Phosphorylation regulates human OCT4

Area of Science:

• Stem cell biology
• Molecular and cellular biology
• Epigenetics

Background:

• Octamer-binding transcription factor 4 (OCT4) is crucial for maintaining embryonic stem cell pluripotency and self-renewal.
• Understanding post-translational modifications, such as phosphorylation, is key to elucidating OCT4's regulatory mechanisms.

Purpose of the Study:

• To identify and characterize novel phosphorylation sites on OCT4.
• To investigate the functional impact of OCT4 phosphorylation on its DNA-binding activity and role in cellular reprogramming.
• To explore the relationship between OCT4 phosphorylation and signaling pathways, particularly ERK signaling.

Main Methods:

• Liquid chromatography-mass spectrometry (LC-MS) was employed to identify phosphosites on OCT4 and its interacting partners.
• Functional assays, including reporter gene assays and cellular reprogramming experiments, were used to assess the impact of specific phosphorylation sites.
• Kinase assays were performed to confirm direct phosphorylation by ERK2.

Main Results:

• 14 localized phosphorylation sites on OCT4 were identified, 11 of which are novel.
• Phosphorylation at T234 and S235 within the homeobox region was found to negatively regulate OCT4's DNA-binding activity and transcriptional function.
• Mutating T234/S235 to mimic constitutive phosphorylation decreased reporter gene activation and reprogramming efficiency.
• 144 unique phosphopeptides were identified on OCT4-interacting proteins (e.g., SOX2, SALL4), enriched for ERK signaling motifs.
• ERK2 was confirmed to directly phosphorylate OCT4 at specific sites in vitro.

Conclusions:

• Phosphorylation of OCT4, particularly at T234/S235, acts as a negative regulator of its function in maintaining pluripotency.
• The study establishes a direct mechanistic link between ERK signaling and the regulation of pluripotency by OCT4 and its associated factors.