Phosphorylation of Sox2 Cooperates in Reprogramming to Pluripotent Stem Cells

Abstract

Somatic cells can be reprogrammed into induced pluripotent stem cells (iPSCs) by transduction of reprogramming factors, including Oct4, Sox2, Klf4, and c-Myc. A coordinated network of these factors was suggested to confer a pluripotency of iPSCs. Together with Oct4, Sox2 plays a major role as a master regulator in ESCs. However, the underlying mechanisms by which Sox2 contributes to selfrenewal or reprogramming processes remain to be determined. Here, we provide new evidence for a phosphorylation-based regulation of Sox2 activity. Akt directly interacts with Sox2 and promotes its stabilization through phosphorylation at Thr118, which enhances the transcriptional activity of Sox2 in ESCs. Moreover, phosphorylation of Sox2 cooperates in the reprogramming of mouse embryonic fibroblasts by enabling more efficient induction of iPSCs. Overall, our studies provide new insights into the regulatory mechanism of Sox2 in ESCs and also provide a direct link between phosphorylation events and somatic cell reprogramming.

Ube2s regulates Sox2 stability and mouse ES cell maintenance

“…These modifications influence its subcellular distribution, protein stability or DNA-binding activity, and subsequently remodel its transcriptional activity towards downstream target genes. [51][52][53] For instance, AKT1 mediates Sox2 phosphorylation at its T118 residue, resulting in increased Sox2 stability and thus ensuring its high protein level in ES cells. 52 On the contrary, acetyltransferase p300 is capable of acetylating Sox2, which is provided as a nuclear export signal and destines Sox2 for ubiquitination and degradation.…”

“…[51][52][53] For instance, AKT1 mediates Sox2 phosphorylation at its T118 residue, resulting in increased Sox2 stability and thus ensuring its high protein level in ES cells. 52 On the contrary, acetyltransferase p300 is capable of acetylating Sox2, which is provided as a nuclear export signal and destines Sox2 for ubiquitination and degradation. 51 Obviously, these studies documented regulation of Sox2 stability by ubiquitination; however, the delicate mechanisms mediating this process remain to be illustrated.…”

Novel AKT phosphorylation sites identified in the pluripotency factors OCT4, SOX2 and KLF4

“…Likewise, for KLF4 we identified the reported AKT target site at S429 31 as well as novel phosphorylation sites at S19, T33, S234 and S326. Despite several attempts, however, we were unable to verify the reported T116 site of SOX2 (equivalent to T118 in the murine protein), 27 but identified a novel SOX2 phosphorylation site at S83.…”

“…[23][24][25] AKT1 has been shown to directly phosphorylate OCT4, SOX2 and KLF4, modulating their nuclear localization, stability and transcriptional activity. [26][27][28] In particular, AKT phosphorylates OCT4 at T235 leading to enhanced apoptosis resistance and tumorigenic potential in mouse embryonic carcinoma cells. 29 Likewise, SOX2 phosphorylation at T118 by AKT results in decreased proteasomal degradation of SOX2 protein and enhanced selfrenewal capacity of mouse embryonic stem cells.…”

“…29 Likewise, SOX2 phosphorylation at T118 by AKT results in decreased proteasomal degradation of SOX2 protein and enhanced selfrenewal capacity of mouse embryonic stem cells. 27,30 In contrast, AKT-mediated phosphorylation of human KLF4 on T429 accelerates its degradation and thereby impairs stemness. 31 In addition to triggering posttranslational modifications, indirect links between AKT and certain OSKM factors, such SOX2, have been described.…”