Akt is transferred to the nucleus of cells treated with apoptin, and it participates in apoptin-induced cell death (original) (raw)
Related papers
Molecular and Cellular Biology, 2008
Apoptin, a protein from the chicken anemia virus, has attracted attention because it specifically kills tumor cells while leaving normal cells unharmed. The reason for this tumor selectivity is unclear and depends on subcellular localization, as apoptin resides in the cytoplasm of normal cells but in the nuclei of transformed cells. It was shown that nuclear localization and tumor-specific killing crucially require apoptin's phosphorylation by an as yet unknown kinase. Here we elucidate the pathway of apoptin-induced apoptosis and show that it essentially depends on abnormal phosphatidylinositol 3-kinase (PI3-kinase)/Akt activation, resulting in the activation of the cyclin-dependent kinase CDK2. Inhibitors as well as dominant-negative mutants of PI3-kinase and Akt not only inhibited CDK2 activation but also protected cells from apoptin-induced cell death. Akt activated CDK2 by direct phosphorylation as well as by the phosphorylation-induced degradation of the inhibitor p27(Kip1). Importantly, we also identified CDK2 as the principal kinase that phosphorylates apoptin and is crucially required for apoptin-induced cell death. Immortalized CDK2-deficient fibroblasts and CDK2 knockdown cells were markedly protected against apoptin. Thus, our results not only decipher the pathway of apoptin-induced cell death but also provide mechanistic insights for the selective killing of tumor cells.
Investigational New Drugs, 2011
The serine/threonine kinase Akt, a downstream effector of phosphatidylinositol 3-kinase (PI3K), is involved in cell survival and anti-apoptotic signaling. Akt has been shown to be constitutively expressed in a variety of human tumors including hepatocellular carcinoma (HCC). In this report we analyzed the status of Akt pathway in three HCC cell lines, and tested cytotoxic effects of Akt pathway inhibitors LY294002, Wortmannin and Inhibitor VIII. In Mahlavu human hepatoma cells Akt was constitutively activated, as demonstrated by its Ser473 phosphorylation, downstream hyperphosphorylation of BAD on Ser136, and by a specific cell-free kinase assay. In contrast, Huh7 and HepG2 did not show hyperactivation when tested by the same criteria. Akt enzyme hyperactivation in Mahlavu was associated with a loss of PTEN protein expression. Akt signaling was inhibited by the upstream kinase inhibitors, LY294002, Wortmannin, as well as by the specific Akt Inhibitor VIII in all three hepatoma cell lines. Cytotoxicity assays with Akt inhibitors in the same cell lines indicated that they were all sensitive, but with different IC50 values as assayed by RT-CES. We also demonstrated that the cytotoxic effect was through apoptotic cell death. Our findings provide evidence for its constitutive activation in one HCC cell line, and that HCC cell lines, independent of their Akt activation status respond to Akt inhibitors by apoptotic cell death. Thus, Akt inhibition may be considered as an attractive therapeutic intervention in liver cancer.
A kinase-independent function of AKT promotes cancer cell survival
35 induced cell death in a PH-domain dependent manner. An AKT kinase domain mutant 36 found in human melanoma (G161V) lacked enzymatic activity in-vitro and in AKT1/AKT2 37 double knockout cells, but promoted growth-factor independent survival of primary 38 human melanocytes. ATP-competitive AKT inhibitors failed to block the kinase-39 independent function of AKT, a liability that limits their effectiveness compared to 40 allosteric AKT inhibitors. Our results broaden the current view of AKT function and have 41 important implications for the development of AKT inhibitors for cancer. 42 43 44 45 46 47 48 49 50 51 52 53 3
Akt phosphorylates and negatively regulates apoptosis signal-regulating kinase 1
Science …, 2001
The Akt family of serine/threonine-directed kinases promotes cellular survival in part by phosphorylating and inhibiting death-inducing proteins. Here we describe a novel functional interaction between Akt and apoptosis signal-regulating kinase 1 (ASK1), a mitogen-activated protein kinase kinase kinase. Akt decreased ASK1 kinase activity stimulated by both oxidative stress and overexpression in 293 cells by phosphorylating a consensus Akt site at serine 83 of ASK1. Activation of the phosphoinositide 3-kinase (PI3-K)/Akt pathway also inhibited the serum deprivation-induced activity of endogenous ASK1 in L929 cells. An association between Akt and ASK1 was detected in cells by coimmunoprecipitation. Phosphorylation by Akt inhibited ASK1-mediated c-Jun N-terminal kinase and activating transcription factor 2 activities in intact cells. Finally, activation of the PI3-K/Akt pathway reduced apoptosis induced by ASK1 in a manner dependent on phosphorylation of serine 83 of ASK1. These results provide the first direct link between Akt and the family of stress-activated kinases.
Akt promotes cell survival by phosphorylating and inhibiting a Forkhead transcription factor
Recently, a signaling pathway by which extracellular * Division of Neuroscience stimuli suppress apoptosis has been characterized. Sur-Children's Hospital and Department of Neurobiology vival factors, such as insulin-like growth factor 1 (IGF1) Harvard Medical School and neurotrophins, bind to their cell surface receptors Boston, Massachusetts 02115 and trigger the activation of several kinases, including † Department of Cell Biology the phosphatidylinositol 3-kinase (PI3K) (Fruman et al., Harvard Medical School 1998) and the Ca 2ϩ /calmodulin-dependent kinase ki-Boston, Massachusetts 02115 nase (Yano et al., 1998). These kinases in turn lead to ‡ Ludwig Institute for Cancer Research the activation of a serine/threonine kinase termed Akt University of California at San Diego or PKB (for reviews, Datta and Greenberg, 1998; Down-San Diego, California 92093 ward, 1998). Akt plays a central role in promoting the survival of a wide range of cell types (Dudek et al., 1997; Kauffmann-Zeh et al., 1997; Kennedy et al., 1997; Summary Songyang et al., 1997). Recently, two Akt substrates that are components of the intrinsic cell death machinery Survival factors can suppress apoptosis in a transcriphave been identified: the Bcl2 family member BAD (Datta tion-independent manner by activating the serine/ et al., 1997; del Peso et al., 1997) and the protease threonine kinase Akt, which then phosphorylates and Caspase 9 (Cardone et al., 1998; Y. Gotoh et al., unpubinactivates components of the apoptotic machinery,
PI3K/Akt and apoptosis: size matters
Oncogene, 2003
Recent research has examined Akt and Akt-related serine-threonine kinases in signaling cascades that regulate cell survival and are important in the pathogenesis of degenerative diseases and in cancer. We seek to recapitulate the research that has helped to define the current understanding of the role of the Akt pathway under normal and pathologic conditions, also in view of genetic models of Akt function. In particular, we will evaluate the mechanisms of Akt regulation and the role of Akt substrates in Akt-dependent biologic responses in the decisions of cell death and cell survival. Here, we hope to establish the mechanisms of apoptosis suppression by Akt kinase as a framework for a more general understanding of growth factor-dependent regulation of cell survival.
Active form of AKT controls cell proliferation and response to apoptosis in hepatocellular carcinoma
Oncology Reports, 2013
Hepatocellular carcinoma (HCC) is the third most common cause of cancer-related mortality worldwide. Deregulation of the AKT signaling pathway has been found in HCC. However, the effect of AKT activation on the proliferation and apoptosis in HCC is not clear. Herein, expression of phosphorylated form of AKT (Ser 473) was investigated in HCC tumor (n=73), cirrhosis (n=17), normal liver (n=22) samples and in HCC cell lines (n=8). The results showed that expression of p-AKT was higher in tumor (53%) than in cirrhotic tissues (12%) while it was absent in normal liver (p<0.0001). p-AKT expression was also associated with number of tumor nodules and differentiation status (p<0.05). LY294002 induced cell cycle arrest at G0/G1 in SNU-449 and Mahlavu cells by decreasing expression of CDK2, CDK4, CycD1, CycD3, CycE, CycA and increasing expression of p21 and p27 as well; it also caused a decrease in the E2F1 transcriptional activity through declining phosphorylated Rb. LY294002 did not affect the basal level of apoptosis; however, it amplified cisplatin-induced apoptosis in SNU-449 cells. When the p-AKT level was decreased specifically after transfection with the DN-AKT plasmid, SNU-449 cells became more sensitive to cisplatin-induced apoptosis. HuH-7 cells with no basal p-AKT, were markedly affected by the treatment of doxorubicin. Thus, Akt signaling controls growth and chemical-induced apoptosis in HCC and p-AKT may be a potential target for therapeutic interventions in HCC patients.
Akt as a mediator of cell death
Proceedings of the National Academy of Sciences, 2003
Protein kinase B͞Akt possesses prosurvival and antiapoptotic activities and is involved in growth factor-mediated neuronal protection. In this study we establish Akt deactivation as a causal mediator of cell death. Akt deactivation occurs in multiple models of cell death including N-methyl-D-aspartate excitotoxicity, vascular stroke, and nitric oxide (NO)-and hydrogen peroxide (H2O2)elicited death of HeLa, PC12, and Jurkat T cells. Akt deactivation characterizes both caspase-dependent and -independent cell death. Conditions rescuing cell death, such as treatment with poly(ADP-ribose) polymerase or NO synthase inhibitors and preconditioning with sublethal concentrations of N-methyl-D-aspartate, restore Akt activity. Infection of neurons with adenovirus expressing constitutively active Akt prevents excitotoxicity, whereas phosphatidylinositol 3-kinase inhibitors or infection with dominant negative Akt induce death of untreated neuronal cells.