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PKB Activity (pkb + activity)
Selected AbstractsEffects of nominally selective inhibitors of the kinases PI3K, SGK1 and PKB on the insulin-dependent control of epithelial Na+ absorptionBRITISH JOURNAL OF PHARMACOLOGY, Issue 3 2010Morag K Mansley BACKGROUND AND PURPOSE Insulin-induced Na+ retention in the distal nephron may contribute to the development of oedema/hypertension in patients with type 2 diabetes. This response to insulin is usually attributed to phosphatidylinositol-3-kinase (PI3K)/serum and glucocorticoid-inducible kinase 1 (SGK1) but a role for protein kinase B (PKB) has been proposed. The present study therefore aimed to clarify the way in which insulin can evoke Na+ retention. EXPERIMENTAL APPROACH We examined the effects of nominally selective inhibitors of PI3K (wortmannin, PI103, GDC-0941), SGK1 (GSK650394A) and PKB (Akti-1/2) on Na+ transport in hormone-deprived and insulin-stimulated cortical collecting duct (mpkCCD) cells, while PI3K, SGK1 and PKB activities were assayed by monitoring the phosphorylation of endogenous proteins. KEY RESULTS Wortmannin substantially inhibited basal Na+ transport whereas PI103 and GDC-0941 had only very small effects. However, these PI3K inhibitors all abolished insulin-induced Na+ absorption and inactivated PI3K, SGK1 and PKB fully. GSK650394A and Akti-1/2 also inhibited insulin-evoked Na+ absorption and while GSK650394A inhibited SGK1 without affecting PKB, Akti-1/2 inactivated both kinases. CONCLUSION AND IMPLICATIONS While studies undertaken using PI103 and GDC-0941 show that hormone-deprived cells can absorb Na+ independently of PI3K, PI3K seems to be essential for insulin induced Na+ transport. Akti-1/2 does not act as a selective inhibitor of PKB and data obtained using this compound must therefore be treated with caution. GSK650394A, on the other hand, selectively inhibits SGK1 and the finding that GSK650394A suppressed insulin-induced Na+ absorption suggests that this response is dependent upon signalling via PI3K/SGK1. [source] Different cellular localization, translocation, and insulin-induced phosphorylation of PKB, in HepG2 cells and hepatocytesJOURNAL OF CELLULAR BIOCHEMISTRY, Issue 1 2002Noor Afshan Syed Abstract Protein kinase B (PKB), a serine/threonine protein kinase, prevents apoptosis and promotes cellular transformation. PKB activity is stimulated by insulin. In this report, we examined the relative amounts of expression, location, and translocation upon insulin stimulation of PKB, in normal primary hepatocytes and carcinoma cells, HepG2 cells. Non-phosphorylated PKB, was present in both types of unstimulated cells. The phosphorylated form of the enzyme was present in the nucleus of unstimulated HepG2 cells but not in normal hepatocytes. In the cytoplasm, PKB, was found in greater abundance in the hepatocytes as compared in HepG2 cells. Insulin induced the translocation of phosphorylated PKB, from the nucleus to the nuclear membrane in HepG2 cells. In contrast, insulin caused translocation and phosphorylation of PKB, from the cytosol to the plasma membrane in normal hepatocytes. In addition, there is a higher expression of PKB, in the HepG2 cells as compared to normal primary hepatocytes. These findings provide an important distinction between hepatocellular HepG2 cells and normal liver cells and suggest that the presence of constitutively active nuclear PKB in the transformed cells might be an important contributor in cell transformation and immortality of hepatoma cells. J. Cell. Biochem. 86: 118,127, 2002. © 2002 Wiley-Liss, Inc. [source] Apolipoprotein E and ,-amyloid (1,42) regulation of glycogen synthase kinase-3,JOURNAL OF NEUROCHEMISTRY, Issue 5 2003A. Cedazo-Mínguez Abstract Glycogen synthase kinase-3, (GSK-3,) is implicated in regulating apoptosis and tau protein hyperphosphorylation in Alzheimer's disease (AD). We investigated the effects of two key AD molecules, namely apoE (E3 and E4 isoforms) and ,-amyloid (A,) 1,42 on GSK-3, and its major upstream regulators, intracellular calcium and protein kinases C and B (PKC and PKB) in human SH-SY5Y neuroblastoma cells. ApoE3 induced a mild, transient, Ca2+ -independent and early activation of GSK-3,. ApoE4 effects were biphasic, with an early strong GSK-3, activation that was partially dependent on extracellular Ca2+, followed by a GSK-3, inactivation. ApoE4 also activated PKC-, and PKB possibly giving the subsequent GSK-3, inhibition. A,(1,42) effects were also biphasic with a strong activation dependent partially on extracellular Ca2+ followed by an inactivation. A,(1,42) induced an early and potent activation of PKC-, and a late decrease of PKB activity. ApoE4 and A,(1,42) were more toxic than apoE3 as shown by MTT reduction assays and generation of activated caspase-3. ApoE4 and A,(1,42)-induced early activation of GSK-3, could lead to apoptosis and tau hyperphosphorylation. A late inhibition of GSK-3, through activation of upstream kinases likely compensates the effects of apoE4 and A,(1,42) on GSK-3,, the unbalanced regulation of which may contribute to AD pathology. [source] The role of phosphoinositide 3-kinase and phosphatidic acid in the regulation of mammalian target of rapamycin following eccentric contractionsTHE JOURNAL OF PHYSIOLOGY, Issue 14 2009T. K. O'Neil Resistance exercise induces a hypertrophic response in skeletal muscle and recent studies have begun to shed light on the molecular mechanisms involved in this process. For example, several studies indicate that signalling by the mammalian target of rapamycin (mTOR) is necessary for a hypertrophic response. Furthermore, resistance exercise has been proposed to activate mTOR signalling through an upstream pathway involving the phosphoinositide 3-kinase (PI3K) and protein kinase B (PKB); however, this hypothesis has not been thoroughly tested. To test this hypothesis, we first evaluated the temporal pattern of signalling through PI3K,PKB and mTOR following a bout of resistance exercise with eccentric contractions (EC). Our results indicated that the activation of signalling through PI3K,PKB is a transient event (<15 min), while the activation of mTOR is sustained for a long duration (>12 h). Furthermore, inhibition of PI3K,PKB activity did not prevent the activation of mTOR signalling by ECs, indicating that PI3K,PKB is not part of the upstream regulatory pathway. These observations led us to investigate an alternative pathway for the activation of mTOR signalling involving the synthesis of phosphatidic acid (PA) by phospholipase D (PLD). Our results demonstrate that ECs induce a sustained elevation in [PA] and inhibiting the synthesis of PA by PLD prevented the activation of mTOR. Furthermore, we determined that similar to ECs, PA activates mTOR signalling through a PI3K,PKB-independent mechanism. Combined, the results of this study indicate that the activation of mTOR following eccentric contractions occurs through a PI3K,PKB-independent mechanism that requires PLD and PA. [source] | ||||||||||