Activation of the Notch1-c-myc-VCAM1 signalling axis initiates liver progenitor cell-driven hepatocarcinogenesis and pulmonary metastasis.

The cellular origin of hepatocellular carcinomas (HCC) and the role of Notch1 signalling in HCC initiation are controversial. Herein, we establish Notch1 as a regulator of HCC development and progression. Clinically, high Notch1 expression correlates with enhanced cancer progression, elevated lung metastasis, increased cancer stem cell (CSC)-like cells' gene signature expression, and poor overall survival in HCC patients. Notch1 intracellular domain (N1ICD) overexpression spontaneously transforms rat liver progenitor cells (LPC) into CSC-like cells (WB C5) under a selective growth environment, while orthotopic injection of these cells generates liver tumors and spontaneous pulmonary metastasis in an isogenic rat model. Mechanistically, the elevated Notch1 activity increases c-myc expression, which then transcriptionally upregulates VCAM1 expression to activate macrophage dependent HCC transendothelial migration. In vivo, silencing c-myc prohibits the tumorigenicity of WB C5 cells, while depletion of VCAM1 reduces spontaneous lung metastasis without affecting primary WB C5 orthotopic liver tumor growth. Importantly, depletion of macrophage or blockade of macrophage VCAM1 binding receptor α4β1-integrin reduces the number of WB C5 lung nodules in an experimental metastasis model. Overall, our work discovers that the Notch1-c-myc-VCAM1 signaling axis initiates LPC-driven hepatocarcinogenesis and metastasis, providing a preclinical model for HCC study and therapeutic targets for an improved HCC treatment.