A research group led by Shota Enomoto (Master’s Program, 2nd year) and Professor Masanori Osawa of the Division of Physics for Life Functions, Graduate School of Pharmaceutical Sciences, Keio University, in collaboration with Dr. Toshiya Senda, Director of the Structural Biology Research Center at the Institute of Materials Structure Science, High Energy Accelerator Research Organization (KEK), and Professor Hideyuki Saya, Director of the Cancer Research Center at Fujita Health University, has elucidated the molecular mechanism by which the cancer suppressor protein FOXO3a is functionally inactivated through its interaction with the 14-3-3ζ protein (hereafter 14-3-3ζ), a key regulator of aberrant cancer cell proliferation.
In cancer cells, phosphorylation signaling is aberrantly enhanced, leading to uncontrolled cell proliferation. One of the transcription factors regulated by phosphorylation signaling is FOXO3a. Under normal conditions, FOXO3a functions as a tumor suppressor by inducing apoptosis (programmed cell death). However, in cancer cells, FOXO3a becomes phosphorylated, binds to 14-3-3ζ, and is forcibly dissociated from DNA, resulting in loss of its function. Therefore, elucidating the mechanism by which 14-3-3ζ binding causes FOXO3a to dissociate from DNA—and identifying compounds that specifically inhibit this interaction—could lead to the development of novel anticancer drugs that restore FOXO3a-mediated apoptosis.
Although the interaction mode between 14-3-3ζ and phosphorylated FOXO3a has been studied, the molecular mechanism by which 14-3-3ζ bound to the phosphorylation site induces DNA dissociation from a spatially distant DNA-binding domain has remained unclear. In this study, to clarify this “competitive inhibition mechanism mediated through distinct binding sites,” we quantified DNA dissociation using fluorescence-detection size-exclusion chromatography (FSEC) and analyzed the interaction between phosphorylated FOXO3a and 14-3-3ζ at atomic resolution using nuclear magnetic resonance (NMR). As a result, we demonstrated that 14-3-3ζ directly interacts not only with the phosphorylation sites of FOXO3a but also with its DNA-binding domain (DBD), competitively displacing DNA.
These findings were published in the international scientific journal Nature Communications on Feb 16, 2026.
