Reticulocalbin-2 enhances hepatocellular carcinoma proliferation via modulating the EGFR-ERK pathway

Hepatocellular carcinoma (HCC) is a major health threat worldwide. Although the involvement of reticulocalbin-2 (RCN2) in cell differentiation has been reported, its function in oncogenesis is poorly understood. Here, we showed that RCN2 was upregulated in tumors compared with adjacent non-tumorous tissues in HCC patients and RCN2 expression clinically correlated with tumor size, disease recurrence and survival rate. Both knockdown and knockout of RCN2 significantly inhibited HCC cell proliferation by inducing G1/S transition arrest and downregulating cyclin D1 expression, while the proliferative ability was restored in knockout HCC cells with exogenously expressed RCN2. Mechanistically, we demonstrated that RCN2 interacted with the epidermal growth factor receptor (EGFR). Knockout of RCN2 in HCC cells not only inhibited activation of the EGFR-ERK pathway by blocking EGF-mediated EGFR dimerization and internalization but also suppressed cell proliferation and EGFR phosphorylation under long exposure to EGF. We further showed that knockout of RCN2 inhibited EGFR phosphorylation, Ki-67 expression and tumor growth in nude mice. Moreover, we demonstrated that RCN2 knockout sensitized HCC cells to tyrosine kinase inhibitors, including erlotinib, lapatinib and sunitinib. Taken together, our results indicate that RCN2 plays a pivotal role in HCC cell proliferation and tumor growth presumably through regulating activation of the EGFR-ERK pathway. Our work also suggests that RCN2 is a potential therapeutic target of HCC.