand-binding pocket but also induced unique dynamic responses that were indicative of higher affinity binding relative to UAB30, especially for Helix 3. UAB110 binding also showed increased dynamics towards the dimer interface through the Helix 8 and Helix 9 regions. These data suggest that UAB110 and UAB111 are potent activators of RXR-RAR signaling pathways but accomplish activation through different molecular responses to ligand binding.
Insights
New rexinoids, UAB110 and UAB111, are potent activators of Retinoid X receptor (RXR)-retinoic acid receptor (RAR) signaling. They enhance all-trans-retinoic acid (ATRA) signaling more effectively than existing compounds by altering RXR ligand-binding pocket dynamics.
Area of Science:
- Molecular Biology
- Pharmacology
- Biochemistry
Background:
- Retinoid X receptors (RXRs) are crucial nuclear transcription factors regulating physiological processes.
- Targeting RXRs therapeutically is promising, but selective ligand (rexinoid) action remains unclear.
- Previous work showed rexinoid UAB30 enhances all-trans-retinoic acid (ATRA) signaling by boosting ATRA biosynthesis.
Purpose of the Study:
- To investigate the mechanism of action of novel, potent rexinoids UAB110 and UAB111.
- To compare their efficacy in enhancing ATRA signaling against UAB30 and Targretin.
- To elucidate the molecular dynamics associated with their binding to RXR.
Main Methods:
- Utilized human organotypic epithelium models to assess ATRA signaling.
- Quantified ATRA levels and gene expression changes.
- Employed hydrogen deuterium exchange mass spectrometry (HDX-MS) to analyze ligand-induced RXR dynamics.
Main Results:
- UAB110 and UAB111 enhanced ATRA signaling and ATRA levels at significantly lower concentrations than UAB30.
- These novel rexinoids demonstrated superior potency in increasing ATRA gene expression compared to Targretin.
- HDX-MS revealed that UAB110/111 reduced ligand-binding pocket dynamics and induced unique responses, indicating higher affinity binding, particularly at Helix 3, Helix 8, and Helix 9.
Conclusions:
- UAB110 and UAB111 are highly potent activators of RXR-RAR signaling pathways.
- Their enhanced efficacy stems from distinct molecular responses to ligand binding within the RXR complex.
- These findings pave the way for developing more effective RXR-targeted therapies.
