Mechanism of the inhibition of leukemia cell growth and induction of apoptosis through the activation of ATR and PTEN by the topoisomerase inhibitor 3EZ, 20Ac-ingenol.

The PI3K/Akt signaling pathway is constitutively activated in various leukemias. In the present study, the topoisomerase inhibitor, 3EZ, 20Ac-ingenol, was more effective in inhibiting the growth of BALL-1 cells than that of normal lymphocyte cells. ATM/ATR protein levels were increased, PTEN protein was upregulated, and p-Akt protein was downregulated at early time points after treatment with 3EZ, 20Ac-ingenol. In further experiments, p53 protein expression was increased, and H2AX phosphorylation and p21 protein expression were induced after treatment with 3EZ, 20Ac-ingenol. Moreover, the activation of caspase 3 followed decrease in the Bcl-2/Bax ratio after treatment with 3EZ, 20Ac-ingenol, and accumulation of sub-G1 phase cells was observed in flow cytometry analyses. These data suggest that 3EZ, 20Ac-ingenol-induced DNA damage downregulates p-Akt and upregulates ATR leading to cell cycle arrest and increased apoptosis in BALL-1 cells.

Berberine Sensitizes Human Ovarian Cancer Cells to Cisplatin Through miR-93/PTEN/Akt Signaling Pathway.

BACKGROUND: Berberine, a well-known component of the Chinese herbal medicine Huanglian, has wide range of biochemical and pharmacological effects, including antineoplastic effect, but the exact mechanisms remain unclear. The aim of the present study was to evaluate the potential chemo-sensitization effect of berberine in ovarian cancer cell line A2780. METHODS: The expression of miR-93 was measure by RT-PCR. The target of miR-93 was confirmed by luciferase activity assay. Hoechst 33258 staining, Annexin V and PI double staining were used for apoptosis analysis. RESULTS: In this study, we found A2780/DDP cells that were incubated with berberine combined with cisplatin had a significantly lower survival than the control group. Berberine enhanced cisplatin induced apoptosis and induced G0/G1 cell cycle arrest in A2780 cells. Next, we observed that the miR-93 levels in cisplatin resistant cell lines were higher than that in cisplatin sensitive cell lines. Furthermore, our study found berberine could inhibit miR-93 expression and function in ovarian cancer, as shown by an increase of its target PTEN, an important tumor suppressor in ovarian cancer. A2780 cells that were treated with PTEN siRNA had increased survival compared to NC group and this could be partly alleviated by the AKT inhibitor Triciribine. More importantly, A2780 cells that were treated with PTEN siRNA had a survival pattern that is similar to cells with miR-93 overexpression. CONCLUSION: The results suggested that berberine modulated the sensitivity of cisplatin through miR-93/PTEN/AKT signaling pathway in the ovarian cancer cells.

Role of PTEN in neutrophil extracellular trap formation.

NETosis has been associated with a particular mode of cell death although it is still controversial as to what extent autophagy is involved in NETosis. Class I/AKT/mTOR pathway is a key regulator of autophagy. PTEN tumor suppressor gene encodes a dual specificity phosphatase that antagonizes the phosphatidylinositol 3-kinase in class the I/AKT/mTOR pathway. In this study, we investigated the effects of PTEN down-regulation as well as overexpression on NETosis. Our results show that 35% of HL-60 differentiated neutrophil-like cells generated NETs by PMA. The portion of the population that produced NETs in PTEN knockdown HL-60 differentiated neutrophils was 9% and in PTEN overexpressed HL-60 differentiated neutrophils, it was 56%. Our results show that increasing PTEN expression increases NETs formation in neutrophils, and its suppression reduces NETs.

Treponema denticola major outer sheath protein impairs the cellular phosphoinositide balance that regulates neutrophil chemotaxis.

The major outer sheath protein (Msp) of Treponema denticola inhibits neutrophil polarization and directed chemotaxis together with actin dynamics in vitro in response to the chemoattractant N-formyl-methionine-leucine-phenylanine (fMLP). Msp disorients chemotaxis through inhibition of a Rac1-dependent signaling pathway, but the upstream mechanisms are unknown. We challenged murine bone marrow neutrophils with enriched native Msp to determine the role of phospholipid modifying enzymes in chemotaxis and actin assembly downstream of fMLP-stimulation. Msp modulated cellular phosphoinositide levels through inhibition of phosphatidylinositol 3-kinase (PI3-kinase) together with activation of the lipid phosphatase, phosphatase and tensin homolog deleted on chromosome 10 (PTEN). Impaired phosphatidylinositol[(3,4,5)]-triphosphate (PIP3) levels prevented recruitment and activation of the downstream mediator Akt. Release of the actin capping proteins gelsolin and CapZ in response to fMLP was also inhibited by Msp exposure. Chemical inhibition of PTEN restored PIP3 signaling, as measured by Akt activation, Rac1 activation, actin uncapping, neutrophil polarization and chemotaxis in response to fMLP-stimulation, even in the presence of Msp. Transduction with active Rac1 also restored fMLP-mediated actin uncapping, suggesting that Msp acts at the level of PIP3 in the hierarchical feedback loop of PIP3 and Rac1 activation. Taken together, Msp alters the phosphoinositide balance in neutrophils, impairing the cell "compass", which leads to inhibition of downstream chemotactic events.

Arsenic trioxide induces G2/M arrest in hepatocellular carcinoma cells by increasing the tumor suppressor PTEN expression.

Arsenic trioxide (As(2)O(3)), an effective agent against acute promyelocytic leukemia, has been reported to inhibit the viability of solid tumors cell lines recently. The detailed molecular mechanism underlying the As(2)O(3)-induced inactivation of the cdc2 and possible functional role of PTEN in the observed G2/M arrest has yet to be elucidated. Here, we assessed the role of PTEN in regulation of As(2)O(3)-mediated G2/M cell cycle arrest in Hepatocellular carcinoma cell lines (HepG2 and SMMC7721). After 24 h following treatment, As(2)O(3) induced a concentration-dependent accumulation of cells in the G2/M phase of the cell cycle. The sustained G2/M arrest by As(2)O(3) is associated with decreased cdc2 protein and increased phospho-cdc2(Tyr15). As(2)O(3) treatment increased Wee1 levels and decreased phospho-Wee1(642). Moreover, As(2)O(3) substantially decreased the Ser473 and Thr308 phosphorylation of Akt and upregulated PTEN expression. Downregulation of PTEN by siRNA in As(2)O(3) -treated cells increased phospho-Wee1(Ser642) while decreased phospho-cdc2(Tyr15), resulting in decreased the G2/M cell cycle arrest. Therefore, induction of G2/M cell cycle arrest by As(2)O(3) involved upregulation of PTEN.

The PTEN-AKT3 signaling cascade as a therapeutic target in melanoma.

Melanocytes undergo extensive genetic changes during transformation into aggressive melanomas. These changes deregulate genes whose aberrant activity promotes the development of this disease. The phosphoinositide-3-kinase (PI3K) and mitogen-activated protein (MAP) kinase pathways are two key signaling cascades that have been found to play prominent roles in melanoma development. These pathways relay extra-cellular signals via an ordered series of consecutive phosphorylation events from cell surface throughout the cytoplasm and nucleus regulating diverse cellular processes including proliferation, survival, invasion and angiogenesis. It is generally accepted that therapeutic agents would need to target these two pathways to be an effective therapy for the long-term treatment of advanced-stage melanoma patients. This review provides an overview of the PI3 kinase pathway focusing specifically on two members of the pathway, called PTEN and Akt3, which play important roles in melanoma development. Mechanisms leading to deregulation of these two proteins and therapeutic implications of targeting this signaling cascade to treat melanoma are detailed in this review.

Imatinib blocks migration and invasion of medulloblastoma cells by concurrently inhibiting activation of platelet-derived growth factor receptor and transactivation of epidermal growth factor receptor.

Platelet-derived growth factor (PDGF) receptor (PDGFR) expression correlates with metastatic medulloblastoma. PDGF stimulation of medulloblastoma cells phosphorylates extracellular signal-regulated kinase (ERK) and promotes migration. We sought to determine whether blocking PDGFR activity effectively inhibits signaling required for medulloblastoma cell migration and invasion. DAOY and D556 human medulloblastoma cells were treated with imatinib mesylate (Gleevec), a PDGFR tyrosine kinase inhibitor, or transfected with small interfering RNA (siRNA) to PDGFRB to test the effects of blocking PDGFR phosphorylation and expression, respectively. PDGFR cell signaling, migration, invasion, survival, and proliferation following PDGF-BB stimulation, with and without PDGFR inhibition, were measured. PDGF-BB treatment of cells increased PDGFRB, Akt and ERK phosphorylation, and transactivated epidermal growth factor receptor (EGFR), which correlated with enhanced migration, survival, and proliferation. Imatinib (1 µmol/L) treatment of DAOY and D556 cells inhibited PDGF-BB- and serum-mediated migration and invasion at 24 and 48 h, respectively, and concomitantly inhibited PDGF-BB activation of PDGFRB, Akt, and ERK but increased PTEN expression and activity. Imatinib treatment also induced DAOY cell apoptosis at 72 h and inhibited DAOY and D556 cell proliferation at 48 h. siRNA silencing of PDGFRB similarly inhibited signaling, migration, and survival and both siRNA and imatinib treatment inhibited PDGF-BB-mediated EGFR transactivation, indicating that the effects of imatinib treatment are specific to PDGFRB target inhibition. These results indicate that PDGFRB tyrosine kinase activity is critical for migration and invasion of medulloblastoma cells possibly by transactivating EGFR; thus, imatinib may represent an important novel therapeutic agent for the treatment of medulloblastoma.