Insulin-like growth factor-1 protects peroxynitrite-induced cell death by preventing cytochrome c-induced caspase-3 activation

We investigated the effect of IGF-1 on cell death induced by peroxynitrite in human neuroblastoma SH-SY5Y cells. Exposure of the cells to 3-morpholinosydnonimine (SIN-1), a peroxynitrite donor, caused cytochrome c release from the mitochondria, caspase-3-like activation, and cell death. Pre-incubation of the cells with the caspase-3 inhibitor partially prevented SIN-1-induced cell death. Simultaneous addition of IGF-1 reduced SIN-1-induced caspase-3-like activation and cell death, whereas IGF-1 failed to reduce the release of cytochrome c. IGF-1 increased Akt phosphorylation, and Akt phosphorylation was inhibited by wortmannin, an inhibitor of phosphatidylinositol 3-kinase. In addition, wortmannin prevented IGF-1-evoked inhibition of cell death and caspase-3-like activation. In a cell-free system, addition of cytochrome c to cytosolic fraction resulted in caspase-3-like activation. The activation was reduced when the cytosolic fraction prepared from IGF-1-treated cells was used. These results suggest that IGF-1 protects peroxynitrite-induced cell death downstream of cytochrome c release through the inhibition of caspase-3-like activation.     

cAMP-guanine exchange factor protection from bile acid-induced hepatocyte apoptosis involves glycogen synthase kinase regulation of c-Jun NH2-terminal kinase

Cholestatic liver disorders are accompanied by the hepatic accumulation of cytotoxic bile acids that induce cell death. Increases in cAMP protect hepatocytes from bile acid-induced apoptosis by a cAMP-guanine exchange factor (cAMP-GEF)/phosphoinositide-3-kinase (PI3K)/Akt pathway. The aim of these studies was to identify the downstream substrate in this pathway and to determine at what level in the apoptotic cascade cytoprotection occurs. Since inhibitory phosphorylation of glycogen synthase kinase-3 (GSK) occurs downstream of PI3K/Akt and this phosphorylation has been implicated in cell survival, we conducted studies to determine whether GSK was downstream in cAMP-GEF/PI3K/Akt-mediated cytoprotection. Our results show that treatment of hepatocytes with the cAMP-GEF-specific analog, 4-(4-chlorophenylthio)-2'-O-methyladenosine-3',5'-cAMP, results in PI3K-dependent phosphorylation of GSK. Direct chemical inhibition of GSK in rat hepatocytes or human HUH7-NTCP cells with several structurally and functionally distinct inhibitors including bromoindirubin-3'-oxime (BIO), maleimides (SB216763, SB415286), thiadiazolidine derivatives, and LiCl attenuates apoptosis induced by glycochenodeoxycholate (GCDC). In addition, genetic silencing of the GSK β isoform with small interfering RNA attenuates GCDC apoptosis in HUH7-NTCP cells. Adenoviral inhibition of the Rap1 blocks both cAMP-GEF-mediated cytoprotection against GCDC-induced apoptosis and Akt/GSK3β phosphorylation. GCDC-induced phosphorylation of the proapoptotic kinase, c-Jun NH(2)-terminal kinase (JNK) is inhibited by GSK inhibition or cAMP-GEF activation. GCDC-induced apoptosis is accompanied by phosphorylation of the endoplasmic reticulum stress markers pIEF2α and IRE-1, and pretreatment with the cAMP-GEF analog or GSK inhibitors prevents this phosphorylation. Collectively, our results support the presence of a cAMP/cAMP-GEF/Rap1/PI3K/Akt/GSKβ survival pathway in hepatocytes that inhibits bile acid-induced JNK phosphorylation.     

Kallikrein/kinin protects against myocardial apoptosis after ischemia/reperfusion via Akt-glycogen synthase kinase-3 and Akt-Bad.14-3-3 signaling pathways

Our previous study has shown that human tissue kallikrein protected against ischemia/reperfusion-induced myocardial injury. In the present study, we investigated the protective role of local kallikrein gene delivery in ischemia/reperfusion-induced cardiomyocyte apoptosis and its signaling mechanisms in promoting cardiomyocyte survival. Adenovirus carrying the human tissue kallikrein gene was delivered locally into the heart using a catheter-based technique. Expression and localization of recombinant human kallikrein in rat myocardium after gene transfer were determined immunohistochemically. Kallikrein gene delivery markedly reduced reperfusion-induced cardiomyocyte apoptosis identified by both in situ nick end-labeling and DNA fragmentation. Delivery of the kallikrein gene increased phosphorylation of Src, Akt, glycogen synthase kinase (GSK)-3beta, and Bad(Ser-136) but reduced caspase-3 activation in rat myocardium after reperfusion. The protective effect of kallikrein on apoptosis and its signaling mediators was blocked by icatibant and dominant-negative Akt, indicating a kinin B2 receptor-Akt-mediated event. Similarly, kinin or transduction of kallikrein in cultured cardiomyocytes promoted cell viability and attenuated apoptosis induced by hypoxia/reoxygenation. The effect of kallikrein on cardiomyocyte survival was blocked by dominant-negative Akt and a constitutively active mutant of GSK-3beta, but it was facilitated by constitutively active Akt, catalytically inactive GSK-3beta, lithium, and caspase-3 inhibitor. Moreover, kallikrein promoted Bad.14-3-3 complex formation and inhibited Akt-GSK-3beta-dependent activation of caspase-3, whereas caspase-3 administration caused reduction of the Bad.14-3-3 complex, indicating an interaction between Akt-GSK-caspase-3 and Akt-Bad.14-3-3 signaling pathways. In conclusion, kallikrein/kinin protects against cardiomyocyte apoptosis in vivo and in vitro via Akt-Bad.14-3-3 and Akt-GSK-3beta-caspase-3 signaling pathways.     

Proteasome inhibition-induced p38 MAPK/ERK signaling regulates autophagy and apoptosis through the dual phosphorylation of glycogen synthase kinase 3β

Proteasome inhibition is a promising approach for cancer treatment; however, the underlying mechanisms involved have not been fully elucidated. Here, we show that proteasome inhibition-induced p38 mitogen-activated protein kinase regulates autophagy and apoptosis by modulating the phosphorylation status of glycogen synthase kinase 3β (GSK3β) and 70kDa ribosomal S6 kinase (p70S6K). The treatment of MDA-MB-231 cells with MG132 induced endoplasmic reticulum stress through the induction of ATF6a, PERK phosphorylation, and CHOP, and apoptosis through the cleavage of Bax and procaspase-3. MG132 caused the phosphorylation of GSK3β at Ser(9) and, to a lesser extent, Thr(390), the dephosphorylation of p70S6K at Thr(389), and the phosphorylation of p70S6K at Thr(421) and Ser(424). The specific p38 inhibitor SB203080 reduced the p-GSK3β(Ser9) and autophagy through the phosphorylation of p70S6K(Thr389); however, it augmented the levels of p-ERK, p-GSK3β(Thr390), and p-70S6K(Thr421/Ser424) induced by MG132, and increased apoptotic cell death. The GSK inhibitor SB216763, but not lithium, inhibited the MG132-induced phosphorylation of p38, and the downstream signaling pathway was consistent with that in SB203580-treated cells. Taken together, our data show that proteasome inhibition regulates p38/GSK(Ser9)/p70S6K(Thr380) and ERK/GSK3β(Thr390)/p70S6K(Thr421/Ser424) kinase signaling, which is involved in cell survival and cell death.     

RNAi and 2DE, a promising combination for analysis of phospho-signalling and substrate identification

The use of RNA interference (RNAi) has provided the study of cell signalling with a specific and relatively easily applicable method of silencing individual components of signalling pathways. RNAi mediated gene muting was combined with two-dimensional electrophoresis (2DE) and immuno-blotting analysis (IB) to study phospho-signalling downstream of the protein kinase, Akt. NIH3T3 mouse fibroblasts were transiently transfected with short interfering RNAs (siRNAs) to Akt with resulting suppression of Akt expression. Down-regulation of Akt reduced the cellular content of phosphorylated FKHR, enhanced GSK3β phosphorylation, and increased the sensitivity of the cells to apoptotic agents. Stable transfection of short hairpin RNAs inserted into a stable expression vector, pRETRO-SUPER (pRS), also proved to be a successful method of downregulating Akt1, and resulted in an altered phosphorylation pattern and a reduced rate of cell proliferation. Akt-regulated phosphorylation was identified by comparison of extracts from Akt RNAi transfected cells with extracts from cells transfected with pRS vector alone. While Akt muting suppressed some phospho-modifications, others were enhanced. The␣PDGF-induced tyrosine phosphorylation cascades were, surprisingly, found to be influenced by RNAi-mediated Akt muting. Tyrosine phosphorylation of some proteins were reduced in cells with down-regulated Akt1 activity, suggesting the existence of either a downstream tyrosine kinase positively regulated by Akt1, or a negatively regulated tyrosine phosphatase, positioned centrally in the cross-talk between the Akt1 regulated signalling pathways and the growth factor induced phospho-tyrosine pathways. Our results illustrate the analytical potential of combining RNAi-mediated regulator muting with 2DE-based analysis of phospho-signalling, and suggest that such a combination could become a highly efficient tool for the identification and characterisation of new kinase substrates.     

TGFbeta intercepts nuclear glycogen synthase kinase 3beta to inhibit PDGF-induced DNA synthesis in mesangial cells

Here, we demonstrate a mechanism of TGFbeta-mediated inhibition of PDGF-induced DNA synthesis in mesangial cells. TGFbeta significantly inhibited nuclear Akt phosphorylation without any effect on PDGF-stimulated phosphorylation of PDGFR at PI 3 kinase binding site (Tyr-751). Remarkably, TGFbeta inhibited cyclin D1 and cyclin E expression with concomitant decrease in CDK2 activity induced by PDGF. More importantly, we demonstrate that TGFbeta significantly abolished Akt-mediated serine-9 phosphorylation of glycogen synthase kinase 3beta (GSK3beta), thus prevented its inactivation. Expression of inactive GSK3betaK85R mutant increased cyclin D1 expression and DNA synthesis similar to PDGF. These results provide the first evidence that TGFbeta intercepts Akt kinase activity in the nucleus to block inactivation of GSK3beta, leading to attenuation of PDGF-induced CDK2 activity and DNA synthesis.     

Inhibition of granulocyte-macrophage colony-stimulating factor signaling and microglial proliferation by anti-CD45RO: role of Hck tyrosine kinase and phosphatidylinositol 3-kinase/Akt

Increasing evidence suggests that CD45, a transmembrane protein tyrosine phosphatase, is an important modulator of macrophage activation. Microglia, resident brain macrophages, express CD45 and proliferate under pathologic conditions. In this study, we examined the role of CD45 in modulating GM-CSF-induced proliferation and signal transduction in primary human microglial cultures. Soluble, but not immobilized anti-CD45RO induced tyrosine phosphatase activity and inhibited GM-CSF-induced microglial proliferation. Microglial proliferation was also inhibited by PP2 (Src inhibitor), LY294002 (PI3K inhibitor), and U0126 (MEK inhibitor). GM-CSF induced phosphorylation of Jak2, Stat5, Hck (the myeloid-restricted Src kinase), Akt, Stat3, and Erk MAPKs in microglia. Of these, anti-CD45RO inhibited phosphorylation of Hck and Akt, and PP2 inhibited phosphorylation of Hck and Akt. In a macrophage cell line stably overexpressing wild-type or kinase-inactive Hck, GM-CSF increased proliferation of the control (empty vector) and wild-type but not kinase-inactive cells, and this was inhibited by anti-CD45RO. Together, these results demonstrate that, in macrophages, Hck tyrosine kinase is activated by GM-CSF, and that Hck plays a pivotal role in cell proliferation and survival by activating the PI3K/Akt pathway. Ab-mediated activation of macrophage and microglial CD45 tyrosine phosphatase may have therapeutic implications for CNS inflammatory diseases.     

Tyrosine phosphorylation regulates the proteolytic activation of protein kinase Cdelta in dopaminergic neuronal cells

Oxidative stress is a key apoptotic stimulus in neuronal cell death and has been implicated in the pathogenesis of many neurodegenerative disorders, including Parkinson disease (PD). Recently, we demonstrated that protein kinase C-delta (PKCdelta) is an oxidative stress-sensitive kinase that can be activated by caspase-3-dependent proteolytic cleavage to induce apoptotic cell death in cell culture models of Parkinson disease (Kaul, S., Kanthasamy, A., Kitazawa, M., Anantharam, V., and Kanthasamy, A. G. (2003) Eur. J. Neurosci. 18, 1387-1401 and Kanthasamy, A. G., Kitazawa, M., Kanthasamy, A., and Anantharam, V. (2003) Antioxid. Redox. Signal. 5, 609-620). Here we showed that the phosphorylation of a tyrosine residue in PKCdelta can regulate the proteolytic activation of the kinase during oxidative stress, which consequently influences the apoptotic cell death in dopaminergic neuronal cells. Exposure of a mesencephalic dopaminergic neuronal cell line (N27 cells) to H(2)O(2)(0-300 microm) induced a dose-dependent increase in cytotoxicity, caspase-3 activation and PKCdelta cleavage. H(2)O(2)-induced proteolytic activation of PKC was delta mediated by the activation of caspase-3. Most interestingly, both the general Src tyrosine kinase inhibitor genistein (25 microm) and the p60(Src) tyrosine-specific kinase inhibitor (TSKI; 5 microm) dramatically inhibited H(2)O(2) and the Parkinsonian toxin 1-methyl-4-phenylpyridinium-induced PKCdelta cleavage, kinase activation, and apoptotic cell death. H(2)O(2) treatment also increased phosphorylation of PKCdelta at tyrosine site 311, which was effectively blocked by co-treatment with TSKI. Furthermore, N27 cells overexpressing a PKCdelta(Y311F) mutant protein exhibited resistance to H(2)O(2)-induced PKCdelta cleavage, caspase activation, and apoptosis. To our knowledge, these data demonstrate for the first time that phosphorylation of Tyr-311 on PKCdelta can regulate the proteolytic activation and proapoptotic function of the kinase in dopaminergic neuronal cells.     

Nicotine-induced phosphorylation of Akt through epidermal growth factor receptor and Src in PC12h cells

Nicotine treatment triggers calcium influx into neuronal cells, which promotes cell survival in a number of neuronal cells. Phosphoinositide (PI) 3-kinase and downstream PI3-kinase target Akt have been reported to be important in the calcium-mediated promotion of survival in a wide variety of cells. We investigated the mechanisms of nicotine-induced phosphorylation of Akt in PC12h cells, in comparison with nicotine-induced ERK phosphorylation. Nicotine induced Akt phosphorylation in a dose-dependent manner. A nicotinic acetylcholine receptor (nAChR) alpha7 subunit-selective inhibitor had no significant effect on nicotine-induced Akt phosphorylation, while a non-selective nAChR antagonist inhibited the phosphorylation. L-type voltage-sensitive calcium channel (VSCC) antagonists, calmodulin antagonist, and Ca2+/calmudulin-dependent protein kinase (CaM kinase) inhibitor prevented the nicotine-induced Akt phosphorylation. Three epidermal growth factor receptor (EGFR) inhibitors prevented the nicotine-induced phosphorylation of both extracellular signal-regulated protein kinase (p42/44 MAP kinase, ERK) and Akt. In contrast, an inhibitor of the Src family tyrosine kinase prevented the nicotine-induced Akt phosphorylation but not ERK phosphorylation. These results suggested that nicotine induces the activation of both PI3-kinase/Akt and ERK pathways via common pathways including non-alpha7-nAChRs, L-type VSCC, CaM kinase II and EGFR in PC12h cells, but Src family tyrosine kinases only participate in the pathway to activate Akt.     

Modulation of curcumin-induced Akt phosphorylation and apoptosis by PI3K inhibitor in MCF-7 cells

Curcumin has been shown to induce apoptosis in various malignant cancer cell lines. One mechanism of curcumin-induced apoptosis is through the PI3K/Akt signaling pathway. Akt, also known as protein kinase B (PKB), is a member of the family of phosphatidylinositol 3-OH-kinase regulated Ser/Thr kinases. The active Akt regulates cell survival and proliferation; and inhibits apoptosis. In this study we found that curcumin induces apoptotic cell death in MCF-7 cells, as assessed by MTT assay, DNA ladder formation, PARP cleavage, p53 and Bax induction. At apoptotic inducing concentration, curcumin induces a dramatic Akt phosphorylation, accompanied by an increased phosphorylation of glycogen synthase kinase 3β (GSK3β), which has been considered to be a pro-growth signaling molecule. Combining curcumin with PI3K inhibitor, LY290042, synergizes the apoptotic effect of curcumin. The inhibitor LY290042 was capable of attenuating curcumin-induced Akt phosphorylation and activation of GSK3β. All together, our data suggest that blocking the PI3K/Akt survival pathway sensitizes the curcumin-induced apoptosis in MCF-7 cells.