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PI3 Kinase (pi3 + kinase)
Selected Abstracts,-MSH and cAMP signalling in normal human melanocytesEXPERIMENTAL DERMATOLOGY, Issue 9 2004R. Buscŕ Melanocytes are neural crest-derived skin cells specialized in the synthesis of melanin pigments responsible, in human, for skin and hair colour. The pro-opiomelanocortin peptide, ,-MSH is a strong melanogenic agent secreted by keratinocytes following UV radiation. ,-MSH through the binding to the MC1R and activation of the cyclic AMP pathway plays a pivotal role in melanocyte differentiation and in the regulation of skin pigmentation. During the last few years, we have elucidated the molecular events linking the cAMP pathway to melanogenesis upregulation. This cascade involves the activation of protein kinase A and CREB transcription factor, leading to the upregulation of the expression of microphthalmia-associated transcription factor (MITF). MITF binds and activates the melanogenic gene promoters thereby increasing their expression, which results in an increased melanin synthesis. Beyond this simplified scheme, other intracellular signalling pathways are regulated by cAMP and participate to the regulation of melanocyte differentiation. Indeed, cAMP inhibits the phosphatidyl inositol 3-kinase pathway, leading to the inhibition of AKT and to the activation of GSK3,. This kinase phosphorylates MITF and allows its binding to the target sequence. Such pathways are involved in the upregulation of melanogenesis. ,-MSH and cAMP signalling also regulate melanocyte dendricity, and melanosome transport through the inhibition of the Rho GTPase cascade that function downstream the PI3 kinase. It should be also mentioned that cAMP activates the ERK pathway through a melanocyte-specific pathway involving Ras and B-Raf. The activation of ERK and RSK1 leads to the phosphorylation of MITF and target MITF to the proteasome degradation pathway. Interestingly, several proteins involved in melanocyte differentiation by ,-MSH (MC1R, PI3K, B-Raf and MITF) have also been implicated in the development of melanoma, suggesting that the cAMP pathway could influence melanocyte transformation. [source] TLR3-mediated signal induces proinflammatory cytokine and chemokine gene expression in astrocytes: Differential signaling mechanisms of TLR3-induced IP-10 and IL-8 gene expressionGLIA, Issue 3 2006Chanhee Park Abstract Viral infection is one of the leading causes of brain encephalitis and meningitis. Recently, it was reported that Toll-like receptor-3 (TLR3) induces a double-stranded RNA (dsRNA)-mediated inflammatory signal in the cells of the innate immune system, and studies suggested that dsRNA may induce inflammation in the central nervous system (CNS) by activating the CNS-resident glial cells. To explore further the connection between dsRNA and inflammation in the CNS, we have studied the effects of dsRNA stimulation in astrocytes. Our results show that the injection of polyinosinic-polycytidylic acid (poly(I:C)), a synthetic dsRNA, into the striatum of the mouse brain induces the activation of astrocytes and the expression of TNF-,, IFN-,, and IP-10. Stimulation with poly(I:C) also induces the expression of these proinflammatory genes in primary astrocytes and in CRT-MG, a human astrocyte cell line. Furthermore, our studies on the intracellular signaling pathways reveal that poly(I:C) stimulation activates I,B kinase (IKK), extracellular signal-regulated kinase (ERK), and c-Jun N-terminal kinase (JNK) in CRT-MG. Pharmacological inhibitors of nuclear factor-,B (NF-,B), JNK, ERK, glycogen synthase kinase-3, (GSK-3,), and dsRNA-activated protein kinase (PKR) inhibit the expression of IL-8 and IP-10 in astrocytes, indicating that the activation of these signaling molecules is required for the TLR3-mediated chemokine gene induction. Interestingly, the inhibition of PI3 kinase suppressed the expression of IP-10, but upregulated the expression of IL-8, suggesting differential roles for PI3 kinase, depending on the target genes. These data suggest that the TLR3 expressed on astrocytes may initiate an inflammatory response upon viral infection in the CNS. © 2005 Wiley-Liss, Inc. [source] Long-term modulation of glucose utilization by IL-1, and TNF-, in astrocytes: Na+ pump activity as a potential target via distinct signaling mechanismsGLIA, Issue 1 2002Céline Véga Abstract Interleukin-1, (IL-1,) and tumor necrosis factor-, (TNF-,) markedly stimulate glucose utilization in primary cultures of mouse cortical astrocytes. The mechanism that gives rise to this effect, which takes place several hours after application of cytokine, has remained unclear. Experiments were conducted to identify the major signaling cascades involved in the metabolic action of cytokine. First, the selective IL-1 receptor antagonist (IL-1ra) prevents the effect of IL-1, on glucose utilization in a concentration-dependent manner, whereas it has no effect on the action of TNF-,. Then, using inhibitors of three classical signaling cascades known to be activated by cytokines, it appears that the PI3 kinase is essential for the effect of both IL-1, and TNF-,, whereas the action of IL-1, also requires activation of the MAP kinase pathway. Participation of a phospholipase C-dependent pathway does not appear critical for both IL-1, and TNF-,. Inhibition of NO synthase by L-NAME did not prevent the metabolic response to both IL-1, and TNF-,, indicating that nitric oxide is probably not involved. In contrast, the Na+/K+ ATPase inhibitor ouabain prevents the IL-1,- and TNF-,-stimulated 2-deoxyglucose (2DG) uptake. When treatment of astrocytes with a cytokine was followed 24 h later by an acute application of glutamate, a synergistic enhancement in glucose utilization was observed. This effect was greatly reduced by ouabain. These data suggest that Na+ pump activity is a common target for both the long-term metabolic action of cytokines promoted by the activation of distinct signaling pathways and the enhanced metabolic response to glutamate. GLIA 39:10,18, 2002. © 2002 Wiley-Liss, Inc. [source] Phosphoinositide 3-kinase is not overexpressed in melanocytic lesionsJOURNAL OF CUTANEOUS PATHOLOGY, Issue 3 2007Rajendra S. Singh Background:, Although various studies have stressed the role of phosphatase and tensin homologue deleted on chromosome 10 (PTEN)-PI3K-AKT pathway in the progression of melanocytic lesions, little is known about the expression pattern of PI3K in these lesions. Objective:, To investigate the expression pattern of PI3K in benign and dysplastic nevi, primary melanomas, and metastatic melanomas and the role of PTEN and PI3K in melanocytic tumor progression. Methods:, Tissue microarrays were constructed using formalin-fixed, paraffin-embedded archival tissue blocks from 89 melanocytic lesions: 17 benign nevi, 18 dysplastic nevi, 23 primary melanomas, and 31 metastatic melanomas. Expression of PTEN and PI3K (p85 and p110 subunits) was evaluated immunohistochemically, and the number of cells and labeling intensity were assessed semiquantitatively. Results:, Both benign and dysplastic nevi showed strong cytoplasmic staining with PTEN, which was subsequently less in melanomas and completely lost in the metastatic lesions. Eleven of 17 (64%) benign nevi, seven of 10 (70%) dysplastic nevi, four of 23 (17%) primaries, and one of 31 (3%) visceral or lymph node metastasis showed strong positivity. Loss of PTEN expression from benign and dysplastic nevi to melanoma was statistically significant (p = 0.001). Although few cells showed reactivity for phosphoinositide 3-kinase (PI3 kinase)-p85 subunit, strong positivity was not detected in the cytoplasm of benign, malignant, or metastatic lesions, except for a single visceral metastasis. Three of 13 (23%) nevi showed positivity for the p110 subunit. No positivity was observed in the dysplastic nevi. Two of 22 (9%) melanomas, one of 14 (7%) visceral metastasis, and three of 12 (25%) lymph node metastasis showed strong positivity. There was no statistical difference in PI3 kinase expression in benign and malignant melanocytic lesions (p = 0.2). Conclusion:, PI3K is not overexpressed in melanocytic lesions. [source] Vitamin E protected cultured cortical neurons from oxidative stress-induced cell death through the activation of mitogen-activated protein kinase and phosphatidylinositol 3-kinaseJOURNAL OF NEUROCHEMISTRY, Issue 4 2006Yumiko Numakawa Abstract The role of vitamin E in the CNS has not been fully elucidated. In the present study, we found that pre-treatment with vitamin E analogs including ,T (,-tocopherol), ,T3 (, -tocotrienol), ,T, and ,T3 for 24 h prevented the cultured cortical neurons from cell death in oxidative stress stimulated by H2O2, while Trolox, a cell-permeable analog of ,T, did not. The preventive effect of ,T was dependent on de novo protein synthesis. Furthermore, we found that ,T exposure induced the activation of both the MAP kinase (MAPK) and PI3 kinase (PI3K) pathways and that the ,T-dependent survival effect was blocked by the inhibitors, U0126 (an MAPK pathway inhibitor) or LY294002 (a PI3K pathway inhibitor). Interestingly, the up-regulation of Bcl-2 (survival promoting molecule) was induced by ,T application. The up-regulation of Bcl-2 did not occur in the presence of U0126 or LY294002, suggesting that ,T-up-regulated Bcl-2 is mediated by these kinase pathways. These observations suggest that vitamin E analogs play an essential role in neuronal maintenance and survival in the CNS. [source] Neoplastic hepatocyte growth associated with cyclin D1 redistribution from the cytoplasm to the nucleus in mouse hepatocarcinogenesisMOLECULAR CARCINOGENESIS, Issue 12 2006Masahiro Yamamoto Abstract Cyclin D1 overexpression is a frequent change in hepatocellular carcinomas (HCCs). Our present study demonstrated that cyclin D1 overexpression with abundant cyclin E, cdk4, cdk2, and p27Kip1 (p27) occurred in neoplastic hepatocytes from the early stage of mouse hepatocarcinogenesis. While cyclin D1 expression was mainly found in the cytoplasm of the tumor cells, it shifted to the nucleus in association with cell proliferation after the animals were subjected to a partial hepatectomy (PH), and then returned once more to the cytoplasm when the cells became quiescent. Inhibition of PI3 kinase (PI3K) by Ly294002 in mouse HCC cells in vitro suppressed the nuclear shift of cyclin D1 as well as cell proliferation, while PI3K activation by PTEN suppression failed to induce nuclear shift of cyclin D1, suggesting that PI3K activation is essential but not sufficient for the cyclin D1 nuclear shift. While MEK-ERK1/2 inhibition by PD98059 and mTOR inhibition by rapamycin affected the cyclin D1 nuclear shift and cell proliferation to a lesser extent, both these inhibitors reduced cyclin D1 levels. Finally, although p27, cdk4 and calmodulin (CaM) were detected in the cyclin D1 immunoprecipitates from both quiescent and proliferating HCC cells, Hsc70 and SSeCKS were detected only in the immunoprecipitate from quiescent cells, and p21Waf1/Cip1 (p21) was detected only in that from proliferating cells, suggesting that the cyclin D1 complex is different in quiescent and proliferating cells. These observations indicate that the nuclear/cytoplasmic localization of cyclin D1 plays an important role in the proliferation/quiescence of neoplastic hepatocytes. © 2006 Wiley-Liss, Inc. [source] Structures of the wild-type and activated catalytic domains of Brachydanio rerio Polo-like kinase 1 (Plk1): changes in the active-site conformation and interactions with ligandsACTA CRYSTALLOGRAPHICA SECTION D, Issue 9 2008Robert A. Elling Polo-like kinase 1 (Plk1) is a member of a family of serine/threonine kinases involved in the regulation of cell-cycle progression and cytokinesis and is an attractive target for the development of anticancer therapeutics. A zebrafish homolog of the human Plk1 (hPlk1) kinase domain (KD) was identified that can be expressed in large quantities in bacteria and crystallizes readily, whether in a wild-type form or as a variant containing the activating Thr196,Asp substitution, in one space group and under similar conditions both in the absence and presence of active-site compounds. This construct was validated by testing a panel of hPlk1 inhibitors against human and zebrafish proteins and it was shown that the selected small molecules inhibited the homologs with a high degree of correlation. Crystal structures of ligand-free wild-type and activated zebrafish Plk1 (zPlk1) KDs revealed the organization of the secondary structural elements around the active site and demonstrated that the activation segment was disordered in the activated form of the domain but possessed a well defined secondary structure in the wild-type enzyme. The cocrystal structure of wild-type zPlk1 KD with ADP documented the hydrolysis of ATP and revealed the phosphorylation site. The cocrystal structure of the activated KD with wortmannin, a covalent inhibitor of Plk1 and PI3 kinases, showed the binding mode of the small molecule to the enzyme and may facilitate the design of more potent Plk1 inhibitors. The work presented in this study establishes the zPlk1 KD as a useful tool for rapid low- and high-throughput structure-based screening and drug discovery of compounds specific for this mitotic target. [source] |