Retinoid X receptor a （RXRα） and its N-terminally trun- cated version tRXRα play important roles in tumorige. nesis, while some RXRg ligands possess potent anti- cancer activities by targeting and modulating the t...Retinoid X receptor a （RXRα） and its N-terminally trun- cated version tRXRα play important roles in tumorige. nesis, while some RXRg ligands possess potent anti- cancer activities by targeting and modulating the tumorigenic effects of RXRo and tRXRa. Here we describe NSC-640358 （N-6）, a thiazolyl-pyrazole derived compound, acts as a selective RXRα ligand to promote TNFα-mediated apoptosis of cancer cell. N-6 binds to RXRa and inhibits the transactivation of RXRα homod- imer and RXRa/TR3 heterodimer. Using mutational analysis and computational study, we determine that Arg316 in RXRa, essential for 9-cis-retinoic acid binding and activating RXRg transactivation, is not required for antagonist effects of N-6, whereas Trp305 and Phe313 are crucial for N-6 binding to RXRα by forming extra w-w stacking interactions with N-6, indicating a distinct RXRα binding mode of N-6. N-6 inhibits TR3-stimulated transactivation of Gal4-DBD-RXRα-LBD by binding to the ligand binding pocket of RXRa-LBD, suggesting a strategy to regulate TR3 activity indirectly by using small molecules to target its interacting partner RXRα. For its physiological activities, we show that N-6 strongly inhibits tumor necrosis factor a （TNFα）-induced AKT activation and stimulates TNFa-mediated apoptosis in cancer cells in an RXRa/tRXRo dependent manner.The inhibition of TNFα-induced tRXRα/p85α complex formation by N-6 implies that N-6 targets tRXRa to inhibit TNFα-induced AKT activation and to induce cancer cell apoptosis. Together, our data illustrate a new RXRa ligand with a unique RXRα binding mode and the abilities to regulate TR3 activity indirectly and to induce TNFa-mediated cancer cell apoptosis by targeting RXRα/tRXRα.展开更多
文摘Retinoid X receptor a （RXRα） and its N-terminally trun- cated version tRXRα play important roles in tumorige. nesis, while some RXRg ligands possess potent anti- cancer activities by targeting and modulating the tumorigenic effects of RXRo and tRXRa. Here we describe NSC-640358 （N-6）, a thiazolyl-pyrazole derived compound, acts as a selective RXRα ligand to promote TNFα-mediated apoptosis of cancer cell. N-6 binds to RXRa and inhibits the transactivation of RXRα homod- imer and RXRa/TR3 heterodimer. Using mutational analysis and computational study, we determine that Arg316 in RXRa, essential for 9-cis-retinoic acid binding and activating RXRg transactivation, is not required for antagonist effects of N-6, whereas Trp305 and Phe313 are crucial for N-6 binding to RXRα by forming extra w-w stacking interactions with N-6, indicating a distinct RXRα binding mode of N-6. N-6 inhibits TR3-stimulated transactivation of Gal4-DBD-RXRα-LBD by binding to the ligand binding pocket of RXRa-LBD, suggesting a strategy to regulate TR3 activity indirectly by using small molecules to target its interacting partner RXRα. For its physiological activities, we show that N-6 strongly inhibits tumor necrosis factor a （TNFα）-induced AKT activation and stimulates TNFa-mediated apoptosis in cancer cells in an RXRa/tRXRo dependent manner.The inhibition of TNFα-induced tRXRα/p85α complex formation by N-6 implies that N-6 targets tRXRa to inhibit TNFα-induced AKT activation and to induce cancer cell apoptosis. Together, our data illustrate a new RXRa ligand with a unique RXRα binding mode and the abilities to regulate TR3 activity indirectly and to induce TNFa-mediated cancer cell apoptosis by targeting RXRα/tRXRα.
