Posttranslational Modifications of Defined Embryonic Reprogramming Transcription Factors

The generation of induced pluripotent stem cells (iPSCs) from somatic cells by expressing ectopic reprogramming transcriptional factors such as Oct3/4, Sox2, Klf4, c-Myc, and Nanog is one of the cutting-edge discoveries in stem cell and cancer research. This discovery has raised several safety issues regarding the use of iPSC technology for human disease research. Tumorigenesis is the major obstacle observed for iPSC-mediated transplantation therapy. Recently, a new method to generate human iPSCs either by a chemical method or by direct delivery of reprogramming factors has become a promising approach for future customized cell therapy of human disorders. These reprogramming transcriptional factors play critical roles in diverse cellular functions such as transactivation, cellular proliferation, differentiation, apoptosis, and tumorigenesis. Posttranslational modifications (PTMs) (phosphorylation, ubiquitination, acetylation, sumoylation, and so on) of these proteins act as a regulatory signal to control protein activity, expression, and stability in a wide variety of cellular processes. We attempt to summarize the accumulated evidence to address the role of PTMs of Oct3/4, Sox2, Klf4, c-Myc, and Nanog in regulating their biological functions. This review allows us to understand the importance of PTMs and their application in developing an efficient and safe reprogramming method without cancer development for cell therapy. Finally, we discuss the importance of PTMs of reprogramming factors in tumor pathogenesis