Abstract 2840: Fusobacterium nucleatum stimulates colorectal cancer progression by activating Annexin A1 in cancerous cells
Authors: Rubinstein Mara R. , Baik Jung Eun , Lagana Stephen M. , Raab William J. , Sahoo Dabashis , Dalerba Piero , Wang Timothy C. , Han Yiping W. 
Published: August 2019

Abstract
Colorectal cancer (CRC) is the second leading cause of cancer death in the U.S., affecting one in 20 individuals. Numerous studies have implicated Fusobacterium nucleatum (Fn), a Gram-negative oral commensal, in CRC; however, mechanistic insight on the role of Fn in this debilitating disease is scarce.
Previously, we have reported that Fn stimulates CRC growth through its unique adhesin FadA, which binds to E-cadherin and modulates β-catenin signaling. In the present study, we tested the specificity of Fn-induced cell growth. Fn did not promote the growth of lung, prostate, breast and bladder cancer cells, indicating specific component(s) on CRC cells are required for stimulation. To identify such component(s), we utilized a CRC progression model consisting of a
series of cell lines sequentially derived from a human colonic adenoma. Fn specifically stimulates growth of the cancerous cells without affecting the non-cancerous cells. The growth stimulation is mediated by Annexin A1 (ANXA1), a member of the Annexin family of Ca2+-dependent phospholipid-binding proteins. ANXA1 is specifically expressed in the proliferating cancerous cells, but not in non-cancerous or non-proliferating cells. Analysis of a database of 466 colon cancer patients reveals that increased level of ANXA1 is associated with cancer reoccurrence independent of cancer stage, grade, sex and age. Knocking down of ANXA1 in CRC cells inhibits cell proliferation due to down-regulation of Cyclin D1. An E-cadherin mediated positive feedback loop between FadA and ANXA1 is identified in the cancerous cells. Fn preferentially binds to ANXA1-expressing cancerous cells, which in turns stimulates ANXA1 expression. FadA, E-cadherin and Annexin A1 form a complex in CRC cells leading to activation of β-catenin signaling.
The correlation between FadA and ANXA1 was investigated in vivo using the APCmin/+ mice. Mice gavaged with wild-type Fn produced significantly increased number of tumors in the colon, compared to those gavaged with sterile PBS, E. coli DH5α, or the fadA-deletion mutant US1. In both mice and humans, increased ANXA1mRNA levels were detected in the tumors compared to the matching normal colonic tissues, and a positive correlation between the fadA gene levels and ANXA1 mRNA levels was identified in the colorectal tumors. Immunofluorescent staining of paired normal and carcinoma tissues from CRC patients confirmed this finding and revealed co-localization of FadA and Annexin A1 in the carcinomas.
We have thus elucidated a novel mechanism by which Fn promotes CRC, i.e. through stimulating Annexin A1, a novel Wnt/β-catenin modulator, in the cancerous cells. Given the non-cancerous cells are not affected by Fn, we propose a “two-hit” model in which the first hit would be the somatic mutation(s) causing normal cells to become cancerous, and Fn serves as the second hit to exacerbate cancer progression.
Citation Format: Mara R. Rubinstein, Jung Eun Baik, Stephen M. Lagana, William J. Raab, Dabashis Sahoo, Piero Dalerba, Timothy C. Wang, Yiping W. Han. Fusobacterium nucleatum stimulates colorectal cancer progression by activating Annexin A1 in cancerous cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2840.