Specific interaction between 14-3-3 isoforms and the human CDC25B phosphatase.

Area of Science:

• Cell biology
• Molecular biology
• Biochemistry

Background:

• CDC25 dual-specificity phosphatases (e.g., CDC25A, B, C) are crucial regulators of cyclin-dependent kinases (CDKs) controlling cell cycle progression.
• CDC25B is implicated in both S phase and G2/M transitions.
• Interactions between CDC25 phosphatases and 14-3-3 proteins have been observed, with phosphorylation proposed as a key mediator for CDC25C.

Purpose of the Study:

• To investigate the molecular basis of the interaction between CDC25B phosphatases and 14-3-3 proteins.
• To determine if phosphorylation regulates CDC25B binding to 14-3-3 proteins.
• To compare the interaction mechanisms of CDC25B and CDC25C with 14-3-3 proteins.

Main Methods:

• Yeast two-hybrid assays to assess interactions between CDC25B splice variants and various 14-3-3 isoforms.
• In vitro binding assays with phosphorylated and dephosphorylated CDC25B.
• Analysis of CDC25B mutants, including a deletion in the amino-terminal region, to identify interaction domains and requirements.

Main Results:

• All CDC25B splice variants showed strong interaction with 14-3-3 eta, beta, and zeta in two-hybrid assays, but weak interaction with epsilon and Theta.
• In vitro, CDC25B exhibited low-level interaction with multiple 14-3-3 isoforms, unaffected by phosphorylation or dephosphorylation.
• A specific, strong interaction between CDC25B and 14-3-3 zeta and eta was observed upon deletion of 288 N-terminal residues, requiring Ser 323 integrity but independent of phosphorylation.

Conclusions:

• CDC25B interaction with 14-3-3 proteins is regulated differently compared to CDC25C.
• CDC25B possesses a low-affinity binding site for all 14-3-3 isoforms.
• In vivo post-translational modification of CDC25B likely exposes a high-affinity, specific binding site for 14-3-3 zeta and eta isoforms, impacting cell cycle control.