Dual Roles of MAPK-Mediated C/EBPβ Phosphorylation in Promoting Maturation and Suppressing EMT During Hepatocyte Differentiation from hESCs

Human embryonic stem cell (hESC)-derived hepatocytes (hEHs) display functional deficits, particularly impaired albumin secretion and ammonia metabolism, compared to primary human hepatocytes (PHHs). Here, we investigated the regulatory role of CCAAT/enhancer-binding protein beta (C/EBPβ) in hepatocyte maturation. Forced C/EBPβ expression enhanced hepatocyte functionality and upregulated hepatocyte-specific genes, while suppressing epithelial-mesenchymal transition (EMT) via downregulating canonical EMT markers. Mechanistically, CUT&Tag and luciferase reporter assays confirmed C/EBPβ directly binds to the promoter regions of CDH1 (E-cadherin) and CPS1 (carbamoyl phosphate synthetase 1). Co-immunoprecipitation identified an interaction between C/EBPβ and the MAPK pathway. RNA interference combined with Western blot analysis revealed that MAPK1-mediated phosphorylation of C/EBPβ at Thr-235 augmented its transactivation activity, accelerating hepatocyte maturation. Our findings establish C/EBPβ as a master regulator that coordinates transcriptional networks and post-translational modifications during hEHs maturation, providing novel insights for generating mature hepatocytes for disease modeling and regenerative medicine applications. The transcriptional activity of C/EBPβ is regulated by MAPK1 protein within the ERK/MAPK signaling pathway. MAPK1 moves from the cytoplasm into the nucleus and transfers phosphate groups to C/EBPβ. This process reverses the "self-inhibition" state of C/EBPβ and enhances its transcriptional activity on downstream target genes.