Increased stability of c-myc and cyclin mRNAs in ALK-expressing cells. (A-B) Total RNAs were extracted from control (pcDNA3) (-), NPM-ALK-, or ATIC-ALK-expressing NIH3T3 cells and used in an RNAse protection assay to compare levels of expression of c-myc and cyclin mRNAs. c-myc riboprobe (A) or cyclin multiprobe template set (B) were used simultaneously with L32 and GAPDH riboprobes, which served as controls for RNA loading. (C-D) Actinomycin D was added at 0 time to control (pcDNA3 or NPM-ALK Dead) or NPM-ALK-expressing NIH3T3 cells. RNAse mapping analysis was performed as in panels A-B. c-myc and cyclin mRNA half-lives in control (Cont.: pcDNA3 or NPM-ALK Dead) and NPM-ALK-expressing cells were calculated from RNAse protection assay data shown in panels C-D. > 24 hours means that the mRNA half-life exceeds 24 hours but could not be calculated precisely, because of the extensive cell death that occurred after this time point.