Rexinoids Induce Differential Gene Expression in Human Glioblastoma Cells and Protein–Protein Interactions in a Yeast Two-Hybrid System

Rexinoids are compounds that bind to the rexinoid X receptor (RXR) to modulate gene expression and have been proposed as a new class of therapeutics to treat Alzheimer's disease. Different rexinoids will initiate downstream effects that can be quite marked even though such compounds can be structurally similar and have comparable RXR binding affinities. RXR can both homo- and heterodimerize, and these protein–protein interactions and subsequent transactivating potential lead to differential gene expression, depending on the RXR dimeric partner, additional cofactors recruited, and downstream transcription factors that are up- or downregulated. Expression analysis was performed in the U87 human glioblastoma cell line treated with a panel of rexinoids, and our analysis demonstrated that rexinoids with similar RXR EC50 values can have pronounced differences in differential gene expression. Rexinoid binding likely leads to distinctive RXR conformations that cause major downstream gene expression alterations via modulation of RXR interacting proteins. Yeast two-hybrid analysis of RXR bait with two RXR interacting partners demonstrates that rexinoids drive differential binding of RXR to distinctive protein partners. Physiochemical analysis of the rexinoids reveals that the molecules cluster similarly to their gene expression patterns. Thus, rexinoids with similar RXR binding affinities drive differential gene expression by stimulating additional binding patterns in RXR and its homo- and heteropartners, driven by the physicochemical characteristics of these molecules.