Abstract
AKT pathway has a critical role in mediating signaling transductions for cell proliferation, differentiation and survival. Previous studies have shown that AKT activation is achieved through a series of phosphorylation steps: first, AKT is phosphorylated at Thr-450 by JNK kinases to prime its activation; then, phosphoinositide-dependent kinase 1 phosphorylates AKT at Thr-308 to expose the Ser-473 residue; and finally, AKT is phosphorylated at Ser-473 by several kinases (PKD2 and others) to achieve its full activation. For its inactivation, the PH-domain containing phosphatases dephosphorylate AKT at Ser-473, and protein serine/threonine phosphatase-2A (PP-2A) dephosphorylates it at Thr-308. However, it remains unknown regarding which phosphatase dephosphorylates AKT at Thr-450 during its inactivation. In this study, we present both in vitro and in vivo evidence to show that protein serine/threonine phosphatase-1 (PP-1) is a major phosphatase that directly dephosphorylates AKT to modulate its activation. First, purified PP-1 directly dephosphorylates AKT in vitro. Second, immunoprecipitation and immunocolocalization showed that PP-1 interacts with AKT. Third, stable knock down of PP-1α or PP-1β but not PP-1γ, PP-2Aα or PP-2Aβ by shRNA leads to enhanced phosphorylation of AKT at Thr-450. Finally, overexpression of PP-1α or PP-1β but not PP-1γ, PP-2Aα or PP-2Aβ results in attenuated phosphorylation of AKT at Thr-450. Moreover, our results also show that dephosphorylation of AKT by PP-1 significantly modulates its functions in regulating the expression of downstream genes, promoting cell survival and modulating differentiation. These results show that PP-1 acts as a major phosphatase to dephosphorylate AKT at Thr-450 and thus modulate its functions.
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Abbreviations
- ARPE-19:
-
retinal pigmental epithelial cells
- bFGF:
-
basic fibroblast growth factor
- CA:
-
Calyculin A
- HLE or HLECs:
-
human lens epithelial cells
- JNK1/2/3:
-
c-Jun terminal kinase 1/2/3
- PKD1/2:
-
phosphoinositide-dependent kinase 1/2
- PHLPPs:
-
PH-domain phosphatases
- PIP3:
-
phosphoinositol-3,4,5-triphosphate
- PP-1:
-
protein serine/threonine phosphatase-1
- PP-2A:
-
protein serine/threonine phosphatase-2A
- OA:
-
okadaic acid
- S or Ser:
-
serine residue
- T or Thr:
-
threonine residue
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Acknowledgements
This study is supported in part by the National Institute of Health Grants 1 R01EY15765 and 1 R01EY18380, the Changjiang Scholar Team Award Funds from Education Ministry of China, the Lotus Scholar Program Funds from Hunan Province Government and the Special Honorary Professorship Funds from Hunan Normal University.
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Xiao, L., Gong, LL., Yuan, D. et al. Protein phosphatase-1 regulates Akt1 signal transduction pathway to control gene expression, cell survival and differentiation. Cell Death Differ 17, 1448–1462 (2010). https://doi.org/10.1038/cdd.2010.16
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DOI: https://doi.org/10.1038/cdd.2010.16
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