Protein phosphatase-1 regulates Akt1 signal transduction pathway to control gene expression, cell survival and differentiation.
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-1alpha or PP-1beta but not PP-1gamma, PP-2Aalpha or PP-2Abeta by shRNA leads to enhanced phosphorylation of AKT at Thr-450. Finally, overexpression of PP-1alpha or PP-1beta but not PP-1gamma, PP-2Aalpha or PP-2Abeta 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.
Xiao
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Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha, 68198-5870, USA.
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D000818:Animals; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology*; D002470:Cell Survival / Q000187:drug effects / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004847:Epithelial Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D005123:Eye / Q000196:embryology / Q000378:metabolism; D016222:Fibroblast Growth Factor 2 / Q000494:pharmacology; D015870:Gene Expression / Q000235:genetics; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology*; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism; D000071679:Glycogen Synthase Kinase 3 beta; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D007908:Lens, Crystalline / Q000166:cytology; D051379:Mice; D016328:NF-kappa B / Q000235:genetics; D010766:Phosphorylation / Q000187:drug effects / Q000502:physiology; D011485:Protein Binding / Q000502:physiology; D054645:Protein Phosphatase 1 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D054648:Protein Phosphatase 2 / Q000037:antagonists & inhibitors / Q000378:metabolism; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism*; D055213:Retinal Pigment Epithelium / Q000166:cytology; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D013912:Threonine / Q000378:metabolism
D004791:Enzyme Inhibitors; D016328:NF-kappa B; D021122:Protein Subunits; D016222:Fibroblast Growth Factor 2; D013912:Threonine; C494918:AKT1 protein, human; C514862:Akt1 protein, mouse; D000071679:Glycogen Synthase Kinase 3 beta; D051057:Proto-Oncogene Proteins c-akt; D048031:JNK Mitogen-Activated Protein Kinases; D038362:Glycogen Synthase Kinase 3; C517187:PPP1CA protein, human; D054645:Protein Phosphatase 1; D054648:Protein Phosphatase 2