title: Integrities of A/B and C domains of RXR are required for rexinoid-induced caspase activations and apoptosis.
abstract: Here we have delineated regions of the retinoid X receptor alpha (RXRalpha) that are required for rexinoid (RXR agonist)-induced growth inhibition and apoptosis. Stable over-expression of RXRalpha in DT40 B lymphoma cells dramatically increased sensitivity to rexinoid-induced growth inhibition. By contrast, DT40 cells that over-expressed RXRalpha with a deletion of either the A/B or DNA binding domain (C domain) were resistant. We confirmed the importance of C domain integrity by point-mutating Cys(135) to Ser (C135S) to disrupt zinc-finger formation. Point mutating RXR Lys(201) to Thr and Arg(202) to Ala (KTRA) impairs RXR homodimer formation and does not affect RXR heterodimerization. When these mutated RXRs were over-expressed in DT40 cells, they failed to increase sensitivity to rexinoid. Over-expression did sensitize to growth inhibition by RAR and PPARgamma agonists. Over-expression of C135S mutated RXRalpha did not sensitize to RAR and PPARgamma agonists. Inhibitors of caspase-3 and/or caspase-9 blocked rexinoid-induced apoptosis, and activations of these caspases correlated with the ability of RXR mutants to induce cell death. These data show that the A/B and C domains of RXR and the ability of RXR to form homodimers are required for rexinoid-driven growth inhibition, caspase activation and subsequent apoptosis.
authors.affiliation: Retinoid Research, Department of Biology and Chemistry, Allergan Inc., Irvine, CA 92612, USA.
authors.forename: Suofu
authors.initials: S
authors.lastname: Qin
authors.forename: Yumiko
authors.initials: Y
authors.lastname: Okawa
authors.forename: Larissa I
authors.initials: LI
authors.lastname: Atangan
authors.forename: Geoffrey
authors.initials: G
authors.lastname: Brown
authors.forename: Roshantha A
authors.initials: RA
authors.lastname: Chandraratna
authors.forename: Yi
authors.initials: Y
authors.lastname: Zhao