IndraLab
Statements
AKT1 is active.
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"Mammalian TOR complex 1 (mTORC1) and mTORC2 exert their actions by regulating other important kinases, such as S6 kinase (S6K) and Akt.Recent findings have revealed novel important roles for mTORC2 in the phosphorylation of AGC kinase family members. mTORC2 phosphorylates and activates Akt, SGK, and PKC, which regulate cell survival, cell cycle progression and anabolism"
"Here, we identify PP1 as a serine/threonine phosphatase that associates with and dephosphorylates AKT in breast cancer cells|The heat shock protein 90 inhibitor geldanamycin and the ErbB inhibitor ZD1839 promote rapid PP1 phosphatase-dependent inactivation of AKT in ErbB2 overexpressing breast cancer cells"
"These results confirm that the activity changes observed are achieved by a reversible phosphorylation mechanism, and also argue that pp2a may negatively regulate rac-pk activity in vivo. Dephosphorylation of the activated rac-pk in itro by pp2ac resulted in an 87% reduction of kinase activity"
"Regulation of Akt/PKB Activation by Tyrosine PhosphorylationAs shown in Fig. 2 d, while mutation of Tyr340 has little effect on either tyrosine phosphorylation or kinase activity of Akt induced by Src527F, substitution of Tyr315 or Tyr326 with a phenylalanine, respectively, dramatically reduces both the tyrosine phosphorylation and kinase activity of Akt. The combination of these two mutations abolishes Src-induced tyrosine phosphorylation of Akt as well as its kinase activity."
"We also showed that phosphorylation of Tyr-315 in Akt induced by Src or EGF is dependent on the integrity of this proline-rich motif. Furthermore, the Akt mutant lacking this proline motif fails to block the transcription activity of Forkhead in 293 cells and poorly stimulates the proliferation of Madin-Darby canine kidney cells. Taken together, our data suggest that the interaction between the SH3 domain of Src family kinases and the proline-rich motif in the C-terminal regulatory region of Akt is required for tyrosine phosphorylation of Akt and its subsequent activation."
"We report that JNKs are necessary for the reactivation of Akt after ischemic injury. We identified Thr450 of Akt as a residue that is phosphorylated by JNKs, and the phosphorylation status of Thr450 regulates reactivation of Akt after hypoxia, apparently by priming Akt for subsequent phosphorylation by 3-phosphoinositide-dependent protein kinase."
"Regulation of Akt/PKB Activation by Tyrosine PhosphorylationAs shown in Fig. 2 d, while mutation of Tyr340 has little effect on either tyrosine phosphorylation or kinase activity of Akt induced by Src527F, substitution of Tyr315 or Tyr326 with a phenylalanine, respectively, dramatically reduces both the tyrosine phosphorylation and kinase activity of Akt. The combination of these two mutations abolishes Src-induced tyrosine phosphorylation of Akt as well as its kinase activity."
"Although multiple sites on Akt could be SUMOylated, K276 was identified as a major SUMO acceptor site. K276R or E278A mutation reduced SUMOylation of Akt but had little effect on its ubiquitination. Strikingly, these mutations also completely abolished Akt kinase activity. In support of these results, we found that expression of PIAS1 and SUMO1 increased Akt activity, whereas expression of SENP1 reduced Akt1 activity."
"Although multiple sites on Akt could be SUMOylated, K276 was identified as a major SUMO acceptor site. K276R or E278A mutation reduced SUMOylation of Akt but had little effect on its ubiquitination. Strikingly, these mutations also completely abolished Akt kinase activity. In support of these results, we found that expression of PIAS1 and SUMO1 increased Akt activity, whereas expression of SENP1 reduced Akt1 activity."
"Furthermore, overall PKB activity, primarily consisting of cytosolic enzyme, was dependent upon levels of PI(3,4)P2, while only membrane-associated PKB activity was dependent upon PI(3,4,5)P3 levels. We conclude that PI(3,4,5)P3 and PI(3,4)P2 have distinct roles in determining PKB phosphorylation and activity. Thus, when investigating PI3K-PKB pathways, the importance of both lipids must be considered"
AKT1 is kinase-active.
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"In vivo 32P labeling and mutagenesis demonstrated that m/p-PKBalpha activity was due to phosphorylation on Thr308 and Ser473, that are normally induced on PKB following stimulation of the cells with insulin or insulin-like growth factor-1 (IGF-1).... Following activation the kinase detached from the membrane and translocated to the nucleus."
"Fig. 1. Insulin-like growth factor 1 (IGF-1)-mediated signaling pathways relevant to hypertrophy. Binding of IGF-1 activates the IGF-1 receptor (purple), which then recruits insulin-receptor substrate (IRS-1). This leads to the activation of two signaling pathways: the Ras-Raf-MEK-ERK pathway and the phosphatidylinositol 3-kinase (PI3K)- Akt pathway. The PI3K-Akt pathway recapitulates hypertrophy caused by IGF-1 stimulation. Akt1 activity can be modulated either by directly controlling its phosphorylation state or by altering the levels of the lipid that it binds at the cell membrane, phosphatidylinositol (3,4,5)-trisphosphate [PtdIns(3,4,5)P3] (orange). Signaling molecules that have been shown to have a negative effect on hypertrophy are colored red, and proteins whose activation induces hypertrophy are shown in green. Proteins that have not been assayed for their role in hypertrophy are shown in blue. Abbreviations: eIF-2B, eukaryotic translation initiation factor 2B; ERK, extracellular-signal-regulated kinase; GSK3b, glycogen-synthase kinase 3b; mTOR, mammalian target of rapamycin; p70S6K, p70 S6 kinase; PDK, phosphoinositide-dependent protein kinase; PtdIns(3,4)P2, phosphatidylinositol (3,4)-bisphosphate; PtdIns(4,5)P2, phosphatidylinositol (4,5)-bisphosphate; PHAS-1, phosphorylated heat- and acid-stable protein 1; PP2A, protein phosphatase 2A; PTEN, phosphatase and tensin homologous on chromosome 10; SHIP2, SH2-domain-containing inositol phosphatase; Tsc1/2, tuberous sclerosis complex 1 and 2. Modified from Ref. [87]. Akt1 activity can be modulated either by directly controlling its phosphorylation state or by altering the levels of the lipid that it binds at the cell membrane, PtdIns(3,4,5)P3 [22] (Fig. 1). Akt1 activity depends on phosphorylation at two sites: Ser473 and Thr309 [29]."
"Activation of PKB alpha and beta is then achieved at the plasma membrane by phosphorylation of Thr308/309 in the A-loop of the kinase domain and Ser473/474 in the carboxy-terminal regulatory region, respectively. The upstream kinase that phosphorylates PKB on Thr308, termed PI-dependent protein kinase-1, has been identified and extensively characterised. A candidate for the Ser473/474 kinase, termed the integrin-linked kinase, has been identified recently."
"As shown in Fig. 2 B, subconfluent HeLa cultures have relatively low levels of active PKB, as detected by antibodies specifically recognizing PKB phosphorylated on serine 473. Phosphorylation of PKB is fully inhibitable by treatment with the specific PI 3-kinase inhibitor LY294002. Sparse cultures have barely detectable levels of phosphorylated PKB; however, dense cultures have much more activated PKB, whereas the total levels of PKB protein remain constant under all conditions examined."
"Upon stimulation with insulin, AKT is recruited to cellular membranes by binding of its amino terminal pleckstrin (PH) domain to membrane bound phosphatidylinositol 3,4,5, trisphosphate (PIP3) [3]. The membrane bound form of AKT then becomes phosphorylated on two regulatory residues, a threonine within the activation loop (Thr308 in AKT1,Thr309 in AKT2, Thr305 in AKT3) and a serine in the C-terminus of the enzyme (Ser473 in AKT1,Ser474 in AKT2, Ser472 in AKT3), and both phosphorylations are considered to be required for AKT to reach maximum kinase activity [1]. The kinase responsible for phosphorylation of Thr308/309/305 has been identified as phosphoinositide-dependent kinase 1 (PDK1) [3]."
"identified four sites (Ser-124, Thr-308, Thr-450, and Ser-473) on Akt1 that are phosphorylated in vivo. Thr-308 and Ser-473 are inducibly phosphorylated after treatment of cells with extracellular stimuli, whereas Ser-124 and Thr-450 appear to be basally phosphorylated The third mechanism by which 3'-phosphorylated phosphoinositides regulate Akt activity is by controlling the accessibility of Akt as a substrate for PDKs. In in vitro reconstitution assays, the binding of PI3,4,5P to the Akt PH domain is required for PDK-1 to phosphorylate Akt In addition, PDK-1 complexed with either a fragment of PRK2, PRK2, or a PRK2-related peptide may be regulated by increased phospholipid concentrations"
"Fig. 1. Insulin-like growth factor 1 (IGF-1)-mediated signaling pathways relevant to hypertrophy. Binding of IGF-1 activates the IGF-1 receptor (purple), which then recruits insulin-receptor substrate (IRS-1). This leads to the activation of two signaling pathways: the Ras-Raf-MEK-ERK pathway and the phosphatidylinositol 3-kinase (PI3K)- Akt pathway. The PI3K-Akt pathway recapitulates hypertrophy caused by IGF-1 stimulation. Akt1 activity can be modulated either by directly controlling its phosphorylation state or by altering the levels of the lipid that it binds at the cell membrane, phosphatidylinositol (3,4,5)-trisphosphate [PtdIns(3,4,5)P3] (orange). Signaling molecules that have been shown to have a negative effect on hypertrophy are colored red, and proteins whose activation induces hypertrophy are shown in green. Proteins that have not been assayed for their role in hypertrophy are shown in blue. Abbreviations: eIF-2B, eukaryotic translation initiation factor 2B; ERK, extracellular-signal-regulated kinase; GSK3b, glycogen-synthase kinase 3b; mTOR, mammalian target of rapamycin; p70S6K, p70 S6 kinase; PDK, phosphoinositide-dependent protein kinase; PtdIns(3,4)P2, phosphatidylinositol (3,4)-bisphosphate; PtdIns(4,5)P2, phosphatidylinositol (4,5)-bisphosphate; PHAS-1, phosphorylated heat- and acid-stable protein 1; PP2A, protein phosphatase 2A; PTEN, phosphatase and tensin homologous on chromosome 10; SHIP2, SH2-domain-containing inositol phosphatase; Tsc1/2, tuberous sclerosis complex 1 and 2. Modified from Ref. [87]. Akt1 activity can be modulated either by directly controlling its phosphorylation state or by altering the levels of the lipid that it binds at the cell membrane, PtdIns(3,4,5)P3 [22] (Fig. 1). Akt1 activity depends on phosphorylation at two sites: Ser473 and Thr309 [29]."
"In vivo 32P labeling and mutagenesis demonstrated that m/p-PKBalpha activity was due to phosphorylation on Thr308 and Ser473, that are normally induced on PKB following stimulation of the cells with insulin or insulin-like growth factor-1 (IGF-1).... Following activation the kinase detached from the membrane and translocated to the nucleus."
"Activation of PKB alpha and beta is then achieved at the plasma membrane by phosphorylation of Thr308/309 in the A-loop of the kinase domain and Ser473/474 in the carboxy-terminal regulatory region, respectively. The upstream kinase that phosphorylates PKB on Thr308, termed PI-dependent protein kinase-1, has been identified and extensively characterised. A candidate for the Ser473/474 kinase, termed the integrin-linked kinase, has been identified recently."
"Fig. 1. Insulin-like growth factor 1 (IGF-1)-mediated signaling pathways relevant to hypertrophy. Binding of IGF-1 activates the IGF-1 receptor (purple), which then recruits insulin-receptor substrate (IRS-1). This leads to the activation of two signaling pathways: the Ras-Raf-MEK-ERK pathway and the phosphatidylinositol 3-kinase (PI3K)- Akt pathway. The PI3K-Akt pathway recapitulates hypertrophy caused by IGF-1 stimulation. Akt1 activity can be modulated either by directly controlling its phosphorylation state or by altering the levels of the lipid that it binds at the cell membrane, phosphatidylinositol (3,4,5)-trisphosphate [PtdIns(3,4,5)P3] (orange). Signaling molecules that have been shown to have a negative effect on hypertrophy are colored red, and proteins whose activation induces hypertrophy are shown in green. Proteins that have not been assayed for their role in hypertrophy are shown in blue. Abbreviations: eIF-2B, eukaryotic translation initiation factor 2B; ERK, extracellular-signal-regulated kinase; GSK3b, glycogen-synthase kinase 3b; mTOR, mammalian target of rapamycin; p70S6K, p70 S6 kinase; PDK, phosphoinositide-dependent protein kinase; PtdIns(3,4)P2, phosphatidylinositol (3,4)-bisphosphate; PtdIns(4,5)P2, phosphatidylinositol (4,5)-bisphosphate; PHAS-1, phosphorylated heat- and acid-stable protein 1; PP2A, protein phosphatase 2A; PTEN, phosphatase and tensin homologous on chromosome 10; SHIP2, SH2-domain-containing inositol phosphatase; Tsc1/2, tuberous sclerosis complex 1 and 2. Modified from Ref. [87]. Akt1 activity can be modulated either by directly controlling its phosphorylation state or by altering the levels of the lipid that it binds at the cell membrane, PtdIns(3,4,5)P3 [22] (Fig. 1). Akt1 activity depends on phosphorylation at two sites: Ser473 and Thr309 [29]."
"Upon stimulation with insulin, AKT is recruited to cellular membranes by binding of its amino terminal pleckstrin (PH) domain to membrane bound phosphatidylinositol 3,4,5, trisphosphate (PIP3) [3]. The membrane bound form of AKT then becomes phosphorylated on two regulatory residues, a threonine within the activation loop (Thr308 in AKT1,Thr309 in AKT2, Thr305 in AKT3) and a serine in the C-terminus of the enzyme (Ser473 in AKT1,Ser474 in AKT2, Ser472 in AKT3), and both phosphorylations are considered to be required for AKT to reach maximum kinase activity [1]. The kinase responsible for phosphorylation of Thr308/309/305 has been identified as phosphoinositide-dependent kinase 1 (PDK1) [3]."
"A consequence of Akt binding to phospholipids is the translocation of Akt from the cytoplasm to the inner surface of the plasma membrane, where PI3K-generated 3'-phosphorylated phospholipids reside Relocalization of Akt to the plasma membrane brings Akt in proximity to regulatory kinases that phosphorylate and activate Akt."
AKT1 is inactive.
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"Here, we describe a protein partner for pkbalpha termed ctmp, or carboxyl-terminal modulator protein, that binds specifically to the carboxyl-terminal regulatory domain of pkbalpha at the plasma membrane. Binding of ctmp reduces the activity of pkbalpha by inhibiting phosphorylation on serine 473 and threonine 308."
"Regulation of phosphorylation of Thr-308 of Akt, cell proliferation, and survival by the B55alpha regulatory subunit targeting of the protein phosphatase 2A holoenzyme to Akt.|Phosphorylation of Akt at regulatory residues Thr-308 and Ser-473 leads to its full activation. The protein phosphatase 2A (PP2A) has long been known to negatively regulate Akt activity. The PP2A holoenzyme consists of the structural |Here we report the identification of the specific B regulatory subunit that targets the PP2A holoenzyme to Akt. We found endogenous association of PP2A AB55C holoenzymes with Akt by co-immunoprecipitation analyses in pro-lymphoid FL5.12 cells.subunit (A), catalytic subunit (C), and a variable regulatory subunit (B)."
"We show that Akt and PDK1 are acetylated at lysine residues in their pleckstrin homology domains, which mediate PIP(3) binding. Acetylation blocked binding of Akt and PDK1 to PIP(3), thereby preventing membrane localization and phosphorylation of Akt. Deacetylation by SIRT1 enhanced binding of Akt and PDK1 to PIP(3) and promoted their activation."
AKT1 is kinase-inactive.
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