NPM-ALK and AUF1 colocalize in cytoplasmic granules. Permeabilized NPM-ALK NIH3T3 and ALCL-derived cells were incubated with monoclonal anti-ALK and/or polyclonal anti-AUF1 or hDCP1 serum, as indicated. AUF1 and NPM-ALK are found in cytoplasmic foci (A-B) that fully colocalize (panel C and magnification of the insert in the right panels). These cytoplasmic foci do not correspond to P-bodies recognized by a polyclonal anti-hDCP1 serum (E), as NPM-ALK-labeled granules (D) and P-bodies (E) do not overlap (panel F and magnification of the insert in the right panel insert). NPM-ALK tyrosine kinase activity is required for granule formation, as granules are not observed in NIH3T3 cells expressing a NPM-ALK kinase-defective mutant (G-I). Colocalization of NPM-ALK and AUF1 is also observed in NPM-ALK-expressing ALCL-derived cells (Karpas, panel J; SU-DHL1, panel K; and COST, panel L and magnification of the insert in the right panel).