Nitrostyrene Derivatives Act as RXRα Ligands to Inhibit TNFα Activation of NF-κB

Abstract

Retinoid X receptor alpha (RXRα) and its N-terminally truncated version - tRXRα are widely implicated in cancer development and represent intriguing targets for cancer prevention and treatment. Successful manipulation of RXRα and tRXRα requires the identification of their modulators that could produce therapeutic effects. Here we report that a class of nitrostyrene derivatives bind to RXRα by a unique mechanism, of which the nitro group of nitrostyrene derivatives and Cys432 of RXRα are required for binding. The binding results in the potent activation of Gal4-DBD-RXRα-LBD transactivation. However, the binding inhibits the transactivation of RXRα homodimer, which might be due to the distinct conformation of RXRα homodimer induced by these nitrostyrene derivatives. Two RXRα point mutants with Cys432 substituted with Tyr and Trp, respectively, could mimic the bindings of two nitrostyrene derivatives and have the ability of auto-transactivation. In studying the functional consequences of the binding, we show that these nitrostyrene derivatives could potently inhibit TNFα/NFκB signaling pathway in a tRXRα dependent manner. tRXRα promotes TNFα-induced NFκB activation through its interacting with TRAF2 and enhancing TNFα-induced ubiquitination of RIP1, which is strongly inhibited by nitrostyrene derivatives. The inhibition of TNFα-induced NFκB activation results in the synergistic effect of the combination of nitrostyrene derivatives and TNFα on the induction of cancer cell apoptosis. Together, our results show a new class of RXRα modulators that induce apoptosis of cancer cells through their unique binding mode and new mechanism of action.

Targeting truncated RXRα for cancer therapy

“…Recent studies showed that RXRα binding to PML/RARα is absolutely required for the development of acute promeylocytic leukemia (APL) in transgenic mice [53][54][55], demonstrating the oncogenic potential of this protein when it acts inappropriately. Several groups have demonstrated that RXRα is proteolytically cleaved in cancer cells [23,45,51,[56][57][58][59][60], and our illustration that tRXRα could enhance TNFα activation of PI3K/AKT and NF-κB pathways revealed that aberration in RXRα signaling by limited proteolysis plays an active role in cancer development [28,29,[61][62][63][64][65].…”

“…This is supported by the observation that Sulindac and analogs inhibit the binding of tRXRα to p85α [29]. Similarly, inhibition of tRXRα-mediated activation of NF-κB survival pathway also leads to apoptosis [65]. These results demonstrate that inhibition of tRXRα-mediated activation of PI3K/AKT and NF-κB pathways could effectively shift TNFα signaling from survival to death.…”

“…Once activated, the IKK complex phosphorylates IκBα, which is subsequently ubiquitinated and degraded via the proteasome pathway. We recently reported that tRXRα could promote TNFα activation of NF-κB pathway through its interaction with TRAF2 and enhance TNFα-induced RIP1 ubiquitination [65]. A nitrostyrene derivative that binds to tRXRα could inhibit tRXRα interaction with TRAF2 and its induction of NF-κB activation.…”

“…Both K-80003 and K-8008 inhibit HepG2 tumor growth in animals and do not show apparent toxic effects. Several natural products including CF31 [28] and nitrostyrene derivatives [65] could also activate this death pathway by directly binding to tRXRα.…”

CYT-Rx20 Inhibits Cervical Cancer Cell Growth and Migration Through Oxidative Stress-Induced DNA Damage, Cell Apoptosis, and Epithelial-to-Mesenchymal Transition Inhibition

“…7 In addition, A-nitrostyrene inhibits gastric cancer cell proliferation, 11 and its derivatives suppress TNF>/NFJB signaling in a retinoid X receptor >Ydependent manner to induce breast cancer cell apoptosis. 12 Our previous work showed that 3 ¶-hydroxy-4 ¶-methoxy-A-methyl-A-nitrostyrene (CYT-Rx20)-induced apoptosis in breast cancer cells through reactive oxygen species (ROS)mediated MEK-ERK signaling. 13 However, to our knowledge, the biologic activities of CYT-Rx20 on cervical cancer cells have not been investigated.…”