PTEN/Akt Axis is Involved in Somatic Cell Reprogramming to Mouse iPS Cells

Tomoe Ueyama¹, Shu Nakao¹, Tasuku Tsukamoto¹, Dai Ihara¹, Yukihiro Harada¹, Yuka Akagi¹, Sae Nakagawa¹, Yasuyuki S Kida³, Takahiro Sogo² and Teruhisa Kawamura*¹

Received: November 28, 2018;   Published: December 10, 2018

DOI: 10.26717/BJSTR.2018.11.002162

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Abstract

Induced pluripotent stem cells (iPSCs) are highly expected to apply for regeneration therapy and disease modeling, although the efficiency of reprogramming to iPSCs remains not high enough. We previously reported that inhibition of p53 tumor suppressor gene exhibits a remarkable increase in the efficiency of reprogramming to iPSCs. While p53 is degraded by Mdm2 and Mdmx with E3 ligase activity, phosphatase and tensin homologue (PTEN) inhibits Mdm-dependent p53 degradation, through phosphoinositol-3-kinase/Akt-dependent and -independent pathways. Therefore, we hypothesized that targeting PTEN may affect the efficiency of reprogramming to iPSCs. Using mouse embryonic fibroblasts prepared from Ptenflox/flox mice, Cre-loxP-based gene ablation of Pten revealed an increase in Akt phosphorylation and downregulation of the protein levels of p53 and one of its downstream targets, p21, resulting in efficient iPSC colony formation. In addition, CRISPR-Cas9-based knock-down of Pten gene also promoted the reprogramming efficiency. Conversely, overexpression of PTEN increased the levels of p53 and p21 and decreased the number of iPSC colonies. Moreover, co-infection of a constitutively active form of Akt (CA Akt) perturbed 4F-induced upregulation of p53 and p21, and increased iPSC production, which was canceled by overexpression of p53. We further found that negative cell cycle regulators, 19Arf and p16Ink4a were also upregulated during reprogramming, both of which were downregulated by CA Akt. Therefore, deficiency of PTEN improved the reprogramming efficiency by activation of Akt at least in part through downregulation of p19Arf and p16Ink4a as well as significant inhibition of p53/p21 pathway. Taken together, regulation of PTEN/Akt axis would be a promising strategy to enhance the efficiency of reprogramming to iPSCs.

Keywords : Induced Pluripotent Stem Cell; Reprogramming; PTEN/Akt pathway; p53/p21 pathway

Abbreviations : CA: Constitutively Active; CRISPR: Clustered Regularly Interspaced Short Palindromic Repeats, ESC: Embryonic Stem Cell; HA: Hemagglutinin; IPSC: Induced Pluripotent Stem Cell; MEF: Mouse Embryonic Fibroblast; PIP3: Phosphatidylinositol (3,4,5)-trisphosphate; PTEN, Phosphatase and Tensin Homolog; 4F: reprogramming four factors