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Query: UNIPROT:P31749 (AKT)
 22,954 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The AKT or PKB family of protein kinases is one of the best characterized targets of phosphoinositide 3-kinases or PI3Ks. The AKT/PKB signal transduction pathway regulates many growth and survival mechanisms including transcription, cell cycle progression, metabolism, apoptosis, invasion and metastasis. Recently, Carpten et al. (Nature 2007;448:439-44) reported a very interesting study on the isoform AKT1 (PKBalpha). They described a novel point mutation (E17K) in the pleckstrin homology domain (PHD) of the AKT1 gene in human breast, colorectal and ovarian cancers, and demonstrated that it induces leukemia in mice. Here we give a critical appraisal of this finding and underline its clinical impact. We also discuss possible interventions for therapeutic development of AKT inhibitors to treat human cancer.
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PMID:Following the tracks of AKT1 gene. 1792 1

The matrix (MA) domain of the HIV-1 structural precursor Gag (PrGag) protein targets PrGag proteins to membrane assembly sites, and facilitates incorporation of envelope proteins into virions. To evaluate the specific requirements for the MA membrane-binding domain (MBD) in HIV-1 assembly and replication, we examined viruses in which MA was replaced by alternative MBDs. Results demonstrated that the pleckstrin homology domains of AKT protein kinase and phospholipase C delta1 efficiently directed the assembly and release of virus-like particles (VLPs) from cells expressing chimeric proteins. VLP assembly and release also were mediated in a phorbol ester-dependent fashion by the cysteine-rich binding domain of phosphokinase Cgamma. Although alternative MBDs promoted VLP assembly and release, the viruses were not infectious. Notably, PrGag processing was reduced, while cleavage of GagPol precursors resulted in the accumulation of Pol-derived intermediates within virions. Our results indicate that the HIV-1 assembly machinery is flexible with regard to its means of membrane association, but that alternative MBDs can interfere with the elaboration of infectious virus cores.
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PMID:Analysis of human immunodeficiency virus matrix domain replacements. 1799 64

Despite its' central role, the precise mechanisms of the phosphoinositide 3-kinase/Akt (PI3K)/Akt pathway activation in acute myeloid leukaemia (AML) have not been elucidated. Recently, a recurrent novel AKT1 pleckstrin homology domain (PHD) mutation leading to membrane translocation, constitutive AKT activation and leukaemia development in mice was described. To assess AKT1 PHD mutations in AML, we sequenced 57 specimens from 49 AML patients, all of whom showed PI3K/AKT pathway activation by analysis of total and phospho-protein expression for AKT, mTor, p70S6Kinase, S6ribosomal protein and PTEN. No mutations in AKT1 PHD were identified, making this mutation an unlikely cause of PI3K/AKT pathway activation in AML.
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PMID:PI3K/AKT pathway activation in acute myeloid leukaemias is not associated with AKT1 pleckstrin homology domain mutation. 1805 70

Cell surface receptors and their associated signaling pathways on the plasma membrane are key targets in understanding cellular responses. However, the isolation and identification of receptor complexes has been elusive. The Fc receptor was captured from the surface of live cells using microbeads coated with the receptor's cognate ligand, gamma globulin (IgG), and analyzed by liquid chromatography and tandem mass spectrometry (LC-MS/MS) alongside several controls. Live-cell affinity receptor chromatography (LARC) resulted in a partially nonredundant list of 288 proteins that were specific to the Fc receptor complex. The proteins identified were in close agreement with previously determined factors in the Fc receptor complex as demonstrated by genetic and biochemical methods and revealed novel complex members. Confocal microscopy was used to confirm recruitment of SRC, SYK, PLC, PKC, PI3K, SHIP, TEC, CDC42, RAP, PAK, GAP, GEF, GRP, and CRK to the receptor complex upon activation by the same ligand microbeads. The expression of mutants and silencing RNA against specific isoforms were used to demonstrate a functional role for novel members of the Fc receptor complex, including RHOG (RAS homologue member G), p115 RhoGEF (protein of 115-kDa RAS homologue guanine exchange factor), and CRKL (CRK-like). The recruitment of AKT pleckstrin homology (PH) domain green fluorescent protein (GFP) was used to quantify the production of phosphorylated inositol at the activated receptor complex. We conclude that it is feasible to capture an activated receptor complex from the surface of live cells using ligand-coated microbeads for identification of members of a receptor complex or pathway by LC-MS/MS.
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PMID:Capture of an activated receptor complex from the surface of live cells by affinity receptor chromatography. 1860 92

Despite the major role of the AKT/PKB family of proteins in the regulation of many growth and survival mechanisms in the cell, and the increasing evidence suggesting that AKT disruption could play a key role in many human malignancies, no major mutations of AKT genes had been reported, until very recently when Carpten et al reported a novel transforming mutation (E17K) in the pleckstrin homology domain of the AKT1 gene in solid tumours. Several laboratories are now screening for this mutation in different malignancies, and, recently, the mutation was described by Malanga et al in 1.9% of lung cancer patients. Considering the importance of the PI3K/AKT pathway in mediating survival and antiapoptotic signals in the B-cell types of chronic lymphocytic leukaemia (CLL) and acute lymphoblastic leukaemia (ALL), we sequenced the AKT1 exon 3 for the above mentioned mutation in 87 specimens, representing 45 CLLs, 38 ALLs and 4 prolymphocytic leukaemia (PLL) cases, which are all of B-cell origin. Our results show that the mutation E17K/AKT1 was not detected in the pleckstrin homology domain of AKT1 of the investigated cases. We conclude that this mutation is not a major event in B-cell-derived lymphoid leukaemias.
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PMID:The transforming mutation E17K/AKT1 is not a major event in B-cell-derived lymphoid leukaemias. 1866 77

Protein kinase B (PKB)/Akt has been strongly implicated in the insulin-dependent stimulation of GLUT4 translocation and glucose transport in skeletal muscle and fat cells. Recently an allosteric inhibitor of PKB (Akti) that selectively targets PKBalpha and -beta was reported, but as yet its precise mechanism of action or ability to suppress key insulin-regulated events such as glucose and amino acid uptake and glycogen synthesis in muscle cells has not been reported. We show here that Akti ablates the insulin-dependent regulation of these processes in L6 myotubes at submicromolar concentrations and that inhibition correlates tightly with loss of PKB activation/phosphorylation. Similar findings were obtained using 3T3-L1 adipocytes. Akti did not inhibit IRS1 tyrosine phosphorylation, phosphatidylinositol 3-kinase signaling, or activation of Erks, ribosomal S6 kinase, or atypical protein kinases C but significantly impaired regulation of downstream PKB targets glycogen synthase kinase-3 and AS160. Akti-mediated inhibition of PKB requires an intact kinase pleckstrin homology domain but does not involve suppression of 3-phosphoinositide binding to this domain. Importantly, we have discovered that Akti inhibition is critically dependent upon a solvent-exposed tryptophan residue (Trp-80) that is present within the pleckstrin homology domain of all three PKB isoforms and whose mutation to an alanine (PKB(W80A)) yields an Akti-resistant kinase. Cellular expression of PKB(W80A) antagonized the Akti-mediated inhibition of glucose and amino acid uptake. Our findings support a critical role for PKB in the hormonal regulation of glucose and system A amino acid uptake and indicate that use of Akti and expression of the drug-resistant kinase will be valuable tools in delineating cellular PKB functions.
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PMID:Use of Akt inhibitor and a drug-resistant mutant validates a critical role for protein kinase B/Akt in the insulin-dependent regulation of glucose and system A amino acid uptake. 1866 36

cAMP-dependent protein kinase A (PKA) is important in processes requiring localized cell protrusion, such as cell migration and axonal path finding. Here, we used a membrane-targeted PKA biosensor to reveal activation of PKA at the leading edge of migrating cells. Previous studies show that PKA activity promotes protrusion and efficient cell migration. In live migrating cells, membrane-associated PKA activity was highest at the leading edge and required ligation of integrins such as alpha4beta1 or alpha5beta1 and an intact actin cytoskeleton. alpha4 integrins are type I PKA-specific A-kinase anchoring proteins, and we now find that type I PKA is important for localization of alpha4beta1 integrin-mediated PKA activation at the leading edge. Accumulation of 3' phosphorylated phosphoinositides [PtdIns(3,4,5)P(3)] products of phosphatidylinositol 3-kinase (PI3-kinase) is an early event in establishing the directionality of migration; however, polarized PKA activation did not require PI3-kinase activity. Conversely, inhibition of PKA blocked accumulation of a PtdIns(3,4,5)P(3)-binding protein, the AKT-pleckstrin homology (PH) domain, at the leading edge; hence, PKA is involved in maintaining cell polarity during migration. In sum, we have visualized compartment-specific PKA activation in migrating cells and used it to reveal that adhesion-mediated localized activation of PKA is an early step in directional cell migration.
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PMID:Integrin-mediated protein kinase A activation at the leading edge of migrating cells. 1878 51

AKT, a phospholipid-binding serine/threonine kinase, is a key component of the phosphoinositide 3-kinase cell survival signaling pathway that is aberrantly activated in many human cancers. Many attempts have been made to inhibit AKT; however, selectivity remains to be achieved. We have developed a novel strategy to inhibit AKT by targeting the pleckstrin homology (PH) domain. Using in silico library screening and interactive molecular docking, we have identified a novel class of non-lipid-based compounds that bind selectively to the PH domain of AKT, with "in silico" calculated K(D) values ranging from 0.8 to 3.0 micromol/L. In order to determine the selectivity of these compounds for AKT, we used surface plasmon resonance to measure the binding characteristics of the compounds to the PH domains of AKT1, insulin receptor substrate-1, and 3-phosphoinositide-dependent protein kinase 1. There was excellent correlation between predicted in silico and measured in vitro K(D)s for binding to the PH domain of AKT, which were in the range 0.4 to 3.6 micromol/L. Some of the compounds exhibited PH domain-binding selectivity for AKT compared with insulin receptor substrate-1 and 3-phosphoinositide-dependent protein kinase 1. The compounds also inhibited AKT in cells, induced apoptosis, and inhibited cancer cell proliferation. In vivo, the lead compound failed to achieve the blood concentrations required to inhibit AKT in cells, most likely due to rapid metabolism and elimination, and did not show antitumor activity. These results show that these compounds are the first small molecules selectively targeting the PH domain of AKT.
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PMID:Discovery of a novel class of AKT pleckstrin homology domain inhibitors. 1879 Jul 45

The PI3K/AKT pathway is frequently activated in human cancer. Recently, a G to A point mutation (E17K) was found in the pleckstrin homology domain of AKT1. We aimed to explore this mutation in cases of urothelial carcinoma. Using chip-based matrix-assisted laser desorption-time-of-flight (MALDI-TOF) mass spectrometer, AKT1 E17K mutation was searched in 26 total RNA samples obtained from 26 patients known to have urothelial carcinoma. Mutation was found in one out of 26 (3.8%) patients - a 46 year old female with a low grade transitional cell carcinoma located to the lamina propria (Ta disease). Our finding is in line with previous studies showing AKT1 E17K mutation to be rare. Yet, further studies are required to determine whether this mutation is indeed related to less aggressive disease and carries better prognosis.
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PMID:AKT1 E17 K pleckstrin homology domain mutation in urothelial carcinoma. 1938 6

The phosphatidylinositol 3-kinase/AKT signaling pathway plays a critical role in activating survival and antiapoptotic pathways within cancer cells. Several studies have shown that this pathway is constitutively activated in many different cancer types. The goal of this study was to discover novel compounds that bind to the pleckstrin homology (PH) domain of AKT, thereby inhibiting AKT activation. Using proprietary docking software, 22 potential PH domain inhibitors were identified. Surface plasmon resonance spectroscopy was used to measure the binding of the compounds to the expressed PH domain of AKT followed by an in vitro activity screen in Panc-1 and MiaPaCa-2 pancreatic cancer cell lines. We identified a novel chemical scaffold in several of the compounds that binds selectively to the PH domain of AKT, inducing a decrease in AKT activation and causing apoptosis at low micromolar concentrations. Structural modifications of the scaffold led to compounds with enhanced inhibitory activity in cells. One compound, 4-dodecyl-N-(1,3,4-thiadiazol-2-yl)benzenesulfonamide, inhibited AKT and its downstream targets in cells as well as in pancreatic cancer cell xenografts in immunocompromised mice; it also exhibited good antitumor activity. In summary, a pharmacophore for PH domain inhibitors targeting AKT function was developed. Computer-aided modeling, synthesis, and testing produced novel AKT PH domain inhibitors that exhibit promising preclinical properties.
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PMID:In vitro and in vivo activity of novel small-molecule inhibitors targeting the pleckstrin homology domain of protein kinase B/AKT. 1949 Dec 72


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