Salmonella Protein AvrA Activates the STAT3 Signaling Pathway in Colon Cancer1

Salmonella infection in humans can become chronic, which leads to low-grade persistent inflammation. These chronic infections increase the risk of several gastrointestinal diseases, including cancer. Salmonella AvrA is a multifunctional protein that influences eukaryotic cell pathways by regulating ubiquitination and acetylation. In an animal model, we have demonstrated that infection with AvrA-expressing Salmonella induces beta-catenin signals and enhances colonic tumorigenesis. Beta-catenin signaling is a key player in intestinal proliferation and tumorigenesis. The relative contributions of AvrA-induced proliferation and inflammation on tumorigenesis, however, are unknown. STAT3 is activated in chronically inflamed intestines in human inflammatory bowel diseases and in colitis-associated colon cancer. In the current study, mice were colonized with Salmonella AvrA-sufficient or AvrA-deficient bacterial strains. Then, inflammation-associated colon cancer was induced through the use of azoxymethane/dextran sulfate sodium. We determined that AvrA-expressing bacteria activated the STAT3 pathway, which is predicted to enhance proliferation and promote tumorigenesis. Transcriptional activity of STAT3 and its target genes were upregulated by Salmonella expressing AvrA, thus promoting proliferation and intestinal tumorigenesis. Our findings provide new insights regarding a STAT3-dependent mechanism by which the specific bacterial product AvrA enhances the development of infection-associated colon cancer. These insights might suggest future biomarkers to risk assessment and early detection of infection-related cancer.