DEREGULATION OF TRANSLATIONAL CONTROL OF THE 65-KDA REGULATORY SUBUNIT (PR65-ALPHA) OF PROTEIN PHOSPHATASE 2A LEADS TO MULTINUCLEATED CELLS

Efficient translation of the mRNA encoding the 65-kDa regulatory subun it (PR65 alpha) of protein phosphatase 2A (PP2A) is prevented by an ou t of frame upstream AUG and a stable stem-loop structure (Delta G = -5 5.9 kcal/mol) in the 5'-untranslated region (5'-UTR). Deletion of the 5'-UTR allows efficient translation of the PR65 alpha message in vitro and overexpression in COS-1 cells. Insertion of the 5'-UTR into the b eta-galactosidase leader sequence dramatically inhibits translation of the beta-galactosidase message in vitro and in vivo, confirming that this sequence functions as a potent translation regulatory sequence. C ells transfected or microinjected with a PR65 alpha expression vector lacking the 5'-UTR, express high levels of PR65 alpha, accumulating in both nucleus and cytoplasm, PR65 alpha overexpressing rat embryo fibr oblasts (REF-52 cells) become multinucleated. These data and previous results (Mayer-Jaekel, R. E., Ohkura, H., Gomes, R., Sunkel, C. E., Ba umgartner, S., Hemmings, B. A., and Glover, D. M. (1993) Cell 72, 621- 633) suggest that PP2A participates in the regulation of both mitosis and cytokinesis.