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)

We demonstrated that enhancement of X-ray-induced apoptosis/rapid cell death by wortmannin accompanied by increased activation of JNK/SAPK in human leukemia MOLT-4 cells. Rapid cell death/apoptosis was determined either by the dye exclusion test or by the appearance of Annexin V-positive cells and cleaved PARP fragments. Enhancement was observed only at higher concentrations of wortmannin, i.e. 1 microM or more. At these high concentrations, both DNA-PK and ATM were inhibited. X-ray-induced phosphorylation of Ser 15 of p53/TP53, accumulation of both p53/TP53 and p21/WAF1/CDKN1A, and phosphorylation of XRCC4 were all suppressed. The enhancement of apoptosis/rapid cell death by wortmannin was prevented by addition of caspase inhibitors, Z-VAD-FMK or Ac-DEVD-CHO, or by transfection and overexpression of mouse Bcl2, which is known as an anti-apoptosis protein. The requirement for a high concentration of wortmannin, i.e. 1 microM or more, indicates that inhibition of both DNA-PK and ATM was necessary for the enhanced apoptosis/rapid cell death. Phosphorylation of AKT/PKB was completely suppressed at a much lower concentration, i.e. 0.1 microM wortmannin, where no enhancement of X-ray-induced apoptosis/rapid cell death was observed. On the other hand, X-ray-induced phosphorylation of JNK and its kinase activity as well as apoptosis/rapid cell death were all significantly enhanced only at high concentrations of wortmannin, i.e. 1 microM or more. Furthermore, the extent of enhancement of both JNK phosphorylation and of apoptosis/rapid cell death by wortmannin was less in Rh1a cells, which are ceramide- and radiation-resistant variant cells compared to the parental MOLT-4 cells. Therefore, activation of the JNK pathway was considered important for the enhancement of X-ray-induced apoptosis/rapid cell death of MOLT-4 cells by wortmannin, because of the requirement for a higher concentration of wortmannin than that required for inhibition of AKT phosphorylation. The suppression of the AKT-dependent pathway by wortmannin may have some underlying role in activating the JNK pathway toward the enhancement of cell death in the current system.
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PMID:Wortmannin-enhanced X-ray-induced apoptosis of human T-cell leukemia MOLT-4 cells possibly through the JNK/SAPK pathway. 1296 28

Extensive evidence implicates activation of the lipid phosphatidylinositide 3-kinase (PI3K) pathway in the genesis and progression of various human cancers. PI3K inhibitors thus have considerable potential as molecular cancer therapeutics. Here, we detail the pharmacologic properties of a prototype of a new series of inhibitors of class I PI3K. PI103 is a potent inhibitor with low IC50 values against recombinant PI3K isoforms p110alpha (2 nmol/L), p110beta (3 nmol/L), p110delta (3 nmol/L), and p110gamma (15 nmol/L). PI103 also inhibited TORC1 by 83.9% at 0.5 micromol/L and exhibited an IC50 of 14 nmol/L against DNA-PK. A high degree of selectivity for the PI3K family was shown by the lack of activity of PI103 in a panel of 70 protein kinases. PI103 potently inhibited proliferation and invasion of a wide variety of human cancer cells in vitro and showed biomarker modulation consistent with inhibition of PI3K signaling. PI103 was extensively metabolized, but distributed rapidly to tissues and tumors. This resulted in tumor growth delay in eight different human cancer xenograft models with various PI3K pathway abnormalities. Decreased phosphorylation of AKT was observed in U87MG gliomas, consistent with drug levels achieved. We also showed inhibition of invasion in orthotopic breast and ovarian cancer xenograft models and obtained evidence that PI103 has antiangiogenic potential. Despite its rapid in vivo metabolism, PI103 is a valuable tool compound for exploring the biological function of class I PI3K and importantly represents a lead for further optimization of this novel class of targeted molecular cancer therapeutic.
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PMID:Pharmacologic characterization of a potent inhibitor of class I phosphatidylinositide 3-kinases. 1757 52

The cyclin-dependent kinase inhibitor p21(CIP1/WAF1) is a key component in cell cycle control and apoptosis, directing an anti-apoptotic response following DNA damage. Chromium exposure resulted in a 500-1000 fold increase in apoptosis-induced cell death in p21-/- HCT116 cells compared to wild-type or p53-/- cells. p53 shRNA (or transient p53 siRNA) into p21-/- HCT116 cells reduced Cr(VI) sensitivity, suggesting the enhanced apoptosis in p21-/- cells is p53-dependent. Under non-DNA damage conditions, the p53 level in p21-/- cells was significantly higher than in wild-type cells, due to enhanced p53 phosphorylation and stabilization rather than elevated p53 transcription. Wild-type cells showed significant p53 protein induction upon DNA damage whereas p21-/- cells showed no p53 increase. p21-/- cells display the constitutive activation of upstream p53 kinases (ATM, DNA-PK, ATR, AKT and p38). 2D gel analysis revealed p53 patterns in p21-/- cells were distinct from those in wild-type cells before and after chromium exposure. Our results suggest that p21 has an important role in the cellular response to normal replicative stress and its absence leads to a "chronic DNA damage" state that primes the cell for p53-dependent apoptosis.
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PMID:Hypersensitivity to chromium-induced DNA damage correlates with constitutive deregulation of upstream p53 kinases in p21-/- HCT116 colon cancer cells. 1802 14

Protein kinase B (PKB/Akt) is a well-established regulator of several essential cellular processes. Here, we report a route by which activated PKB promotes survival in response to DNA insults in vivo. PKB activation following DNA damage requires 3-phosphoinositide-dependent kinase 1 (PDK1) and DNA-dependent protein kinase (DNA-PK). Active PKB localizes in the nucleus of gamma-irradiated cells adjacent to DNA double-strand breaks, where it colocalizes and interacts with DNA-PK. Levels of active PKB inversely correlate with DNA damage-induced apoptosis. A significant portion of p53- and DNA damage-regulated genes are misregulated in cells lacking PKBalpha. PKBalpha knockout mice show impaired DNA damage-dependent induction of p21 and increased tissue apoptosis after single-dose whole-body irradiation. Our findings place PKB downstream of DNA-PK in the DNA damage response signaling cascade, where it provides a prosurvival signal, in particular by affecting transcriptional p21 regulation. Furthermore, this function is apparently restricted to the PKBalpha isoform.
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PMID:PKBalpha/Akt1 acts downstream of DNA-PK in the DNA double-strand break response and promotes survival. 1843 99

We have already reported that epidermal growth factor receptor/phosphatidylinositol 3-kinase/AKT signaling is an important pathway in regulating radiation sensitivity and DNA double-strand break (DNA-dsb) repair of human tumor cells. In the present study, we investigated the effect of AKT1 on DNA-dependent protein kinase catalytic subunit (DNA-PKcs) activity and DNA-dsb repair in irradiated non-small cell lung cancer cell lines A549 and H460. Treatment of cells with the specific AKT pathway inhibitor API-59 CJ-OH (API; 1-5 micromol/L) reduced clonogenic survival between 40% and 85% and enhanced radiation sensitivity of both cell lines significantly. As indicated by fluorescence-activated cell sorting analysis (sub-G(1) cells) and poly(ADP-ribose) polymerase cleavage, API treatment or transfection with AKT1-small interfering RNA (siRNA) induced apoptosis of H460 but not of A549 cells. However, in either apoptosis-resistant A549 or apoptosis-sensitive H460 cells, API and/or AKT1-siRNA did not enhance poly(ADP-ribose) polymerase cleavage and apoptosis following irradiation. Pretreatment of cells with API or transfection with AKT1-siRNA strongly inhibited radiation-induced phosphorylation of DNA-PKcs at T2609 and S2056 as well as repair of DNA-dsb as measured by the gamma-H2AX foci assay. Coimmunoprecipitation experiments showed a complex formation of activated AKT and DNA-PKcs, supporting the assumption that AKT plays an important regulatory role in the activation of DNA-PKcs in irradiated cells. Thus, targeting of AKT enhances radiation sensitivity of lung cancer cell lines A549 and H460 most likely through specific inhibition of DNA-PKcs-dependent DNA-dsb repair but not through enhancement of radiation-induced apoptosis.
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PMID:Targeting of AKT1 enhances radiation toxicity of human tumor cells by inhibiting DNA-PKcs-dependent DNA double-strand break repair. 1864 89

As demonstrated recently, ionizing radiation (IR) can mediate phosphorylation of DNA-PKcs in human tumor cells through stimulation of the PI3K/Akt pathway. It is also known that DNA-PKcs directly interacts the X-ray repair cross-complementing group 1 protein (XRCC1) involved in base excision repair (BER). Therefore, in the present study we investigated the role of PI3K/Akt activity and DNA-PKcs on XRCC1 expression/stabilization. In contrast to the DNA-PKcs-deficient glioblastoma cell line MO59J, the DNA-PKcs-proficient counterpart MO59K as well as human lung adenocarcinoma A549 cells presented a high basal level of XRCC1 expression. Radiation doses of 3-12Gy did not stimulate a further enhanced expression of XRCC1 in DNA-PKcs-proficient cells (MO59K and A549) within 180min post-irradiation. However, a marked induction of XRCC1 expression was apparent in DNA-PKcs-deficient MO59J cells. Targeting of DNA-PKcs as well as PI3K/Akt pathway by specific kinase inhibitors and/or siRNA reduced basal XRCC1 expression in un-irradiated DNA-PKcs-proficient cells to the level observed in DNA-PKcs-deficient cells. Reduction of basal expression of XRCC1 by XRCC1-siRNA, AKT-siRNA as well as DNA-PKcs inhibitor facilitated IR-induced XRCC1 expression. XRCC1 expression induced by irradiation, however, was independent of PI3K/Akt signaling, but dependent of MAPK-ERK1/2. By immuno-precipitation experiments and confocal microscopy a complex formation of XRCC1 and DNA-PKcs was shown. Applying gamma-H2AX foci analysis it was shown that basal expression of XRCC1 is important for the repair of IR-induced DNA-double strand breaks (DNA-DSBs). These data indicate that IR-induced XRCC1 expression is dependent on the expression level of DNA-PKcs and basal activity status of PI3K/Akt signaling. Likewise, potential of IR-induced XRCC1 expression depends on its basal expression level.
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PMID:PI3K-Akt signaling regulates basal, but MAP-kinase signaling regulates radiation-induced XRCC1 expression in human tumor cells in vitro. 1867 86

The epidermal growth factor receptor (EGFR) is frequently dysregulated in malignant glioma that leads to increased resistance to cancer therapy. Upregulation of wild type or expression of mutant EGFR is associated with tumor radioresistance and poor clinical outcome. EGFR variant III (EGFRvIII) is the most common EGFR mutation in malignant glioma. Radioresistance is thought to be, at least in part, the result of a strong cytoprotective response fueled by signaling via AKT and ERK that is heightened by radiation in the clinical dose range. Several groups including ours have shown that this response may modulate DNA repair. Herein, we show that expression of EGFRvIII promoted gamma-H2AX foci resolution, a surrogate for double-strand break (DSB) repair, and thus enhanced DNA repair. Conversely, small molecule inhibitors targeting EGFR, MEK, and the expression of dominant-negative EGFR (EGFR-CD533) significantly reduced the resolution of gamma-H2AX foci. When homologous recombination repair (HRR) and non-homologous end joining (NHEJ) were specifically examined, we found that EGFRvIII stimulated and CD533 compromised HRR and NHEJ, respectively. Furthermore, NHEJ was blocked by inhibitors of AKT and ERK signaling pathways. Moreover, expression of EGFRvIII and CD533 increased and reduced, respectively, the formation of phospho-DNA-PKcs and -ATM repair foci, and RAD51 foci and expression levels, indicating that DSB repair is regulated at multiple levels. Altogether, signaling from EGFR and EGFRvIII promotes both HRR and NHEJ that is likely a contributing factor towards the radioresistance of malignant gliomas.
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PMID:Pro-survival AKT and ERK signaling from EGFR and mutant EGFRvIII enhances DNA double-strand break repair in human glioma cells. 1925 15

This study aimed to evaluate the radiosensitizing effect of a COX-2 inhibitor, NS398, and its mechanism in radioresistant esophageal cancer Eca109R50Gy cells. NS398 enhanced radiosensitivity of Eca109R50Gy cells, characterized by redistribution of cell cycle, inhibition of DNA-dependent protein kinase catalytic subunit expression and induction of apoptosis. NS398 also reduced phospho-AKT level, upregulated expression of Bax and both procaspase-3 and active caspase-3, and downregulated Bcl-2 expression. Finally, NS398-induced radiosensitization was partly reversed by insulin-like growth factor-1, but not by prostaglandin E2. Our results suggest that NS398 may enhance radiosensitivity of Eca109R50Gy cells through blocking AKT activation and inducing apoptosis.
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PMID:Cyclooxygenase-2 inhibitor NS398 enhances radiosensitivity of radioresistant esophageal cancer cells by inhibiting AKT activation and inducing apoptosis. 2048 53

Protein kinase B (PKB/Akt) is a serine/threonine protein kinase that created serious interest when it was revealed as a mediator of the PI3K pathway. It comprises three isoforms that play both unique and redundant roles. Upon binding to phosphatidylinositol-(3,4,5)-trisphosphate (PIP3) generated by PI3K, PKB is phosphorylated by PDK1 at T308. To achieve full kinase activity, PKB needs to be phosphorylated at a second key residue, S473, by members of the PI3K-related kinase family mTORC2 or DNA-PK, depending on the stimulus and the context. Besides, a number of phosphatases and interacting partners have been shown to further modulate its subcellular localization, phosphorylation, and kinase activity. This review aims at illustrating the remarkable complexity in the regulation of PKB signaling downstream of PI3K. Such regulation could be attributed to the specific roles of the PKB isoforms, their expression pattern, subcellular localization, targets, phosphorylation by upstream kinases in a stimulus- and context-dependent manner and by phosphatases, and interaction with binding partners. This allows this key kinase to fulfill physiological functions in numerous processes, including embryonic development, thymocyte development, adipocyte differentiation, glucose homeostasis, and to avoid pathological loss of control such as tumor formation.
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PMID:Protein kinase B (PKB/Akt), a key mediator of the PI3K signaling pathway. 2051 22

Recurrence is frequently associated with the acquisition of radioresistance by tumors and resulting failures in radiotherapy. We report, in this study, that long-term fractionated radiation (FR) exposures conferred radioresistance to the human tumor cells, HepG2 and HeLa with cyclin D1 overexpression. A positive feedback loop was responsible for the cyclin D1 overexpression in which constitutively active AKT was involved. AKT is known to inactivate glycogen synthase kinase-3beta (GSK3beta), which is essential for the proteasomal degradation of cyclin D1. The resulting cyclin D1 overexpression led to the forced progression of S-phase with the induction of DNA double strand breaks. Cyclin D1-dependent DNA damage activated DNA-dependent protein kinase (DNA-PK), which in turn activated AKT and inactivated GSK3beta, thus completing a positive feedback loop of cyclin D1 overproduction. Cyclin D1 overexpression led to the activation of DNA damage response (DDR) consisted of ataxia telangiectasia mutated (ATM)- and Chk1-dependent DNA damage checkpoint and homologous recombination repair (HRR). Long-term FR cells repaired radiation-induced DNA damage faster than non-FR cells. Thus, acquired radioresistance of long-term FR cells was the result of alterations in DDR mediated by cyclin D1 overexpression. Inhibition of the AKT/GSK3beta/cyclin D1/Cdk4 pathway by the AKT inhibitor, Cdk4 inhibitor or cyclin D1 targeting small interfering RNA (siRNA) suppressed the radioresistance. Present observations give a mechanistic insight for acquired radioresistance of tumor cells by cyclin D1 overexpression, and provide novel therapeutic targets for recurrent radioresistant tumors.
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PMID:Acquired radioresistance of human tumor cells by DNA-PK/AKT/GSK3beta-mediated cyclin D1 overexpression. 2056 19


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