The oncogenic role of Streptococcus gallolyticus subsp. gallolyticus is linked to activation of multiple cancer-related signaling pathways

Streptococcus gallolyticus subsp. gallolyticus (SGG), an opportunistic gram-positive pathogen responsible for septicemia and endocarditis in the elderly, is often associated with colon cancer (CRC). In this work, we investigated the oncogenic role of SGG strain UCN34 using the azoxymethane (AOM)-induced CRC model in vivo, organoid formation ex vivo and proteomic and phosphoproteomic analyses from murine colons. We showed that SGG UCN34 accelerates colon tumor development in the murine CRC model. Full proteome and phosphoproteome analysis of murine colons chronically colonized by SGG UCN34 or the closely related non-pathogenic S. gallolyticus subsp. macedonicus (SGM) revealed that 164 proteins and 725 phosphorylation sites were differentially regulated following colonization by SGG UCN34. Ingenuity Pathway Analysis (IPA) indicates a pro-tumoral shift specifically induced following colonization by SGG UCN34, as most proteins and phosphoproteins identified were associated with digestive cancer. Comprehensive analysis of the altered phosphoproteins using ROMA software revealed significantly elevated activities in several cancer hallmark pathways affecting tumoral cells and their microenvironment, i.e. MAPK (ERK, JNK and p38), mTOR and integrin/ILK/actin signaling, in SGG UCN34 colonized colon. Importantly, analysis of protein arrays of human colon tumors colonized with SGG showed up-regulation of PI3K/Akt/mTOR and MAPK pathways, providing clinical relevance to our findings. To test SGGs capacity to induce pre-cancerous transformation of the murine colonic epithelium, we grew ex vivo organoids which revealed unusual structures with compact morphology following exposure to SGG. Taken together, our results reveal that the oncogenic role of SGG UCN34 is associated with activation of multiple cancer-related signaling pathways. Author SummaryColorectal cancer is the third most common cause of cancer mortality worldwide. The colon is a very singular organ, colonized by a vast and complex community of microorganisms, known as the gut microbiota. Strong evidence supports a role of the microbiota in colon cancer development. Streptococcus gallolyticus subsp. gallolyticus (SGG), a gut commensal, was one of the first bacteria to be associated with colorectal cancer. A better understanding of the role of SGG in colon cancer development is critical to developing novel strategies to improve clinical diagnosis and treatment of this disease. Here, using a global proteomic analysis of mouse colonic tissue colonized by SGG, we show that over 90% of the proteins with altered levels are involved in cancer. SGG colonization promotes autocrine and paracrine pro-tumor signals contributing to transformation of the colonic epithelium but also modifying the stromal microenvironment, which in turn sustains tumor development. Importantly, two tumor hallmark pathways (PI3K/Akt/mTOR and MAPK) identified in our mouse model were also found in human colon tumor biopsies colonized by SGG, strengthening the clinical relevance to our study.