Hepatitis B Doubly Spliced Protein (HBDSP) drives hepatoma cell EMT, migration, and invasion via SP1/ETS1-dependent YAP activation.

Chronic hepatitis B virus (HBV) infection is a major global health burden, significantly contributing to the development of hepatocellular carcinoma (HCC). While the roles of canonical HBV proteins in hepatocarcinogenesis are relatively well-understood, the pathological contributions of HBV spliced variants and their encoded proteins remain largely unexplored. This knowledge gap hinders a complete understanding of HBV's oncogenic mechanisms and limits the identification of novel therapeutic targets. This study specifically investigates the cancer-promoting potential of hepatitis B doubly spliced protein (HBDSP), a protein encoded by a specific HBV spliced variant, and its underlying mechanism in HCC progression.

Researchers investigated the role of HBDSP, encoded by the 2.2 kb doubly spliced variant of HBV, in hepatoma cells. In vitro functional assays were performed using HepG2 and Huh7 cell lines to assess HBDSP's impact on epithelial-mesenchymal transition (EMT), migration, and invasion. Mechanistic studies employed cellular and molecular approaches to identify how HBDSP influences gene expression. To confirm the role of YAP, cells were treated with the pharmacological inhibitor Verteporfin or YAP-specific siRNA. The findings were further validated in HBV-replicating HepG2.2.15 cells and HBV-infected HepG2-NTCP cells to ensure pathological relevance.

Hepatitis B Doubly Spliced Protein (HBDSP) consistently induced epithelial-mesenchymal transition (EMT) and significantly enhanced both migration and invasion capabilities in HepG2 and Huh7 hepatoma cells. Mechanistically, HBDSP was found to enhance the nuclear translocation of transcription factors SP1 and ETS1. This enhanced translocation facilitated their binding to the yes-associated protein (YAP) promoter, leading to the transcriptional activation of YAP. The critical role of YAP in these malignant phenotypes was confirmed when its inhibition, either pharmacologically with Verteporfin or genetically using YAP-specific siRNA, effectively abolished the HBDSP-induced EMT, migration, and invasion.

These HBDSP-mediated effects were robustly validated in both HBV-replicating HepG2.2.15 cells and HBV-infected HepG2-NTCP cells, underscoring the protein's pathological relevance in HBV-driven hepatocarcinogenesis.