HHLA2 Expression in Human Clear Cell Renal Cell Carcinoma is Significantly Associated with Patient’s Prognosis and Promotes Cancer Progression

Abstract

Abstract HHLA2, a recently reported member of B7 family, plays an important role in the functional inhibition of T cells. Herein, we found that higher HHLA2 mRNA expression level in human ccRCC tissues compared with that in adjacent normal tissues based on TCGA data, and the HHLA2 mRNA level was positively and significantly correlated with PD-L1, PD-L2, B7-H6, but negatively and significantly correlated with B7-H3. Moreover, our immunohistochemistry study showed that HHLA2 staining intensity in human ccRCC tissues was significantly higher than that in normal tissues, and higher HHLA2 expression was significantly correlated with poorer survival of the patients. Higher HHLA2 expression in ccRCC tissues was positively and significantly associated with larger tumor size, advanced pathological stage, and advanced TNM stage. COX model revealed that the parameters including patient’s age, TNM stage and HHLA2 expression level could serve as independent risk factors for prognostic prediction of the patients. Furthermore, our cellular study showed that upon knockdown of HHLA2 expression in human ccRCC cell lines, the cell viability, migration and invasion ability were significantly inhibited, while the cell cycle arrest at G1 phase was induced and the expressions of Cyclin D1, c-Myc and Cyclin E1 were decreased. In addition, based on the microarray analysis data, we also confirmed that the expressions of epithelia-to-mesenchymal transition markers, such as E-cadherin, N-cadherin and Vimentin, were significantly decreased after knockdown of HHLA2 expression. Collectively, our findings indicated that HHLA2 was involved in the progression of human ccRCC and could be used as an important prognostic predictor for this malignancy.