Apoptosis of human neutrophils induced by protein phosphatase 1/2A inhibition is caspase-independent and serine protease-dependent

PDGFR and IGF-1R Inhibitors Induce a G2/M Arrest and Subsequent Cell Death in Human Glioblastoma Cell Lines

Glioblastomas are highly resistant to radiation and chemotherapy. Currently, there are no effective therapies for this type of tumor. Signaling mechanisms initiated by PDGFR and IGF-1R are important in glioblastoma, and inhibition of the signal transduction pathways initiated by these receptors could be a useful alternative strategy for glioblastoma treatment. We have studied the effects of the PDGFR inhibitor JNJ-10198409 (JNJ) and the IGF-1R inhibitor picropodophyllin (PPP) in glioblastoma cell lines as well as in primary cultures derived from patients affected by this type of tumor. JNJ and PPP treatment blocked PDGFR and IGF-1R signaling respectively and reduced Akt and Erk 1/2 phosphorylation. Both inhibitors diminished cell proliferation, inducing a G2/M block of the cell cycle. Cell death induced by JNJ was caspase-dependent, Annexin-V positive and caused PARP cleavage, especially in T98 cells, suggesting an apoptotic mechanism. However, cell death induced by PPP was not completely inhibited by caspase inhibitors in all cell lines apart from LN-229 cells, indicating a caspase-independent mechanism. Several inhibitors targeted against different cell death pathways could not block this caspase-independent component, which may be a non-programmed necrotic mechanism. Apoptotic arrays performed in T98 and LN-229 cells upon JNJ and PPP treatment revealed that procaspase 3 levels were augmented by both drugs in T98 cells and only by JNJ in LN229-cells. Furthermore, XIAP and survivin levels were much higher in LN-229 cells than in T98 cells, revealing that LN-229 cells are more susceptible to undergo caspase-independent cell death mechanisms. JNJ and PPP combination was more effective than each treatment alone.

The effect of inhibition of PP1 and TNFα signaling on pathogenesis of SARS coronavirus

BACKGROUND

The complex interplay between viral replication and host immune response during infection remains poorly understood. While many viruses are known to employ anti-immune strategies to facilitate their replication, highly pathogenic virus infections can also cause an excessive immune response that exacerbates, rather than reduces pathogenicity. To investigate this dichotomy in severe acute respiratory syndrome coronavirus (SARS-CoV), we developed a transcriptional network model of SARS-CoV infection in mice and used the model to prioritize candidate regulatory targets for further investigation.

RESULTS

We validated our predictions in 18 different knockout (KO) mouse strains, showing that network topology provides significant predictive power to identify genes that are important for viral infection. We identified a novel player in the immune response to virus infection, Kepi, an inhibitory subunit of the protein phosphatase 1 (PP1) complex, which protects against SARS-CoV pathogenesis. We also found that receptors for the proinflammatory cytokine tumor necrosis factor alpha (TNFα) promote pathogenesis, presumably through excessive inflammation.

CONCLUSIONS

The current study provides validation of network modeling approaches for identifying important players in virus infection pathogenesis, and a step forward in understanding the host response to an important infectious disease. The results presented here suggest the role of Kepi in the host response to SARS-CoV, as well as inflammatory activity driving pathogenesis through TNFα signaling in SARS-CoV infections. Though we have reported the utility of this approach in bacterial and cell culture studies previously, this is the first comprehensive study to confirm that network topology can be used to predict phenotypes in mice with experimental validation.

Inhibition of protein phosphatase-1 and -2A decreases the chemosensitivity of leukemic cells to chemotherapeutic drugs

The phosphorylation of key proteins balanced by protein kinases and phosphatases are implicated in the regulation of cell cycle and apoptosis of malignant cells and influences anticancer drug actions. The efficacy of daunorubicin (DNR) in suppression of leukemic cell survival was investigated in the presence of tautomycin (TM) and calyculin A (CLA), specific membrane permeable inhibitors of protein phosphatase-1 (PP1) and -2A (PP2A), respectively. CLA (50 nM) or TM (1μM) suppressed viability of THP-1 and KG-1 myeloid leukemia cell lines to moderate extents; however, they significantly increased survival upon DNR-induced cell death. CLA increased the phosphorylation level of Erk1/2 and PKB/Akt kinases, the retinoblastoma protein (pRb), decreased caspase-3 activation by DNR and increased the phosphorylation level of the inhibitory sites (Thr696 and Thr853) in the myosin phosphatase (MP) target subunit (MYPT1) as well as in a 25kDa kinase-enhanced phosphatase inhibitor (KEPI)-like protein. TM induced enhanced phosphorylation of pRb only, suggesting that this event may be a common factor upon CLA-induced PP2A and TM-induced PP1 inhibitory influences on cell survival. Silencing PP1 by siRNA in HeLa cells, or overexpression of Flag-KEPI in MCF-7 cells coupled with inducing its phosphorylation by PMA or CLA, resulted in increased phosphorylation of pRb. Our results indicate that PP1 directly dephosphorylates pRb, while PP2A might have an indirect influence via mediating the phosphorylation level of PP1 inhibitory proteins. These data imply the importance of PP1 inhibitory proteins in controlling the phosphorylation state of key proteins and regulating drug sensitivity and apoptosis in leukemic cells.

Okadaic acid induces morphological changes, apoptosis and cell cycle alterations in different human cell types

Okadaic acid (OA) is a marine toxin produced by dinoflagellate species which is frequently accumulated in molluscs usual in the human diet. The exact action mechanism of OA has not been described yet and the results of most reported studies are often conflicting. The aim of this work was to evaluate the OA effects on morphology, cell cycle and apoptosis induction by means of light microscopy and flow cytometry, in three different types of human cells (leukocytes, HepG2 cells and SHSY5Y cells). Cells were treated with a range of OA concentrations in the presence and absence of S9 fraction. OA induced morphological changes in all the cell types studied, and cell cycle disruption only in leukocytes and neuronal cells. SHSY5Y cells were the most sensitive to OA assault. Results obtained in the presence and absence of metabolic activation were similar, suggesting that OA acts both directly and indirectly. Furthermore, OA was found to increase the subG(1) region in the flow cytometry cell cycle analysis, suggesting induction of apoptosis. These results were confirmed by the employment of specific methodologies for studying apoptosis such as caspase 3 activation and annexin V staining. Increases in the apoptosis rate were obtained in all the cells treated in the absence of S9 fraction, accompanied by increases in caspase 3 activation, suggesting that apoptosis induced by OA is a caspase 3-dependent process. Nevertheless, in the presence of S9 fraction no apoptosis was detected, indicating a metabolic detoxifying activity, although necrosis was observed in neuroblastoma cells.

Regulation of DNA fragmentation: the role of caspases and phosphorylation

DNA fragmentation is a hallmark of apoptosis that is induced by apoptotic stimuli in various cell types. Apoptotic signal pathways, which eventually cause DNA fragmentation, are largely mediated by the family of cysteinyl aspartate-specific protease caspases. Caspases mediate apoptotic signal transduction by cleavage of apoptosis-implicated proteins and the caspases themselves. In the process of caspase activation, reversible protein phosphorylation plays an important role. The activation of various proteins is regulated by phosphorylation and dephosphorylation, both upstream and downstream of caspase activation. Many kinases/phosphatases are involved in the control of cell survival and death, including the mitogen-activated protein kinase signal transduction pathways. Reversible protein phosphorylation is involved in the widespread regulation of cellular signal transduction and apoptotic processes. Therefore, phosphatase/kinase inhibitors are commonly used as apoptosis inducers/inhibitors. Whether protein phosphorylation induces apoptosis depends on many factors, such as the type of phosphorylated protein, the degree of activation and the influence of other proteins. Phosphorylation signaling pathways are intricately interrelated; it was previously shown that either induction or inhibition of phosphorylation causes cell death. Determination of the relationship between protein and phosphorylation helps to reveal how apoptosis is regulated. Here we discuss DNA fragmentation and protein phosphorylation, focusing on caspase and serine/threonine protein phosphatase activation.

Okadaic acid induces DNA fragmentation via caspase-3-dependent and caspase-3-independent pathways in Chinese hamster ovary (CHO)-K1 cells

DNA fragmentation is a hallmark of apoptosis that occurs in a variety of cell types; however, it remains unclear whether caspase-3 is required for its induction. To investigate this, we produced caspase-3 knockout Chinese hamster ovary (CHO)-K1 cells and examined the effects of gene knockout and treatment with caspase-3 inhibitors. Okadaic acid (OA) is a potent inhibitor of the serine/threonine protein phosphatases (PPs) PP1 and PP2A, which induce apoptotic cellular reactions. Treatment of caspase-3(-/-) cells with OA induced DNA fragmentation, indicating that caspase-3 is not an essential requirement. However, in the presence of benzyloxycarbonyl-Asp-Glu-Val-Asp (OMe) fluoromethylketone (z-DEVD-fmk), DNA fragmentation occurred in CHO-K1 cells but not in caspase-3(-/-) cells, suggesting that caspase-3 is involved in OA-induced DNA fragmentation that does not utilize DEVDase activity. In the absence of caspase-3, DEVDase activity may play an important role. In addition, OA-induced DNA fragmentation was reduced but not blocked in CHO-K1 cells, suggesting that caspase-3 is involved in caspase-independent OA-induced DNA fragmentation. Furthermore, OA-induced cleavage of caspase-3 and DNA fragmentation were blocked by pretreatment with the wide-ranging serine protease inhibitor 4-(2-aminoethyl)-benzenesulfonyl fluoride hydrochloride. These results suggest that serine proteases regulate DNA fragmentation upstream of caspase-3.

A new pathway of staphylococcal pathogenesis: apoptosis-like death induced by Staphopain B in human neutrophils and monocytes

Circulating neutrophils and monocytes form the first line of cellular defense against invading bacteria. Here, we describe a novel and specific mechanism of disabling and eliminating phagocytes by Staphylococcus aureus. Staphopain B (SspB) selectively cleaved CD11b on phagocytes, which rapidly acquired features of cell death. SspB-treated phagocytes expressed phosphatidylserine as well as annexin I and became permeable to propidium iodide, thus demonstrating distinctive features of both apoptosis and necrosis, respectively. The cell death observed was caspase and Syk tyrosine kinase independent, whilst cytochalasin D efficiently inhibited the staphopain-induced neutrophil killing. Neutrophil and monocyte cell death was not affected by integrin clustering ligands (ICAM-1 or fibrin) and was prevented, and even reversed, by IgG. This protective effect was dependent on the Fc fragment, collectively suggesting cooperation of the CD16 receptor and integrin Mac-1 (CD11b/CD18). We conclude that SspB, particularly in the presence of staphylococcal protein A, may reduce the number of functional phagocytes at infection sites, thus facilitating colonization and dissemination of S. aureus.

Serine protease inhibitor nafamostat given before reperfusion reduces inflammatory myocardial injury by complement and neutrophil inhibition

Animal data strongly support a role for inflammation in myocardial ischemia reperfusion injury. Attempts at cardioprotection by immunomodulation (such as with the specific C5 antibody pexelizumab) in humans have been disappointing. We hypothesized that a broader spectrum antiinflammatory agent might yield successful cardioprotection. The serine protease inhibitor nafamostat (FUT-175), which is already in clinical use, is a potent antiinflammatory synthetic serine protease inhibitor with anticomplement activity that we tested in a well-established rabbit model of 1 hour of myocardial ischemia followed by 3 hours of reperfusion. Compared to vehicle-treated animals, nafamostat (1 mg/kg of body weight) administered 5 minutes before reperfusion significantly reduced myocardial injury assessed by plasma creatine kinase activity (38.1 +/- 6.0 versus 57.9 +/- 3.7I U/g protein; P < 0.05) and myocardial necrosis (23.6 +/- 3.1% versus 35.7 +/- 1.0%; P < 0.05) as well as myocardial leukocyte accumulation (P < 0.05). In parallel in vitro studies, Nafamostat was a significantly more potent broad spectrum complement suppressor than C1 inhibitor. Nafamostat appears to have capability as an inhibitor of both complement pathways and as a broad-spectrum antiinflammatory agent by virtue of its serine protease inhibition. Administration of nafamostat before myocardial reperfusion after ischemia produced significant, dose-dependent cardioprotection. Reduced leukocyte accumulation and complement activity seem involved in the mechanism of this cardioprotective effect.

Anti-inflammatory actions of aprotinin provide dose-dependent cardioprotection from reperfusion injury

BACKGROUND AND PURPOSE

Myocardial injury following ischaemia and reperfusion has been attributed to activation and transmigration of polymorphonuclear leukocytes (PMNs) with release of mediators including oxygen-derived radicals and proteases causing damage.

EXPERIMENTAL APPROACH

We studied the serine protease inhibitor aprotinin in an in vivo rabbit model of 1 h of myocardial ischaemia followed by 3 h of reperfusion (MI+R). Aprotinin (10,000 Ukg(-1)) or its vehicle were injected 5 min prior to the start of reperfusion.

KEY RESULTS

Myocardial injury was significantly reduced with aprotinin treatment as indicated by a reduced necrotic area (11+/-2.7% necrosis as percentage of area at risk after aprotinin; 24+/-3.1% after vehicle; P<0.05) and plasma creatine kinase activity (12.2+/-1.5 and 17.3+/-2.3 IU g(-1) protein in aprotinin and vehicle groups, respectively, P<0.05). PMN infiltration (assessed by myeloperoxidase activity) was significantly decreased in aprotinin-treated animals compared to vehicle (P<0.01). Histological analysis also revealed a substantial increase in PMN infiltration following MI+R and this was significantly reduced by aprotinin therapy (44+/-15 vs 102+/-2 PMN mm2 in aprotinin vs vehicle-treated animals, P<0.05). In parallel in vitro experiments, aprotinin inhibited neutrophil-endothelium interaction by reducing PMN adhesion on isolated, activated aortic endothelium. Finally, immunohistochemical analysis illustrated aprotinin significantly reduced myocardial apoptosis following MI+R.

CONCLUSIONS AND IMPLICATIONS

Inhibition of serine proteases by aprotinin inhibits an inflammatory cascade initiated by MI+R. The cardioprotective effect appears to be at least partly due to reduced PMN adhesion and infiltration with subsequently reduced myocardial necrosis and apoptosis.

A single intrauterine injection of the serine protease inhibitor 4-(2-aminoethyl)benzenesulfonyl fluoride hydrochloride reversibly inhibits embryo implantation in mice

BACKGROUND

The study was conducted to investigate the inhibitory effect of 4-(2-aminoethyl)benzenesulfonyl fluoride hydrochloride (AEBSF) on embryo implantation in mice with a view to identifying whether it might be a suitable agent for postcoital contraception.

STUDY DESIGN

The anti-implantation efficacy of AEBSF was determined by counting the number of visible implanted embryos on Day 8 of pregnancy following a single intrauterine injection of AEBSF at doses of 30, 300 and 3000 microg per mouse uterine horn on Day 3 of pregnancy. The reversibility of the inhibitory effect of AEBSF on implantation was further evaluated by observing the outcome of a subsequent pregnancy without AEBSF treatment.

RESULTS

A dose-dependent inhibitory effect of AEBSF on embryo implantation in vivo was observed. Morphological analysis revealed no significant cytotoxicity of AEBSF on the mouse uterine epithelia. Furthermore, the anti-implantation effect of AEBSF was reversible.

CONCLUSION

Intrauterine administration of AEBSF at an appropriate dose might provide a basis for the development of novel contraception.