Hepatic Stellate Cell Regulation of Metastatic Growth in the Liver

The development of liver metastasis is dependent upon bidirectional interactions between cancer cells and the liver microenvironment. Transforming growth factor beta (TGFβ), released from cancer cells and other resident liver cells, induces activation of hepatic stellate cells (HSCs) into myofibroblasts that in turn promote liver metastasis. The long-term goal of our program is to define mechanisms governing HSC activation and develop strategies to target HSCs and the prometastatic liver microenvironment. Recent advances suggest that HSCs are fueled by aerobic glycolysis, glutaminolysis, and free cholesterol, but mechanistic regulation of HSC metabolism is not fully defined. Glucose transporter 1 (Glut1) is a predominant glucose transporter isoform expressed by hepatic fibroblasts and it has to be on the plasma membrane for glucose to be transported into cells. Our Preliminary Data demonstrate that TGFβ1 induces endosome-to-plasma-membrane translocation of Glut1 and glucose uptake into HSCs by a mechanism dependent on non-receptor tyrosine kinase c-Src (Src) and vasodilator-stimulated phosphoprotein (VASP). While Src interacts with the small Rab GTPase Rab11 and Glut1 at the endosome, VASP interacts with Glut1 at the plasma membrane. Additionally, knockdown of Glut1 suppresses myofibroblastic activation of HSCs in vitro and tumor-promoting effects of HSCs in a tumor/HSC co-implantation mouse model. These findings led to the Central Hypothesis that the TGFβ1-induced localization of Glut1 on the plasma membrane and the subsequent glucose transport into HSCs that fuels HSC activation are mediated by Src at the endosome and VASP at the plasma membrane. In Aim 1, we will study how Src promotes Glut1 trafficking towards the plasma membrane, with a focus on its regulation on Rab11 activation at the endosome. We will also investigate how Src is activated in TGFβ1-stimulated HSCs. In Aim 2, we will elucidate how VASP retains Glut1 at the plasma membrane and promotes glucose transport into HSCs. We will also interrogate whether a lipid signaling pathway induces VASP phosphorylation in TGFβ1-stimulated HSCs. In Aim 3, we will use conditional SLC2A1/Glut1 knockout mice and portal vein tumor injection to test if HSC-specific Glut1 deletion suppresses HSC activation and colorectal liver metastasis in mice. We will also co-inject HSCs and tumor cells into the livers of mice to test if the interplay between Src and VASP modulates plasma membrane Glut1, glucose transport into HSCs, and HSC activation within the hepatic tumor microenvironment. The proposed work will reveal novel mechanisms related to metabolic regulation of HSC activation induced by TGFβ, which will help to identify new targets to inhibit HSC activation and the prometastatic liver microenvironment.