Comprehensive analysis of gene expression induced by IFN-γ in the human oral mucosal epithelial cell line HSC-2

Lipopolysaccharide (LPS) derived from Gram-negative bacteria is recognized by Toll-like receptor 4 (TLR4) on the host cell surface and by inflammatory caspases such as caspase-4 (CASP4) in the cytoplasm. LPS from the periodontal pathogen Porphyromonas gingivalis (PgLPS) is known to be recognized by TLR4, but whether it is sensed in the cytoplasm remains unclear. We investigated the intracellular recognition mechanism of PgLPS using the oral epithelial cell line HSC-2. Transfection of PgLPS alone did not elicit a response in HSC-2 cells; however, when PgLPS was transfected following priming with interferon (IFN)-γ, maturation of IL-18, activation of gasdermin D, and pyroptotic cell death were induced. These responses of HSC-2 cells were unaffected by TLR4 inhibition but were strongly suppressed by CASP4 inhibition. These findings suggest that IFN-γ–inducible genes likely play an auxiliary role in the CASP4-dependent responses of HSC-2 cells induced by PgLPS transfection. To examine the impact of IFN-γ priming on HSC-2 cells, we performed RNA sequencing (RNA-seq). This analysis identified 974 genes whose expression was upregulated by IFN-γ. Among these genes were members of the guanylate-binding protein (GBP) family (GBP1–5, GBP7) as well as CASP5. This analysis provides useful insights into the effects of IFN-γ on oral epithelial cells and into the characterization of IFN-stimulated factors in HSC-2 cells.