KLF4 Nuclear Export Requires ERK Activation and Initiates Exit from Naive Pluripotency

Abstract

Summary: Cooperative action of a transcription factor complex containing OCT4, SOX2, NANOG, and KLF4 maintains the naive pluripotent state; however, less is known about the mechanisms that disrupt this complex, initiating exit from pluripotency. We show that, as embryonic stem cells (ESCs) exit pluripotency, KLF4 protein is exported from the nucleus causing rapid decline in Nanog and Klf4 transcription; as a result, KLF4 is the first pluripotency transcription factor removed from transcription-associated complexes during differentiation. KLF4 nuclear export requires ERK activation, and phosphorylation of KLF4 by ERK initiates interaction of KLF4 with nuclear export factor XPO1, leading to KLF4 export. Mutation of the ERK phosphorylation site in KLF4 (S132) blocks KLF4 nuclear export, the decline in Nanog, Klf4, and Sox2 mRNA, and differentiation. These findings demonstrate that relocalization of KLF4 to the cytoplasm is a critical first step in exit from the naive pluripotent state and initiation of ESC differentiation. : Dhaliwal and colleagues show that KLF4 is exported from the nucleus to initiate embryonic stem cell differentiation. KLF4 nuclear export is caused by FGF-MEK-ERK signaling whereby activated ERK phosphorylates KLF4, allowing interaction with nuclear export factor Xportin1. Blocking KLF4 nuclear export prevents embryonic stem cell exit from naive pluripotency and slows development of the embryo. Keywords: KLF4, embryonic stem cell, nuclear export, pluripotency, XPO1, ERK, transcription factor, proximity ligation amplification