Protein Phosphatase-1 Dephosphorylates Akt1 At Thr-450 To Modulates Its Functions

AKT pathway plays 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(PDK1) phosphorylate 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 possibly Thr-308.In addition,PP-2A also dephosphorylates Thr-308.However, it remains unknown regarding what phosphatase dephosphorylates AKT at Thr-450 during its inactivation.In the present study,we present both in vitro and in vivo evidence to show that protein serine/threonine phosphatase-1α(PP-1α) is a major phosphatase which directly dephosphorylates AKT1 at Thr-450 to modulate its activation.First,purified PP-1αdirectly dephosphorylates AKT1 in vitro. Second,immunoprecipitation-linked Western blot and colocalization revealed that PP-1αinteracts with AKT1.Thirdly,overexpression of PP-1αbut not PP-2A in two ocular cell lines leads to dephosphorylation of AKT1 at Thr-450.Finally,inhibition of PP-1αactivity by calyculin A leads to enhanced phosphorylation of AKT1 at Thr-450.Moreover,our results also demonstrate that dephosphorylation of AKT1 by protein phosphatase-1αsignificantly modulates its functions in regulating expression of the downstream genes,promoting cell survival and modulating lens differentiation.These results demonstrate that PP-1αacts as a major phosphatase to dephosphorylate AKT1 at Thr-450 and thus modulate its functions.