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Exp Neurobiol 2020; 29(3): 189-206
Published online July 1, 2020
https://doi.org/10.5607/en20021
© The Korean Society for Brain and Neural Sciences
Tae-young Lee1,2,3, In-Su Cho1, Narayan Bashyal1,2, Francisco J Naya4, Ming-Jer Tsai5, Jeong Seon Yoon1, Jung-Mi Choi1, Chang-Hwan Park6, Sung-Soo Kim1,2* and Haeyoung Suh-Kim1,2,3*
1Department of Anatomy, Ajou University School of Medicine, Suwon 16499, 2Department of Biomedical Sciences, Graduate School, Ajou University School of Medicine, Suwon 16499, 3Research Center, CelleBrain Ltd., Jeonju 54871, Korea, 4Department of Biology, Life Science and Engineering Building, Boston University, Boston, MA 00215, 5Department of Medicine and Program in Developmental Biology, Baylor College of Medicine, Houston, TX 77030, USA, 6Graduate School of Biomedical Science and Engineering, Hanyang University, Seoul 04763, Korea
Correspondence to: *To whom correspondence should be addressed.
Sung-Soo Kim, TEL: 82-31-219-5036, FAX: 82-31-219-5034
e-mail: kimdmg@ajou.ac.kr
Haeyoung Suh-Kim, TEL: 82-31-219-5036, FAX: 82-31-219-5039
e-mail: hysuh@ajou.ac.kr
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Neurogenic differentiation 1 (NeuroD1) is a class B basic helix-loop-helix (bHLH) transcription factor and regulates differentiation and survival of neuronal and endocrine cells by means of several protein kinases, including extracellular signal-regulated kinase (ERK). However, the effect of phosphorylation on the functions of NeuroD1 by ERK has sparked controversy based on context-dependent differences across diverse species and cell types. Here, we evidenced that ERK-dependent phosphorylation controlled the stability of NeuroD1 and consequently, regulated proneural activity in neuronal cells. A null mutation at the ERK-dependent phosphorylation site, S274A, increased the half-life of NeuroD1 by blocking its ubiquitin-dependent proteasomal degradation. The S274A mutation did not interfere with either the nuclear translocation of NeuroD1 or its heterodimerization with E47, its ubiquitous partner and class A bHLH transcription factor. However, the S274A mutant increased transactivation of the E-box-mediated gene and neurite outgrowth in F11 neuroblastoma cells, compared to the wild-type NeuroD1. Transcriptome and Gene Ontology enrichment analyses indicated that genes involved in axonogenesis and dendrite development were downregulated in NeuroD1 knockout (KO) mice. Overexpression of the S274A mutant salvaged neurite outgrowth in NeuroD1-deficient mice, whereas neurite outgrowth was minimal with S274D, a phosphomimicking mutant. Our data indicated that a longer protein half-life enhanced the overall activity of NeuroD1 in stimulating downstream genes and neuronal differentiation. We propose that blocking ubiquitin-dependent proteasomal degradation may serve as a strategy to promote neuronal activity by stimulating the expression of neuron-specific genes in differentiating neurons.
Keywords: Neurogenic differentiation factor 1, Neurite outgrowth, Extracellular signal-regulated kinase, Phosphorylation