Protein kinase B alpha (PKB-alpha), also known as AKT1, is one of three closely related serine/threonine-protein kinases: AKT1/alpha, AKT2/beta and AKT3/gamma. PKBs contain an N-terminal pleckstrin homology (PH) domain and a C-terminal catalytic domain []. PKB-alpha is predominantly expressed in endothelial cells. It is critical for the regulation of angiogenesis and the maintenance of vascular integrity []. It also plays a role in adipocyte differentiation []. Mice deficient in PKB-alpha exhibit perinatal morbidity, growth retardation, reduction in body weight accompanied by reduced sizes of multiple organs, and enhanced apoptosis in some cell types. PKB-alpha activity has been reported to be frequently elevated in breast and prostate cancers [, ]. In some cancer cells, PKB-alpha may act as a suppressor of metastasis [].
Proline-rich AKT1 substrate 1 protein (AKT1S1, PRAS40) is part of the mammalian target of rapamycin complex 1 (mTORC1, contains MTOR, MLST8, RPTOR, AKT1S1/PRAS40 and DEPTOR), which regulates cell growth and survival in response to nutrient and hormonal signals []. Within mTORC1, AKT1S1 negatively regulates mTOR activity in a manner that is dependent on its phosphorylation state and binding to 14-3-3 proteins. AKT1S1 is a substrate for AKT1 phosphorylation, but can also be activated by AKT1-independent mechanisms. It may also play a role in nerve growth factor-mediated neuroprotection [, ].
Potassium (K+) is an essential nutrient for plant growth and development. This entry represents a group of potassium channel proteins from plants, including KAT1-3, SKOR, GORK and AKT1/2/5/6 from Arabidopsis []. Together with AtHAK5, AKT1 mediates high-affinity K+ uptake into roots during seedling establishment and post-germination growth []. KAT1 is required for guard cell K+ uptake during light-induced stomatal opening []. AKT6, also known as SPIK, plays a role in K+ uptake in the growing pollen tube []. AKT1 has been shown to be regulated by the CBL1-CIPK23 complex [, ]. SKOR and GORK are both outward-rectifying potassium channels [, ].
Protein kinase B (PKB), also called Akt or RAC, is a phosphatidylinositol 3'-kinase (PI3K)-dependent Ser/Thr kinase which alters the activity of the targeted protein []. Akt regulates numerous cellular processes, including cell growth, differentiation, proliferation, apoptosis, and glucose metabolism. Among its many roles, Akt appears to be common to signaling pathways that mediate the metabolic effects of insulin in several physiologically important target tissues [, ]. Human Akt has three isoforms derived for distinct genes: Akt1/PKBalpha, Akt2/PKBbeta, and Akt3/PKBgamma.This entry includes the isoforms alpha. Akt1 and Akt2 have distinct functions; they are involved in the control of growth and metabolism, respectively [, ].
This entry represents the phosphatase domain found in PTEN, which is a magnesium-dependent bifunctional phosphatidylinositol-3,4,5-trisphosphate 3-phosphatase/dual-specificity protein phosphatase PTEN (; ; ), which possesses the following catalytic activities:Phosphatidylinositol 3,4,5-trisphosphate + H(2)O = phosphatidylinositol 4,5-bisphosphate + phosphate.A phosphoprotein + H(2)O = a protein + phosphate.Protein tyrosine phosphate + H(2)O = protein tyrosine + phosphate.This protein acts as a dual-specificity protein phosphatase, dephosphorylating tyrosine-, serine- and threonine-phosphorylated proteins []. It also acts as a lipid phosphatase, removing the phosphate in the D3 position of the inositol ring from phosphatidylinositol 3,4,5-trisphosphate, phosphatidylinositol 3,4-diphosphate, phosphatidylinositol 3-phosphate and inositol 1,3,4,5-tetrakisphosphate. The lipid phosphatase activity is critical for its tumour suppressor function []. PTEN antagonizes the PI3K-AKT/PKB signalling pathway by dephosphorylating phosphoinositides and thereby modulating cell cycle progression and cell survival. The unphosphorylated form of PTEN cooperates with AIP1 to suppress AKT1 activation. PTEN dephosphorylates tyrosine-phosphorylated focal adhesion kinase and inhibits cell migration and integrin-mediated cell spreading and focal adhesion form [].
This entry represents the magnesium-dependent bifunctional phosphatidylinositol-3,4,5-trisphosphate 3-phosphatase/dual-specificity protein phosphatase PTEN (; ; ), which possesses the following catalytic activities:Phosphatidylinositol 3,4,5-trisphosphate + H(2)O = phosphatidylinositol 4,5-bisphosphate + phosphate.A phosphoprotein + H(2)O = a protein + phosphate.Protein tyrosine phosphate + H(2)O = protein tyrosine + phosphate.This protein acts as a dual-specificity protein phosphatase, dephosphorylating tyrosine-, serine- and threonine-phosphorylated proteins []. It also acts as a lipid phosphatase, removing the phosphate in the D3 position of the inositol ring from phosphatidylinositol 3,4,5-trisphosphate, phosphatidylinositol 3,4-diphosphate, phosphatidylinositol 3-phosphate and inositol 1,3,4,5-tetrakisphosphate. The lipid phosphatase activity is critical for its tumour suppressor function []. PTEN antagonizes the PI3K-AKT/PKB signalling pathway by dephosphorylating phosphoinositides and thereby modulating cell cycle progression and cell survival. The unphosphorylated form of PTEN cooperates with AIP1 to suppress AKT1 activation. PTEN dephosphorylates tyrosine-phosphorylated focal adhesion kinase and inhibits cell migration and integrin-mediated cell spreading and focal adhesion form [].
