期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2015
卷号：112
期号：15
页码：4666-4671
DOI：10.1073/pnas.1502855112
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceMaintenance and reprogramming of pluripotency are among the most important issues in stem cell biology and regenerative medicine. Pluripotency is governed by several key transcription factors regulating transcription of other factors. Among these, regulation of OCT4 transcription by NANOG (from Irish myth-ology Tir na nOg) is a critical interaction. We present here the crystal structure of human NANOG homeodomain in complex with the OCT4 promoter DNA and, through a series of ration-ally designed mutations, we identify key functional residues in the protein-DNA interaction, protein stability, and maintenance of mouse ESC self-renewal. Furthermore, we describe a mutation, NANOG L122A, which enhances DNA binding affinity, protein stability, mouse ESC self-renewal, and reprogramming into ground state from primed state pluripotency. NANOG (from Irish mythology Tir na nOg) transcription factor plays a central role in maintaining pluripotency, cooperating with OCT4 (also known as POU5F1 or OCT3/4), SOX2, and other pluripotency factors. Although the physiological roles of the NANOG protein have been extensively explored, biochemical and biophysical properties in relation to its structural analysis are poorly understood. Here we determined the crystal structure of the human NANOG homeodomain (hNANOG HD) bound to an OCT4 promoter DNA, which revealed amino acid residues involved in DNA recognition that are likely to be functionally important. We generated a series of hNANOG HD alanine substitution mutants based on the protein-DNA interaction and evolutionary conservation and determined their biological activities. Some mutant proteins were less stable, resulting in loss or decreased affinity for DNA binding. Overexpression of the orthologous mouse NANOG (mNANOG) mutants failed to maintain self-renewal of mouse embryonic stem cells without leukemia inhibitory factor. These results suggest that these residues are critical for NANOG transcriptional activity. Interestingly, one mutant, hNANOG L122A, conversely enhanced protein stability and DNA-binding affinity. The mNANOG L122A, when overexpressed in mouse embryonic stem cells, maintained their expression of self-renewal markers even when retinoic acid was added to forcibly drive differentiation. When overexpressed in epiblast stem cells or human induced pluripotent stem cells, the L122A mutants enhanced reprogramming into ground-state pluripotency. These findings demonstrate that structural and biophysical information on key transcriptional factors provides insights into the manipulation of stem cell behaviors and a framework for rational protein engineering.
