[Show abstract][Hide abstract]ABSTRACT: It is not yet understood how the enhanced expression of pancreatic adenocarcinoma up-regulated factor (PAUF; a novel oncogene identified in our recent studies), contributes to the oncogenesis of pancreatic cells. We herein report that PAUF up-regulates the expression and transcriptional activity of β-catenin while the suppression of PAUF by shRNA down-regulates β-catenin. The induction of b-catenin by PAUF is mediated by the activities of Akt and GSK-3β, but inhibition of downstream ERK does not reduce β-catenin expression. To test whether PAUF emulates either the Wnt3a-mediated or the protein kinase A-mediated signaling pathway for the stabilization of β-catenin, we examined the phosphorylation status of β-catenin in the presence of PAUF compared with that of β-catenin during treatment with Wnt3a or dibutyryl cAMP, a cell permeable cyclic AMP analogue. PAUF expression induces phosphorylation at Ser-33/37/Thr-41 and Ser-675 of β-catenin but no phosphorylation at Ser-45, indicating that a unique phosphorylation pattern of b-catenin is caused by PAUF. Finally, the expression of PAUF up-regulates both cyclin-D1 and c-Jun, target genes of β-catenin, leading to a rapid proliferation of pancreatic cells; conversely decreased PAUF expression (by shRNA) results in the reduced proliferation of pancreatic cells. Treatment with hexachlorophene (an inhibitor of β-catenin) reduces the proliferation of pancreatic cells despite the presence of PAUF. Taken together, we propose that PAUF can up-regulate and stabilize β-catenin via a novel pattern of phosphorylation, thereby contributing to the rapid proliferation of pancreatic cancer cells.
Full-text · Article · Dec 2010 · Experimental and Molecular Medicine
[Show abstract][Hide abstract]ABSTRACT: The tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) has been used to treat a variety of cancer cells. However, since some gastric cancer cells are resistant to TRAIL, we explored whether reovirus induces cytolysis in TRAIL-resistant gastric cancer cells. We found that TRAIL-resistant SNU-216 gastric cancer cells were susceptible to apoptosis by reovirus infection. Furthermore, co-treatment with reovirus and TRAIL accelerated apoptosis of SNU-216 cells by down-regulation of Akt activation as assessed by a very low activation of Akt in TRAIL-sensitive SNU-668 gastric cancer cells. Inhibition of Akt signaling with wortmannin or suppression of Akt expression with sh-Akt lentivirus promoted reovirus-mediated apoptosis of SNU-216 gastric cancer cells. Reovirus infection also down-regulates the activation of signaling molecules such as Ras and ERK involved in cell proliferation and survival but not the activation of p38 MAPK involved in cellular stress. In addition, the co-treatment with reovirus and TRAIL resulted in cleavage of caspase-8, caspase-9 and Bid, leading to a decrease in the mitochondrial membrane potential, indicating that reovirus may utilize the mitochondrial intrinsic apoptotic pathway in TRAIL-resistant SNU-216 gastric cancer cells. Accordingly, we first demonstrate that reovirus infection down-regulates Akt activation, leading to apoptosis of TRAIL-resistant gastric cancer cells.
No preview · Article · Apr 2010 · International Journal of Oncology
[Show abstract][Hide abstract]ABSTRACT: Reovirus functions as an oncolytic agent for many types of cancer including colon cancer. Although most studies have emphasized the role of activated Ras signaling in enhancing reoviral oncolysis in susceptible cells, we note that many colon cancers also display elevated beta-catenin. Thus, it is possible that enhanced beta-catenin may augment reoviral susceptibility in colon cancer cells. To explore this hypothesis, HEK293 cells were treated with the glycogen synthase kinase (GSK)-3beta inhibitor LiCl, thereby inducing beta-catenin, followed by reoviral infection. Co-administration with LiCl indeed enhanced cell death compared to reovirus infection alone, but this was not associated with elevated reoviral replication. Similarly, HEK293 cells expressing the Frizzled-1 receptor in Wnt3a-conditioned medium also showed reovirus replication equivalent to that in cells in control medium, further suggesting that up-regulation of beta-catenin does not enhance the replication of reovirus. Instead, we observed that inhibition of GSK-3beta with LiCl decreased reovirus-induced NF-kappaB activation, leading to accelerated apoptosis via caspase 8 activation. We further found that colon cancer HCT116 cells were sensitized to apoptosis by co-treatment with reovirus and a GSK-3beta inhibitor, AR-A014418. Finally, we identified that inhibition of NF-kappaB sensitized apoptosis of HEK293 or HCT 116 cells during reovirus infection. Taken together, we propose that inhibition of GSK-3beta sensitizes reovirus-induced apoptosis of colon cancer cells by down-regulation of NF-kappaB activity, offering a potentially improved therapeutic strategy for the treatment of colon cancer.
No preview · Article · Oct 2009 · International Journal of Oncology
[Show abstract][Hide abstract]ABSTRACT: Many studies have shown that the activation of beta-catenin signaling can promote oncogenesis, and it is therefore of interest to find agents that modulate this pathway. Recent work has shown using B lymphoma cells that infection by Epstein-Barr virus (EBV) and expression of its latent membrane protein (LMP)-1, cause increases in the expression of beta-catenin and cellular transformation. Conversely, results from cell-based small molecule screening studies have shown that the antibiotic hexachlorophene can down-regulate beta-catenin in colon cancer cells. Here we report that hexachlorophene also counteracts the elevated beta-catenin levels in EBV-infected B lymphomas. This is associated with restoration in levels of Siah-1 (an E3 ubiquitin ligase that is active in beta-catenin regulation) which had been diminished by LMP-1. Our results suggest that Siah-1 is targeted by both LMP-1 and hexachlorophene with opposite effects. The hexachlorophene modulation of Siah-1 and beta-catenin is independent of p53 and results in reduced expression of cyclin-D1 and c-Myc (target genes of beta-catenin), leading to the growth arrest of B lymphoma cells. From these results we propose that hexachlorophene may provide a novel therapeutic strategy for EBV-infected B lymphoma cells by reducing beta-catenin levels via the restoration of Siah-1.