Identification of a novel crosstalk between casein kinase 2α and NPM-ALK in ALK-positive anaplastic large cell lymphoma

It was previously reported that β-catenin contributes to the tumorigenesis of ALK-positive anaplastic large cell lymphoma (ALK⁺ALCL), and the oncogenic effects of β-catenin in these tumors are promoted by NPM-ALK, an abnormal fusion protein characteristic of ALK⁺ALCL. In this study, we hypothesized that NPM-ALK promotes the oncogenic activity of β-catenin via its functional interactions with the Wnt canonical pathway (WCP). To test this hypothesis, we examined if NPM-ALK modulates the gene expression of various members in the WCP. Using a Wnt pathway-specific oligonucleotide array and Western blots, we found that the expression of casein kinase 2α (CK2α) was substantially downregulated in ALK⁺ALCL cells in response to siRNA knockdown of NPM-ALK. CK2α is biologically important in ALK⁺ALCL, as its inhibition using 4,5,6,7-tetrabromobenzotriazole or siRNA resulted in a significant decrease in cell growth and a substantial decrease in the β-catenin protein level. Furthermore, CK2α co-immunoprecipitated with NPM-ALK and regulated its level of serine phosphorylation, a feature previously shown to correlate with the oncogenic potential of this fusion protein. To conclude, this study has revealed a novel crosstalk between NPM-ALK and CK2α, and our data supports the model that these two molecules work synergistically to promote the tumorigenicity of these lymphomas.