Figure 5.

In vitro characterization of saturated fatty acids as RXR ligands. (a) Myristic acid (MA), palmitic acid (PA) and stearic acid (SA) dose-dependently induced steroid receptor co-activator 1 (SRC-1) recruitment to the RXRα LBD in a HTRF-based assay with low micromolar potencies. (b) MA, PA and SA activated RXRα, RXRβ and RXRγ in cellular reporter gene assays at 100 µM concentration and above. (c,d) Efficacy of saturated fatty acids in promoting SRC-1 recruitment to the RXRα LBD (c) and in activating RXR in a cellular setting (d) was low compared with the synthetic agonists, SR11237 and bexarotene. (e) In the presence of 0.3 µM bexarotene (~EC₅₀), MA, PA and SA showed no competitive behavior, but caused enhanced SRC-1 recruitment at higher concentrations. Inset shows dose response of bexarotene in the same setting with the 0.3 µM concentration used for competition experiments highlighted in red. (f) At a low concentration (10 µM), saturated fatty acids showed a tendency to promote bexarotene (0.1 µM or 1 µM)-induced RXR activation in Gal4 hybrid reporter gene assays too, while weak competitive behavior was observed at a higher concentration (100 µM). (g) RXR activation by MA, PA and SA (200 µM each) in the cellular reporter gene assay was blocked by the RXR antagonist, UVI3003. All data are mean ± SEM values, n = 3. * p < 0.05, ** p < 0.01, *** p < 0.001 (t-test vs. bexarotene alone (f) or as indicated (g))