Crosstalk between the microbiome and cancer cells by quorum sensing peptides
Introduction
Studies of the human microbiome revealed an individual and age-related diversity of microbes, occupying different habitats like skin, mouth, mammary gland, vagina and gut [1], [2], [3], [4], [5]. The beneficial effects of the gastrointestinal microbiota are currently being exploited in daily life by the use of probiotics. These products, most often positioned as functional foods, claim to restore the gut microbiota composition, possibly preventing gut inflammation or other intestinal or systemic disease phenotypes [6]. The most commonly studied organisms for probiotic therapies in the treatment of gastrointestinal diseases include organisms of the genera Bacillus, Enterococcus, Escherichia, Faecalibacterium and Propionibacterium. Enterococcus faecium, together with Bacillus subtilis and Lactobacillus spp., were investigated as probiotics for acute gastroenteritis, while Streptococcus spp., B. subtilis and Escherichia coli were explored for their use as probiotics in irritable bowel syndrome; a reduced duration or decreased abdominal pain of both gastrointestinal diseases was established. Manipulation of the microbiota with rationally selected pre- or probiotics can inhibit pathogens, strengthen epithelial barrier functions and supply the host with key nutrients (e.g. vitamins) [7]. Despite these claimed health benefits, it has also to be cautioned that certain safety aspects should be taken into account when using probiotics: taxonomic identification of the probiotic strain is necessary to avoid pathogenicity, as well as inhibiting the risk of infection and antimicrobial resistance [8]. The use of probiotics is indeed already associated with diverse side effects, e.g. bacteremia, fungemia and gastrointestinal ischemia; critically ill patients and immune-compromised individuals are the most-at-risk populations [9].
However, the interactions with the host can affect metabolic, neurological, inflammatory and immunological functions as well, and also the development of cancer can directly or indirectly be promoted [10]. For example, the progress of colorectal cancer can directly be initiated by DNA-damaging superoxide radicals or genotoxins, both produced by gut (mucosa-associated) bacteria. Indirectly, bacteria can induce cell proliferation or pro-carcinogenic pathways by T-helper cells or Toll-like receptors, respectively [11]. Human microbiome studies have revealed significant differences between cancer patients and healthy controls regarding the relative abundance of certain microbes. In colon cancer patients, an increased population of e.g. E. coli was observed in feces, inducing colitis and colibactin synthesis and thereby promoting inflammation and cancer [12].
Although the quorum sensing process within Gram-positive bacterial colonies is already extensively described in literature, the direct link between quorum sensing peptides and tumor development remains unexplored. Recent investigations revealed that the quorum sensing process is activated in the human gut: a set of acylhomoserine lactone (AHL) molecules, i.e. signaling molecules produced by Gram-negative bacteria, were identified in human feces of gastrointestinal disease patients as well as healthy subjects [13]. Moreover, bacterial quorum sensing molecules are likely to play a role in bacterial colonization of mucosa, thus requiring quorum sensing-mediated biofilm formation [14]. Finally, Casula and Cutting showed the germination of B. subtilis spores in the murine gastrointestinal tract, thereby probably requiring signaling peptides for quorum sensing pathway activation [15]. Although thus not yet investigated, it is very likely that also quorum sensing peptides are found in the human intestinal tract.
In this study, we utilize a collagen invasion assay, transcriptome assay, Chick Chorioallantoic Membrane (CAM) assay, cytokine profiling and phospho-receptor tyrosine kinase array to investigate the influence of quorum sensing peptides on mammalian cancer cells. Our preliminary observations unexpectedly reveal that quorum sensing peptides stimulate metastasis behavior of human colon cancer cells, thereby opening new perspectives on the role and applications of the microbiome on the guest's health, with the possibility of translating these findings into other biological and applied medical fields as well.
Section snippets
Cell culture
An epithelial subclone from human ileocecal colorectal adenocarcinoma cells (ATCC® CCL-224), i.e. HCT-8/E11, was grown in high-glucose Dulbecco's Modified Eagle's Medium (DMEM), supplemented with 10% (v/v) fetal bovine serum (FBS), 1% (w/v) l-glutamine, 100 U/ml penicillin and 100 μg/ml streptomycin (all from Invitrogen/GIBCO, Gent, Belgium) in a humidified atmosphere of 5% CO2.
Collagen type I invasion assay
Morphology changes of HCT-8/E11 cells were investigated using previously described methods [16]. In brief, 10 000 cells
Epithelial to mesenchymal (EMT)-like transition and related cell migration activities
To investigate the potential role of chemically diverse quorum sensing peptides in oncology [19,Wynendaele et al., unpublished results], we explored their morphologic effect on a human epithelial colon cancer cell line, i.e. HCT-8/E11. Three quorum sensing peptides, or metabolites thereof, were found to significantly induce tumor cell invasion through a collagen type I extracellular matrix: Phr0662 (ERNNT, 98.24%), an EntF-metabolite (SNLVECVFSLFKKCN, 80.63%) and an EDF-analog (NWN, 98.40%) (
Discussion
Despite our small quorum sensing peptide set, our results suggest that some quorum sensing peptides can exert (part of) their effects through the epidermal growth factor receptor (EGFR), thereby activating the Ras/raf/MEK/MAPK, PI3K/Akt and STAT intracellular signaling cascades [41], leading to an altered gene transcription and finally tumor metastasis (Fig. 5). β-Arrestin 1, which is linked to HIST1H4 and thus possibly upregulated after peptide treatment, can activate the EGFR pathway as well,
Acknowledgements
We thank G. Wagemans and M. De Meulemeester for technical support and assistance with the CAM assays and H&E staining. This work was supported by the Special Research Fund of Ghent University [Grant Number BOF 01J22510 to B.D.S. and E.W.] and the Institute for the Promotion of Innovation through Science and Technology in Flanders (IWT-Vlaanderen) [Grant Numbers 131356 to F.V. and 101529 to M.D.]. The microarray data are deposited at AROS Applied Biotechnology under project numbers A2224 and
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2022, Biochemical and Biophysical Research CommunicationsCitation Excerpt :In addition, the gut microbiota also plays an important role in the development of lung cancer [7]. The gut microbiota characteristics of lung cancer patients are different from those of healthy people [8–12], suggesting that gut microbiota may affect the treatment and prognosis of lung cancer [13–16]. It affects susceptibility to carcinogenesis in a variety of ways, including regulation of host inflammation, production of carcinogenic metabolites, genotoxicity and virulence effects, and cell cycle disruption [17,18].