Notch Signaling Mediates Differentiation in Barrett's Esophagus and Promotes Progression to Adenocarcinoma

BACKGROUND & AIMS

Studies are needed to determine the mechanism by which Barrett's esophagus (BE) progresses to esophageal adenocarcinoma (EAC). Notch signaling maintains stem cells in the gastrointestinal tract and is dysregulated during carcinogenesis. We explored the relationship between Notch signaling and goblet cell maturation, a feature of BE, during EAC pathogenesis.

METHODS

We measured goblet cell density and levels of Notch messenger RNAs in BE tissues from 164 patients, with and without dysplasia or EAC, enrolled in a multicenter study. We analyzed the effects of conditional expression of an activated form of NOTCH2 (pL2.Lgr5.N2IC), conditional deletion of NOTCH2 (pL2.Lgr5.N2fl/fl), or loss of nuclear factor κB (NF-κB) (pL2.Lgr5.p65fl/fl), in Lgr5+ (progenitor) cells in L2-IL1B mice (which overexpress interleukin 1 beta in esophagus and squamous forestomach and are used as a model of BE). We collected esophageal and stomach tissues and performed histology, immunohistochemistry, flow cytometry, transcriptome, and real-time polymerase chain reaction analyses. Cardia and forestomach tissues from mice were cultured as organoids and incubated with inhibitors of Notch or NF-kB.

RESULTS

Progression of BE to EAC was associated with a significant reduction in goblet cell density comparing nondysplastic regions of tissues from patients; there was an inverse correlation between goblet cell density and levels of NOTCH3 and JAG2 messenger RNA. In mice, expression of the activated intracellular form of NOTCH2 in Lgr5+ cells reduced goblet-like cell maturation, increased crypt fission, and accelerated the development of tumors in the squamocolumnar junction. Mice with deletion of NOTCH2 from Lgr5+ cells had increased maturation of goblet-like cells, reduced crypt fission, and developed fewer tumors. Esophageal tissues from in pL2.Lgr5.N2IC mice had increased levels of RelA (which encodes the p65 unit of NF-κB) compared to tissues from L2-IL1B mice, and we found evidence of increased NF-κB activity in Lgr5+ cells. Esophageal tissues from pL2.Lgr5.p65fl/fl mice had lower inflammation and metaplasia scores than pL2.Lgr5.N2IC mice. In organoids derived from pL2-IL1B mice, the NF-κB inhibitor JSH-23 reduced cell survival and proliferation.

CONCLUSIONS

Notch signaling contributes to activation of NF-κB and regulates differentiation of gastric cardia progenitor cells in a mouse model of BE. In human esophageal tissues, progression of BE to EAC was associated with reduced goblet cell density and increased levels of Notch expression. Strategies to block this pathway might be developed to prevent EAC in patients with BE.

Abstract 2840: Fusobacterium nucleatum stimulates colorectal cancer progression by activating Annexin A1 in cancerous cells

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.

Fusobacterium nucleatum promotes colorectal cancer by inducing Wnt/β-catenin modulator Annexin A1

Fusobacterium nucleatum, a Gram-negative oral anaerobe, is a significant contributor to colorectal cancer. Using an in vitro cancer progression model, we discover that F. nucleatum stimulates the growth of colorectal cancer cells without affecting the pre-cancerous adenoma cells. Annexin A1, a previously unrecognized modulator of Wnt/β-catenin signaling, is a key component through which F. nucleatum exerts its stimulatory effect. Annexin A1 is specifically expressed in proliferating colorectal cancer cells and involved in activation of Cyclin D1. Its expression level in colon cancer is a predictor of poor prognosis independent of cancer stage, grade, age, and sex. The FadA adhesin from F. nucleatum up-regulates Annexin A1 expression through E-cadherin. A positive feedback loop between FadA and Annexin A1 is identified in the cancerous cells, absent in the non-cancerous cells. We therefore propose a "two-hit" model in colorectal carcinogenesis, with somatic mutation(s) serving as the first hit, and F. nucleatum as the second hit exacerbating cancer progression after benign cells become cancerous. This model extends the "adenoma-carcinoma" model and identifies microbes such as F. nucleatum as cancer "facilitators".

Screening β-arrestin recruitment for the identification of natural ligands for orphan G-protein-coupled receptors

A variety of G-protein-coupled receptor (GPCR) screening technologies have successfully partnered a number of GPCRs with their cognate ligands. GPCR-mediated β-arrestin recruitment is now recognized as a distinct intracellular signaling pathway, and ligand-receptor interactions may show a bias toward β-arrestin over classical GPCR signaling pathways. We hypothesized that the failure to identify native ligands for the remaining orphan GPCRs may be a consequence of biased β-arrestin signaling. To investigate this, we assembled 10 500 candidate ligands and screened 82 GPCRs using PathHunter β-arrestin recruitment technology. High-quality screening assays were validated by the inclusion of liganded receptors and the detection and confirmation of these established ligand-receptor pairings. We describe a candidate endogenous orphan GPCR ligand and a number of novel surrogate ligands. However, for the majority of orphan receptors studied, measurement of β-arrestin recruitment did not lead to the identification of cognate ligands from our screening sets. β-Arrestin recruitment represents a robust GPCR screening technology, and ligand-biased signaling is emerging as a therapeutically exploitable feature of GPCR biology. The identification of cognate ligands for the orphan GPCRs and the extent to which receptors may exist to preferentially signal through β-arrestin in response to their native ligand remain to be determined.

Measurements of β-arrestin recruitment to activated seven transmembrane receptors using enzyme complementation

The recruitment of arrestins to activated 7TMRs results in the activation of alternative signaling pathways, quenching of G-protein activation, and coupling to clathrin-mediated endocytosis. The nearly ubiquitous involvement of arrestin in 7TMR signaling has spurred the development of several methods for monitoring this interaction in mammalian cells. Nonetheless, few maintain the reproducibility and precision necessary for drug discovery applications. Enzyme fragment complementation technology (EFC) is an emerging protein-protein interaction technology based on the forced complementation of a split enzyme that has proven to be highly effective in monitoring the formation of GPCR-arrestin complexes. In these systems, the target proteins are fused to two fragments of an enzyme that show little or no spontaneous complementation. Interaction of the two proteins forces the complementation of the enzyme, resulting in an enzymatic measure of the protein interaction. This chapter discusses the utility and methods involved in using the PathHunter β-galactosidase complementation system to monitor arrestin recruitment and the advantages of exploiting this pathway in the characterization of 7TMR function.