Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P31749 (AKT)
 22,954 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Cancer cells in which the PTEN lipid phosphatase gene is deleted have constitutively activated phosphatidylinositol 3-kinase (PI3K)-dependent signaling and require activation of this pathway for survival. In non-small cell lung cancer (NSCLC) cells, PI3K-dependent signaling is typically activated through mechanisms other than PTEN gene loss. The role of PI3K in the survival of cancer cells that express wild-type PTEN has not been defined. Here we provide evidence that H1299 NSCLC cells, which express wild-type PTEN, underwent proliferative arrest following treatment with an inhibitor of all isoforms of class I PI3K catalytic activity (LY294002) or overexpression of the PTEN lipid phosphatase. In contrast, overexpression of a dominant-negative mutant of the p85alpha regulatory subunit of PI3K (Deltap85) induced apoptosis. Whereas PTEN and Delta85 both inhibited activation of AKT/protein kinase B, only Deltap85 inhibited c-Jun NH2-terminal kinase (JNK) activity. Cotransfection of the constitutively active mutant Rac-1 (Val12), an upstream activator of JNK, abrogated Deltap85-induced lung cancer cell death, whereas constitutively active mutant mitogen-activated protein kinase kinase (MKK)-1 (R4F) did not. Furthermore, LY294002 induced apoptosis of MKK4-null but not wild-type mouse embryo fibroblasts. Therefore, we propose that, in the setting of wild-type PTEN, PI3K- and MKK4/JNK-dependent pathways cooperate to maintain cell survival.
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PMID:Evidence that phosphatidylinositol 3-kinase- and mitogen-activated protein kinase kinase-4/c-Jun NH2-terminal kinase-dependent Pathways cooperate to maintain lung cancer cell survival. 1271 85

We previously demonstrated that erbB-2-overexpressing human mammary epithelial (HME) cells exhibit several transformed phenotypes including growth factor independence, anchorage-independent growth, motility, and invasiveness. Because phosphatidylinositol 3'-kinase (PI3K) is a major target of erbB-2 activation, we tested the contribution that PI3K and its downstream signaling pathways make to these phenotypes. Utilizing a constitutively active form of PI3K, p110CAAX, we show that PI3K can mediate most phenotypes observed in erbB-2-overexpressing cells. To identify pathways leading from PI3K to specific phenotypes, we expressed constitutively active AKT or PTEN in erbB-2-overexpressing cells or in HME cells. HME cells expressing constitutively active AKT were growth factor independent, anchorage independent and motile, but not invasive. PTEN expression blocked erbB-2-mediated invasion but none of the other phenotypes. Rottlerin blocked invasion induced by p110CAAX and erbB-2, suggesting that protein kinase C delta (PKC-delta) is the downstream effector of PI3K responsible for the invasive capacity of the cells. Consistent with these observations, phospho-AKT remained detectable in erbB-2 cells treated with LY294002 or expressing exogenous PTEN, but was abolished by treatment with the p38MAP kinase inhibitor SB202190. Thus, both PI3K-dependent and p38MAP kinase-dependent pathways lead to activation of AKT, and activation of PKC-delta, via PI3K, mediates invasion.
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PMID:The role of phosphatidylinositol 3'-kinase and its downstream signals in erbB-2-mediated transformation. 1275 2

We reported previously in HepG2 cells that estradiol induces cell cycle progression throughout the G1-S transition by the parallel stimulation of both PKC-alpha and ERK signaling molecules. The analysis of the cyclin D1 gene expression showed that only the MAP kinase pathway was involved. Here, the presence of rapid/nongenomic, estradiol-regulated, PI3K/AKT signal transduction pathway, its modulation by the levels of the tumor suppressor PTEN, its cross-talk with the ERK pathway, and its involvement in DNA synthesis and cyclin D1 gene promoter activity have all been studied in HepG2 cells. 17beta-Estradiol induced the rapid and biphasic phosphorylation of AKT. These phosphorylations were independent of each other, being the first wave of activation independent of the estrogen receptor (ER), whereas the second was dependent on ER. Both activations were dependent on PI3K activity; furthermore, the ERK pathway modulated AKT phosphorylation by acting on the PTEN levels. The results showed that the PI3K pathway, as well as ER, were strongly involved in both G1-S progression and cyclin D1 promoter activity by acting on its proximal region (-254 base pairs). These data indicate that in HepG2 cells, different rapid/nongenomic estradiol-induced signal transduction pathways modulate the multiple steps of G1-S phase transition.
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PMID:Biphasic estradiol-induced AKT phosphorylation is modulated by PTEN via MAP kinase in HepG2 cells. 1280 53

Tissue microarray technology facilitates rapid assessment of expression of molecular markers by enabling the simultaneous analysis of hundreds of tissue specimens. We have applied this technology to establish a microarray composed of cell pellets derived from 40 human lymphoma/leukemia-derived cell lines harboring a variety of molecular abnormalities. The application of cell line microarrays to the assessment of biologic marker evaluation was validated by studying the immunohistochemical expression of PTEN and phosphorylated AKT, two mediators of the phosphatidylinositol (PI)-3-kinase pathway. In addition to the high throughout analysis of protein expression in lymphoma/leukemia cells, this methodology also enables the evaluation of subcellular localization of protein expression. Cytoplasmic PTEN expression was observed in the majority of cell lines (87%), whereas a minor subset demonstrated nuclear expression. Phosphorylated AKT was also expressed predominantly within the cytoplasm in 65% of cell lines, whereas nuclear expression was seen in a minority. An inverse relationship between PTEN and phosphorylated AKT was observed in 63% of cell lines. No cell lines showed absence of PTEN expression, whereas 50% of cell lines showed low PTEN expression. Our data support the integrity of the PI-3-kinase-PTEN-AKT pathway in a majority of cell lines derived from hematologic malignancies and clearly demonstrates the utility of microarray technology in the in situ assessment of expression of molecular markers in tumor-derived cell lines.
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PMID:Analysis of the PI-3-Kinase-PTEN-AKT pathway in human lymphoma and leukemia using a cell line microarray. 1280 67

The serine/threonine kinase AKT, also known as PKB or RAC-PK, is a key molecule for protecting cells from undergoing apoptosis. Several studies have suggested that the AKT-mediated survival-signaling pathway is an attractive target for cancer chemotherapy: (1) the AKT pathway is relatively inactive in resting cells; (2) amplification of the AKT gene occurs in some tumors; (3) loss of the tumor suppressor gene PTEN (phosphatase and tensin homolog deleted on chromosome 10) is common in tumors and its loss constitutively activates AKT; (4) AKT is activated at the cancer invasion front. To clarify which drugs exhibit their cytotoxicity by inhibiting the AKT pathway, we screened anticancer drugs that could downregulate phospho-AKT levels and AKT kinase activity. We found that UCN-01 (7-hydroxystaurosporine), heat-shock protein 90 (HSP90) inhibitors, and topotecan (10-hydroxy-9-dimethylaminomethyl-(S)-camptothecin) possessed the ability to interfere with the AKT pathway. UCN-01 directly suppressed upstream AKT kinase 3-phosphoinositide-dependent protein kinase-1 (PDK1) (IC(50) <33 nM) both in vitro and in tumor xenografts. HSP90 inhibitors and topotecan suppressed AKT activity via indirectly downregulating PDK1 and phosphatidylinositide-3-OH kinase activities. Transfection of the constitutively active AKT complementary DNA into cells attenuated the cytotoxic effects of the drugs, indicating that inhibition of the AKT pathway plays an important role in exerting their cytotoxic effects. These results strongly suggest that the AKT-mediated survival-signaling pathway is a promising and attractive target for cancer chemotherapy.
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PMID:Survival-signaling pathway as a promising target for cancer chemotherapy. 1281 31

Signal transducers and activators of transcription (STAT) proteins nuclear translocation and transcriptional activity are regulated by diverse protein kinases in response to extracellular stimuli by cytokines, growth factors and stress. Using two melanoma-derived cell lines that exhibit marked differences in basal activities of MAPKs and PI3K-AKT, we studied changes both in STAT activities and in their sensitization to apoptosis. Activating mutations of B-RAF (T1796A) and impaired expression of PTEN are detected in LU1205, but not in FEMX melanoma cells, and are reflected in high basal levels of expression and activities of MAPKs and PI3K-AKT. Treatment with either PD98059 (PD) or LY294002 (LY), the pharmacological inhibitors of MEK-ERK and PI3K, respectively, markedly increased GAS-Luc activity in LU1205, but not in FEMX cells. Tyrosine phosphorylation of STAT3/5 and of JAK2 also increased upon treatment of LU1205 cells with either PD or LY, suggesting that constitutive active MAPK and PI3K signals inhibit tyrosine phosphorylation of JAK/STATs. Treatment of FEMX and LU1205 with PD sensitized the cells to apoptosis, albeit by TNFalpha and TRAIL death cascades, respectively, indicating that additional yet distinct targets are affected by each signaling pathway. Indeed, the combination of LY and PD treatment synergistically increased the apoptosis of LU1205 and FEMX cells. Overall, whereas PI3K and MAPK downregulate JAK-STAT signaling, additional targets are affected by these kinases and sensitizes melanoma to apoptosis via distinct death cascades.
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PMID:ERK and PI3K negatively regulate STAT-transcriptional activities in human melanoma cells: implications towards sensitization to apoptosis. 1282 43

The Hepatitis B Virus X (HBx) protein of hepatitis B virus plays a major role in hepatocellular carcinoma. It has been reported that the mutation and disruption of PTEN, a known tumor suppressor and a negative regulator of phosphatidylinositol 3'-kinase/AKT might be involved in tumor progression. However, the relationship between HBx and PTEN expression in hepatocellular carcinoma (HCC) development is not fully understood. This study reports on an investigation of whether PTEN expression in HBx-transfected cells is modulated by HBx or not. HBx decreased the expression of PTEN in HBx-transfected cells, as evidenced by Western as well as Northern blot analysis. In addition, AKT was found to be activated by HBx, as evidenced by not only the phosphorylation of AKT at serine 473 but by the phosphorylation of the exogenous substrate histone H2B as well, and these were specifically blocked by the presence of wortmannin. Moreover, The growth rate of HBx-transfected liver cells was higher than that of Chang and Chang-pEGFP cells. HBx had no effect on the expression of p53, a known transcriptional activator of PTEN. However, we confirmed that the binding of the p53 protein to p53 binding site-oligo of PTEN promoter is decreased in HBx-transfected liver cells by electrophoretic mobility shift analysis and, in addition, that HBx disrupts p53-mediated PTEN transcription, as evidenced by a PTEN promoter assay. Therefore, we conclude that HBx in liver cells down-regulates the expression of PTEN and activates AKT. This constitutes the first report to demonstrate that HBx has an effect on the p53-mediated transcription of PTEN, which, in turn, is associated with tumor suppression.
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PMID:Hepatitis B Virus X protein modulates the expression of PTEN by inhibiting the function of p53, a transcriptional activator in liver cells. 1283 24

Previous work from our laboratory demonstrated that PTEN regulates tumor-induced angiogenesis and thrombospondin 1 expression in malignant glioma. Herein, we demonstrated the first evidence that the systemic administration of a phosphatidylinositol 3'-kinase (PI3K) inhibitor (LY294002) has antitumor and antiangiogenic activity in vivo. We show that PTEN reconstitution diminished phosphorylation of AKT, induced the transactivation of p53 (7.5-fold induction) and increased the expression of p53 target genes, p21(waf-1) and insulin-like growth factor binding protein 3 in glioma cells. PTEN and LY294002 induced p53 activity in human brain endothelial cells, suggesting that PTEN and PI3K pathways can suppress the progression of cancer through direct actions on tumor and endothelial cells. The capacity of PTEN and LY294002 to inhibit U87MG or U373MG glioma growth was tested in an ectopic skin and orthotopic brain tumor model. LY294002 inhibited glioma tumor growth in vivo, induced tumor regression, decreased the incidence of brain tumors, and blocked the tumor-induced angiogenic response of U87MG cells in vivo. These data provide evidence that both PTEN and PI3K inhibitors regulate p53 function and display in vivo antiangiogenic and antitumor activity. These results provide evidence that the two tumor suppressor genes, PTEN and p53, act together to block tumor progression in vivo. Our data provide the first preclinical evidence for the in vivo efficacy for LY294002 in the treatment of malignant gliomas.
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PMID:PTEN and phosphatidylinositol 3'-kinase inhibitors up-regulate p53 and block tumor-induced angiogenesis: evidence for an effect on the tumor and endothelial compartment. 1283 45

Src family protein-tyrosine kinases, which play an important role in signal integration, have been implicated in tumorigenesis in multiple lineages, including breast cancer. We demonstrate, herein, that Src kinases regulate the phosphatidylinositol 3-kinase (PI3K) signaling cascade via altering the function of the PTEN tumor suppressor. Overexpression of activated Src protein-tyrosine kinases in PTEN-deficient breast cancer cells does not alter AKT phosphorylation, an indicator of signal transduction through the PI3K pathway. However, in the presence of functional PTEN, Src reverses the activity of PTEN, resulting in an increase in AKT phosphorylation. Activated Src reduces the ability of PTEN to dephosphorylate phosphatidylinositols in micelles and promotes AKT translocation to cellular plasma membranes but does not alter PTEN activity toward water-soluble phosphatidylinositols. Thus, Src may alter the capacity of the PTEN C2 domain to bind cellular membranes rather than directly interfering with PTEN enzymatic activity. Tyrosine phosphorylation of PTEN is increased in breast cancer cells treated with pervanadate, suggesting that PTEN contains sites for tyrosine phosphorylation. Src kinase inhibitors markedly decreased pervanadate-mediated tyrosine phosphorylation of PTEN. Further, expression of activated Src results in marked tyrosine phosphorylation of PTEN. SHP-1, a SH2 domain-containing protein-tyrosine phosphatase, selectively binds and dephosphorylates PTEN in Src transfected cells. Both Src inhibitors and SHP-1 overexpression reverse Src-induced loss of PTEN function. Coexpression of PTEN with activated Src reduces the stability of PTEN. Taken together, the data indicate that activated Src inhibits PTEN function leading to alterations in signaling through the PI3K/AKT pathway.
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PMID:Src family protein-tyrosine kinases alter the function of PTEN to regulate phosphatidylinositol 3-kinase/AKT cascades. 1286 65

PTEN tumor suppressor serves as a major negative regulator of survival signaling mediated by PI3 kinase/AKT/protein kinase B pathway, and is inactivated in various human tumors. Elucidation of mechanisms responsible for PTEN expression is important for providing insight into strategies to control the loss of PTEN expression in human cancers. Although recent studies suggested that p53 and Egr-1 can modulate induced PTEN expression, the mechanism responsible for ubiquitous constitutive expression of PTEN remains elusive. PTEN mRNA contains a highly conserved and GC-rich 5'-untranslated region (5'-UTR). Recently, it has been shown that the long 5'-UTR sequences of several growth-regulated mRNAs contain promoters that can generate mRNAs with shorter 5'-UTRs. In this paper, we tested whether the 5'-UTR sequence of mouse PTEN contains a promoter that is responsible for constitutive expression of PTEN. We found that the long 5'-UTR sequence of mouse PTEN severely inhibits translation of PTEN and a heterologous gene firefly luciferase. Deletion of the most 5'-UTR sequence would enhance translation efficiency 100-fold. We also showed that the 5'-UTR sequence of mouse PTEN does not have an internal ribosome entry site (IRES) that can mediate cap-independent initiation of translation. Instead, we found that the 5'-UTR sequence of mouse PTEN contains a strong promoter that drives the production of a transcript with shorter 5'-UTRs, which can be translated with higher efficiency. This promoter was mapped to the region between -551 and -220 bases upstream of the translation start codon. Cotransfection analysis using Drosophila SL2 cells showed that Sp1 is one of the major transcription factors that can constitutively activate this promoter. Two endogenous PTEN transcripts with 5'-UTRs of 193 and 109 bases were found in DU145 and H226 cell lines. Based on these observations, we conclude that the PTEN expression may be regulated at both transcriptional and translational levels, and that the 5'-UTR sequence of PTEN contains a promoter that is responsible for constitutive PTEN expression.
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PMID:Regulation of constitutive expression of mouse PTEN by the 5'-untranslated region. 1291 34


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