Differential effects of Akt isoforms on somatic cell reprogramming

Abstract

Akt plays an important role in cell growth, proliferation and survival. The specific roles of the three Akt isoforms in somatic cell reprogramming have not been investigated. Here we report that, during iPSC generation, enhanced Akt1 activity promotes complete reprogramming mainly through increased activation of Stat3 in concert with leukemia inhibitory factor (LIF) and, to a lesser extent, through promotion of colony formation. Akt1 augments Stat3 activity through activation of mTOR and upregulation of LIF receptor expression. Similarly, enhanced Akt2 or Akt3 activation also promotes reprogramming and coordinates with LIF to activate Stat3. Blocking Akt1 or Akt3 but not Akt2 expression prohibits cell proliferation and reprogramming. Furthermore, the halt in cell proliferation and reprogramming caused by mTOR and Akt inhibitors can be reversed by inhibition of GSK3. Finally, we found that expressing the GSK3b target Esrrb overrides inhibition of Akt and restores reprogramming. Our data demonstrated that during reprogramming, Akt promotes establishment of pluripotency through co-stimulation of Stat3 activity with LIF. Akt1 and Akt3 are essential for the proliferation of reprogrammed cells, and Esrrb supports cell proliferation and complete reprogramming during Akt signaling.

Direct comparison of distinct naive pluripotent states in human embryonic stem cells

“…Increased AKT1 phosphorylation is facilitated by the mTORC2 subunit, hence promoting cell proliferation and growth. PTEN , required in maintaining the negative feedback loop mechanism in PI3K/AKT pathway was expressed in all hESCs38. RICTOR and MAPKAP1 , known genes exclusive to mTORC2 subunit39 showed increased expression compared to DEPTOR , a common subunit between mTORC1 and mTORC2 subunits, in the naive lines.…”

Proliferation, survival and metabolism: the role of PI3K/AKT/mTOR signalling in pluripotency and cell fate determination

“…Although the role of PI3K/AKT/mTOR in this process has not been fully uncovered, several reports have demonstrated that PI3K/ AKT signalling promotes iPSC generation through inhibition of GSK3β and FOXO1, while concurrently enhancing the glycolytic metabolism (Silva et al, 2008;Yu et al, 2014;Zhu et al, 2011). This is further supported by experimental evidence indicating that inhibition of AKT hinders somatic cell reprogramming, which is alleviated by the inhibition of GSK3 (Tang et al, 2014).…”

Akt3 is responsible for the survival and proliferation of embryonic stem cells

“…We previously reported Akt isoform-specific knockdown in mouse embryonic fibroblasts (MEFs) using lentiviral shRNA constructs: shAkt1, shAkt2, and shAkt3 (for maximum Akt3 knockdown, shAkt3 consists of two constructs: shAkt3a and shAkt3b targeting different coding regions of Akt3) (Tang et al, 2014). We first tested the effectiveness of these constructs in ESCs.…”

“…Akt3 is predominantly activated in a number of cancers such as malignant melanoma and glioma, and plays important roles in the survival of immortalized MEFs (Liu et al, 2006; Mure et al, 2010; Stahl et al, 2004). In a recent study we reported that Akt1 and Akt3 play non-redundant roles in promoting primary MEF cell proliferation during somatic cell reprogramming (Tang et al, 2014), indicating different mechanisms governing cell growth by these two isoforms. One possible mechanism that these Akt isoforms play different functions for cell growth may be through differential cellular localization.…”