Hypomethylation‐mediated activation of cancer/testis antigen KK‐LC‐1 facilitates hepatocellular carcinoma progression through activating the Notch1/Hes1 signalling

Objectives Kita-Kyushu lung cancer antigen-1 (KK-LC-1) is a cancer/testis antigen reactivated in several human malignancies. So far, the major focus of studies on KK-LC-1 has been on its potential as diagnostic biomarker and immunotherapy target. However, its biological functions and molecular mechanisms in cancer progression remain unknown. Materials and Methods Expression of KK-LC-1 in HCC was analysed using RT-qPCR, Western blot and immunohistochemistry. The roles of KK-LC-1 on HCC progression were examined by loss-of-function and gain-of-function approaches. Pathway inhibitor DAPT was employed to confirm the regulatory effect of KK-LC-1 on the downstream Notch signalling. The interaction of KK-LC-1 with presenilin-1 was determined by co-immunoprecipitation. The association of CpG island methylation status with KK-LC-1 reactivation was evaluated by methylation-specific PCR, bisulphite sequencing PCR and 5-Aza-dC treatment. Results We identified that HCC tissues exhibited increased levels of KK-LC-1. High KK-LC-1 level independently predicted poor survival outcome. KK-LC-1 promoted cell growth, migration, invasion and epithelial-mesenchymal transition in vitro and in vivo. KK-LC-1 modulated the Notch1/Hes1 pathway to exacerbate HCC progression through physically interacting with presenilin-1. Upregulation of KK-LC-1 in HCC was attributed to hypomethylated CpG islands. Conclusions This study identified that hypomethylation-induced KK-LC-1 overexpression played an important role in HCC progression and independently predicted poor survival. We defined the KK-LC-1/presenilin-1/Notch1/Hes1 as a novel signalling pathway that was involved in the growth and metastasis of HCC.