Protein phosphatase-1 regulates Akt1 signal transduction pathway to control gene expression, cell survival and differentiation

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-1a or PP-1b but not PP-1c, PP-2Aa or PP-2Ab by shRNA leads to enhanced phosphorylation of AKT at Thr-450. Finally, overexpression of PP-1a or PP-1b but not PP-1c, PP-2Aa or PP-2Ab 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.

Role of Vimentin in the Inhibitory Effects of Low-Molecular-Weight Heparin on PC-3M Cell Adhesion to, and Migration through, Endothelium

“…PP-1 is a major phosphatase that can directly dephosphorylate proteins, such as AKT, to modulate their activation and regulate the expression of downstream genes. It may be related with the inhibitory effect of heparin on tumor growth as other studies have reported; PP-1 can promote cell survival and modulate cell differentiation (Xiao et al, 2010). TGF-␤ has profound effects on all cell types that comprise the vasculature, including endothelial cells.…”

Sumoylation activates the transcriptional activity of Pax-6, an important transcription factor for eye and brain development

“…S1C). A thorough analysis of Pax-6 in four human ocular cell lines (20,21) revealed that p46, p43, and p32 were all present in these cells (Fig. S1D).…”

Akt2 and acid ceramidase cooperate to induce cell invasion and resistance to apoptosis

“…Similar results were obtained with PC3 cells where the inhibition of invasion was 44, 64 and 87% for ASAH1, Akt2 and ASAH1 + Akt2, pro-apoptotic roles via dephosphorylating RB, [53][54][55] Bad, 56 Bax, 57 caspase-9 58 and T450 in Akt. 59 Therefore, inhibition of both Akt and ASAH1 would be predicted to result in maximal dephosphorylation of key regulators of the malignant phenotype.…”