Phosphorylation of Threonine 343 Is Crucial for OCT4 Interaction with SOX2 in the Maintenance of Mouse Embryonic Stem Cell Pluripotency.

OCT4 is required to maintain the pluripotency of embryonic stem cells (ESCs); yet, overdose-expression of OCT4 induces ESC differentiation toward primitive endoderm. The molecular mechanism underlying this differentiation switch is not fully understood. Here, we found that substitution of threonine343 by alanine (T343A), but not aspartic acid (T343D), caused a significant loss of OCT4-phosphorylation signal in ESCs. Loss of such OCT4-phosphorylation compromises its interaction with SOX2 but promotes interaction with SOX17. We therefore propose that threonine343 -based OCT4-phosphorylation is crucial for the maintenance of ESC pluripotency. This OCT4-phosphorylation-based mechanism may provide insight into the regulation of lineage specification during early embryonic development.