Threonine 209 phosphorylation on RUNX3 by Pak1 is a molecular switch for its dualistic functions

Area of Science:

• Oncology
• Molecular Biology
• Cell Biology

Background:

• P21 Activated Kinase 1 (Pak1) is an oncogenic kinase regulating cytoskeleton and cellular morphology.
• Runx3, traditionally a tumor suppressor, exhibits oncogenic roles in various cancers, with unclear regulatory mechanisms.

Purpose of the Study:

• To investigate the interaction between Pak1 and Runx3.
• To elucidate the mechanism controlling Runx3's paradoxical functions in cancer.

Main Methods:

• Mass spectrometry and site-directed mutagenesis to identify Runx3 phosphorylation site.
• Development of a site-specific antibody for confirmation.
• Functional studies on Runx3 phosphorylation.
• In vivo tumor xenograft studies in nude mouse models.
• Analysis of clinical samples.

Main Results:

• Runx3 is a direct substrate of Pak1, with phosphorylation occurring at Threonine 209.
• Threonine 209 phosphorylation causes Runx3 mislocalization from the nucleus to the cytoplasm, altering its function.
• Runx3-T209E mutant cells exhibited increased tumorigenic potential in vivo.
• Clinical samples suggest Threonine 209 phosphorylation is relevant in cancers where Runx3 is oncogenic.

Conclusions:

• Runx3-Threonine 209 phosphorylation by Pak1 acts as a molecular switch, dictating Runx3's dualistic functions.
• This phosphorylation is a potential therapeutic target for cancers where Runx3 plays an oncogenic role.