Several studies reported linkage between bacterial infections and carcinogenesis. Streptococcus bovis was traditionally considered as a lower grade pathogen frequently involved in bacteremia and endocarditis. This bacterium became important in human health as it was shown that 25-80% of patients who presented a S.bovis bacteremia had also a colorectal tumor. Moreover, in previous experiments, we demonstrated that S.bovis or S.bovis wall extracted antigens (WEA) were able to promote carcinogenesis in rats. The aim of the present study was: (i) to identify the S.bovis proteins responsible for in vitro pro-inflammatory properties; (ii) to purify them; (iii) to examine their ability to stimulate in vitro IL-8 and COX-2 expression by human colon cancer cells; and (iv) to assess in vivo their pro-carcinogenic potential in a rat model of colon carcinogenesis. The purified S300 fraction, as determined by proteomic analysis, contained 72 protein spots in two-dimensional gel electrophoresis representing 12 different proteins able to trigger human epithelial colonic Caco-2 cells and rat colonic mucosa to release CXC chemokines (human IL-8 or rat CINC/GRO) and prostaglandins E2, correlated with an in vitro over-expression of COX-2. Moreover, these proteins were highly effective in the promotion of pre-neoplastic lesions in azoxymethane-treated rats. In the presence of these proteins, Caco-2 cells exhibited enhanced phosphorylation of the three classes of MAP kinases. Our results show a relationship between the pro-inflammatory potential of S.bovis proteins and their pro-carcinogenic properties, confirming the linkage between inflammation and colon carcinogenesis. These data support the hypothesis that colonic bacteria can contribute to cancer development particularly in chronic infection/inflammation diseases where bacterial components may interfere with cell function.

The human bowel contains a large and dynamic bacterial population that is not only essential for intestinal health, but also critical for the development of diseases such as cancer. In this respect, the Gram-positive bacterium Streptococcus bovis has been associated with colon cancer for many years. To investigate the clinical importance of this association, an immunocapture mass spectrometry assay was developed that can generate infection-related protein profiles. The composition of these profiles is governed by the capture of specific antigens by serum antibodies from colon cancer patients. This assay showed that S. bovis antigen profiles could distinguish 11 out of 12 colon cancer patients from 8 control subjects, whereas antigen profiles derived from the gut bacterium Escherichia coli were not diagnostic for colon cancer. Moreover, S. bovis antigen profiles were also detected in polyp patients, indicating that infection with this bacterium does occur early during carcinogenesis. Highly accurate tandem mass spectrometry was used to identify one of the diagnostic antigens as a surface-exposed heparin-binding protein, which might be involved in attachment of S. bovis to tumor cells. Together, these findings corroborate the hypothesis that colonic lesions provide a specific niche for S. bovis, resulting in tumor-associated ''silent'' infections. These infections, however, only become apparent in colon cancer patients with a compromised immune system (bacteremia) or coincidental cardiac valve lesions (endocarditis). This makes profiling of the humoral immune response against ''silent'' S. bovis infections a promising diagnostic tool for the early detection of human colon cancer, which is crucial for the effective treatment of this disease. ' 2006 Wiley-Liss, Inc. Key words: colon cancer; early detection; diagnostic bacterial antigens; Streptococcus bovisThe human bowel is the natural habitat for a large and dynamic bacterial community, which is essential for the control of intestinal epithelial homeostasis and human health.1,2 However, gut flora might also be an essential factor in certain diseases, including multisystem organ failure, inflammatory bowel diseases, and colon cancer.3 Although bacterial infections were originally not considered to be a major cause of cancer, accumulating evidence suggests that bacteria can induce or promote cancer by inflammation. In this model, tumor formation is caused or promoted by induction of cell proliferation and the production of mutagenic free radicals and n-nitroso compounds. In this respect, Helicobacter pylori has been the first invasive bacterium to be identified as a definite cause of gastric cancer. 4 Similarly, an association between Streptococcus bovis infection and colon cancer has been known for at least 25 years. Moreover, recent research has shown that S. bovis can promote intestinal carcinogenesis in a rat model for colon cancer.6 Certain cell surface proteins of this bacterium can induce inflammation, supporting a linkage between S. bovis, inflammation and ...

As in rheumatoid arthritis (RA), it was demonstrated recently that bacterial fragments of DNA or rRNA are present in the joint and therefore could play a role in inducing or perpetuating the disease, this work was initiated to define mechanisms that account for the stimulatory activities of the oral streptococcal modulin, protein I/II, on fibroblast‐like synoviocytes (FLSs) from RA patients. FLSs from RA patients were stimulated with protein I/II, and expression of interleukin (IL)‐6 and IL‐8 mRNA was evaluated by reverse transcription–polymerase chain reaction (RT–PCR). Immunoblotting by antibodies specific for activated forms of MAPKs and electrophoretic mobility shift assays (EMSAs) were performed to study downstream signalling, which allowed the synthesis of IL‐6 and IL‐8. We reported that protein I/II interactions with FLSs from RA patients trigger the synthesis and release of IL‐6 and IL‐8. We also demonstrated that protein I/II enhances the phosphorylation of ERK 1/2, p38 and JNKs and that ERK 1/2 and JNK MAPKs seem to play a more important role than p38 in protein I/II‐mediated synthesis of IL‐6 and IL‐8. Our experiments also indicated that stimulation of FLSs with protein I/II induces nuclear translocation of NF‐κB, AP‐1‐binding activity and that NF‐κB plays a major role in IL‐6 and IL‐8 secretion from activated cells.

Geraniol, a natural component of plant essential oils, has antiproliferative effects on human colon cancer cells. To obtain more insight into its mechanism of action, we studied its effect on the resting membrane potential and on the expression of proteins involved in cell signaling pathways. Since geraniol is a well known inhibitor of mevalonate metabolism, the effect of mevalonate supplementation on geraniol-triggered growth inhibition was also determined. Geraniol (400 M) induced membrane depolarization with a decrease of membrane resistance due to local perforation of the cell membrane. Incubation of Caco-2 cells with geraniol (400 M) for 6 h caused a 60% reduction of protein kinase C (PKC) activity. After 16 h of incubation, geraniol decreased by 50% the amount of active forms of p44/p42 extracellular signal-regulated protein kinases (ERK). Mevalonate supplementation did not reverse inhibition of cell growth by geraniol. These results indicate that the antiproliferative effect of geraniol on Caco-2 cells was not related to a limitation of the mevalonate pool but was directly linked to the perturbation of cell membrane function leading to the reduction of PKC activity and to the decreased expression of p44/p42 ERK active forms.

Streptococcus mutans possesses different cell wall molecules, such as protein of the I/II family, the serotype f polysaccharide rhamnose glucose polymer (RGP), and lipoteichoic acid (LTA), which act as adhesins and modulins, allowing S. mutans to colonize teeth and cause dental caries and pulpitis. We tested several isogenic mutants of S. mutans defective in protein I/II and/or RGP, as well as purified modulins such as protein I/II, RGP, and LTA, for their binding and activation abilities on monocytic, dental pulp (DP), and periodontal ligament (PDL) cells. Our results demonstrate that both protein I/II and RGP play important roles in streptococcal adherence to human monocytic and fibroblastic cells, whereas LTA is only a minor adhesin. In the activation process, the cytokine response elicited is polarized toward a Th1 response which seems principally due to protein I/II and RGP. Even if protein I/II seems to be more efficient in its purified form in triggering cells to release interleukin-8 (IL-8), RGP is the most efficient cytokine-stimulating component in intact bacteria, while LTA plays only a minor role. In cell activation, we showed, by using either cytochalasin D or coated ligands, that internalization of either S. mutans, S. mutans isogenic mutants, or purified ligands is not necessary to trigger cells to release IL-8. We also showed that, besides the implication of monocytes in pulpal inflammation, fibroblast-like cells such as DP and PDL cells are also actively implicated in local inflammation and in the generation of a Th1 response after stimulation with S. mutans cells or antigens