Suppression of ADAM17-mediated Lyn/Akt pathways induces apoptosis of human leukemia U937 cells: Bungarus multicinctus protease inhibitor-like protein-1 uncovers the cytotoxic mechanism

Effect of Bitis gabonica and Dendroaspis angusticeps snake venoms on apoptosis-related genes in human thymic epithelial cells

Background:

Certain environmental toxins permanently damage the thymic epithelium, accelerate immune senescence and trigger secondary immune pathologies. However, the exact underlying cellular mechanisms and pathways of permanent immune intoxication remain unknown. The aim of the present study was to demonstrate gene expressional changes of apoptosis-related cellular pathways in human thymic epithelial cells following exposure to snake venom from Bitis gabonica and Dendroaspis angusticeps.

Methods:

Snake venoms were characterized by analytical methods including reversed phase high-performance liquid chromatography and sodium dodecyl sulphate-polyacrylamide gel electrophoresis, then applied on human thymic epithelial cells (1889c) for 24 h at 10 μg/mL (as used in previous TaqMan Array study). Gene expressional changes restricted to apoptosis were assayed by TaqMan Array (Human Apoptosis Plate).

Results:

The most prominent gene expressional changes were shown by CASP5 (≈ 2.5 million-fold, confirmed by dedicated quantitative polymerase chain reaction) and CARD9 (0.016-fold) for B. gabonica, and BIRC7 (6.46-fold) and CASP1 (0.30-fold) for D. angusticeps.

Conclusion:

The observed apoptotic environment suggests that pyroptosis may be the dominant pathway through which B. gabonica and D. angusticeps snake venoms trigger thymic epithelial apoptosis following envenomation.

Phospholipase A2 from krait Bungarus fasciatus venom induces human cancer cell death in vitro

Background

Snake venoms are the complex mixtures of different compounds manifesting a wide array of biological activities. The venoms of kraits (genus Bungarus, family Elapidae) induce mainly neurological symptoms; however, these venoms show a cytotoxicity against cancer cells as well. This study was conducted to identify in Bungarus fasciatus venom an active compound(s) exerting cytotoxic effects toward MCF7 human breast cancer cells and A549 human lung cancer cells.

Methods

The crude venom of B. fasciatus was separated by gel-filtration on Superdex HR 75 column and reversed phase HPLC on C18 column. The fractions obtained were screened for cytotoxic effect against MCF7, A549, and HK2 cell lines using colorimetric assay with the tetrazolium dye MTT- 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide. The primary structure of active protein was established by ultra high resolution LC-MS/MS. The molecular mechanism of the isolated protein action on MCF7 cells was elucidated by flow cytometry.

Results

MTT cell viability assays of cancer cells incubated with fractions isolated from B. fasciatus venom revealed a protein with molecular mass of about 13 kDa possessing significant cytotoxicity. This protein manifested the dose and time dependent cytotoxicity for MCF7 and A549 cell lines while showed no toxic effect on human normal kidney HK2 cells. In MCF7, flow cytometry analysis revealed a decrease in the proportion of Ki-67 positive cells. As Ki-67 protein is a cellular marker for proliferation, its decline indicates the reduction in the proliferation of MCF7 cells treated with the protein. Flow cytometry analysis of MCF7 cells stained with propidium iodide and Annexin V conjugated with allophycocyanin showed that a probable mechanism of cell death is apoptosis. Mass spectrometric studies showed that the cytotoxic protein was phospholipase A₂. The amino acid sequence of this enzyme earlier was deduced from cloned cDNA, and in this work it was isolated from the venom as a protein for the first time. It is also the first krait phospholipase A₂ manifesting the cytotoxicity for cancer cells.

Thioredoxin-1 Negatively Modulates ADAM17 Activity Through Direct Binding and Indirect Reductive Activity

AIMS

A disintegrin and metalloprotease 17 (ADAM17) modulates signaling events by releasing surface protein ectodomains such as TNFa and the EGFR-ligands. We have previously characterized cytoplasmic thioredoxin-1 (Trx-1) as a partner of ADAM17 cytoplasmic domain. Still, the mechanism of ADAM17 regulation by Trx-1 is unknown, and it has become of paramount importance to assess the degree of influence that Trx-1 has on metalloproteinase ADAM17.

RESULTS

Combining discovery and targeted proteomic approaches, we uncovered that Trx-1 negatively regulates ADAM17 by direct and indirect effect. We performed cell-based assays with synthetic peptides and site-directed mutagenesis, and we demonstrated that the interaction interface of Trx-1 and ADAM17 is important for the negative regulation of ADAM17 activity. However, both Trx-1^K72A and catalytic site mutant Trx-1^C32/35S rescued ADAM17 activity, although the interaction with Trx-1^C32/35S was unaffected, suggesting an indirect effect of Trx-1. We confirmed that the Trx-1^C32/35S mutant showed diminished reductive capacity, explaining this indirect effect on increasing ADAM17 activity through oxidant levels. Interestingly, Trx-1^K72A mutant showed similar oxidant levels to Trx-1^C32/35S, even though its catalytic site was preserved. We further demonstrated that the general reactive oxygen species inhibitor, Nacetylcysteine (NAC), maintained the regulation of ADAM17 dependent of Trx-1 reductase activity levels; whereas the electron transport chain modulator, rotenone, abolished Trx-1 effect on ADAM17 activity.

INNOVATION

We show for the first time that the mechanism of ADAM17 regulation, Trx-1 dependent, can be by direct interaction and indirect effect, bringing new insights into the cross-talk between isomerases and mammalian metalloproteinases.

CONCLUSION

This unexpected Trx-1^K72A behavior was due to more dimer formation and, consequently, the reduction of its Trx-1 reductase activity, evaluated through dimer verification, by gel filtration and mass spectrometry analysis. Antioxid. Redox Signal. 29, 717-734.

Hydroquinone-induced FOXP3-ADAM17-Lyn-Akt-p21 signaling axis promotes malignant progression of human leukemia U937 cells

Hydroquinone (1,4-benzenediol; HQ), a major marrow metabolite of the leukemogen benzene, has been proven to evoke benzene-related hematological disorders and myelotoxicity in vitro and in vivo. The goal of the present study was to explore the role of FOXP3 in HQ-induced malignant progression of U937 human leukemia cells. U937 cells were treated with 5 μM HQ for 24 h, and the cells were re-suspended in serum-containing medium without HQ for 2 days. The same procedure was repeated three times, and the resulting U937/HQ cells were maintained in cultured medium containing 5 μM HQ. Proliferation and colony formation of U937/HQ cells were notably higher than those of U937 cells. Ten-eleven translocation methylcytosine dioxygenase-mediated demethylation of the Treg-specific demethylated region in FOXP3 gene resulted in higher FOXP3 expression in U937/HQ cells than in U937 cells. FOXP3-induced miR-183 expression reduced β-TrCP mRNA stability and suppressed β-TrCP-mediated Sp1 degradation, leading to up-regulation of Sp1 expression in U937/HQ cells. Sp1 up-regulation further increased ADAM17 and Lyn expression, and ADAM17 up-regulation stimulated Lyn activation in U937/HQ cells. Moreover, U937/HQ cells showed higher Lyn-mediated Akt activation and cytoplasmic p21 expression than U937 cells did. Abolishment of Akt activation decreased cytoplasmic p21 expression in U937/HQ cells. Suppression of FOXP3, ADAM17, and Lyn expression, as well as Akt inactivation, repressed proliferation and clonogenicity of U937/HQ cells. Together with the finding that cytoplasmic p21 shows anti-apoptotic and oncogenic activities in cancer cells, the present data suggest a role of FOXP3/ADAM17/Lyn/Akt/p21 signaling axis in HQ-induced hematological disorders.

Src family kinases and their role in hematological malignancies

The Src family protein tyrosine kinases (SFKs) are non-receptor intracellular kinases that have important roles in both hematopoiesis and leukemogenesis. The derangement of their expression or activation has been demonstrated to contribute to hematological malignancies. This review first examines the mechanisms of SFK overexpression and hyperactivation, emphasizing the dysregulation of the upstream modulators. Subsequently, the role of SFK up-regulation in the initiation, progression and therapy resistance of many hematological malignancies is also analyzed. The presented evidence endeavors to highlight the influence of SFK up-regulation on an extensive number of hematological malignancies and the need to consider them as candidates in targeted anticancer therapy.

A novel piperazine derivative potently induces caspase-dependent apoptosis of cancer cells via inhibition of multiple cancer signaling pathways

Despite rapid progress in anticancer drug development and improvement in clinical outcomes, the survival rate for many types of cancer is still unacceptably low. Therefore, it is crucial to discover novel anticancer drugs to both prevent and treat the disease. In recent years, the advent of combinatorial chemistry allows the design and parallel synthesis of millions of small compounds that have drug-like properties. In vitro high throughput screening of such compound libraries has allowed the identification of many new drug candidates that may be further evaluated for their efficacy and mechanism of action. The overall objective of this study was to identify small molecule compounds as candidates for anti-cancer drug development. We first used cell proliferation and cytotoxicity assays to identify compounds exhibiting anti-cancer activity in vitro in a leukemia cell line (K562). Six top compounds selected from the initial screening of a library of 2,560 compounds were further evaluated in multiple cancer cell lines to rank the drug candidates. The top candidate was further investigated to elucidate the molecular mechanism underlying its anticancer activity. Our studies suggest that this piperazine derivative effectively (GI50 = 0.06-0.16 μM) inhibits cancer cell proliferation and induces caspase-dependent apoptosis via inhibiting multiple cancer signaling pathways including the PI3K/AKT, the Src family kinases and the BCR-ABL pathways.

Hydroquinone-induced miR-122 down-regulation elicits ADAM17 up-regulation, leading to increased soluble TNF-α production in human leukemia cells with expressed Bcr/Abl

Studies on HQ-treated human leukemia K562 (Bcr/Abl-positive) cells were conducted to address the hydroquinone (HQ) mechanism that promotes soluble TNF-α (sTNF-α) production. HQ post-translationally down-regulated cell surface TNF-α expression increases the release of sTNF-α into K562 cell culture medium. Meanwhile, HQ increased ADAM17 mRNA stability, leading to ADAM17 up-regulation in HQ-treated cells. Knock-down of ADAM17 abrogated HQ-induced sTNF-α secretion. HQ-evoked miR-122 down-regulation was proven to promote ADAM17 mRNA stability and up-regulate ADAM17 expression. HQ-induced p38 MAPK and JNK activation were responsible for suppression of miR-122 promoter luciferase activity and miR-122 expression. Activation of p38 MAPK and JNK elicited phosphorylation of c-Jun, ATF-2 and c-Fos, and knock-down of c-Jun, ATF-2 and c-Fos restored miR-122 expression in HQ-treated cells. Chromatin immunoprecipitating and DNA affinity purification assay revealed c-Jun, ATF-2 and c-Fos binding to the miR-122 gene promoter region. Moreover, HQ-induced sTNF-α production in Bcr/Abl-positive leukemia cell lines KU812 and MEG-01 was also connected with miR-122 down-regulation and ADAM17 up-regulation, while HQ was unable to affect miR-122 and ADAM-17 expression on Bcr/Abl-negative leukemia U937 cells. Taken together, our data indicate that HQ induces down-regulation of miR-122 expression, leading to ADAM17 up-regulation and ADAM17-mediated TNF-α shedding. Consequently, HQ treatment increases the production of sTNF-α in leukemia cells with expressed Bcr/Abl.

ADAM17 mediates hypoxia-induced drug resistance in hepatocellular carcinoma cells through activation of EGFR/PI3K/Akt pathway

A disintegrin and metalloproteinase-17 (ADAM17) is a member of the metalloproteinase superfamily and involved in the cleavage of ectodomain of many transmembrane proteins. ADAM17 is overexpressed in a variety of human tumors, which is associated with tumor development and progression. In the present study, we sought to investigate the expression and function of ADAM17 in hypoxia-treated hepatocellular carcinoma (HCC) cells. Western blot analysis was used to measure the expression of ADAM17 in HCC cell lines (Hep3B and HepG2 cells). Annexin V/PI double staining was performed to analyze the effects of ADAM17 on hypoxia-mediated cisplatin resistance. ADAM17 expression was upregulated by hypoxia treatment in HCC cells at both mRNA and protein levels. Overexpression of ADAM17 reduced cisplatin-induced apoptosis in HCC cells, accompanies by less cleavage of caspase-3 and poly (ADP-ribose) polymerase (PARP). Forced expression of ADAM17 enhanced the phosphorylation of epidermal growth factor receptor (EGFR) and Akt without affecting the expression of total EGFR and Akt. Pretreatment with EGFR inhibitor AG1478 or phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 rescued ADAM17-mediated cisplatin resistance of HCC cells. ADAM17 silencing attenuated hypoxia-induced cisplatin resistance and enhanced the accumulation of cleaved caspase-3 and PARP. Western blot analysis showed that overexpression of hypoxia-inducible factor-1α (HIF-1α), a transcription factor, upregulated the expression of ADAM17 and HIF-1α silencing downregulated the expression of ADAM17 in hypoxia-treated HCC cells, indicating the regulation of ADAM17 by HIF-1α. Taken together, our results indicated that ADAM17 is upregulated by hypoxia and contributes to hypoxia-induced cisplatin resistance via EGFR/PI3K/Akt pathway.

p38 MAPK/PP2Acα/TTP pathway on the connection of TNF-α and caspases activation on hydroquinone-induced apoptosis

This study investigated tumor necrosis factor-α (TNF-α)-mediated death pathway contribution to hydroquinone (HQ) cytotoxicity in human leukemia U937 cells. HQ-induced apoptosis of human leukemia U937 cells was characterized by the increase in mitochondrial membrane depolarization, procaspase-8 degradation and tBid production. Downregulation of Fas-associated death domain protein (FADD) blocked HQ-induced procaspase-8 degradation and rescued the viability of HQ-treated cells, suggesting the involvement of a death receptor-mediated pathway in HQ-induced cell death. HQ induced increased TNF-α mRNA stability led to TNF-α protein expression upregulation, whereas HQ suppressed TNF-α-mediated NFκB pathway activation. HQ elicited protein phosphatase 2A catalytic subunit α (PP2Acα) upregulation via p38 mitogen-activated protein kinase (MAPK)-mediated CREB/c-Jun/ATF-2 phosphorylation, and PP2Acα upregulation was found to promote tristetraprolin (TTP) degradation. Suppression of p38 MAPK activation and protein phosphatase 2A (PP2A) activity abrogated TNF-α upregulation and procaspase degradation in HQ-treated cells. Overexpression of TTP suppressed HQ-induced TNF-α upregulation and restored the viability of HQ-treated cells. Moreover, TTP overexpression increased TNF-α mRNA decay in HQ-treated cells. Taken together, our data indicate that HQ elicits TNF-α upregulation via p38 MAPK/PP2A-mediated TTP downregulation, and suggest that the TNF-α-mediated death pathway is involved in HQ-induced U937 cell death. The same pathway was also proven to be involved in the HQ-induced death of human leukemia HL-60 and Jurkat cells.

Suppression of Akt/Foxp3-mediated miR-183 expression blocks Sp1-mediated ADAM17 expression and TNFα-mediated NFκB activation in piceatannol-treated human leukemia U937 cells

To address the mechanism of piceatannol in inhibiting TNFα-mediated pathway, studies on piceatannol-treated human leukemia U937 cells were conducted. Piceatannol treatment reduced TNFα shedding and NFκB activation and decreased the release of soluble TNFα into the culture medium of U937 cells. Moreover, ADAM17 expression was down-regulated in piceatannol-treated cells. Over-expression of ADAM17 abrogated the ability of piceatannol to suppress TNFα-mediated NFκB activation. Piceatannol-evoked β-TrCP up-regulation promoted Sp1 degradation, thus reducing transcriptional level of ADAM17 gene in U937 cells. Piceatannol treatment induced p38 MAPK phosphorylation but inactivation of Akt and ERK. In contrast to p38 MAPK inhibitor or restoration of ERK activation, transfection of constitutive active Akt abolished the effect of piceatannol on β-TrCP, Sp1 and ADAM17 expression. Piceatannol-elicited down-regulation of miR-183 expression was found to cause β-TrCP up-regulation. Inactivation of Akt resulted in Foxp3 down-regulation and reduced miR-183 expression in piceatannol-treated cells. Knock-down of Foxp3 and chromatin immunoprecipitating revealed that Foxp3 genetically regulated transcription of miR-183 gene. Taken together, our data indicate that suppression of Akt/Foxp3-mediated miR-183 expression blocks Sp1-mediated ADAM17 expression in piceatannol-treated U937 cells. Consequently, piceatannol suppresses TNFα shedding, leading to inhibition of TNFα/NFκB pathway.

The role of ADAM-mediated shedding in vascular biology

Within the vasculature the disintegrins and metalloproteinases (ADAMs) 8, 9, 10, 12, 15, 17, 19, 28 and 33 are expressed on endothelial cells, smooth muscle cells and on leukocytes. As surface-expressed proteases they mediate cleavage of vascular surface molecules at an extracellular site close to the membrane. This process is termed shedding and leads to the release of a soluble substrate ectodomain thereby critically modulating the biological function of the substrate. In the vasculature several surface molecules undergo ADAM-mediated shedding including tumour necrosis factor (TNF) α, interleukin (IL) 6 receptor α, L-selectin, vascular endothelial (VE)-cadherin, the transmembrane CX3C-chemokine ligand (CX3CL) 1, Notch, transforming growth factor (TGF) and heparin-binding epidermal growth factor (HB-EGF). These substrates play distinct roles in vascular biology by promoting inflammation, permeability changes, leukocyte recruitment, resolution of inflammation, regeneration and/or neovascularisation. Especially ADAM17 and ADAM10 are capable of cleaving many substrates with diverse function within the vasculature, whereas other ADAMs have a more restricted substrate range. Therefore, targeting ADAM17 or ADAM10 by pharmacologic inhibition or gene knockout not only attenuates the inflammatory response in animal models but also affects tissue regeneration and neovascularisation. Recent discoveries indicate that other ADAMs (e.g. ADAM8 and 9) also play important roles in vascular biology but appear to have more selective effects on vascular responses (e.g. on neovascularisation only). Although, targeting of ADAM17 and ADAM10 in inflammatory diseases is still a promising approach, temporal and spatial as well as substrate-specific inhibition approaches are required to minimise undesired side effects on vascular cells.