Abstract
The oncogenic fusion protein nucleophosmin-anaplastic lymphoma kinase (NPM-ALK), found exclusively in a subset of ALK-positive anaplastic large cell lymphoma, promotes tumorigenesis by exerting its constitutively active tyrosine kinase activity. Thus, characterization of the NPM-ALK-induced changes in the phosphoproteome will likely provide insights into the biology of this oncoprotein. To achieve this goal, we used a strategy of combining sequential affinity purification of phosphopeptides and LC/MS. GP293 cells transfected with either NPM-ALK or an NPM-ALK mutant with decreased tyrosine kinase activity (negative control) were used. We identified 506 phosphoproteins detectable in NPM-ALK-expressing cells but not in the negative control. Bioinformatics analysis revealed that these phosphoproteins carry a wide diversity of biological functions, some of which have not been described in association with NPM-ALK, such as the tumor necrosis factor (TNF)/Fas/tumor necrosis factor-related apoptosis-induced ligand (TRAIL) signaling pathway and the ubiquitin proteasome degradation pathway. In particular, modulations of the TNF/Fas/TRAIL pathway by NPM-ALK were supported by our antibody microarray data. Further validation of the TNF/Fas/TRAIL pathway was performed in ALK(+) anaplastic large cell lymphoma (ALCL) cell lines with knockdown of NPM-ALK using short interference RNA, resulting in the loss of the tyrosine phosphorylation of tumor necrosis factor receptor-associated protein 1 (TRAP1) and receptor-interacting protein 1, two crucial TNF signaling molecules. Functional analyses revealed that knockdown of TRAP1 facilitated cell death induced by TRAIL or doxorubicin in ALK(+) ALCL cells. This suggests that down-regulation of TRAP1 in combination with TRAIL or doxorubicin might be a potential novel therapeutic strategy for ALK(+) ALCL. These findings demonstrated that our strategy allowed the identification of novel proteins downstream of NPM-ALK that contribute to the maintenance of neoplastic phenotype and holds great potential for future studies of cellular tyrosine kinases in normal states and diseases.