Deregulation of translational control of the 65-kDa regulatory subunit (PR65α) of protein phosphatase 2A leads to multinucleated cells

Abstract

Efficient translation of the mRNA encoding the 65-kDa regulatory subunit (PR65α) of protein phosphatase 2A (PP2A) is prevented by an out of frame upstream AUG and a stable stem-loop structure (ΔG = -55.9 kcal/mol) in the 5'-untranslated region (5'-UTR). Deletion of the 5'-UTR allows efficient translation of the PR65α message in vitro and overexpression in COS-1 cells. Insertion of the 5'-UTR into the β-galactosidase leader sequence dramatically inhibits translation of the β-galactosidase message in vitro and in vivo, confirming that this sequence functions as a potent translation regulatory sequence. Cells transfected or microinjected with a PR65α expression vector lacking the 5'-UTR, express high levels of PR65α, accumulating in both nucleus and cytoplasm. PR65α overexpressing rat embryo fibroblasts (REF-52 cells) become multinucleated. These data and previous results (Mayer-Jaekel, R. E., Ohkura, H., Gomes, R., Sunkel, C. E., Baumgartner, 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.