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

To better understand the roles of TGF-beta in bone metabolism, we investigated osteoclast survival in response TGF-beta and found that TGF-beta inhibited apoptosis. We examined the receptors involved in promotion of osteoclast survival and found that the canonical TGF-beta receptor complex is involved in the survival response. The upstream MEK kinase TAK1 was rapidly activated following TGF-beta treatment. Since osteoclast survival involves MEK, AKT, and NFkappaB activation, we examined TGF-beta effects on activation of these pathways and observed rapid phosphorylation of MEK, AKT, IKK, IkappaB, and NFkappaB. The timing of activation coincided with SMAD activation and dominant negative SMAD expression did not inhibit NFkappaB activation, indicating that kinase pathway activation is independent of SMAD signaling. Inhibition of TAK1, MEK, AKT, NIK, IKK, or NFkappaB repressed TGF-beta-mediated osteoclast survival. Adenoviral-mediated TAK1 or MEK inhibition eliminated TGF-beta-mediated kinase pathway activation and constitutively active AKT expression overcame apoptosis induction following MEK inhibition. TAK1/MEK activation induces pro-survival BclX(L) expression and TAK1/MEK and SMAD pathway activation induces pro-survival Mcl-1 expression. These data show that TGF-beta-induced NFkappaB activation is through TAK1/MEK-mediated AKT activation, which is essential for TGF-beta to support of osteoclast survival.
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PMID:TGF-beta coordinately activates TAK1/MEK/AKT/NFkB and SMAD pathways to promote osteoclast survival. 1858 26

Apoptosis of human neutrophils is a crucial mechanism for the resolution of inflammation. We previously showed that insulin-like growth factor-1 (IGF1) delays spontaneous neutrophil apoptosis without influencing the secretion of cytokines by these cells. In the present study, we further addressed the role of IGF1 in regulating neutrophil survival in the presence of other factors present during inflammation, and the mechanism involved in delaying apoptosis. We show that IGF1 delays neutrophil apoptosis triggered by the agonistic anti-Fas antibody CH11 and that the effect of IGF1 is comparable in magnitude to that of the acknowledged anti-apoptotic cytokines interferon-gamma (IFNG) and granulocyte-macrophage colony-stimulating factor (GM-CSF; now known as CSF2). Furthermore, IGF1 exerted additional effects on cell survival in the presence of these cytokines. IGF1 did not affect Fas expression or activation by anti-Fas of caspase-8, but inhibited the depolarization of the mitochondrial membrane. Inhibitor studies indicate that the phosphatidylinositol-3 kinase (PI3K) pathway, but not the MEK-ERK pathway, mediates the effects of IGF1. However, in contrast to CSF2, IGF1 did not induce phosphorylation and translocation to the membrane of AKT, the canonical downstream target of PI3K. We therefore speculate that other downstream targets of PI3K are involved in the delay of neutrophil apoptosis by IGF1, possibly through stabilization of the mitochondrial membrane.
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PMID:Insulin-like growth factor-1 delays Fas-mediated apoptosis in human neutrophils through the phosphatidylinositol-3 kinase pathway. 1865 23

In acute myeloid leukemia (AML), aberrant signal transduction enhances the survival and proliferation of hematopoietic progenitor cells. Activation of signal transduction in AML may occur through a variety of genetic alterations affecting different signaling molecules, such as the FLT3 and KIT receptor tyrosine kinases (RTKs) and members of the RAS family of guanine nucleotide-binding proteins. These mutant signaling proteins are attractive therapeutic targets; however, developing targeted therapies for each genotypic variant and determining the relationships between different genotypes and critical functional dependencies of the leukemic cells remain major challenges. As the large number of mutant signaling proteins that have been identified in AML are likely to reflect activation of a more limited number of downstream effector pathways, such as the RAF/MEK/ERK and PI3K/AKT cascades, targeting these unifying pathways may represent a more broadly applicable therapeutic strategy. Furthermore, integrative genomic studies combining DNA sequencing, DNA copy number analysis, transcriptional profiling, and functional genetic approaches hold great promise for identifying additional signaling abnormalities in AML that are relevant to leukemogenesis and can be exploited therapeutically. Eventually, it may become possible to use pathogenesis-oriented combinations of signal transduction inhibitors to improve the cure rate in AML patients.
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PMID:Deregulation of signaling pathways in acute myeloid leukemia. 1869 84

The AKT/mammalian target of rapamycin (AKT/mTOR) and ERK MAPK signaling pathways have been shown to cooperate in prostate cancer progression and the transition to androgen-independent disease. We have now tested the effects of combinatorial inhibition of these pathways on prostate tumorigenicity by performing preclinical studies using a genetically engineered mouse model of prostate cancer. We report here that combination therapy using rapamycin, an inhibitor of mTOR, and PD0325901, an inhibitor of MAPK kinase 1 (MEK; the kinase directly upstream of ERK), inhibited cell growth in cultured prostate cancer cell lines and tumor growth particularly for androgen-independent prostate tumors in the mouse model. We further showed that such inhibition leads to inhibition of proliferation and upregulated expression of the apoptotic regulator Bcl-2-interacting mediator of cell death (Bim). Furthermore, analyses of human prostate cancer tissue microarrays demonstrated that AKT/mTOR and ERK MAPK signaling pathways are often coordinately deregulated during prostate cancer progression in humans. We therefore propose that combination therapy targeting AKT/mTOR and ERK MAPK signaling pathways may be an effective treatment for patients with advanced prostate cancer, in particular those with hormone-refractory disease.
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PMID:Targeting AKT/mTOR and ERK MAPK signaling inhibits hormone-refractory prostate cancer in a preclinical mouse model. 1872 93

Mammalian target of rapamycin (mTOR) is a component of a signaling pathway (PTEN/PI3K/AKT) that is frequently dysregulated in cancer. However, its precise relationship to the MAPK cascade (Ras/Raf/MEK/ERK), another pathway often implicated in tumorigenesis, has not been well defined. Recent evidence from tissue specimens obtained from patients who have received mTOR inhibitors suggests that ERK may be activated in response to mTOR interruption. In this issue of the JCI, Waugh Kinkade et al. and Carracedo et al. examine the relationship between these pathways in prostate and breast cancer cell model systems (see the related articles beginning on pages 3051 and 3065, respectively). Their findings suggest a link between inhibition of mTOR and ERK activation, possibly reflecting interruption of a novel negative S6K1-dependent feedback loop. Significantly, both groups observed that simultaneous inhibition of MEK/ERK and mTOR resulted in substantially enhanced antitumor effects both in vitro and in vivo. Together, these findings suggest that concurrent interruption of complementary signaling pathways warrants further investigation in cancer therapy.
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PMID:Cotargeting survival signaling pathways in cancer. 1872 89

Chlamydia are obligate intracellular bacteria that cause variety of human diseases. Host cells infected with Chlamydia are protected against many different apoptotic stimuli. The induction of apoptosis resistance is thought to be an important immune escape mechanism allowing Chlamydia to replicate inside the host cell. Infection with C. trachomatis activates the Raf/MEK/ERK pathway and the PI3K/AKT pathway. Here we show that inhibition of these two pathways by chemical inhibitors sensitized C. trachomatis infected cells to granzyme B-mediated cell death. Infection leads to the Raf/MEK/ERK-mediated up-regulation and PI3K-dependent stabilization of the anti-apoptotic Bcl-2 family member Mcl-1. Consistently, interfering with Mcl-1 up-regulation sensitized infected cells for apoptosis induced via the TNF receptor, DNA damage, granzyme B and stress. Our data suggest that Mcl-1 up-regulation is primarily required to maintain apoptosis resistance in C. trachomatis-infected cells.
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PMID:Mcl-1 is a key regulator of apoptosis resistance in Chlamydia trachomatis-infected cells. 1876 17

TIMP-1 (Tissue inhibitor of matrix metalloproteinase-1) is typically associated with inhibition of matrix metalloproteinases (MMP) induced invasion. However, TIMP-1 is overexpressed in many malignancies and is associated with poor prognosis in breast cancer. The mechanisms by which TIMP-1 promotes tumorigenesis are unclear. Reduced levels of TIMP-1 mediated by shRNA in MDA-MB-231 breast cancer cells had no effect on cellular physiology in vitro or tumor growth in SCID mice compared to vector control MDA-MB-231 cells. However, overexpression of TIMP-1 in MDA-MB-231 cells resulted in inhibition of cell invasion and enhanced phosphorylation of p38 MAPK and AKT in vitro. Additionally, treatment of parental MDA-MB-231 cells with purified TIMP-1 protein led to activation of p38 MAPK and MKK 3/6. cDNA array analysis demonstrated that high expression of TIMP-1 in MDA-MB-231 cells resulted in alterations in expression of approximately 200 genes, 1.5 fold or greater compared to vector control cells (P < 0.1). Real-time RT-PCR confirmed changes in expression of several genes associated with cancer progression including DAPK1, FGFR4 and MAPK13. In vivo, high TIMP-1 expression induced tumor growth in SCID mice compared to vector control cells and increased tumor vessel density. Affymetrix array analysis of vector control and TIMP-1 MDA-MB-231 xenograft tumors revealed that TIMP-1 altered expression of approximately 600 genes in vivo, including MMP1, MMP13, S100A14, S100P, Rab25 and ID4. These combined observations suggest that the effects of TIMP-1 differ significantly in a 2-D environment compared to the 3-D environment and that TIMP-1 stimulates tumor growth.
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PMID:TIMP-1 overexpression promotes tumorigenesis of MDA-MB-231 breast cancer cells and alters expression of a subset of cancer promoting genes in vivo distinct from those observed in vitro. 1878 47

Elevation of CD74 is associated with a number of human cancers, including clear cell renal cell carcinoma (ccRCC). To understand the role of CD74 in the oncogenic process of ccRCC, we ectopically expressed CD74 in human embryonic kidney 293 cells (HEK/CD74) and evaluated its oncogenic potential. Through overexpression of CD74 in HEK293 and Caki-2 cells and down-regulation of CD74 in Caki-1 cells, we show that vascular endothelial growth factor-D (VEGF-D) expression is modified accordingly. A significant, positive correlation between CD74 and VEGF-D is found in human ccRCC tissues (Pearson's correlation, r = 0.65, p < 0.001). In HEK/CD74 xenograft mice, CD74 significantly induced the formation of tumor masses, increased tumor-induced angiogenesis, and promoted cancer cell metastasis. Blockage of VEGF-D expression by small interference RNA resulted in a decrease in cell proliferation, invasion, and cancer cell-induced HUVEC migration enhanced by CD74. Furthermore, we provide evidence that the intracellular signaling cascade responsible for VEGF-D up-regulation by CD74 is both PI3K/AKT- and MEK/ERK-dependent, both of which are associated with NF-kappaB nuclear translocation and DNA-binding activity. These results suggest that VEGF-D is crucial for CD74-induced human renal carcinoma cancer cell tumorigenesis.
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PMID:Up-regulation of vascular endothelial growth factor-D expression in clear cell renal cell carcinoma by CD74: a critical role in cancer cell tumorigenesis. 1894 Dec 49

Death-associated protein kinase (DAPK) is a multidomain enzyme that plays a central role in autophagic and apoptotic signaling, although the protein-protein interactions regulating DAPK functions are not well defined. Peptide aptamer libraries were used to identify the tumor suppressor protein tuberin (TSC2) as a novel DAPK death domain-binding protein, and we evaluated whether DAPK is a positive or negative effector of the TSC2-regulated mammalian target of rapamycin (mTORC1) signaling pathway. Binding studies using death domain miniproteins in vitro and deletion analysis in vivo determined that the death domain of DAPK is the major site for the interaction with TSC2. Recombinant DAPK phosphorylates TSC2 in vitro, and DAPK kinase activity is stimulated by growth factor signaling. Transfection of DAPK promotes phosphorylation of TSC2 in vivo, whereas short interfering RNA-mediated attenuation of DAPK reduces growth factor-stimulated phosphorylation of TSC2. DAPK-dependent phosphorylation leads to TSC1-TSC2 complex dissociation, and consequently manipulation of DAPK by transfection or short interfering RNA demonstrated that DAPK is a positive regulator of mTORC1 in response to growth factor activation. Epistatic studies suggest that DAPK functions downstream from the RAS-MEK-ERK and phosphatidylinositol 3-kinase-AKT growth factor signaling pathways. DAPK(+/-) mouse embryo fibroblasts have attenuated mTORC1 signaling compared with DAPK+/+ counterparts, and overexpression of DAPK in DAPK(+/-) MEFs stimulates mTORC1 activity. These data uncover a novel interaction between DAPK and TSC2 proteins that has revealed a positive link between growth factor stimulation of DAPK and mTORC1 signaling that may ultimately affect autophagy, cell survival, or apoptosis.
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PMID:Peptide combinatorial libraries identify TSC2 as a death-associated protein kinase (DAPK) death domain-binding protein and reveal a stimulatory role for DAPK in mTORC1 signaling. 1897 95

Tumor cells with genomic amplification of MET display constitutive activation of the MET tyrosine kinase, which renders them highly sensitive to MET inhibition. Several MET inhibitors have recently entered clinical trials; however, as with other molecularly targeted agents, resistance is likely to develop. Therefore, elucidating possible mechanisms of resistance is of clinical interest. We hypothesized that collateral growth factor receptor pathway activation can overcome the effects of MET inhibition in MET-amplified cancer cells by reactivating key survival pathways. Treatment of MET-amplified GTL-16 and MKN-45 gastric cancer cells with the highly selective MET inhibitor PHA-665752 abrogated MEK/mitogen-activated protein kinase (MAPK) and phosphoinositide 3-kinase (PI3K)/AKT signaling, resulting in cyclin D1 loss and G(1) arrest. PHA-665752 also inhibited baseline phosphorylation of epidermal growth factor receptor (EGFR) and HER-3, which are transactivated via MET-driven receptor cross-talk in these cells. However, MET-independent HER kinase activation using EGF (which binds to and activates EGFR) or heregulin-beta1 (which binds to and activates HER-3) was able to overcome the growth-inhibitory effects of MET inhibition by restimulating MEK/MAPK and/or PI3K/AKT signaling, suggesting a possible escape mechanism. Importantly, dual inhibition of MET and HER kinase signaling using PHA-665752 in combination with the EGFR inhibitor gefitinib or in combination with inhibitors of MEK and AKT prevented the above rescue effects. Our results illustrate that highly targeted MET tyrosine kinase inhibition leaves MET oncogene-"addicted" cancer cells vulnerable to HER kinase-mediated reactivation of the MEK/MAPK and PI3K/AKT pathways, providing a rationale for combined inhibition of MET and HER kinase signaling in MET-amplified tumors that coexpress EGFR and/or HER-3.
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PMID:HER kinase activation confers resistance to MET tyrosine kinase inhibition in MET oncogene-addicted gastric cancer cells. 1897 95


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