Abstract C58: IL-1 receptor regulates calprotectin-dependent accumulation of pathogenic bacteria in oral carcinoma
Authors: Sorenson Brent S. , Khammanivong Ali , Guenther Brian , Ross Karen , Herzberg Mark 
Published: May 2012

The oral epithelium represents the mucosal immune system's initial line of defense against invasive bacterial and viral pathogens. Invasion of bacterial pathogens into oral epithelial cells increases expression of inflammatory cytokines, including interleukin-1α (IL-1α). Head and neck squamous cell carcinomas (HNSCC) express more IL-1α and have greater numbers of colonizing bacteria than normal oral tissues. Previously, we showed that exogenous IL-1α induces expression of antimicrobial proteins (AMP), including calprotectin, a heterodimer of S100A8 and S100A9 and increases IL-1 receptor-dependent resistance of buccal carcinoma cells to the invasive bacterial pathogen, Listeria monocytogenes. Since S100A9 is down-regulated in HNSCC, we knocked down calprotectin using siRNA against S100A8 and S100A9 in human buccal carcinoma cells (TR146) to further characterize the role of calprotectin in the IL-1α-dependent pathogen response. First, we examined the time course IL-1α expression in TR146 cells in response to coincubation with L. monocytogenes. We then assessed the exogenous IL-1α dose-dependent regulation of intracellular (calprotectin) and extracellular (human β-defensin-2; h-BD2) AMPs using comparative real-time RT-PCR. Lastly, we examined the role of calprotectin, in response to exogenous IL-1α, for modulation of resistance to L. monocytogenes invasion in TR146 cells expressing siRNA against S100A8 and S100A9 (A8A9c10) or non-specific siRNA (Neg3) using an antibiotic protection assay.

We found that L. monocytogenes increases IL-1α gene expression in a time-dependent manner in wild type (WT) TR146 cells. Exogenous IL-1α induces a dose-dependent increase in expression of h-BD2 and calprotectin subunits in Neg3, A8A9c10 and WT TR146 cells. Furthermore, exogenous IL-1α provides IL-1 receptor-mediated protection against L. monocytogenes invasion in WT TR146 cells. In calprotectin-silenced A8A9c10 cells, however, exogenous IL-1α increases the proportion of intracellular bacteria when compared to Neg3 cells (123% to 77% of the vehicle control, respectively; p&lt;0.0299 one-tailed Student's t-test with equal variance). Invasion by L. monocytogenes is independent of carcinoma cell size and viability of extracellular bacteria.

These data strongly suggest that IL-1α signaling through the IL-1 receptor regulates calprotectin-mediated, cell-autonomous resistance to bacterial invasion as modeled by L.monocytogenes. Exogenous IL-1α increases expression of IL-8 and GM-CSF in HNSCC, which enhances invasion of inflammatory tumor-promoting immune cells and malignant progression. Therefore, for the first time, we show the loss of calprotectin in oral carcinoma cells, combined with increased IL-1α, as seen in HNSCC, can lead to increased bacterial colonization of oral carcinoma cells and expression of proinflammatory signals. These events may contribute to tumor growth and progression.

Citation Information: Cancer Res 2009;69(23 Suppl):C58.