Reciprocal Regulation of Akt and Oct4 Promotes the Self-Renewal and Survival of Embryonal Carcinoma Cells

Abstract

SUMMARY Signaling via the Akt serine/threonine protein kinase plays critical roles in the self-renewal of embryonic stem cells and their malignant counterpart, embryonal carcinoma cells (ECCs). Here we show that in ECCs, Akt phosphorylated the master pluripotency factor Oct4 at threonine 235, and that the levels of phosphorylated Oct4 in ECCs correlated with resistance to apoptosis and tumorigenic potential. Phosphorylation of Oct4 increased its stability, and facilitated its nuclear localization and its interaction with Sox2, which promoted the transcription of the core stemness genes POU5F1 and NANOG. Furthermore, in ECCs, unphosphorylated Oct4 bound to the AKT1 promoter and repressed its transcription. Phosphorylation of Oct4 by Akt resulted in dissociation of Oct4 from the AKT1 promoter, which activated AKT1 transcription and promoted cell survival. Therefore, a site-specific, post-translational modification of the Oct4 protein orchestrates the regulation of its stability, subcellular localization and transcriptional activities, which collectively promotes the survival and tumorigenicity of ECCs.

PD‐L1 promotes OCT4 and Nanog expression in breast cancer stem cells by sustaining PI3K/AKT pathway activation

“…Several phosphorylation sites have been reported for OCT‐4 30. Subsequent study demonstrated that phosphorylation of OCT‐4 at threonine 235 leads to its stabilization and nuclear localization 25. Further study has confirmed the importance of OCT4 phosphorylation at this site (T235) for the stemness of cancer stem cells 31.…”

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

“…32 AKT mediates posttranslational modifications of the OSKM factors but, conversely, posttranslational modifications of OCT4 might also modulate AKT activity, thereby forming a positive feedback loop. 26,29 Thus, these data point to multiple mutual links between AKT and the OSKM factors, which might be critical for maintenance of stemness in malignant and non-malignant stem cells.…”

“…[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. 27,30 In contrast, AKT-mediated phosphorylation of human KLF4 on T429 accelerates its degradation and thereby impairs stemness.…”

“…Previous in vitro phosphorylation studies have been solely performed with recombinant OSKM proteins expressed in bacteria. 29,33 This approach exhibits several limitations, because the transcription factors are mostly expressed in inclusion bodies and need to be denatured and refolded in vitro. However, refolding of proteins from inclusion bodies is challenging and usually results in poor yields of natively folded, bioactive proteins.…”

Akt suppresses DLK for maintaining self-renewal of mouse embryonic stem cells

“…20 In addition, Akt is reported to phosphorylate Oct4 directly in embryonic carcinoma cells for maintaining tumorigenicity. 25 These studies revealed that Akt may regulate multiple substrates to orchestrate complex signaling within mouse ES cells. The phenomenon is similar to its master regulatory functions in somatic cells.…”