Abstract
Protein phosphorylation is a common mechanism for the regulation of cell cycle progression. The opposing functions of cell cycle kinases and phosphatases are crucial for accurate chromosome segregation and exit from mitosis. Protein phosphatases 2A are heterotrimeric complexes that play essential roles in cell growth, proliferation, and regulation of the cell cycle. Here, we review the function of the protein phosphatase 2A family as the counteracting force for the mitotic kinases. We focus on recent findings in the regulation of mitotic exit and cytokinesis by PP2A phosphatases in S. cerevisiae and other fungal species.
Highlights
Protein phosphatases type 2A (PP2A) are a group of abundant protein phosphatases present in all organisms with conserved structure among eukaryotes
PP2A phosphatases are involved in a myriad of essential processes, including cell growth, proliferation, and cell cycle regulation
The PP2A phosphatase is composed by the scaffold protein Tpd3 and Paa1 [3], one of the related catalytic subunits Pph21-22 and Ppa1-2, and one of the three regulatory subunits: a KDa regulatory B subunit Cdc55 in S. cerevisiae and Pab1 in S. pombe, the KDa regulatory B’ subunit Rts1 in S. cerevisiae and Par1 and Par2 in S. pombe, or the predicted B-subunit Rts3 in S. cerevisiae
Summary
Protein phosphatases type 2A (PP2A) are a group of abundant protein phosphatases present in all organisms with conserved structure among eukaryotes. The regulatory subunit confers specificity to the substrates and determines the subcellular localization of the PP2A phosphatase [4,7]. In Saccharomyces cerevisiae, Cdc and Tpd are found at the same subcellular localizations at the cytoplasm and the nucleus throughout the cell cycle (Figure 1). In the case of Schizosaccharomyces pombe, the B regulatory subunit, Pab, is localized at the cytoplasm, the nucleus, and the mitotic spindle [9]. During most of the cell cycle, Par is localized at the cytoplasm and the nucleus and translocate to the division site in late mitosis [10]. PP2ACdc counteracts the Cdk phosphorylation of the APC/C subunit Cdc16 [26,43], keeping SAC active until the cell is prepared for anaphase. PP2ACdc contributes indirectly to the prevention of untimely mitotic entry by inhibiting premature Cdc release from the nucleolus and precocious cleavage of sister chromatid cohesin (discussed below)
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