RXRA and leukemia: To investigate NR protein stability, we first interrogated RARA, a well-studied hormone receptor whose degradation is necessary for the efficacy of leukemia therapy.15 Whole-proteome mass spectrometry analysis revealed that protein levels of RARA and its heterodimeric partner, retinoid X receptor alpha (RXRA), were significantly and selectively decreased following 24 h of ATRA treatment (Figures 1A and S1A).