Cell cycle dependent subcellular distribution of Cdc25B subtypes

Abstract

The dual speci®city phosphatase and oncogene Cdc25B has been implicated in the G2/M cell cycle checkpoint, but the mode by which it is regulated remains poorly understood. Regional subcellular redistribution of proteins represents a unique potential regulatory mechanism. Thus, we examined in live cells the subcellular localization characteristics of Cdc25B 2 and Cdc25B 3 fused to green¯uorescent protein. Cdc25B 2 partitioned primarily in the cytoplasm during G1 and progressively migrated to the nucleus as cells transited from S to G2/ M phase. In contrast, Cdc25B 3 maintained a homogeneously staining diuse phenotype irrespective of cell cycle phase. Treatment of the Cdc25B 2 -green¯uorescent protein stable transfectants with vanadate inhibited the cell cycle dependency of intracellular distribution, while okadaic acid had little eect except in G1, suggesting regulation by at least one phosphorylation-dependent pathway. The DNA topoisomerase II poison and DNA damaging agent, etoposide, inhibited nuclear localization of Cdc25B 2 in S phase, possibly by invoking a sequestration cascade. Thus, dierences in the spatial distribution of Cdc25B subtypes exist within cells and the 41 amino acid insert in the N-terminus of the Cdc25B 3 splice variant encodes an important inhibitory determinant for such regulation. The subcellular redistribution of Cdc25B 2 could be functionally important for G2/M checkpoint regulation.

CDC25B Phosphorylated by pEg3 Localizes to the Centrosome and the Spindle Poles at Mitosis

“…One possible explanation of the discrepancies between the expression patterns reported for CDC25B at various stages of the cell cycle 4,[10][11][12][13] is the existence of a family of splice variants. A least three CDC25B variants exist in humans, resulting from the presence or absence of domains A and B (14 and 41 residues respectively) that are located within the amino-terminal regulatory region.…”

Human pEg3 kinase associates with and phosphorylates CDC25B phosphatase: a potential role for pEg3 in cell cycle regulation

“…In human three splicing variants (CDC25B1, CDC25B2 and CDC25B3) have been identified (Baldin et al, 1997). Until now only differences in the subcellular localization of CDC25B2 and CDC25B3 have been found (Woo et al, 1999), however, these differences were not observed by Davezac et al (2000). As for CDC25C, the CDC25B phosphatase is able to associate with 14-3-3 proteins (Conklin et al, 1995;Mils et al, 2000).…”

Ser149 Is Another Potential PKA Phosphorylation Target of Cdc25B in G2/M Transition of Fertilized Mouse Eggs

“…In addition to protein levels and phosphorylation status, the subcellular distribution of the Cdc25 family may be an important regulator of G 2 /M transition. Using CHO cells, Woo et al (39) observed that Cdc25B partitioned primarily in the cytoplasm during G 1 and progressively migrated to the nucleus as cells transitioned from the S to the G 2 /M phase. It is reported that 14-3-3 binding to the Ser 323 site of Cdc25B directly inhibits the activity of Cdc25B in HeLa cells, thereby blocking the access FIGURE 7.…”