ATIC activity is enhanced in the presence of NPM-ALK in vitro. (A) Immunoprecipitated ATIC was combined with the active NPM-ALK kinase (isolated from wild-type HEK-293T cells and NPM-ALK⁺ HEK-293T cells, respectively) or with a mutated NPM-ALK^K210R kinase (from NPM-ALK^K210R–positive HEK-293T cells), with and without the ALK inhibitor CEP14083 (6 hours). Total or specific ATIC activity was measured as described in “Measurement of AICAR-FT/IMP-CHase activity.” (B) ATIC enzymatic activities were also determined in the presence of lambda phosphatase (1 mg for 1 hour). *P < .001.