Induction of abnormal nuclear shapes in two distinct modes by overexpression of serine/threonine protein phosphatase...

Okadaic acid-sensitve serine/threonine protein phosphatase 5 (PP5) is expressed ubiquitously in various tissues and is considered to participate in many cellular processes. PP5 has a catalytic domain in the C-terminal region and three tetratricopeptide repeat (TPR) motifs in the N-terminal region, which are suspected to function as a protein-protein interaction domain. Physiological roles of PP5 are still largely unknown, although several PP5-binding proteins were reported and a few in vivo functions of PP5 were suggested. In the present study, the effects of expression of the full-length wild-type PP5 fused with EGFP (EGFP-PP5(WT)) and its phosphatase-dead mutant EGFP-PP5(H304A) were investigated. Transient expression of either EGFP-PP5(WT) or EGFP-PP5(H304A) in HeLa cells induced deformed nuclei with a 10-fold frequency compared to that of EGFP. Abnormal-shaped nuclei were also substantially increased by induced moderate expression of PP5 in tet-on HeLa cells. Many HeLa cells expressing EGFP-PP5(WT) possessed multi-nuclei separated from each other by nuclear membrane, while expression of EGFP-PP5(H304A) induced deformed nuclei which were multiple-like in shape, but not separated completely and were surrounded by one nuclear membrane. These results suggest that PP5 plays important roles at the M-phase of the cell cycle, especially in separation of chromosomes and formation of nuclear membrane.