Ser149 is another potential 14-3-3 epsilon binding site of Cdc25B in the G2/M transition of mouse fertilized eggs

Cell cycle division 25B (CDC25B) belongs to the family of cell cycle regulatory proteins. It drives G2/M transition by activating cyclin-dependent protein kinases (CDK1), also known as CDC2, whose activity is directly related to its subcellular localization and phosphorylation state.14-3-3 (YHWA) regulates cell division cycle by binding to Cdc25B as a chaperone protein in mammals. Previously, we found that Cdc25B-Ser149 plays an important role in G2/M transition of mouse fertilized eggs, but the molecular mechanism of this transition remains unclear. In this study, we assessed the role of 14-3-3{varepsilon} (YHWAE) interaction with phosphorylated Cdc25B-Ser149 in G2/M transition of mouse fertilized eggs. Co-expression of Cdc25B-Ser149A and 14-3-3{varepsilon} could effectively activate maturation promoting factor (MPF) through direct dephosphorylation of Cdc2-Tyr15, and induce G2 fertilized eggs to enter mitosis rapidly. However, co-expression of the phosphomimic Cdc25B-Ser149D or Cdc25B-WT and 14-3-3{varepsilon} showed no significant difference in comparison with control groups. 14-3-3{varepsilon} binds to Cdc25B-WT, which is abolished when Ser149 is mutated to Ala. In addition, we found that 14-3-3{varepsilon} and Cdc25B were co-localized in the cytoplasm at the G1, S and early G2 phases. Cdc25B was translocated from the cytoplasm to the nucleus at the late G2 phase. However, when Ser149 is mutated to Ala, the cytoplasmic localization of Cdc25B is completely abolished. Our findings suggest that Cdc25B-Ser149 is another specific binding site for 14-3-3{varepsilon} in G2/M transition of one-cell fertilized mouse eggs, which plays essential roles in the regulation of early development of fertilized mouse eggs.