Prolonged and repetitive exposure to Porphyromonas gingivalis increases aggressiveness of oral cancer cells by promoting acquisition of cancer stem cell properties

Abstract

Periodontitis is the most common chronic inflammatory condition occurring in the human oral cavity, but our knowledge on its contribution to oral cancer is rather limited. To define crosstalk between chronic periodontitis and oral cancer, we investigated whether Porphyromonas gingivalis, a major pathogen of chronic periodontitis, plays a role in oral cancer progression. To mimic chronic irritation by P. gingivalis in the oral cavity, oral squamous cell carcinoma (OSCC) cells were infected with P. gingivalis twice a week for 5 weeks. Repeated infection of oral cancer cells by P. gingivalis resulted in morphological changes of host cancer cells into an elongated shape, along with the decreased expression of epithelial cell markers, suggesting acquisition of an epithelial-to-mesenchymal transition (EMT) phenotype. The prolonged exposure to P. gingivalis also promoted migratory and invasive properties of OSCC cells and provided resistance against a chemotherapeutic agent, all of which are described as cellular characteristics undergoing EMT. Importantly, long-term infection by P. gingivalis induced an increase in the expression level of CD44 and CD133, well-known cancer stem cell markers, and promoted the tumorigenic properties of infected cancer cells compared to non-infected controls. Furthermore, increased invasiveness of P. gingivalis-infected OSCC cells was correlated with enhanced production of matrix metalloproteinase (MMP)-1 and MMP-10 that was stimulated by interleukin-8 (IL-8) release. This is the first report demonstrating that P. gingivalis can increase the aggressiveness of oral cancer cells via epithelial-mesenchymal transition-like changes and the acquisition of stemness, implicating P. gingivalis as a potential bacterial risk modifier.

Role for the Aryl Hydrocarbon Receptor and Diverse Ligands in Oral Squamous Cell Carcinoma Migration and Tumorigenesis

“…CS L Cs contribute to tumor progression and recurrence in multiple cancer types, including OSCCs [15, 16, 19, 17, 18, 20–22]. Previous studies with normal tissue-specific stem cells suggest that the AHR contributed to properties of “stem-ness” [36, 37, 42, 43].…”

“…With regard to P. gingivalis , this is the first demonstration of an AHR ligand being produced by this common oral pathogen, a finding that has significant implications for the possible role for P. gingivalis in OSCC. In this vein, it has recently been shown that infection of OSCC with P. gingivalis induces EMT and increases the percentage of CS L Cs in OSCC [17]. In those studies, it was suggested that these outcomes were due in part to increased IL-8 expression, a cytokine regulated by the AHR in human macrophages [48, 49].…”

Gingipains of Porphyromonas gingivalis Affect the Stability and Function of Serine Protease Inhibitor of Kazal-type 6 (SPINK6), a Tissue Inhibitor of Human Kallikreins

“…More recent reports further strengthen the correlation between P. gingivalis infection and oral and stomach cancer development in vitro and in vivo (28,47). This effect is usually attributed to the direct effect of bacterial toxins and virulence factors promoting the development of chronic inflammation.…”

“…However, activation of tissue prokallikreins, especially locally abundant KLK13, with simultaneous degradation of this protease endogenous inhibitor have not been investigated. This is of significant interest because recent discoveries implicate that infection with oral pathogens may promote tumor progression via facilitation of the epithelial-to-mesenchymal transition and an increase in the malignancy of the tumor (28). Therefore, analysis of the interaction network of pathogen proteases and tumor-related proteinases of the KLK family may provide valuable insights into the mechanistic background of oral infectioncancer correlation.…”

Bacterial protease uses distinct thermodynamic signatures for substrate recognition

“…Porphyromonas gingivalis 4 is the major causative agent in periodontitis and Porphyromonas endodontalis 5 is another abundant bacterium in periodontal sites. Considerable attention has been drawn to these organisms due to recent reports associating periodontitis to systemic diseases 6 like type II diabetes mellitus 7 , rheumatoid arthritis 8 , oral cancers 9, 10 , cardiovascular diseases 11 , Alzheimer et al . 12 and respiratory diseases 13 .…”