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Combined-modality treatment has improved the outcome in cases of various solid tumors, and radiosensitizers are used to enhance the radiotherapeutic efficiency. Rosiglitazone, a synthetic ligand of peroxisome proliferator-activated receptors gamma used in the treatment of type-2 diabetes, has been shown to reduce tumor growth and metastasis in human cancer cells, and may have the potential to be used as a radiosensitizer in radiotherapy for human colorectal cancer cells. In this study, rosiglitazone treatment significantly reduced the cell viability of p53-wild type HCT116 cells but not p53-mutant HT-29 cells. Interestingly, rosiglitazone pretreatment enhanced radiosensitivity in p53-mutant HT-29 cells but not HCT116 cells, and prolonged radiation-induced G(2)/M arrest and enhanced radiation-induced cell growth inhibition in HT-29 cells. Pretreatment with rosiglitazone also suppressed radiation-induced H2AX phosphorylation in response to DNA damage and AKT activation for cell survival; on the contrary, rosiglitazone pretreatment enhanced radiation-induced caspase-8, -9, and -3 activation and PARP cleavage in HT-29 cells. In addition, pretreatment with a pan-caspase inhibitor, zVAD-fmk, attenuated the levels of caspase-3 activation and PARP cleavage in radiation-exposed cancer cells in combination with rosiglitazone pretreatment. Our results provide proof for the first time that rosiglitazone suppresses radiation-induced survival signals and DNA damage response, and enhances the radiation-induced apoptosis signaling cascade. These findings can assist in the development of rosiglitazone as a novel radiosensitizer., (Copyright 2010 Elsevier Inc. All rights reserved.)

Although induction of apoptosis by avian reovirus has been demonstrated in primary chicken embryonic fibroblast and several cell lines, to date, the potential significance of avian reovirus (ARV)-induced apoptosis and its pathways in cultured cells are still largely unknown. We now provide the first evidence of upregulation of p53 and Bax and specifically for Bax translocation from cytosol to mitochondria following infection with a cytoplasmically replicating RNA virus. Bax translocation to the mitochondria led to the release of mitochondrial proapoptic factors cytochrome c and Smac/DIABLO from mitochondria to the cytosol, but not the release of apoptosis-inducting factor. Activation of caspases-9 and -3 which cleaves the enzyme poly(ADP-ribose) polymerase in ARV-infected BHK-21 cells was also detected. Internucleosomal DNA cleavage was prevented by caspase inhibitors, further demonstrating that ARV-induced apoptosis was executed through caspase-dependent mechanisms. Stable expression of human bcl-2 in BHK-21 cells not only blocked ARV-induced apoptosis and DNA fragmentation but also reduced the level of infectious virus production and its spread in BHK-21 cells infected with ARV at a low multiplicity of infection. All our data suggest that p53 and the mitochondria-mediated pathway played an important regulatory role in ARV-induced apoptosis in BHK-21 cells. To further study the pathogenesis of ARV infection, a dual-labeling assay was used for the simultaneous detection of cells containing viral antigen and apoptotic cells. Dual-labeling assay revealed that the majority of antigen-expressing cells were not apoptotic. Remarkably, some apoptotic but non-antigen-expressing cells were frequently located in the vicinity of antigen-expressing cells. Syncytium formation in ARV-infected BHK-21 cells undergoing apoptosis, was apparent in large syncytia at late infection times, indicating a correlation between virus replication and apoptosis in cultured cells.

The second open reading frame of avian reovirus S1 gene segment encodes a 17 kDa non-structural protein, named p17. The biological role of p17 is fully unknown so far. Using trypan blue dye exclusion and MTT assay, we demonstrated that the ectopic expression of p17 results in the reduction of viable cell number and cell proliferation rate of Vero, BHK, 293, and HeLa cells. Measurement of LDH activity and DNA fragmentation analysis revealed that p17 expression did not cause cell death or apoptosis. These data indicated that the p17 possessed the growth retardation function. Semi-quantitative RT-PCR and Western blotting revealed that p17-expressing cells induced the expression of CDK inhibitor p21cip1/waf1 in a time- and dose-dependent manner, but the transcripts of CDK inhibitor p15INK4b, p16INK4a, or p27kip were not altered. In the presence of p17, the p53 protein level and p53-driven reporter activity were elevated significantly. Dominant negative p53 alleviated the p21 accumulation, p53 activation, and growth inhibition effect induced by p17. Taken together, these studies revealed a possible intrinsic function of p17 in growth regulation through the activation of p53 and p21cip1/waf1.

Phosphoglucose isomerase/autocrine motility factor (PGI/AMF) catalyzes the isomerization between glucose-6-phosphate and fructose-6-phosphate, and is involved in cytokine activity, mitogenesis, differentiation, oncogenesis, and tumor metastasis. Presently, we demonstrate that exogenous PGI/AMF stimulates the migration of Huh7 and HepG2 hepatoma cells, but not Hep3B cells. Inhibition of PGI/AMF by PGI/AMF specific inhibitor 5-phospho-D-arabinonate markedly repressed the cellular migration. RT-PCR was used to examine the expression profile of matrix metalloproteinases (MMPs). MMP-3 transcripts, protein level, and secreted form were significantly upregulated in PGI/AMF-treated Huh7 and HepG2 cells, but not in Hep3B cells. MMP-3 inhibition abolished the PGI/AMF-induced cell motility. The observations are consistent with a downstream mediation role of MMP-3 in PGI/AMF-stimulated tumor cell metastasis.