Salmonella infections can become chronic and increase the risk of cancer. The mechanisms by which specific Salmonella organisms contribute to cancer, however, are still unknown. Live and attenuated Salmonella are used as vectors to target cancer cells, but there have been no systematic studies of the oncogenic potential of chronic Salmonella infections in cancer models. AvrA, a pathogenic product of Salmonella, is inserted into host cells during infection and influences eukaryotic cell pathways. In the current study, we colonized mice with Salmonella AvrA-sufficient or AvrA-deficient Salmonella typhimirium strains and induced inflammation-associated colon cancer by azoxymethane/dextran sulfate sodium (AOM/DSS). We confirmed Salmonella persisted in the colon for up to 45 weeks. Salmonella was identified not only in epithelial cells on the colonic luminal surface and base of the crypts but also in invading tumors. Tumor incidence in the AvrA+infected group was 100% compared with 51.4% in the AOM/DSS group without bacterial gavage and 56.3% in mice infected with the AvrA- strain. Infection with AvrA+ strain also altered tumor distribution from the distal to proximal colon that might reflect changes in the microbiome. AvrA-expressing bacteria also upregulated beta-catenin signaling as assessed by decreased beta-catenin ubiquitination, increased nuclear beta-catenin and increased phosphorylated-beta-catenin (Ser552), a marker of proliferating stem-progenitor cells. Other β-catenin targets increased by AvrA included Bmi1, a cancer stem cell marker, matrix metalloproteinase-7, and cyclin D1. In summary, AvrA-expressing Salmonella infection activates β-catenin signals and enhances colonic tumorigenesis. Our findings provide important new mechanistic insights into how a bacterial protein targets proliferating stem-progenitor cells and contributes to cancer development. Our observations also raise a note of caution regarding the use of mutant Salmonella organisms as vectors for anti-cancer therapy. Finally, these studies could suggest biomarkers (such as AvrA level in gut) to assess cancer risk in susceptible individuals and infection-related dysregulation of β-catenin signaling in cancer.

Activation of the nuclear transcription factor peroxisome proliferator-activated receptor ; (PPAR;) inhibits growth and survival of hepatocellular carcinoma (HCC) cell lines. To further investigate the function of PPAR; in HCC, PPAR; expression patterns in primary tumors were examined, and the responses of two HCC cell lines to PPAR; activation and inhibition were compared. PPAR; expression was increased in HCC and benign-appearing peritumoral hepatocytes compared with remote benign hepatocytes. Both compound PPAR; inhibitors and PPAR; small interfering RNAs prevented HCC cell lines from adhering to the extracellular matrix. Loss of adhesion was followed by caspase-dependent apoptosis (anoikis). PPAR; inhibitors had no effect on initial B B1 integrin-mediated adhesion, or on total focal adhesion kinase levels but did reduce focal adhesion kinase phosphorylation. The PPAR; inhibitor T0070907 was significantly more efficient at causing cancer cell death than the activators troglitazone and rosiglitazone. T0070907 caused cell death by reducing adhesion and inducing anoikis, whereas the activators had no direct effect on adhesion and caused cell death at much higher concentrations. In conclusion, PPAR; overexpression is present in HCC. Inhibition of PPAR; function causes HCC cell death by preventing adhesion and inducing anoikis-mediated apoptosis. PPAR; inhibitors represent a potential novel treatment approach to HCC.

The nuclear transcription factor peroxisome proliferator-activated receptor-gamma (PPARc) has been identified as an important therapeutic target in murine models of colorectal cancer (CRC). To examine whether PPARc inhibition has therapeutic effects in late-stage CRC, the effects of PPARc inhibitors on CRC cell survival were examined in CRC cell lines and a murine CRC model. Low doses (0.1-1 lM) of PPARc inhibitors (T0070907, GW9662 and BADGE) did not affect cell survival, while higher doses (10-100 lM) of all 3 PPARc inhibitors caused caspase-dependent apoptosis in HT-29, Caco-2 and LoVo CRC cell lines. Apoptosis was preceded by altered cell morphology, and this alteration was not prevented by caspase inhibition. PPARc inhibitors also caused dual G and M cell cycle arrest, which was not required for apoptosis or for morphologic alterations. Furthermore, PPARc inhibitors triggered loss of the microtubule network. Notably, unlike other standard antimicrotubule agents, PPARc inhibitors caused microtubule loss by regulating tubulin post-transcriptionally rather than by altering microtubule polymerization or dynamics. Proteasome inhibition by epoxomicin was unable to prevent tubulin loss. siRNA-mediated reduction of PPARc and PPARd proteins did not replicate the effects of PPARc inhibitors or interfere with the inhibitors' effects on apoptosis, cell cycle or tubulin. PPARc inhibitors also reduced CRC cell migration and invasion in assays in vitro and reduced both the number and size of metastases in a HT-29/ SCID xenograft metastatic model of CRC. These results suggest that PPARc inhibitors are a novel potential antimicrotubule therapy for CRC that acts by directly reducing microtubule precursors. ' 2006 Wiley-Liss, Inc.