Hepatitis B Doubly Spliced Protein (HBDSP) Promotes Epithelial-Mesenchymal Transition, Migration, and Invasion via SP1/ETS1-Dependent YAP Activation in Hepatoma Cells.

Chronic hepatitis B virus (HBV) infection remains a significant global health burden. Although the canonical HBV proteins are well-studied, the pathological roles of HBV spliced variants and their encoded proteins are poorly understood. In this study, we investigate the cancer-promoting potential of hepatitis B doubly spliced protein (HBDSP), encoded by the 2.2 kb doubly spliced variant of HBV, and its underlying mechanism in hepatocellular carcinoma (HCC). In vitro functional assays demonstrated that HBDSP induces epithelial-mesenchymal transition (EMT) and enhances migration and invasion in HepG2 and Huh7 cells. Mechanistically, cellular and molecular approaches revealed that HBDSP enhanced the nuclear translocation of SP1 and ETS1, thereby facilitating their binding to the yes-associated protein (YAP) promoter and activating YAP transcription. Inhibition of YAP using either the pharmacological inhibitor Verteporfin or YAP-specific siRNA effectively abolished HBDSP-induced malignant phenotypes, confirming the essential role of YAP in this process. Notably, these effects were consistently validated in both HBV-replicating HepG2.2.15 cells and HBV-infected HepG2-NTCP cells, further reinforcing the pathological relevance of HBDSP in HBV-driven hepatocarcinogenesis. Taken together, we identify HBDSP as a novel viral effector that facilitates EMT, migration, and invasion in hepatoma cells via transcriptional activation of YAP in an SP1- and ETS1-dependent manner. These findings suggest that HBDSP-mediated activation of YAP may play a role in HBV-driven HCC progression and could be explored further as a potential therapeutic axis, particularly in contexts where spliced HBV variants are prevalent.