Wen-Hsin Liu

Involvement of p38 MAPK- and JNK-modulated expression of Bcl-2 and Bax in Naja nigricollis CMS-9-induced apoptosis of human leukemia K562 cells.

CMS-9, a phospholipase A(2) (PLA(2)) isolated from Naja nigricollis venom, induced apoptosis of human leukemia K562 cells, characterized by mitochondrial depolarization, modulation of Bcl-2 family members, cytochrome c release and activation of caspases 9 and 3. Moreover, an increase in intracellular Ca2+ concentration and the production of reactive oxygen species (ROS) was noted. Pretreatment with BAPTA-AM (Ca2+ chelator) and N-acetylcysteine (NAC, ROS scavenger) proved that Ca2+ was an upstream event in inducing ROS generation. Upon exposure to CMS-9, activation of p38 MAPK and JNK was observed in K562 cells. BAPTA-AM or NAC abrogated CMS-9-elicited p38 MAPK and JNK activation, and rescued viability of CMS-9-treated K562 cells. SB202190 (p38 MAPK inhibitor) and SP600125 (JNK inhibitor) suppressed CMS-9-induced dissipation of mitochondrial membrane potential, Bcl-2 down-regulation, Bax up-regulation and increased mitochondrial translocation of Bax. Inactivation of PLA(2) activity reduced drastically the cytotoxicity of CMS-9, and a combination of lysophosphatidylcholine and stearic acid mimicked the cytotoxic effects of CMS-9. Taken together, our data suggest that CMS-9-induced apoptosis of K562 cells is catalytic activity-dependent and is mediated through mitochondria-mediated death pathway triggered by Ca2+/ROS-evoked p38 MAPK and JNK activation.

Amsacrine suppresses matrix metalloproteinase-2 (MMP-2)/MMP-9 expression in human leukemia cells.

This study explores the suppression mechanism of amsacrine (4‐(9‐Acridinylamino)‐N‐(methanesulfonyl)‐m‐anisidine hydrochloride) on matrix metalloproteinase‐2 (MMP‐2) and MMP‐9 expression in human leukemia cells. Amsacrine attenuated cell invasion with decreased MMP‐2/MMP‐9 protein expression and mRNA levels in U937, Jurkat, HL‐60, K562, KU812, and MEG‐01 cells. Moreover, amsacrine reduced both MMP‐2/MMP‐9 promoter luciferase activity and MMP‐2/MMP‐9 mRNA stability in leukemia cells. Studies on amsacrine‐treated U937 cells revealed that amsacrine‐elicited ROS generation induced JNK and p38 MAPK activation but reduced the phospho‐ERK level. Amsacrine‐induced ERK inactivation and p38 MAPK/JNK activation were demonstrated to suppress MMP‐2/MMP‐9 promoter luciferase activity and promote MMP‐2/MMP‐9 mRNA decay, respectively. p38 MAPK/JNK activation led to up‐regulation of protein phosphatase 2A catalytic subunit α (PP2Acα) in amsacrine‐treated U937 cells. Okadaic acid (PP2A inhibitor) treatment increased MMP‐2/MMP‐9 mRNA stability in amsacrine‐treated cells, whereas PP2Acα over‐expression increased MMP‐2/MMP‐9 mRNA decay. Amsacrine‐induced MMP‐2/MMP‐9 down‐regulation was also related to PP2Acα up‐regulation on Jurkat, HL‐60, K562, KU812, and MEG‐01 cells. Collectively, our data indicate that amsacrine induces MMP‐2/MMP‐9 down‐regulation via simultaneous suppression of genetic transcription and mRNA stability in human leukemia cells. J. Cell. Physiol. 229: 588–598, 2014.

Cross talk between p38MAPK and ERK is mediated through MAPK-mediated protein phosphatase 2A catalytic subunit α and MAPK phosphatase-1 expression in human leukemia U937 cells.

This study explores the signaling transduction cascade of ERK and p38 MAPK on regulating MAPK phosphatase-1 (MKP-1) and protein phosphatase 2A catalytic subunit α (PP2Acα) expression in caffeine-treated human leukemia U937 cells. Caffeine induced an increase in the intracellular Ca(2+) concentration and ROS generation leading to p38 MAPK activation and ERK inactivation, respectively. Caffeine treatment elicited MKP-1 down-regulation and PP2Acα up-regulation. The transfection of constitutively active MEK1 or pretreatment with SB202190 (p38 MAPK inhibitor) abolished the caffeine effect on MKP-1 and PP2Acα expression. Caffeine repressed ERK-mediated c-Fos phosphorylation but evoked p38 MAPK-mediated CREB phosphorylation. Knockdown of c-Fos and CREB by siRNA showed that c-Fos and CREB were responsible for MKP-1 and PP2Acα expression, respectively. Promoter and chromatin immunoprecipitating assay supported the role of c-Fos and CREB in regulating MKP-1 and PP2Acα expression. Moreover, transfection of dominant negative MKP-1 cDNA led to p38 MAPK activation and PP2Acα down-regulation in U937 cells, while PP2A inhibitor attenuated caffeine-induced ERK inactivation and MKP-1 down-regulation. Taken together, our data indicate that a reciprocal relationship between ERK-mediated MKP-1 expression and p38 MAPK-mediated PP2Acα expression crucially regulates ERK and p38 MAPK phosphorylation in U937 cells.

Catalytic activity-independent pathway is involved in phospholipase A2-induced apoptotic death of human leukemia U937 cells via Ca2+-mediated p38 MAPK activation and mitochondrial depolarization

In view of the controversial role of catalytic activity on the cytotoxicity of phospholipase A(2) (PLA(2)), the present study is conducted to explore whether PLA(2) induces apoptotic process of human leukemia U937 cells through catalytic activity-independent pathway. Modification of His-48 (according to the sequence alignment with porcine pancreatic PLA(2)) with p-bromophenacyl bromide (BPB) caused over 99.9% drop in enzymatic activity Naja naja atra PLA(2). It was found that BPB-PLA(2)-induced apoptotic death of U937 cells was associated with mitochondrial depolarization, modulation of Bcl-2 family members, cytochrome c release and activation of caspases 9 and 3. Upon exposure to BPB-PLA(2), elevation of intracellular Ca(2+) levels and p38 MAPK activation were observed in U937 cells. Pretreatment with BAPTA-AM (Ca(2+) chelator) and nifedipine (L-type Ca(2+) channel blocker) abrogated Ca(2+) increase and p38 MAPK activation, and rescued viability of BPB-PLA(2)-treated U937 cells. BPB-PLA(2)-induced dissipation of mitochondrial membrane potential and down-regulation of Bcl-2 were suppressed by SB202190 (p38MAPK inhibitor). Although PLA(2) mutants in which His-48 and Asp-49 were substituted by Ala and Lys, respectively, did not display detectable PLA(2) activity, they induced death of U937 cells. The signaling pathway of PLA(2) mutants in inducing cell death was indistinguishable from that of BPB-PLA(2). Taken together, our data indicate that catalytic activity-independent pathway is involved in PLA(2)-induced apoptotic death of human leukemia U937 cells via mitochondria-mediated death pathway triggering by Ca(2+)-mediated p38 MAPK activation.

Roles of lysine residues and N-terminal α-amino group in membrane-damaging activity of Taiwan cobra cardiotoxin 3 toward anionic and zwitterionic phospholipid vesicles.

In contrast to a slight increase in activity toward phosphatidylcholine (EYPC)/dimyristoyl phosphatidic acid (DMPA) vesicles, guanidination of Naja naja atra cardiotoxin 3 (CTX3) and selective trinitrophenylation of N-terminal alpha-amino group enhanced notably membrane-damaging activity on EYPC/egg yolk sphingomyelin (EYSM) vesicles. Chemically modified CTX3 showed a reduction in its hemolytic activity and cytotoxicity. These reflected that membrane-damaging activity of CTX3 was affected by phospholipid compositions. Phospholipid-binding capability and oligomeric assembly upon binding with lipid vesicles did not closely correlate with membrane-damaging potency of native and modified CTX3. Moreover, different topographical contacts and distinctive modes for the binding of CTX3 and its modified derivatives with anionic phospholipid vesicles (EYPC/DMPA) and zwitterionic phospholipid vesicles (EYPC/EYSM) were observed. Compared with in the case of EYPC/DMPA, the interaction between CTX molecules and EYPC/EYSM was drastically reduced by increasing salt concentration and heparin. Taken together, our data indicate that guanidination of Lys residues and trinitrophenylation of alpha-amino group alter differently the interacted modes upon absorption on anionic phospholipid vesicles and zwitterionic phospholipid vesicles. The findings also suggest that positively charged residues of CTX3 play a distinctive role in damaging anionic and zwitterionic phospholipid vesicles.

Membrane-damaging activity with A chain and B chain of β-bungarotoxin.

Beta-bungarotoxin (beta-Bgt) consists of A chain (a phospholipase A2 subunit) and B chain, cross-linked by an intersubunit disulfide bridge. In contrast to a marginal activity noted with beta-Bgt, recombinant A1 chain and B1 chain markedly induced release of calcein from phospholipid vesicles. Reduction of intersubunit disulfide bond by dithiothreitol or glutathione enhanced membrane-damaging activity of beta-Bgt. Moreover, phospholipid-binding capability of recombinant A1 and B1 chains was higher than that of beta-Bgt. In contrast to beta-Bgt, A1 and B1 chains preferably bound lipids with a preference for anionic over zwitterionic phospholipids. Removal of positively charged residues lying on the interface between A chain and B chain resulted in abolishment of membrane-permeabilizing activity of B chain. Taken together, our data indicate that both A and B chains possess the capability to induce vesicle leakage, and reduction of interchain disulfide bond markedly releases this ability from intact beta-Bgt molecule.

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 5xa0μM HQ for 24xa0h, and the cells were re-suspended in serum-containing medium without HQ for 2xa0days. The same procedure was repeated three times, and the resulting U937/HQ cells were maintained in cultured medium containing 5xa0μM 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.

The Association Between p38 MAPK‐Mediated TNF‐α/TNFR2 up‐Regulation and 2‐(4‐Aminophenyl)‐7‐Methoxybenzothiazole‐Induced Apoptosis in Human Leukemia U937 Cells

The primary cause of treatment failures in acute myeloid leukemia is usually associated with defects in the apoptotic pathway. Several studies suggest that 2‐(4‐aminophenyl)‐7‐methoxybenzothiazole (7‐OMe‐APBT) may potentially induce apoptosis of cancer cells. Thus, the present study was conducted to explore the cytotoxic effect of 7‐OMe‐APBT on human leukemia U937 cells. The apoptosis of human leukemia U937 cells induced by 7‐OMe‐APBT was characterized by an increase in mitochondrial membrane depolarization, procaspase‐8 degradation, and tBid production. Down‐regulation of FADD blocked 7‐OMe‐APBT‐induced procaspase‐8 degradation and rescued the viability of 7‐OMe‐APBT‐treated cells, suggesting the involvement of a death receptor‐mediated pathway in 7‐OMe‐APBT‐induced cell death. Increased TNF‐α expression, TNFR2 expression, and p38 MAPK phosphorylation were noted in 7‐OMe‐APBT‐treated cells. Pretreatment with a p38 MAPK inhibitor abolished 7‐OMe‐APBT‐induced TNF‐α and TNFR2 up‐regulation. 7‐OMe‐APBT stimulated p38 MAPK/c‐Jun‐mediated transcriptional up‐regulation of TNFR2, while the increased TNF‐α mRNA stability led to TNF‐α up‐regulation in 7‐OMe‐APBT‐treated cells. Treatment with 7‐OMe‐APBT up‐regulated protein phosphatase 2A catalytic subunit α (PP2Acα) expression via the p38 MAPK/c‐Jun/ATF‐2 pathway, which, in turn, promoted tristetraprolin (TTP) degradation. Pretreatment with a protein phosphatase 2A inhibitor or TTP over‐expression abrogated TNF‐α up‐regulation in 7‐OMe‐APBT‐treated cells. Abolishment of TNF‐α up‐regulation or knock‐down of TNFR1/TNFR2 by siRNA restored the viability of 7‐OMe‐APBT‐treated cells. Taken together, our data indicate a connection between p38 MAPK‐mediated TNF‐α and TNFR2 up‐regulation and 7‐OMe‐APBT‐induced TNF‐α‐mediated death pathway activation in U937 cells. The same pathway also elucidates the mechanism underlying 7‐OMe‐APBT‐induced death of human leukemia HL‐60 cells. J. Cell. Physiol. 230: 130–141, 2016.