Gastroenterology

Gastroenterology

Volume 160, Issue 4, March 2021, Pages 1179-1193.e14
Gastroenterology

Original Research
Full Report: Basic and Translational—Alimentary Tract
Streptococcus thermophilus Inhibits Colorectal Tumorigenesis Through Secreting β-Galactosidase

https://doi.org/10.1053/j.gastro.2020.09.003Get rights and content

Background & Aims

Streptococcus thermophilus was identified to be depleted in patients with colorectal cancer (CRC) by shotgun metagenomic sequencing of 526 multicohort fecal samples. Here, we aim to investigate whether this bacterium could act as a prophylactic for CRC prevention.

Methods

The antitumor effects of S thermophilus were assessed in cultured colonic epithelial cells and in 2 murine models of intestinal tumorigenesis. The tumor-suppressive protein produced by S thermophilus was identified by mass spectrometry and followed by β-galactosidase activity assay. The mutant strain of S thermophilus was constructed by homologous recombination. The effect of S thermophilus on the gut microbiota composition was assessed by shotgun metagenomic sequencing.

Results

Oral gavage of S thermophilus significantly reduced tumor formation in both Apcmin/+ and azoxymethane-injected mice. Coincubation with S thermophilus or its conditioned medium decreased the proliferation of cultured CRC cells. β-Galactosidase was identified as the critical protein produced by S thermophilus by mass spectrometry screening and β-galactosidase activity assay. β-Galactosidase secreted by S thermophilus inhibited cell proliferation, lowered colony formation, induced cell cycle arrest, and promoted apoptosis of cultured CRC cells and retarded the growth of CRC xenograft. The mutant S thermophilus without functional β-galactosidase lost its tumor-suppressive effect. Also, S thermophilus increased the gut abundance of known probiotics, including Bifidobacterium and Lactobacillus via β-galactosidase. β-Galactosidase-dependent production of galactose interfered with energy homeostasis to activate oxidative phosphorylation and downregulate the Hippo pathway kinases, which partially mediated the anticancer effects of S thermophilus.

Conclusion

S thermophilus is a novel prophylactic for CRC prevention in mice. The tumor-suppressive effect of S thermophilus is mediated at least by the secretion of β-galactosidase.

Section snippets

Bacterial Strain and Culture Condition

Streptococcus salivarius (2593) and S thermophilus (19258) were purchased from the American Tissue Culture Collection (ATCC, Manassas, VA). Bacillus halodurans (DSM 18197) was obtained from Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH (Braunschweig, Germany). They were cultured in Brain Heart Infusion (BHI) broth (CM1135B; Thermo Fisher Scientific, West Palm Beach, FL) for 24 hours at 37°C in aerobic conditions. A nonpathogenic human commensal intestinal bacterium, E coli strain

Streptococcus thermophilus Is Depleted in Stool Samples of Patients With Colorectal Cancer

Our previous shotgun metagenomic sequencing showed that there were 62 depleted bacteria species in CRC patients compared with normal individuals.6 We reanalyzed the top 20 depleted strains with the largest fold change and found that S salivarius and S thermophilus were 2 known probiotics (Supplementary Figure 1A). To determine the effect of the most significantly CRC-depleted S salivarius on intestinal tumorigenesis, we gavaged Apcmin/+ mice with S salivarius (1 × 108 CFU/d) for 8 weeks. Two

Discussion

In this study, we validated the depletion of S thermophilus using an orthogonal method. In 2 animal models of colon tumorigenesis, S thermophilus significantly lowered tumor number and tumor volume. Moreover, CRC but not normal colonic cell viability was suppressed by S thermophilus. Previous studies have already revealed the anti-inflammatory effect of S thermophilus18 and its production of lactate as a signal for modulating colonic epithelium.19 However, this is the first study to

Conclusion

In summary, we demonstrated that S thermophilus prevents colon tumorigenesis in animal models. The antitumor effect was mediated by the secretion of β-galactosidase for producing galactose and possibly its synergistic effect with other well-known probiotics. Galactose production then interferes with energy homeostasis and activates AMPK kinase, leading to the phosphorylation of YAP and activation of OXPHO, thus culminating in an anti-Warburg phenotype to inhibit tumorigenesis. Taken together, S

Acknowledgments

The authors thank Siu Hong Chu (Institute of Digestive Disease, CUHK) for his help with animal experiments.

CRediT Authorship Contributions

Qing Li, MD (Data curation: Lead; Project administration: Lead; Validation: Lead; Writing – original draft: Lead);

Wei Hu, PhD (Methodology: Equal);

Wei-Xin Liu, MPhil (Data curation: Equal; Formal analysis: Equal);

Liu-Yang Zhao, PhD (Methodology: Supporting; Visualization: Supporting);

Dan Huang, PhD (Data curation: Supporting; Formal analysis: Supporting);

Xiao-Dong Liu, PhD (Methodology:

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    Conflicts of interest The authors declare that they have no conflicts of interest.

    Funding This project was supported by Science and Technology Program Grant Shenzhen (JCYJ20170413161534162), National Key R&D Program of China (2017YFE0190700), Health and Medical Research Fund (HMRF) Hong Kong (17160862), and Lim Peng Suan Charitable Trust. The study sponsor did not play any role in the study design or in the collection, analysis, and interpretation of data.

    Author names in bold designate shared co-first authorship.

    Authors are co-corresponding authors.

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