Abstract 5184: Expression and role of regulator of G-protein signing 5 in squamous cell carcinoma of the tongue

Objective: Regulator of G-protein signing (RGS) 5 is a member of the RGS family and acts as GTPase-activating proteins for heterotorimeric G protein αsubunits, negatively regulating G-protein signaling. RGS5 was reportedly expressed in the heart, lung, skeletal muscle and small intestine and relates with tumor angiogenesis and gestational hypertension. It was reported that RGS5 was related with the invasion and metastasis of cancers, such as non-small lung cancer and hepatocellular carcinoma. In the present study, we examined RGS5 expression and its relation with invasion in squamous cell carcinoma (SCC) of the tongue. Materials and Methods: For immunohistochemical analysis for RGS5, we used SCC tissues of the tongue obtained from 43 patients who underwent resection at Kurume University Hospital from 2011 to 2015. The staining intensity was graded as 0, negative; 1, weak; 2, moderate; 3, strong. The staining intensity in the normal epithelium was used as an internal control. We examined relationship between RGS5 expression in invasive portions and clinicopathological features (e.g., lymph node metastasis, depth of tumor, and mode of invasion, and so forth). Mode of invasion was classified into 3 levels, i.e., IFNa (expansive), IFNc (invasive), IFNb (between INFa and INFc). Depth of tumor was measured and classified into 2 levels: < 5 mm and ≥ 5mm. Comparison and estimation of cumulative survival rates were performed using the Kaplan-Meier curves and log rank test. Result: Non-cancerous squamous cells expressed RGS5 solely in nucleus. SCC cells in superficial portion of tumor nodules often expressed weak nuclear RGS5 expression. In invasive portions of the tumor nodules, SCC cells expressed significantly lower nuclear and higher cytoplasmic RGS5 expression. A significant correlation was found between the expression score of RGS5 at invasive portions and mode of invasion (P=0.009). When the 43 cases were subdivided into two groups, i.e., expression group (score 1-3) and non-expression group (score 0), significant differences were observed in mode of invasion (P=0.0042), lymph node metastasis (p=0.0314), depth of tumor (p=0.0239) between the two groups. The log-rank test revealed that postoperative early lymph node metastasis was significantly higher in the expression group (p= 0.0415). Conclusion: This study suggests that RGS5 expression is related with tumor invasion in SCC of the tongue and that RGS5 can be a predictor of postoperative early lymph node met