Involvement of RNase 7 in the malignant potential of oral squamous cell carcinoma cells.

RNase 7 is involved in the innate immunity of the oral epithelium. Variations in the expression levels of RNase 7 have been reported in cutaneous squamous cell carcinoma, but not in oral squamous cell carcinoma (OSCC). The present study investigated the expression levels of RNase 7 in OSCC and its role in the malignant potential of these cells. The localization of RNase 7 in OSCC tissue sections was determined via immunohistochemistry. Positive staining for RNase 7 was observed around the epithelial pearls and spinous cells of the OSCC tissues. Four different types of OSCC cell lines (OSC-19, BSC-OF, SAS, and HSC-2) and a normal keratinocyte (HaCaT) were used. The mRNA and protein expression levels of RNase 7 were significantly higher in the OSCC cells compared to the HaCaT cells. Based on our hypothesis that high levels of RNase 7 expression may be involved in the malignant potential of OSCC cells, the effect of RNase 7 knockdown on both proliferation and invasion were evaluated by transfecting the cells with siRNA. Cell numbers, cell invasion, and MMP 9 expression levels were significantly higher in the siRNA-BSC-OF, -SAS, and -HSC-2 cells compared to the BSC-OF, SAS, and HSC-2 cells. The extent of differentiation of the siRNA-OSCC cells was examined using the differentiation and undifferentiation markers involucrin (INV) and K14, respectively. The expression level of K14 was significantly higher in the siRNA-OSCC cells compared to the OSCC cells. Alternatively, HSC-2 and SAS cells demonstrated higher expression levels of INV compared to the siRNA-HSC-2 and -SAS cells. These findings indicate that RNase 7 may contribute to the suppression of the malignant potential of OSCC.