Extrinsic Apoptosis Is Impeded by Direct Binding of the APL Fusion Protein NPM-RAR to TRADD

Abstract

A subset of acute promyelocytic leukemia (APL) cases have been characterized by the t(5;17)(q35;q21) translocation variant which fuses nucleophosmin (NPM) to retinoic acid receptor alpha (RARA). The resultant NPM-RAR fusion protein blocks myeloid differentiation, and leads to a leukemic phenotype similar to that caused by the t(15;17)(q22;q21) PML-RAR fusion. The contribution of the N-terminal 117 amino acids of NPM contained within NPM-RAR has not been well studied. As a molecular chaperone, NPM interacts with a variety of proteins implicated in leukemogenesis. Therefore, a proteomic analysis was conducted to identify novel NPM-RAR associated proteins. Tumor necrosis factor receptor type 1-associated DEATH domain protein (TRADD) was identified as a relevant binding partner for NPM-RAR. This interaction was validated by co-precipitation and co-localization analysis. Biological assessment found that NPM-RAR expression impaired TNF-induced signaling through TRADD, blunting TNF-mediated activation of caspase 3 (CASP3) and caspase 8 (CASP8), to ultimately block apoptosis. Implications This study identifies a novel mechanism through which NPM-RAR impacts leukemogenesis.

NPM-RAR binding to TRADD selectively inhibits caspase activation, while allowing activation of NFκB and JNK

“…We have previously shown that NPM-RAR interacts with TRADD, and inhibits TNF-R mediated activation of the extrinsic apoptosis pathway[16]. We now show that NPM-RAR does not impede TNF-mediated activation of either NFκB or JNK pathways.…”

“…Nuclear TRADD has been implicated in regulating an ill-defined caspase 9-dependent, capase 8-independent apoptotic pathway. Our prior immunofluorescent localization studies indicated that NPM-RAR was expressed primarily in the nucleus, but to a lesser extent in the cytoplasm as well[16]. We speculated that the cytoplasmic component was responsible for the interaction with TRADD, but it is possible that the nuclear component could also interact with nuclear TRADD.…”

“…Through a proteomic analysis of NPM-RAR-interacting proteins, we have recently identified NPM-RAR as specifically binding to the tumor necrosis factor receptor type-I –associated DEATH domain protein TRADD[16]. TRADD is a scaffold protein downstream of the TNF receptor.…”

“…NPM-RAR interaction with TRADD inhibits TNF-dependent activation of the initiator caspase 3 and the effector capsase 8, cleavage of PARP, and initiation of apoptosis[16]. In this manuscript we describe the impact of NPM-RAR on the other pathways activated by TNF-R: NFκB and JNK.…”

Molecular Characteristics and Clinical Significance of 12 Fusion Genes in Acute Promyelocytic Leukemia: A Systematic Review

“…In addition, unlike ZBTB16-RARα, NPM-RARα interacts with coactivator and corepressor proteins in a manner similar to that involving PML-RARα [53]. NPM-RARα also binds to the tumor necrosis factor receptor type-I-associated death domain protein and selectively inhibits caspase activation, while allowing NF-κB and JNK activation that stimulates cell growth and promotes survival [54,55], which might be a novel mechanism underlying the role of NPM-RARα in the etiology of leukemia.…”